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THE PYROLYSIS OF FORMALDOXIME

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University Microfilms
300 North Zeeb Road
Ann Arbor, Michigan 48106
A Xerox Education Company
T5-n^is
LD3907 '
.G7
Bender, Harry.
*
1941
The pyrolysis' of formaldoxime. A
.B4
study of the kinetics and mechanism of
the decomposition. Energy of activa­
tion for the decomposition of formal­
doxime...
New York, 1941.
4p.l.,48 typewritten leaves,
tables,
diagrs. 29ciu.
Thesis (Ph.D.) - New York university,
Graduate school, 1941.
"References": p.47-48.
A67958
Shelf List
Xerox University Microfilms,
Ann Arbor, Michigan 48106
T H IS D IS S E R T A T IO N HAS BEEN M IC R O F IL M E D E X A C T L Y AS R E C E IV E D .
L
ib r a r y
N. Y.
TH1 PYB0LYSX8 OF FOBMALDOXIMI.
U
n iv
.'
A STODY OF THX KIHXTICS ASD
MXCHAIISM OF THB D*50*>0SITI0I.
BTSBOY OF ACTIVATION FOB THK
DIOOlffOSI TXOV OF FOBMALDOXIM1.
A THBIS
Sakltiti In Partial Fulfillment
of tha Requirements for the
Degree
of
Doctor of Philosophy
at
Vow York University
by
Harry Bonder. H.A*
April
19^1
PLEASE NOTE:
Some pages may have
indistinct
print.
Fi I med as r e c e i v e d .
University Microfilms,
A Xerox Ed uc a t i on Company
TABLX OF COBTBBTS
FAGS
Forward • • • • • • • • • • • ■ • • • • • • •
A
Introduction . . .
1
...........
Summary of Introduction • • • • • • • • *
15
Experimental
(a) Preparation and Purification of
Foraaldoxlme » • « • • • • • • • • •
16
(b)
Physical State of Formaldoxime Vapor
17
(c)
Deconposition of Formaldoxime in
Bomb Tubes • « • • » • • • • • • • •
18
(d)
Kinetics ^f Deconposition • » • * « .
2U
(e)
Discussion of Kinetics • • • • • • • •
29
(f)
Analyses of Oases,(From The Deconposltlon of Formaldoxims), • ■ • • • • • «
31
The Beaotion of HC¥ and Water in
Bomb Tubes « • • • • » • « • • • • • •
3^
Reaction of 00 and Ammonia in Bomb
Tubes...........
35
(1)
Pyrolysis of Formamide « • • • • • • •
jS
(j)
The Xffect of Air and BO On The De­
composition of Fonsaldoxime • • « • •
J8
(g)
(h)
Discussion of Besults • • • • • • • • • • • • •
Final Suanary
Bibliography • • . . • • • • • • • • • • • • • •
Ho
TABUS, DIAGRAMS AID GRAPHS
Page
Diagrams
A Modified Victor Meyer Apparatus, , . . .
15a
Apparatus Used Tor Kinetics • • • • • • • •
23a
Graphs
Activation Energy • • • • • • • • • • • • •
27a
Velocity of Reaction • • . • • • • • • • • •
26a
Tables
Data on the Decoapositlon of Tormaldoxlde ••
26b
Velocity Constants • • • • • • • • • • • • •
27^
Ha salt s of Gas Analyses • • • • • » • • • • •
30a
T0B1KARD
The woik to bo reported in this research ie the
outcome of researches carried out by John (25)
othere in which CHj and NO were postulated to unite
and fora formaldoxime.
The presence of substances
resembling formaldoxime has been reported and it
was thought important to acquire more knowledge
concerning thie compound.
AfiKSOWUDGBIBrV
The author vlahea to re­
cord hie gratitude to
Profeesor H. A. Taylor for
hie advice aid guidance
during the course of the
investigation.
Introduction
To understand the reasons for this research, it will he best to
traoe briefly the history of the experiments and theories which have
led to thie work.
It has long been known that the presence of small amounts of sub­
stance have a marked effect on the rate of chemical reactions.
Many
theories have been advanced to account for this phenomenon and a comprehenslve account of catalytic action has been given (1),
Hinahelwood (2. h) dlecovered the unusual phenomenon that email
amounts of 10 will inhibit the decomposition of diethyl ether and propeldebyde, whereas if SO is present in larger quantities an acceleration will
take place.
To quote from his work, "as far as we were aware no examples
had hitherto been found of homogeneous reactions subject to inhibition by
minute amounts of a foreign gas." (2)
Since that inportant research was announced a great quantity of ex­
perimentation and hypothesis have appeared in the literature.
That work
will be described in relation to this research.
In this initial (2) research the following effects were noticed.
Small amounts of HO (0-15 mm,) gave an inhibition, while amounts greater
than this accelerated the reaction rate.
HO is not coopletely used up,
outlasting large amounts of diethyl ether,
Vitrogen appears and was
determined by difference so that the presence of small quantities of
other eubstances probably escaped detection.
The HO reduced the initial
rate to about 150 of the uninhibited rate, and over the range 5-lU mm.
of VO. the inhibition was a constant.
The energy
of activation at' the
nornml rate was $3 keel} for the inhibited 67heal. The energy ef activation
for the accelerated rata was lower than either.
There is a complete
similarity for the dependence of the rate on pressure for the inhibited
and uninhibited reactions.
To Interpret these results (£j), it was
postulated that many short chains were operating and that the 10 cut
down the number or the length of the chains.
It was previously known that ID will accelerate the rate of nitrous
oxide, acetaldehyde and chloral decompositions (3)* Nitrogen was found
reactions
present in the product s. These/are similar in many respects to an oxidation. .
The positive effect of the 10 was explained by Verhoek (3)jM
due
to the unbalanced electrical coalition of K), causing the molecules with
which it comes in contact^to become unstable.
A more detailed treatment
of this condition appears in the article by Taylor and Burton (£).
They
postulate two mechanisms for the decomposition of acetaldehyde.
1. OBjOBJ + ll-Xfti^OO + M
2.
OBjOBD -^CHj +■CUD
CH^CHO 4* CHj
OH^OO
->
4*CHjOO
CHj+00
Vow M may be a foreign substance or another molecule of acetaldehyde
and if the pressure is increased we should expeot reaction (1) to be
favored,
Ixperlment shows that the activation energy decreases with ln»
creasing pressure, indicating that the activation energy for (1) is lower
than for reaction (2) since we do not expeot reaction (2) to be affected
by change of pressure.
If we now add BO to acetaldehyde, reaction (2)
would be cut down due to the combination of 10 with the free methyl
radicals and we should expect the activation energy to fall, since (1) is
(2)
favored.
This i* what actually eccure.
BO
Verhoek (3) shows the/catalyeed
reaction of HO an acetaldehyde to give an activation energy of 37,3 keel,
which supports the mechanisms advanced.
In the work on propaldehyde (7),
Staveley and Hlnshelwood found the following!
the HD inhibited pyrolysis
has an activation energy ef 58.5 at 30mm. and 51.O at 350 mm. while the
uninhibited has 63•*> pad 56,0 for tharrespeetive pressures,
This is also
in agreement with their theory.
It may be remarked that Hinshelwood attenpted to explain the BO effects
by assuming that HO would deactivate activated molecules when present in
small amounts!
this aseunption appears to lead to the result that if in
the absence of chemical change, the inhibitor could displace the normal
energy distribution, then the principle of detailed balancing would be
violated.
The special importance of the work of Taylor and Burton (6) with re*
spect to the ideas of Hinshelwood on the mechanism of HO inhibition is
great.
If we accept the hypothesis that HO will cut down the rate of re*
action, if free radicals are present, then the fact that no inhibition is
detected, as in the acetaldehyde work, would mean the absence ef chains
or free radicals.
This result would be in conflict with the work of Bice
(19) and Taylor and Burton (6).
further work showed (7), (8) that HO would inhibit the deconpositlon
of dimethyl, methyl,ethyl, diethyl, ethyl propyl, dipopyl and di isopopyl
ethers, but no inhibitions were found for methyl alcohol, acetone and
acetaldehyde.
It was suggested (7) that in the eonpounds giving no in­
hibition free radicals were not present.
Semenov (9 ) explained that
great energy fluctuations in a molecule may act to give a decomposition
rate conparable with that produced by short chains.
(3 )
Thus it appears that
reactions thought to he chain reactions might not really he so, and in
these cues the MD inhibition would need some other explanation.
It was calculated in the ether work that the activation energies
for the inhibited reactions were higher than for the uninhibited.
Turther, maximum inhibition occurs between 1-2 ran. ef MO.
Quantitative
measurements showed that MO was used up and dimethyl ether gave the
greatest removal of MO per molecule of ether reacting.
It is interest*
ing that formaldehyde is produced in the dimethyl ether reaction, and
that MO will polymerise formaldehyde.
Thus a double effect of MO is
present.
An effort to discover the nature of the mechanism was made, in the
photolysis of acetaldehyde, by studying the effect of MO on the rate (10).
This reaction was known to give a high quantup yield and explanations
based on a chain mechanism involving free radicals had been given.
The
chain mechanism proposed was as follows:
CHjCHO
CHj + CHO
OHjO®
CH3
0 % + CO + CH-j
The chain could be broken as follows:
20Hj
OH. +
OgHg
BD -> lDMtiT. product.
It was found that MO disappeared and a definite inhibition appeared. To
account for the products of the reaction which took place at 300° C.,the
following mechanism was proposed^
The quantum yield of acetaldehyde dropped from a few hundred to unity and
this was Interpreted to mean that 1 molecule of MO reacted for each
acetaldehyde mblecule decomposed.
yield
A almllar quantuny chance will he found
in the work of Thonpson and Linnett (to he deaerihed).
The poaaihility that the HO complex might yield HCH was excluded eisce
no positive teat w&a obtained.
Our researches have shown that if the
complex were formaldoxime no HOH would result at 300° C, whereas, if it
were formamide there is only a small probability that HCH would form.
It
should be interesting to see what would happen if this reaction were
carried out in the range 350°«1K)0o C,
The photolysis of acetone gawe no inhibition with ID bat propionic
aldehyde did.
Most of the work was carried out at 3000 c so that no HCH
would be expected to form.
Staveley (10) tested the effect of HO on ethane and discovered an
inhibition and^/%e MO disappeared.
Since the chain length varied with
pressure, it was postulated that the Bic^-Hersfeld free radical mechanism
was operating.
This mechanism depends on the production of hydrogen atoms.
The possibility of hydrogen and 10 reacting to form HID Is similar to the
mechanism proposed in Bice's article (10).
The first attempt to follow directly the mechanism of the 10 inhibit
tion was made by Thonpson and Melssner (11).
These investigators studied
the absorption spectra of the reaction of HO on dimethyl ether.
found that as the HO lines weakened HHj bands appeared.
Zt was
The HH^ does not
affect the rate of reaction and it was therefore postulated that formal*-*
doxime might be the intermediate product causing the inhibition.
Using
diethyl ether in a similar experiment,the HO bands disappeared and bands
which might ha do been methyl amine form.
OgBjj 4- HO
CHjIHg •+• 00
(5)
The mechanism proposed was:
An unstable nitroso compound may hare been present since, when the
reaction products were froien out, a blue solution resulted.
The produc­
tion of 00 may have come from the formation of formamide, since formamide
will giro ammonia and carbon monoxide.
The ammonia may then react with
the free radicals to give methyl amine.
This reaction might be studied
using ammonia as a foreign gas to see if these effects can be determined.
1H a summary of the work Hinshelwood (12) reported that ethane, di
methyl, methyl ethyl, dl propyl, di ethyl, di isopropyl ethers, propalde­
hyde, butyraldehyde gave inhibitions in the thermal decompositions with
10, whereas acetaldehyde, chloral, acetone, methyl ethyl ketone, methyl
alcohol and some esters did not.
To explain these results Hinshelwood reasoned as follows:
competing reactions processes were operating.
two
The molecule might r»»
arrange directly to final products or a split to free radicals could take
place initiating a chain mechanism.
Which mechanism will actually pre­
dominate depends on the energies of activation for the processes.
If
the activation energy for the split to free radicals is much greater
than that for the rearrangement process we should expect the rearrange­
ment to predominate, unless the chain length is very great, and the number
of free radicals formed
is
negligible.
Only at a temperature shore
reaction velocity would be immeasureably great, would free radicals be
expected to be present in large amounts.
To illustrate, the calculated energy of activation for acetaldehyde
is U6 kcah(6) and the 0-0 bond strength is 75* - (1*0*
We should therefore
expect few free radicals to form, and the direct rearrangement to pre­
dominate.
(6 )
This simple theory Is however dependent on the nature of the chain
mechanism for its applicability.
To illustrate:
acetaldehyde may decompose as follows:
a.
OHjCHD
OHj + CHD
b.
OHj + CH3CHO - ^ C % + CHjOO
c. 2QHj -> CgHg
d.
The activation energy for (a) is larger than that for (d), However
step (b) has a low activation energy so that taken together the overall
activation energy for (a) and (b) Is U6.0keal.which is in agreement with
the experimental value of H5.5 kcsd.(15).
the activation energies for
Thus a simple comparison of
the primary stepsin rivalmechanisms will
not suffice to decide which is more probable.
If NO inhibits. Hinshelwood assumes free radicals to be present, while
if inhibition is absent, no
free radicals arepresent. This would not
apply in the case of acetaldehyde where both mechanisms are believed to
be operating.
The accelerating effect of NO on (d) more than compensates for the
inhibition of (b) by forming complexes with the radicals so that the ab*>
sence of inhibition is not an absolute iadloation that free radicals are
not present.
The ideas concerning the activity of free radicals in causing de­
composition were farther clarified by the experiments of 8iekman and
Allen (16).
It was reasoned that If one step in the chain mechanism was
the combination of a free radical with the substance undergoing decomposi­
tion then the activation energy for this step was lower than that for the
<7)
activation for the primary atop to free radicals.
If a compound yielding
free radicals were put into a compound stable at that temperature, then
the stable conpound might be expected to decompose at a temperature where
it is ordinarily stable,
Asomethane was found to decompose acetaldehyde,
at temperatures at thioh aoetaldehyde is ordinarily stable, in agreement
with the theory,
Ichola and Pease (17) discovered that the pyrolysis of butane sla :d
c inhibited by HO, the rate falling from oris'. to ,03
as the HO pressure rose from 0 to 20mm.
> relatively,
She normal decomposition rate
was found to fall off with time but the inhibited rate rose after 10)1 of
the HO had been used up by the reaction.
To explain these unusual re*
■i
suits they postulated that an equilibrium would be set 19 between BO
and the free radicals, which at the beginning of the decomposition would
bind every free radical, but as the number of free radicals increased
with time, and the HO concentration remained constant, the gradual builds
ing up of radicals would cause the reaction to speed up.
Our work does
not lead to the necessity for postulating any such equilibrium.
At the
temperature of Pease*s investigation (520°0) we would not expect any
complex of HD to be stable.
Bice and Polly (18) point out that propylene is a chain breaker and
will inhibit the decomposition of hydrocarbons, ethers, acetone and acetal*
dehyde.
Propylene unites with the free radical forming saturated compounds
and allyl radicals,
B -t- OHjGH a
CHg -*> HH 4- <®2
m C H ^ CHg—
The allyl radical will cot continue the chain as efficiently as the
previous radical according to Bioe.
The allyl radical has a resonating
structure which makes it unusually stable, and relatively unreactive.
(8)
This unuiurl unreactivity of the free allyl radical will causa its coneen*
tration to be built up, replacing the more efficient chain carriers, such
as the methyl radicals, thus cutting down the rate of reaction.
Alkyl
«
nitrates are found to behave similarly to ID, acting as follows:
S + OHjOW
MS -h OHgOBO -w BE + HOBO + VO
Vow it is found that propylene will inhibit the decomposition of
butane and is quite stable at the tenperature at trhieh butane will begin
to decompose.
Ve would expect that as the pyrolysis of butane progresses
the rate would fall off, due to the increasing concentration of propylene
and this is found to occur.
If we add VO to butane the initial inhibi­
tion will fall off with time since propylene will swasp out the effect
of the VO.
This is what is observed and we therefore do not need to ac­
cept the postulation of Pease and Schols concerning an equilibrium between
VO and the free radicals.
periment is suggested.
To further prove this point, the following ex­
At a point where the VO effect is couplet sly cut
out by the propylene, add VO} if no effect were observed, propylene would
be the controlling factor; if an inhibition resulted further explanation
would be necessary.
In this connection we cite the work of Travers (19), where it was
shown that a conplex did form between dlmethyleadne and VO.
This conplex
decomposed above 100° 0.
In the investigation of the effect of VD on the pyrolysis of methane,
propane and hexane, inhibition was found in each case,
T6 account for the
reaction products in the diethyl ether reaction, the following mechanism
was proposed by Hinshelwood;
(9)
CgH^QCgH^ — > OHj + CHgOCgH^
CHj -4- CgH^OCgB^ — * CgHg ■+• OHgOCgB^
CEgOOg^ -► OH-j +■ OHjOHO
CHj +• CHgOOgB^ — ^ products
BO +
CHgOCgE^ — > products
This mechanism was thought most likely to occur as the life time of
methyl radicals would he small in comparison with that of OEgOCgH^ and BO
would he much more likely to react with the radical haring the longer life*
time.
The presence of ethane and 00 in the reaction products may hare re*
suited from the decomposition of formaldoxime.
If the presence of ammonia
could he detected in the reaction products it would make the mechanism un­
likely.
Another point in its disfaror is step two.
According to Bice (Il8 )»
this step is impossible because the energy required to effect it is enormous
in comparison with the other steps.
Thompson and Linnett (21) hare inrestigated the effect of BO on the
photolysis of Mercury dimethyl.
position.
BO was found to inhibit the rate of deconw
The reaction gare a white solid, at 273°0.
They were unable to
determine the nature of this substance but suspected it to be formaldoxime.
▲t higher temperatures they report complications which seem quite clear in
the light of this investigation, since the formaldoxime would begin to
decompose and the HCB or other products formed might well complicate the
decomposition.
They found that one BO disappeared for each half molecule
of mercury dimethyl reacting.
or formamide
We would suspect that* either formaldoxime
to be the possible products.
Thdy mention that 00 and.
were found in some work on ether and BO. which is to be presented in a
future peper.
These products are found in the pyrolysis of formamide and
(10)
formaldoxime.
It would "be interesting to see if sufficient white solid
could he formed to make a mloroanalysis*
In the decomposition of acetaldehyde* Verhoek (j), showed that SO
would catalyse the decomposition hut found no ammonia.
article in Journal Sen. Ohem, Bussla
He refers to an
in which ammonia was fepmHed
present in the oxidation of hydrocarbons hy SO at 500° C.
Tree radicals
at 500° G, without a catalyst, might react with the SO to give the inter**
mediate products which would then give ammonia.
If 00 can he shown to he present in these reactions in excessive quan»
titles, we could interpret this to mean the formation and decomposition
of formaldoxime and formamide,
Travers (19) in his work on the pyrolysis of the methyl amines added
SO to the reaction and found inhibition.
He postulated the formation of
an equilibrium between dimethyl amine asd SO*
above 100° 0.
This conplex was unstable
The connection between this and the work of lchola has al<*
ready been indicated*
In the photolysis of trlmethyl amine, Bamford (2U) found that when SO
was present inhibition took place and the HO would disappear during the
course of the reaction.
The presence of HCH was confirmed and evidence
indicated CHj radicals to be present in the decomposition.
Since the re-
action took place at 100° C it would be difficult to account for the presence
of HOT resulting from the deconposition of formaldoxime at such a tenpera*ture.
The HOS might come from the deconposltion of the amines themselves*
In the work of Davis, Jahn and Burton (25) the effect of SO on the
photolysis of asomethane was studied*
It was found that the results could
best be Interpreted on the assuaptlon that ID and free radicals reacted to
(U)
form eonioMatioa products*
e
Thm presence of a white solid in the Tgpler
i,*.?.
pump leads us to suspset the presence of formaldoxime.
The pressure in*
crease noted at 100° 0.may possibly hare been the depolymerlsation of
formaldoxime.
Jahn proposes that the formaldoxime formed will deconpoee to
HCH and eater. This is unlikely at the temperatures of the experiments and
only the possibility that the compound is unstable in the presence of ato*
n*thane or the light used, would make this assumption tenable.
The possi*
bility of SO forming a complex with the asomethane complexes, formed from
asomethane and free methyl radicals, is not inprobable, since Travers reports
a complex of a not very dissimilar nature (19).
The three mechanisms by which HO might be removed from the system, as
proposed by Jahn may be reexamined in the light of the results of this re~
search.
They give:
1. CHj +■ HO -» CI3HO
2.
CH3I H
I, + HO — ^OHjHMHO
3. CEjL + HO
CHjAlTC
(A =- asomethase)
The first equation is highly probable as is indicated by the reports of
e
various investigators and the presence of white material in the Toiler pumps.
The pressure changes reported, while consisting of a non reversible part, make
the presence of formaldoxime seem probable.
An X) conplex might also account
for the reversible pressure changes as Travers reported (19),
The complex
in the third equation seems more probable than that of the second equation
from analogies to the work of Travers.
In the work of Jahn and Taylor on the pyrolysis ofasomethane (26) in the
presence of HD, an inhibition was reported and the presenceof awhitesolid
(12)
which collected in the trap* was seen.
Attempts to determine the nature of
this white compound which had some of the physical properties of formaldoxime
yielded the result that it contained
Jljt litrogen.
litrogen, whereas formaldoxime has
The report of a small pressure Increase during the ID inhibited
reaction might hare ions from the formaldoxime decomposition since the tempera*
tures of the research are not too low (325® C), for decomposition to occur.
Steacie (27) points out that the hypothesis of 10 suppressing all chains
has not been established.
gives a mean chain length.
of activation!
ment.
The ratio of uninhibited rate to inhibited rate
This mean chain length depends on three energies
1. radical formation;
2. chain propagation;
3, rearrange*
Is cannot deoide by the 10 method whether some free radicals initiate
long chains of whether many radicals initiate short chains.
The method of sensitised deeosposltion was used by Steacie (27) to decide
whether the Hinshelwood ideas would explain the results of his investigation.
The decomposition of butane was studied at a temperature where the rate of re*
action was very slow (half life 160 hours).
free radioals forming is negligible.
At this tenperature the number of
Zf ethylene oxide is placed into this,
the free radicals known to corns from the ethylene oxide, would initiate the de*
composition of butane.
If 10 will suppress all chains, as Hinshelwood assumes.
then the reaction should cease when 10 is added.
It was found that the reaction
did not show complete inhibition and a chain length of about 1.3
for the point of maximum inhibition.
was calculated
Although certain assumptions are present
in the work which might make the conclusions untenable, the possibility remains
all
that K> will not cut out/the free rcdleals in some reactions. Thus Chain lengths
calculated in the past on this assumption of complete suppression of chains map
be in error.
There is also the possibility that 10 is accelerating the reactions
as in the acetaldehyde mechanism prppossd by Taylor and Burton thus further
(13)
vitiating the chain length calculations.
It is interesting to note that this type of research was done hy Hinshel*
wood many years ago.
The decomposition of methyl formate was induced by
acetaldehyde at U 600 C.
down.
10 was added and the velocity was definitely cut
The conclusion drawn was that 10 completely suppressed the reaction
by cutting the free radicals concentration down to a point where no reaction
would take place.
In this particular case then all radical mechanism may
have been inhibited.
Summary of researches on MO.
The effect* of HO on the rate of decomposition* offers a direct method
for the detection of raAioal ohains.
This method of detection is not absoluts.
▲ reaction which is not inhibited by HO may still be decomposing by a chain
mechanism.
HO is removed in the decompositions of many substances and in these cases
the presence of anmonla and MCI is sometimes reported.
The best explanation
for these products is that they are formed by the decomposition of conplezes
of HO with free radicals such as formamide of formaldoxime.
One molecule of HO will stop the decomposition of hundreds of molecules.
Chains are thought to bs present in these inhibitions.
Tor the ethers, the energy of activation for the inhibited reaction is
greater than that for the normal.
The interpretation that the primary step
in the chain mechanism, the formation of radicals, is suppressed leaving the
direct rearrangement, is offered as explanation.
In propaldehyde on the other
hand, the inhibited reaction has a lower energy of activation than the normal
and this explanation would not apply.
The estimation of chain length on the assumption that HO will suppress
all the free radicals is untenable.
We may assume that the chain lengths
calculated on this basis, are, in many eases, in great error.
There is a competition between frequent molecular reactions of low
activation energy and infrequent free radical formation of high activation
energy followed by chains.
Both types may be operating at the same time.
(15)
\
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UPBtllOSHTjI.
Part 1, (a) Preparation and purification of formaldoxime
Formaldoxime was prepared after the method of Scholl (28),
formaldehyde used eae a UojC solution from Baker aai Jdsmaon.
hydrochloride was obtained from Merck and Co.
The
Hydroxylamlne
lo attenpt was made to
purify these products.
Hydroxylamlne hydrochloride was dissolved in a minimum amount of
water and sufficient sodium carbonate added to completely neutralise the
acid, leaving the free base.
cooled below 5°C.
This solution was placed in an ice bath and
It might be mentioned that it was necessary to grind
the sodium carbonate in a mortar after it was added to the solution due
to clusping, in order to speed t q the reaction.
Formaldehyde solution
was now added with constant stirring, being careful to keep the tempera­
ture below 5°C.
▲ heavy white precipitate of Formaldoxime soon separated auai turned
to a thick white mass.
This was allowed to stand in an ice box for a
few hours to insure eonplete reaction, and then filtered on a Buchner
funnel.
Portions of water at about 50°0 were added until the filtrate
was free of ohloride.
The material was allowed to stand in the air until
dry.
To purify the product advantage was taken of the fact that Formaldoxime
will sublime below 100°C without appreciable decomposition.
watch glasses were used.
Two large
One was placed on a steam bath and the compound
put into it, over this another watch glass was placed and this covered
with dry ice.
The product obtained was a pure, white, amorphous material
which upon farther sublimation did not leave any residue behind.
This
was stored in a dessioator over caloium chloride and used as needed, ■
Part 1. (b) The physical state of formaldoxime
repo*
Purlas the coarse of the investigation it ess found necessary to
determine whether Tormaldoxime vapor was polymerised at the tesperatures
of the work.
A modified Victor Meyer apparatus was constructed for this purpose
and is shown in the aceospaaylng diagram (I).
The procedure is as follows! an amount of material is weighed out
such that the pressure would be conveniently measureable when the solid
was completely vaporised (less than one atmosphere).
This is then trans­
ferred to the bulb (A) through a side arm and the bulb sealed off.
The
mercury in the constant volume manometer (B) is lowered and the pumps
turned on.
After the system is evacuated as shown by the mercury levels,
which are allowed to rise at intervals and then lowered again, the stopcock is closed and the mercury allowed to rise to a predetermined height.
The oil is heated to a suitable tenperature and pressure, and readings
taken until no further rise is noted.
Calculations were made assuming that the errors in using the gas
laws were small in cosparison to the other experimental errors, (including
loss of Tormaldoxime during evacuation).
Using the perfect gas laws,
PV
=~
5
~
BT where P= pressure in atmospheres (of mercury)
Vr volume in c.c, of the bulb 300 c.c,
m = grams of material weighed out
M e gram molecular weight of cospound
B cgas constant, 82.06 c.c. atmospheres
f » absolute tenperature
we get the following results for the molecular weights at the tesperatures
Indicated.
(17)
■ (grama)
C (centigrada)
p (cm.)
U (grama)(calculated)
0.1160
116
20.0
U^.9
0.0UO8
89
6.8
W5.S
0.1223
96
20.U
U6.0
la can therefore conclude that the vapor la completely depolymerited
acted
at 100° 0 since the/molecular weight of Xdrmaldoxime la U5.O.
Due to the fact that we were unfamiliar with the phyalcal propertiea
of formaldoxime at the beginning of our work, it was auggeated that we
begin the investigation of the decomposition producta and the kinetics,
using the bomb tube method of Travers.
Bomb tubea were conatructed aa follows;
tubes were blown and wide
glass tubing sealed to the ends as shown in the diagram (II).
The weighed
amount of compound (0.1830,grams) calculated so as to give pressures less
than two atmospheres, assuming that one molecule of Tormaldoxime will give
two molecules of decomposition products, was plaeed in the clean, perfectly
dry bomb tubes.
Constrictions were made in the neck and the tube connected
to the pumps with pressure tubing.
After pumping for a reasonable length
of timages indicated by the mercury level, the tube was sealed off and
wired around the neck;about the first constriction^to facilitate handling.
These prepared tubes were now placed in a furnace at about U00°C and'bl**
lowed to stand for varying periods of time.
They were then withdrawn and
allowed to cool.
The following procedure was decided on after various trials.
The tube
is placed neck down in a large beaker of water, and a pliers is used to
break the tip of the neck so that water will rise into the bomb tube until
equilibrium is reached.
A mark is made at this equilibrium level and the
(18)
bulb withdrawn.
The tuba la inverted and the liquid la poured Into a 100 o.c.
volumetric flaak.
The content a of the bomb tube ire waahed -out with amall
quant itlea of water and the washings poured into the volumetric flaak up to
the mark.
A quantitative investigation of the solution was first attempted.
from the formula for fomaldoxime we might produce the following poa»
sibilitiest
OHgHOH
HO* -t HgO
or^ and, 00 4- IRj
It was found that all four products were obtained under the conditions
of the experiments.
Anraonia was detected using Hessl*r4ireagent prepared as follows: (29)
2.5 grams of KX are dissolved in 3 c.c. of water and 3.5 grams of Qgl2 added.
To this solution we add 100 c.c. of KOH solution (15^).
Preservative solu^
tlon is made by mixing 50 grams of Bochelle salt in 100 c.c^of water and
adding 5 c.c. of Nes*lse%reagent.
The test for ammonia was confirmed by
the litmus paper reaction (adding strong base to the solution, boiling and
testing the vapors) and also by the unmistakable odor of ammonia.{>-0 .
Hydrogen cyanide was detected using the alkaline picric acid method,
modifying the procedure of Chapman (30).
A saturated solution of piefie
acid is saturated with sodium carbonate.
The clear solution is used in
the determinations. To the solution to be tested two c.c. of the prepared
solution
picric'aclA/added and the solution placed in a water bath. The water bath
is heated to boiling and after five minutes the color is conpared with a
known treated identically.
dicating cyanide.
In each oase a definite red color appeared inn
This was confirmed using the ferrocyanide method: a
(19)
few drop* of ToflOii
added to the unknown and the solution made alkaline
to litmus with KOH.
One drop of TeOl^ wae added and the contents heated.
CL
The solution was acidified with HC1 andAblue color indicated cyanide.
There was no at tempt made at this stage to analyse the unabsorbed gases
except for a few tubes.
In a few cases the presence of water was detected
using anhydrous copper sulfate.
ammonia.
A blue color appeared showing prOsenee'of
In these tests the contents of the tubes had to be wasted.
Having completed satisfactorily our qualitative investigation of the
contents of the tubes, absorbable in Water, it was decided to atteiqpt a
quantitative estimation of the products of pyrolysis.
The procedure was essentially the same as in the qualitative work, more
care being observed, however, in the weiring of the sample and in trans»
ferring the contents using weighing
paper which could not adhere to the
formaldoxime.
The Kessler reagent was the same as previously described.
The sample
was withdrawn from the 100 c.c. flask by means of pipettes, and placed in
Kessler tubes of 100 c.c. capacity.
were used in each determination.
One and two c.c. sanples of unknown
Water was added almost to the mark^at
this point, and 5 c.c. of preservative solution added.
This was immediately
followed by 3 c.c. of the Kessler reagent and the solution shaken to
thoroughly mix the substances.
After standing about five minutes, eompari*»
son was made with a standard which had been treated 8t the same time in an
identical manner.
The standard solution of KI^Cl was made by weighing
0.3lhl grams of amnonium chloride and placing in a liter volumetric flask.
Distilled water was added to the mark.
The determination of HCH was made Similarly to that in the qualitative
(20)
work more
care being obsorred ia tbs manipulations* The staaiard solution
was made by weighing out 0*5000 grass of HOT aad placing it into a liter
flask and filling to tbs mark with distilled eater.
One aad two e.c.
samples ears withdrawn in each case from tbs 100 c.c. flask for each de­
termination.
The standard solution was treated identically ia each case.
(Using tbe picric acid method).
The eooparIsons were first made using tbe unaided eye and the follow­
ing results obtained.
It most be remembered that the rainss obtained from
our analysis sere for one and too c.c, of the original 100 e.c. and thus
must be multiplied by the appropriate factor in each case to giro tbe totals
reported in the following table.
unabsorbed
IHj (grass)
gas (c.c.)
(at 298°C. 760 m.m«)
CO (grass)
(estimated)
HOT (grams)
HgO (grams)
(estimated)
39
0.01
0.02
0.0b
0.03
33
0.02
0.03
0.0b
0.03
39
0.02
0.03
o.ob
0.03
m
0.02
0.03
0.05
0.03
22
0.01
0.02
o.ob
0.03
36
0.01
0.02
0.05
0.03
To check aad sake our work more accurate, a colorimeter was used.
procured a Klett ph colorimeter of the Dubosq type.
deriation from Beer's law was below
Ve
It was found that tbe
5% in tbe range of dilutions we were
to use. so no attespt was made to correct.
The color produced was found
$o be quite stable aad unaffected by ammonium salts.
In each determination one aad two c.c. samples of unknown were used
and these were matched against freshly prepared standards using one aad
two e.c. of standard solution.
The results obtained in these determinations were as follows:
average of 3 results
■
■
"
*
0*020 IHj (grama)
0*0*12 HOI (grams)
0*016 »
O.0U6
■
■
■
The consistency of these results is satisfactory considering the sources
of error.
According to Toe (29) the ammonia determinations should he ac­
curate to 5jf and experiments carried out by the author showed that errors
are from
*n the HON determinations.
We can therefore summarise the
results and choose the most reliable values talcing into account certain
observations which will shortly be discussed.
TJnabserbed gas
kO c.c*
HE, (grams)
CO (grams)
(estimated)
0*030
0*018
Discussion of results:
HCI (grams)
0*0^
HgO (grams)
(estimated)
0*030
It is assumed that under the conditions of
temperature (U00° C ±. 10)* pressure (1-2 atmospheres) and time(§ - 24 hours)
the reaction went to completion.
The HCI was found to polymerize as the
tube cooled so that it was necessary to make the determination as soon as
possible after the tubes had cooled sufficiently to handle.
It may be
assumed that the value of HCI given i ^ AC-aaytbAag* a minimum value*
Ve
estimate the amounts of 00 assuming that for every molecule of HHj produced*
we get one molecule of CO*
A similar assumption is made concerning the
amount of water present, that the moIs of HCI equals the mols of water.
Knowing the moles of 00 present* we can estimate its volume assuming
?▼ m nBT where n is the moles'of CO.preeefct*
We find that this gives a
value of aboutl$;t0'25*&e."a£ QQi]ln the bomb tubes at the conditions of pres­
sure and temperature of the determination. There is therefore a discrepancy
to 25
of about 15/c.c. of gas which is not 00. The nature of this gas will be
(22)
discussed in connection with the work using the static set-up and in the
gas analysis.
The material balance of the reaction can now be more completely made.
As a result of the work on the bomb tubes, it is found that 0*123 grams
could be accounted for on the basis of materials found and materials esti­
mated.
Assuming the composition of the unabsorbed gas to be 25 cc. of CO
and the remaining portion to be 7*5 cc. of ethane and 7*5 cc. of nitrogen,
the following calculations can be made} ethane and nitrogen weigh 0*02
grams.
Aiding 0.123 grams to this value gives 0*1^3 &a m s accounted for.
This is
77# of the original material. Although the value is low. it is'
not unexpected, since the polymerisation of HCH which undoubtedly took
place, cut down the value.
Since each molecule of HCI polymerised would
lower the water estimation by a corresponding amount, the values would be
subject to a double source of error.
(23)
<*
Diagram of apparatus used for
the kinetics ef the decomposition
of formaldoxime and formamido0
f-
The kinetics of the decomposition using a i f tic method.
It was daoided after the investigation into the physical properties of
formaldoxime to huild an apparatus for measuring the rate of deconposition
using a static method.
Description of apparatus.
The final apparatus decided upon after many changes, necessitated hy
the peculiarities of the compound, was as followst
A storage huio (0) of 250 c.c, capacity was connected to a liter hulh (r)
hy means of a stopcock: (H).
500 c.c. flask (A).
The storage flask and liter flask was so arranged that
water baths covered them.
using Bunsen burners.
ings.
The liter hulb was in turn connected to the
These water baths could be heated to boiling
A constant volume manometer (B) is used for pressure read**
The system is evacuated through a two way stopcock (C) by means of a
mercury diffusion pump backed up by a hynvac oil pump (Cenco) which gave
pressures of less than 0.001 mm.
The other side of the two way stopcock (C)
was connected to a mercury well so that mercury could be run into the system
up to the point (T).
All the tubing, through which formaldoxime ran,was heated
by means of nichrome wire/to a temperature sufficient, to prevent condensation
of formaldoxime.
The stopcocks were at first mercury sealed but these would not hold a
high vacuum.
They were taken off aad stopcocks using plicene cement (Oenco)
were substituted.
These held the vacuum but required much attention and
would frequently leak during a run.
It was finally decided to use a
special plastic kindly supplied by the Dow Chemical Company.
The results
as
were.satisfactory as those described by Jones (31).
The Topler pump was of liter capacity and was connected directly to
the reaction flask through the stopcock.
(24)
The other aide of the Topler punp
«m
connected to a Vlecher gas analysis apparatus which oonsisted of the fol*>
lowing:
▲ CuOl bubbler pipette for 00
A XOH solution (50^6) in a bubbler pipette for acid gasos and 002
A pyrogallol pipette for <>2
A dilute solution of sulphuric acid for alkaline gases
A slow combustion tube for hydrocarbons
A OuO tube which could be heated to 310* 0, by means of a furnace, for H2
The furnace was constructed of a tin can 9 inches in diameter cowered with
asbestos paper.
About this was wound nichrome ribbon using a helix arrangement
on the bottom of the can.
This can was placed in a larger can of one and a
half feet diameter, and packed with asbestos paper.
Two cowers were constructed
of heawy asbestos board, the inner board was a tight fitting arrangement with
small holes to permit the Platinum resistance element to entexf the outer board
cowered the top of the furnace loosely,
Exploration of the furnace with a Hoskins pyrometer showed a three degree
gradient from top to bottom.
By placing the reaction wessel in the geometric
center of the inner can, this gradient was reduced to about two degrees at the
maximum.
The temperature of the furnace fluctuated as much as three degrees
during a period of an hour.
At night, howewer, a much steadier current was
present.
Tor the runs of shorter duration (15-30 minutes) we may safely say
measured
that the temperature did cot wary by more than one degree ss/hy the platinum
resistance thermometer.
Buns were rejected if too great a fluctuation was
noted during the course of the run.
Temperature readings were taken at fre­
quent interwals.
(25)
Proodure for mating a ran.
The pumps were turned on end etepeeeke (H) (l) opened while (0) wee opened
to the pumps,
(K) and (J) were closed and the mercury taken out of the c o m
stant Tolume manometer, hy means of a leveling bulb.
After a sufficiently
good vacuum was obtained as determined by running the mercury into the manometer
at intervals until no pressure reading could be observed, the stopcocks at
(H) (l) (C) were closed.
boiling.
The waters covering (<J) and (T) were now heated to
Stopcock (B) was now opened and the stopcock at (C) turned so as
to allow mercury to run 19 to (T).
The manometer was now adjusted and the
temperature of the furnace recorded,
Experiments carried out at low temperatures showed that the gas would
reach thermal equilibrium in a few seconds so that for runs above 350° C
the error in the initial reading would be negligible.
was opened for a few seconds and then closed.
The stopcock at (I)
Pressure readings were taken
at convenient interval*^ along with temperature readings.
At the end of a run the pumps were again put into operation and the
Topler pump made ready.
The mercury in the system at (7) was allowed to
run out into (L) where it was taken from the tubes.
was then opened and that at (J) closed.
The stopcock at (£)
The gas was drawn over by means
of the iQpler punp and placed in the Hespel burette of the gas analyser.
When most of the gas had been removed by repeated strokes of the Topler pump,
the system was pumped out and the mercury well (D) made ready for the next
run.
The results of these runs appears in the follewlng tablef
(26)
i.H| | M
nmltt
I
1
s
Z6 x
mmm
26 *
Bata on tho Dacoqpoaltlon of Poraaldoxlaa
t a Ml2°0
Initial Preaanra
of Toraaldoxiaa
* a 385°o
103*5
Tiaain
aoeonAa
Initial Pr.atnre
0f PorwlOoxiaa
68*3 * * •
£ p (m u )
T i m in
admtoa
A p (aau)
60
6.U
1 .0
0*2
75
8.8
1.5
0*6
90
io*5
2.0
l.U
105
12*0
2.5
1.6
120
13*0
3.0
2.2
150
16.7
3.5
2.9
180
19.5
u.o
3.6
210
22*0
^•5
M
2l*0
2U.9
5.5
5.^
270
26.8
6.5
6.U
300
29*0
7.5
7 .1*
330
31*0
8.5
8*0
360
33.0
1*20
3^*5
U80
35.3
5b0
39.2
600
**l.9
660
UU.5
900
51.2
(26*)
T - 350°C
9 s 376*0
Initial Pritnrt
of foraalAoziao
129.3 » .
Initial Proarare
of VoraaldoxiM
81.0 M U
Tina in
ainatoa
A P (■»*)
ln
adnutoa
1
0*3
1
0.5
2
0.8
1.5
0.9
3
1.0
2.0
i.5
4
1.9
2.5
1.9
5
2.8
3.0
2.b
6
3.8
3.5
2.9
4.0
3.8
7
A P (“ •)
9
6.9
5.0
b.7
15
9.8
6.0
5.5
7.0
6.9
10.0
8.9
15.0
10.8
(26b)
1
Results of kinetics using » first order equation*
fs. o
▼eleoity constant
413
1 .08 «1C^5
412
1.01
412
1.15
412
1,02
408
1.00‘
408
8.81'ICT1*
405
•
7*50
401
6,62
398
5.06
386
2,88
385
3.oi
381
2,44
378
2,U0
378
2.30
376
2,20
375
2.11
374
1.92
365
1.15
370
1,40
«
These results are plotted on the accompanying graph.
(27)
(27a)
The Telocity constant* bar* boon calculated on the assuaption that one
molecule of Toraaldoxlne will give two molecules of reaction products*
perimental results hare not quite fitted this assuaption*
final to initial pressure range from l«g to 1*9*
Bc-
The ratios of
At lower tesperatures, the
fatio falls off from the value of 1*9 attained at 410°C.
Chemical analysis bears out our initial assmption that a 2 to 1 ratio
for final to initial pressure should result since the products of deconposi*
tlon can be sinply added together to give formaldoxime* as assumsd in the
bomb tube decospositlon of Formaldoxime.
The most likely explanation for this lowered final ratio is that BOH
is a very reactive substance and in the presence of Hj>0 and HHyis even
more likely to form polymers (32).
andne (33)*
BOH will give a dicyanide of methyl
Since polymer formation was noted in the bomb tubes and is
abundantly verified in the literature* the lowering of the final pressure
and even the falling off of the rate is probably due to secondary reactions*
Thus a 2 to 1 ratio is not to be expected when such reactive materials are
present*
The velocity constant is calculated as follows: since pressure is
proportional to mols if the tesperature and volume remain the seam, then
letting the initial pressure of formaldoxime be P0 and the pressure of
undeeo^posed formaldoxime at time t be ft. the following calculations can
be made*
Since each mol of formaldoxime is assumed to give two mols of
products then 2(?0«$t) will be proportional to the formaldoxime decomposed.
The values of A p given are equal to Pt4-2(*©-*t )-P0 * Po*#t *£ p *
This
value subtracted from f0 will give the pressure of undecomposed formaldoxime*
\
This value is substituted for e in the equation
U S i dt
(28)
a*k
and a plot of In e against tins in seconds is mads.
Tbs slops of this lino
is ths value of -k.
Plots sods of a largo number of runs have revealed ths following
characteristics.
At high temperatures (370°C and ovsr) ths plot of In e
against t is a straight lins from ths very beginning.
At temperatures
hslow this there is some indication, especially at very low temperatures
(350°C), that
e snail induction period of about k ainutss is present dur­
ing which no change in pressure can he noted*
According to Semenov (3U),
this characteristic is usually associated with chain reactions.
In the
thermal, decomposition of acetone, it was observed (35) that at low tempera­
tures the rate of pressure change develops an induction period*
Since the
decomposition is assuaed to proceed by a direct rearrangement, there is no
reason for the induction period except some sort of condensation which does
not occur at higher temperatures.
At temperatures above U00°0, the reaction is first order to about the
half life.
At temperatures below UoO°C, the reaction reaains first order
for shorter periods of time until at 370°G, we find it first order for only
about one fifth of the tiae for total decomposition.
In order to explain the falling off in the unimolecular constants,
there is the following possibility!
HCI will polyasrise to fora the dimer
IH = 0 ° 0 => IH
If this equilibrium is assuaed then at higher temperatures aore BOV
will be present since the reaction as written is probably displaced to
the left by a temperature increase.
At lower tesperatures therefore the
uniaolocular constant will fall off aore rapidly because nost BOV foraed
(29)
will polymerise, cutting down the total pressure increase.
It is assuaed
that the rate of polymerisation has a very snail energy of activation.
The constants were all calculated by taking that part of the curve
which fitted on a straight line.
In most cases, satisfactory results were
obtained in the latter part of the work after some variables had been
discovered and eliminated,
fluctuations did appear from time to time
but their exact nature was not discovered.
It was found that the reaction was very sensitive to small traces
of air.
The reaction bulb was coated with the decosposltion products
of acetone until a dark coating was visible over the inner surfiee.
This surface could be destroyed by air.
After these changes had been
made, it was found that the velocity constants decreased and that most
of the fluctuations disappeared.
after all these changes.
The conetants reported are those made
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Analysis of Oases
from the previous work on the bomb tubes* s qualitative ides of the
composition of c m s s sss known*
Zt wss decided not to analyse the gases
from the decomposition in their entirety because of the HOV asd HgO
present*
The method finally chosen was to wash the gases from the re»
action vessel in dilute a d d and alkali*
The percentages of these ah*
sorptions on the basis of unwashed gas ere recorded la the columns narked
dilute IfeflOii and KOH*
The gases ere assumed to be mostly HOV and IHj*
Since HgO was present in the system* they presumably dissolved or poly­
mericed to an unknown extent before absorption*
Thus the values recorded
are not quantitative and will aot be discussed from a quantitative stand*
point*
The volume of washed gas is recorded and then the gas passed
through the reagents and slow combustion tube in the order of the column
headings*
The percentages of gases on the basis of the volume of washed
gas are recorded in the appropriate column*
The total of these percentages
(excluding the KOH and dilute HgVOij. columns) is recorded in the last
column*
The column marked .JBL la calculated as follows*
Tw
reaction vessel is $2$ cc*
The volume of the
The temperature is known and the amount of
gas withdrawn is estimated from the pressure change in the reaction vessel
by using the gas law*
and 760 am.
This volume of gas Tc is assumed to be at 298°ibs.
The actually measured volume of washed gas Vm is divided
into this to give the ratio shown*
The ooluma marked
‘Q0g‘t‘ is the total contraction in the slow eokbus*
tion tube divided by the carbon dioxide produced by the slew combustion as
measured by KOH absorption*
(3D
The column headed "conditions” is the tine ths formaldoxime
rtpor
wot in ths reaction Tossel plus other information.
The apparatus employed was a Tischer pas analyser Model 10-600*18.
Solutions for the absorption pipettes were nade up according to directions
in the Tischer Oas Analysis Manual (1UP. Matussak).
11trie oxide was tested for by asking use of the following equation
expressing the volune relationship
2KM-02-* 2MD2
of three molecules giving two.
A contraction should be observed when oxygen and the uaknown gas
are nixed if 10 is present.
nixing.
In all eases no contraction was noted on
Also the 10•> formed should be absorbed in alkali.
So absorption
of the gases was noted after nixing.
In a few eases the gases were passed through OuCl before washing
with pyrogallol.
In these cases.no pyrogaliol absorption was noted.
Ko
further attempt was nade to analyse this tiny fraction of gas.
In analysis one to seven the gas was treated in such the fens fashion.
Toraaldoxins was allowed to stand in the reaction vessel fToa one to three
days.
The final pressure reading did not cfaange on further standing, in­
dicating no condensation or decomposition, since it is unlikely that con­
densation and decomposition would exactly balance one another.
Tc
The ratio of ^
„
appears larger for the runs 2, 3, 6 but the dif*
ficulties of these nsasurenents are great so that no significance can
be attached to anall differences.
The fact that the ratio did not reach
2, indicates that^a&l the HOT and water formed in the primary step have
v. * changed to CO fit IHj.
In runs 1 and 3, ths ratio does spproach 2
(3«)
indicating that practically all tha SOI and water have reacted to giro
CO and VEj.
(A discussion of the reaction of BOV and water to form 00
and asaaonia will appear in the following section.)
In runs 8 to 13, formaldoxime stood in the reaction Tassel until
no further change of pressure was noted and then withdrawn.
In all these latter runs, with the exception of 8 and 9, the re*
action is practically coaplete at the time of withdrawal of gas as
indicated by the fact that the manometer did not rise further.
the ratio of Tc to
However,
Vm indicates clearly that a large proportion of the
gas condensed on withdrawal from the reaction ressel.
This is due to
the fact that BCV and water react slowly to form 00 and ammonia, so
that if the gas is withdrawn soon after pressure changes cease, a large
proportion of the gas will consist of BCV and water.
Analyses of runs 8 to 13 were very difficult since only smell frac­
tions of gas (10 to 20 cc.) were anelysahle in the gas analyser.
The ratio of T.C. to 00g is in most cases close to 1.23 and ethane
is therefore assumed to be the only saturated hydrocarbon formed.
Vo
attenpt was made to determine the nature of the unsaturated fraction.
It will?noticed that the amount of ethane in runs 10 to 13 is; much
larger than in runs 1 to 7*
The converse is true for the 00 percentages.
It appears therefore that most of the ethane is formed issMdlately and
does not appreciably change in quantity upon standing.
Since the volume
of 00 Increases on standing, the ethane percentage appears to fall, al­
though its absolute value changes only slightly with time.
The further significance of these results will be discussed after
the bomb tube work on BCV and water will be described.
(33)
Bonk Tub* Xiperlmnta (HCN+ Hg0);(C04- NH^)
In ordar to investigate the change of ratio of !& . boab tub** **r* aad* us
fa
,
a* follows:
HCX was prepared from KOV and Bg80^ and dried by passing through calcium
chloride*
A matured solum of this was placed in the calculated solum of Wfter*
Since the density of BOX is known (*7), it was possible to wake a solution which
contained equiaolocular fractions of HOI and HgO.
The prepared boab tube was placed
in liquid nitrogen and a solum of HOX solution matured into it.
The might of
solution used was calculated froa the density so as to gise a pressure ofiatma*
phere when coapletoly wporised* at the temperature to be used (U500 ).
The solum
of the boab tube was about 200 c.c.
The boab tubes (still imersed in liquid l2)veie connected to the puaps and
evacuated.
After about 1 half lour of puaping the tubes were sealed and placed in
the furnace for periods ranging froa 1 hour to
and cooled*
2h hours* They were then withdrawn
Son* tubes were inserted over water and opened*
part way* indicating the presence of nomabsorbable gas.
The water rose only
The water was analysed
for HCV, and XHj and both found to be present in all eases*
Other tubes were at*
tached to the gas anslyser and the gases drawn into the Toepler puap.
Analysis of
the gases gave the following average percentages:
t *c >
Pyrogall
00
not deteridned
61.0
E^SOl* fUaing(uasaturet*s)
Hg
00g
1*22
traces
C^'
U,U
Ig
20*0
Pyrogallol absorption was not recorded because of the ispossibility of ex­
cluding air froa the connection between the bosh tube and the pas analyser*
To study the reaction batmen 00 and XHj* an apparatus was constructed which
consisted of a generator for HHj and one for OCX XH^ was aade froa calciua hydroxide
and anmniua chloride: 00 froa sulfuric acid and sodlua fornate.
(3ft)
The gases were
dried by patting through solid KOH aad through a toluene dry iee trap to take out
residual moisture.
on.
The bomb tube was sealed into the system and the pumps turned
After the manometer indicated a good vacuum, the puaps were disconnected by
a stopcock and ammonia gas allowed to enter the bomb tube until a predetermined
preesure was reached.
The amnonia was frosen out of the bomb tube with liquid
nitrogen and 00 passed in until the pressure was equal to the previously measured
HHy
The HB^ was now passed back into the tube aad this mas sealed off the system
with a blow torch.
and withdrawn.
tube.
The boab tube was placed in the furnace at U500 for one week
Upon cooling* a white deposit was seen to form on the sides of the
The bomb was inverted over water and opened.
HHj and HCN.
The solution was tested for
Only the test for amnonia was positive.
The white substance dis­
solved in the water and no further attempt was made to analyse it.
Beferring to the gas analyses of the preceding page, it is apparent that these
values could be substituted for the values found in the kinetic experiments (see
table 30a) Evidently, whether Toraaldoxime or equinolecular quantities of BOV and
water are the initial substances, the final products are practically identical.
The most likely conclusion to be drawn from this is that Tormaldoxime deconposes in a primary split to give HCN and water.
react and give 00, amnonia, and other products.
These substances subsequently
The explanation for the change
of the ratio of Tc to fn with time is now quite clear.
Since the reaction of
HCN and water is slower than the deconposition of Tormaldoxime, the ratio will
continue to change even though all the Tormaldoxime has deconposed, since 00 does
not condense at these tenperatures and the measured volume of gas, which containes
the 00. will continue to Increase with time.
A mechanism for the primary rupture will be discussed in the conclusion.
The Pyrolysis of TomanIda
The foresaid# used was an Isstaan Kodak product.
fho material was
plaeod in a storage bulb aad a part of it puaped oat through tho apparataa
boforo run* were aade by beating the storage bolb aad opening tbe epparatos
to the puaps.
The apparatus was essentially tbe saae as that used for tbe Toraaldon*
iae except that bulb-O was taken oat and bulb-Y eas innersed in an oil bath*
She runs were nade using a sinilar procedure as in tbe Tornaldoxlae writ,
fa bare undertaken tbe pyrolyais of Tonanide in order to aseertain
whether tbe reaaraageannt of the oxiae to tbe anlde would giro a substance
■ore or less stable under tbe conditions of the experimente,
According to Sheraan (50) Yoraaaide gives VBj and 00 fpoa distillation
aad when heated above 195°0 yields also BOV aad water*
Trca a knowledge of the structure of the aside* we would expect IHj aad
00 to result froa a staple decomposition but BOV aad BgO could result -c
froa soae sort of rcarraageaent*
It seeas significant that both the oxiae
aad the amide will yield the saae products upon heating*
The oxiae will give
a larger aaouat of BOV aad HgO than the snide which leads us to suspect re­
arrangements of both forms to some sort of intermediate*
Bxperlaonti ware undertaken to determine the range of teaperatore for
the aeasurablo decomposition of Toraaalde aad also to attempt a study of
the kinetios*
Since tbe vapor pressure of Yorasaide is very saall (boils ad about
100°0 a£ 0|$aa* pressure), it was necessary to place the liquid in a reser­
voir surrounded by an oil bath capable of reaching a temperature shore
measurable pressuree of Yoraaaide could be obtained*
identical with that used for Yoraaldoxiae.
<#)
The apparatus was
The Iffeet of Air and litrio Oxide on the Decomposition
of Tornaldoxim*
Daring the earlier work oa Tormaldoxime, very erratic reanlte were
obtained for the velocity constant*.
The constants fluctuating too greatly
for an energy of activation to be calculated.
It was found that the stop­
cock* of the mercury seal type leaked when a certain pressure was reached.
Thus, Tormaldoxime, was being decomposed in the presence of snail amounts
of air.
After the necessary changes were made, the reaction rate was found
to decrease greatly.
In tbe later experiments precautions were taken to
exclude traces of air and no difficulty was experienced in keeping this
factor from influencing the reaction.
At a later time it was thought interesting to test the effects of ID
on tbe decomposition rate.
between ID +■ CH^ -* CHjBO.
According to Pease, an equilibrium is set up
Therefore the decomposition should be decreased
if 10 shifted the equilibrium to the right*
■0 was prepared by dropping pure distilled mercury into a solution
of
nltrosyl sulfuric acid in concentrated sulfuric acid according to
the directions given by Bilts and Bilts (51).
The solution turned blue*
but according to the experience of investigators at this laboratory, the
product Is pure*
impurities.
The gas was passed through Ygp^ and EOH tubes to remove
Tbe solution was dogansed by puxping aad allowing a few drops
of mercury to drop on the solution a few times aad then puxping for a
while, until bubbles rose slowly in the liquid.
The experiments were performed by first allowing some 10 to enter
the reaction vessel to the desired pressure aad then the Tormaldoxime
was admitted to the system.
The ID was found to accelerate the bate
of reaction oven though present in small amounts.
Large quantities of 10 bed a marked affect on the rate and in our at­
tempts to raise the pressure op 10 during the course of a run* a violent
explosion occurred, shattering the apparatus.
It was decided to abandon
this work aad to conclude that the reaction was an oxidation of the com­
pound.
This indioated that the hypothesis of Pease was not supported by
the facts since if 10 were an accelerating factor, as shown^aad larger
amounts of 10 would be present at h i g h e r temperatures^ then we would expect
that the rate of reaction would increase greatly with texperature aad give
a very small energy of activation.
lo such results were.noticed.
It nay
be possible that Tormaldoxime does break up into CH^ and 10 but no equili­
brium can be said to exiat from tbe results of this research.
Discussion of Besults
The problem before us ia to devise some mechanism to explain the
deooqposltion of lornaldoxlae, to give HOY aad ammonia*
Since there
la no report of work on other oxiae decompositions in the gaa phase,
no comparisons are possible*
Considering the classical picture of Tormaldoxime;
H
C a SDH
H -
The question arises how will this nolocale rearrange or decompose
(or both) if heated to U00°C.
Tor lack of suitable data on Tormaldoxime
a bond strength of 37*6 kcal is assumed for I -0 (U3).
If this value is assumed to apply relatively in the molecule, then
the S-0 bond is the weak qpot compared to the other bonds.
Significantly
it is about the energy of activation for the split to HCY and H£0
(39*6 kcal).
The following night well occur:
1*
?
H - C = YtOH
CHgY + OH
HgO 4- BOY
H
2*
?
H • C S BOH
(
H
)
H ■* 0 3 YDH -*■ (H • 0 3 I • OH) -> HCH+ HgO
(
)
The mechanism indicated by the kinetic studies calls for a unlmolseulcx decomposition*
Before attenpting to choose one of these, it might be well to point
out sons peculiarities of the deoooposltion*
Tutting the Arrhenius equation into the fora
l/BT
k a Ae"
aad substituting the following values taken from experiments:
(UO)
k r i.oi*io~3
f s 685°A
1 = 39.6
«i™.
I.«.icr3 s i»-
•oiTiae a s io9*6^ sec.-1
How A is tbs so calltd frequency factor sod for Host unimolecular
rsactIons is about 1 0 ^ .
Vhs low Talus iadicatss an unusual say of split*
tiqg.
Referring to othar similar easas, ths IgO decomposition has a low
Q
A ralua (4*2*10 )• This is attributed to an electronic transition in
going from reactants to products (44).
in the cases of isoaerlcations;
2 methylmaleic ester, cis methyl cinnamic ester, low A factors are found.
To account for these, Rice and Qershinowits (45) hare formulated the
eoncspt of exact orientation.
To quote from Kistiakowsky (52), *TJpon
considering tbe hypothetical equilibrium between tbe reactant molecule
and its immediate decomposition products and tbe mechanism of tbe reverse
(association) reaction, they (Rice aad Qersblnowits) conclude that when
considerable sterlc hindrance or, to be more precise, a necessity for
strict orientation exists in reforming the molecule from its products
(ethylidene dlacetate and Its bomologues), the A factor of the forward
fceactio n must be small.
In the case of aalelc ester, isomeri sations or
other aliphatic double bond coupwinds, no satisfactory explanation of
low A Taluss exists.*
Thus it is indicated that the decomposition of Tormaldoxime is being
inhibited by some eonplexlty of the molecule aad in all probability there
is a necessity for some rearrangement of tbe molecule as indicated by tbe
hypothetical step in mechanism (2).
Zt sssms preferable therefore to choose a nechanism like 2 In pro*
ference to 1, since In 1, the second step night he the rate determining
one giving a binoleculer reaction*
This mechanism will give no HCH aad HgO.
The next point is the
explanation of large amounts of 00 aad SH^ found in the bomb tube and gae
analyses*
Zt was at first thought that 00 aad VHj were produced in a
primary split by a rearrangement of Tormaldoxime to Tormenide.
experiments
on Tormaadde (see section on Tormamide) showed it would decompose to 00
and SSj*
Beferring to the gas analysis* consider the ratio
Yc
.
The
ratios decrease with time of standing in reaction vessel even though the
decooposition is conplete.
To confirm this, samples of gas were taken
froa the reaction vessel at Intervals and analysed*
They contained more
00 aad IHj the later the sanple was withdrawn after pressure changes had
ceased, indicating cosplete decooposition.
gas analyses results are these saaples*
The analyses reported in the
Thus I d aad HgO are evidently
reacting to fora 00 aad IH^.(See discussion under section "Analyses of Oases")
Considering the free energy of the reaction:
HOT + HgO
00 + IHj
the following falues are given
A * 198.1
HCH - 27,730calories
(5U)
"
H2OS.5h.U67
■
(55)
"
IE5 - - M 50
■
(56)
"
00 s-32,510
*
(57)
AYfggjfor the reaction is— £F,923 therefore the reaction
is possible as written.
Thus the reaction is permissible theraodynssdeally, assuming no
other more favored aide reaction*.
Sinoe thermodynamic* tell* u* nothing
about the speed of the reaction, it was thought wise to prepare bomb tube*
containing equimolecular portions of HOT and HgO and analyse the reaction
product* (see section on bomb tubes).
The bomb tube work confirmed the
theory and in addition indicated that 0gHfi, Hg, Hg and unsaturates may
result from the reaction of HOT and HgO and not from Tormaldoxime,
The explanation of the above considered reaction may well be the
following:
the formation of polymers of HOT has long been known, among
the polymers whose structure has been confirmed are diamino malelc di»
nitrile (U6, »*7)f
SHo ** 0
CN
U
HHg ** C - OT
(which is probably formsd from the HOT dimer HH * 0 s C * HH (diiminoethylene))
and
^
HHg - CH
OT
^
OT
Diiminoethylene Should form without any difficulty from HOT and in
the presence of water might well react as follows:
i
!
HH • 0 » 0 ■ HH
I
*
-► 2G0+2HH,
Hg j 0
0|
; Hg
9
This qppears the most likely mechanism with the meagre knowledge at
hedtsince approximately equal quantities of 00 aad HH^ were reported in
the early boab tube work on Tormaldoxime decomposition.
The task of scoounting for CgHg, unsaturates Hg, Hg aad the pyrogallol
(**3)
absorption Is a vary difficult one considering the paucity of information
on HCH polymers.
The presence of hydrogen, however, may well be the key
to the hydrocarbon formation*
Zt is not unreasonable to assume that nitro-
gen and hydrogen are produced by the complete break 19 of some higher
polymers or as reported (53)
HCH-fr(CH)g + Hg+Hg-t-wnreported products
aad froa this assumption, it is possible that hydrogenation of the un­
saturated polymers might occur.
Considering the large number of polymers
and hydrogen available, it is not difficult to conceive that hydrocarbons
would result.
The possibility of
GHgHOH
-¥ CHj+lD
2CHJ+-1I
OgHg+H
was under consideration*
HO was not found present but might well have
oxidised the cospounds present*
However HCH aad HgO give ethane so
that this hypothesis is not necessary*
The pyrogallol absorption has proven a very annoying problem
since oxygen produced by the decomposition would molt probably react
with the other products aad not appear in the reaction*
Considering Tormamide the reaction might proceed in one of two
ways
1*
HOOHHg
00 + HHj
2*
HCOHHg
H00 + HHg
H00+- IHg*^ 00+- HEj
Reaction 1 appears more likely since ee get no hydrogen which might
he possible from 2HCO
Hg
CO, since the H-C bond strength is very
small (1*0 , and Tormamide appears according to oar gas analysis to give
only CO and HH^,
in reaction 2 the possibility of the reaction products
reacting with the Tormaalde might produce complications which gas
analysis does not appear to bear oat*
The conclusion which seems to best fit the experiments performed,
would be a split of Tormaldoxime to HCH and HgO followed by a reaction
of these two substances to produce CO and NHj, aad the other products
found*
Polymerisation aad hydrolysis satisfactorily account for CO
and HH^,
Couplets explanation for the Hg, Hg and hydrocarbons is not
possible.
CO and HHj evidently react but it appears this should not
affect the primary split since a few days are necessary to fora any of
the white compound noted*
It appears that the energy of activation is
for the primary split to HCH and HgO aad all other reactions are purely
secondary*
final Soanary
Tormaldoxime deconposes to giro HCH and HgO.
The energy of activation
for thie step is 39.6 kcal.
HCH and HgO react to give X
aad HHj , small amounts of CgHg, un»
saturates, Hg and large amounts of nitrogen.
Tomemide decomposes to give X
and HH3*
The energy of activation
appears to be quite small, decooposition taking place very rapidly
at 200°C.
These experiments do hot contradict the work of John and others in
which Tormaldoxime was postulated to bo'formedJChe presence of HHj re*
ported in some eases is confirmed by this work, although Tormsmide
will also give HHj.
The reaction CHg HOH -*CHj + H0 is shown to be unnecessary to explain
the results of this work.
The reverse reaction CH^+ HO —> CHSHOH is
possible but nothing can be said about it froa these results.
Beferaaeas
1«
Paul Sabatier, La Thaorle Catalyse
2*
Starsly and Hinahelvood, Prsc. Boy« 3oc. (London) A 154, 335 (1936)
3«
Ysrhoek, Trana. Faraday 3oc. £1, 1521, 1533 (1935)
4.
C.B. Hinshalvood, J. Chao. 80c. 818, (1936)
5a
C.B. Hinshalvood, J. Cham. Soc. 812, (1936)
6. H.A. Taylor aad II. Barton, J. Cham. P h y s i c s , ^ 4l4 (1939)
7.
Staraly and Einahalaood, Proe. Boy. Soc. A 159» 32. (1937)
8. C.B. Hinshalvood, Proe. Boy. 8oe. (London) A 159* 192 (1937)
9a
Saaenor, latore 137, 29, 193 6)
10.
L. Staralay. Proe. Boy. 8oe. A 162, 557 (1937)
11,
Thoapaon aad Msissaar, Hatore lffi, 1018 (1937)
12«
C.B. Hinahelvood, J, Cham. Soc. 1568 (1937)
14.
M. Birton. Saylar and Oarla, Jau*. Cbem.Physics. 7, 1080 (1939)
15.
CaV. Hinshalvood, Proe, Boy. Soc. A 111. 380(1926)
16.
Allan aad Slekaan, J. la. Cham, Soc., §6, 2031* 1251 (193*0
17*
Behola aad Paaaa, J. im. Cham. Soe. 59. 766, (1937)
18,
P.O. Blea aad O.L. Polly, J. Cham. Physics
19.
Trarars, J. Cham. Soc., 1360 (1939)
20.
J. !• Hohhs and C.B. Hinshalvood, Proe. Boy, Soc., A 167,447 (1932)
21,
Thoapaon aad Linnatt, Trans. TsradaySoc. 874, (1937) Vol. 33
24,
Bamford, J,Cham. Soe«, 17 (1939)
25,
Baris, Jahn aad Barton, J. Am. Cham,Soc., 60, 10 (1932)
26,
H.A* Taylor aad P« Jahn, J. Cham. Physics J, 470 (1939)
27,
lafaBa Stascia aad H.Oa Yolkins, Can. J. Basaareh 18 B, 1*11 (19*10)
(4?)
273 U932)
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28*
Scholl, Bar.
2U, 573
(I89I)
29• Toe, Photometric Analysis, John Wiley A 80ns (1928)
30,
Chapmen, J* Soc, Chem. Industry 2$, IU13
31,
L, Joaes, J, Am, Chem, Soc,, £&* 328**, (1939)
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E, Lescoeur aad A,Higaut, Coiqpt, rend, gg,
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R. fippernan, Ber.J, 768 (187*0
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Semenov, Chemical Kinetics and Chain Beactloas, Clarendon Press (1933)
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A.Q.Allen, J, Am. Chem, Soc,, 52, 1032, (1936)
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(Jiauque, J. Am. Chem, Soc. 5f=»
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