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Патент USA US2108390

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Patented Feb. 15, 1938
Whit?eld Price, Charleston, W. Va, assignor, by
assignments, to ‘Westvaco Chlorine
Products Corporation, New York, N. Y., a cor
poration of Delaware
No Drawing. Application July 20, 1936,
Serial No. 91,620
14 Claims.
(Ci. 23-250)
ternal changes by dissolving a modicum of an al
are particularly effective stabilizers for chlorin
ated hydrocarbons. The reason for this is not
obvious, but the fact is as stated. For practical
reasons, alkyl thiocyanates are employed, these
kyl thiocyanate, most advantageously methyl
all being volatile materials. The isothiocyanates
thiocyanate, therein; a similar method being ap
plicable to other chlorinated. hydrocarbons; and
it also comprises a chlorinated hydrocarbon show
ing on test the presence of a volatile thiocyanate
10 ester; all as more fully hereinafter set forth and
are serviceable, albeit not better than the thic
cyanates. In these compounds, there is a char
acteristic nucleus. They contain a single hydro
carbon group connected by a single bond to the
This invention relates to stabilizing chlorinated
hydrocarbons; and it comprises a method of sta
bilizing trichlorethylene against deteriorative in
as claimed.
Chlorinated hydrocarbons'are in large commer
group SCN and the latter group in turn has the 10
carbon atom thereof attached to a single nitrogen
atom by at least two bonds; in the isothiocy
cial use because of their unin?ammability, con
anates the carbon and nitrogen are linked by a
venient boiling points and good properties as
solvents for grease, resins, rubber, etc. Trichlor
ethylene in particular ?nds much favor. It. is a
substance of convenient boiling point, around
double bond and in the thiocyanates by a triple
bond. The best of these alkyl thiocyanates is 15
87° 0. Most of these chlorinated hydrocarbons
are bodies of good stability, insofar as attack by
reagents is concerned. They are quite inert
chemically. All, however, have some tendency
to undergo internal changes in time, this being
particularly marked in the case of trichlorethyl
ene. The nature of these changes, that is, the
25 chemical mechanism involved, is not quite de?
nitely known, but in all cases there is ‘a develop
ment of acidity. Exposure to both light and air
favor these changes; neither singly having as
much e?ect as the two together. The particular
susceptibility of trichlorethylene may be due .to
its unsaturated character.
Various additions to these chlorinated hydro
the methyl ester, CH3._SCN. Methyl thiocyanate
has the lowest boiling point of these alkyl esters
having a boiling point between 130 and 131° C. I
have found it most advantageous for my pur
poses, partly because of this fact and partly be 20
cause it seems to have a characteristic stabiliz
ing effect greater than that of the other alkyl
Among these other thiocyanates '
which I have used and found desirable are ethyl
thiocyanate, isopropyl thiocyanate, butyl thio
cyanate, methyl isothi cyanate, ethyl isothiocy—
anate, and allyl isothidgyanate.
In degreasing with trichlorethylene, all these
esters stabilize the boiling liquid and stabiliza
tion is not impaired by accumulating impurities.
When the trichlorethylene is recovered by distil
lation the thiocyanate can also be distilled over.
vWhile the ‘stabilizing e?ect of these thiocy
carbons have been proposed in enhancing their
stability and inhibiting internal changes. To
anates is most marked with trichlorethylene, they
85 some extent, these are e?‘ectiv‘e, but the difficulty
are also advantageous with carbon tetrachloride,
arises that any inhibitor in the chlorinated hy
drocarbons must itself withstand trying ‘condi
tions; it must itself be stable. In many of the
commercial uses of these chlorinated hydrocar
bons, the ‘same portion of solvent may be kept ,
at a boiling temperature inde?nitely in the pres-l
ence of various, impurities. For example, in a
current method of degreasing metal and other
articles, the article is passed through a body of
45 vapor of trichlorethylene overlying a body of boil
ing liquid. ‘Condensed solvent trickles off the
article, carrying grease with it, and the solvent
is revaporized to serve anew. In this operation,
a limited amount of trichlorethylene at its boil
50 ing temperature is continually passing back and
forth between the liquid and the vapor states and
the stabilizer must persist over an inde?nitely
long time.
I have found that various thiocyanate esters,
or sulfocyanides, containing the radical .SCN,
chloroform, ethylene dichloride, the tetrachlor
ethanes and even with chlorinated aromatics.
Ordinary unstabilized trichlorethylene. in a
loosely stoppered bottle exposed to diffused day
light in a few hours becomes heavily acid on test;
an aqueous extract made with neutral water ex
hibits enough acidity to titrate. Phenolphthalein
is a suitable indicator for this purpose. With a
loose stopper, a little» access of air occurs, but
there is not much-evaporation. On the other
hand, a similar test'made with the same tri-.
chlorethylene containing a trace of methyl thio
cyanate does not develop appreciable acidity after
long standing.
In accelerated tests of similar character but
under more drastic conditions as regards illumi-_v
nation and access of air, trlchlorethylene contain
ing a little methyl thiocyanate does not develop‘
substantial acidity over long periods of .time.
Some of these tests simulate in a few days what
would happen in years of normal storage at the
are in constant contact with the metals. In the
In one test a quantity of the liquid is placed in
the ?ask of a Soxhlet apparatus. The compart
case of trichlorethylene, experience has shown
that with a little dissolved methyl thiocyanate,
the trichlorethylene becomes stable inde?nitely
long in the degreaser, whatever the character of
ordinary temperature.
Cl ment of the Soxhlet which acts as a receiver for
condensate, and which is equipped to siphon back
into the ?ask at intervals, contains a piece of
copper. A second piece of copper is placed in the
?ask itself and is of such dimensions that part
10 of its surface is below the liquid and part in the
vapor space above. Corrosion of the copper is
evidence of decomposition of the solvent. In this
particular accelerated test conditions are like
those occurring in a degreaser system.
Heat is applied to the ?ask at such a rate that
mild re?uxing occurs, so that over a period of
time, such as an hour or two, the siphon com
partment ?lls up and discharges back into the
?ask, Precautions are taken that the equip
ment stands in di?used light rather than direct
sunlight. Acidity determinations are made at
intervals on the liquid at a time when the siphon
compartment is empty. One‘of the features of
this test is the fact that liquid is distilled out of
the ?ask and condensed, and is exposed to the
the metal used in making the apparatus or
treated for degreasing.
While I have spoken of the stabilizing effect
of methyl thiocyanate and the other thiocyanates '
used with pure liquid: chlorinated hydrocar 10
bons, the same stabilizing e?ect is secured in
admixtures; either of chlorinated hydrocarbons
with each other or with other compounding
In chlorinated materials containing the thio
cyanates of the present invention its presence
can be recognized by e?’ecting saponi?cation of
a sample of the chlorinated hydrocarbon with
caustic soda, thereby making a thiocyanate. This
can be identi?ed by the usual ferric iron test.
What I claim is:
1. 'I‘richlorethylene stabilized by the presence
of a small amount of an alkyl thiocyanate.
2. The composition of claim 1 in which the
alkyl thiocyanate is methyl thiocyanate.
3. A chlorinated hydrocarbon stabilized by the
action of light and oxygen away from the main
body. It is assumed that certain stabilizers will . presence therein of a fraction of a per cent of
follow the vapor and condense with it so as to
stabilize the liquid in the siphon chamber, while
30 others of lower vapor pressure will remain in the
?ask while unstabilized vapor passes into the
siphon compartment.
Using this accelerated test, a sample of tri
chlorethylene containing 0.004 per cent methyl
thiocyanate developed no substantial acidity in_
a period of 72 days, whereas unstabilized trichlor
ethylene in the same test will show high acidity
in a very short time.
. In another accelerated test, a sample of tri
40 chlorethylene without stabilizer in 2 days devel
oped an acidity requiring 550 drops of hundredth
normal NaOH for neutralization, per 10 cc. of
the sample. The sample was extracted with neu
tral water and the water titrated. On the other
45 hand, the same trichlorethylene with an addi
tion of 0.01 per cent methyl thiocyanate, after 4
days’ exposure, had an acidity requiring only 7
drops per 10 cc., while trichlorethylene contain
ing 0.05 per cent isopropyl thiocyanate, after 3
50 days’ exposure developed only an acidity of the
same order of magnitude, requiring 8 drops per
10 cc. for neutralization in lieu of '7 drops.
Similar results are given by other chlori
nated hydrocarbons, such as, perchlorethylene
(CClzICClz). Ethylene dichloride is a solvent
much in use and it shows some tendency to de
an alkyl thiocyanate.
4. The composition of claim 3 wherein the
chlorinated hydrocarbon is ethylene dichloride. 39
5. The composition of claim 3 'wherein the
chlorinated hydrocarbon is trichlorethylene.
6. The composition oi.’ ‘claim 3‘ wherein the
chlorinated hydrocarbon is perchlorethylene.
'7. In the stabilization of chlorinated hydro
carbons against deteriorative internal changes,
the process which comprises dissolving therein
an alkyl thiocyanate in an amount correspond
ing to a fraction of a per cent by weight.
8. The process of claim 'I‘wherein the alkyl 40
thiocyanate is methyl thiocyanate.
9. The process of claim 7 wherein the addition
of thiocyanates is in amounts between 0.001 per
cent and 1.00 per cent.
10. The process of claim 7 wherein the alkyl 45
thiocyanate is methyl thiocyanate.
11. The composition of claim 1 wherein the
alkyl thiocyanate is the normal thiocyanate.
12. The composition of claim 1 wherein the
alkyl thiocyanate is an iso-cyanate.
13. As a composition of matter, a substan
tially neutral, stable liquid comprising a vola
tile liquid chlorinated hydrocarbon containing
dissolved therein between 0.001 to 1.000 per cent
by weight of a thiocyanate having the follow 55
ing structure:
composition under drastic industrial conditions.
- R—S-C EN
A sample of a particular ethylene dichloride of
wherein R is an alkyl group, the amount of the .
high commercial grade subjected to an acceler
60 ated test for 10 days developed in 10 cc. an acid , said thiocyanate being su?lcient to stabilize the
ity requiring 260 drops of the hundredth normal said chlorinated hydrocarbon against deteriora
caustic soda, for neutralization while the same tive internal changes.
ethylene dichloride with an addition of 0.02 per
14. As a composition of matter, a substan
cent methyl thiocyanate, after 10 days’ exposure. tially neutral, stable liquid comprisingv a volatile
65 developed an acidity requiring only 10 drops per liquid chlorinated hydrocarbon containing dis
solved thereln between 0.001 to‘ 1.000 per cent by 65
10 cc. for neutralization.
'As stated, the chlorinated hydrocarbons are weight of a thiocyanate having the following
bodies of tolerably inert character. In aapure structure:
neutral anhydrous state, they do not affect, nor
70 are they affected by, the common metals. But wherein R isan alkyl group, the amount of the
with any .development of acidity, the situation said thiocyanate being su?icient to stabilize the 70
It is, 01' course, of enormous practical
importance to maintain the inert character of
these solvents, this being especially true with the
solvents used in degreasing metals, where they
said chlorinated‘hydrocarbon against deteriora
tive internal changes.
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