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Carbon Suboxide in Preparative Organic Chemistry. New synthetic methods (1)

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Volume 13 Number 8
August 1974
Pages 491 - 558
International Edition in English
Carbon Suboxide in Preparative Organic Chemistry
New synthetic
methods (1)
By Thomas Kappe and Erich Ziegler[*]
Although it has been known for nearly 70 years, carbon suboxide was used almost exclusively
for the preparation of simple malonic acid derivatives until about 1960. Since then, however,
the significance of this unusual “bisketene” has steadily increased in synthetic chemistry (especially
that of heterocyclic compounds). This progress report surveys the possible applications of
C 3 0 2 in preparative organic chemistry, including photochemical reactions.
1. Introduction
While studying the action of phosphorus pentoxide on diethyl
malonate at 300“C, Dield’] observed that the generation of
ethylene and some COz was accompanied by formation of
small quantities of another gas which first caught his attention
by virtue of its powerful irritating action on the mucous
membranes. He was able to isolate a substance having a
boiling point of 6.8“C, to which he assignedl2] the structure
of allenedione ( I )
ery. Results of such studies have been presented in a recent
reviewt5].In the following we shall therefore only briefly touch
upon the most recent results concerning the structure of C302.
The aim of this progress report is primarily to present recently
developed applications of carbon suboxide to preparative
organic chemistry, particularly in the synthesis of heterocyclic
compounds“’
2. Preparation of Carbon Suboxide
Of the many reactions known to afford C 3 0 2 there are four
which lend themselves to laboratory preparations:
on the basis ofelemental analysis, molecular-weight determination, and, above all, a series of reactions leading to malonic
acid derivatives. He named the compound “carbon suboxide”[31. The following year Dielsr4]published another much
more productive synthesis from malonic acid and P4010which
is still used for the preparation of ( I ) in many laboratories.
The name carbon suboxide for ( I ) is somewhat misleading
since the compound does not behave as a “normal” oxide
of carbon but as a bisketene. Viewed in this way, ( 1 ) can
be considered as a doubly dehydrated malonic acid; most
of its reactions furnish derivatives of this acid. Owing to
its unusual structure, carbon suboxide has mainly attracted
the interest of theoretical and physical chemists since its discov-
____- _ _
[*] Prof. Dr. Th. Kappe and Prof Dr. E. Ziegler
lnstitut fur Organische Chemie der Universitiit
A-8010 Graz. Heinrichstrasse 28 (Austria)
Angew. Chem. internat. E d i t / Val. 13 (1974)
No. 8
0
a) Dehydration of makmic acid (2) with P,O
as used by Dield4] (ca. 23% yield);
at 140-1 50 “C,
b) Thermolysis of 0,O-diacetyltartaric anhydride (2,Sdioxotetrahydrofuran-3,4-diyI diacetate) (3) in vacuo at 601)-70O0C
491
(46-68%)
yield)I7];
or under normal pressure at 770 C (ca. 45%
c) Pyrolysis of diethyl oxaloacetate ( 4 ) in the presence of
acetic anhydride at 850-880 -C (48 % yield)[']; and
d ) Dehalogenation of dibromomalonyl chloride ( 5 ) with zinc
turnings in boiling ether (cu. 80% yield)'"
These preparations are considered in the available
review^[^*^], in some
with diagrams of apparatus.
Thermal decomposition of silver ketenide (6), which is accessible from silver acetate and acetic anhydride in pyridine,
is also reported to yield compound ( I ) quantitatively and
in high purity'] 21:
2Ag2C=C=0
16 i
'50C
C,02
+
C
+
4Ag
(I)
This route does not yet seem to have been exploited in preparative work, probably owing to the danger of explosion of
(6).
The most important preparation of (1) is that starting from
diacetyltartaric anhydride (3). However, until very recently
the formation of ( I ) was interpreted erroneously.
the discoverer of the reaction, initially formulated elimination
of acetic acid to give acetoxymaleic anhydride (7), as was
later confirmed ;further loss of acetic acid was assumed to give
acetylenedicarboxylic anhydride ( 8 ) which undergoes fragmentation with decarbonylation to form ( I ) . In contrast to
the results of D u s h k e ~ i c h who,
' ~ ~ in 1960, deduced the intermediacy of the hetaryne ( 8 ) in formation of ( 1 ) from both
(3) and ( 4 ) on the basis of 14C-labeling studies, in 1968
Crombie, Gilbert, and Houghron''] unequivocally ruled out
( 8 ) (or any other symmetrical derivative) as intermediate
by application of five differently "C-labeled diacetyltartaric
anhydrides (3) and acetoxymaleic anhydrides ( 7 ) and of
(3) bearing an 8O label in the ester oxygen function. instead,
C' in (3) and ( 7 ) is eliminated and an 0 atom of the 2-hydroxy
group of the original tartaric acid is retained; i. e. C 3 0 2arises
from the atoms shown in bold print in formula (7)[141.
3. Structure of Carbon Suboxide
The geometrical and electronic structure of carbon suboxide
has been a subject of detailed study in recent years''s-171.
The question whether C3O2 possesses a linear, angled, or
zigzag structurei1*I seemed to have been definitely answered
in favor of a linear geometry on the basis of exact analysis
of the IR spectrumr'9-221
when in 1969 Smith and Burrett[23]
put forward the hypothesis that C 3 0 z is only a quasilinear
molecule, the frequency of the bending mode at the central
C atom being 63cm-', on the basis of certain peculiarities
in the vibrational spectrum. Deflection experiments on molecular beams of C 3 0 2 in inhomogeneous electric fields have
recently demonstrated that the angle at the central carbon
atom can deviate by at most 9 from the linear configuration.
Electron diffraction studies["' on C302 lead to a similar
result.
Recent ab initio calculations with geometrical searching by
failed to show a low energy barrier for
Suhin and
a bending vibration about the central C atom. Instead, a
steep energy gradient is found even for small deviations ( 1 ,)
from the linear structure. According to this calculation^' 'I,
theC=CandC=Odistancesare 1.332and 1.243A (+0.005A)
respectively [the measured values are ~ 1 . 2 and
9 1.17 .&]12s1;
the resulting x-orbital energies are listed in Table 1, together
with the uh initio results and values calculated by Sirghahn[2h]
from photoelectron spectra.
T d b k I . rr-Orbital energies [ev] in carbon suboxide 1 1 )
-~
- -_
~ _.____
In,
Method
Zn,
- _ ~ _ ~ _ ~ _ _ _ - _ ~
ah initio [ 171
- 18.66
-
ah inirio [26]
from ESCA values [26]
- 17.74
- 16.0
~
~
- 11.89
- 17.69
- 1 X.72
- 11.12
- I0.8*0.2
- 15.0
.
__
~
.
..~
.-
Table 2 shows the charge distribution in carbon suboxide,
which is also of significance in its chemical behavior. The
unusually high negative charge on the central atom C 2 is
surprising. Noteworthy is the good agreement between the
values calculated from experimentally determined ESCA
Table 2. Charge distribution in O=C'=C2=C=0
(/J
_.
~
i
- co
0
C'
C'
-0.28
+ 0.45
+ 0.46
-033
- 0.36
-0.318
- 0.68
...-...~.~
Calc. from
ESCA values [26]
CNDO!2 [27]
uh initio [ I 7 1
rib inifio [26]
- 0.28
- 0.260
- 0.25
+0.419
+0.59
~-~_ ~ -~ _- ~ ~_
- _ ~
~-
-.~ _ ~ _ ~ _ ~ .
_
-~
. _ - .
The question whether the hetaryne (8) occurs as an intermediate in the pyrolysis of ( 3 ) , ( 4 ) , and ( 7 ) is of significance
since in the case of an affirmative answer other methods
values[2h1and those of a CNDO/2 calculation by Ohlsen and
B ~ i r n e l l e [ ~and
' ~ the uh initio calculation by Suhir7 and Kin?["];
the ah initio values obtained by Sieghahnr2'l predict an even
greater polarization.
4. Reactions of Carbon Suboxide
of aryne chemistry could be employed in the preparation
of ( I ) : e.g. diazotization of the anhydride ( 9 ) or reaction
of the aminotriazole (10) with lead tetraacetate.
492
As doubly dehydrated malonic acid, carbon suboxide ( I )
is extremely reactive. I t is therefore hardly surprising that
C 3 0 2can be used for reactions which give only unsatisfactory
AngPw. Chrm. inrrrnat. Edit.
1 Yol. 13 ( 1974) / No. 8
yields, if they proceed at all, when attempted with other
malonic acid derivatives. Many reactions of ( I ) even take
place below 0 C . Moreover, C3O2 is a "clean" reagent: viewed
formally all the reaction products are adducts of ( I ) to the
substrate, i.e. the reaction gives no by-products like HCI
or chlorinated phenols such as are formed with malonyl chloride or reactive malonic esters[2s.29! The advantage of using
( I ) with sensitive substrates or products is clearly seen. Catalysts such a s AIC13, and H 2 S 0 4 or p-toluenesulfonic acid,
can considerably enhance the electrophilicity of f' I ).
4.1. Reactions with Nucleophiles to Give Open-Chain Malonic
Acid Derivatives
When present in excess, nucleophiles (NuH) such as aliphatic
301, phenols[hd, 301.
or aromatic amines["d6'], alcohols1hd*6e.
or
react smoothly with C 3 0 , to form malonamides, esters, or thioesters.
+ 2NuH
O=C=C=C=O
ill
-
+
C,O,
ili
ROCO-CH=C=O
+
I IS)
k,
+ R-OH
A
k,
"'R
70
k , >2k,
ROCO-CH,-COOR
116J
I \
t 6o
Fig. I . Plot of reaction of C 3 0 1( I ) (3.3mmol) with I-propanol (IOmmol)
in ether (30ml)at.ZO C lafter [4X]). Intermcdiatc, wpropyl kctenecarhoxylate
I I S a ) : product. di-11-propyl maionate ( 1 6 a ) .
O=C=C=C=O
(1)
-
Nucleophiles add to C 3 0 2 in a stepwise reaction involving
ketenecarboxylic acid derivatives such as ( I5 ). Sta~idinyer'~'~
discovered in 1912 that, e. y. the non-catalyzed reaction of
alcohols with ( I ) is slower than with other ketenes, and
that unreacted C 3 0 2 is still detectable after several days at
low temperatures. Relevant quantitative studies have been
performed only very recent1y.with the aid of gds chromatography[47.48! Remarkably, these investigations show (in contrast
to previous assumptions["]) that the rate constant of the initial
step, i. c. formation of the ketenecarboxylic acid derivative
[e.y. the ester ( 1 5 ) ] is more than double that of the second
step in all the cases considered. A relatively high concentration
of intermediate must therefore always be expected in reactions
of ( i ) with nucleophiles, even when the latter are present
in excess. Figure 1 shows the course of addition of 1-propanol
to C 3 0 r .
Nu-CO-CH,-CO-NU
Reaction with water is relatively slow (perdeuteriomalonic
acid is formed with D201321). Hence the reaction with
a m i n e ~ l ~aniline~[~']
~],
amino acids[33,351, and proteins[3h1can
be carried out in buffered aqueous solution. Hrgar[-"' studied
the addition of e.y. phenol to ( I ) in aqueous solution in
the pH range 1-14 at 0 C. He obtained diphenyl malonate
as sole product; the maximum yield was found at pH 11.
Alkyl malonate formation is catalyzed not only by acids[301
(enhanced electrophilicity of C 3 0 2 ) ,but also by the corresponding Na alkoxides (conversion of substrate into the more
nucleophilic anion). The yield of ester then becomes almost
q ~ a n t i t a t i v e r ~Oximes['".
~].
301 , hydroxylamine and its N-substituted derivatives[40! amide ~ x i m e s [ ' ~and
]
also some of
their ethers[''] generally give linear malonic acid derivatives.
In some cases, open-chain N,N'-diacylmalonamides ( I I ) have
also been obtained from carboxamides (but not from thioamides, cf. Section 4.3.2)[431.
2R-CONH,
4.2. Reactions Affording Ketenecarboxylic Acid Derivatives and
Acylketenes
R-CO-NH-CO-CH,-CO-NH-CO-R
ill)
Action of excess organolithium compounds (12) or Grignard
compounds (13) on C 3 0 , in ether followed by hydrolysis
likewise furnishes p-diketones ( 14)[44.4s1,sometimes in enolized form.
The reverse reaction, formation of such ketenecarboxylic acid
derivatives as reactive intermediates on thermolysis of malonic
esters [i. CJ. (16) + ( 1 5 ) ] was postulated a s early as 195S~4y~28!
In 1967 Zieyler and Strrkl5"] were able to show in an I R
study that heating of malonyl chloride (18) to 80 C affords
the same ketenecarbonyl chloride { 1 7 ) as is formed on mixing
of gaseous HCI and C 3 0 2 .Addition of alcohols to ( I ) with
formation of ( I S ) can likewise be observed by IR spectroscopy
whereas cleavage of aryl malonates to ketenecarboxylic esters
can only be detected above u i . 250 'C by this method["'!
C,O,
0i
aCI-CO-CH=C=O.-HC'
1/71
80 C
CI-CO-CH,-CO-CI
(1x1
The intermediate formation of relatively inert ketenecarboxylic
acid derivatives or acylketenes in reactions of ( I ) with nucleophiles can be exploited for preparation of mixed-functional
493
derivatives of malonic acid. Friedel-Crafts acylation of aromatics with C 3 0 2 followed by hydrolysis and decarboxylation
of the aroylacetic acids (20) generally affords only the methyl
ketones (23)[”]. The existence of the aldoketene ( 1 9 ) can
however be established by treating the reaction mixture with
ethanol or aniline instead of water. In this case, ethyl aroylacetates (21 ) or aroylacetanilides ( 2 2 ) are formed[s31.
Reaction of the Grignard compounds (13a)--(13c) with
the molar ratio 1 : 1 also proceeds Eia the non-isolable
acylketenes to yield the 2,4,6-triacylphloroglucinols ( 2 6 ~ ) ( 2 6 c ) as major products; the 4-hydroxy-2-pyrones ( 2 7 a ) and
( 2 7 b ) can be isolated as side product^['^*^^^. In the most
thoroughly studied[S51reaction of f 1 3 a ) , formation of acetophenone, P-hydroxy-P,P-diphenylpropionic acid, benzophenone, triphenylmethanol, and biphenyl was also
c302 in
boxylic acid intermediates). However, systematic studies on
this point have yet to be performed.
4.3.1. Heterocycles Containing Two N Atoms
The reaction of c 3 0 2
with phenylhydrazineyielding -phenylpyrazolidine-3,5-dione (29a) was described by Van A l ~ h e n [ ’ ~ ~
as long ago as 1924. Later reports[60-6z1are concerned with
reactions of other substituted hydrazines to form pyrazolidinediones, including that of hydrazobenzene ( 2 8 b ) which otherwise tends to resist “malonylation”. Unsubstituted hydrazine
itself gives only linear
0
Slow introduction of C 3 0 z into dilute ethereal solutions of
the aliphatic diamines (30a)-(3Ue) furnishes the 7- to 15membered cyclic malonamides (33a)-(33e) in quantitative
yield[61.631.
Rapid addition of{f)(e.g.by shaking ofa toluene
C,Oz solution with an aqueous diamine solution) leads to
linear p ~ l y a r n i d e d641.
~~.
detectedls6]. Most probably, trimerization to the phloroglucinols (26) and dimerization to the pyrones ( 2 7 ) does not
occur uia the free acylketenes ( 2 5 ) , but proceeds directly
cia the corresponding MgBr complexes[’’1. While dimerization
of acylketenes to 6-substituted 3-acyl-4-hydroxy-2-pyrones of
type ( 2 7 ) has long been known[”1, the trimerization of an
aldoketene to a phlorogiucinol derivative has hitherto apparently been observed only with ber~zylketene[~~].
4.3. Reactions Yielding Heterocycles
On reaction of C302 with substances whose molecules possess
two nucleophilic centers, ring closures can of course occur
ilia the intermediate acylketenes. Prerequisites for such a reaction course are:
a) A favorable mutual spatial orientation of the two nucleophilic atoms (1,2; 1,3; or 1,4 position, the number ofsix-membered
heterocycles resulting from a I ,3-arrangement so far having
been found to greatly outweigh the other possibilities), and
b) approximately comparable nucleophilicity of the two
centers (otherwise mainly open-chain products result).
In borderline cases where both open-chain malonic acid derivatives and cyclic products are formed, the yield of the latter
should increase on application of the dilution principle (particularly in view of the relatively long lifetimes of the ketenecar494
o-Phenylenediamine (31 ) gives 1 H-l,5-benzodiazepine2,4(3H,5H)-dione (34)[’91, and urea (32) smoothly yields barbituric acid ( 3 5 ) (75% in acetone+AIC1&hll, 85% in
DMF[6’1). While reaction of diphenylguanidine affords two
isomeric 2-iminobarbituric acids alongside an open-chain
malonic acid derivative, the threefold substituted guanidines
( 3 6 a ) and ( 3 6 6 ) give only the 2-iminobarbituric acids ( 3 7 u J
and ( 3 7 b ) respectively[661.
((:EII,NH)2C=N-li
(361
+ C302
i1)
-
5
f k C S \ ~
0
K-NAN I
C&
[ff),
It = C‘bIls;
(h), t i
137)
CGIIS-NH-CO
Amidines (38) react with malonic esters in the presence of
Na a l k ~ x i d e ‘or~ ~with
] malonyl chloride[681to give moderate
Angew. Chern. iiitcrnaf. Edit.
1 Val. 13
(1974)
NO.8
yields of hydroxypyrimidones (39)[691;however, as a cyclizing
reagent, carbon suboxide leads to almost quantitative conversion even in the cold. Especially good results are obtained
with N-aryl-substituted ben~amidines"~](cf. also Section
4.3.5.2).
. ,
A'
I
R'
(38), R' p r e f e r a b l y A r
(39) [691
Amide oxime ethers react with malonyl chloride to give exclusively pyranopyrirnidinedione~[~
I. Experiments on acetamide
oxime ether and benzamide oxime ether ( 4 0 ) , however, showed
that the parent compounds, in this case the N-alkoxypyrimidones (41), are also accessible by reaction with C302 at
- 2o*,c[42.711
'
r-Amino-N-heterocycles such as 2-aminopyridines, -pyrimidines, -oxazoles, -thiazoles, etc. can be regarded as cyclic
amidines. It therefore comes as no surprise that substances
of this class undergo exceptionally ready reaction with C 3 0 2
to give fused hydroxypyrimidones, some of which are accessible
only with difficulty, ifat all, by other routes. Thus 2-aminopyridine (42a) furnishes "malonyl-cc-aminopyridine" (43a)[73-751
which was first synthesized by Chichibabin in 1924"21. The
2-aminopyrimidines (42 b ) and ( 4 2 c ) likewise afford almost
quantitative yields of the pyrimidopyrimidines (43 b ) and
( 4 3 ~ respectively[431.
)
A more complicated reaction course
i s observed in the cyclization of non-symmetrically substituted
2-aminopyrimidines for which ring closure can adopt two
different directions, depending upon the s u b s t i t ~ i e n t [ ~ ~ ~ .
(42)
(a), X
(h), X
= CH, R =
= N, R = H[431
741
(43)[751
and compounds (49)"". "1, respectively. Finally, (SO) and
(51) respectively can be obtained from 2-amino-5,6-dihydro4H-1,3-oxazine and -thiazineC7'!
4.3.2. Heterocycles Containing One N and One S Atom
As mentioned in Section 4.1, carboxamides yield only openOwing to the
chain malonic acid derivatives with c302[431.
approximately comparable nucleophilicity of their N and S
atoms, thioamides (52) behave differently. Thus thiobenzamide[431and substituted thiobenzamides give almost quantitative yields of 6-hydroxy-1,3-thiazin-4-ones
(53) at as low a
temperature as - 60. C[6s.8 0 - R21. Heterocyclic thioamides like
nicotinthioamide, isonicotinthioamide, and picolinthioamide
behave ~ i m i l a r l y [ ~ ~ . ~ ~ 1 .
On use of an excess of C 3 0 2 and at higher temperatures,
further reaction with ( I ) occurs. Pyrone derivatives ( 5 4 ) are
easily isolated in pure form, whereas higher polypyrones can
only be obtained as mixtures (cf. also Section 4.6)[43.6s1.
Addition of ca. 15 C 3 0 z molecules (statistical average) could be
detected with a product that was insoluble in boiling dioxane[431.
According to Dashkevich[61.
831, thiourea (55) and N-arylthioureas afford thiobarbituric acid ( 5 7 ) and its N-aryl derivatives in the presence of AICI3. However, Zieyler'431 found
that in the absence of AIC13 thiourea readily adds two moles
of C 3 0 2 . It could recently be demonstrated that the sulfur
isincorporated into the bicyclic ring system to form the pyrimidothiazine (S6)[821. In contrast, the thioxo group remains
intact on reaction of thiobarbituric acid ( 5 7 ) with C3O2
to give the pyranopyrimidine (58)[821.Hence it follows that
( c ) , X = N, R = CH3[431
2-Aniinooxazole and 2-aminothiazole react similarly to form
the fused pyrimidines (44)["] and (4S)[43. 781 respectively.
2-Anunobenzoxazoleand Zaminobenzothiazole yield (46)[741
and 4 7 ) L 7 4'*I,. respectively. Reaction of 2-amino- 1,3,4-oxadiazole and 2-amino-l,3,4-thiadiazoles
with ( I j gives (48)[74J
0
Angeu, Chem. internut. Edit. / Vol. 13 (1974)
0
/ No. 8
157)
l N )
( 5 7 ) cannot be an intermediate in the formation of (56).
Instead, thiourea reacts with C 3 0 2as a "thioamide" to form
a reactive 2-aminothiazinone which, as an "amidine", immediately reacts with a second molecule of ( I ) to give (56) (see
Section 4.3.1).
N-Acylthioureas (59a) afford 2-acylamino-6-hydroxy-l,3thiazin-4-ones (60)[831whereas dithiocarbamic esters (59b)
react with ( 1 ) in acetonitrile or ethyl acetate to form the
corresponding 2-alkylthio derivatives (61 )la41.
495
Benzimidazole-2-thiol (62) exhibits a remarkable behavior
in that it undergoes cycloadditionwithC302 to form a thermolabile I : 1 adduct ( 6 3 ) . If this compound is heated for a
l.CY,),
(SYhj,
X = R-CO-NIi
x = K-S
OH
160), X = IGCO NII
(bl),
x=
It-s
few minutes in five times the amount of pyridine, it decomposes
to benzimidazole-2-thiol ( 6 2 ) and the pyrone derivative
(64)1741.Naphthimidazole-2-thiol behaves similarly[741.
0
Another class of compounds containing an active methyl or
methylene group 3 to a C=N double bond is found in the
imidic esters. CyclIc imidic esters such as the 2-oxazolines
OH
ca. l3-30%/+
(I)
164)
The addition product (66) formed from 1,2,4-triazole-3-thiol
( 6 5 ) and C3O2 is even more labile and decomposes to the
starting materials on heatingr7'] [cf. the retrocleavage of mesomeric thiazine betaines ( I 2 1 )-( 223)].
Kn = CH3,
3, 4, C6H5
5, 6
(74,
( C&OH
W"
y o
NRz
( 7 5 ) afford only addition products with 2mol of C302 even
when the reaction is carried out in ether at 20 'C[ssl.
0
4.3.3. Heterocycles Containing One N Atom
Enamine derivatives ( 6 7 ) , which are accessible from P-0x0
esters or P-diketones by treatment with ammonia or primary
aliphatic or aromatic amines, undergo ready reaction with
C 3 0 2at 20 'C to form 4-hydroxy-2-pyridones (68)[851.
1
2-Picoline does not react with C 3 0 2 . However, if the side
chain is activated by an
nitrile[2y1,or acyl group[*'],
then ( 7 7 ) gives almost quantitative yields of the 2-hydroxy-4quinolizinones (78 ). In the same manner, 2-quinolylacetic
ester also yields the corresponding benzo derivative["!
(77)
Reaction of the anils (69a)-(69d) with C 3 0 2 ( 1 ) in ether
to give the bicyclic 4-hydroxy-2-pyridones (70a)--(7#d)
proceeds somewhat less easilyLs6! The anil of camphor
proves to be an exception: it reacts with ( I ) only under
drastic conditions (100 C, 4 h ) to give a poor yield of the
pyranopyridinedione ( 7 1 ) [ 8 h l .
In anaiogous manner, the hydrazones ( 7 2 ) can be converted
into N-amino-4-hydroxy-2-pyridones in ether at 40-80 'C
in an autoclave; the (readily separable) pyrone derivatives
(74) are invariably formed as side
496
X = CO&, C N , C o R '
(78)
The reaction of C 3 0 2 with an excess of aniline affords malondianilide (82) quantitatively. This is frequently utilized in
the quantitative determination[6e1of the C 3 0 2content of solutions in a method already employed by did.^[^^]. However,
0rnori'"'I has recently shown that, in the presence of AIC13
in refluxing benzene, reaction of C 3 0 2 and aniline in a molar
ratio of 3 : 1 yields 17 "/o of 4-hydroxyquinolone (81 u ) alongside ( $ 2 ) . The transient occurrence of ketenecarboxanilide
(80) can be demonstrated by formation of malonmonoanilide
Angew. Chi,m. internor. Edit.
1 Vol. 13
(1974)
/ No. 8
( 8 3 ) ( 7 8 % ) on addition of water to' the reaction mixture
(prior to heating in benzene). Higher yields (up to 67%) of
substituted quinolones (81 h ) - ( 8 1 d ) are obtained on use
of methoxyanilines ( 74,h)-( 7 9 d ) . Malondianilide ( 8 2 ) is
known to afford 4-hydroxyquinolone ( 8 l a ) in 93% yield
on heating to 245-25O:'C in the presence 0 f A l C 1 , ' ~ ~not
~ ;even
traces of this compound are formed from (82) and AICI,
in refluxing benzene (80"C)1931.
Direct reaction of C i 0 2 with phenol in the presence of
AICl,["'] (0. y. in tetrachloroethane) affords 28 /o' of diphenyl
malonate ( 8 7 ) as major product,alongside very small amounts
of compounds ( 8 4 ) and (85). On use of 0-,m-, and p-cresol
the yield of 4-hydroxycoumarins rises to ca. 10% while that
of the pyrone derivatives remains constant at 0.5 to 1.1 '10.
In the presence of H z S 0 4 however, only malonic esters are
Ring closure with ( I ) to give heterocycles containing one
0 atom also takes place with methyl(pheny1)pyrazolone ( 8 8 I.
Depending upon the reaction conditions, the pyranopyrazolone (8Y) is accompanied by varying amounts of pyranopyranopyrazoledione (
4.3.4. Heterocycles Containing One 0 Atom
Ring closure reactions of C 3 0 to yield heterocycles containing
one 0 atom as side or subsequent reactions have repeatedly
been mentioned in the foregoing Sections; examples included
formation of the pyrone derivatives ( 5 4 ) , ( 5 8 ) , ( 6 4 ) . ( 7 1 ) .
( 7 4 ) , and ( 7 6 ) . This property of C 3 0 2 to react with heterocycles containing the malonyl grouping and with other electron-rich phenols in a process involving annelation of a 4-hydroxy-2-pyrone system was discovered by Zieg/er[941as long
ago as 1961. Since 4-hydroxy-2-pyrones again contain a reactive malonyl grouping and can be regarded as an electron-rich
phenolic system, this reaction can be induced to yield polypyrone derivatives if conducted in the presence of excess C302.
The structural relationship of this class of compounds to
"red coal" is discussed in Section 4.6. In the following we
shall consider the reaction of carbon suboxide with phenolic
compounds, ketones, and 1,3-diketones.
4-Hydroxycoumarin ( M ) ,which is itself a "malonic acid derivative" formed in high yield by self-cyclization of diphenyl
malonate ( 8 7 ) at 150 C in the presence of A1C13f951,
adds
o n e m o l e o f C 3 0 z a t90 C i n T H F togive the pyronederivative
(85) (a.50% yield). The reaction also yields polypyrones
such as ( 8 6 ) which formally arises by addition of 4mol of
C,O, to phenol, and which can also be synthesized in stepwise
manner ria reactive malonic esters[94.9hl.
The action of C 3 0 2 on P-diketones and 8-0x0 esters in the
presence of H2SO4 was first described by H e y ~ r [ ~ This
'~.
author showed that, e.g., pentanedione ( 9 1 ) reacts with 2mol
o f C 3 0 2in ether, and formulated the product as the cyclobutapyran derivative (Y2 h ) . However, Hradetzky and Ziegler'981
were able to demonstrate that the product is actually the
isomeric pyranopyrandione ( 9 2 0 ) and that the reaction with
ZC,Oz can be applied to a series of further P-diketones.
Omorif9"] subsequently found that the 1 : 1 adduct (Y3) is
also accessible in good yield on reaction of ( 9 1 ) with (1 )
in equimolar amounts below 5 C ; under analogous conditions
he obtained the tetrahydrocoumarin derivative (Y4) from
dimedonel"'].
0
0
A much more complicated course is taken by the reaction
of C.302 w i t h unsymmetrical P-diketones like benzoylacetone
(95). A 2 : 1 addition would be predicted to yield the isomeric
pyranopyrandiones ( 9 6 a ) and ( 9 6 h ) owing.to the ambifuncAngun,. Chcm. internat. Edit.
1 Vol. I3
i I Y 7 4 ) I No. X
497
tional character of (95). In fact, O r n ~ r i ' isolated
~~]
two products on reaction of (95) with C,O,, which he formulated
as (96a) and (966), probably being ignorant of an earlier
study"'". According to Zivgler et ~ l . ~ ' ~ ' ' however,
,
the major
product of prolonged reaction (8 days) between ( I ) and (95)
in ether and in the presence of H 2 S 0 4 is the "r,y-pyronopyrone" (98) and the deacylated['"] 'k,x-pyronopyrone"
(97)['0z1. Owing to the similarity in themelting points['"~ 'I
and the spectroscopic data"'2c1, there is good reason for
assuming that the substance formulated as ( 9 6 a ) by O r n ~ r i [ ~ ~ ]
is in fact (97)[''31.
explanations have so far been proposed for the catalytic
action of H 2 S 0 4 : formation of an electrophilic cation
8
(O=C=CH-C=O)
by protonation of C3021991;
generation
of reactive sulfuric malonic anhydridesf9*]; and finally
rupture of the hydrogen bonds in the enolized dicarbonyl
compounds by the mineral acidr9'].
This apparently somewhat obscure behavior of benzoylacetone
(95) can be explained, not only by the fact that reaction of (95)
with, v. g., malonyl chloride leads initially to the two isomeric
4-hydroxy-2-pyrones (99) and (100) (which are undoubtedly
intermediates in the reaction with c3oz) but above all by
the rearrangement of (100) to (99) at the melting point
(168°C) or on acid catalysis[L04!Hence it isalso understandable
why the stable substance ( 9 9 ) gives exclusively ( 9 8 ) in good
yield on treatment with C 3 0 2 in the presence of H 2 S 0 4
f97)
f 98)
011
i 99)
011
( 100)
whereas the rearrangeable compound (100) furnishes a mixture of (96u), (Y7), and ( 9 8 ) which can only be separated
by chromatography[1001.
While acetoacetic ester and ( I ) give a 70% yield of the
pyranopyrandione ( I 0 1
simple ketones lacking an additional activated methylene group are converted only with
difficulty and in unsatisfactory yields into pyranopyrandiones.
Thus cyclohexanone ( 1 0 2 ~and
) cycloheptanone (l02h) merely give I C r l 5 0 / , of the pyranopyrandiones (IO3a) and
(103b).respectively after six to eight weeks' reaction (without
H 2 S 0 4 as catalyst)[431.Reaction of acetone with ( 2 3 0 2 (in
ether with HzS04)furnishes only 8 % of the pyranopyrandione
( 104)[9y1;
a somewhat higher yield of (104) can be obtained
from triacetolactone (105) and c 3 0 2 ' 9 x 1 .
It appears remarkable that 1,3-dicarbonyl compounds react
with C 3 0 2 only in the presence of protic acids. Three
498
0
All pyranopyrandiones react with ferric salts to give intensely
colored 3 : 1 complexes which can be extracted from aqueous
media by chloroform[931.
Particular mention should be made of the following fact:
All pyranopyrandiones of the kind considered in this Section
are "protected polyoxocarboxylic acids. The significance of
this class of compounds-especially
the polypyrones such
as compounds of type (86)-for the biosynthesis of phenolic
natural products is known'1051.The protected P-trioxocarboxylic acid chain is shown in bold print in formula (104).
Action of alkalis on this compound under various conditions
yields orsellinic acid, orcine, and other phenolic compounds
which can themselves act as intermediates for natural produ c t ~ [1051.
~ ~ Other
.
synthetic pathways have hitherto been
commonly employed for the preparation of such polypyrone
compounds. The above results would suggest that C302 may
also be used to advantage for the production of such polypyrones ( = polymalonyl compounds) (cf. also Section 4.6).
4.3.5. Reactions Leading to Mesoionic Heterocycles
4.3.5. I . Five-Membered Systems
It has been shown in Section 4.3.3 *at azomethines with
?-methyl or a-methylene groups afford 4-hydroxy-2-pyridones.
In the absence of the acylatable group, as in the azomethines
( 106) derived from benzaldehydes, a completely novel reaction
takes place with C302.
The reaction of benzylideneaniline with ( I ) was first reported
by Dashkroich[L061,who assigned the spiro structure (108)
to the product and assumed a primary [2+2] addition to
the p-lactam ketene (107) followed by [2+ 21 dimerization
(cf. Section 4.4). In fact, however, the reaction does not afford
Anqrw. Chrm. infernat. Edit. Vol. 13 (1974)
1 No. X
a 2 :2 adduct but (as can be shown by mass spectrometry)
instead a 1 : 1 adduct. Srerk et a/.['071proposed a zwitterionic
structure (109) describable only in terms of a series of
and ( 1 15 1 react very smoothly with reactive acetylencs, v. y.
( 1 1 5 ) with dimethyl acetylenedicarboxylate to form the addition compound ( I 18 j , which is, however, extremely prone
to stabilization by loss of phenyl isocyanate, yielding 2-pyridones ( I 1Y)110y~111.112! Thisconcept of preparing mesoionic
heterocycles with the malonyl grouping can be applied to
N-substituted thioamides (cf. Section 4.3.2); thus thiobenzamides (Z20) react with C,O, in ether to give the mesomeric
thiazine betaines (121 )I1 Similarly, pyridine- and pyrimi-
resonance formulas ( e ,g. AHB). The charge distribution in
compounds (109) is probably best described by formulation
C. Besides benzylideneaniline, a large number of other Schiff
bases react similarly with C3O2[Io7,
lo8]. In the preparation
of compounds such as ( IOY), carbon suboxide can be successfully replaced by malonyl chloride[Io7!
4.3.5.2. Six-Membered Systems
Amidines and monosubstituted amidines react with ( 2 3 0 2
to form hydroxypyrimidones (see Section 4.3.1) which exist
predominantly in the tautomeric zwitterionic form[691.N,N'Disubstituted amidines such as ( I 10) and ( I 1 2 ) which contain
only one replaceable H atom should accordingly yield "fixed"
zwitterionic pyrimidines directly on reaction with ( 1 ). That
this does in fact occur was demonstrated simultaneously by
Potts'Io9' and K a p p r [ l l oinl 1971 for N-substituted 2-aminopyridines ( I 1 0 ) which afford the betaines ( I I I ) on reaction
in ether.
8
H
(110)
dine-2-thiol furnish the zwitterionic 1,3-thiazines ( 1 2 2 ~ and
)
( 1 2 2b ) , respectively, and 2-thiazoline-2-thiol the zwitterion
(123)" 51. Thiazine betaines also undergo 1,4 dipolar cycload-
( a ) , R = CH3[1091
( h i , R C6H5'1'0'
(111)
(IZZaj, X
This reaction can also be applied to simple N,N'-disubstituted
amidines ( I 1 2 ) (including formamidines, R = H)I"Z1. In similar fashion, N-substituted amide oxime ethers (113) can yield
N-alkoxypyrirnidine betaines ( I 16)" 31. Finally, further
extension of this synthetic principle to N,N'-disubstituted Salkylisothioureas (1 1 4 ) affords the 2-alkylthiopyrimidine zwitterions ( I 17
41.
Derivatives, e . g . of (1151, substituted at C-5 can also be
prepared from reactive malonic esters and malonyl chlorides" l o ] ; however, satisfactory results are obtained only with
carbon suboxide for compounds that bear no substituents
in the malonyl moiety. The resulting pyrimidine betaines ( I I 1 )
and (115)-(117)
can also be described only by a series
of canonical resonance formulasil 1 Formula B best describes
the charge distribution, while the "sextet canonical structure"
C indicates that these compounds are potential starting materials for 1,4-dipolar cycloadditions. Indeed, compounds ( I 1 I )
Angrw. Chem. internat. Edit. ,IVol. 13 11974)
1 No. 8
= CH
i 123)
(122h), X = Ti
ditions; for instance, reaction with aryl isocyanates proceeds
ria an intermediate analogous to compound ( I / # ) with elimination of carbon oxide sulfide to give mesoionic pyrimidines,
e.g. ( 1 2 1 ) + ( l l S ) i 1 1 6 1 . When heated to above their melting
point the thiazine betaines (121)--( I23 j eliminate C 3 0 2 .
These substance can therefore be used a s sources of carbon
suboxide[' 51.
4.4. "Cycloadditions"
As already mentioned, C 3 0 2appears to behave as a "double
ketene", and thus as a double electrophile, in all its reactions:
hence any substrate is doubly acylated stepwise ciu a
ketenecarboxylic derivative to form open-chain or cyclic
malonic acid derivatives.
499
However, the question has repeatedly been raised whether
C,O, might not also undergo electrocyclic [2 21-cycloadditions (c>. y. .2,+.2,). For instance, Ljlrich'"" formulated the
reaction of ( I ) with enamines such as ( 6 7 ) and ( 6 9 ) as
proceeding uia a bicyclic intermediate by analogy with the
behavior of simple ketenes, albeit without experimental evidence.
+
Assumption of a double [2+2] cycloaddjtion led Dashkecic.h1'061to (erroneously) assign the structure ( 1 0 8 ) to the
reaction product obtained from ( / I and benzylideneaniline.
As early as 1924, die/^[^'] described the reaction of acetone
with ( 1 ) in the presence of oxalic acid and H z S 0 4 as a
[2 + 21-cycloaddition of the transient ketenecarboxylic acid
(124) (the water arises from decomposition of the oxalic
acid) to the C=O bond of acetone with formation of the
@-lactone (12.5). This concept of the reaction course has hitherto been incorporated in nearly all reviews'6b, 6 e l . However,
the reaction product obtained by Diels has been
to be Meldrum's acid (/26)[1171
and not ( / Z S ) . Remarkably,
the ester of the substituted ketenecarboxylic acid can indeed
ucts are compounds (130a)--/130c) having a Meldrum's
acid skeleton and not the @-lactoneswhich are usuaIIy obtained
from ketenes. Cinnamaidehyde ( 128) and thiophene-Zcarbaldehyde ( 1 2 9 ) react in an analogous manner. The structure
of the products is indicated unequivocally by degradation
experiments. Moreover, Wesse/y['2'I prepared (130a) independently and almost simultaneously by condensation of
"phenyl-Meldrum's acid" with benzaldehyde. This synthesis
also throws some light on the probable formation of ( / 3 0 )
(132): A certain amount of water is inevitably introduced
into the reaction system by the sulfuric acid; the resulting
malonic acid (or malonic sulfuric anhydride) reacts with the
aldehydes affording Meldrum's acids which undergo ready
condensation with aldehydes to form unsaturated derivatives"
(the water functioning as catalyst being released in
the process).
A detectable primary [2 +2]-addition of C 3 0 2 seems to have
been reported only recently by R. W H o f f i n ~ n n [ for
' ~ ~an
~
electron-rich olefin. After reaction of C , 0 2 with tetramethoxyethylene (133) in ether, approximately equal yields of a
1 . 2 adduct ( 1 3 4 ) and a 2:2 adduct ( 1 3 5 ) can be isolated.
Since the structure of these compounds appears to be estab-
2
x x
x x
1.5
f;
Reaction of the benzaldehydes ( 1 27a)-( 1 2 7 ~ with
)
( 1 ) in
ether and in the presence of H 2 S 0 4 likewise circumvents
[2+ 21-addition. According to Hopf and Hega'r"zol, the prod-
1 2 7 ) ( a ) , K = CbH5, (h), R
I28)
I 29)
500
= p - C B H I C H 3 , (c), H = / ? - C 6 H 4 C l 1 / 3 0 )
K = C&,-CH-CH
(1311
H = 2-Tliienyl
(132)
0
&x
-
x
X
x
O
xx
+
X
x o o
0
1133)
i 1)
(134), 22@0
1 :2-a d d u c t
( 1 3 5 ) , 19%
2:Z- a d d u c t
d
(136)
act as a .2, component in [2+2]-cycloadditions, as Sterk
recently demonstrated in the case of their dimerimtion[' "1.
Furthermore, the addition of ethyl ethylketenecarboxylate to
benzylideneaniline yields a p-lactam as [2 + 21-adduct; however, the reaction involves an isolable zwitterionic intermediatel'ly!
jyfx
0
I1
X = OCH3
(137)
lished, we are compelled to make the following mechanistic
assumptions: The primary step is indeed a [2+ 21-addition
to yield the acylketene (136). This reacts as a typical acylketenel' 231, either by [4+ .?]-addition with another molecule
of tetramethoxyethyleiie ( 1 3 3 ) yielding the 1: 2 adduct (134)
or by dimerization to ( 1 3 7 ) which undergoes stabilization
by a known type of rearrangement[' 241 to the pyranopyrandione (135).
Summarizing, even though the available experimental evidence
is still very sparse, the known reactions of (1) permit formulation of the following rule: In principle, carbon suboxide avoids
the usual ketene addition reactions as long as the substrate
contains two (or even only one, see Section 4.3.5) H atoms
susceptible'to electrophilic displacement.
4.5. Photochemical Reactions
Carbon suboxide undergoes a simple photochemical reaction
with olefins[125-1291;
a single carbon atom is inserted into
the C=C double bond to form allenes and two molecules
of CO. Thus ethylene furnishes allene ( 1 41 ) as major product
alongside a little methylacetylene. By labeling the central C
atom of C 3 0 z with I4C it can be shown that this atom
mainly provides the central C atom of the aliene['2h1.This
reaction therefore bears a close formal resemblance to the
Angrw. Chem. internat. Edit. / Vol. I3 ( 1 9 7 4 ) J No. 8
attack of carbon atoms on ole fin^['^^^]. However, decomposition of C,O, into 2 C O and C(,P) requires 141.5 kcajjmol.
whereas the above photochemical reaction occurs already
with 3000-A light (corresponding to 95.3 kcal/einstein)l' 27b1.
The initial photochemical step has therefore always been
assumed to be decomposition of C,O, into CO and carbonylcarbene ( 138)['2.5',which reacts with ethylene (and other
alkenes) to give the high-energy ketene ( 1 3 9 ) . Subsequent
elimination of another molecule of CO furnishes cyclopropylidene (140) which undergoes cyclopropylidene-allene rearrangement in the usual manner"z7c1.
is also formed (yields based on reacted cyclopropene). 3.3Didcuteriocyclopropene ( 145 h ) affords acetylene. monodcuterioacetylene. and dideuterioacetylene i n the ratio I : 4 : I .
This result rules out all plausible mechanisms for acetylene
formation except that proceeding ria the tetrahedrane ( 1 4 7 ) .
KIwnppand h i Dijl\"""attempted to synthesize the unknown
compound tetracyclo[3.3.0.02.".h]oct-7-ene ( 1 3 0 ) from norbornadicne ( 1 4 8 ) riti the carbene ( 149) by a C-H insertion
reaction. However, photolysis of C 3 0 2 in the presence of
( 1 4 X ) affords only a C8Hx compound which is isomeric with
61-50), namely the alkyne ( 1 5 2 ) . The reaction can proceed
ricr the strained allene ( 1 5 1 ) as intermediate"331';however.
other routes are also conceivablel'~'.'3i1.
Interestingly, it follows from the above observations that in
photochemical reactions C.30 undergoes successive loss of
two CO molecules. showing a close resemblance to the reactionsofatomic carbon" 2 7 d 1 . Photolysis has so far been studied
" ~ ~ ~the existence
Studies by Wiffiumson and B u ~ ~ e ssuggest
of (138) as a triplet and a singlet species. Photolysis of [ I )
at 3000w is reported to give C,O (X3Z), while C,O (2'A)
is generated at 2500w. Whereas the singlet carbene reacts
fairly unselectively, the triplet species clearly displays electrophilic properties (in contrast to the views held by other
authors" 2y1). Thisobservation accords with the fact that ( 138)
reacts faster with ethylene homologs (e.q. 40 x faster with
isobutylene) than with ethylene itself["'. 18'.
The reactions with cyclopropene derivatives are also interesting since cyclopropylidene-allene rearrangement would then
lead to a highly strained structure. Thus, according to A . P.
Worf" 301, 1.2-dirnethylcyclopropene ( 1 4 2 ) undergoes an
alternative reaction riu the carbene ( 1 4 3 ) to yield 2-methyl-lpenten-3-yne (144) as major product. N o evidence could
be found for the intermediacy o f a tetrahedrane in this reaction.
( 14-71
In a later study, however, the same research
were
unable to rationalize a reaction of cyclopropene ( 1 4 5 ~ and
)
its 3.3-dideuterated derivative ( 1 4 5 h ) except by assuming a
tetrahedrane intermediate. In accord with the above
mechanism, cyclopropene and C 3 0 , give a 3 3 % yield of
vinylacetylene riu the bicyclic carbene ( 146). 24 YOof acetylene
Angew. Chrm. internar. Edit. J Hil. 13
(
1974) J No. X
i IS I )
(IS.?)
in detail only for olefins. I i may be expected that the possible
appllcations of :CCO In preparative organic chemistry are
much greater.
4.6. Polymerization
Since its discovery"', the polymerization of carbon suboxide
has been studied by numerous chemists. Results prior to 1968
are surveyed in "Gmelins Handbuch'"''. Reference should
be made here to a widespread fallacy concerning the ease
of polymerization"" hC. "'1 of C 3 0 2 . As early as 1922, Otr
and Schmirfr" 31 demonstrated that carefully purified C 3 0 2
can be kept unchanged for long periods, and this observation
has repeatedly been confirmed[5."X.yJ.
' ''I. Even then, our
experience has shown that polymerization only occurs when
traces of water or other proton-releasing (or nucleophilic)
substances are present. "High-temperature polymerization",
as well as polymerization^'^^ induced by radiolysis or photolysis. appear to be exceptions.
The intensely colored polymers are usually termed "red carbon"in theearlier literature; this rather inaccurate designation
was later['
changed to "red coal". The similarity between
"polymeric C302" and C 3 0 2addition product$ with a variety
of substrates (e.y. phenolic compounds) prompted
Zicg/rr['".
in 1960 to postulate a close constitutional relationship between polypyrone compounds~--4. y. ( 8 6 ) -and
"red coal". Supportingevidence for these views on the structure
of poly-a-pyrones has been gathered by other
'""I
from spectroscopic and X-ray studies.
Water-induced['"I polymerization has already been formulated as proceeding ria an acetonedicarboxylicanhydride intermediate ( 153b)['J"1,whose formation is simply explained by
501
addition of ( I ) to rnalonic acid and decarboxylation of the
primary product ( 1 5 3 a ) . This concept received support from
of the “polymeriIR and L‘V studies on the induction
zation” of C 3 0 z to “red coal”[’351. In this way it also proved
possible to discount structural inve~tigations[’~~1
on “red coal”.
in which U V spectra were interpreted in a manner supporting
the former Diels formulation[‘”. 391 as polyspirocyclobutanedione ( 1 5 5 ) .
OH
[lo] H. Sruirdinqcr and S. Brrezu. Ber Deut. Chem. Ges 41. 4461 (l90X).
[ I I] H . Hopfand G. H q u r , Helv. Chim. Acta 44. 2016 (1961)
(121 E. T Bliies, D. Brj cc,-Smirh, H. H i r s c l ~ a n dM . J . Simon\. Chem. Comniun.
1Y70. 699.
[ I 3 1 E. O f t . Ber. Deut Chem. Ges. 47. 2388 (1914): E. Oft and K . Schmidt,
ihid. 55, 2126 (1922).
[ 141 A discussion of all mechanistic possibilities of formation of ( 1 ) from
f 7 ) which also explain the occurrence of acetic acid and CO will be found
in rei [XI.
[I51 Earlier results are given in ref. [5]. A critical treatment of more recent
literature is to be found in refs. 116, 171.
[16] T R . Dykr. W K l r m p w r r . A. P. Cinsbery, and W E.
Fo/roncr. J . Chem.
Phys. 56. 3993 (1972).
[ I 7 1 J . R Sabin and H . Kim, J. Chem. Phys 56, 2195 (1972)
[ 181 H.D. R i r , J. Chem. Phys. 22, 429 I 1954).
[I91 F. A . Miller and W C . Fut6,ly. Spectrochim Acta 20, 253 (1964): and
further references cited therein.
[20] F . A . .Mi/ler, D. H. Lemmon, and R E. WirnowsAi. Spectrochim. Acta
21. 1709 (1965).
[21]
W H Smith and G. E. Lcmi, J. Chem. Phys. 45, 1767 (1966)
[22] W J . Luflerty. A. C. Muki, and E. K
f 1964).
Plj./er. J. Chem. Phys 40, 224
[23] W H. Smirh and J . J . Burrrrr. J Chem. Phys. 5 1 . 1475 (1969).
[24] R L Liiitigsfoiir and R . N C Ruo, J. Amer. Chem. Soc. HI. 285
(1959): A AlmmninyPn, S P. Bu.stiunsm, H. M . Seip, and R Seip. Chem.
Phys Lett. 1, 569 (1968).
[25] For experimentally determined internuclear distances see ref. [5]. p.
83.
[26] L. Grliiis, C . J . Allon, D. 4 .4llison, H. Siryhuhn, and K . Sieyhohn,
Chem. Phys. Lett. 1 1 . 224 (1971): J W Ruhuluis. T Brrgmurk, L. 0. Wurmr,
L. Kurlaon, M. Hiissoin, and K . Sirybuhn. Electron Spectrosc., Proc. Int.
Conf. 1971 (Pub 1972) 425-39: Chem. Abstr. 78, 9987v (1973).
[27] J . F. O l s ~ nand L. Burnrlk, J. Phys. Chem. 73. 2298 (1969).
[28] E. Zirylrr, Chimia 24, 62 (1970): survey
1291 Th. Kuppr. Monatsh. Chem. 98, 874 (1967).
[30] G. Hayelloch and E. Fres, Chem. Ber. 84, 75 I ( I 95 1 ).
The use of c302 to produce graft polymers represents a
[,I] L. B. Dushkurich and E. N . Knt.orru. Tr. Leningrad Khim.-Farm. Inst.
16, 59 (1962): Chem. Abstr 61, 2965c (1964): L. B. DcishkEwh and I/ A .
recent application. Bukowski and Porqjko have copolymerized
Pidwnyiik. Zh. Org. Khim. 3, 636 (1967).
“polyamide 6 (polycaprolactam) in toluene with C3021’43a1
[32] C. L. Wilson, J. Chem. Soc. 1Y35. 492: A . F . Potrrr and H . L. Ritrrr,
Grafting of C 3 0 2 onto polyethylene films proved possible
J. Phys. Chem. 58, 1040 (1954): cf. also L. 5. Dushircich and J/ M. S i r u p ,
after initial activation of the polyethylene by UV or y irradiaZh Obshch. Khim. 32, 2747 (1962): Engl. Transl. 2706.
tion or by o z ~ n i z a t i o n [ ~Cross-linked
~~~].
products having
13.33 L. 8. D a s h k i r h and I! Berlin. Zh. Obshch. Khim. 31, 1671 (1961)
novel properties are obtained in both cases.
[34] L 8. Du.shkerich and E. N. Kiirurvu. Zh. Obshch. Khim. 31, 1669
f I961).
Received. August 6, 1973 [A 9 IE]
German version: Angew Cliem. X6, 529 (1974)
[I] 0. Dirk and B. WOK Ber. Deut. Chem. Ges. 3Y, 689 (1906).
[2] Formulation as the lactone of hydroxypropiolicacid. a s was first proposed
by A. Michurl, Ber. Deut. Chem. Ges. 4 1 , 925 (1908), was a subject of
protracted controversy [6a-6e].
[3] Regarding the influence of this unexpected discovery of a new oxide
of carbon on the further career of Diuls. see the obituary by S. Olsrn. Chem.
[35] W F . Ross and H. N Christerism, J. Biol. Chem. 137, 89. 101 (1941):
W F. R o u and L S. Grecui, ihid 137, 105 (1941); A. H. E u c j and W
F . Ross, hid. 142, 871 (1942). 146, 63 (1942).
1361 H L. Fruenkrl-Conrut. J. Biol. Chem. 152, 385 (1944).
[37] G. H q u r , Dissertation. ETH Zurich 1961.
[3S] L. B. Doshkerich and !I
( I 965). Engl. transl. 256
A . Pzchenyiik, Zh. Obshch. Khim. 35, 253
[39] 0. Dicls. R . Be<krnann. and G. Tdn~ies,Liebigs Ann Chem 43Y. 76,
92 ( 1924).
D. Hirrd and F . D Pilgrim. J. Amer. Chem Soc.
Ber. 95. V (1962).
[40] C.
141 0 Die1.s and G. Mryurhrim. Her. Deut. Chem. Ges. 40, 355 (1907).
[41] H. Strunyus. Dissertation, Universitit Graz 1973.
[5] Gmelins Handbuch der Anorganischen Chemie. Kohlenstoff, C, Section
1, Syst. No. 14, pp. 75-99. Verlag Chemie, Weinheim 1970 (the literature
is covered up t o 1968).
( 1972).
161 For earlier surveys. see: a) 0.Diels, Z. Angew. Chem. 39, 1025 (1926):
b) L. H. Rryrrson and K . Kohr, Chem. Rev. 7, 479 (1930): c) R . Gruurr,
Chimia 14, 1 1 (1960); d) L. B. Dushkecich, Russ. Chem. Rev. 36, 391 (1967):
e) D.Borrmunn in Houben-Weyl-Muller: Methoden der Organischen Chemie.
Thieme, Stuttgart 1968, Vol. 7/4, p. 286.0 H. Ulrich: Cycloaddition Reactions
of Heterocumulenes. Academic Press, New York 1967, p. 100.
[7] For a critical and comparative review of the literature on this method,
see ref. [ X I .
[ X I L. Crombrr, P. A . Gilberr, and R . P. Houghron, J. Chem. Sac. C1968.
5.5, 758 (1933).
[42] E. Zirylrr, A. Aryyridrs, and W Sfriyrr. 2. Naturforsch. 27h. 1169
[43] E. Zirylrr and H. Biemunn, Monatsh. Chem. 93. 34 (1962).
[443 L. 5. Dushkrrich and L. N . Kuzmunkow. Zh. Obshch Khim. 2Y. 2367
(1959): Engl. transl. 2330.
[45] L. B. Dushkrcich and E . 1. Boksinur. Zh. Obshch. Khim. 28.2845 (1958):
Chem. Abstr. 53, X065b (1959).
[46] H. Sruudinyer- Die Ketene. Enke, Stuttgart 1912.
[47] H. Binder and W Lindnrr. J. Chromatogr. 77, 323 (1973).
130.
[48] W Lindnrr. Dissertation, Universitlt Graz 1972.
[49] E. Zirglur and H. Jiinrk, Monatsh. Chem. 86. 506 (1955): X7. 212.
218 (19S6): cf. also E. Zieyler, Osterr. Chem.-Ztg. 5Y. 155 (19581, survey
[9] L. B. Dushkroich, Dokl Akad. Nauk SSSR 132, 1319 (1960); Engl. Transl
707; L B. Du.sbki,cr<.h, I< A Buecrch. and 8.E Kuhurr. Zh. Obshch. Khim.
30, 1946 (1960), Engl. Trdnsl. 1925: cf. also V M a x i u , S . Mrloni, G. Purenti,
M A . Rofliwu, and M . Srcci, Ric. Sci. Rend. 2 A , 273 (1962).
Concerning the detection of intermediate ketenecarboxylic acid derivatives by isotopic labeling, see E. Z q l r r , H. Strrk, and W Steigrr. Monatsh.
Chem. 101. 762 (1970).
502
[ S O ] E Zieglrr and H . Strrk, Monatsh. Chem. YX, I104 (1967).
[Sl]
Angew. Chem. internat. Edit. / Vol. 13 (1974)
/ No. 8
[ 5 1 ] J Bi11iiiuii. G E 7i.ipp. a n d R. I . (.u.\/i. J. Amer. Chem. Soc. 62. 770
(IY40). 1. B. D ~ i . d i h ~ i ~ain~d1 1L. G. 1:i-uilcr.. Zh. Obshch. Khim. 30. 3060
I 196O): I-ngl. Transl. 3033.
[ 5 3 ] I-. B. I ) ~ i s / i A e r ~11,i ~ Dissertation. Institute of Chemistry and Pharmacy.
Lcningrad 1966
[54] J B i i l i i i u i i and C. M Sfiiith. J. Amer C h e m Soc 61. 458 (1939): 74,
3174 (I'l52).
[C] D. J . ['rum a n d R. I-. Z i i i i i i i ~ ~ r i i i u i i i iJ.. Amcr. Chcm Soc. 74. 2646
(lYi2)
[56] T h e incchanisms leading t o these side products :ire discussed in ref.
[Si].
[ i 7 ] Sce rcf [6f]. p. 40. a n d the litcratiire cited i n ref [55]: compare.
v . thc dimerii.ation of the "masked" acetylketene dikctene to dehydroacctic
acid 1?7h).
If. U'irtiiiun. l! liii. and E. Zirylrr. Monatsh. C'heni. YK, 1108 11967):
H Wir/iiiuti a n d 11. R o t h n i u i ~ w .2. Naturforsch. 27h. 52X 11972).
[SX]
[X9] 711.K u p p e xnd Y
[YO]
L i n i i u r i , to be published.
Tb. Kuppe. Monatsh. Chem. YK. 2148 (1967)
[Y I ] .4. Oiiiori. M. Si)iiodo. and S. Tsiir.~iiiiii.Bull. Chcm. Soc. Jap. 43. I 135
(1970): Chcm Abstr 73, 14642e (1970).
[92] t.%irylc,r, R. WCJ/{,and Th. Koppe, Monatsh. Chem. Y6. 418 (1965):
concerning ( X O ) as intermediate. see E. Ziryiw a n d H. JIIIICJ~,
ihrd 87. 503
( 1956).
[93] 711.Kuppr, unpublished results.
1941 E Zicylrr. H .
Jiiiieh.
a n d ! I . Biriiiunii. Monatsh Chem. YZ, 927 11961).
[95] E . Zieylvr a n d I I . JiiiieL. Monatsh. Chern. 86, 29 (1955).
[96] For the extension of.this method a n d the application of the procedure
to other substances such as (1114) a n d (1051, see 7: Moiit,!. izr ul., Tetrahedron
73. 3435 (1967); cf. also ref. [105].
[97] 4 . Oiiiori. N. Sonodo. Y L'(,hidu, and S. Tsiitwini. Bull. Chem. Soc.
Jap. 47. 3233 (1969).
[YX] I . ffrodetzhr a n d E . Zit&r, Monatsh. C'hem. Y7. 398 (1966).
[59] J 12ru 41phrw. Rec T r a v C'him. Pays-Bas 43. 823 11924).
[ 6 0 ] J . $4 Qiiiiiriilo. Span Pat. 211 2x5 (19531: C h r m . Abstr. 4Y. 14x12
11955).
1611 1. 8. Du\/ihcridi a n d I: ,M Siruw. Zh. Obshch. Khim $7. 2330 11962):
Chcm. Abstr iN. 79462111963).
[ 1001 E. Ziiqlcr. M. Eder. F. HrudcrzLx. and E. Prowdoiiruki.\. Monatsh.
Chcm. YX, 2432 (1967)
[62] I: S r < q ~ . \ .Belg. Pat. 50X.085 (1952): C'hcm. Abstr 52. 9218 119581.
[ 6 3 ] See :iIso earlier piiblications by: 8.E. Poiin.. Rec. Trav. Chim. Pays-Bas
ii. 215 (19.36): J . Th L. B RUI~IW~I.ihid. 57. 199 (1938).
[ 1021 a ) E .
[64] I ' I ' K ~ J ~ . \ / ~S.U AI ' . Roqo:/iiii, and I: 1. I ? J / ~ <Vysokornol.
JI~.
Soedin
1 . 7Y9 (1959). Chem. Abstr 54. 1 7 2 6 0 ~(1960): S. Pori,/ku 1'1 u . , Polymcry
Y. S X 11964): Chcm. Abstr 61. 9 5 x 7 ~11964).
1651 E % i I q / r r and R. Miif: Monatsh. C'hem Y5. 1061 11964)
[66] I,. G Beiiiii. L. B. l h \ / i L ( , r i ~ . / i . and S. 1'. Sorii(~/iiih. Zh. Org. Khim.
6 . 1932 llY70): Chcm. Abstr. 73. 1205X7a (1970).
M.: DOU :ind L. Y i ~ d r r .J. Amer. Chem. Soc. 44. 361 (1921):L. P
F w r i \ a n d A . R. R(JII:IO, ihid 62. 606 (1940).
[hX] M Frcriiid a n d K . F/&cIiw. Liebigs Ann. Chem. 379. 27 (191 I )
[69] Regarding tlic tatitomerism of class of suhstances. see A R. Kurt-irzhr.
F. D Popp. and A . J . Wiriti~g.J. Chem. Soc. B IY66. 565.
[70] L B. Du.s/ihrr i d i . Zh. Obhhcb Kliim. 37. 2346 (1962). Chem. Abstr.
5 x . 7946c (1963).
[71] E. %iry/c,r, .4. 4r<girides. a n d W Srriycr. Monatsh. Chem. 1/12. 301
[67]
[99] .4. Oiiiori, N . Soiiorlo. and S. Eirt,sirnii, J. Org. Chem. 34. 2480 I1969).
[loll
Removal of acyl groups from positions 3 o r 5 of 4-hydrory-2-pyroncs
by thcrmolysis [102a] or the action of H2SOI is a known reaction: cf..
<., 0.. ref. [ 1041 a n d literature cited therein.
%i~q/t,r
a n d H . Jutid,. Monatsh. Chem. XY. 323 (1958): b) C.
Gocr.\~./ic/a n d C. M e n / : c r . Bull. Soc. Chim. Fr. 1962, 356. c) J . L. Doiiylu.\
and 7: ;Moiiri.. Can. J. Chcm 45. 1990 (1967).
[ 1031 I t cannot bedecided unequivocally whether 196h1 a n d (YHI a r e identical: both rcscarch groups [99. 1001 give practically the same melting point
(226- 22X a n d 229 C)hut differing spectroscopic dara. Rearrangement of
o n c form into the other bclow the melting point is conceivable
Ipr and F. H i - a d ~ ~ r : h yMonatsh.
.
('hem Y7. 710. 1046 11966):
ipylw. a n d E. l'ri~ir.edoiirnki~,ihid. YY. 1395 ( 1968).
4
[ 1051 T M o r i r i . . Chem. Rev. 70, 553 (1970): a n d references cited therein.
[I061 L. B D ~ i . d i h ~ ~and
i r / i E. N . K i i r u m i . Tr. Leningrad. Khim.-Farm
Inst. 16. 55 11962): Chem Abstr 61. 2 Y X l c (1964)
Eitthart. a n d E. Z i e y / c r , Monatsh. Chem 102. 1090
11073 H Srrrk. P
11971).
[ 10x1 E
Z i q k r . W Srriyur. and I / Srroiiyu.\, to be published.
I I97 I ).
[I091 K . 7: Ports a n d M . Sorin. J. Org. Chem. 36. X (1971).
[ I 101 Th. Kuppe a n d W Liiht,. Monatsh. Chem. 102, 781 (1971).
i , i . Deut. Chem. Ccs. 57. I16X (1924).
[71] 1 I:. 7 i ~ ~ h i r . ~ ~ . h i h u hBer.
1731 E. S. Korhduiiicii, "Mster. Nauch. K o n f L K h F l 1Y66. 42.
[ I I I] Tli. Kuppv a n d W Liihe. Angew. Chem X3, 967 (197 I): Angew. Chcm.
internat. Edit. 10. 925 (1971).
[74] 1;. %wy/c,r and R. WM/. Monatsh. Chem Y3. 1441 (1962).
[75] In thc follov+iiig all condcnsed hydroxypyrimidones Ic. y. ( 4 4 ) .-f 5 I ).
(.MI) will bc represented by o n l y o n e tautomeric hydroxy form since n o
detailed studies a r c a\ailablc on this point (especially concerning compounds
with annelatcd five-membered rings). See: -1. R. K u r r i t z h r and J . M . L u y o w d i ,
Advan. Heterocycl. Chem. I . 339 (1963): -1. R. K a f r i t A i , , Chirnia 14. 134
(1970). Only in the c:isc of / 4 3 i i J ii tautonit'ric ratio of 20.1 in favor of
t h e hetaine form has been determined: .4. R . K u r r i f z k i a n d 4. J . !&iring.
J ('hem. Soc. IYhZ. 1544.
[76] L. B Du\h/,c~ri
/On>. 597.
d
and E .S. Korhclurntw. Khrm. gcterotsikl. Soedin.
[ 1121 K . 7: Port< a n d M . S o n i t , J. Org. Chem. 37, 1422 (1972).
[ I 131 E. Z i r y l c r a n d 4. A r y w i d i s , to be published.
[ I 141 t. Zicylcr. H. Sri.iiiicqm, a n d W S / m ~ r rt,o be published.
[ I 151 T h K u p p c a n d W G o l w r . Synthesis 1Y72. 312.
[ I 161 711.K u p p r a n d W Golwr. to be published.
[I171 a ) .4. N. .Mddt-iiiii. J. Chem. Soc. Y3, 601 (1908): b) regarding the
structure. see D. Dur-idso!i a n d S. A . Brrniird. J. Amer. Chem Soc 70. 3426
(1948):c ) for significance of the unsaturated derivatives a s Lewis acids see
F J . K i i n z . P. Maryurrfliu, a n d 0. E. P o I u i i s l \ ~ ~Chirnia
,
24. 165 (1970).
[ I I81 lf. S t c d . 2. Naturforsch. 27h. 143 (1972): a n d further references cited
[77] I-. B Do.dil\wi~ha n d E. S Kurhduiiic~ii,Zh. Obshch. Khlm. 34, 3427
I1964). t n g l transl. 3470: C'hem. Ahstr 62. 4030 b (1965).
therein.
[7X] L. B. Dushhcvi~b. Zh. Obshch. Khim. 31. 3723 (1961): Fngl. transl
3477: C'hcm. Abstr. 57. X556a (1962).
[ I 2 0 1 H . Hupfand G Hegui.. Helv. C h i m Acta 44, 2016(1961).
j79] 1.. B. D u \ h h ~ ~ r ~ i dKhim.
i,
geterotsikl. Soediii. 1Y66. 601
[ I Z I ] J Swohodu. J. D d o s < . h . a n d F. Wc\.s~,.(r. Monatsh Chcm. Y l . I X X
I1960).
F o r the preparation of this clitss with other malonic acid derivatives
li. H ~ ~ r . ~ / i i i i i i Chem.
iii.
Ber. Y3, 671 (1960). E. Ziryllv
a n d E . Sliwn.. Monatsh. Chem. YS. 147 (1964)
[I221 J
(1971).
[XO]
sce: J. (;ourlrlw a n d
[ X I ] T h e formulations chosen here for ( 5 3 ) a n d ( 5 4 ) (tautomers and isomers
respecti\ely) deviate i n s o m c cascs from the original literature a n d a r e based
011 more recent studie5 [82].
[X2] T h K u p p r . G. Luiiy. a n d I.. Ziiylw. Z Naturforsch. 2Yh. 258 (1974).
[X3] S . '1. Biiroiioi~a.I: G. Brilin. a n d L. B. Do.shhtwch, Zh. Org. Khim.
6. 1734 11970): Chem. Ahstr. 73, 109757k (1970).
[X4] !I G. Bcvliii. I.. B. Da.>hkvridi. and E. N . Ki r i l l or o, Zh. Org. Khim.
6. 2609 (1970): Chem. Abatr. 74. 6423211 (1971).
[8] E. Ziryicr and F. H r u d e r z k i . Monatsh. C h e m Y5. 1247 (1964).
[X6] E. Ziiyln.. F. Hi.rrderzh!. and M . Edrr. Monatsh. Chem. Y7. 1394 (1966).
[X7] E. Ziiy/<,i-.E. Prcir.i,doiirii~i\,H .
('hem. 1 0 1 . 6x0 (1970).
Wiitiiiunii,
a n d G KiA/eii:,
Monatsh.
Th. Koppc. M. A . Chiruzi. H . P. S r d : d , a n d E Zit,g/rr. Monatsh.
Chem. 103. 586 (1972) Oxarolidines react merely t o give open-chain malondiamides: L. B Dushkerich a n d F . G . Sepel. Khim. geterotsikl. Soedin. 196.5.
832.
[XX]
Angcrt.. Chrm. i n f w m f . E d i f . i Vol 13
(
IY74)
1 No. X
[ I 191 W S/r.iyrr. 19. Srrrk. a n d E. Ziry1rr. MonatFh. Chem. 101. X Y I (1970).
Giz//iUii.\.
R W! Hofliiiuiiii, a n d If. J . Liiidiic,r. Chem. Ber. 1 0 4 . Xhl
[I231 R. Goiiipprr, Angew Chem. X I . 34X (1969): Angcw. C'hem. internat
Edit. 8. 312 11969): H . S i ? t ! t v and K . Kwhs. Chem. Ber. YX, 11x1. 2099
(1965): G . Jiiycjr. <hid.105. 137 11972): a n d references cited therein.
A . Cboiidross. Tetrahedron Lett. IYSY, (20) I .
J. Amer. Chem. Sot. 83. 3712 (1961); X4, 4077 (1962).
WrI1i.s a n d K . D. Buyrs, ihid. NK, 3203 (1966).
[ I 2 6 1 R. 7: M t d l r i i a n d A. P. Wolf J. Amer Chem.- Soc. 84. 3712 (1962).
[ 1271 U:
Kiriii.w Carbene. Carbenoide und Carhenanaloga. Vcrlag Chemie,
Weinheim 1969: a ) pp. 157, b) 158. c ) 156.d) 231
[ 1283 D G. !4'i/li~ini.~~~ii
a n d K . D. B a w s , J. Amer. Chem. Soc. YO. 1957
11968).
[ 1291 R. 7 K . Buker, J . 4 . K w r , a n d .4. F. Tr[irniun-Dirkenson. J . C'hem.
Soc. A IY66, 975.
[I301 H. W Clioiiy. A . Lonrztvi/wi\i,r. a n d A . P Way. Tetrahedron Lett.
IY66. 6295.
[ I 3 I] P B. Sh?r hi a n d A . P W d f . J. Amer. Chem. Soc. Y2. 406 (1970).
503
[I321 G. W Klirinpp and P. M . Kin DOk. Rec. Trav. Chim. Pays-Bas 90.
381 (1971)
[I381 R. N. Snirrh. D A. Young, t. N. Smirh. and C . c'. Ciirrer. lnorg
Chem. 2. 829 I 196.3).
[ 1331 For instance, 1.2-cyclohexadirne could he trapped as the simplest
six-membered cyclic allenc: W R. Moore and W R. Mosrr. J. Org. Chem.
35. YO8 (7970).
[ 1391 4 R. Bluke, W 7: E c l r s , and P. P. Jc~iiniiiq.\.Trans. Faraday Soc.
60. 691 (1964): cf. also A. 0 Diullo, J. C'him. Phys. h l . 1409 (1964).
[I341 1 / 4 9 ) and ( 1 5 2 ) can be regarded. ~ . g . as
. hornovinylogs of ( 1 4 3 )
and ( 1 4 4 ) .
[ I 3 5 1 H . Sterk. P. Tritrhurt. and E. Zirylrr, Monatsh. Chem. 1 0 1 . 1851
( 1970).
[ 1361 L S<hmidl. H. P. Borhni, and L'.
HuflJnuJiri, Z. Anorg. Allg. Chem
282. 241 (1955): 296. 246 (1958).
[ 1371 E. Zirglrr. Angew Chem. 72, 582 ( 19601.
[I401 B. D. K ) , h d l . G. K ~ ~ J / l r i s u i C.
i , K . Bar.Xer, and J . L. ,Mur:gru~c,.J.
Phys Chem. 69. 3603 (1965).
[I411 Small amounts of acetic acid arlsing in the preparation can initiate
polymerization in a similar manner. r , y . r i u malonic acetic anhydrides.
[I421 J . Wi)jrcuk. L. Wt*i~nunii.and J . M. Kufrui'di. Monatah. C-hem. YY.
501 ( 19681.
[I431 a ) A. B u k < i ~ s k and
i
S. Porejko, J . Polym. Sci.. Part A - I . 8, 2491 (1970):
h) ihid. X , 2501 (1970).
State of Development of Atomic Absorption Spectrometry[**]
New analytical
By Hans Massmann[*J
Atomic absorption spectrometry has developed extremely rapidly in recent years, and is now
used in many analytical laboratories. The purpose of this progress report is to show the
present position and to examine critically the possibilities and limitations of atomic absorption
met hods.
1. The Physical Principle
To be able to measure the atomic absorption, the sample
must be-converted into atomic vapor. This step is common
to all methods of optical atomic spectroscopy, i.r. emission
spectral analysis,atomicabsorption analysis,and atomic fluorescence analysis.
Atomic absorption is based on the ability of free atoms to
absorb electromagnetic radiation of the wavelengths that they
are also able to emit. Since the atoms can only pass into
certain discrete higher energy states on absorption of radiation
energy, they can only absorb radiation quanta that haveexactly
the energy required for the transition. The absorption spectra
of free atoms are therefore line spectra. Atomic absorption,
like atomic emission and atomic fluorescence, can be observed
only at certain wavelengths that are characteristic of each
element. This is the reason for the high selectivity and specificity''] of atomic spectral methods of analysis, and hence also
of atomic absorption methods.
Only the most sensitive lines, i.e. the resonance lines, can
be used in the main for atomic absorption analysis. These
lines are based on transitions from the ground state to an
excited state. Some elements, such as titanium, offer a wide
selection of lines having similar sensitivities. For other elements, however, there is often only one line that can be used.
For example, the zinc lines at 2138A and 3076A differ by
a factor of about 5000 in their sensitivity.
_~____
[*] Dr. H. Massmann
Institut fur Spektrochemie und angewandtr Spektroskopre
46 Dortmund. Bunsen-Kirchhoff-Strasse 1 1 (Germany)
[**I Based o n a plenary lecture at the Confercnce of the "Analytical Chemistry" G r o u p of the G D C h on the subject of "Trace Analysis" in Erlangen
o n April 2--5. 1973
504
A number of elements cannot be determined with the usual
atomic absorption methods and instruments. This is because
the resonance lines of these elements, which are indicated
by a black triangle in the periodic system in Figure I , lie
in the vacuum U V at wavelengths below 2000A. Radiation
with wavelengths in this range is unable to penetrate the
Ce
P i N,d PmSF E
;
I
G,d T,b lDJ lHo
o lEr
o l Trn
o iYb
o ,ILu
o i
name gases and the air. Much more expensive special methods
are necessary for the measurement of atomic absorption in
this range, but these are not yet of any importance in practical
analysis.
However, in the case of mercury, whose most sensitive
resonance line is situated at 1850A, a less sensitive resonance
line at 2537 k can be used for determination purposes. This
Anguw. Chem. rntn'nat: Edit.
Vol. 13 ( 1 9 7 4 )
No. X
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