Peculiarities of the behavior of succinyl dichloride in Friedel-Crafts reaction with thiophenes

Article abstract of DOI:10.1007/s10593-011-0653-z

The reactions of thiophene, 2-methyl-, and 2-bromothiophene with succinyl dichloride in the presence of AlCl₃, TiCl₄, and SnCl ₄ have been studied. The effect of the acylation conditions, the relative amounts and nature of the Lewis acid on the ratio and yields of the 1,4-di(2-thienyl)-1,4-diones and 4-oxo-4-(2-thienyl)butyric acids formed have been demonstrated. Under the reaction conditions, the formation of 4,4-di(2-thienyl)but-3-enoic acids (the main products in many cases) and also 4,4-di(2-thienyl)-butyrolactones was demonstrated.

Full text of DOI:10.1007/s10593-011-0653-z

Chemistry of Heterocyclic Compounds, Vol. 46, No. 10, 2011
PECULIARITIES OF THE BEHAVIOR OF SUCCINYL DICHLORIDE
IN FRIEDEL-CRAFTS REACTION WITH THIOPHENES*
V. I. Smirnov1, A. V. Afanas'ev1, and L. I. Belen'kii2**
The reactions of thiophene, 2-methyl-, and 2-bromothiophene with succinyl dichloride in the presence of
AlCl3, TiCl4, and SnCl4 have been studied. The effect of the acylation conditions, the relative amounts
and nature of the Lewis acid on the ratio and yields of the 1,4-di(2-thienyl)-1,4-diones and 4-oxo-4-(2-
thienyl)butyric acids formed have been demonstrated. Under the reaction conditions, the formation of
4,4-di(2-thienyl)but-3-enoic acids (the main products in many cases) and also 4,4-di(2-thienyl)-
butyrolactones was demonstrated.
Keywords: 4,4-di(2-thienyl)but-3-enoic acids, 4,4-di(2-thienyl)butyrolactones, 4-oxo-4-(2-thienyl)butyric
acids, succinyl dichloride, 1,4-(2-thienyl)butane-1,4-diones, thiophenes, acylation.
1,4-Di(2-thienyl)butane-1,4-diones are convenient starting materials for the preparation of 2,5-di(2-
thienyl)pyrroles, -furans, and -thiophenes which, in turn, can serve as precursors of polymers and monomers
which show electrical conductivity and particular photochemical properties [1]. The known syntheses of
1,4-dihetarylbutane-1,4-diones are very varied. With regard to the most frequently used of these, the Stetter
method is based on a Michael addition of aldehydes to the activated double bond of enones in the presence of
cyanide or thiazolium salt [2, 3]. Particularly promising for the preparation of unsymmetrical 1,4-diketones
(although somewhat time consuming) is the method due to Kulinkovich et al. based on the reaction of methyl-
and -bromomethyl ketones [4]. The reactions of diesters or N,N,N',N'-tetrasubstituted succinic acid diamides
with hetaryl lithium [5] or reaction of sodium acetylide with hetarenecarbaldehydes and subsequent conversion
of the 1,4-dihetarylbut-2-en-1,4-diol to the corresponding 1,4-diketone in the presence of alcoholic alkali
solution [6] are relatively simple but they give low yields.
We consider in more detail the data available for the Friedel-Crafts reaction of thiophene 1a,
2-methylthiophene 1b, and 2-bromothiophene 1c with succinyl dichloride (SDC) as the method for synthesizing
the di(2-thienyl)-1,4-dione 2a and the substituted bis(5-methyl-2-thienyl)-1,4-dione 2b, and bis(5-bromo-
2-thienyl)-1,4-dione 2c, respectively. This apparently simple and obvious route meets a series of complications,
_______
* Dedicated to the memory of an outstanding heterocyclic chemist and unsurpassed editor, Alexey Nikolaevich
Kost,
** To whom correspondence should be addressed, e-mail: mitht406@mail.ru.
1M. V. Lomonosov Moscow State Academy of Fine Chemical Technology, Moscow 119571, Russia.
2N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 119991, Russia, e-mail:
libel@ioc.ac.ru.
__________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1485-1496, October, 2010.
Original article submitted December 27, 2009; revision submitted July 6, 2010.
0009-3122/11/4610-1199©2011 Springer Science+Business Media, Inc.
1199

however. Firstly, the reaction of thiophene with succinyl dichloride under conditions standard for the thiophene
series (i.e. the presence of tin tetrachloride) leads to the monoacylation product, 4-oxo-4-(2-thienyl)butyric acid
(3a) [7] after work up. Without a detailed discussion of the reason for this occurrence, it should just be noted
that it is evidently due to the interaction of two closely spaced COCl groups activated by complex formation
with the SnCl4. Indeed, for glutaryl dichloride, the main product is 5-oxo-5-(2-thienyl)pentanoic acid, and
reaction to give the bisacylation product, 1,5-di(2-thienyl)pentane-1,5-dione, occurs in only 5% yield [8].
However, the reaction of adipyl dichloride in the presence of SnCl4 occurs smoothly to give the 1,6-di(2-
thienyl)hexane-1,6-dione in 80% yield [9, 10].
Merz and Ellinger reported in 1991 a successful acylation of thiophene by succinyl dichloride [11] using
dry dichloromethane or 1,2-dichloroethane at room temperature with about 2 mol of AlCl3 per mole of acid
chloride (i.e. one mol for each of the COCl groups). The yield of the unpurified diketone 2a was 55-60%. At the
same time and under the similar conditions, a yield of 45% for this product was reported in a patent [12]. In the
case of 2-methylthiophene and using the same conditions or with refluxing in dichloromethane, the diketone 2b
was obtained in only 30% yield [13]. When an excess of AlCl3 was used for 2-bromothiophene (~ 3 mol per mol
of acid chloride), the yield of diketone 2c was 61% [14].
According to the data given above, the 4-oxo-4-thienylbutyric acid chlorides 4a-c formed in the first
stage of the acylation as a ncomplex with the Lewis acid in the first stage of acylation (in our scheme the
complexes are not shown for simplicity) are less active as electrophiles than the starting complex with succinyl
dichloride. Thus it is clear why, upon acylation of thiophene and its substituted derivatives, the use of a weak
Lewis acid gives mainly the keto acids 3 after hydrolysis of the reaction mixture whereas a strong acid gives the
diketone 2 (Scheme 1).
Scheme 1
R
R
COCH2CH2COCl
R
COCH2CH2COOH
3a–c
S
S
S
4a–c
1a–c
R
COCH2CH2CO
R
S
S
2a–c
a R = H, b R = Me, c R = Br
At the same time, the reasons for the modest overall yields of products 2 and 3 obtained in the presence
of AlCl3 and also the unexpectedly low yield of diketone 2b formed from 2-bromothiophene (apparently
activated by comparison with thiophene and 2-bromothiophene) remain unclear. It must also be assumed that, in
the course of the reaction, there arise some kind of products other than the diketones 2 and keto acids 3 which
previously simply could not be found or separated. In this paper we have carried out a detailed study of the
composition of the products formed upon acylation of thiophenes 1a-c using succinyl dichloride in the presence
of different amounts of AlCl3, as well as SnCl4 and TiCl4, in order to optimize the synthesis of the diketones 2.
The results obtained are given in Table 1.
In our view one of the reasons for the low yields of the acylation products is the formation of a type A
complex (Scheme 2). As noted in the studies [15, 16] the hydrogen chloride formed upon acylation of a
thiophene series compound in the presence of AlCl3 is not removed from the reaction medium but protonates the
starting thiophene to form an approximately equimolar quantity of the type A -complex. Under standard work
up of the reaction mixture this complex is converted to the starting thiophene.
1200

Scheme 2
.....
.
.
.
–
H
H
.
+
.
.
.
+
AlCl4
.
1a–c
HCl
+ AlCl3
R
S
A
Bearing in mind that a single molecule of diketone 2 can bind 2 molecules of AlCl3 as the n-complex
and the hydrogen chloride (2 molecules) formed upon acylation can bind a further 2 molecules of AlCl3 as the
-complex A and 2 molecules of thiophene 1, the yield of the target product 2 with a ratio of compound 1 to
AlCl3 to succinyl dichloride of 2:2:1 should not exceed 50%. That the yield of diketone 2 in a number of cases is
somewhat higher can be related to a reversibility of the protonation (although the equilibrium is shifted to the
right) and the presence of some excess of the starting thiophene compound beyond 2 mol per mol of acid
chloride. The lower yields in the case of the 2-methylthiophene can be explained by the higher stability of the A
type -complex due to the effect of the methyl group. However, the fact that the yield of diketone 2b is always
below 50% supports the occurrence of some other reactions beyond those shown in Scheme 1.
1
Our analysis of the H NMR spectra of the mixture of products formed in the system thiophene
compound–succinyl dichloride–AlCl3 allowed us to identify a previously unknown reaction route for this system
which yielded the 4,4-di(2-thienyl)but-3-enoic acids 5a-c and also the lactones 6a-c (Table 1). Acids 5a-c were
quite readily separated by acidification of an alkaline extract of the admixture of reaction products of thiophenes
1a-c with succinyl dichloride. Purification of the lactones 6a-c from the mixture with acids 5a-c caused
significant difficulty and was carried out only for the lactone 6b. The most favourable case for separation of the
lactone involved the use of TiCl4 as condensation agent (experiment 12) where the diketone 2b was not found
overall. Fivefold washing of the mixture of reaction products with saturated sodium bicarbonate solution gave a
mixture of acid 5b and the lactone 6b which still contained 60% of the acid 5b (1H NMR). Only a further
sevenfold washing allowed the preparation of sufficiently pure (> 95%) lactone 6b. Formation of the indicated
products can be regarded as the result of alkylation of thiophenes 1a-c with the participation of the keto group of
the acid chloride and subsequent reaction of the 4-hydroxy-4,4-di(2-thienyl)butyric acid chlorides 7a-c
produced. Dehydration of compounds 7 gives the acids 5 while dehydrochlorination of 7 leads to the -lactones
6a-c. In principle the latter can also be formed from the acids 5a-c via ring-chain tautomerism (Scheme 3).
Scheme 3
R
S
1a–c + 4a–c
S
R
C
CH2CH2COCl
OH
7a–c
R
O
R
S
S
S
S
R
R
C=CHCH2COOH
5a–c
6a–c
O
a R = H, b R = Me, c R = Br
1201

1202

1203

Similar transformations are known for Stobbe reaction intermediates involving benzophenone and
diethyl succinate where it was possible to separate some of the analogs of lactones 6 [17, 18] and in several
cases analogs of the acids 5 also [19] with determination of the ratio of their tautomers [20]. Further, 4,4-
diphenylbutyrolactone has been reported as the reaction product of succinyl dichloride with benzene in the
presence of AlCl3 [21, 22]. For certain 4,4-diarylbutyrolactones with prolonged heating in acid medium it was
possible to record conformation to the corresponding unsaturated acids as analogs of acid 5 [20, 23]. At the same
time, 4,4-diphenyl-3-butenoic acid in conc. H2SO4 was rapidly converted in 92% yield to 4,4-
diphenylbutyrolactone [24]. The fact that the compounds observed and separated by us exist as the acid form 5a-
c was established on the basis of the 1H NMR spectroscopic data and is found to be in agreement with the results
of alkaline titration and elemental analysis.
1
It should also be noted, in the H NMR spectra of the mixture of succinylation products of the
thiophenes 1a-c, there are present signals for the protons of two CH2 groups as triplets or doublets of triplets in
the ranges 2.70-2.73 and 2.85-2.98 ppm which we assigned to a small amount (~ 5-15 mol. %) of the lactones
6a-c. The choice between the latter and the corresponding 4-hydroxy-4,4-di(R-thienyl)butanoic acids was made
from examination of literature data for similar structures with 1H NMR spectra showing a characteristic AA'BB'
1
system of signals for a CH2CH2 fragment. In the H NMR spectra of the 4,4-diarylbutyrolactones (Ar = Ph,
4-FC6H4, 4-MeOC6H4, or 3,4-(MeO)2C6H3) [25] and a single example we found in the literature with
substituents relating to the thiophene series (Ar = 2,2':5',2'-terthiophen-5-yl) [11], the A,A'B,B' system is
described as two multiplets but in [24] for Ar = Ph as two triplets (the difference evidently being due to
variations in instrumental resolution). It is important to note that the spread of chemical shift values for the CH2
groups for a rather broad series of substituents is small and they vary in the range 2.5 and 2.9 to 2.6 and 2.9
ppm. A shift to high field would be expected for the hydroxy acid 7. The single related compound we found in
the literature as tert-butyl 4-hydroxy-4,4-bis(4-dimethylaminophenyl)butyrate [26] shows signals for the CH2
groups as triplets at 2.25 and 2.51 ppm which markedly differ from the values we observed.
The composition of the reaction mixtures obtained (before their separation) was determined by us using
1H NMR spectroscopy. The molar ratios of the main product keto acids 3a-c, diketones 2a-c, acids 5a-c, and
lactones 6a-c as well as their overall yields were calculated for each experiment with regard to the weight of the
obtained mixture, quantity of succinyl dichloride, variation of reaction conditions, and amounts of reagents (see
1
Table 1). The H NMR parameters for the reaction products which were used for the analysis of the mixtures
obtained are given in Table 2.
From our data presented in Table 1 the 4,4-di(2-thienyl)but-3-enoic acids 5a-c proved, in most cases, to
be main components of the mixture formed upon succinylation of the thiophenes 1a-c. The use of titanium or tin
tetrachlorides as condensing agents which cannot promote formation of the diketones 2a-c leads to a mixture of
products with an acid 5a-c content of 70-80%. It is most likely that the reason why the latter were not identified
is their loss during work up. The formation of -complexes of type A in reactions with AlCl3 agrees with the
recovery of up to 20% of starting thiophene compound in experiments 1-4, 7-11, and 14-16. In addition, such
-complexes can be partially decomposed by the water evolved upon formation of acids 5 and lactones 6. The
maximum yields of diketones 2a-c are achieved upon prolonged refluxing of a solution of the starting
components in dichloromethane which contains 6 mol of AlCl3 per mol of succinyl dichloride. These conditions
evidently enable liberation of the thiophene compound from the -complex A and ensure a fuller use of the
former in the acylation reaction.
EXPERIMENTAL
1H NMR and 13C NMR spectra were recorded on a Bruker DPX 300 radio frequency spectrometer (300
and 75 MHz respectively) using CDCl3 with TMS or the residual signal of chloroform at  7.265 ppm as
1204

internal standard. EI mass spectra were obtained on a Kratos instrument (70 eV). Monitoring of the reaction
course and the purity of the products obtained was carried out by TLC on Silufol UV-254 plates (Kavalier,
Czech Republic) using the system ethyl acetate–hexane (1:4) and dichloromethane–petroleum ether (40-60ºC)
(1:2) and were displayed using iodine vapor. Preparative separation of the products was carried out on a Merck
SiO2-60 silica gel column (0.060-0.200 mm) using petroleum ether (40-60ºC), ethyl acetate, dichloromethane,
methanol or their mixtures as eluents. Melting points were measured on a Boetius microscope stage.
The 2-methylthiophene and 2-bromothiophene used in this work came from the Acros Company and the
remaining reactants are native products. Succinyl dichloride was prepared by method [29].
Reaction of Thiophenes 1a-c with Succinyl Dichloride (General Method used in experiments 1-18).
A solution of succinyl dichloride (1 ml, 9.08 mmol) and the thiophene 1a, 2-methylthiophene 1b, or
2-bromothiophene 1c (19.5 mmol) in dry dichloromethane (6 ml) was added with cooling and stirring to a
suspension or solution of the Lewis acid (20.0 mmol) in dry dichloromethane (25 ml). The mixture obtained was
stirred for 3 h at room temperature. The product was poured onto ice (100 g), conc. HCl (2 ml) was added, and
the product was then stirred for 1 h before removing the organic layer. The aqueous layer was extracted with
dichloromethane (2×30 ml) and the combined extract was washed with 2N HCl, then twice with water, dried
over Na2SO4, and filtered. The filtrate was evaporated on a rotary evaporator and the residue was examined by
1H NMR. The methods for synthesis or separation of the individual products are given below.
1,4-Di(2-thienyl)butane-1,4-dione (2a). A solution of thiophene 1a (17.4 ml, 217.9 mmol) and succinyl
dichloride (10 ml, 90.8 mmol) in dry dichloromethane (25 ml) was stirred vigorously over 40 min with addition
of a suspension of AlCl3 (29 g, 211.8 mmol) in dry dichloromethane (30 ml). The temperature was maintained in
the range 0-8ºC by cooling with ice/salt. The reaction mixture became dark-red in color. Stirring was continued
for a further 3 h, the reaction mixture was poured onto ice (400 g), conc. HCl (10 ml) was added, and the
emulsion produced was stirred for 30 min. The dark-green colored organic layer was separated and the aqueous
layer was extracted with dichloromethane (3×50 ml). The combined extract was washed with 2 N HCl solution
(20 ml), water (2×50 ml), and then NaHCO3 solution (20 ml), dried over Na2SO4, and filtered. The filtrate was
evaporated on a rotary evaporator to give a mixture of products (18 g). The latter was triturated with a small
amount of alcohol, filtered, washed twice on the filter, and dried in air to give the product (15.9 g) which was
recrystallized from ethanol (400 ml) to give the pale-blue diketone 2a (9.65 g, 42.5%); mp 127-129ºC (mp 130-
131ºC [8]).
1,4-Bis(5-methyl-2-thienyl)butane-1,4-dione (2b) and 4,4-Bis(5-methyl-2-thienyl)but-3-enoic acid
(5b). A solution of 2-methylthiophene (15 ml, 151.8 mmol) and SDC (7 ml, 63.25 mmol) in dry
dichloromethane (20 ml) was added with vigorous stirring over ~ 40 min to a suspension of AlCl3 (20.2 g,
151.8 mmol) in a mixture of dry dichloromethane (22 ml) and petroleum ether (14 ml). The temperature was
maintained at 5-15ºC by cooling in ice. Stirring was continued at room temperature for a further 5 h. The
reaction mixture was poured onto ice (300 g), conc. HCl (8 ml) was added, and the emulsion obtained was
stirred for 60 min. The organic layer was separated and the aqueous layer was worked up as described above for
diketone 2a. Evaporation on a rotary evaporator gave a mixture of products (17 g) which was dissolved in
dichloromethane and filtered through a layer (15 g) of silica gel. The filtrate was evaporated to give an oil (11 g)
which was dissolved at 0ºC in methanol (5 ml) and the solution was held for ~16 h at 4ºC. The green crystals
(3.12 g) were filtered off and recrystallized from ethyl acetate to give blue crystals of the diketone 2b (1.2 g,
7.5%) with mp 170-171ºC (mp 176ºC [13]). The diketone 2b was obtained in 10% yield by a method analogous
to the above for the synthesis of diketone 2a from the 2-methylthiophene (3.3 g, 21.8 mmol), SDC (1 ml, 9.08
mmol), and AlCl3 (2.905 g, 21.8 mmol); mp 168-170ºC (mp 176ºC [13]).
Addition of petroleum ether to the mother liquor obtained when separating diketone 2b (see above) gave
brown crystals of acid 5b (1.6 g, 9.4%) which were recrystallized from a mixture of ethyl acetate and petroleum
ether (1:1); mp 101-102ºC. 13C NMR spectrum, , ppm: 15.99; 16.14; 35.68; 119.91; 125.67;
1205

126.06; 126.73; 133.10; 136.83; 140.33; 141.48; 143.98; 178.66 (COOH). Mass spectrum, m/z: 278 [M]. Found,
%: C 59.99; H 5.04; S 22.91. C14H14S2O2. Calculated, %: C 60.40; H 5.07; S 23.04.
1,4-Bis(5-bromo-2-thienyl)butane-1,4-dione (2c). A mixture of SDC (2 ml, 18.15 mmol),
2-bromothiophene (4.1 ml, 41.7 mmol), and dry dichloromethane (9 ml) was added slowly, dropwise, and with
cooling to 0-10ºC to a suspension of AlCl3 (5.81 g, 43.5 mmol) in dry dichloromethane (10 ml). The product
was stirred for a further 2.5 h at room temperature, and then refluxed for 30 min. The cooled reaction product
was poured onto ice (200 g), conc. HCl (2 ml) was added, and stirring continued for 1 h. The organic layer was
separated and the aqueous layer was worked up as described for diketone 2a. Evaporation on a rotary evaporator
gave a mixture of products as an oil (6.7 g) which was dissolved in hot ethanol. The crystals formed on cooling
were filtered off and dried in air to give diketone 2c (2.73 g, 37%); mp 175-176ºC (mp 181ºC [14]; mp 177ºC
[30]).
4-Oxo-4-(2-thienyl)butyric Acid (3a). A solution of SDC (9 g, 50 mmol) in chlorobenzene (40 ml) was
added dropwise over 2.5 h to a solution of thiophene (8.4 g, 100 mmol) and SnCl4 (26 g, 100 mmol) in
chlorobenzene (100 ml) maintained at 2-4ºC. The mixture obtained was stirred for 1 h and then at 10-15ºC and a
solution of HCl (4%, 100 ml) was added. The organic layer was separated and extracted with a 20% solution of
Na2CO3 (3x10 ml). Acidification of the alkaline extract with HCl gave the acid 3a (6.1 g, 66%); mp 117-119ºC
(water) (mp 119-120ºC [31]).
4-(5-Methyl-2-thienyl)-4-oxobutyric Acid (3b). The mixture of reaction products obtained in
experiment 9 was separated by flash chromatography on silica gel eluting with, in sequence, a mixture of
dichloromethane and petroleum ether (1:1.5), dichloromethane, and a mixture of ethyl acetate and methanol
(10:1) and monitored by TLC. The final fraction was evaporated, the oil obtained was triturated with ether, and
the crystals produced were filtered and dried in air to give the acid 3b (0.261 g, 7.3%); mp 106-108ºC (hexane)
(mp 108-109ºC [3]).
4,4-Di(2-thienyl)-3-butenoic Acid (5a). The mixture of products obtained from experiment 4 from SDC
(9.08 mmol) was dissolved in methylene chloride and the solution obtained was washed with Na2CO3 solution
(5%, 3×10 ml). The combined aqueous layer was acidified to pH 3 with conc. HCl and extracted with ethyl
acetate (3×20 ml). The extract was evaporated on a rotary evaporator to give an oil (0.76 g) which was extracted
three times by refluxing for 1 h with hexane (20 ml). The hot hexane extract was decanted each time.
Evaporation of the combined hexane extracts on a rotary evaporator gave acid 5a (0.4 g, 18%); mp 80-81ºC
13
(hexane). C NMR Spectrum, , ppm: 35.65; 121.61; 125.68; 126.79; 127.08; 127.60; 127.92; 128.95; 132.70;
139.23; 146.24; 178.01 (COOH). Found, %: C 57.41; H 4.03. C12H10S2O2. Calculated, %: C 57.57; H 4.03.
4,4-Bis(5-bromo-2-thienyl)-3-butenoic Acid (5c). The mixture of products obtained in experiment 18
was dissolved in dichloromethane, washed with Na2CO3 solution, the aqueous layer was acidified with HCl (see
the preparation of acid 5a), and then extracted with dichloromethane (3×20 ml). Solvent was evaporated on a
rotary evaporator to give a viscous, brown oil which, as in the case of acid 5a, was extracted with hexane. The
hexane extract was evaporated and the residue was triturated in a minimal volume of dichloromethane to give
the acid 5c (0.29 g, 7.8%); mp 119-120ºC (hexane). 13C NMR spectrum, , ppm: 35.56; 112.98; 114.23; 122.62;
127.05; 129.66; 130.60; 131.48; 139.83; 146.67; 177.62 (COOH). Found, %: C 35.41; H 1.92. C12H8Br2O2S2.
Calculated, %: C 35.31; H 1.98.
5,5-Bis(5-methyl-2-thienyl)dihydrofuran-2(3H)-one (6b). The mixture of products obtained in
experiment 12 from SCD (9.08 mmol) was dissolved in dichloromethane, the solution was washed with a
saturated solution of NaHCO3 (12×20 ml), dried over Na2SO4, and evaporated on a rotary evaporator to give an
1
oil (1.05 g) which contained an admixture of acid 5b according to H NMR data. Column chromatography of
this oil (0.6 g) on silica gel (eluent petroleum ether and dichloromethane, 3:1) gave lactone 6b (0.14 g, 9.5%) as
a viscous oil. 13C NMR spectrum, , ppm: 15.16; 29.33; 37.99; 85.76 (C–O); 124.64; 125.39; 128.02; 139.23;
140.97; 143.26; 175.20 (CO). Found, %: C 60.76; H 5.55. C14H14S2O2. Calculated, %: C 60.40; H 5.07.
1206

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