[CONT’RIBUTION FROM
THE
CHEMICAL LABORATORIES OF THE UNIVERSITY OF NOTREDAME]
T H E ADDITION OF ACETYL CHLORIDE TO ALKYLACETYLENES* JOHN W. KROEGER, FRANK J. SOWA,
AND
JULIUS A. NIEUWLANDt
Received February 14, 1996 INTRODUCTION
A number of reports concerning the reactions of acyl halides with 01efins~~~J have been presented in the literature, but none on the analogous addition to acetylenic hydrocarbons. Acetyl chloride has been reported to add to olefins to form saturated chloro ketones which lose hydrogen chloride on distillation. The chloro ketones from acetylenic compounds were found to distill undecomposed and lost hydrogen chloride only to a slight (extent even after standing for rather long periods of time. Krapivin,* in his report on the condensation of olefins with acid chlorides in the presence of aluminum chloride, mentioned as by-products “halogensubstituted, saturated hydrocarbons of the series C,H2,+1X”, which obviously are formed by the addition of hydrogen chloride to the double bond in a manner analogous to the formation of the chloro olefins herein described. Daraens3 carried out a very careful investigation along similar lines and found that, of all the catalysts tried, anhydrous stannic chloride gave the best results. His conclusions were verified in the present investigation, and stannic chloride was selected from a number of covalent metal chlorides which were found to catalyze the reaction. These included zinc chloride, aluminum chloride, antimony pentachloride, phosphorus tri- and penta-
* Paper VI11 on the addition reactions of alkyl acetylenes. Previous paper, .T. Am. Chem. Soc., 68, 80 (1936). t Dr. Nieuwland, a member of the Board of Editors of THIS JOURNAL,died suddenly of a heart attack on June 11th [Znd. Eng. Chem., News Ed., 14, 248 (June 20, 1936)l. 1 KCINDAKOW, Bull. SOC. chim., 7,576 (1892); ZELINSKI, J . Russ. Phys. Chem. SOC., 31, 402 (1899); BLANC,Bull. SOC. chim., 19, 699 (1890); NORRISAND COUCH,J . Am. Chem. SOC.,42,2329 (1930); WIELANDAND BETTAQ,Ber., 66, 2246 (1922); SCHOELLER AND ZOLLNER,
U. S. Patent 1,737,203 (Nov. 1929).
* KILAPIVIN, Bull. Soc. Imp. Nut. MOSCOW, 1, (1908); Chem. Abstr.; 6,
a
DARZENS, Compt. rend., 160, 707 (1910). 163
1281 (1911).
164
J. W. KROEGER, F. J. SOWA, AND J.
A. NIEUWLAND
chlorides, phosphorus oxychloride, mercuric chloride, and cuprous chloride. Stannic chloride in amounts greater than 401, caused an immediate violent reaction. In addition it had the advantage of being completely soluble in the reaction mixture. We found that acetyl chloride reacts with alkylacetylenes in the presence of catalysts to form, mainly, chloro-olefinic ketones together with smaller amounts of 2-chloro-1-olefins and traces of alkyl acetates. The principle reaction is : R-CeC-R'
+ CH-CO-Cl-+
R-C=C-CO-CH,
I 1
C1 R'
(A)
(R'= hydrogen or R)
The chloro-olefinic ketones are pleasant-smelling liquids, and have a light yellow color when freshly distilled, but darken slightly on standing. They decompose readily in the presence of traces of acid but can be kept indefinitely by the addition of a small amount of anhydrous potassium carbonate. They have a slight vesicant and lachrymatory action which decreases with increase in the molecular weight of the compound. They were found to be oxidized to some extent by air-especially the lower members of the series. In the case of the lowest member of the group, 4-chloro-3-hexene-2-one,a temperature of 75" was reached by bubbling air through the pure substance. The cis and trans isomers of these ketones were found to be rather readily separable and were isolated in certain cases. On standing for a few weeks the pure isomers reverted completely to an equilibrium mixture. By analogy to the known pairs of liquid cis-trans isomers, the higherboiling fraction has been designated cis and the lower-boiling, trans. This assignment is supported by the fact that an alcoholic solution of sodium acetate gives an almost immediate precipitation of sodium chloride with the trans isomers of the normal ketones, while several days are required for the precipitate to form from the cis isomers; moreover when hydrogen chloride is added to an acetylenic ketone the product is mainly the trans isomer. Hydrogen chloride is generally conceded to add to and split out from the trans positions. By keeping the amount of catalyst low, usually 2 to 4% of the mixture, the reaction was prevented from going to completion. In spite of this precaution the reaction was always accompanied by the formation of some tarry polymerized products. The yields were usually from 20 to 35% of the chloro olefin and from 25 to 40% of the ketone. The larger yields of chloro olefin were obtained in the case of the dialkylacetylenes. Traces of alkyl acetates were also formed, and could not be accounted for.
ADDITION OF ACETYL CHLORIDE TO ALKYLACETYLENES
165
Both hexyne-1 and decyne-5 formed about 1% of n-butyl acetate, which was identified by fractionation and saponification. A satisfactory explanation for the formation of the chloro olefin, as yet, has not been advanced. The following mechanism might be considered plausible : CHrCO-Cl*+
CH?C=O
+ HC1
(B)
Hydrogen chloride and ketene might then react with the alkylacetylene as follows: R-CrCH R-C=CH
+ HC1----+
+ CH?C=O
(C)
R-CCbCHZ
-+ R-CZZC-CO-CH~
HC1
(D)
R-CCl=CH-CO-CH3 And in the case of dialkylacetylenes: R-C-C-R R-CeC-R
+ HC1+ CH?C=O
R-CClECH-R R-C=C-R
-+
[
R-CCkCR-CO-CH,
H2&--&=0]
-
(E)
HC1
(F)
Direct addition of acetyl chloride to the triple bond might also take place as written previously (A). The acetylenic ketones were found to add hydrogen chloride very readily, which may explain the fact that no such ketones, nor those of the cyclobutenone type, were isolated. EXPERIMENTAL
Mai'eria1s.-The monoalkylacetylenes were prepared from the corresponding alkyl bromides and sodium acetylide in liquid ammonia. The sym-dialkylacetylenew were prepared in a similar manner from the sodium compound of the monoalkylacetylenes. Commercial acetyl chloride was fractionated and the fraction boiling from 50.0 to 50.5" was saved. Stannic chloride, anhydrous, was used after redistillation. The, procedures for the preparation of the ketones were all quite similar and a description of one such preparation will be sufficient. Addition of acetyl chloride to hezyne-1 .-In a three-liter, three-necked flask, equipped with a reflux condenser, dropping funnel and mercury-sealed stirrer, was placed 850 g. (10.4 moles) of hexyne-1, b.p. 70.0 to 70.5", and 820 g. (10.4 moles) of acetyl chloride. T o this mixture, which was stirred vigorously, a solution of 40 g. of anhydrous stannic chloride in 100 g. of acetyl chloride was added dropwise. The addition was carried on rapidly enough to keep the reaction mixture refluxing slowly. The color of the solution changed rapidly from yellow to dark-red. The mixture was then refluxed for one hour.
166
J. W. KROEGER, F. 3. SOWA, AND J. A. NIEUWLAND
TABLE PHYSICAL CONSTANTS AND ANALYSESOF ADDITIONCOMPOUNDS
I b.p.
COMPOUND
~~
I I1
I11
IV
V
VI VI1 VI11
IX
X XI XI1 XI11 XIV
4-chloro-3-ethyl3-hexene-%one (trans) 4-chloro-3-ethyl3-hexene-2-one (cis) 4-chloro-3-npropyl-3heptene-2-one (trans) 4-c hloro-3-npropyl-3heptene-2-one (cis) 4-chloro-3-nbutyl-3-octene -2-one 4-chloro-3-namyl-3-nonene -Zone 4-c hloro-3hexene-2-one 4-chloro-3heptene-2-one (trans) 4-chloro-3heptene-2-one (cis) 4-c hloro-3octene-2-one (trans) 4-chloro-3oc tene-2-one (cis) 4-chloro-3nonene-Zone (trans) -chloro-3nonene-2-one (cis) 3-c hloro-3-hexen
