D. D. COFFMAN AXD H . N. CRIPPS
2S80
[CONTRIBUTION No. 432 FROM THE CENTRAL RESEARCH DEPARTMENT, EXPERIMENTAL STATION, E. I. AND CO.]
Vol. 80 DU P O N T D E r\TEMOURS
Syntheses by Free-radical Reactions. IV. Additive Dimerizations of Butadiene with Radicals from Acyclic Ketone Peroxides BY D. D. COFFMAN AND H. N. CRIPPS RECEIVED NOVEMBER 25, 1957 Long-chain, unsaturated dicarboxylic acid esters have bcen prepared by reductive cleavage of keto ester peroxides in the presence of butadiene. The synthesis is brought about by the additive dimerization of butadiene with the carbethoxy and the carbethoxyalkyl radicals generated from the ketone peroxides Diketones were obtained similarly from acetonylacetone peroxide and the diene.
The principles of additive dimerization have been demonstrated in the synthesis of dicarboxylic acids,1,2nitriles,2 glycols2 and diketones.2s3 In an extension of these principles, carbethoxy and carbethoxyalkyl radicals have been used for the first time in the preparation of long-chain, unsaturated dicarboxylic acid esters by reductive cleavage of acyclic keto ester peroxides in the presence of butadiene. The sequence of reactions in the synthesis can be viewed as generation of a radical R . which combines with butadiene to form the resonancestabilized allylic radical RCHzCH=CHCH2. that dimerizes. The radicals R. were generated in situ by ferrous sulfate reduction of the ketone peroxides obtained by reaction of an ethereal solution of hydrogen peroxide with the keto Although several types of peroxides may form in the reaction of ketones with hydrogen p e r ~ x i d e ,the ~ ketone peroxides have been found to undergo reductive cleavage analogous t o that of cyclohexanone peroxide6 and cyclopentanone peroxide. Thus, the ketone peroxides I represented as hydroxy hydroperoxides of ethyl oxomalonate (n = O), ethyl acetoacetate ( n = 1) and ethyl levulinate ( n = 2) gave rise to the carbethoxy, carbethoxymethyl and carbethoxyethyl radicals, respectively. OOH
I I
R’-C(CH2),LCOOC2FIb OH
I
+ Iic2
+
+
,(CH2),,COOC2Hs+ FeaR’COOH In reactions with butadiene, these radicals formed the esters Et00C(CH2)n-M-LI-(CH2)nCOOEt(11) in which n equals 0, 1 or 2, and 51 is a butenylene group. Formation of the straight-chain dicarboxylic acid esters I17 was demonstrated by hydrogenation of the esters and hydrolysis of saturated products to obtain sebacic acid, dodecanedioic acid and tetradecanedioic acid, respectively. The yields of crude esters ranged from about 50 to 7 0 s ; the yields of straight-chain esters separated by smallscale fractional distillation were much lower, e . g . , or less. Products formed along with thc Khnrasch anti W. Nudenberg, J . O r g , C h ~ m, 19, 1 9 2 1 (1954). (2) D. n. Coffman and E, I,. Jenner, TITIS J O U R X A L , 80,2872 (1938) (3) D . D. Coffman and H. N. Cripps, ibid., 80, 2877 (1958). ( 4 ) N. A. Rfilas and P. C. Panagiotakus, i b i d . , 68, 583 (1940). (5) N. A. Milas, S. A. Harris and P. C. Panagiotakos, i b i i f . , 61, 2430 (1939); K. Criegee, W .Schorrenberg and J. Becke, .‘tlZ?z., 566, 7 (1949). (6) U’. Cooper a n d W. H. T. Davidson, J . Chem. SOC.,1180 (195%). (7) D. D . Coffman and €1, N. Cripps, U. S. Patent 2,811,531, Oct 2 9 , 1957.
straight-chain dimers were not investigated. They are presumed to have been, in part, the isomeric branched-chain dimers, since such products have been formed in analogous syntheses.’,? Although the ketone peroxides were usually prepared in ethereal solution, aqueous 30% hydrogen peroxide and acetoacetic ester formed a peroxide that underwent reductive cleavage to the carbethoxymethyl radical which pxticipated normally in additive dimerization. The types of radicals obtainable from peroxides of 2-substituted acetoacetic esters were not investigated. However, the +substituted ethyl trifluoroacetoacetate formed a peroxide that did not cleave to a trifluoromethyl radical but produced the carbethoxytnethyl radical which was also obtained from ethyl acetoacetate. Thus, generation of the radical K’ by reductive cleavage of the ketone peroxide I has not been ohserved, although possibilities for that type of cleavage are formally presented, and such cleavage may have been an undetected competitive reaction. The reductive cleavage of an aqueous mixture of acetonylacetone and hydrogen peroxide with ferrous sulfate gave 2-acetylethyl radicals that reacted with 1 ,%butadiene t o yield isomeric CISdiketones. Hydrogenation of the isomeric ketones gave 2,lqT-hexadecanedioneas one of the products. Experimental -%I1 melting points Rere taken on a hot block and are uncorrected. The yields were calculated by assuming that the ketone peroxides n ere siniple 1.1 ketone-hydrogen peroxide adducts and hence would yield one radical on reductive cleavage. C.LZUTIOS.-Reactions of 907, hydrogen peroxide should lie carried out in areliminarv trials on a small scale, and all experiments sliouid be perfo;med behind a heavy barricade. Rstreme Drecautions should be taken in the isolat ioii and handling of ketone peroxides. I. Generation and Reaction of Carbethoxy Radicals
? (.COC2Ha). A . Preparation of Ketone Peroxide from Ethyl 0xomalonate.-The kctrine periiside [ i f cthyl oxoobtained by :I variaticin c i f the prixxtlure Milas ani1 I-’anagiotakos.8 A n :iiiliytlrous ethereal siilution o f Iiytirugen peroxide was prclinretl b y adding 20 g. of RO(;% hytlrcigen peroxide9 to 3 0 0 1111. o f COIIIinercinl anhydrous ether i m t 1 drying with 12 g. of anhydrous rn:ignesiutn sulfate. This si)lutic>n, when diluted t r i 500 nil. with nnli~-rlrousether, w a 5 aboilt 1.1 JI as iiidic:rted by iotliimetric titmtiiin. .I\ iriisture of 98.3 g. (0.16 mole) of ethyl oxornnlr)iiatel0 and 1-15 nil. of 1.I .lf etlicrenl liytlrogen peroxide was stirred until tlle yellow ccilor was disc1i:trgetl (8) N. A. lIilas and P. C. Pauagiotakos. ’l‘irrs (1946). (9) Buffalo Electrochemical Cri. ( I 0 ) C
