The Wittig reaction between alkylidene triphenylphosphoranes [R CH = P(C6Hs)3, where R varied from H to n-C17H35] and methyl 12-oxooctadecanoate or methyl 10-oxohexadecanoate in dimethylformamide (DMF) has been employed in the synthesis of a partial homologous series of esters of branched chain fatty acids in high yields. The effect of various ratios of reactants in both DMF and dimethylsulfoxide (DMSO) was investigated. Purification from triphenylphosphine oxide was readily accomplished by chromatography on a column of silicic acid-Celite impregnated with silver nitrate.
The mass spectral fragmentation patterns of these compounds were studied, More like the mass spectra of a, fl-unsaturated esters, and in contrast to normal chain unsaturated esters, the fragmentation pattern allowed location of the double bond at the branch point. A fragment ion [C,~H2,~] + resulting from two proposed allylic cleavages and McLafferty transfers of ~,-hydrogen atoms was present in 51 100% relative abundance and allowed unambiguous determinations of the length of the alkenyl branch. The mass spectra of the trimethylsilyloxy (di-OTMS) derivatives of these compounds, however, in contrast to the di-OTMS derivatives of normal chain unsaturated esters, did not allow the unambiguous determination of the double bond position. The PNMR spectra of the series of branched chain esters are described. * Abstracted from the dissertation submitted by D.C.G. to the University of Illinois Graduate College, September, 1969, in partial fulfillment of the requirements for the Ph. D. degree.