Homogeneous catalytic hydrogenation of sorbic acid with pentacyanocobaltate II

Abstract

The homogeneous hydrogenation of sodium sorbate, with pentaeyanoeobaltate II used as the catalyst, was followed manometrically at room temperature and atmospheric hydrogen pressure. One mole of hydrogen was absorbed by one mole of sorbate. UV and II~ analyses demonstrated the reduction of sorbate to hexenoate. Gas liquid chromatography (GLC) of hexenoate indicated 82, 17, and 1% yields of 2-,3-, and 4-hexenoates, respectively, with traces of sorbate. Increasing either the period of hydrogenation or the ratio of catalyst to sorbate, or both, did not cause the formation of caproate or change the ratio of the three isomers. Homogeneous catalytic hydrogenation in methanolic solutions showed higher selectivity since 2-hexenoate was present in 96% yield.To standardize GLC columns, hexenoic acid isomers were synthesized by the Knoevenagel condensation. Trans-2-hexenoic and t r~r~s-3-hexenoie acids were prepared in 75 and 85% yields by a condensation of n-butanal and malonic acid in the presence of pyridine and triethanolamine, respectively. Trans-4-hexenoic acid was prepared in 70% yield by condensing diethyl malohate with erotyl bromide. Physical properties, including UV and IR spectra, were determined for the purified synthetic adds and methyl esters.Although the absolute specificity of attack at the 4,5-double bond of sorbic acid was not confirmed, the high degree of selectivity obtained does encourage further study of homogeneous catalysis on higher fatty acids.

cis‐bond‐producing hydrogenation of polyunsaturates catalyzed by polymer‐complexed Cr(CO)3 catalysts

“…Methods for gas liquid chromatography (GLC) and infrared spectrometry (IR) were described previously (1,11). Methyl palmitate was employed as an internal standard for GLC of conjugated linoleate and its hydrogenation products.…”

Use of Transition Metal Complexes as Selective Hydrogenation Catalysts

“…Hydrogenation of IX or cr-complex X would lead to trans-2-butene. On the other hand, hydrogenation of the sterically unfavored to 98% when the solvent is changed from water to methanol (Mabrouk et al, 1964). The structures of the dienes are also important in their reductions.…”

Homogeneous catalytic hydrogenation of unsaturated fats: Iron Pentacarbonyl

“…This evidence suggests that eonjugation may be a requirement for the homogeneous catalytic hydrogenation reaction. There is nlueh evidence to indicate that conjugated unsaturated systems are required for homogeneous hydrogenation (8,13,19,21). Therefore, a catalyst that isomerizes fats and also activates hydrogen should be one of the best ways to achieve homogeneous hydrogenation.…”

“…For example, the selective reduction of sorbic acid (2,4hexadienoie acid) was achieved by using pentaeyanocobaltate (II) as catalyst under homogeneous conditions (8,19). With this catalyst the selective formation was obtained of 82% 2-hexenoie acid in aqueous solution and 93% in methanolie solution (21). Homogeneous catalytic hydrogenation, however, has been achieved in relatively few polyunsaturated compounds (13,19).…”