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

Abstract

cis‐Bond‐producing chromium carbonyl catalysts were prepared by complexing conventional or macroreticular, styrene‐divinylbenzene copolymers or cross‐linked poly (vinyl benzoate) with Cr(CO)6. With one exception, these polymer‐Cr(CO)3 catalysts were as selective as the corresponding homogeneous arene‐Cr(CO)3 complexes for the formation ofcis‐monoenes from methyl sorbate and from conjugated, polyunsaturated fatty esters in cyclohexane. Although several of the polymer catalysts were very active when fresh, they all lost activity on recycling. They could not be recycled more than two times before a marked decrease in activity occurred due to loss of Cr, as shown by elemental analysis and infrared absorption in the recovered catalyst. Thermal analysis indicated instability of the polymer complexes at hydrogenation temperatures.

Hydrogenation

“…Greater activity can be obtained using poly(vinylbenzoate) as the support in line with the relative activities of the homogeneous [Cr(arene) (COh] catalysts, which decrease in activity as the arene is altered in the order arene = PhCOOMe > PhH > PhMe [57]. Greater activity can be obtained using poly(vinylbenzoate) as the support in line with the relative activities of the homogeneous [Cr(arene) (COh] catalysts, which decrease in activity as the arene is altered in the order arene = PhCOOMe > PhH > PhMe [57].…”

Immobilized transition-metal carbonyls and related catalysts

“…This was attributed to mass-transfer limitations. 49 Although initial activities were in substantial agreement, Awl et al 50 found a greater loss in activity with recycling than Pittman and co-workers. 49 They ascribed it to leaching of arene-Cr(CO)3 moieties.…”

Selective conjugation of soybean esters to increase hydrogenation selectivity

“…Pd (0.2% Pd-on-alumina) and Ni (Girdler-G-15; 25% nickel) catalysts was carried out in a glass manometric apparatus described previously (15), Hydrogenation with chromium carbonyl complexes was performed according to a previously described procedure (4)(5)(6). Hydrogenation selec-tivity ratios were determined with a digital computer (16).…”

“…Heterogeneous catalysts also form higher melting transisomers, which decrease the winterized oil yield. In contrast, certain homogeneous and heterogeneous chromium carbonyl complexes were found to hydrogenate polyunsaturates to cis-monoenes (4)(5)(6). Selective conjugation prior to hydrogenation was suggested as an alternate approach to improving the selectivity of homogeneous catalysts (7).…”