Hydrogenation of crotonic acid

Further, Maxted (36) studied the influence of several sulfur compounds on the activity of platinum black for the hydrogenation of crotonic acid in the liquid phase. He noticed that between 15 and 50°C the toxicity remains constant for a sulfur compound, pointing out the irreversibility of sulfur adsorption. Conversely, the toxicity of various compounds increases with the molecule size. For molecules containing two sulfur atoms, losing all freedom of rotation through this double adsorption, the toxicity is less than for molecules of the same length containing only one atom of sulfur. 

In contrast to the case of maleic and fumaric acids, hydrogenation of crotonic acid was sharply inhibited by an excess of TPPMS - again, behavior analogous to that of [RhCl(PPh3)3] in hydrogenation of alkenes. 

Figure SJ.a-I Hydrogenation of crotonic acid on a Pt catalyst. Catalyst activity measured by rate coefficient k)asa fimction of poison content. After Maxted andEmns Xi ... 

Fio. 8. Form of a typical poisoning curve. The figure shows the depression of the activity of a supported platinum catalyst, by increasing amounts of thiophene, in the liquid-phase hydrogenation of crotonic acid. 

RuC12(TPPMS)2]2 is an active catalyst for the hydrogenation of water-soluble al-kenes, such as maleic, fumaric, and crotonic acids, in aqueous solutions [26]. A thorough kinetic study of crotonic acid (CA) hydrogenation was undertaken. The rate law derived is given by Eq. (16) ... 

Hydrohalogenation of crotonic acid in a crystalline a-cyclodextrin complex gives ( + )-(S)-3-bromobutanoic acid with 58% enantiomeric excess146. Asymmetric reactions catalyzed by cyclodcxtrin have been attempted in solution but all of these reactions afforded the products in low optical yields. Exposure of crystalline cyclodextrin complexes to gaseous hydrogen bromide and hydrogen chloride at 20 °C gives better optical yields. 

Isocrotonic acid can be prepared by the stereospecific cia-hydrogenation of tetrolic acid or, mixed with the frans-isomer, by reduction of 3-chloro-cis-crotonic acid with sodium amalgam. The ci -acid can also be prepared in small amounts by isomerization of the froTia-acid. The method herein described is much less laborious than the older procedures. ... 

This point may be illustrated by some hydrogenation tests carried out by the author on the sensitivity of a platinum catalyst to poisoning by thiophene at 15 and at 50 respectively. The system examined contained in each case 0.025 g. of stock platinum black suspended in 10 cc. of a 1 iV solution of crotonic acid in acetic acid containing various known amounts of thiophene, hydrogenation being carried out in a shaker under standardized conditions. The results are summarized in Table V, from... 

CH3OH) across the carbon-carbon double bond of crotonic acid [( )-2-butenoic acid] followed by potassium bromide treatment of the initial adduct to yield the corresponding mercuric bromide and then the formation of 2-bromo-3-methoxybutanoic acid by the addition of bromine (Br2) to the latter. Acidification to the free acid, followed by amination (NH3), formylation with the equivalent of acetic-formic anhydride, hydrogen bromide (HBr) ether cleavage, and a final pH adjustment with ammonium hydroxide produced the desired amino acid. 

Quantitative studies of the effect of pyridine on the rate of hydrogenation of imns-crotonic acid in the presence of a platinum catalyst have been carried out by Maxted and Walker who concluded that... 

With regard to the use of tungsten-based systems, Payne and Williams reported on the selective epoxidation of maleic, fumaric, and crotonic acids with a catalytic amount of sodium tungstate (2mol%) in combination with aqueous hydrogen... 

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