Methylester Hydrogenation

The 0 -phenyl-0 -piperidyl-(2)-acetic acid methylester of BP 135° to 137°C under 0.6 mm pressure is obtained in theoretical yield by hydrogenation of 50 g of 0 -phenyl-0 -pyridyl-(2)-acetic acid methylester in glacial acetic acid in the presence of 1 g of platinum catalyst at room temperature, while taking up 6 hydrogen atoms. Reaction with HCI gives the hydrochloride. Resolution of stereoisomers is described in U.S. Patent 2,957,880. 

A mixture of 4.98 g of acetoacetic acid N-benzyl-N-methylaminoethyl ester, 2.3 g of aminocrotonic acid methyl ester, and 3 g of m-nitrobenzaldehyde was stirred for 6 hours at 100°C in an oil bath. The reaction mixture was subjected to a silica gel column chromatography (diameter 4 cm and height 25 cm) and then eluted with a 20 1 mixture of chloroform and acetone. The effluent containing the subject product was concentrated and checked by thin layer chromatography. The powdery product thus obtained was dissolved in acetone and after adjusting the solution with an ethanol solution saturated with hydrogen chloride to pH 1 -2, the solution was concentrated to provide 2 g of 2,6-dimethyl-4-(3 -nitrophenyl)-1,4-dihydropyridlne-3,5-dicarboxylic acid 3-methylester-5- -(N-benzyl-N-methylamino)ethyl ester hydrochloride. The product thus obtained was then crystallized from an acetone mixture, melting point 136°Cto 140°C (decomposed). 

In the process we are describing here , the esterification reaction was carried ont in the homogeneous phase and followed by distillation under vacuum of the resinic acids. Hydrogenation of Tall Oil methylesters obtained in this way gave the resnlts reported in Table 31.2. 

Nevertheless the non-hydrogenated, distilled Tall Oil methylester has a Rancimat induction time lower than 1 hour, demonstrating... 

Arkad, O., Weiner, H., Garti, N., and Sasson, Y. 1987. Catalytic transfer hydrogenation of soybean oil methylester using inorganic formic salts as donors. J. Am. Oil Chem. Soc., 64,1529-1531. 

Novel catalysts (141) such as Ru-Sn and Re-Sn can be used to hydrogenate fatty acids or methylesters to fatty alcohols. Using these catalysts, the hydrogenation can be carried out at the same temperature (250°C) but lower pressure (50 bars), and the unsaturations present remain unaffected. The presence of tin has been found to be instrumental in the preservation of the unsaturation during hydrogenation. Ru-Sn supported on alumina was found to be most selective when they were prepared via the sol-gel method. 

In the present work, the dependence of the catalytic activity and diastereoselectivity in the hydrogenation of the methylester 1, was studied on rhodium catalysts, as a function of the nature of the support (active carbon, graphite and alumina) and of catalyst pretreatments under hydrogen. 

The biochemical conversion of magnesium protoporphyrin mono-methylester to protochlorophyll probably also involves the primary formation of a jr-cation radical [Cox (41)]. Whether the hydrogenation of protochlorophyll to chlorophyll involves phlorin intermediates [Woodward (214)] is still not known. 

Complex forms of CRM 3 with (a) (R)- and (S)-Af-acetylmethionine methylester, and (b) (R)- and (S )-N-3,5-dinitrobenzoylleucine methyl-ester. White, light-gray, dark-gray, and black balls, represent hydrogen, carbon, nitrogen, and oxygen, respectively. 

Table 8.7 (a) Molecular properties of some N-ace(ylamino acid methylesters and their complexes with CRM 5. FS represents the final energy, HB the hydrogen-bonding energy, and VW the van der Waals energy (kcal mol ). Reproduced by permission of Elsevier, ref. 29. 

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