Alcohols from ester hydrogenation

Both older methods for the reduction of esters to alcohols, catalytic hydrogenation and reduction with sodium, have given way to reductions with hydrides and complex hydrides which have revolutionized the laboratory preparation of alcohols from esters. 

Alcohols from esters. The major problem is reaction selectivity. Paraffin by-product in alcohol results if the catalyst activity is too high. Yet the reduction of esters to alcohols is a difficult reaction. Copper chromite catalyst, 3000-5000 psig hydrogen, and a temperature of 270-300°C are required for the reduction. An alternate catalyst is CuO/ZnO, which is used for methyl ester reduction only. Hydrogen solubility in alcohol is limiting. 

Alexander Mikhaylovich Saytzev (Saytzeff) (Kazan 20 June 1841 (O.S.)-2 September 1910) studied with Kolbe in Marburg and Leipzig, and was professor in the University of Kazan. He discovered the synthesis of primary and secondary alcohols from esters, ketones, and aldehydes by the action of zinc and alkyl iodides (see Reformatsky, p. 858). He also discovered aliphatic sulphoxides. His brother Mikhayl Mikhaylovich (b. Kazan, 30 August 1845), at first his assistant and later manager of a chemical works in Kazan, discovered the reduction of acid chlorides to aldehydes by hydrogen gas in presence of palladium. ... 

Metallic sodium. This metal is employed for the drying of ethers and of saturated and aromatic hydrocarbons. The bulk of the water should first be removed from the liquid or solution by a preliminary drying with anhydrous calcium chloride or magnesium sulphate. Sodium is most effective in the form of fine wire, which is forced directly into the liquid by means of a sodium press (see under Ether, Section II,47,i) a large surface is thus presented to the liquid. It cannot be used for any compound with which it reacts or which is affected by alkalis or is easily subject to reduction (due to the hydrogen evolved during the dehydration), viz., alcohols, acids, esters, organic halides, ketones, aldehydes, and some amines. 

Place 0 -5 g. of 3 4 5 triiodobenzoyl chloride in a small test-tube, add 0 -25 ml. of the alcohol - ether and heat the mixture gently over a micro burner until the evolution of hydrogen chloride ceases (3-5 minutes). Pour the molten mass into 10 ml. of 20 per cent, alcohol to which crushed ice has been added. Some derivatives solidify instantly those which separate as oils change to solids in a few minutes without further manipulation. Recrystallise from rectified spirit (use 50 per cent, alcohol for esters of methyl and butyl carbitol ). 

The catalytic hydrogenation of esters is of great commercial importance. It is one of the industrial methods used to produce long-chain fatty alcohols (eg, dodecyl and decyl alcohols) from fatty acid methyl esters (33). The method is also suitable for the conversion of dimethyl 1,4-cyclohexanedicarboxylate [94-60-0] into 1,4-cydohexanedimethanol [105-08-8] an important intermediate in the manufacturing of polyesters. 

Resolution of alcohols (cf., l-(naphthyl)cthyl isocyanate, 8, 356 357). A practical synthesis of the methyl ester of (S)-5-HF,TF. (1) from arachidonic acid involves chromatographic separation of the diastereomeric urethanes preparecT from the Isocyanate derived from dehydroabietylamine (hydrogen chloride and phosgene).1 Urethanes from other chiral amines are less useful. The urethanes are cleaved with triethylamine and trichlorosilanc to give the corresponding pure enantiomeric esters, which can be hydrolyzed by base. 

Directed asymmetric reduction of a ketone has been brought about by the use of an intramolecular homochiral boronate ester250. The latter was readily introduced at a hydroxyl group in the molecule and has allowed the production of the enantiomeric alcohol, from the ketone by use of BH3-complex as the reductant (equation 64). The boronate ester may be readily removed by treatment with hydrogen peroxide-sodium hydroxide, using standard methodology. Other similar reductions have also been reported251-253. 

A characteristic ion formed from esters of long-chain alcohols results from rearrangement of two hydrogen atoms ( McLafferty -I- 1 rearrangement). 

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