Preparation of mercaptans

摘要

Mercaptans are prepared by reacting an ether of formula R-O-R1, where R and R1 are hydrocarbon groups which contain an aliphatic carbon atom at the point of attachment to the ether oxygen, or a primary or secondary alcohol having at least 3 carbon atoms and containing the group with hydrogen sulphide in the presence of a solid oxygen-containing acidic catalyst, the reaction being carried out at an elevated temperature, e.g. 100-500 DEG C., and, in the case of an alcohol reactant, at a pressure of at least 50 psig. Elevated pressures are preferably used with ethers also. The molar ratio of H2S to alcohol or ether may be up to 10:1 or higher. Suitable catalysts include oxides and oxyacids of boron, silicon, sulphur and phosphorus, e.g. phosphoric acid/kieselguhr, or silica promoted with an oxide of a group IIIB metal, e.g. alumina or beryllia, preferably in an amount of 1-20%. Fixed or fluidised beds may be used. The alcohols and ethers may be aliphatic, cycloaliphatic or arylaliphatic. Primary alcohols yield secondary mercaptans, the mercaptan group being introduced on the carbon atom a to that originally carrying the hydroxyl. This isomerism also occurs with secondary alcohols unless both a -carbons are terminal when the mercaptan group merely replaces the hydroxy, or unless the symmetry of the molecule means that the same product is formed in either case. Examples describe the conversion of n-propanol to isopropyl mercaptan, isopropanol to isopropyl mercaptan, sec-butanol to sec-butyl mercaptan, sec-amyl alcohol to sec-amyl mercaptan, n-dodecanol to secondary dodecyl mercaptan, diisopropyl ether to isopropyl mercaptan and cyclohexylethyl ether to cyclohexyl and ethyl mercaptans.