GB519721A - Improvements in and relating to the dealkylation of alkyl substituted phenols - Google Patents

Abstract

519,721. Dealkylation of alkyl phenols BAKELITE, Ltd. Aug. 30, 1938,No. 25430 Convention date, Sept. 14, 1937. [Class 2(iii) Alkyl substituted phenols are dealkylated to obtain lower phenolic homologues by passing a 'mixture of hydrogen and an alkylated phenol over a heated catalyst which has been obtained by heating nickel sulphide, or the silicate oxide or sulphide of barium, cadmium, iron, aluminium, or zinc in a finely divided form in an atmosphere of hydrogen. The activation of the catalyst is preferably conducted at 350‹C. or above, and should be at least 50‹C. above the initial dealkylation temperature. The catalysts may be conveniently obtained by precipitation by double decomposition, as this lends to small particle size. The relative volume of phenol and hydrogen is of importance and the preferred quantities are 4-4¢ parts by volume of hydrogen to one part by volume of phenol. In cases where a crude mixture of phenols is to be dealkylated it is preferred to first fractionate the mixture. and dealkylate each fraction at its most favourable temperature, since the temperature at which dealkylation is most effective is in the inverse ratio to the boiling points. The Specification contains examples of suitable .dealkylation temperatures for the various fractions. Catalysts suitable for the process may be made by (a) precipitating ferric chloride with ammonia and reducing ; (b) an acidified ferric acid chloride solution is treated with sodium ortho silicate and the gel dried and reduced ; (c) nickel sulphate is precipitated with hydrogen sulphide and then reduced ; (d) cadmium nitrate is precipitated with sodium hydroxide in dilute aqueous solution, dried and reduced ; (e) zinc nitrate is precipitated and reduced as in (d) above. In an example a xylenol fraction boiling between 218‹-222‹C. was passed through a tube containing a catalyst prepared as in (a) above together with hydrogen in the proportion of 4¢ parts to 1, the temperature being 400‹-600‹C. Specifications 277,394, [Class 2(iii)], 450,473, 452,095, and 452.158 are referred to.