GB814278A - Process for the preparation of 2.4.6 trialkylated phenols - Google Patents

Abstract

The invention comprises a process for the preparation of a 2,4,6-trialkyl-phenol by reacting a 2,6-dialkyl-phenol with a C1-C8 acyclic saturated aldehyde, in the presence of a C1-C6 alcohol and an alkaline metal hydroxide, the reaction mixture having a pH greater than 7, and hydrogenolizing the 4-alkoxyalkyl-2,6-dialkyl phenol so formed in the presence of a hydrogenation catalyst. The aldehyde used should preferably contain not more than 4 carbon atoms per molecule and the alcohol used is preferably methanol, although ethanol, propanol, isopropanol and butanol are also specified. Aldehydes specified are formaldehyde, paraform, acetaldehyde, propionaldehyde, n-caproaldehyde. A compound forming formaldehyde under the reaction conditions may also be used. Suitable alkaline metal hydroxides are, e.g., sodium or potassium hydroxide. The alkyl substituents in the starting materials may be the same or different and preferably contain up to 6 carbon atoms. The reaction is preferably carried out using 1.05 to 7 mols. of aldehyde and about 5 to 30 mols. of alcohol per mol. of 2,6-dialkyl phenol, the pH of the solution preferably being between about 9 and 12. The preparation of the ether may be carried out between about 35 DEG to about 100 DEG C. or higher. Bis-phenol by-products, e.g. 4,41-methylene bis-(2,6-ditert.-butylphenol), 4,41-methylene bis(2,6-diisopropylphenol) are formed during the ether preparation, and may be removed by distillation at reduced pressures, e.g. 1 to 5 mm. or more at about 100-175 DEG C., although the hydrogenolysis step is preferably carried out immediately, without separation of the byproduct. The hydrogenolysis may be conducted in the liquid phase in e.g. C1-C8 alcohols, n-alkanes, or aromatic hydrocarbons at e.g. 110-170 DEG C., and 100-700 p.s.i.g. or higher, wherein a substantial portion of the pressure may be due to the partial pressure of the solvent. Suitable catalysts are preferably selected from metals of Groups I, II, IV, V, VI, VII and VIII of the Periodic Table, their alloys and derivatives such as their sulphides, oxides and chromites, e.g. silver, copper, iron, manganese, molybdenum, platinum, chromium cobalt, rhodium, tungsten, nickel, copper-silver mixtures, copper-chromium mixtures, nickelcobalt mixtures, and their derivatives. Copper chromite is the preferred catalyst. The catalysts may be finely divided and dispersed or supported on an inert carrier, e.g. pumice, kieselguhr, diatomaceous earth, clay alumina, charcoal or carbon, suitable amounts of catalyst are from about 0.1 per cent to 35 per cent by weight of the ether. After the hydrogenolysis the by-product is separated from the reaction product. Examples are given of the preparation of the following compounds: 4-methoxymethyl - 2,6 - ditert. - butyl phenol, 4 - ethoxymethyl 2,6 - di - isopropyl phenol, 4,41 - methylene bis (2,6 - diisopropylphenol), 4 - (1 - methoxyethyl) - 2,6 - ditert. - butyl phenol, 2,6 - di - tert. - butyl p - cresol, 2,6 - diisopropyl p - cresol, and 4-ethyl-2,6-ditert.-butyl phenol.