GB661368A - Improvements in vinyltetrahydronaphthalenes and methods of preparing the same - Google Patents

Abstract

A method of preparing a monovinyltetrahydronaphthalene which comprises causing the vapours of a tetrahydronaphthalene methyl carbinol to contact activated alumina thereby to dehydrate the tetrahydronaphthalene methyl carbinol to a monovinyltetrahydronaphthalene. The activated alumina may be mixed with one or more metallic oxides chosen from the oxides of chromium, tungsten, molybdenum and man-ganese and the dehydration preferably takes place under reduced pressure, the carbinol being maintained in the vapour phase as long as it is in the presence of the catalyst or at such a temperature that polymerization of the vinyl tetrahydronaphthalene or an undesirable condensation of the carbinol might result, The starting materials may be prepared by reacting tetrahydronaphthalene with acetic acid or acetic anhydride or other acetylating agents in the presence of a Friedel-Crafts catalyst such as aluminium chloride or bromide, zinc chloride, boron fluoride and sulphuric acid. The proportions of a - and b -monoacetyltetrahydronaphthalene produced may be varied by altering the temperature, solvent or catalyst concentration. Increased temperature results in the production of increased quantities of polyketones. The reaction is more easily controlled in the presence of an inert solvent such as carbon disulphide, nitrobenzene or carbon tetrachloride and in general the mixture of tetrahydronaphthalene and acetylating agent is added to the catalyst suspended or dissolved in the solvent at such a rate that the temperature remains in the range necessary for the production of the desired ketone. At the completion of the reaction the mass is hydrolysed with water, the organic layer allowed to separate and the ketone, obtained by distillation, is reduced to the carbinol by hydrogenation in the presence of a catalyst such as finely-divided platinum, platinum oxide, palladium or copper chromate, and preferably a solvent such as methyl alcohol. In examples: (I) b -vinyltetrahydronaphthalene and (II) a -vinyltetrahydronaphthalene are prepared by flashing the appropriate tetrahydronaphthalene methyl carbinol through a heated column under reduced pressure, packed with alumina pellets and immediately cooling the product. Polymerization of the monovinyltetrahydronaphthalenes may be inhibited by the compounds that inhibit the polymerization of styrene, e.g. catechol and hydroquinone, and these may be washed out of the dissolved monomer with alkali prior to polymerization or polymerization may be carried out in the presence of a small amount of inhibitor at elevated temperature with or without a polymerization catalyst. The Specification as open to inspection under Sect. 91 comprises also the use as acetylating agents of acetyl chloride or bromide or ketene in preparing the mono-acetyl tetrahydronaphthalenes. This subject-matter does not appear in the Specification as accepted.