GB800529A - Improvements relating to the manufacture of organic hydroxylamine compounds - Google Patents

Abstract

Hydrogenation catalysts used in the production of aliphatic and cycloaliphatic hydroxylamines from the corresponding nitro-compounds may either be a mixture of the oxides or silver and chromium with or without another metal such as cobalt, copper, lead, cadmium, aluminium, iron, thorium and preferably manganese, or a mixture of the oxides of silver and manganese with or without the oxide of another metal such as chromium, lead, cobalt, copper, cadmium, and preferably nickel or zinc. A stabilizer such as barium or calcium oxide may also be present. The catalysts of the first type may be prepared by adding an ammoniacal solution of an alkali metal bichromate dropwise to the metal nitrates dissolved in water at 60-80 DEG C. The mixture is then cooled and the precipitate filtered and dried at 100 DEG C. The catalyst may be treated with acetic acid. The active catalysts are obtained by drying at room temperature in a vacuum. The ratio of silver nitrate to manganese nitrate is preferably between 5 and 40 per cent by weight. The content of alkaline earth metal nitrate should not exceed about 10 per cent by weight. The second type of catalyst may be prepared by treating an aqueous solution zinc and barium nitrate and potassium permanganate with an aqueous solution of silver and manganese nitrate at 60-80 DEG C. and filtering the precipitate. The catalyst may be dried or decomposed at elevated temperature or treated with acetic acid. The ratio of silver nitrate to zinc nitrate calculated as silver is preferably between 5 and 30 per cent by weight.ALSO:Aliphatic and cycloaliphatic hydroxylamines are prepared by catalytic hydrogenation of the corresponding nitro compounds, in the liquid phase, according to which the process is carried out at a temperature below 90 DEG C. and a pressure above 50 atmospheres in the presence of a mixed catalyst comprising silver oxide and one or more heavy metal oxides. The hydrogenation may be carried out with or without a solvent such as methanol, ethanol, cyclohexane, dioxane or tetrahydrofurane. The concentration of solvent is preferably between 5 and 20 per cent by weight of the nitro compounds. Small amounts of oximes and amines are also formed during the reaction. The process is preferably carried out in a reaction vessel kept at elevated temperature and hydrogen is circulated through the mixture of nitro compound, hydroxylamine, oxime, amine and catalyst. The reaction solution may then be continuously removed being replaced by a fresh solution of the nitro compound. The reaction solution may then be worked up by removing the catalyst, removing the solvent if necessary, cooling the residual solution and filtering the crystallized hydroxylamine. The mother liquor can again be returned to the hydrogenation process. The hydrogenation is preferably interrupted when 80-90 per cent of the nitro compound has been used. The catalyst may either be a mixture of the oxides of silver and chromium with or without another metal such as cobalt, copper, lead, cadmium, aluminium, iron, thorium and preferably manganese, or a mixture of the oxides of silver and manganese, with or without another metal such as chromium, lead, cobalt, copper, cadmium and preferably nickel or zinc. A mixture of the two types of catalyst may also be used. A stabilizer such as barium or calcium oxide may also be present in either case. The amount of catalyst required is between 2 and 20 per cent by weight of the nitro compound. Examples are given of the preparation of isopropylhydroxylamine together with small amounts of acetoxime and isopropylamine, and cyclohexylhydroxylamine together with small amounts of cyclohexylamine and cyclohexanoneoxime.