GB641250A - Process for the manufacture of di-isopropyl-benzene hydro-peroxides and products resulting therefrom - Google Patents

Abstract

Di-isopropyl-benzene is emulsified in an aqueous solution and the resulting dispersion brought into intimate contact with molecular oxygen at an elevated temperature, whereby the mono- and di-hydroperoxides are formed. The reaction occurs most readily with p-di-isopropyl-benzene, less easily with the m-isomer and not at all or only very slightly with the o-isomer. The commercially available material (obtained as a by-product in the condensation of propylene and benzene) consists of a mixture of all three isomers, from which the p-form can be separated by fractionation. The p-form may be used to prepare the p-hydroperoxides, and the residual mixture of o- and m-forms to give the m-hydroperoxides. Alternatively, the commercial product may be treated directly, when a mixture of m- and p-hydroperoxides is obtained. It is preferred to hydrogenate the commercial product over Raney nickel to remove unsaturated compounds. The aqueous dispersion is preferably made with the aid of emulsifying agents such as alkali stearates, ricinoleates or lauryl sulphates as in Specification 610,293, and is free from heavy metal compounds or other substances which catalyse the decomposition of peroxides. The pH is preferably between 7.5 and 10.5. The oxygen may be pure, or a mixture rich in oxygen or air may be used. The reaction temperature is preferably between 60 DEG C. and the boiling point of the liquid, preferably 80-95 DEG C., and the pressure may be atmospheric or higher. The introduction of oxygen is continued until the peroxides start to decompose, this point being determined by analysis of the mixture. Absorption of oxygen may be promoted by peroxides previously formed in the liquid or added thereto, or by the addition of benzene diazoacetate or lead tetra-acetate which liberate free radicals at the reaction temperature. The process may be continuous or batch. Two methods are available for the separation of the products: (1) the emulsion is allowed to break and is separated while hot into aqueous and oily layers, the former containing some peroxides and being returned for re-use. The p-di-hydroperoxide crystallizes from the oily layer on cooling and is purified by washing with benzene; residual amounts in the liquid are precipitated by adding benzene. The oily layer may be distilled under reduced pressure (before or after crystallization of the p-di-hydroperoxide) to remove unchanged hydrocarbons, and if the distillation is carried to completion some mono-hydroperoxides are found in the distillate. The residue is cooled or diluted with benzene to precipitate any p-di-hydroperoxide, leaving the mono-hydroperoxides and the m-di-hydroperoxide in the liquid fraction. Method (2) may be applied to the product of method (1) or to the initial emulsion, and depends on the relative solubilities of the peroxides in aqueous sodium hydroxide. The mixture is treated with 10 per cent sodium hydroxide and the aqueous and oily layers separated. The former is brought to a pH around 7 (e.g. 6.5-8), preferably by bubbling in carbon dioxide, and the precipitate filtered off and washed with benzene, giving the p-di-hydroperoxide. The benzene is distilled from the washings to give the m-di-hydroperoxide. The oily layer insoluble in 10 per cent sodium hydroxide is treated with 40-50 per cent sodium hydroxide, when the sodium salt of the p-mono-hydroperoxide is precipitated; this can be hydrolysed to the free peroxide by warming with water. The solution from the 40-50 per cent alkali is separated into aqueous and oily layers, the former being rejected. The latter is distilled in vacuo to remove hydrocarbons leaving the m-mono-hydroperoxide. Examples are given. Phenols are obtained by treating the hydroperoxides with mineral acids. Thus the p-mono-hydroperoxide gives p-isopropyl-phenol, and the di-hydroperoxides yield resorcinol and hydroquinone respectively. Ketones result from the treatment of the hydroperoxides with aqueous ferrous sulphate, the mono-hydroperoxides giving isopropylacetophenones and the di-hydroperoxides diacetyl benzenes. Acetone is a by-product in the conversion into phenols as above. Carbinols which are mono- and di-(b -hydroxyisopropyl)-benzenes are obtained by reduction of the hydroperoxides with aqueous sodium sulphite. On dehydration with alkali bisulphates they yield (a -methyl-vinyl)-benzenes. Specification 626,095 also is referred to.