Patent GB-757164-A (GB)
Title: Oxidation of ª -isopropylnaphthalene to ª -isopropylnaphthalene hydroperoxide
IPC: C07C409/08
Filed: 1954-08-30
Abstract: b -Isopropylnaphthalene hydroperoxide substantially free from a -isopropylnaphthalene hydroperoxide is prepared by oxidizing a mixture of a - and b -isopropylnaphthalenes containing at least 75 per cent of the b -isomer with elementary oxygen until a hydroperoxide content is attained in the range of 10-30 per cent and determined by the equation <FORM:0757164/IV(a)/1> where X is the percentage conversion and Y is the percentage of b -isomer in the mixture.  The b -isopropylnaphthalene hydroperoxide is removed by either distillation with or without steam and under reduced pressure, or extraction with aqueous alkali solution or with selective solvents, or by decomposition of the hydroperoxide to b -naphthol with an acidic catalyst followed by removal of the naphthol by distillation or alkali extraction, or by reduction of the hydroperoxide to a ,a -dimethyl-2-naphthyl carbinol and separation of the carbinol.  The recovered isopropylnaphthalene is cooled to obtain a crystalline mixture containing at least 75 per cent of the b -isomer which is recycled to the oxidation stage.  The mother liquors are isomerized to a mixture containing isopropylnaphthalene of at least 75 per cent b -isomer which is separated and recycled to the oxidation stage.  The oxidation stage is conducted at atmospheric or elevated pressure at temperatures between 20 DEG  and 150 DEG  C., in the presence of alkali such as an alkali metal carbonate, an alkali metal hydroxide or an alkaline earth metal hydroxide such as sodium or potassium carbonate or hydroxide or calcium hydroxide, which is aqueous to introduce water into the system and may be added gradually during the oxidation to maintain alkalinity without an excess of alkali being present at any stage.  Water may also be introduced as steam.  The oxidizing gas which must be highly dispersed in the reaction mixture may be oxygen, air, or mixtures of oxygen with nitrogen carbon dioxide, steam or other inert gases.  The oxidation may be a batch or a continuous process and may be initiated by the addition of peroxidic compounds such as b -isopropylnaphthalene hydroperoxide, benzoylperoxide, cumene hydroperoxide and tertiary butyl hydroperoxide.  The oxidation may be carried out in aqueous emulsion with the addition of dispersion agents such as alkali metal stearates, oleates, or lauryl sulphate to the aqueous phase which may amount to 0.5 to 4 times the volume of the isopropylnaphthalene and which is maintained at a pH between 7.5 and 12.  In the crystallization, the recovered isopropylnaphthalene is cooled to between - 50 DEG  and 10 DEG  C. without a solvent or to between - 70 DEG  and 10 DEG  C. with a solvent which may be ethanol, propane butanes, pentanes, hexanes or heptanes and the crystalline material separated.  In the isomerization, isopropylnaphthalene mother liquors containing less than 90 per cent of b -isomer are isomerized by heating at between 55 DEG  and 150 DEG  C. with 0.5 to 5 mol. per cent of anhydrous aluminium chloride based on the total naphthalene ring compounds present for 1 to 60 minutes preferably in a solvent such as a paraffinic hydrocarbon or a mixture of paraffinic hydrocarbons boiling at less than 150 DEG  C. which may be used in the liquid phase and under pressure at a temperature below the critical temperature of the solvent and in the proportion of up to ten times the weight of the isopropylnaphthalene to give an isopropylnaphthalene containing about 90 per cent of the b -isomer and separated by distillation followed by crystallization before recycling to the oxidation stage.  The mother liquors and other isomerization products such as naphthalene and diisopropylnaphthalene are recycled to the isomerization stage.  In the process of the invention the isopropylnaphthalene is either oxidized in stages by reoxidizing the recovered material until its b -isomer content is about 75 per cent before crystallization and isomerization or the recovered material is crystallized and isomerized after each oxidation.  In an example of the former method, isopropylnaphthalene containing 90 per cent b -isomer and b -isopropylnaphthalene hydroperoxide is heated to 90 DEG  C. with 2 per cent aqueous sodium carbonate and air introduced until the hydroperoxide content is 30 per cent, the mixture extracted with sodium hydroxide in ethanol to remove the hydroperoxide, the recovered isopropylnapthalene containing 86 per cent b -isomer oxidized as before and after four oxidations the recovered isopropylnaphthalene containing 75 per cent b -isomer is purified by distillation, diluted with hexane, cooled to - 20 DEG  C., seeded and crystals containing 85 per cent b -isomer are removed, a second crop containing 78 per cent b -isomer is obtained and the mother liquors are diluted with hexane, dried and heated at 70 DEG  C. with anhydrous aluminium chloride, poured into aqueous sodium hydroxide and ice, and isopropylnaphthalene containing 90 per cent b -isomer is separated by distillation, crystallized and recycled to the oxidation stage.  As an example of the latter method, isopropylnaphthalene containing 90 per cent b -isomer is oxidized as above to isopropylnaphthalene containing 30 per cent of hydroperoxide which is decomposed with 95 per cent sulphuric acid at 70 DEG  C., the acid neutralized with sodium hydroxide, the acetone removed by distillation, the b -naphthol extracted with sodium hydroxide to leave isopropylnaphthalene containing 84 per cent b -isomer which is cooled to - 5 DEG  C. to give crystals containing 96 per cent b -isomer for recycling, the mother liquors are distilled and isomerized as above to give isopropylnaphthalene containing 85 per cent b -isomer.  Another example illustrating the isomerization stage is given. Specification 654,035 is referred to.