Patent GB-837006-A (GB)
Title: Improvements in and relating to the production of phthalic acids
Inventor: FIELD GORDON HOWARD WHIT
IPC: C07C51/265
Filed: 1956-08-20
Abstract: The invention comprises a process for the production of o-phthalic acid by the oxidation of xylene or a closely related oxygenated derivative thereof, or the halomethylation product of toluene or a closely related oxygenated derivative thereof, comprising at least some o-compound, in the liquid phase, by means of oxygen or ozone, or an oxygen containing gas, using preferably a solvent, and as catalyst, the halide, especially the bromide, of at least one metal of variable valence; subjecting the mixture, either during oxidation, subsequently, or in a separate stage, to conditions which decrease the partial pressure of water over the liquid whereby o-phthalic anhydride is formed and remains in solution in the liquid; removing insoluble iso and/or terephthalic acids; subjecting the residual solution including solvent to hydrolysis in the liquid phase, with at least the stoichiometric proportion of water; and separating the resulting o-phthalic acid from the liquid reaction medium.  The partial pressure of the water over the liquid may be decreased, e.g. by distilling off the water formed in the reaction conveniently under reflux, flash distillation, evaporation, passing gas through the liquid or by a combination of these methods, at atmospheric, superatmospheric, or subatmospheric pressure.  The hydrolysis is carried out in the presence of a solvent which may be the same one as used in the oxidation step, preferably between 100-300 DEG  C. Suitable solvents are benzoic acid, o, m and p toluic acids and mixtures thereof, o, m or p ethyl or isopropyl benzoic acids, dimethyl benzoic acids, toluene, ethylbenzene, xylenes, chlorobenzene, bromobenzene, o-dichlorbenzene, xylene chlorides, xylylene dichlorides, nitrobenzene, propionic acid acetone, dioxan and ethyl acetate. The water content of the solvents may be reduced by distillation if the solvent is to be recycled.  The solvents may be produced in situ in the oxidation step.  The oxidation step is preferably carried out between ambient temperature and 300 DEG  C., and the mixture preferably kept at its boiling point, water and exit gases being continuously removed from the reaction mixture.  The process may also be carried out continuously.  The oxygen or oxygen containing gas may be introduced through a distributer such as a rose or sinter glass.  Suitable catalysts are the bromides of cobalt or manganese, or mixtures thereof and suitable proportions of the catalyst are from 1 to 0.0005 gm. atom of total metal per gramme mol. of starting material, the ratio of manganese to cobalt may be up to about 9 : 1.  The metal halides are preferably introduced as such, but may be produced in situ by using salts of the metals which are soluble in the reaction mixture, e.g. the acetates or naphthenates, and introducing halogen, e.g. bromine in the oxygen stream or hydrobromic acid or an alkali metal bromide such as sodium.  The catalytic metal may also be introduced as reduced metal, e.g. of Raney type, or as a carbonyl or oxide.  Chlorides or iodides may also be used.  Any halogen lost during the process may be replaced by introducing hydrogen halide, the halogen itself, or a halogeno derivative of the aromatic starting material.  The oxygen may also be introduced in situ, e.g. by the decomposition of a compound such as hydrogen peroxide and ozone may be used to accelerate the reaction. The o-phthalic acid may be washed, e.g. with o-xylene, and then purified by washing with a light petroleum distillate (b.p. 40-60 DEG C.).  Suitable starting materials are mixed xylene isomers, or such isomers mixed with ethyl benzene in which case benzoic acid may be formed as a by-product.  Other starting materials specified are o-methyl benzyl alcohol, o-methyl benzaldehyde, toluic acid, or phthalide, o-aldehyde benzoic acid compounds containing two CH2OH, or two CHO groups or one CH2OH and one CHO group in the para-position to each other, also o- and p-chloro or bromo methyl toluenes, halo methyl benzyl alcohol, halo methyl benzaldehyde halo-toluic acid. When the process is carried out continuously a suitable system is that comprising an oxidation reactor, fitted with a distillation column, and if necessary with a separate auxiliary vessel for dehydrating, a filter or centrifuge, a hydrolysis reactor and a second filter or centrifuge.  The o-phthalic acid may be converted into phthalic anhydride by heating to 190 DEG  C., and the anhydride so produced further purified by distillation or sublimation, preferably under reduced pressure in the presence of sulphuric acid. Examples are given.  Specifications 804,612 and 837,007 are referred to.