GB873874A - Method of producing anthraquinones - Google Patents

Abstract

A method of producing anthraquinones comprises contacting a mixture containing naphthaquinone vapour and phthalic anhydride vapour with an inert liquid water-immiscible solvent having a boiling point at or above about 230 DEG C. and a density different from that of water, said liquid being held at a temperature between ambient temperatures and 200 DEG C. and thereby recovering said <PICT:0873874/IV (b)/1> naphthaquinone and phthalic anhydride from the gas mixture as a solution in said solvent; removing the phthalic anhydride from the resulting solution by contacting it with an aqueous extracting medium at a temperature above 70 DEG C., reacting the resulting raffinate with a butadiene by passing into said raffinate a butadiene (as herein defined) while keeping said raffinate at a temperature of at least 80 DEG C. and keeping the pressure sufficient to keep said butadiene liquid at the temperature used to form a condensation product containing tetrahydroanthraquinone, and oxidising the tetrahydroanthraquinone and recovering the anthraquinone from the oxidation mixture. The butadiene may be butadiene-1,3 or butadiene-1,3 substituted by one or more substituents such as halogen, alkyl, alkenyl, aryl, alkoxy and acyloxy. These substituted 1,3-dienes give rise to the correspondingly substituted anthraquinone. A preferred embodiment of the process is illustrated in Fig. 1 where naphthalene is vaporized in 1 and oxidised in 2 to a mixture containing naphthaquinone and phthalic anhydride. This gaseous mixture is contacted with the inert liquid, e.g. a chlorinated hydrocarbon, a ditolyl ethane or diphenyl ether in absorber 3, which may be in the form of three scrubbers connected in series. The solution is then scrubbed with water in 4 to give an aqueous extract which is re-extracted with the inert liquid in 5 to recover all the naphthaquinone and then worked up to recover the phthalic anhydride. The naphthaquinone solution is reacted with the butadiene in 8 which may be a two-stage reactor; the resulting tetrahydroanthraquinone extracted, in the form of a salt, using aqueous alkali, and then oxidised, again in one or more stages, using air to give the anthraquinone. Examples describe the preparation of anthraquinone and 2-methyl and 2-chloro-anthraquinone. Specification 731,370 is referred to.