GB896911A - Method of preparing nitro-2,3-dihalo-1,2,3,4-tetrahydroanthraquinone and mononitroanthraquinones - Google Patents

Abstract

A nitro-2,3-dihalo-1,2,3,4-tetrahydro-anthraquinone is obtained by adding nitric acid to a solution of 2,3-dihalo-1,2,3,4-tetrahydroanthraquinone in sulphuric acid of above 93% concentration while keeping the temperature below 60 DEG C. The halo substituent may be chlorine, bromine, or iodine. The nitro-dihalo compound may be heated with aqueous caustic alkali so as to obtain by dehydrohalogenation the 1- or 2-nitroanthraquinones. The dihalo-tetrahydro compound may be obtained by subjecting a 1,4,4a,9a-tetrahydroanthraquinone, in aqueous solution adjusted to a pH of 4-8, to oxidation with gaseous oxygen at 85 DEG C.-100 DEG C., separating the resulting 1,4-dihydroanthraquinone, suspending it in a solvent inert to halogenation, and reacting it with chlorine, bromine, or iodine, or a chlorinating agent such as sulphuryl chloride, to form a 2, 3 - dihalo - 1,2,3,4 - tetrahydroanthraquinone. As solvent inert to halogenation there may be used carbon tetrachloride chloroform, nitrobenzene, chlorobenzene, or ethylene chloride. The halogenation may be effected at 0 DEG C. or below. The dihalo compound may be isolated and then redissolved in sulphuric acid for the nitration or it may be transferred directly by extraction from the organic solvent with the acid. Nitration occurs in the 5- and 6-positions. The nitrated product may be isolated by drowning in water and filtering the product, or the nitration mixture may be extracted with nitrobenzene and the extract may be used directly for the dehydrohalogenation. If the nitrated product is isolated it may be separated into the individual isomers by recrystallisation or other procedures. The 5-and 6 - nitro - 2, 3 - dichloro - 1, 2, 3, 4 - tetrahydroanthraquinones, and the corresponding dibromo compounds may thus be isolated. For the dehydrohalogenation step the caustic alkali used may be an alkali or alkaline earth metal hydroxide, preferably caustic soda or potash, and the temperature may be about 50 DEG C. If the nitro isomers are separated before dehalogenation the product is the 1- or the 2-nitro-anthraquinone, but if a mixture of the nitro isomers is used, separation after dehydrohalogenation may be effected by crystallisation or by extraction with sulphuric acid followed by dilution of the solution and fractional separation. The 1,4,4a,9a-tetrahydroanthraquinones used as starting materials may be obtained by reacting dienes with naphthoquinone. Specified dienes are butadiene and the 2-chloro-3-methyl-, 2,3-dimethoxy-, 2,3-dimethyl, 1-phenyl-, 1,4-diphenyl-, 2-chloro, 2-methyl-, 2-butyl-, 2-heptyl-, 2-phenyl-, 2-acetoxy-, 2-ethoxy-, and 2-bromoderivatives of butadiene, and 3-chloro-1,3-pentadiene, -hexadiene, and -octadiene, and cyclopentadiene. Specification 873,874 and U.S.A. Specification 2,642,445 are referred to.