Anthraquinone and anthrone series

Summary

The synthesis of 4-chloro-, bromo- and iodo- alizarins is described. Bromination of 2-O-p-toluene sulphonylalizarin (I) in glacial acetic acid gave a monobromo derivative (II), which on hydrolysis yielded a new bromoalizarin (III). Methylation of (III) gave the known 4-bromoalizarin-2-methyl ether, showing that (III) is 4-bromoalizarin. Chlorination of (I) with sulphuryl chloride in nitrobenzene gave 4-chloro-2-O-p-toluene-sulphonylalizarin (XII), which on hydrolysis yielded 4-chloroalizarin. Condensation of (II) and (XII) with aniline andp-toluidine led to 4-anilino-and 4-p-toluidinoalizarins. In addition to the 4-arylaminoalizarins, 1:2:4-trianilino and 1:2:4-tri-p-toluidinoanthraquinones were isolated by chromatography. Condensation of 4-nitroalizarin with aniline in presence of boric acid gave 4-anilinoalizarin, which was different from the product described by Gonsalves,et al., as 4-anilinoalizarin. 6:7-Dihydroxyanthraquinoneacridone was prepared from (II) in the usual manner and examined as a vat dye. 4-Iodoalizarin-2-methyl ether (XV) was prepared from alizarin-2-methyl ether by nitration, reduction, and replacement of the amino group by iodinevia the diazonium salt. Demethylation of (XV) with aluminium chloride gave 4-iodoalizarin.