The Synthesis of 1-Chloroxanthone and Related Dichloroxanthones

1-Chloroxanthone (2) was obtained by cyclization of 2-chloro-6-phenoxybenzoic acid (10) prepared from 2-nitro-6-phenoxybenzoic acid (8) via 2-amino-6-phenoxybenzoic acid (9). Similarly, 1, 5-dichloroxanthone (14a) and 1, 7-dichloroxanthone (14b) were obtained from 2-(2-chlorophenoxy)-6-nitrobenzoic acid (11a) and 2-(4-chlorophenoxy)-6-nitrobenzoic acid (11b), respectively. Furthermore, 2, 6-dichloroxanthone (19) was prepared by cyclization of 4-chloro-2-(4-chlorophenoxy)benzoic acid (18). Dichloroxanthone B, obtained by cyclization of 5-chloro-2-(3-chlorophenoxy)benzoic acid (16) and reported by Nargund et al. as 1, 7-dichloroxanthone, could not be separated into 1, 7-(14b) and 2, 6-dichloroxanthone (19) by recrystallization, column chromatography or thin-layer chromatography, but was proved here to be a mixture of 14b and 19 by gas chromatography.