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Thus, e.g. 4-chloro-thiophenol and 2-iodo-benzoic acid are condensed to give 2-carboxy-4'-chlorodiphenylsulfide, which is then cyclized to 2-chloro-thioxanthone (cf. J. O. Jilek, M. Rajsner, J. Pomykacek and M. Protiva, Cesk. Farm. 14, (1965) 294-303). In an analogous manner, 4,5-dichlorothioxanthone is obtained from 2-(o-chlorophenylthio)-3-chlorobenzoic acid (cf. V. G. Kalawar, V. V. Badiger and K. S. Nargund, J. Karnatak Univ. 11, (1966) 37-41). Selenoxanthone is obtained from 2-(phenylseleno)-benzoic acid, made by the condensation of selenophenol with 2-iodobenzoic acid; 2-chloro-selenoxanthone is synthesized from 2-(p-chlorophenylseleno)-benzoic acid, obtained from 4-chloroselenophenol and 2-iodobenzoic acid (cf. K. Sindelar, E. Svatek, J. Metysova, J. Metys and M. Protiva, Collection Czechoslovak Chem. Commun. 34, (1969) 3792-3800). 3-Methoxy xanthone is analogously obtained from 2-carboxy-3'-methoxy diphenyl ether, 3-chloro-6-methoxy-xanthone from 2-carboxy,5-chloro-3'-methoxy diphenyl ether and 3-methyl-xanthone from 2-carboxy,5-methyl diphenyl ether. 3,6-Dimethoxy-xanthone is obtained from the abovementioned 3-chloro,6-methoxy-xanthone by the facile replacement of chloride with methoxy (cf. A. A. Goldberg and A. H. Wragg, J. Chem. Soc. 1958, 4227-4234 and ibid. 4234-4241). Similarly, 3-nitro-xanthone is obtained from 2-carboxy,5-nitrodiphenyl ether and 4-nitroxanthone from 2-carboxy,6-nitro diphenyl ether, whereas 2-nitroxanthone and 2,7-dinitro-xanthone may be obtained by direct nitration of xanthone (cf. A. A. Goldberg and H. A. Walker, J. Chem. Soc. 1953, 1348-1357).