1-Chlorothioxanthen-9-one (IV) (mp 112-114°) was prepared by cyclization of 2-chloro-6-phenylthiobenzoic acid (III), and also through a reaction between benzene and 2-chloro-6-mercaptobenzoic acid (V) in concentrated sulfuric acid, by starting with 6-chloroanthranilic acid (II) in both cases. A product (IV')(mp 146°), which was formed by cyclization of o-(m-chlorophenyl-thio) benzoic acid (I) and reported by Mahishi, et al.³⁾ as 1-chlorothioxanthen-9-one, proved not to be a single compound, but a mixture of IV and 3-chlorothioxanthen-9-one. As IV reacted easily, but not 3-chlorothioxanthen-9-one, with p-toluenesulfonamide to afford 1-(p-toluenesulfonamido)thioxanthen-9-one (VI), IV' gave a mixture of VI and unreacted 3-chlorothioxanthen-9-one when treated with the amide. Based on this fact, an approximate composition of IV' was estimated by titrating the liberated chloride ion from a reaction of IV' with p-toluenesulfonamide, and the values were 55% of IV and 45% of 3-chlorothioxanthen-9-one. IV was alternatively derived from VI by hydrolysis to 1-aminothioxanthen-9-one (VII), followed by the Sandmeyer reaction. 1-Chlorothioxanthen-9-ol (VIII) was prepared by the reduction of IV with sodium amalgam and ethanol. VIII was condensed with malonic acid to 1-chlorothioxanthene-9-malonic acid (IX), and the acid was decarboxylated to 1-chlorothioxanthene-9-acetic acid (X). 2-Diethylaminoethyl ester hydrochloride (XI) of X was obtained. Oxidation of X with hydrogen peroxide gave 1-chlorothioxanthene-9-acetic acid 10, 10-dioxide (XII) from which was derived its 2-diethylaminoethyl ester hydrochloride (XIII).