1911 Encyclopædia Britannica/Benzophenone
BENZOPHENONE (Diphenyl Ketone), C6H5·CO·C6H5, the simplest representative of the true aromatic ketones. It may be prepared by distilling calcium benzoate; by condensing benzene with benzoyl chloride in the presence of anhydrous aluminium chloride; by the action of mercury diphenyl on benzoyl chloride, or by oxidizing diphenylmethane with chromic acid. It is a dimorphous substance existing in two enantiotropic forms, one melting at 26° C. and the other at 48° C: (Th. Zmcke, Berichte, 1871, 4, p. 576). It boils at 306.1° C., under a pressure of 760.32 mm. It is reduced by sodium amalgam to benzhydrol or diphenyl carbinol C6H5·CHOH·C6H5; a stronger reducing agent, such as hydriodic acid in the presence of amorphous phosphorus converts it into diphenylmethane (C6H5)2·CH2. Potash fusion converts it into benzene and benzoic acid. With phenylhydrazine it forms a hydrazone, and with hydroxylamine an oxime, which exists in one form only; if, however, one of the phenyl groups in the oxime be substituted in any way then two stereo-isomeric oximes are produced (cf. Stereo-Isomerism); thus parachlorbenzophenone oxime exists in two different forms (V. Meyer and K. F. Auwers, Berichte, 1890, 23, p. 2403). Many derivatives are known, thus ortho-amino-benzophenone, melting at 106° C., can be obtained by reduction of the corresponding nitro compound; it condenses under the influence of heated lead monoxide to an acridine derivative and with acetone in presence of caustic soda it gives a quinoline. Tetramethyl-diamido-benzophenone or Michler’s ketone, CO[C6H4N·(CH3)2]2, melting at 173°, is of technical importance, as by condensation with various substances it can be made to yield dye-stuffs. It is prepared by the action of carbonyl chloride on dimethyl aniline in the presence of aluminium chloride: COCl2 + 2C6H5N(CH3)2 = 2HCl + CO[C6H4N(CH3)2]2.