One of the most important derivatives of diphenyl, from the theoretical point of view, is diphenic acid or diorthodiphenyl carboxylic acid, which can be obtained from diparadiaminodiphenyldiorthocarboxylic acid, H2N < j - < I > NH 2, or from phenanthrene, the consti Hooc Cooh tution of which it determines.
It may be obtained synthetically by Fittig and Tollens's method (above); by Friedel and Craft's process, devised in 1877, of acting with aluminium chloride on a mixture of benzene and methyl chloride; this reaction leads to the production of higher homologues which may, however, break down under the continued action of the aluminium chloride; or by heating the toluene carboxylic acids obtained by oxidizing the higher homologues of benzene.
Soc., 1888, 53, p. 1 94): C2H4Br2+2NaCH(C02R)2--->(CH 2) 2 C(CO 2 R) 2 +CH 2 (CO 2 R) 2; ethyl butane tetracarboxylate is also formed which may be converted into a tetramethylene carboxylic ester by the action of bromine on its disodium derivative (W.
C02R CH 3 CH: CBr CO 2 R+NaCH (CO 2 R) 2 --->CH 3 C. I C(C02R)2 by the action of diazomethane or diazoacetic ester on the esters of unsaturated acids, the pyrazoline carboxylic esters so formed losing nitrogen when heated and yielding acids of the cyclo- propane series (E.
Cyclo-propane carboxylic acid, C 3 H 5 CO 2 H, is prepared by heating the 1.1- dicarboxylic acid; and by the hydrolysis of its nitrile, formed by heating y-chlorbutyro-nitrile with potash (L.