, 130 REPORT— 1902. 



benzoic acids,' and dihydrobenzoic acids from the oxidation of dihydro- 

 benzaldehyde,- and by the action of alcoholic potash on dibromo-Aj-tetra- 

 hydrobenzoic acid.'* Homologues result from the reduction of homologues 

 of benzoic acid,'' and by heating hexamethylene dicarboxylic acids."' In 

 chemical properties these acids exhibit great similarity with the hydro- 

 phthalic acids (which see below). The hexahydro-acids appear to be 

 isomeric, but not identical with the natural naphthenic acids occurring in 

 petroleum.'' 



Hydroxylbexahydi'obenzoic acids,' dihydroxyhexahydroheyizoic acid,^ 

 tetrahydroxyliexahydrohenzoic acid (quinic acid),^ pentaliydroxyhexahydro- 

 benzoic acid,^'^ trihydroxytetrahydrobenzoic {shikiniic) acid.^^ 



lietohexahydrobenzoic acid,^^ diketohexahydrobenzoic acid (ethyl resor- 

 cylates) (see p. 127). 



Hydropiitiialic Acids. 



The hydrophthalic acids have been minutely studied by Baeyer in 

 his investigations on the constitution of benzene,'-* and these papers must 

 be consulted for a detailed description. Here it is only possible to 

 mention some of the more important properties, which show the striking- 

 resemblance between these bodies and acids of the aliphatic series. 



Generally speaking the di- and tetra-hydro-acids were obtained by 

 the direct reduction of the phtlialic acid, and the hexahydro-acids by the 

 reduction of the hydrobromide of the tetrahydro-acid. 



8ome idea of the numerous isomerides may be gained from the 

 following scheme, which shows the constitution and nomenclature '* of the 

 ten possible hydroterephthalic acids. In the case of the orthophthalic 

 acids there are fifteen possibilities ; and trans-hexahydrophthalic acid can 

 exist in two optically active forms.''' 



Hexahydroterephthalic arid, CgHufCOOH).,. — Two possibilities de- 

 pencling on the position of the carboxyl groups relative to the plane of 

 the hexamethylene ring. 



Hv .COOH H. XOOH 



H^ .-^^ H, H, ,/\ H, 



H, 1; Hj H, '.\ H, 



/\ /\ 



COOH H. H COOH 



Cis trans. Cis. 



Tetrahydroterephthalicacid,C^^{COO'S.).2. — Depending on the position 



' 7?«r., 1893, 26, 4.51. - Jitrf., p. 454. 



» Aschan, Ber., 1891, 24, 2028. 



■" Ber., 1892, 25, 3355 ; 1894,27, R. 195; J.C.S., 1897, 71. 157; 1901, 79, 344, 

 1379.- 



•■* Perkin and Freer, J.C.S., 1888, 53, 208. 



" Bcr., 1892, 25, 3665 ; 1894, 27, R. 195, 197. » 



' Ber., 1894, 27, 1231, 2472, 247C; 1890, 29, R. 549. 



« AnnalcJh, 271, 280. ' B<:ilstein, 3'' Auf., i. 804. 



'" Ber., 1891, 24, 1294. " Ber., 1891, 24, 1279. 



'- Bcr., 1894. 27, 103 ; 1896, 29, R. 550. 



'■' Annalen, 1888, 245, 107; 1889, 251, 257; 1890, 256, 1 : 258. 1, 145 ; 1891, 266, 

 169 ; 1892, 269. 145 ; also Viliiger, Annalen, 1893, 276, 255. 

 " For an explanation of which see Annalen, 1888, 245, 107. 

 '' Werner and Conrad, Ber., 1899, 32', 3040. 



