ON THE STUDY OF HYDRO-AROMATIC SUBSTANCES. 113 
Perkin and Pope’s acid is 1-methyl A*-tetrahydrobenzeneacetic acid, and 
CH,—CH 
OH, . cue So . cH, . COOH 
CH,—CH,/ 
that the methyleyclohexylideneacetic acid, which would be produced at 
the same time, was overlooked on account of its extreme solubility in all 
organic solvents. 
m-Hydroxybenzoic acid can be readily reduced by sodium and alcohol ' 
to form cyclohexanol-3-carboxylic acid, which exists in well-defined cvs and 
/ SHOH—CH, 
CH, CH . COOH 
New. Cn: 
trans modifications. When oxidised with chromic acid it is converted 
into cyclohexanone-3-carboxylic acid, the ethyl salt of which has been 
used as the starting point in the synthetical preparation of carvestrene. 
The method of preparing 6-ketohexahydrobenzoic acid from pentane-aye- 
tricarboxylic acid is very laborious, and a decided improvement has now 
been introduced 2 by heating the ethyl ester of the above acid with sodium, 
when ethyl cyclohexanone-2 : 4-dicarboxylate is formed, which, when 
CH, . CH, . COOC,H, 
C,H,COO . CHS 
Nou, . CH, . C0OC,H, 
CH,—CH, 
C,H, . 000. cag co 
CH,—CH,Z. C000,H, 
Q- 
digested with dilute sulphuric acid, is readily decomposed with formation 
of 6-ketohexahydrobenzoic acid, carbon dioxide, and ethyl alcohol. 
Confirmation of the formule assigned by Baeyer* to the different 
forms of dihydrophthalic acids has been furnished through the resolution 
of trans-A*°-dihydrophthalic acid + into two active isomerides by erys- 
tallising the strychnine hydrogen salt, the isomerides having [a], 126°. 
Baeyer stated that when treated with caustic soda the trans A*? acid was 
converted into the A**-variety ; and with acetic anhydride it passed the 
cis A*° modification. As neither of these forms contains an asymmetric 
carbon atom, the optical activity ought to be destroyed by treatment 
with these reagents. This takes place in both cases, the change from one 
modification to the other proving to be a unimolecular reaction under the 
conditions of experiment. 
A comparison of the electrical conductivities of a- and B-naphthoic, 
_ benzoic, and phthalic acids with their hydrogenised derivatives leads 
Abati® to the conclusion that, apart from the strongly negative character 
of the aromatic nucleus, the presence and position of double bonds in 
these acids has an undoubted influence on their conductivities, which is 
‘increased by a double bond in the aa or By positions, whereas if in the 
aB or yd positions practically the same value is obtained as for the 
corresponding saturated acids. The author considers this to be contrary 
to the declarations of Fichter and Pfister,® and does not consider that 
1 Perkin and Tattersall, J.C.S., 1907, 91, 480. 
2 Kay and Perkin, ibid., 1906, 89, 1640. 
§ Annalen, 1892, 269, 145. 4 Neville, J.C.S., 1905, 89, 1744. 
5 Cent. Biatt., 1907, 1, 886. ® Annalen, 1904, 334, 201. 
1907. I 
