Studies on cyclohexane derivatives. Part VIII: Preparation and mass spectra of the seven <i>t</i>‐butylcyclohexanecarboxylic acids

Abstract

Abstract 1‐ t ‐Butylcyclohexanecarboxylic acid ( 1 ) has been synthesized from t ‐butyl‐cyclohexanols as well as from 2‐(1‐methylcyclohexyl)‐2‐propanol by the Koch ‐Haaf carboxylation. A side product in these preparations is 2‐methyl‐2‐(1‐methylcyclohexyl)propionic acid ( 5 ). Details are given for the preparation of the cis ‐ and trans ‐isomers of 2‐, 3‐and 4‐ t ‐butylcyclohexanecarboxylic acid ( cis ‐ and trans ‐ 2, 3 and 4 ) starting from the corresponding t ‐butylbenzoic acids. The t ‐butylbenzoic acids and their methyl esters have been hydrogenated over transition metal catalysts at 25°. Palladium differs from platinum, rhodium and ruthenium by, in all cases, giving in excess the most stable isomer. In the hydrogenation of 2‐ t ‐butylbenzoic acid over rhodium desorbed 6‐ t ‐butyl‐1‐cyclohexene‐1‐carboxylic acid is shown to be the main source of the trans ‐ 2 formed. The mass spectra of 1 − 4 are presented and discussed. The mode of fragmentation of cis ‐ 4 and cis ‐ 3 was found to differ in a characteristic way from that of their trans ‐isomers.