Catalytic cycloalkylation of 4-hydroxyphenylpropionic acid methyl ester with methylcycloalkenes

Research has been carried out in the field of catalytic cycloalkylation of phenol derivatives. In the course of research, was developed the method for the synthesis of hindered phenols by cycloalkylation of 4-hydroxyphenylpropionic acid methyl ester with 1-methylcyclopentene, 1- and 3-methylcyclohexenes in the presence of a KU-23 cation exchanger catalyst. The influence of different kinetic parameters (temperature, time of the reaction, molar ratio of the initial components, amount of catalyst) on the yield and selectivity of the target product was determined, thereby determining the optimal process mode. It has been established that at low temperatures (60-80°C) of the reaction of cycloalkylation of phenol with 1(3)-methylcycloalkenes in the presence of a KU-23 catalyst, O-alkylation of phenol is observed, with the formation of alkylphenyl ethers. With an increase in the temperature of the cycloalkylation reaction, the concentration of alkylphenyl ethers gradually decreases, and the alkyl substituent migrates to the ortho position (Claisen rearrangement). The optimal conditions for the reaction of cycloalkylation of methyl ester of 4-hydroxyphenylpropionic acid with methylcyclenes are: temperature 90-110ºС, reaction time 5-5.5 h, molar ratio of ether to cyclene 1:1, amount of catalyst - 10% per taken ether. Under these conditions, the yield of target products is 68.7-79.5% of theory per taken ether, and the selectivity is 93.4-97.3% for the target product. The structure and composition of the products of the cycloalkylation reaction were confirmed by spectral and chromatographic methods of analysis. Synthesized methyl esters of 3-mono-cycloalkyl-substituted 4-hydroxyphenylpropionic acid were tested as stabilizers for polyurethane polymer, the tests gave positive results.