Dehydrogenation of Substituted Alcohols to Aldehydes on Zinc Oxide-Chromium Oxide Catalysts

Abstract

Sixteen primary alcohols of the structure RCH 2 OH (R = CH 3 , C 2 H 5 , (CH 3 ) 2 CH, (CH 3 ) 3 CCH 2 , HOCH 2 , CH 3 OCH 2 , C 6 H 5 , C 6 H 5 CH 2 , C 6 H 5 OCH 2 , ClCH 2 , BrCH 2 , F 3 C, CNCH 2 , (CH 3 ) 2 NCH 2 , (C 2 H 5 ) 2 NCH 2 and tetrahydrofurfuryl) were explored for the possibility of obtaining the corresponding aldehydes by dehydrogenation on solid catalysts. Various catalysts were tested and two zinc oxide-chromium oxide catalysts were selected for further work because their activity and selectivity was satisfactory; moreover, the selectivity could be improved by addition of sodium into the catalysts and of water into the feed. The reaction was performed in the temperature range 250-450 °C and at atmospheric pressure. 2-Chloroethanol, 2-bromoethanol, ethylene glycol, 2-cyanoethanol and 2-( N,N -diethylamino)ethanol decomposed and deactivated the catalyst. The other alcohols were studied from the point of kinetics of dehydrogenation, which was described by a Langmuir-Hinshelwood type rate equation ( 3 ), and of substituent effects on rate, which were correlated by Taft equation ( 1 ) with the slope ρ = -1.46. The preparative value of catalytic dehydrogenation for obtaining substituted aldehydes was confirmed by prolonged runs and isolation of the aldehydic product by distillation using as the feeds 2-methoxyethanol and 2-( N,N -dimethylamino)ethanol, respectively.