INFRARED-LASER INDUCED ORGANIC-REACTIONS .2. LASER VS THERMAL INDUCEMENT OF UNIMOLECULAR AND HYDROGEN BROMIDE CATALYZED BIMOLECULAR DEHYDRATION OF ALCOHOLS

It has been demonstrated that a mixture of reactant molecules can be induced by pulsed infrared laser radiation to react via a route which is totally different from the pathway resulting from heating the mixture at 300 °C. The high-energy unimolecular elimination of H2O from ethanol in the presence of 2-propanol and HBr can be selectively induced with a pulsed CO2 laser in preference to either a lower energy bimolecular HBr-catalyzed dehydration or the more facile dehydration of 2-propanol. Heating the mixture resulted in the almost exclusive reaction of 2-propanol to produce propylene. It was demonstrated that the bimolecular ethanol + HBr reaction cannot be effectively induced by the infrared laser radiation as evidenced by the detrimental effect on the yield of ethylene as the HBr pressure was increased. The selective, nonthermal inducement of H2O elimination from vibrationally excited ethanol in the presence of 2-propanol required relatively low reactant pressures. At higher pressures intermolecular V-V energy transfer allowed the thermally more facile dehydration from 2-propanol to become the predominant reaction channel. © 1979, American Chemical Society. All rights reserved.