The kinetics and mechanisms of gas phase elimination of primary, secondary, and tertiary 2-hydroxyalkylbenzenes

2-Phenylethanol, racemic 1-phenyl-2-propanol, and 2-methyl-1-phenyl-2-propa nol have been pyrolyzed in a static system over the temperature range 449.3 -490.6 degrees C and pressure range 65-198 torr. The decomposition reaction s of these alcohols in seasoned vessels are homogeneous, unimolecular, and follow a first-order rate law. The Arrhenius equations for the overall deco mposition and partial rates of products formation were found as follows: fo r 2-phenylethanol, overall rate log k(1)(s(-1)) = 12.43 - 228.1 kJ mol(-1) (2.303 RT)(-1), toluene formation log k(1)(s(-1)) = 12.97 - 249.2 kJ mol(-1 ) (2.307 RT)(-1), styrene formation log k(1)(s(-1)) = 12.40 - 229.2 kJ mol( -1)(2.303 RT)(-1), ethylbenzene formation log k(1)(s(-1)) = 12.96 - 253.2 k J mol(-1)(2.303 RT)(-1); for 1-phenyl-2-propanol, overall rate log k(1)(s(- 1)) = 13.03 - 233.5 kJ mol(-1)(2.303 RT)(-1), toluene formation log k(1)(s( -1)) = 13.04 - 240.1 kJ mol(-1)(2.303 RT)(-1), unsaturated hydrocarbons + i ndene formation log k(1)(s(-1)) = 12.19 - 224.3 kJ mol(-1)(2.303 RT)(-1); f or 2-methyl-1-phenyl-2-propanol, overall rate log k(1)(s(-1)) = 12.68 - 222 .1 kJ mol(-1)(2.303 RT)(-1), toluene formation log k(1)(s(-1)) = 12.65 - 22 2.9 kJ mol(-1)(2.303 RT)(-1), phenylpropenes formation log k(1)(s(-1)) = 12 .27 - 226.2 kJ mol(-1)(2.303 RT)(-1). The overall decomposition rates of th e 2-hydroxyalkylbenzenes show a small but significant increase from primary to tertiary alcohol reactant. Two competitive eliminations are shown by ea ch of the substrates: the dehydration process tends to decrease in relative importance from the primary to the tertiary alcohol substrate, while tolue ne formation increases. (C) 1999 John Wiley & Sons, Inc.