Experimental and theoretical studies of the elimination kinetics of 3‐hydroxy‐3‐methyl‐2‐butanone in the gas phase

The kinetics of the gas‐phase elimination of 3‐hydroxy‐3‐methyl‐2‐butanone was investigated in a static system, seasoned with allyl bromide, and in the presence of the free chain radical inhibitor toluene. The working temperature and pressure range were 439.6–489.3°C and 81–201.5 Torr (1 Torr = 133.3 Pa), respectively. The reaction was found to be homogeneous, unimolecular and to follow a first‐order rate law. The products of elimination are acetone and acetaldehyde. The temperature dependence of the rate coefficients is expressed by the following equation: log[ k 1 (s −1 )] = (13.05±0.53)−(229.7±5.3) kJ mol −1 (2.303 RT ) −1 . Theoretical estimations of the mechanism of this elimination suggest a molecular mechanism of a concerted non‐synchronous four‐membered cyclic transition‐state process. An analysis of bond order and natural bond orbital charges suggests that the bond polarization of C(OH)—C(O)—, in the sense of C(OH) δ+ &·C(O) δ− , is rate limiting in the elimination reaction. The rate coefficients obtained experimentally are in reasonably good agreement with the theoretical calculations. The mechanism of 3‐hydroxy‐3‐methyl‐2‐butanone elimination is described. Copyright © 2005 John Wiley & Sons, Ltd.