Rates of gas-phase ionic acetylation of some alkylbenzenes by acetyl cations formed from acetone and butane-2,3-dione

Rates of product formation by the attack of CH3CO+ on neutral alkylbenzenes follow the order o-xylene > m-xylene > p-xylene > n-butylbenzene > ethylbenzene > toluene > benzene. Absolute rates determined by a comparative method using ion cyclotron resonance are lower than the theoretical upper limit, but do not conform to physical theory in its present form. The rate is a strong function of the source of CH3CO+, that formed from butane-2,3-dione reacting at least 4 times more rapidly than that formed from acetone. Comparison with results for the attack of other gas-phase electrophiles upon alkylbenzenes shows reproducibility in trends.