SITE OF GAS-PHASE METHYLATION OF ALKYL PHENYL KETONES

The CH3+ adducts of benzaldehyde, acetophenone, propiophenone and buty rophenone were prepared using CH3F-CH4 and CH3Cl-CH4 mixtures under ch emical ionization conditions and the unimolecular and collision-induce d fragmentation reactions of their adduct ions were studied For compar ison, the fragmentation reactions of the protonated p-methylphenyl alk yl ketones were studied as models of the ring-methylated species and t he fragmentation reactions of [C6H5C(R)=OCH3](+), produced by electron impact ionization of the appropriate methyl ether, were studied as mo dels of the O-methylated species. From these comparisons it is conclud ed that methyl cation addition occurs predominantly at the carbonyl ox ygen under our experimental conditions. However, for methyl-cationated acetophenone there is extensive migration of the methyl group from th e oxygen to the ring prior to fragmentation of the adduct.