AROMATIC ACYLATION IN HOMOGENEOUS SOLUTION AND IN THE GAS-PHASE - THEMECHANISTIC RELEVANCE OF THE MESITYLENE DURENE REACTIVITY RATIO

By means of a mixed acetic-trifluoroacetic anhydride a scale of relati ve substrate reactivity for aromatic acetylation is obtained, which sp ans over eight powers of ten from benzene to 2-methylthiophene. Correl ation of these reactivity data with relevant substrate parameters is a ttempted, to gain an understanding of the possible nature of the elect rophilic substitution mechanism at work, i.e. either an ionic (two-ele ctron) or a single-electron route. The study includes gas-phase reacti vity data on the reaction of free acetylium ion, which has been genera ted by a radiolytic method. From this comparative approach a 'conventi onal' ionic mechanism for the aromatic acetylation reaction is substan tiated.