Protonic Acids in Nonprotonic Solvents

Amines react with protonic acids in nonprotonic solvents or in the gas phase to form ammonium ions. From studies of gas-phase equilibrium reactions between amines and protonic reference acids ... 

On the other hand, dipolar solvent molecules may also compete with the aquo ligands in the coordination sphere of the metal cation, e.g., in the nonprotonated acid form (HX). Adduct formation in the absence of proton exchange or ion association (e.g., in nonaqueous solvents) is denoted as an Lewis acid-base interaction. The adduct formation may be described and evaluated by using the Hammett function introduced previously (Equations 8.54 and 8.55) according to - °... 

If the mechanism in acid and without acid are the same, one might have expected 4-alkylation under both conditions, and the failure to observe any 4-alkylation when acid is not present is as yet unexplained. Possibly with nonprotonated bases the hydroxyalkylation occurs according to Scheme 11, in which dimerization of two radicals within the solvent cage would lead to attack only at position 2, while in acid the attack could take place, at least in part, according to Scheme 12 but with protonated base, leading to both the isomers (2 and 4), as in the hydroxyalkylation by oxidation of alcohols. The much higher affinity of alkyl radicals toward protonated heteroaromatic bases in comparison with nonprotonated bases would support this interpretation. 

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