Proton transfer from heterocyclic compounds. Part III. Adenine and adenosine

Rates of detritiation from C-8 of adenine and adenosine have been measured over a pH range at 85°. Analysis of the data enables the pKa values for protonation at N-7 to be calculated. For adenine, measurements have been made at several temperatures and the observed entropy of activation, taken in conjunction with other available information, supports a mechanism involving rate-determining hydroxide ion attack on the N-7 protonated species. For adenosine at high pH, an additional mechanism involving hydroxide catalysed exchange of the neutral compound is important.