The Kinetics of the Hydrolysis of 6-Trichloromethylpurine in Dilute Aqueous Solutions

Above pH 5, the hydrolysis of 6-trichloromethylpurine (HPuCCh) to purinoic and hydrochloric acids in dilute, aqueous solutions proceeds as follows. (1) HPuCCh is ionized to (PuCCl₃), the relative concentration of which depends on the pH and the pKa of HPuCCh. (2) (PuCCh)- loses Cl~ in a rate-determining step, yielding a reactive intermediate, Pu=CCk. (3) The latter is sufficiently stable to discriminate between various nucleophiles, its relative reaction rates with water, Cl~, or OH~ being 1, 233, and 1290, respectively. Non-ionized HPuCCh is capable of undergoing hydrolysis, but at a rate much slower than (PuCCl₃)~, the first-order rate constants being 8 X 10~⁷ and 1.09 X 10~³ sec¹, respectively. The relative stability of the CCl³ group in HPuCC₃, compared to structurally related systems, is ascribed to the double bond-no bond resonance of the molecule.