Kinetics and Mechanism of Hydroxymethylation of Melamine and Acetoguanamine in Carboxylate Buffers -Discussion on the Basis of Bronsted Plot- -Studies on Formaldehyde Resin. XXIX.-

Abstract

Hydroxymethylations of melamine (MH) and acetoguanamine (AGH) with formaldehyde (F) were kinetically investigated in aqueous carboxylate buffers at 40°C. For melamine hydroxymethylation, chloroacetate, 3-chloropropionate, and acetate buffers were used, and for acetoguanamine hydroxymethylation, in addition to above three buffers, formate, and propionate buffers were used. As a result, the second-order rate constant k given by the initial rate R₀=k[Ml_f]₀[F]₀ or R₀=k[AGH_f]₀[F]₀ was approximately given by k-k′ =k_HA[HA]. Here, MH_f and AGH _f show the free bases of MH and AGH, respectively, and k′ is the rate constant in unbuffered media, HA being the acidic constituent of the buffer. Next, Brφnsted plots obtained by the use of the k_HA, values, thus estimated, are linear with the slope of 0.35in each case. From this result, the general acid-catalyzed reaction mechanism was dicussed.