Aspects of the hydrolysis of formamide: revisitation of the water reaction and determination of the solvent deuterium kinetic isotope effect in base

Abstract

A study of the hydrolysis of formamide is reported with the aims of isolating the water reaction for hydrolysis from the acid and base hydrolysis terms and determining the solvent deuterium kinetic isotope effect (dkie) on base-catalyzed hydrolysis. Respective activation parameters (ΔH‡ and ΔS‡) of (17.0 ± 0.4) kcal mol–1 and (–18.8 ± 1.3) cal mol–1 K–1 for the acid reaction and (17.9 ± 0.2) kcal mol–1 and (–11.1 ± 0.5) cal mol–1 K–1 for the base reaction were determined from Eyring plots of the second-order rate constants over the range of 27–120°C. Kinetic studies at the minima of the pH/rate profiles in the pH range from 5.6 to 6.2 in MES buffers at 56°C, and in the pH range of 4.25–6.87 in acetate and phosphate buffers at 120°C are reported. At 56°C the available data fit the expression k56obs = 0.00303[H3O+] + 0.032[HO–] + (3.6 ± 0.1) × 10–9, while at 120°C the data fit k120obs = (0.15 ± 0.02)[H3O+] + (3.20 ± 0.24)[HO–] + (1.09 ± 0.29) × 10–6. Preliminary experimental estimates of Ea (ln A) of 22.5 kcal mol–1 (15.03) for the water rate constant (kw) are calculated from an Arrhenius plot of the 56 and 120°C data giving an estimated kw of 1.1 × 10–10 s–1 (t1/2 = 199 years) at 25°C. Solvent dkie values of kOH/kOD = 1.15 and 0.77 ± 0.06 were determined at [OL–] = 0.075 and 1.47 M, respectively. The inverse value is determined under conditions where the the first step of the reaction dominates and is analyzed in terms of a rate-limiting attack of OL–.Key words: formamide, activation parameters, water reaction, acid and base hydrolysis, solvent kinetic isotope effect.

Mechanically activated rupture of single covalent bonds: evidence of force induced bond hydrolysis

“…Without mechanical stress, hydrolysis of these bonds requires rather harsh reaction conditions, such as extreme pH values and elevated temperatures. Experimentally determined activation energies for the amide bond lie in the range between 76 kJ mol À1 and 105 kJ mol À1 , [35][36][37][38][39] the corresponding values for the siloxane bond are between 67 kJ mol À1 and 96 kJ mol À1 . 35,[40][41][42] Theoretical values are 63-113 kJ mol À1 for the amide [43][44][45][46][47][48][49] and 71-142 kJ mol À1 for the siloxane bond.…”

Formamide Chemistry and the Origin of Informational Polymers

“…This reaction is known to be catalyzed by different metal oxides [52]. Moreover, even though formamide is hydrolyzed slowly to ammonium formate (K w ¼ 1.1 Â 10 À 10 s À 1 at 258), with a half life t 1/2 of nearly 200 years at ambient temperature, the reaction can be efficiently accelerated under acidic-clay conditions [53]. …”

The Mechanism of Formamide Hydrolysis in Water from Ab Initio Calculations and Simulations

“…Some experiments favor a base-catalyzed mechanism even in neutral aqueous solution, [9] but recent experiments [10] have allowed the reaction in water to be isolated from the acid-and basehydrolysis terms.…”

“…Kinetic constants, comparison with experiment: Experimentally, [10] the pseudo-first-order kinetic constant for the neutral hydrolysis of formamide has been determined at 56 8C (3.6 AE 0.1 10 À9 s…”