Theoretical study of the neutral hydrolysis of hydrogen isocyanate in aqueous solution via assisted-concerted mechanisms.
A procedure is described for the theoretical study of chemical reactions in solution by means of molecular dynamics simulation, with solute-solvent interaction potentials derived from ab initio quantum calculations. We apply the procedure to the case of neutral hydrogen isocyanate hydrolysis, HNCO + 2 H(2)O --> H(2)NCOOH + H(2)O, in aqueous solution, via the assisted-concerted mechanisms and the two-water model. We used the solvent as a reaction coordinate and the free-energy curves for the calculation of the properties related to the reaction mechanisms, with a particular focus on the reaction and activation energies. The results showed that the mechanism with two water molecules attacking the C=N bond is preferred to the mechanism with three waters forming a ring of eight members. In addition, the aqueous medium significantly reduces the activation barrier (DeltaG(double dagger) = 13.9 kcal/mol) and makes the process more exothermic (DeltaG = -11.1 kcal/mol) relative to the gas-phase reaction, increasing the rate constant of the process to k = 4.25 x 10(5) s(-1).
Tolosa Arroyo
S
S
Departamento de Quísica, Universidad de Extremadura, 06071 Badajoz. Spain. santi@unex.es
Hidalgo Garcia
A
A
Sansón Martín
J A
JA
D000465:Algorithms; D002219:Carbamates; D003485:Cyanates / Q000737:chemistry*; D006868:Hydrolysis; D056004:Molecular Dynamics Simulation; D015394:Molecular Structure; D011789:Quantum Theory; D012996:Solutions; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
D002219:Carbamates; D003485:Cyanates; D012996:Solutions; D014867:Water; C070766:carbamic acid; C005057:isocyanic acid