FAST-FLOW KINETIC-STUDIES OF THE REACTION CH2OH-REVERSIBLE-ARROW-CH3OH+CL - THE HEAT OF FORMATION OF HYDROXYMETHYL(HCL)

The kinetics of the chlorination equilibrium of methanol, CH2OH + HCl half arrow right over half arrow left CH3OH + Cl (1, -1), have been st udied using the fast flow technique with Laser Magnetic Resonance and Electron Paramagnetic Resonance detection. The rate constants of the f orward and reverse reactions were found to be k1 = (2.3+/-0.9) .10(11) exp [-(20.9+/-2.9) kJ.mol-1/RT] cm3/mol.s in the temperature range 50 0 K less-than-or-equal-to T less-than-or-equal-to 812 K and k-1 = (3.7 +/- 0.4).10(13) cm3/mol.s at room temperature. These kinetic results were utilized in third law and second law procedures to obtain the val ue of the heat of formation of the hydroxymethyl radical. The entropy of CH2OH, S(f,298)0(CH2OH) = (254+/-4) J/mol.K, and the activation ene rgy of reaction (-1), E-1 = (0+/-4) kJ/mol, which are required for the calculations, were selected by critical assessment of the available l iterature data. The average of the third law and second law determinat ions provided DELTA(f)H298(0)(CH2OH) = -(9+/-6) kJ/mol. This value is higher by 17 kJ/mol than the heat of formation value in common use and implies a stronger C-H bond energy in methanol, D298(H-CH2OH) = 410 k J/mol. These new thermochemical quantities are in excellent agreement with the very recent recommendations of Seetula and Gutman [J. Phys. C hem. 96, 5401 (1992)] and have important implications for modeling stu dies of complex chemical systems such as the combustion of methanol.