The kinetics and mechanisms of the gas phase elimination of primary, secondary and tertiary β-hidroxynitriles

Primary, secondary and tertiary beta -hydroxynitriles have been pyrolyzed in a static system over the temperature range of 360-450 degrees C and pressure range of 47-167torr. The elimination reactions of these nitriles, in seasoned vessels, are homogeneous, unimolecular and follow a first-order rate law The Arrhenius equations for the decomposition reactions were found to be as follows. for 3-hydroxypropinitrile log k(1) (s(-1)) = (14.29+/-0.47) - (234.9+/-6.3) kJmol(-1) (2.303RT)(-1); for 3-hydroxybutyronitrile log k(1) (s(-1)) = (13.76+/-0.10) - (222.6+/-0.7) kJmol(-1) (2.303RT)(-1); and for 3-hydroxy -3-methylbutyronitrile log k(1) (s(-1)) = (13.68+/-0.68) - (212.5+/-8.7) kJmol(-1) (2.303RT)(-1). The elimination rates of the beta -hydroxynitriles increase significantly from primary to tertiary carbon containing the hydroxy group. The rates of the beta -hydroxynitriles have been found to be slower than he corresponding beta -hydroxyacetylenes analogs. The values of the frequency factor (log A=13.7-14.4) lead to a small positive entropy of activation suggesting a dissociative transition state rather than the six-membered cyclic transition state postulated for the beta -hydroxyalkenes and beta -hydroxyacetilenes.