Elimination kinetics of β-hydroxynitriles in the gas phase

✍ Scribed by Gabriel Chuchani; Rosa M. Dominguez; Alexandra Rotinov; Jairo Quijano; Cristina Valencia; Bernardo Vicente; Dimas Franco

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 63 KB
• Volume: 12
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/(sici)1099-1395(199901)12:1<19::aid-poc90>3.0.co;2-l

✦ Synopsis

The gas-phase elimination kinetics of primary, secondary and tertiary b-hydroxynitriles were examined in static seasoned vessels over the temperature range 360-450 °C and pressure range 47-167 Torr (1 Torr = 133.3 Pa). These reactions are homogeneous, unimolecular and follow a first-order rate law. The rate coefficients are given by the Arrhenius equation: for 3-hydroxypropionitrile log k 1 = (14.29 AE 0.47) À (234.9 AE 6.3) kJ mol À1 (2.303 RT) À1 ; for 3-hydroxybutyronitrile log k 1 = (13.76 AE 0.10) À (222.6 AE 0.7) kJ mol À1 (2.303RT) À1 ; and for 3-hydroxy-3methylbutyronitrile log k 1 (s À1 ) = (13.68 AE 0.68) À (212.5 AE 8.7) kJ mol À1 (2.303RT) À1 . The decomposition rates of the b-hydroxynitriles increase from primary to tertiary carbon containing the OH group. The rates for the bhydroxynitriles are found to be slower than those for the corresponding b-hydroxyacetylene analogs. The value of log A from 13.7 to 14.4 and the small positive DS ≠ indicate a mechanism different from a six-centered cyclic transition state. These data appear to indicate that a four-membered cyclic transition state or a quasi-heterolytic mechanism is conceivable.