The retro-aldol mechanism in the pyrolysis kinetics of primary, secondary, and tertiary β-hydroxy ketones in the gas phase

✍ Scribed by Alexandra Rotinov; Gabriel Chuchani; Ruben A. Machado; Carlos Rivas; Jairo Quijano; Maria Del Socorro Yepes; Iliana Restrepo

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 400 KB
• Volume: 24
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550241009

✦ Synopsis

Abstract

The pyrolysis kinetics of primary, secondary, and tertiary β‐hydroxy ketones have been studied in static seasoned vessels over the pressure range of 21–152 torr and the temperature range of 190°–260°C. These eliminations are homogeneous, unimolecular, and follow a first‐order rate law. The rate coefficients are expressed by the following equations: for 1‐hydroxy‐3‐butanone, log k~1~(s^−1^) = (12.18 ± 0.39) − (150.0 ± 3.9) kJ mol^−1^ (2.303__RT__)^−1^; for 4‐hydroxy‐2‐pentanone, log k~1~(s^−1^) = (11.64 ± 0.28) − (142.1 ± 2.7) kJ mol^−1^ (2.303__RT__)^−1^; and for 4‐hydroxy‐4‐methyl‐2‐pentanone, log k~1~(s^−1^) = (11.36 ± 0.52) − (133.4 ± 4.9) kJ mol^−1^ (2.303__RT__)^−1^. The acid nature of the hydroxyl hydrogen is not determinant in rate enhancement, but important in assistance during elimination. However, methyl substitution at the hydroxyl carbon causes a small but significant increase in rates and, thus, appears to be the limiting factor in a retroaldol type of mechanism in these decompositions. © John Wiley & Sons, Inc.