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The retro‐aldol mechanism in the pyrolysis kinetics of primary, secondary, and tertiary β‐hydroxy ketones in the gas phase
Author(s) -
Rotinov Alexandra,
Chuchani Gabriel,
Machado Ruben A.,
Rivas Carlos,
Quijano Jairo,
Yepes Maria Del Socorro,
Restrepo Iliana
Publication year - 1992
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550241009
Subject(s) - chemistry , kinetics , pyrolysis , aldol reaction , medicinal chemistry , limiting , torr , homogeneous , gas phase , reaction rate constant , organic chemistry , stereochemistry , catalysis , thermodynamics , mechanical engineering , physics , quantum mechanics , engineering
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.