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Kinetics and mechanisms of gas‐phase decarbonylation of α‐methyl‐trans‐cinamaldehyde and E‐2‐methyl‐2‐pentenal under homogeneous catalysis of hydrogen chloride
Author(s) -
Julio Libia L.,
Lezama Jesus,
Maldonado Alexis,
Mora José R.,
Chuchani Gabriel
Publication year - 2014
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.3282
Subject(s) - chemistry , carbon monoxide , decarbonylation , catalysis , photochemistry , transition state , hydrogen chloride , hydrogen , organic chemistry
The kinetics of the gas‐phase elimination of α‐methyl‐trans‐cinamaldehyde catalyzed by HCl in the temperature range of 399.0–438.7 °C, and the pressure range of 38–165 Torr is a homogeneous, molecular, pseudo first‐order process and undergoing a parallel reaction to produce via (A) α‐methylstyrene and CO gas and via (B) β‐methylstyrene and CO gas. The decomposition of substrate E‐2‐methyl‐2‐pentenal was performed in the temperature range of 370.0–410.0 °C and the pressure range of 44–150 Torr also undergoing a molecular, pseudo first‐order reaction gives E‐2‐pentene and CO gas. These reactions were carried out in a static system seasoned reactions vessels and in the presence of toluene free radical inhibitor. The rate coefficients are given by the following Arrhenius expressions:Products formation from α‐methyl‐trans‐cinamaldehydeα‐methylstyrene : log k 1 ′s − 1 lmo l − 1= 12.67 ± 0.02 − 183.3 ± 0.31 kJmo l − 12.303 RT− 1β‐methylstyrene : log k 1 ′s − 1 lmo l − 1= 13.19 ± 0.03 − 183.0 ± 0.45 kJmo l − 12.303 RT− 1Products formation from E‐2‐methyl‐2‐pentenalE‐2‐pentene : log k 1 ′s − 1 lmo l − 1= 12.79 ± 0.06 − 174.5 ± 0.80 kJmo l − 12.303 RT− 1The kinetic and thermodynamic parameters for the thermal decomposition of α‐methyl‐trans‐cinamaldehyde suggest that via (A) proceeds through a bicyclic transition state type of mechanism to yield α‐methylstyrene and carbon monoxide , whereas via (B) through a five‐membered cyclic transition state to give β‐methylstyrene and carbon monoxide . However, the elimination of E‐2‐methyl‐2‐pentenal occurs by way of a concerted cyclic five‐membered transition state mechanism producing E‐2‐pentene and carbon monoxide . The present results support that uncatalyzed α‐β‐unsaturated aldehydes decarbonylate through a three‐membered cyclic transition state type of mechanism. Copyright © 2014 John Wiley & Sons, Ltd.