Kinetics of the gas‐phase elimination of isopropyl α‐substituted acetates

Abstract

In the past decade the mechanism for the gas-phase elimination of esters has been more favorably described in terms of a discrete semipolar transition state [l-101 rather than a concerted [ll], ion pair [12,13], or concerted heterolysis [14]. A recent communication [lo] on the gas-phase pyrolysis of isopropyl a-haloacetates has erroneously questioned the general idea of direct proportionality between acid strength of carboxylic acid and rate decomposition of the corresponding esters [9,. Furthermore, the sequence I > Br > C1> F obtained in pyrolysis rates was later attributed to steric effect [33]. In this sense, the present work was to study the steric factors and/or the inductive release of alkyls as described in (l), and also to relate them to the corresponding carboxylic acid dissociation constants if possible:where Z = H, Me, Et, iso-Pr, t-Bu, MeO, and Ph.Isopropyl butyrate (Merck-Schuchard) was distilled several times and the fraction 98.9% (gas-liquid chromatography) was used. Isopropyl isovalerate, isopropyl tert -butylacetate, isopropyl methoxyacetate, and isopropyl phenylacetate were prepared from isopropanol and the corresponding acid chlorides by the common method for synthesis of esters [19, p. 3791. These chlorides were made from the related carboxylic acid as described 119, p. 3821: isopropyl isovalerate, boiling point 132"-133°C at 633 mm Hg; 142°C at 756 mm Hg [20]; isopropyl tert-butylacetate, boiling point 8Oo-81"C at 60 mm Hg; 82"-82°C at 69 mm Hg [21]; isopropyl methoxyacetate, boiling point 38"-40°C a t 5 mm Hg; 67"-68°C at 21 mm Hg [22]; isopropyl phenylacetate, boiling point 69"-70°C a t 0.5 mm Hg; nD20 1.4950 [23]. These esters were also fractionated several times and the fractions over 99.0% as determined by gas-liquid chromatography were used. The starting materials were determined quantitatively, using internal standards, on a Perkin-Elmer F-11 gas chromatograph with a flame ionization detector. Di-isodecylphthalate 5%-Chromosorb G A. W. D.M.C.S. 60-80 mesh was used as a column for the ester analyses. The

Structures and Energetics of Unimolecular Thermal Degradation of Isopropyl Butanoate as a Model Biofuel: Density Functional Theory and Ab Initio Studies

“…Therefore, studying isopropyl ester as a model biodiesel will shed some light onto the combustion behavior of a branched ester as a biodiesel. There are some experimental studies on isopropyl acetate and isopropyl propanoate esters concerned with determination of the rate coefficients of their unimolecular decompositions. − Only one theoretical study has been reported on the mechanistic details of pyrolysis of isopropyl acetate to propene and acetic acid . Better simulation of fatty acid esters can be achieved by increasing the alkyl chain length at the acid side.…”

Gas-phase pyrolysis kinetics of 5-acetoxy-2-methylpent-2-ene

“…1964, 86, 3773. lO^j.s"1 0.84 1.63 2.95 3.99 5.62 9.84 17.62 participate in the rate of pyrolysis of this ester; it only increases the elimination rate due to an allylic weakening of the Cfl-H bond. 5 The loosening of C^-H has also been found to be caused by other x-bonds adjacent to the ßcarbon atom in ethyl acetates, where the sequence in py- rolysis rates CH=C > Ph > CH2=CH6 is in accord with their effect on the acidity of C^-H.7…”