Bond cleavage during isobutanol thermal decomposition and the breaking of C-C bonds in alcohols at high temperatures.

Isobutanol was thermally decomposed in a single pulse shock tube under conditions where chain processes were suppressed. The main reaction is the breaking of C-C bonds. Literature rate expressions, experimentally determined, are found in some cases to be in disagreement. The rate expressions for the decomposition processes at temperatures of 1090 to 1240 K and pressures of 1.5 and 6 atm are k(isobutanol → isopropyl + hydroxymethyl) + k(isobutanol → methyl + 1-hydroxypropyl-2) = 10(16.7±0.3) exp(-41097 ± 750) s(-1), where k(isobutanol → isopropyl + hydroxymethyl) = 10(16.45 ±0.3) exp(-40910 ± 750/T) s(-1) and k(isobutanol → methyl + 1-hydroxypropyl-2) = 10(16.38±0.3) exp(-41560 ± 750/T) s(-1). These values permit comparisons with recent estimates including those from ab initio calculations. A new procedure is presented that uses information on the kinetics of bond breaking reactions of alkanes and the effect of OH substitution to derive rate coefficients for similar reactions of alcohols. This leads to the following rate expression for the smaller alcohols, at temperatures of 1090 to 1240 K and pressures of 1.5 and 6 atm, k(ethanol → methyl + hydroxymethyl) = 10(16.42±0.3) exp(-43496 ± 750 K/T) s(-1), k(isopropanol → methyl + 1-hydroxyethyl) = 10(16.54±0.3) exp(-42495 ± 750 K/T) s(-1), k(n-propanol → ethyl + hydroxymethyl) = 10(16.43±0.3) exp(-41696 ± 750 K/T) s(-1), and k(n-propanol → methyl + 2-hydroxymethyl) = 10(16.53±0.3) exp(-42945 ± 750 K/T) s(-1). Extension of this approach to other alcohols is straightforward. The resulting correlations along with the data on dehydration of alcohols provide novel information of the kinetic stability of alcohols.