Allan Maccoll

Gas-phase eliminations. Part XIV. The pyrolysis of 1-(1-chloroethyl)-2-methylbenzene

The gas-phase thermal decomposition of the title compound was studied in the temperature range 285–325° and with initial pressures between 25 and 105 mmHg. The only products detected were o-methylstyrene and hydrogen chloride. The reaction, which was homogeneous and unimolecular, followed the Arrhenius equation (i). log (k/s–1)= 13.55 – 44.83 (2.303RT/kcal mol–1)–1(i) The mechanism was identified as a four-centred type related to that of the aliphatic halides rather than the six-centred one proposed for 1-chloromethyl-2-methylbenzene.

Thermolysis of azoalkanes in a stirred-flow system

The gas-phase thermal decomposition of azoethane, ethaneazo-1′-methylethane, and azo-2′-methylpropane have been investigated in a stirred-flow system using the toluene carrier technique. The order of the reaction for the disappearance of the azoalkanes has been found to be nearly unity in each case. The temperature dependence of the rate coefficients is given by the Arrhenius equations: azoethane, log k= 14.2 ± 0.2 –(186 ± 2 kJ mol–1)/2.30RT; ethaneazo-1′-methylethane, log k= 16.5 ± 0.5 –(206 ± 3 kJ mol–1)/2.30RT, and azo-2′-methylpropane, log k= 15.6 ± 0.3 –(170 ± 3 kJ mol–1)/2.30RT. No evidence was found for hydrogen atom abstraction by alkyl radicals from the toluene carrier. An average value of 0.14 ± 0.03 was obtained for the disproportionation : combination ratio of the ethyl radicals in the temperature range 280–400 °C. For the t-butyl radicals this ratio had a value of 2.9 ± 0.2 between 210 and 260 °C.

Catalysis by hydrogen halides in the gas phase. Part XXVII. N-t-Butylacetamide and hydrogen chloride

The gas-phase hydrogen chloride catalysed decomposition of N-t-butylacetamide (NBA) into t-butylamine, isobutene, acetonitrile, and acetic acid at 380 °C is reported. Acetyl chloride is believed to be formed as the intermediate. The experimental evidence presented also suggests that acetyl chloride is in equilibrium with keten and hydrogen chloride, the former reacting with NBA to yield the observed products. The decomposition appears to be homogeneous and molecular. The kinetic form, which is basically first-order in each reactant, is altered by t-butylamine either produced in the reaction or added initially.

Catalysis by hydrogen halides in the gas phase. Part XXVI. Isopropylamine and hydrogen bromide

The hydrogen bromide catalysed deamination of isopropylamine between 435 and 490 °C is described. Propene and ammonia are the major products of the decomposition. The reaction is believed to be homogenous, first order in both the acid and the substrate, and is molecular. The rate constant is expressed by the equation: k2= 1012·41 exp (–33,115/RT) cm3 mol–1 s–1(where R= 1·987 cal mol–1; 1 cal = 4·187 J). A relatively smaller effect of α-methyl substitution in the hydrogen bromide catalysed deamination of amines as compared with that observed in the catalysed dehydration of alcohols is explained in terms of the greater basicity of amines.