G.J. Hutchings, R. Hunter, W. Pickl and Jansen van Rensburg

Department of Chemistry, University of the Witwatersrand, 1 Jan Smuts Avenue, 

A mechanistic study of in.itial C-C bond formation in the methanol conversion reaction is reported. Reaction of methanol with added hydrogen using W0,/A1203 and H-ZSM-5 catalysts does not significantly alter the product distribution from that of normal methanol conversion. This is considered to be clear evidence against the involvement of a gas phase methylene intermediate. In addition the behaviour of the methoxymethyl radical in the gas phase has been studied and the results demonstrate that this species is also not involved as an intermediate in initial C-C bond formation. 

Experiment Reagent Catalyst Temp °C WHSV3 h-1 Conversion % Hydrocarbon CH4 C2 4 Selectivity C2H6 C3H6 (% C3H8, , b by mass) 0 c 4 5+ mole % ycv mole ratio 

Reaction of dimethyl ether with dibenzoyl peroxide 

Dimethyl ether was reacted over a radical initiator, pre-dried dibenzoyl peroxide supported a celite, at various temperatures (Table 2). Although dibenzoyl peroxide was short lived under these conditions sufficient was reactive in the timescale of the experiments, typically 5 min. Under all conditions only dimethoxyethane was observed as a dimerisation product showing that the methoxymethyl radical was generated under these conditions. The absence of other products, e.g. alkenes or ethanol, discounts the methoxymethyl radical fragmentation/recombination pathway (mechanism 1, Fig. 1). 

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