Reactions of free radicals with sulphur dioxide. Part I - methyl radicals

Anthony Good, John C.J. Thynne

Research output: Contribution to journalArticlepeer-review


The reaction of sulphur dioxide with methyl radicals, generated from the photolysis of azomethane at λ >3400 Å, has been studied in the temperature range 25-164°C. At low temperatures, the addition reaction to form methyl-sulphonyl radicals is fast but as the temperature increases methylsulphonyl radicals become increasingly unstable and appear not to be formed at 164°C. Arrhenius parameters (based upon a value of 1013.34 mole-1 cm3 sec-1 for the rate of combination of methyl radicals) have been measured or deduced using a material balance method for the following reactions:                                                                                                      log A (mole-1 cm3 sec-1) E  (kcal mole-1)
CH3 + CH3N2CH3 → CH4 + CH2N2CH3              11.55                   8.7
            CH3 + SO2 → CH3SO2                           10.8                     1.5
               CH3SO2 → CH3 + SO2                        13.0 (sec-1)        22.4

A value of 0-04 has been obtained for the disproportionation : combination ratio of methyl and methylsulphonyl radicals. The addition reaction of methyl radicals with sulphur dioxide has been compared with their reaction with oxygen, carbon monoxide and ethylene. Although the reaction with oxygen requires zero activation energy the three-body limitation for the oxygen reaction leads to the conclusion that in the gas phase at pressures of ∼50 mm Hg the overall rates of addition of methyl radicals to sulphur dioxide and oxygen are similar. 

Original languageEnglish
Pages (from-to)2708-2719
JournalTransactions of the Faraday Society
Publication statusPublished - 1967

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