The thermal decomposition (dediazoniation) of i5N-labelled benzenediazonium tetrafluoroborate in 2, 2, 2-trifluoroethanol has been studied. At atmospheric pressure the reaction proceeded with a significant accompanying amount (w8%) of isotopic rearrangement, and under 300 atm of unlabelled nitrogen approximately 3% of "external" nitrogen was incorporated in the residual diazonium ion after 65% dediazoniation. Dediazoniation kinetics at high pressure showed that nitrogen was a chemical entity in the exchange reaction at 300 atm pressure. These results have been interpreted in terms of a "molecule-ion" pair and a phenyl cation intermediate. The reverse step of the formation of the phenyl cation and nitrogen is the first example of the reaction of nitrogen molecules with a purely organic reagent in solution. The relatively small influence of para-substituents (4-OCH , 4-CH , 4-NO ) on the amount of isotopic rearrangement and exchange with external nitrogen indicates that these reactions are mechanistically of the same type as the solvolysis, namely addition of a nucleophile (nitrogen) to the phenyl cation. An investigation into the mechanism of formation of aryl radicals from the reaction of 1, 3-diaryltriazenes with amyl nitrite in benzene has been carried out. The proposed reaction mechanism is analogous to the chain reaction mechanism suggested by Ruchardt for the radical decomposition of N-nitrosoacetanilide in benzene. Interest in the intermediacy of the benzenediazotate radical (PhN2O-) led to an esr study of the triazene reaction. The reaction of 1, 3-diphenyltriazene with pentyl nitrite in bromotrichloromethane has also been studied and the results compared with those of similar reactions of Nnitro soac etanilide. The participation of benzenediazonium chloride has been demonstrated in both reactions and a mechanism involving formation of the diazonium chloride has been offered. This mechanism is based on the transient intermediacy of radical-derived trichloromethyl benzenediazotate (Ph-N=N-QDCC13) which decomposes into benzenediazonium chloride and phosgene.
|Landells, Robin Guy Marshall
|University of Edinburgh
|Electronic Thesis or Dissertation
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