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Bass, Kenneth Cyril (1959) Free radical reactions of organometallic compounds in solution. Doctoral thesis, Sir John Cass College.
The preparation of benzylmercuric chloride and mercury dibenzyl from the Grignard reagent have been examined with the object of improving the yields of these mercurials and the preparation of mercury di-β-phenylethyl by the Grignard method has been developed.
The reactions occurring when mercury dibenzyl was heated in solution in a large excess of aromatic compounds of different chemical types have been investigated. The mercurial decomposed readily in all the solvents used and two types of reaction have been observed.
(i) Decomposition of the mercurial in aromatic halogen compounds, ethers, nitriles, amines, ketones or hydrocarbons, heterocyclic nitrogen compounds, octanol-2 or with duroqulnone in phenetole gave almost quantitative yields of mercury and high yields of dibenzyl, but no products derived in any way from the solvents were detected,
(ii) Decomposition of the mercurial in phenol, nitrosobenzene, 9:10 dihydroanthracene or tetralin and with p-benzo quinone or 2:4:6 trinitrotoluene in phenetole gave almost quantitative yields of mercury, some dibenzyl and other products derived from reaction of the mercurial or its decomposition products with the solvent.
With the exception of the decomposition in phenol, which is probably heterolytic, both types of reaction have been interpreted as the homolysis of the mercury dibenzyl to mercury and free benzyl radicals and subsequent reactions of the benzyl radical. The types of reaction of the benzyl radical which have been observed in the present investigation are dimerisation to dibenzyl (type (i) reactions), hydrogen abstraction from 9:10 dihydroanthracene to give toluene and oxygen transfer from nitrosobenzine to give benzaldehyde, an oxidation product of benzyl. Oxygen transfer may also have occurred with 2:4:6 trinitrotoluene. The reaction of mercury dibenzyl with phenol gave toluene and benzyl phenyl ether in addition to mercury and dibenzyl. The former two products probably arose from a heterolytic fission of some of the mercurial by phenol.
Kinetic measurements have been made on the rates of decomposition of mercury dibenzyl in phenetole and benzonitrile (unreactive solvents) and nitrobenzene (reactive solvent). The decompositions were shown to be first order with respect to the mercurial and the same results were obtained in phenetole and benzonitrile in the presence of various added inert substances. The activation energies of the decompositions in phenetole and benzonitrile have also been calculated.
The reactions of mercury dibenzyl with reactive solvents appear to fall into two classes with regard to rates of reaction. In one class the rate of reaction is apparently equal to the rate of the simple homolysis of the mercurial and in the other class it is greater than the rate of homolysis of the mercurial, indicating a chain reaction involving reactant molecules.
The mechanisms of the reactions are discussed.
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