Spencer, Michael David; (1990) Some Reactions of Peroxides Involving Peroxonium Ion Intermediates. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The reactions of isomeric n-butyl β-iodopentyl peroxides with silver trifluoroacetate have been shown to parallel those of the corresponding r-butyl compounds. Regio- and stereochemical evidence points to the formation of an o-butyl cis-ethylmethylperepoxide (trialkylperoxonium ion) intermediate, and to an SN2(cyclic) mechanism being preferred to the formation of the corresponding trans-methylethyl species. MINDO/3 calculations have been carried out on a series of 3-membered ring peroxonium ions (R2O+-OR1). The most stable conformation was found to involve the group R1 being placed awav from the ring-carbon substituents, in contrast to an earlier suggestion. A series of 11 alkenes R1R2C=CHR3has been treated with mercury(II) acetate in the presence of 30% aqueous hydrogen peroxide to produce mixtures of the corresponding β-hydroperoxyalkyl and p-hydroxyalkyl mercurials, from which the hydroperoxides have been isolated and characterised. 1-Hydroperoxycyclo-oct-4-ene and l-hydroperoxycyclo-oct-3-ene have been synthesized by oxidation of N-tosylhydrazines. During the cyanoborohydride reduction of the corresponding N-tosylhydrazones under acid conditions, both oct-3-ene and oct-4-ene N-tosylhydrazine isomers are produced. An aziridinium intermediate is suggested to explain the isomerisation. The reactions of 1-hydroperoxycyclo-oct-4-ene with a series of electrophiles have been studied and, except for that with mercury (II) acetate, afford bicyclic ethers. A Raman spectroscopic study of the decomposition of the cis and trans epoxides derived from 1-hydroperoxycyclo-oct-4-ene and MCPBA shows that oxygen is evolved. These results lead to the proposal that gem-dialkylperoxonium ions are formed which transfer oxygen by a heterolytic oxygen-oxygen bond-forming step to an epoxyhydroperoxide to yield a hydrotrioxide intermediate, which subsequentiy decomposes to give oxygen. The t-butoxy-initiated radical reactions of l-hydroperoxycyclo-oct-4-ene result in cyclo-oct-4-en-l-one being produced in three times greater quantity than cyclo-oct-4-en-l-ol, these products also being observed in the reactions with electrophiles in non-polar solvents. The reaction with mercury(II) acetate proceeds with ultrasonic irradiation and gives both bicycHc[3.3.2] and [4.2.2]peroxides. The reaction of l-r-butylperoxycyclo-oct-4-ene with electrophiles have been studied and also result in formation of bicyclic ethers. The production of trialkylperoxonium ions which undergo Baeyer-Villiger-type O-O cleavage is indicated. l-Hydroperoxycyclo-oct-3-ene reacts with both electrophiles and radical initiators to produce bicyclic[5.2.1]peroxides. The radical conditions also result in the formation of large quantities of cyclo-oct-3-en-l-one and smaller amounts of cyclo-oct-3-en-l-ol. In all the reactions with electrophiles, the yields of ketone and alcohol are reduced on shifting to a more polar solvent.

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