Free Radical Chemistry of αHydroperoxydiazenes Synthetic Applications And Mechanistic Studies

Abstract

<p>The Structure of the products of autoxidation of hydrazones were first established in the early 1950's. Although those compounds have been known for many years, relatively little is known about their chemistry. Recent reports indicate that they can be used as oxidizing agents for a number of organic substances and as sources of hydroxyl and carbon-centered radicals. The free radical chemistry of the title compounds is the main subject of this thesis.</p> <p>Alkyl(1-hydroperoxyl-1-methylethyl) diazenes (28) [(CH₃)₂C(OOH)N=NR:a, R=CH₂CF₃; b, R= CH₂CH₂OCH₃ c, R=CH₂CH₂OC₆H₅; e, R=CH(CH₃)₂; f, R=C(CH₃)₃; g, R= CH₂C₆H₅] and phenyl (1-hydroperoxyl-1-methylethyl)-diazene, 28d, were prepared in solution by autoxidation of the corresponding hydrazones of acetone. these compounds show broad bands between 3600 and3200 cm⁻¹ in their infrared spectra. The intensities of the bands decrease at different rates with decreasing hydroperoxydiazenes concentrating indicating the presence of hydrogen-bonded species.</p> <p>Themolysis of 28 in enol ethers produces carbonyl compound; thus 28b decomposed in 1-ethoxyethylene (ethyl vinyl ether) and in 2-methoxypropene to give 4-methoxypropene to give 5-methoxy-2-pentanone, respectively. yields ranged between 50% and 70%. In some alkenes the compounds decompose to give alcohols. For example, 28a decompose in 1,1-diphenyl-4,4,4-trifluorobutanol.</p> <p>Other alkenes, particularly those that are highly hindered, give hydroalkylation products and epoxides. For Example, decompostition of 28a in bicyclo[2.2,1]hept-2-ene (norbornene), leads primarily to formation of 2-(2,2,2-trifluoroehtyl) norbornane and exo-2,3-epoxynorbornane.</p> <p>The reactions of 28 in olefinic substrate involve free radical intermediates. Product formation takes place via radical chain hydroxylalkylation and radical chain hydroalkylation. The chain-initiation step involves the unimolecular decomposition of the hydroperoxydiazene to give alkyl and hydroxyl radicals with concomittant formation of nitrogen and acetone.</p> <p>In the case of hydroalkylation , the first chain-propagating step involves addition of the alkyl radical to the double bond. The adduct radical so formed the chain-tranfers by inducing the decomposition of 28 at the hydroperoxyl oxygen. According to this mechanism, the first-formed products from enol ethers are hemiacetal and hemiketals which do not survive the reaction conditions but decompose to the corresponding carbonyl compounds.</p> <p>In hydroalkylation reactions, the sterically crowded alkyl radical, formed by the addition of R to the hindered alkene, propagates by abstracting the hydroperoxyl hydrogen to generate α-azoperoyl radical and alkane. The peroxyl radical, in the next, adds to the alkene and the adduct β-peroxyalkyl radical undergoes intramolecular induced decompostion by γ-scissors to give the epoxide. In less reactive, and in hindered alkenes, additions seem to be slow and that leads to very poor yields of epoxide.</p> <p>Evidence for the mechanisms is presented and discussed.</p>