Hydroperoxides, alkyl reaction with base

Because primary and secondary alkyl hydroperoxides are base-sensitive they are converted to peroxyesters by reaction with a ketene or by the reaction of their barium salts with acid chlorides (44). 

O3yhydroperoxides. Peroxides of the oxyhydro type are obtained by the addition of hydrogen peroxide to ketones. High yields of alkyl radicals are then often obtained by reaction with ferrous salts. 1-Meth-oxycyclohexyl hydroperoxide is easily obtained from cyclohexanone and hydrogen peroxide in methanol. It gives rise to the 5-(methoxy-carbonyl)-pentyl radical, which has been used to alkylate protonated heteroaromatic bases in high yield [Eq. (6)]. 

A number of transition metals are now known147-156 to form stable dioxygen complexes, and many of these reactions are reversible. In the case of cobalt, numerous complexes have been shown to combine oxygen reversibly.157 158 Since cobalt compounds are also the most common catalysts for autoxidations, cobalt-oxygen complexes have often been implicated in chain initiation of liquid phase autoxidations. However, there is no unequivocal evidence for chain initiation of autoxidations via an oxygen activation mechanism. Theories are based on kinetic evidence alone, and many authors have failed to appreciate that conventional procedures for purifying substrate do not remove the last traces of alkyl hydroperoxides from many hydrocarbons. It is usually these trace amounts of alkyl hydroperoxide that are responsible for chain initiation during catalytic reaction with metal complexes. 

Theorell (79) has suggested an alternative mechanism based on the combination of substrate and acceptor molecules with two hematin groups. Chance (78) has pointed out that this mechanism cannot apply to the primary alkyl hydroperoxide complexes reacting with an alcohol or hydrogen peroxide (as in reactions ii and iii) because all hematin groups are attached to hydroperoxide molecules in these complexes however, it is applicable to the catalytic decomposition of hydrogen peroxide. The mechanism may be represented ... 

The mechanism of the oxidation reaction shows that a hydroperoxide ion (a Lewis base) reacts with R3B (a Lewis acid). Then, a 1,2-alkyl shift displaces a hydroxide ion. These two steps are repeated two more times. Then, hydroxide ion (a Lewis base) reacts with (R0)3B (a Lewis acid), and an alkoxide ion is eliminated. Protonation of the alkoxide ion forms the alcohol. These three steps are repeated two more times. 

Reaction with HO2 converts alkyl peroxy radicals to the corresponding hydroperoxides. These reactions are relatively fast, with rate constants on the order of 10 cm s. Where temperature-dependent studies have been reported, a negative temperature dependence has been found, suggesting that the reaction proceeds via complex formation [12]. There is only a limited number of literature references to studies of HOj -I- ROj reactions in general, whereas only a few preliminary reports of rate-constant measurements are available for HCFC-based peroxy radicals. There are two loss mechanisms expected for the hydroperoxides [7]. The first is via ultraviolet... 

An examination of the deuterium solvent kinetic isotope effects (SKIEs) for the reactions with (l)Feffl(X)2 and (2)Fe (X)2 show that the SKIEs values are comparable for alkyl hydroperoxides and hydrogenperoxide. Moreover, the SKIEs for the decomposition of IH2 (k lk P) display values that are >2 and <3, while the values for the decomposition of IIH ( k4 lk4 ) are - l.O. This establishes that the decomposition of IIH2 at low pH represents general-base catalysis with water solvent as the catalyst. In contrast, the reactions at intermediate pH (i.e., IIH decomposition) are not subject to such catalysis. Recall that 4-substituted 2,6-dimethylpyridines act as general base catalysts in the decomposition of IIH2 . 

This chapter contains kinetic and mechanistic information on the reactions of OH, NO3, O3, and Cl with saturated-, unsaturated-, halogenated-, and aromatic-alcohols, and alkyl hydroperoxides. The reactions of OH radicals with saturated alcohols presented here are based on the recent review by Calvert et al. (2008) with relevant updates. Rate coefficients are combined with the tropospheric concentrations of OH, NO3, and O3 to estimate atmospheric lifetimes of these compounds. 

The susceptibihty of dialkyl peroxides to acids and bases depends on peroxide stmcture and the type and strength of the acid or base. In dilute aqueous sulfuric acid (<50%) di-Z fZ-butyl peroxide is resistant to reaction whereas in concentrated sulfuric acid this peroxide gradually forms polyisobutylene. In 50 wt % methanolic sulfuric acid, Z fZ-butyl methyl ether is produced in high yield (66). In acidic environments, unsymmetrical acychc alkyl aralkyl peroxides undergo carbon—oxygen fission, forming acychc alkyl hydroperoxides and aralkyl carbonium ions. The latter react with nucleophiles,... 

Reaction conditions depend on the reactants and usually involve acid or base catalysis. Examples of X include sulfate, acid sulfate, alkane- or arenesulfonate, chloride, bromide, hydroxyl, alkoxide, perchlorate, etc. RX can also be an alkyl orthoformate or alkyl carboxylate. The reaction of cycHc alkylating agents, eg, epoxides and a2iridines, with sodium or potassium salts of alkyl hydroperoxides also promotes formation of dialkyl peroxides (44,66). Olefinic alkylating agents include acycHc and cycHc olefinic hydrocarbons, vinyl and isopropenyl ethers, enamines, A[-vinylamides, vinyl sulfonates, divinyl sulfone, and a, P-unsaturated compounds, eg, methyl acrylate, mesityl oxide, acrylamide, and acrylonitrile (44,66). 

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