G. B. Shul’pin

The influence of organic additives on the regioselectivity of oxygenation of alkanes with hydrogen peroxide in the presence of TS-1titanium silicalite

Hydrogen peroxide oxidizes n-hexane, n-heptane, and n-octane at 50°C in the presence titanium silicalite TS-1 as a catalyst, forming isomeric mixtures of ketones and alcohols. Admixtures of organic acids, alcohols, benzene, and ethylbenzene sharply change the ratio of position isomers. For example, the normalized ratio is C(4): C(3): C(2) = 0.44: 1.0: 0.47 for n-heptane oxidation in the absence of additives, but it becomes 0.52: 1.0: 1.00 in the presence of benzyl alcohol and the addition of ethylbenzene changes it to 0.16: 1.0: 0.94.

Vanadate ion-catalyzed oxidation of methane with hydrogen peroxide in an aqueous solution

It was shown that, unlike methane oxidation with the reagent “hydrogen peroxide-vanadate anion-pyrazine-2-carboxylic acid (PCA)” in acetonitrile, the performance of the process in an aqueous solution is accompanied by the intense parallel degradation of the cocatalyst. Therefore, relatively high yields of methane oxidation products (largely, formic acid) cannot be attained unless a rather high PCA concentration is used. Admixtures of a strong acid (sulfuric, trifluoroacetic, or perchloric) increase the yield of the products. It was found that perchloric acid can also be used as a cocatalyst instead of PCA.

Benzene oxidation with hydrogen peroxide catalyzed by soluble and heterogenized copper compounds

Copper(II) salts (acetate, perchlorate, and chloride) catalyze the oxidation of benzene with hydrogen peroxide in an acetonitrile solution to give phenol and quinone. The initial rates, the yield of products, and the phenol: quinone ratio depend on the salt chosen and on the presence of 2,2′-dipyridyl as an additive. For example, catalysis by copper perchlorate in the presence of 2,2′-dipyridyl at 50°C results in the formation of phenol and quinone with a yield of 12.5 and 1.5%, respectively (the turnover number reaches 1900). Copper chloride coordinated to solid polymers, poly(4-vinylpyridine) or poly(4-methyl-4′-vinyl-2,2′-dipyridyl), also acts as a catalyst for benzene oxidation into phenol and quinone. It was shown that the catalysis is mediated by the copper ions on the surface of the solid support. The heterogenized catalyst may be reused with some loss of activity.

The Kinetics and Mechanism of Oxidation of Isopropanol with the Hydrogen Peroxide-Vanadate Ion-Pyrazine-2-Carboxylic Acid System

The vanadate anion in the presence of pyrazine-2-carboxylic acid (PCA) was found to effectively catalyze the oxidation of isopropanol to acetone with hydrogen peroxide. The electronic spectra of solutions and the kinetics of oxidation were studied. The conclusion was drawn that the rate-determining stage of the reaction was the decomposition of the vanadium(V) diperoxo complex with PCA, and the particle that induced the oxidation of isopropanol was the hydroxyl radical. Supposedly, the HO· radical detached a hydrogen atom from isopropanol, and the Me2 C· (OH) radical formed reacted with HOO· to produce acetone and hydrogen peroxide. The electronic spectra of solutions in isopropanol and acetonitrile and the dependences of the initial rates of isopropanol oxidation without a solvent and cyclohexane oxidation in acetonitrile on the initial concentration of hydrogen peroxide were compared. The conclusion was drawn that hydroxyl radicals appeared in the oxidation of alkanes in acetonitrile in the decomposition of the vanadium diperoxo complex rather than the monoperoxo derivative, as was suggested by us earlier.

Oxidation of benzene with hydrogen peroxide catalyzed with ferrocene in the presence of pyrazine carboxylic acid

It is found that ferrocene in the presence of small amounts of pyrazine carboxylic acid (PCA) effectively catalyzes the oxidation of benzene to phenol with hydrogen peroxide. Two main differences upon the oxidation of two different substrates, i.e., cyclohexane and benzene, with the same H2O2-ferrocene-PCA catalytic system are revealed: the rates of benzene oxidation and hydrogen peroxide decomposition are several times lower than the rate of cyclohexane oxidation at close concentrations of both substrates, and the rate constant ratios for the reactions of oxidizing particles with benzene and acetonitrile are significantly lower than would be expected for reactions involving free hydroxyl radicals. The overall rate of hydrogen peroxide decomposition, including both the catalase and oxidase routes, is lower in the presence of benzene than in the presence of cyclohexane. It is suggested on the grounds of these data that a catalytically active particle different from the one generated in the absence of benzene is formed in the presence of benzene. This particle catalyzes hydrogen peroxide decomposition less efficiently than the initial complex and generates a dissimilar oxidizing particle that exhibits higher selectivity. It is shown that reactivity of the system at higher concentrations of benzene differs from that of an initial system not containing an aromatic component with the capability of π-coordination with metal ions.

Kinetics and mechanism of 1-phenylethanol oxidation by the system hydrogen peroxide-manganese(IV) binuclear complex-oxalic acid

Hydrogen peroxide was found to oxidize 1-phenylethanol to acetophenone in acetonitrile homogeneous solution efficiently at room temperature in the presence of a dimeric complex of manganese (IV) [LMn(O)3MnL](PF6)2(where L = 1,4,7-trimethyl-1,4,7-triazacyclononane) as the catalyst and oxalic acid as a co-catalyst. The number of catalytic cycles was 15 000 3 h after the onset of the reaction. The dependences of the initial rate of acetophenone accumulation on the initial concentrations of the reagents were studied. Based on an analysis of the kinetic data, we conclude that phenylethanol is oxidized by a manganyl particle containing an Mn = O fragment that interacts competitively with hydrogen peroxide.

Kinetics and mechanism of benzene oxidation by peroxymonosulfate catalyzed with a binuclear manganese(IV) complex in the presence of oxalic acid

It is established that Oxone (peroxymonosulfate, 2KHSO5 · KHSO4 · K2SO4) oxidizes benzene to p-quinone very efficiently and selectively in a homogeneous solution in aqueous acetonitrile in the presence of a catalyst, i.e., dimeric manganese(IV) complex [LMn(O)3MnL](PF6)2 where L is 1,4,7-trimethyl-1,4,7-triazacyclononane, and a cocatalyst, i.e., oxalic acid. The dependences of the maximum rate of quinone accumulation on the initial concentrations of reagents are studied. It is proposed that benzene is oxidized by the manganyl particle containing the Mn(V)=O fragment that forms upon the reaction of the reduced form of the starting dimeric manganese complex with Oxone.