Hydroxylation, benzene acetonitrile

A rhodium carbonyl cluster, Rh (CO)j, catalyzed benzene hydroxylation in acetonitrile via the formation of an arene x-complex containing also an activated form of HjO [75]. A decamethylosmocene-based system, (MegCgl Os/H O /py, that effectively generates HO radicals, produced phenol in a yield of 22% [76]. 

Figure A. Hydroxylation of benzene in acetonitrile under degassing (0) and under oxygen (Q) ...

In acetonitrile 5 mM H20 is oxidized at +2.80 V versus SCE the presence of benzene would facilitate electron removal by stabilizing the resulting hydroxyl radical to give an ECEC process ... 

The hydrophobicity of TS-1 could also explain why the oxidation of hydrocarbons in aqueous H2C>2 is faster without added organic solvent (triphase catalysis) than in organic solution (biphase catalysis) e.g. benzene hydroxylation under triphase conditions was up to 20 times faster than in acetonitrile or acetone (biphase conditions).1741 Indeed, benzene competes more favourably with water than with organic solvents for adsorption within the micropores of hydrophobic TS-1, as furthermore confirmed through adsorption experiments.1471... 

Aromatic hydrocarbons can be oxidized to the corresponding phenols by transition metal peroxo complexes and, in particular, vanadium(V) peroxo complexes, which act either as electrophilic oxygen transfer reagents or as radical oxidants -, depending on the nature of the ligands coordinated to the metal and on the experimental conditions. Vanadium picolinato peroxo complex (V0(02)PIC(H20)2) (39) (PIC = picoUnic acid anion) has been reported to be particularly effective in the hydroxylation of benzene and substituted benzenes (equation 50) . Accordingly, 39 smoothly oxidizes substituted benzenes 38 to the corresponding monophenols 40 in acetonitrile at room temperature. 

Although hydroxyl radicals are apparently the active species in oxygenation of benzene [40a], cyclohexane [40a] and even methane [40b] by oxygen-containing derivatives of xenon (which may be generated by dissolution of XeOs or Xep2 in water of aqueous acetonitrile), the mechanism of direct arene epoxidation as the first stage is not excluded [40a] ... 

Disuccinimidyl (DS)-PEG, a crosslinker of hydrogel, has been synthesised by the reaction between N,N -disuccinimidyl carbonate (DSC) and the hydroxyl groups at both ends of PEG-diol. Firstly, DSC and triethylamine were added to anhydrous acetonitrile containing PEG-diol. The synthesised polymer was precipitated, filtered and then lyophilised in benzene. The molecular weight of the obtained polymers was then determined using gel permeation chromatography and H-nuclear magnetic resonance [83]. 

The Fenton-type system, Fe(II)/Cu(n)/H202, produced phenol with a moderate selectivity [28b]. In the absence of Cu(II) or Fe(III), biphenyl was the main product. Quinones, in particular l,2-naphthoquinone-4-sulfonate, played a vital role in the Fe(III)-promoted hydroxylation of benzene with HjOj, giving moderate yields of phenol [70]. The addition of polyethyleneglycol to Fe(III)/ HjOj in aqueous acetonitrile enhanced the phenol yield and selectivity [71]. A heterophase reaction in the presence of surfactants (quaternary ammonium salts, crown ethers, and polymers) has led to a further improvement. Biphasic benzene hydroxylation in the system composed of aqueous H O, Fe SO modified with 2-pyrazinecarboxylic acid (Hpca) derivatives, and CF COOH produced phenol with a selectivity of 97% (based on benzene) at substrate conversion of 8.6% (Eq. 14.22)... 

Another metallocene, namely, decamethylosmocene, (Mc5C5)20s (catalyst 1.2), turned out to be a good precatalyst in a very efficient oxidation of alkanes with hydrogen peroxide in acetonitrile at 20 — 60 °C [9]. The reaction proceeds with a substantial lag period that can be reduced by the addition of pyridine in a small concentration. Alkanes, RH, are oxidized primarily to the corresponding alkyl hydroperoxides, ROOH. TONs attain 51,000 in the case of cyclohexane (maximum turnover frequency was 6000 h ) and 3600 in the case of ethane. The oxidation of benzene and styrene afforded phenol and benzaldehyde, respectively. A kinetic study of cyclohexane oxidation catalyzed by 1.2 and selectivity parameters (measured in the oxidation of n-heptane, methylcyclohexane, isooctane, c -dimethylcyclohexane, and trans-dimethylcyclohexane) indicated that the oxidation of saturated, olefinic, and aromatic hydrocarbons proceeds with the participation of hydroxyl radicals. 

Similar trinuclear carbonyl hydride cluster, Os3(CO)xq (m-H)2 (compound 1.4), catalyzes the oxidation of cyclooctane to cyclooctyl hydroperoxide by hydrogen peroxide in acetonitrile solution [12]. Selectivity parameters obtained in oxidations of various linear and branched alkanes as well as kinetic features of the reaction indicated that the alkane oxidation occurs with the participation of hydroxyl radicals. A similar mechanism operates in the transformation of benzene into phenol and styrene into benzaldehyde. The system also oxidizes 1-phenylethanol to acetophenone. The kinetic study... 

Simulation of catalytic cycles of three vanadium catalysts in the hydroxylation of benzene with HP in acetonitrile, at the B3LYP(IEF-PCM)//B3LYP/6-31 lG(2r/,2p) level, indicated that the main form of the operative catalyst is the binuclear vanadium species. 

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