Triphenylmethyl Hydroperoxide

Howard and Ingold studied this equilibrium reaction in experiments on the oxidation of tetralin and 9,10—dihydroanthracene in the presence of specially added triphenylmethyl hydroperoxide[41]. They estimated the equilibrium constant K to be equal to 60 atm-1 (8 x 103 L mol-1, 303 K). This value is close to T=25atm-1 at 300 K (A/7=38kJ mol-1), which was found in the solid crystal lattice permeable to dioxygen [84], The reversible addition of dioxygen to the diphenylmethyl radical absorbed on MFI zeolite was evidenced and studied recently by the EPR technique [85],... 

Three examples serve to document the effect of tetrahedral distortion in peroxides, in which the 0-0 unit is connected to an acyclic or to a cyclic framework . 2,5-Dimethyl-2,5-dihydroperoxyhexane (23) (C2/c, 0—0 = 1.47 A, C—O—O—H = 110.6°, Figure 12) exhibits in the solid state two larger and one smaller 0-C-C angle (0-01-02=101.3°, 0-01-03 = 110.5° and 0-01-04 = 110.7°), similar to the situation outlined for ferf-butyl hydroperoxide (1) and triphenylmethyl hydroperoxide (8) (Table 4) °. Oomparable distortions are observed for the peroxide bound 0 atoms in... 

Materials. Chemically pure solvents and reagent grade ceric ammonium nitrate were used as received. Cumene hydroperoxide was purified via the sodium salt. Lucidol tert-butyl hydroperoxide was purified by low temperature crystallization. Tetralin hydroperoxide, cyclohexenyl hydroperoxide, and 2-phenylbutyl-2-hydroperoxide were prepared by hydrocarbon oxidation and purified by the usual means. 1,1-Diphenyl-ethyl hydroperoxide and triphenylmethyl hydroperoxide were prepared from the alcohols by the acid-catalyzed reaction with hydrogen peroxide (10). 

Triphenylmethyl hydroperoxide appeared to react relatively slowly with ceric ion and the peroxy radicals decayed extremely rapidly, probably by the unimolecular decomposition faCOO — < 3C + 02 (3, 21, 28). Only traces of peroxy radicals could be detected even at high flow rates, and so the decay kinetics could not be examined. 

With a twist on the Sharpless asymmetric epoxidation protocol, Yamamoto and co-workers <99JOC338> have developed a chiral hydroxamic acid (17) derived from binaphthol, which serves as a coordinative chiral auxiliary when combined with VO(acac)j or VO(i-PrO)j in the epoxidation of allylic alcohols. In this protocol, triphenylmethyl hydroperoxide (TiOOH) provides markedly increased enantiomeric excess, compared to the more traditional t-butyl hydroperoxide. Thus, the epoxidation of E-2,3-diphenyl-2-propenol (18) with 7.5 mol% VO(i-PiO)3 and 15 mol% of 17 in toluene (-20 °C 24 h) provided the 2S,3S epoxide 19 in 83% ee. 

Although the proposals advancing 4 and 6 as intermediates in the epoxidation explain most of the experimental data reported to date, there are a few remaining enigmas such as the reversal of enantioselectivity which accompanies the use of primary amide analogs of tartrates (Table 3) and when ferf-butyl hydroperoxide is replaced by triphenylmethyl hydroperoxide in epoxidations employing catalyst 840. 

There have been very few reports of azide decompositions induced by radicals. It has been found that the decomposition of phenyl azide was accelerated by thiyi radicals, particularly when it was carried out in thiols as solvents in the presence of free radical sources, such as tetraphenylhydrazine, hexaphenylethane and triphenylmethyl hydroperoxide When the decomposition was carried out in thiophenol, the major product was aniline, along with a small amount of o-aminodiphenylsulphide (232)... 

Peroxy radicals have also been observed by the one-electron reduction of cumyl, diphenylethyl, and triphenylmethyl hydroperoxides by cobaltous salts (Shchennikova et al., 1965). 

The oxidation of hydrocarbons and alcohols with TBHP is presumed to involve oxidation of the substrate by oxochromium(VI) followed by reoxidation of Cr by TBHP, i.e. an oxometal pathway. When O, is the oxidant the substrate undergoes initial chromium-catalyzed autoxidation to the corresponding hydroperoxide. The latter undergoes catalytic decomposition and/or functions as the oxidant. The observation that the bulky triphenylmethyl hydroperoxide, which cannot be accommodated in the micropores, gave no reaction was construed as evidence for the reactions taking place in the micropores. This subsequently proved to be a misinterpretation of the results (see later). 

Oxidation of carbanions by molecular oxygen is also an important reaction. Equation (3.10) shows the oxidation of the anion of triphenylmethane by molecular oxygen in a solution composed of 80% DMF and 20% t-butyl alcohol. Addition of water to the reaction mixture allowed isolation of triphenylmethyl hydroperoxide in high yields (e.g., 87%). When the reaction was carried out in 80% DMSO-20%... 

These reactions became widely studied in 1950-60 owing to N.M. Emanuel initiation. The first studies of the decomposition of hydroperoxides formed during oxidation were performed as early as in the thirties in 1931 H. Wieland and J. Mayer studied the decomposition of triphenylmethyl hydroperoxide, in 1935 S.S. Medvedev and A.Ya. Pod yampol skaya studied methyl hydroperoxide decomposition, and in 1939 K.I. Ivanov with co-workers studied the decomposition of a-tetra-lyl hydroperoxide. In 1950 V. Langenbek and W. Pritzkow proposed the scheme of transformation of intermediate products of paraffin oxidation. A little later (1953) I.V. Berezin studied the composition of products and kinetics of cyclohexane oxidation. 

---