Silyl hydroperoxide

Poly(hydrosilane)s are stable compounds and can be manipulated in the air only for a short period since they are oxygen-sensitive. The oxidized products obtained from poly(phenylhydrosilane) exposed to the air contain the units 119-122 without the formation of silyl hydroperoxides and peroxides. In particular, units 119,120, and 121+122 were present in the relative percentages of 27,54, and 19%, respectively, which means that more than 70% of the catenated silicons are altered. 

Poly(hydrosilane)s are stable compounds and can be manipulated in the air only for a short period since they are oxygen sensitive. In order to study the oxidation products, a xylene solution of poly(phenylhydrosilane)(Mw = 2340, Mw/Mn = 1.72) was refluxed (140 °C) for 12 h in a system exposed to the air [15]. Only minor changes were observed by GPC analysis whereas FTIR showed characteristic absorptions due to siloxane-type structures on the polymer backbone. A detailed NMR analysis, based on H NMR, Si INEPT and H- Si HMQC spectroscopies, indicated that the oxidized material contains the units 7-10 shown in Scheme 8.2. In particular, units 7,8 and 9+10 were present in relative percentages of 27%, 54% and 19%, respectively, which mean that more than 70% of the catenated silicons were altered. It has also been reported that silyl hydroperoxides and peroxides are not found as products in the autoxidation of poly(phenylhy-drosilane) [16]. 

Silicon and germanium peroxides TABLE 1. Preparation of silyl hydroperoxides 1... 

The thermal stability of the silyl hydroperoxides is increased with increasing the steric bulk of the silyl group triphenylsilyl hydroperoxide with a melting point of 110-112 °C, for example, is indefinitely stable at room temperature8. 

It was reported early that alumina with H2O2 and silyl hydroperoxides, like PhsSiOOH, were active for epoxidation of substituted olefins [193]. Alumina has been studied further, and it is believed that it forms a surface hydroperoxide species by the interaction of H2O2 with surface OH groups of low acidity [194,195]. A sol-gel-derived material has good performance [196], but the catalyst deactivates slowly by an apparent structural change of the surface induced by the condensation of adjacent OH groups [197]. 

Since we could detect no peroxide as product in the ozonization of tricyclohexylsilane, it is reasonable to conclude that no tricyclohexylsilyl peroxide is formed either as a stable intermediate or as an intermediate which decomposes in a way analogous to the decomposition of trimethyl-silyl hydroperoxide described above. The reaction is therefore more likely to proceed through a transition state of Type I rather than II since the former should lead to the observed product, tricyclohexylsilanol. 

Among the other unknown homoatomic 1,2-anionic rearrangements, several will be detectable only with great difficulty. For example, in silyl hydroperoxide anions, RjSi—O—0 , silicon may migrate from one... 

TBDMSCl, imidazole, DMF, 25°, 10 h, high yields. This is the most common method for the introduction of the TBDMS group on alcohols with low steric demand. The method works best when the reactions are mn in very concentrated solutions. This combination of reagents also silylates phenols, hydroperoxides, and hydroxyl amines. Thiols, amines, and carboxylic acids are not effectively silylated under these conditions. ... 

SCHEME 12. Synthesis of hydroperoxides from silyl enol ethers TABLE 3. Preparation of alkyl hydroperoxides via singlet oxygen oxygenation... 

The mechanism of singlet oxygen detoxification involves quenching by Vitamin Be (215a). After silylating this compound, in order to make it soluble in CD2CI2 to work at low temperature, the quenching process proceeds as shown in equation 75 (Section V.C.4). The main product is endoperoxide 217, probably in equilibrium with hydroperoxide 216. The structure of 217 can be established from the H and NMR spectra, e.g. 5h = 6.06 ppm (IH, d, 7 = 4.4 Hz, HCOO), 4.19 (IH, broad, NH), 5c = 96.8 ppm (MeCOO), 86.6 ppm (HCOO), and DEPT, phase-sensitive COSY, HMQC and HMBC spectra . 

Silyl alkyl and silyl aryl peroxides 7 are prepared by reaction of alkyl, aryl or aralkyl hydroperoxides with halosilanes (equation 12). Such reactions are carried out in an inert solvent in the presence of an acid acceptor, such as pyridine, ammonia or a tertiary amine in ether or petroleum ether (Table 3) . ... 

Alkyl hydroperoxides can form 2 1 adducts with DABCO. Both nitrogens of DABCO are involved and the resulting adduct contains 2 mol of hydroperoxide per mol of DABCO. Table 4 lists the silyl alkyl peroxides prepared using the DABCO-hydroperoxide adduct techniques. 

Alkyl(chloro)silyl peroxides 8 and alkyl alkoxysilyl peroxides are prepared by the alkyl hydroperoxidation of dichlorodiorganosilane (equations 13-15). 

Oxidation of 1,4-thioxane by BTSP and f-butyl(trimethylsilyl) peroxide in CHCI3 at 25 °C is compared to those of the same substrate by the more common oxidants, f-butyl hydroperoxide and di-f-butyl peroxide, in the same solvent. The two silyl peroxides give similar oxidations rates, which are over 50 times higher than that measured for f-BuOOH, while f-Bu202 is almost unreactive under the conditions adopted. Oxidation... 

SCHEME 12. Synthesis of hydroperoxides from silyl enol ethers... 

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