Peroxides disubstituted

Rubber Chemicals. Sodium nitrite is an important raw material in the manufacture of mbber processing chemicals. Accelerators, retarders, antioxidants (qv), and antiozonants (qv) are the types of compounds made using sodium nitrite. Accelerators, eg, thiuram [137-26-8J, greatly increase the rate of vulcaniza tion and lead to marked improvement in mbber quaUty. Retarders, on the other hand (eg, /V-nitrosodiphenylamine [156-10-5]) delay the onset of vulcanization but do not inhibit the subsequent process rate. Antioxidants and antiozonants, sometimes referred to as antidegradants, serve to slow the rate of oxidation by acting as chain stoppers, transfer agents, and peroxide decomposers. A commonly used antioxidant is A/,AT-disubstituted Nphenylenediamine which can employ sodium nitrite in its manufacture (see Rubber chemicals). 

The hydroboration step, being very sensitive to steric effects, yields only secondary alkylboranes from trisubstituted double bonds, whereas the less hindered alkylborane is formed predominantly from disubstituted steroidal double bonds. The diborane attack occurs usually towards the a-side and hence results in overall a-hydration of double bonds after alkaline hydrogen peroxide oxidation. ... 

This chemoselectivity stands in contrast to that of 2,6-disubstituted pyridines. For example, 2,6-dimethylpyridine 35 was reacted with hydrogen peroxide and acetic anhydride to produce the expected acetoxy derivative 36. A second iteration of the previous reaction conditions did not afford an aldehyde, as in the previous example, but 2,6-bis-acetoxy derivative 37. 

Alkynes are reactive toward hydroboration reagents. The most useful procedures involve addition of a disubstituted borane to the alkyne, which avoids complications that occur with borane and lead to polymeric structures. Catechol borane is a particularly useful reagent for hydroboration of alkynes.212 Protonolysis of the adduct with acetic acid results in reduction of the alkyne to the corresponding cw-alkene. Oxidative workup with hydrogen peroxide gives ketones via enol intermediates. 

The oxidation of thioamides 63 with a wide variety of oxidizing agents is a well-employed method for the synthesis of 3,5-disubstituted-l,2,4-thiadiazoles 64 <1982AHC285>. However, this method is limited mainly to arylthioamides. The most common oxidizing agents tend to be halogens, hydrogen peroxide, dimethyl sulfoxide (DMSO), and nitrous acid. Yields from these reactions are variable and depend on the thioamide, oxidant, and conditions used (Equation 19). By-products such as nitriles and isothiocyanates are usually formed. 

Quinone is produced in small yield by direct oxidation of benzene itself with silver peroxide, but better by the action of oxidising agents on a large number of its p-disubstitution products. Thus, in addition to quinol, p-aminophenol (experiment, p. 176), p-anisidine, p-toluidine, and sulphanilic acid as well as p-phenylenediamine and many of its derivatives yield quinone in this way. 

Epoxidation of ot.fl-unsaturated ketones by hydrogen peroxide or /-butyl peroxide is promoted by the addition of tetra-n-butylammonium fluoride [10], whereas the corresponding reaction with 1,4-disubstituted but-2-en-l,4-diones is catalysed by quaternary ammonium iodides [11], Oxiranes are also produced by the catalysed reaction of /-butyl peroxide with a,f)-unsaturated sulphonates under basic conditions [12]. 

Much more exciting biologic properties have been revealed for the equally 1,6-disubstituted phenazoviridin (56) isolated from Streptomyces sp. HR04. The new free radical scavenger showed strong in vitro inhibitory activity against lipid peroxidation and displayed in vivo antihypoxic activity in mice [57]. 

Based on mechanistic studies, the antioxidant property of diaryl teUurides is related to their conversion into 4,4 -disubstituted telluroxides. Also has been described to retard peroxidation of linolenic acid in methanol. ... 

Direct oxidation of primary amines with peroxide oxidants does not provide appreciable yield of hydroxylamines. As was mentioned above, oxidation of secondary amines usually proceeds smoothly giving moderate to good yields of iV,iV-disubstituted hydroxylamines. Oxidation of sterically hindered secondary amines such as 125 (equation 88) can also be done with peracids . Further oxidation of the resulting Af,A-disubstituted hydroxylamines 126 with an excess of m-chloroperbenzoic acid is known to end up with the corresponding nitroxyl radicals of type 127 (equation 88) ° although the reaction can be stopped at the hydroxylamine stage. 

Reaction of 3,5-disubstituted-1,2,4-trioxolanes (89) with oxidants (usually under basic conditions) leads to carboxylic acids (Equation (14)). This reaction is often carried out as the work up procedure for alkene ozonolysis, avoiding the need to isolate the intermediate ozonide. Typical oxidants are basic hydrogen peroxide or peracids and this type of oxidative decomposition is useful for both synthetic and degradative studies. 

Tetraphenylporphyrin-sensitized photooxygenation of 1,2-disubstituted digermirane (383 X = CH2) and 1,2,3-disubstituted azadigermiridine (383 X = NPh) (Equation (36)) leads to corresponding cyclic peroxides <92CC457>. 

Three peroxides with aromatic substituents have reported enthalpy of vaporization data, all from the same source". The enthalpies of vaporization of cumyl hydroperoxide and ferf-butyl cumyl peroxide are the same, which makes us skeptical of at least one of these values. The calculated b value for cumyl hydroperoxide is 31.5, consistent with the alkyl hydroperoxides. The calculated b value for tert-butyl cumyl peroxide is 15.4 and more than twice that for the mean of the dialkyl peroxides. The structurally related tert-butyl p-isopropylcumyl peroxide has a b value of 8.8 and so is consistent with the other disubstituted peroxides. 

Following this work on NMR spectra of ozonides, there is an extensive paper by the Griesbaum group" where 35 ozonides (6-14 with different stereochemistries) have been studied. The widely different structures examined allowed the influences of structural features on "O NMR spectra of ozonides to be shown. Five structurally different types of ozonides can be recognized symmetrically tetrasubstituted (type 6), unsymmetrically tetrasubstituted (type 7), unsymmetrically tri- and tetrasubstituted (type 8), unsymmetrically disubstituted (type 9-13) and bicyclic ozonides (type 14). "O NMR chemical shifts of peroxidic and ethereal oxygens are collected in Table 3. All spectra were obtained at natural isotopic abundance, in benzene-dg solution mainly at 25 °C, although in some cases higher temperatures had to be used. These experimental conditions make for an easy comparison with the previously discussed data. 

Similarly to aromatic jt system, olefinic 7r-electron donors also readily react with bissulfonyl peroxides. Norbomene, when reacted with bis(arylsulfonyl) peroxides, gives a disubstituted product following Wagner-Meerwein rearrangement (equation 6). ... 

A new method for the preparation of 7,9-disubstituted 8-oxoadenines (216) has been reported, involving hydrogen peroxide or photochemical oxidation of adeninium salts 215 (83S849) (Scheme 38). 

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