Peroxides, substituted

Peptisers, too, are seldom needed in butyl rubber compounding. It is usually simpler to buy a grade of butyl rubber that already has the viscosity required, than to break down a higher-viscosity grade the improvements in extrusion properties that peptisers produce can usually be achieved more economically with process oils. However, when a peptiser is needed, various organic peroxides, substituted aromatic mercaptans and chlorothiophenols are effective. Peroxides are very efficient peptisers for standard butyl rubbers but act as curatives for crosslinked and brominated butyl rubbers. 

A further extension of the concept of thermosetting polysilazanes with peroxide initiators has been the preparation of new polysilazanes with peroxide groups bound directly to the polymer 20). Potential advantages of a peroxide-substituted polysilazane over systems in which the peroxide is simply admixed with the polymer include 1) segregation of the peroxide upon storage cannot occur, 2) dissolution or dispersion of a peroxide in the polysilazane is not necessary, and 3) homogeneous distribution of e peroxide in solid, as well as liquid, polysilazanes is possible. We have prepared a new class of peroxide-substituted polysilazanes by the reaction of a hydroperoxide with a poly(methylvinyl)silazane. The liquid polymers may be thermoset, even with extremely low levels of peroxide substitution. This chemistry provides access to a class of polysilazanes previously unknown as ceramic precursors. 

No examples, however, were reported in which a lower hydroperoxide/Si-N stoichiometry was used. Such a ratio would be expected to produce silylperoxides containing silylamine moieties. We adopted this strategy for the preparation of peroxide-substituted polysilazanes. 

The reaction mixture which contained 6 had no other products by si NMR spectroscopy. This peroxide-substituted silylamine was successfully prepared by control of the reaction stoichiometry to supply the hydroperoxide as Ae limiting reagent, which prevented complete conversion to an alkyl silylperoxide as in equation 3. This approach was then used to prepare a peroxide-substituted polysilazane. 

Table I. Peroxide-Substituted Polysilazane Cure/TGA Results ...

The thiazolyl radicals are, in comparison to the phenyl radical, electrophilic as shown by isomer ratios obtained in reaction with different aromatic and heteroaromatic compounds. Sources of thiazolyl radicals are few the corresponding peroxide and 2-thiazolylhydrazine (202, 209, 210) (see Table III-34) are convenient reagents, and it is the reaction of an alky] nitrite (jsoamyl) on the corresponding (2-, 4-, or 5-) amine that is most commonly used to produce thiazolyl radicals (203-206). The yields of substituted thiazole are around 40%. These results are summarized in Tables III-35 and IIT36. 

As we saw when discussing allylic brommation m Section 10 4 N bromosuccm imide (NBS) is a convenient free radical brommatmg agent Benzylic brommations with NBS are normally performed m carbon tetrachloride as the solvent m the presence of peroxides which are added as initiators As the example illustrates free radical bromi nation is selective for substitution of benzylic hydrogens... 

The presence of ammonia and hydrogen peroxide in permanent hair color products is a disadvantage. Both are considered by consumers to be harsh chemicals. The odor of ammonia is unpleasant for a personal care product. Monoethanol amine has been used as a substitute for ammonia in some commercial permanent hair color products. It is not as effective as ammonia in allowing the hair to be lightened but it does not have as strong an odor. 

Hydrogen peroxide is used in many applications throughout a wide variety of industries. The principal use areas are shown in Table 9. Most ate based on the oxidizing properties of hydrogen peroxide. Some are derived from substitution, decomposition, or the formation of perhydrates. 

Make acid yields coumaUc acid when treated with fuming sulfuric acid (19). Similar treatment of malic acid in the presence of phenol and substituted phenols is a facile method of synthesi2ing coumarins that are substituted in the aromatic nucleus (20,21) (see Coumarin). Similar reactions take place with thiophenol and substituted thiophenols, yielding, among other compounds, a red dye (22) (see Dyes and dye intermediates). Oxidation of an aqueous solution of malic acid with hydrogen peroxide (qv) cataly2ed by ferrous ions yields oxalacetic acid (23). If this oxidation is performed in the presence of chromium, ferric, or titanium ions, or mixtures of these, the product is tartaric acid (24). Chlorals react with malic acid in the presence of sulfuric acid or other acidic catalysts to produce 4-ketodioxolones (25,26). 

In the absence of air or peroxides, only cycHc dimers are formed in the thermal dimerization of isoprene (33). Six cycHc dimers are formed in good yields four substituted cyclohexenes (3—6) and two dimethylcyclooctadienes (7—8). The latter two are, of course, not Diels-Alder dimers. There is some evidence that the isoprene dimerization mechanism differs from the usual Diels-Alder route. 

Saponification of alkyl peroxyesters yields alkyl hydroperoxides and carboxylic acids or their alkali metal salts. a-Ether-substituted peroxides can be hydrolyzed to the unsubstituted alkyl hydroperoxides, eg, tert-huty hydroperoxide from tert-huty 2-oxacyclohexyl peroxide [28627-46-5] (62) ... 

Dialkyl peroxides have the stmctural formula R—OO—R/ where R and R are the same or different primary, secondary, or tertiary alkyl, cycloalkyl, and aralkyl hydrocarbon or hetero-substituted hydrocarbon radicals. Organomineral peroxides have the formulas R Q(OOR) and R QOOQR, where at least one of the peroxygens is bonded directly to the organo-substituted metal or metalloid, Q. Dialkyl peroxides include cyclic and bicycflc peroxides where the R and R groups are linked, eg, endoperoxides and derivatives of 1,2-dioxane. Also included are polymeric peroxides, which usually are called poly(alkylene peroxides) or alkylene—oxygen copolymers, and poly(organomineral peroxides) (44), where Q = As or Sb. 

Symmetrical diaLkyl peroxides are commonly named as such, eg, dimethyl peroxide. For unsymmetrical diaLkyl peroxides, the two radicals usually are hsted ia alphabetical order, eg, ethyl methyl peroxide. For organomineral peroxides or complex stmctures, ie, where R and R are difficult to name as radicals, the peroxide is named as an aLkyldioxy derivative, although alkylperoxy is stUl used by many authors. CycHc peroxides are normally named as heterocychc compounds, eg, 1,2-dioxane, or by substitutive oxa nomenclature, eg, 1,2-dioxacyclohexane however, when the two oxygens form a bridge between two carbon atoms of a ring, the terms epidioxy or epiperoxy are frequendy used. The resulting polycycHc stmcture has been called an endoperoxide, epiperoxide, or transaimular peroxide. 

Substitution reactions on dialkyl peroxides without concurrent peroxide cleavage have been reported, eg, the nitration of dicumyl peroxide (44), and the chlorination of di-/ fZ-butyl peroxide (77). Bromination by nucleophilic displacement on a-chloro- or a-hydroxyalkyl peroxides with hydrogen bromide produces a-bromoalkyl peroxides (78). 

Consequendy, most organomineral peroxides must be prepared and stored under anhydrous conditions. In addition, anhydrous hydrogen chloride converts alkyl-substituted organomineral peroxides to alkyl hydroperoxides (33). 

Basic hydrolysis of secondary alkyl-substituted siUcon and germanium peroxides results in oxygen—oxygen bond cleavage. 

The reduction of alkyl-substituted siUcon and tin peroxides with sodium sulfite and triphenylphosphine has been reported (33,93). Alkyl-substituted aluminum, boron, cadmium, germanium, siUcon, and tin peroxides undergo oxygen-to-metal rearrangements (33,43,94), eg, equations 22 and 23. 

The a-oxygen-substituted hydroperoxides and dialkyl peroxides comprise a great variety as shown in Figure 1. When discussing peroxides derived from ketones and hydrogen peroxide, (1) is often referred to as a ketone peroxide monomer and (2) as a ketone peroxide dimer. 

Secondary alcohols, such as isopropyl alcohol, j -butyl alcohol, 2-pentanol, 3-pentanol, cyclopentanol, and cyclohexanol, have been autoxidized to hydroxyaLkyl hydroperoxides (1, X = OH R = H) (10,44). These autoxidations usually are carried out at ca 20°C with uv radiation in the presence of a photosensitizer, eg, benzophenone. a-Oxygen-substituted dialkyl peroxides (2, X = Y = OH and X = Y = OOH), also are formed and sometimes they are the exclusive products (10). 

Hydroxyall l Hydroperoxyall l Peroxides. There is evidence that hydroxyalkyl hydroperoxyalkyl peroxides (2, X = OH, Y = OOH) exist in equihbrium with their corresponding carbonyl compounds and other a-oxygen-substituted peroxides. For example, reaction with acyl haUdes yields diperoxyesters. Dilute acid hydrolysis yields the corresponding ketone (44). Reduction with phosphines yields di(hydroxyalkyl) peroxides and dehydration results in formation of cycHc diperoxides (4). 

Polymeric OC-Oxygen-Substituted Peroxides. Polymeric peroxides (3) are formed from the following reactions ketone and aldehydes with hydrogen peroxide, ozonization of unsaturated compounds, and dehydration of a-hydroxyalkyl hydroperoxides consequendy, a variety of polymeric peroxides of this type exist. Polymeric peroxides are generally viscous Hquids or amorphous soHds, are difficult to characterize, and are prone to explosive decomp o sition. 

Miscellaneous OC-Substituted Peroxides. 3-Aryl-3-(/ i alkylperoxy)-phthaHdes (12) are prepared from the corresponding 3-chlorophthaHdes and alkyl hydroperoxide (156). 2-Methyl-2-(/ f2 -alkylperoxy)-l,3-benzodioxan-4-ones (13) are obtained from 0-acetylsaHcyloyl chloride and alkyl hydroperoxides (157). Trisubstituted 2-(/ f2 -alkylperoxy)-l,3-dioxolan-4-ones (14) are synthesized from stericaHy favored a-acyloxy acid chlorides and alkyl hydroperoxides (158). 

---