Intermediate alkoxyl

In this context Fernandez-Mateos and his group reported efficient cyclizations with aldehydes and ketones as radical traps [115]. The authors propose a reduction of the intermediate alkoxyl radicals by a second equivalent of... 

Due to the ability of tertiary peroxyl radicals to disproportionate with the formation of alkoxyl radicals, the chain decomposition of tertiary hydroperoxides proceeds via the action of intermediate alkoxyl radicals [9,135]. 

Methyl eicosanoate intermediate, alkoxylate synthesis Octyidodecanol intermediate, alkyd coatings Methylpropanediol intermediate, alkyds 3,3, 4,4 -Benzophenone tetracarboxylic dianhydride 1,2,4-Butanetriol Coconut acid Dipentaerythritol Dodecenylsuccinic anhydride... 

Hydroperoxides decompose relatively slowly at ambient temperatures in the dark, but in light they are readily photolysed to free radicals, (Scheme 1.1, reaction d). Consequently, the rate of photo-oxidation of the hydrocarbon polymers is orders of magnitude higher than thermal oxidation. In addition, small amounts of transition metal compounds, notably iron, cobalt, manganese and copper, have a powerful catalytic effect on radical formation from hydroperoxides [14], leading to rapid molecular weight reduction by breakdown of the intermediate alkoxyl radical and the formation of carboxylic acids and esters as oxidation end products (see Scheme 1.2) [15]. 

Extending an investigation of the double )S-scission reaction of alcohols with nitrogen substitution at the )3-carbon (Scheme 37), Japanese authors have reported that the intermediate alkoxyl radical can be generated more effectively photochemically, using hypoiodite, or oxidatively, with lead tetraacetate, rather than by the earlier method of nitrite ester irradiation. 

Since this early work, studies from the late 1950s until the 1960s by Walling, Green, Kochi and their collaborators using t-alkyl hypohalites disclosed some fundamental characteristics of the principal radical chain reactions, such as intermolecular hydrogen abstraction and P-scission of intermediate alkoxyl radicals in hypohalite photolysis. This work was summarized in a review article by Kochi."... 

Halogenated intermediates, dibromoneopentyl glycol [3296-90-0] (DBNPG), and alkoxylated derivatives of tetrabromobisphenol A are used extensively in flame-retardant apphcations. Similar properties can be derived from halogenated dibasic acids, chlorendic anhydride [115-27-5] (CAN), and tetrabromophthahc anhydride [632-79-1] (TBPA). Processes can be used to produce brominated products by the in situ bromination of polymers derived from tetrahydrophthahc anhydride. 

Halogenated intermediates based on chlorendic anhydride and alkoxylated, brominated bisphenol are quite stable and are used extensively in flame-retarded high temperature compositions, but brominated aUcychcs, such as dibromotetrahydrophthahc resin, are rapidly dehydrohalogenated at lower temperatures. 

Aromatic ethers and furans undergo alkoxylation by addition upon electrolysis in an alcohol containing a suitable electrolyte.Other compounds such as aromatic hydrocarbons, alkenes, A -alkyl amides, and ethers lead to alkoxylated products by substitution. Two mechanisms for these electrochemical alkoxylations are currently discussed. The first one consists of direct oxidation of the substrate to give the radical cation which reacts with the alcohol, followed by reoxidation of the intermediate radical and either alcoholysis or elimination of a proton to the final product. In the second mechanism the primary step is the oxidation of the alcoholate to give an alkoxyl radical which then reacts with the substrate, the consequent steps then being the same as above. The formation of quinone acetals in particular seems to proceed via the second mechanism. ... 

The versatility of pyrimidine substituted chloroquinazolines as intermediates is due to the ready replacement of the halogen atoms by hydrogen, alkyl, alkoxyl, amino, and mercapto groups (see Section VI, A). 

Organic peroxides such as cumene hydroperoxide and t-butyl hydroperoxide have extensively been used as experimental agents. They provoke lipid peroxidation in hepatocytes, probably by the generation of alkoxyl and peroxyl radical intermediates after reaction with cytochrome P450. Other cytotoxic mechanisms are probably involved including protein thiol and non-protein thiol oxidation and deranged calcium homeostasis (Jewell et al., 1986). In fact, the addition of cumene hydroperoxide to isolated bUe duct cells, devoid of cytochrome P450 activity, still results in cell death but lipid peroxidation is not detectable (Parola et al., 1990). 

In addition to /3-H elimination, olefin insertion, and protonolysis, the cr-metal intermediate has also proved to be capable of undergoing a reductive elimination to bring about an alkylative alkoxylation. Under Pd catalysis, the reaction of 4-alkenols with aryl halides affords aryl-substituted THF rings instead of the aryl ethers that would be produced by a simple cross-coupling mechanism (Equation (126)).452 It has been suggested that G-O bond formation occurs in this case by yy/z-insertion of a coordinated alcohol rather than anti-attack onto a 7r-alkene complex.453... 

In the field of enzyme catalysis, heme-proteins such as cytochrome P450, for example, exhibit both types of 0-0 bond cleavages in organic hydroperoxides and peroxy acids (178). Heterolytic cleavage of HOOH/ROOH yields H20 or the corresponding alcohol, ROH and a ferryl-oxo intermediate (Scheme 4). Homolytic 0-0 bond cleavage results in the formation of a hydroxyl (HO ) or an alkoxyl (RO ) radical and an iron-bound hydroxyl radical. 

Analogous to the annulation of the Sonogashira adducts (see Section 6.4.), a spontaneous cyclization via the intramolecular alkoxylation of alkyne 117 (the coupling adduct of o-bromophenol and phenyl acetylene) took place under the reaction conditions to give 2-phenylbenzofuran 119 [93]. Benzofurylpalladium complex 118 was the putative intermediate during the cyclization. 

In order to circumvent the lack of selectivity in the cleavage of trialkylb-oranes, B-alkylcatecholboranes can be used as precursor of alkyl radicals. They are extremely sensitive towards oxygen and they react readily with alkoxyl radicals. It was clearly demonstrated by ESR that the perboryl radical intermediate resulting from the complexation of B-methylcatecholborane with the alkoxyl radical is stabilized by delocalization onto the aromatic ring (Scheme 30) [79]. 

Industrial metal-zeolite catalysts undergo a bifunctional, monomolecular mechanism [1-5, 7]. Carbenium ions are the critical reaction intermediates to complete chain reactions. In the zeolite channels, carbenium ions likely exist as an absorbed alkoxyl species, rather than as free-moving charged ions [8], Figure 14.2 illustrates the accepted reaction mechanism, using hexanes as an example. 

The characteristics of the HERON transition states for both steps in the thermal decomposition of Ai,Ai -diacyl-Ai,A -diaIkoxyhydrazines facilitate the synthesis of esters. Notably, the alkoxyl group migrations in the internal 8 2 displacement of the 1,1-diazene in the first step, and nitrogen in the second step, do not involve a tetrahedral alkoxide intermediate and both Barton and coworkers and Glover and have utilized... 

The obvious candidates for the two competing reactions are those shown in Eqs. (24) and (25). The mechanisms of the two reactions are probably similar, although it was not possible to show whether reaction 25 produced isobutene. The expected chemistry is shown in more detail in Eq. (32). In a less appealing possibility, the tentative peroxo intermediate would cleave homolytically to yield alkyl and alkoxyl radicals, a route that is thermodynamically much less favorable than reaction 32. 

Label scrambling in propene occurs through the framework-bound alkoxyl intermediate 23, which is seen at 89 ppm in studies of propene-2-l3C on HZSM-5 (45). Analogous alkoxyl species have been reported on acidic zeolites from the reactions of certain alcohols and acetylene. In the latter case, structure 24 was proposed as the product obtained by heating acetylene on HZSM-5 (126). Evidence for this assignment included the formation of acetaldehyde as a hydrolysis product. Acetylene also reacts... 

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