Free-radical reaction with alcohols

Mechanistic studies of autoxidation have concentrated on methylene-interrupted fatty acids, but many of the observations are valid for other compounds. Conjugated fatty acids such as CLA also oxidize through an autocatalytic free radical reaction, with the predominant hydroperoxide determined by the geometry of the conjugated diene system (45). Other groups with activated methylenes may be susceptible to oxidation, for example, the ether methylenes of ethoxylated alcohols used as surfactants (46). 

Alkanes from alcohols ROH is deoxygenated via the thioxocarbamates by a free radical reaction with (Me3Si)3SiH-AIBN in refluxing benzene. 

Nitrations are highly exothermic, ie, ca 126 kj/mol (30 kcal/mol). However, the heat of reaction varies with the hydrocarbon that is nitrated. The mechanism of a nitration depends on the reactants and the operating conditions. The reactions usually are either ionic or free-radical. Ionic nitrations are commonly used for aromatics many heterocycHcs hydroxyl compounds, eg, simple alcohols, glycols, glycerol, and cellulose and amines. Nitration of paraffins, cycloparaffins, and olefins frequentiy involves a free-radical reaction. Aromatic compounds and other hydrocarbons sometimes can be nitrated by free-radical reactions, but generally such reactions are less successful. 

The photochemistry of four triphenylmethane acid dyes was studied in poly(vinyl alcohol), methylcellulose and gelatin films. These model systems were chosen with a view to elucidating the complex free-radical reactions taking place in the heterogeneous dyed wool/ water/air system on exposure to UV radiation. The dye fading mechanism seems to involve an excited triplet state of the dye molecule [ 164] The rate of fading is governed by ... 

We begin by bringing you up to speed on mechanisms and reminding you how to push electrons around with those curved arrows. We jog your memory with a discussion of substitution and elimination reactions and their mechanisms, in addition to free radical reactions. Next you review the structure, nomenclature, synthesis, and reactions of alcohols and ethers, and then you get to tackle conjugated unsaturated systems. Finally, we remind you of spectroscopic techniques, from the IR fingerprints to NMR shifts. The review in this part moves at a pretty fast pace, but we re sure you can keep up. 

The large group of inhibitors of free radical chain reactions are frequently used in combination with metal salts or organometallic stabilizers. They are amines, sulfur- or phosphorus-containing compounds, phenols, alcohols, or chelates. Aromatic phosphites at about 1 p.p.r. chelate have undesirable metal impurities and inhibit oxidative free radical reactions. Some of the more popular are pentaerythritol, sorbitol, melamine, dicyan-diamide, and benzoguanamine. Their synergistic effect is utilized in vinyl floors where low cost is imperative. 

In such a case reaction 3 or 3 could be rate-determining and give a rate law first order in adsorbed alcohol. Since, however, the dehydrogenation reactions are facilitated by metal catalysts, particularly the transition metals, it is just as likely that the surface reaction proceeds via free radical species with moderately strong bonding to the metal atoms in the surface. By denoting metal atoms in the surface by M, such a mechanism could be represented by... 

Free radical reactions of purines with amines gave similar products to those produced in alcohol solution although deamination may also occur, probably at the post- rather than the pre-adduct stage. Whereas purine and n-propylamine afforded 6-n-propylpurine (71MI40907), adenine and caffeine produced both the 8-aminoalkyl and corresponding 9-alkyl derivatives (74MI40904). Also irradiation of 8-aminoalkylpurines in methanol furnished the 8-alkyl derivatives. Amino acids as an amine source are of special biochemical interest. They also tend to produce 8-alkylpurines by concomitant deamination and decarboxylation (69CC905). 

Free-radical reactions of purities with amines give similar products to those produced in alcohol solution although deamination may also occur, probably at the post- rather than the preadduct stage,... 

In the past 10 years other reductants of the C— Hg bond have been used, mainly thiols and sodium amalgam. Reduction with hydrogen sulfide, sodium dithionite, metals,alcohols, alkaline aqueous bases, aromatic amines, Wilkinson s catalyst and electrochemical reductions have also been described. Organomercurials react with thiols by free radical substitutions with an 5h2 mechanism (Scheme 34). The reaction between PhSH and A -hexenylmercury chloride initiated by light or AIBN gives a mixture of 1-hexene and methylcyclopentane. ... 

This dependence on the polarity of the environment is not experienced with free radical reactions in general, but it follows the same pattern as oxidation-reduction potentials of metal compounds in these solvents a striking example is the case FeCl4 /FeCl4 2 where a jump of half a volt occurs in a very narrow range of ethyl alcohol-water mixtures (22). 

Because oxidations with oxygen are free-radical reactions, free radicals should be good initiators. Indeed, in the presence of hydrogen bromide at high enough temperatures, lower molecular weight alkanes are oxidized to alcohols, ketones, or acids [5 7]. Much more practical are oxidations catalyzed by transition metals, such as platinum [5, 6, 55, 56], or, more often, metal oxides and salts, especially salts soluble in organic solvents (acetates, acetylacetonates, etc.). The favored catalysts are vanadium pent-oxide [3] and chlorides or acetates of copper [2, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66], iron [67], cobalt [68, 69], palladium [60, 70], rhodium [10], iridium [10], and platinum [5, 6, 56, 57]. 

The results of experiments on the reduction on 5-substituted adamantanones 1 and 5-azaadamantan-2-one N-oxide (2) with NaBHq show that electron-withdrawing substituents favour attack by the complex hydride syn to the substituent or nitrogen [30, 34, 51] (Fig. 6-17). In the case of 2, the effect is striking, with a synlanti attack ratio of 96/4 for the formation of the anti syn alcohols respectively (Table 6-1). Electron-donating substituents show a marginal preference for anti attack. Similarly, syn facial selectivity is found in free-radical reactions [63], ther-... 

Oxidations.1 The reagent compares favorably with N-haloamides and chromic acid for oxidation of secondary alcohols. Cyclohexanol is oxidized to cyclohexanone in 90-95% yield at room temperature. Less easily oxidized alcohols may require higher temperatures to initiate the free-radical reaction. The oxidation may become too vigorous if cooling is insufficient or if run on a large scale. 

With the growth of PTC, various new technologies have been developed where PTC has been combined with other methods of rate enhancement. In some cases, rate enhancements much greater than the sum of the individual effects are observed. Primary systems studied involving the use of PTC with other rate enhancement techniques include the use of metal co-catalysts, sonochemistry, microwaves, electrochemistry, microphases, photochemistry, PTC in single electron transfer (SET) reactions and free radical reactions, and PTC reactions carried out in a supercritical fluid. Applications involving the use of a co-catalyst include co-catalysis by surfactants (Dolling, 1986), alcohols and other weak acids in hydroxide transfer reactions (Dehmlow et al., 1985,1988), use of iodide (traditionally considered a catalyst poison, Hwu et... 

All the preceding reactions of chelated ligands can be shown or have been presumed to occur via an ionic mechanism. A preliminary report on the free radical reactions of a series of chelated acetylacetonates has been published recently. A solution of the metal chelate in bromobenzene was heated with ferf-butyl peroxide. The butoxy radicals that were formed either abstracted a hydrogen atom by cleavage of a carbon-hydrogen bond in the acetylacetonate molecule to form ferf-butyl alcohol, or decomposed to form acetone and a methyl radical. Thus, the ratio alcohol acetone that is obtained experimentally is a measure of the strength of the carbon-hydrogen bond that is cleaved. The butoxy radical abstracted a hydro-... 

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