Alkyl ketones degradative oxidation

The benzylic position of an alkylbcnzene can be brominated by reaction with jV-bromosuccinimide, and the entire side chain can be degraded to a carboxyl group by oxidation with aqueous KMnCfy Although aromatic rings are less reactive than isolated alkene double bonds, they can be reduced to cyclohexanes by hydrogenation over a platinum or rhodium catalyst. In addition, aryl alkyl ketones are reduced to alkylbenzenes by hydrogenation over a platinum catalyst. 

Sodium hypobromite, NaOBr, is prepared in situ from bromine and aqueous sodium hydroxide under cooling. Its almost exclusive application is the degradation of methyl ketones to acids with one less carbon [635, 735, 736, 737]. Such degradation is achieved not only with methyl ketones but also with other alkyl ketones [103, 160], Other oxidations, such as the conversion of hydroxylamines into nitroso compounds, are rare [738]. 

A special category of ethers are trimethylsilyl ethers. Trimethylsilyl ethers of primary alcohols, on treatment with Jones reagent, give acids [590]. On treatment with A-bromosuccinimide under irradiation, trimethylsilyl ethers yield esters [744]. Secondary alkyl trimethylsilyl ethers are converted into ketones by oxidation with both reagents [590, 744, 981]. Oxidation with Jones reagent is regiospecific the 2-ferf-butyldimethylsilyl 11-Krf-butyldiphenylsilyl ether of 2,11-dodecanediol is oxidized only in the sterically less hindered position [590]. Trimethylsilyl ethers of tertiary alcohols are degraded by periodic acid to carboxylic acids with shorter chains [755] (equations 336-339). 

Frequent use is made in the laboratory of oxidative degradation of methyl ketones. With alkyl ketones the resistance of the methyl group to attack by the usual oxidants is so great that reaction occurs only at one point thus an unbranched alkyl methyl ketone, for instance, on oxidation by chromic and sulfuric acid in glacial acetic acid affords, besides acetic acid, the alkanoic acid containing two fewer carbon atoms than the ketone e.g., palmitic acid from 2-octadecanone 128... 

Alkylation of carbonyl compounds and derivatives. The 02/Co(OAc)2-Mn(OAc)2 system is useful to accomplish a-alkylation of ketones with 1-alkenes. Acetals also add to acrylic esters under O2 in the presence of catalytic amounts of Co(OAc)2 and A-hydroxyphthalimide to afford a-hydroxy-y-oxo ester acetals. The adducts of methyl vinyl ketone suffer oxidative degradation in situ. 

Diazomethane furnishes the methyl ether which has been degraded to 3-methoxyfuran which, however, is more easily available from 3-iodofuran. 3-Methoxyfuran is cleaved by acid to furan-3(2H)-one. Other 3-furanols with ester, acetyl or benzoyl substituents at the 2-position are also available. They exist in the enolic form but their chemistry has not been investigated (76JCS(P1)1688>. Furan-3(2H)-ones with acetyl or ester substituents at the 4-position are readily available. They exist in the keto form but show some evidence for enolic behaviour and their chemistry is similar to that of enolizable ketones. They enter into cycloaddition with maleic anhydride, are alkylated at the 2-position, condense with aldehydes and ketones and are oxidized by LTA to the 2-acetoxy compounds (74BSF2061). 

Unlike the reactions discussed previously in this chapter, oxidation of alcohols involves the alkyl portion of the molecule, or more specifically, the C-H bonds of the hydroxyl-bearing carbon (the a carbon). Secondary alcohols, which have only one such C-H bond, are oxidized to ketones, whereas tertiary alcohols, which have no C-H bonds to the hydroxylic carbon, are oxidized only with accompanying degradation into smaller fragments by cleavage of carbon-carbon bonds. 

Soil. Readily degraded, ultimately to C02 oxidation on the /-butyl moiety and des-alkylation of the amine are the primary reaction steps. The des-alkylated compounds were either further oxidised to the corresponding acids or further degraded to a ketone metabolite. Soil DT50 (lab. and field) in the range 35-64 days. Bound rapidly to the sediment... 

Example 5.5. Oxidation of paraffins to secondary alcohols. Alcohols can be produced by oxidation of paraffins with air or oxygen at moderate temperatures (typically 120 to 180° C) in the presence of boric-acid esters or boroxines [16-18], These intercept the alkyl peroxide, the first oxidation product, preventing it from generating free radicals that would cause further degradation including scission of carbon-carbon bonds and produce aldehydes, ketones, and acids (see also Section 9.6.2). The peroxy borates so formed then are hydrolyzed to yield the alcohol. The carbon atoms at the chain ends are largely immune to oxidation, so the product consists predominantly of isomeric secondary alcohols. The reaction does not stop at... 

A -Bromosuednimide is used in the dehydrogenation of hydrazo compounds to azo compounds [744] and in the oxidative degradation of a-hydroxy acids to aldehydes or ketones [745]. This reagent also oxidizes alkyl trimethylsilyl ethers to esters or ketones [744],... 

Pyrroles which have a ketone or ester substituent are more resistant to ring degradation and high-yielding side-chain oxidation can be achieved using cerium(IV) ammonium nitrate, with selectivity for an a-alkyl. ... 

According to Carlin et al. (1986), the exact mechanism of oxazole formation is not known, despite the previous schemes proposed by Vitzthum and Werkhoff (1974a,b) and by Ohloff and Flament (1978). Formation pathways were proposed by Baltes and Bochmann (1987d) and Mottram (1991). For Vitzthum and Werkhoff (1974b), one pathway could be the decarboxylation of serine or threonine into ethanolamine or methylethanolamine condensation with an aldehydic compound into an oxazolidine, then oxidation into an oxazole unsubstituted or methylated on position 5 and bearing an alkyl or an acyl radical on position 2. Another pathway could be the condensation of amino acids with a-dicarbonyl compounds, followed by a Strecker degradation, formation of an a-amino ketone which, after acylation... 

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