OXIDATION OF THE ESTERS

Rate Coefficients and Mechanisms of Atmospheric Oxidation of the Esters 

Esters are emitted directly into the atmosphere from both natural and anthropogenic sources and are produced during the atmospheric oxidation of ethers. Methyl acetate and ethyl acetate have found widespread use as solvents. Vegetable oils and animal fats are esters. Transesterification of vegetable oils and animal fats with methanol gives fatty acid methyl esters (FAMEs) which are used in biodiesel. Many esters have pleasant odors and are present in essential oils, fruits, and pheromones, and are often added to fragrances and consumer products to provide a pleasant odor. Table VII-A-1 provides a list of common esters and their odors. 

Ethyl acetate C2H50C(0)CH3 Nail polish remover 

Isobutyl acetate (CH3)2CHCH20C(0)CH3 Cherry, raspberry, strawberry 

Benzyl acetate C6H50C(0)CH3 Pear, strawberry, jasmine 

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The sirup and the crystalline acid (VIII), when oxidized with sodium periodate, gave the same aldehydes as those produced by the oxidation of the ester from D-glucose (II) and its saponification product (XXX), respectively. Hence, the mechanism of the reaction of D-galactose is the same as that of D-glucose and D-mannose. Moreover, the approximate yield from... 

H- 1,4-Thiazines and benzothiazines undergo oxidation to dehydro dimers (83) and (84) which are of considerable interest as they are the parent chromophores of the trichosiderin (trichochrome) pigments which occur in mammalian red hair and in the feathers of some birds (74T2781). In the case of monocyclic thiazines, reagents such as nitrobenzene or picric acid are required, but air oxidation is sufficient in the bicyclic series. It is curious that whereas aerial oxidation of the ester (85) gives both the dehydro dimers (86) and (87), ethyl azodicarboxylate only yields the tautomer (87) <70AC(R)35l). 

The scope of the strategy was then extended in spectacular fashion (Scheme 6). The mixture of 19 and 20 was transformed into the corresponding aldehydes 26 through reduction/oxidation of the ester groups. Treatment with the dianion derived from ethyl acetoacetate then led to hydroxyketones 27. Chelation-controlled, syn-selective reduction [9] of this mixture followed by menthonide formation gave 28 as four diaste-... 

An approach to lactone [12] similar in concept to that just described, but not requiring a resolution, involved asymmetric Diels-Alder reaction of (benzyloxymethyl)cyclopentadiene [21] with the chiral ester of acrylic add and 8-phenylmenthoI (22), The adduct [22] was obtained in undetermined but apparently quite high e.e. Oxidation of the ester enolate of [22], followed by lithium aluminum hydride reduction, gave diol [23] as an... 

The pyrolytic oxidation of the esters generates mainly the esterifying acid and, when the acid has a longer chain, some aldehydes and acids with shorter chain length but which are formed from the esterifying acid. Formaldehyde, formic acid, CO2, CO, etc. are formed from the glucose units. 

RP(SR )NRP have thus been oxidized to the corresponding phosphorus(V) esters. The attempted oxidation of the esters 65 and 67 by elemental oxygen merely results in their isomerization to a phosphine sulphide (66) and in the second case to the thiophosphonic diester 68 . The case of 20 (X = l.p., R = SCH2Ph) is more unusual still, since such oxidation leads not only to the thiophosphonic ester (20 X = S, R = PhCH2), but also to the dithiophosphoric ester (20 X = S, R = SCH2Ph), together with other products ... 

Further work showed that higher yields of ( + )-PGEi are obtainable if the glycols used have the endo configuration at C-13 (XXXV) rather than the exo form as in (XXXIV) [129]. These p do-glycols were derived from the ketone (XXXVI) which was prepared, using essentially the same procedure as for the exo-compounds, from the bicyclo ester (XXXVII). The latter was obtained via hydroboration and oxidation of the ester (XXXVIII), readily available from norbornadiene. 

The rate of ceric oxidation of malonic add and its diethyl ester in acetic acid/sul-furic acid solutions has recently been reported by Vaidya et al. (1987). They find no evidence for precursor complex formation in either system. The reactive Ce(IV) species appear to be Ce(S04)2 ( 2) and CefSO ) " k 2). The second-order rate parameter for the oxidation of malonic add is 40 times greater than that for the ester. Oxidation of the ester is proposed to occur through the enol form yielding a malonyl radical analogous to that identified by Amjad and McAuley. Foersterling et al. (1987) find that the second-order rate constant for malonic acid oxidation by Ce(lV) in sulfuric acid is in excellent agreement with the value of Vaidya et al. They observe that Ce(III) does inhibit the reaction in sulfuric add, which they attribute to a reversible Ce(IV) malonic acid rate-controlling step. 

Compounds of this type have considerable biochemical interest because they may explain the antiketogenic action of D-glucose in preventing the X formation of ketone bodies during animal metabolism. In vitro studies have shown that the oxidation of the ester of acetoacetic acid by hydrogen peroxide proceeds much more rapidly in the presence of D-glucose than in its absence 187),... 

Following up on the allylic oxidation and the interesting requirement of an ester solvent, the Yeung group attempted the allylic oxidation reaction in the absence of the alkene, and noticed some oxidation of the ester solvent. Development of this as its own reaction demonstrated the successful oxidation of a number of 0-alkyl and A-alkyl esters such as 23 and amides 24. The oxidation typically occurred on a methylene carbon on the alkoxy- or amino-carbon chain several carbons away from the ester center. Attempts to oxidize n-octane resulted in no reaction, further corroborating the necessity of carbonyl coordination to the iodine center. 

Rate Coefficients and Mechanisms of Atmospheric Oxidation of the Esters 775 Table Vll-A-I. Some common esters and their odors... 

Rate Coefficients and Mechanisms of At Table VII-B-22. Rate coefficients k = Ax atoms with n-butyl acetate [ -C4H90C(0)CH3] mospheric Oxidation of the Esters 815 cm molecule s ) for reaction of chlorine ... 

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