Carboxylic acids, photochemical

Fig. 21. Representative nonionic photoacid generators. A variety of photochemical mechanisms for acid production ate represented. In each case a sulfonic acid derivative is produced (25,56,58—60). (a) PAG that generates acid via 0-nitrobenzyl rearrangement (b) PAG that generates acid via electron transfer with phenohc matrix (c) PAG that is active at long wavelengths via electron-transfer sensitization (d) PAG that generates both carboxylic acid and...

Methyl-3,4-dihydro-j3-carboline-3-carboxylic acid has been reported to undergo photochemical and pyrolyticoxidation to yield a mixture containing l-methyl-j8-carboline and l-methyl-j8-carboline-3-carboxylic acid. The methyl ester of this 3,4-dihydro-j8-carboline acid appears to be oxidized to methyl l-methyl-j8-carboline-3-carboxylate on alumina chromatography. ... 

A similar reaction sequence starting from tryptophan yields 1-methyl-3,4-dihydro-)3-carbohne-3-carboxylic acid (465). This compound has been shown to undergo photochemical oxidation to l-methyl-)3-carbohne-3-carboxyhc acid (466). Such a sequence of events may account for the biogenetic origin of the amino acid 466. 

An a-diazo ketone 1 can decompose to give a ketocarbene, which further reacts by migration of a group R to yield a ketene 2. Reaction of ketene 2 with water results in formation of a carboxylic acid 3. The Woljf re arrangement is one step of the Arndt-Eistert reaction. Decomposition of diazo ketone 1 can be accomplished thermally, photochemically or catalytically as catalyst amorphous silver oxide is commonly used ... 

A direct method for preparing a carboxylic acid treats an alkyl halide with NaN02 in acetic acid and DMSO. Reaction of an alkyl halide with ClCOCOaMe and (Bu3Sn)2 under photochemical conditions leads to the corresponding methyl... 

A hydroxymethyl group can be introduced (ArH —> ArCH20H) by several variations of this method. Alkylation of these substrates can also be accomplished by generating the alkyl radicals in other ways from hydroperoxides and FeS04, from alkyl iodides and H2O2—Fe V from carboxylic acids and lead tetraacetate, or from the photochemically induced decarboxylation of carboxylic acids by iodoso-benzene diacetate. 

Although Ce(IV) oxidation of carboxylic acids is slow and incomplete under similar reaction conditions , the rate is greatly enhanced on addition of perchloric acid. No kinetics were obtained but product analysis of the oxidations of -butyric, isobutyric, pivalic and acetic acids indicates an identical oxidative decarboxylation to take place. Photochemical decomposition of Ce(IV) carbo-xylates is highly efficient unity) and Cu(ll) diverts the course of reaction in the same way as in the thermal oxidation by Co(IIl). Direct spectroscopic evidence for the intermediate formation of alkyl radicals was obtained by Greatorex and Kemp ° who photoirradiated several Ce(IV) carboxylates in a degassed perchloric acid glass at 77 °K in the cavity of an electron spin resonance spectro-... 

The occurrence of C and C9 dicarboxylic acids in samples of atmospheric particles and in recent sediments (Stephanou 1992 Stephanou and Stratigakis 1993) has been attributed to photochemical degradation of unsaturated carboxylic acids that are widespread in almost all biota. 

Alkanes are formed when the radical intermediate abstracts hydrogen from solvent faster than it is oxidized to the carbocation. This reductive step is promoted by good hydrogen donor solvents. It is also more prevalent for primary alkyl radicals because of the higher activation energy associated with formation of primary carbocations. The most favorable conditions for alkane formation involve photochemical decomposition of the carboxylic acid in chloroform, which is a relatively good hydrogen donor. 

The literature presents a large number of examples concerning the use of known oxazolidinones as chiral auxiliaries in many kinds of reactions. Rare is the use of A-amino derivatives of oxazolidinones, which were used to synthesise new A-acylhydrazones 207. Radical addition reactions occurred with high diastereoselectivity <00JA8329>. The use of glycolate oxazolidinones 210 proved to be efficient for the enantioselective preparation of a-alkoxy carboxylic acid derivatives . Photochemical reaction of vinyl... 

Photochemical a-cleavage of carboxylic acids results in loss of carbon dioxide (decarboxylation) rather than loss of carbon monoxide. The compound 2,4-dichlorophenoxyacetic acid, commonly known as (2,4-D), has been used extensively as a herbicide. This has posed a problem, because of the slow natural decomposition of 2,4-D in the environment. 2,4-D undergoes a-cleavage, undergoing decarboxylation ... 

Figure 18.12 Effect of fluorescent device exposure on carboxylic acid production in Spectar copolymer as determined by SF4 treatment 1816cm-1, aromatic acid peak 1841 cm1, aliphatic acid peak [11]. Reprinted from Polymer, 41, Grossetete, T., Rivaton, A., Gardette, J.-L., Hoyle, C. E., Ziemer, M., Fagerburg, D. R. and Clauberg, H., Photochemical degradation of poly(ethylene terephtha-late)-modified copolymer, 3541-3554, Copyright (2000), with permission from Elsevier Science...

Organic aerosols formed by gas-phase photochemical reactions of hydrocarbons, ozone, and nitrogen oxides have been identified recently in both urban and rural atmospheres. Aliphatic organic nitrates, such dicarboxylic acids as adipic and glutaric acids, carboxylic acids derived from aromatic hydrocarbons (benzoic and phenylacetic acids) and from terpenes emitted by vegetation, such as pinonic acid from a pinene, have been identified. The most important contribution in this held has been that of Schuetzle et al., who used computer-controlled... 

Scheme 25.—Photochemical Release of Free Carboxylic Acid from a 2-Nitrobenzyl-substituted Poly(vinyl Alcohol).

Esters of 2-(2-azidophenyl)ethyl alcohol are photolyzed under a high-pressure mercury lamp to a reactive nitrene intermediate which, following insertion into the alkyl side-chain, undergoes elimination to give the free carboxylic acid (up to 32%) and producing indole. The photochemical release was somewhat improved (65-80%) when 5-azido-4-(hydroxy-methyl)-l-methoxy naphthalene was used (see Scheme 27). 

The synthesis of compounds 39, 41, and 43 by the ODPM rearrangement opens a novel photochemical route to chrysanthemic acid and other cyclopropane carboxylic acids present in pyrethrins and pyrethroids [52]. In fact, aldehyde 43 can be transformed to tran -chrysanthemic acid by simple oxidation. This new synthetic route to ecologically benign insecticides competes with the one previously described by us using the 1-ADPM rearrangement of p,y-unsaturated oxime acetates [30,53]. 

Phenol esters of a,(3-unsaturated carboxylic acids have an interesting reactivity due to the synthetic utility of the resulting hydroxychalcones (Scheme 19). This aspect will be illustrated in Section IV. However, from the basic point of view, it is worth mentioning that the cis or trans configuration of the olefinic part of the acyl moiety can have a marked influence on the photochemical reactivity of the ester. When para-methoxyphenyl fumarates are irradiated, the normal ortho-rearranged products are obtained. By contrast, irradiation of para-me-thoxyphenyl maleates does not lead to rearrangement. Instead, cyclization products are obtained (Scheme 20). 

In spite of being carboxylic acid derivatives, these two families of compounds have been put together in this section because their photochemical rectivity is... 

The mechanism of the photochemical alkylation shows particular characteristics as regards the formation of alkyl radicals, the reaction of these radicals with the heteroaromatic substrates, and the rearomatization of the intermediate products. A variety of alkylating agents (hydrocarbons, alcohols, amines, carboxylic acids, amino acids) have been used for photochemical and y-ray-induced alkylation. " ... 

FORMATION AND PHOTOCHEMICAL WOLFF REARRANGEMENT OF CYCLIC a-DIAZO KETONES D-NORANDROST-5-EN-3U-OL-16-CARBOXYLIC ACIDS, 52,53 FORMIC ACID, AZIDO, f-BUTYL ESTER, 50, 9... 

Eaton and co-workers also reported the synthesis of 1,3,5-trinitrocubane and 1,3,5,7-tetranitrocubane (39) ° The required tri- and tetra-substituted cubane precursors were initially prepared via stepwise substitution of the cubane core using amide functionality to permit ort/jo-lithiation of adjacent positions. The synthesis of precursors like cubane-1,3,5,7-tetracarboxylic acid was long and inefficient by this method and required the synthesis of toxic organomercury intermediates. Bashir-Hashemi reported an ingenious route to cubane-1,3,5,7-tetracarboxylic acid chloride (35) involving photochemical chlorocarbonylation of cubane carboxylic acid chloride (34) with a mercury lamp and excess oxalyl chloride. Under optimum conditions this reaction is reported to give a 70 8 22 isomeric mixture of 35 36 37... 

Litter, M.I. Baumgartner, E.C. Urmtia, G.A. Blesa, M.A. (1991) Photodissolution of iron oxides. 3. Interplay of photochemical and thermal processes in maghemite/carboxylic acid systems. Environ. Sci. Technol. 25 1907-1913... 

Efforts have been made to find stereoselective routes which provide disubstituted azetidines. Palladium catalysed cyclization of an enantiomer of allene-substituted amines and amino acids gives the azetidine ester 2 and a tetrahydropyridine in variable yield and ratio, depending on the substituents and conditions <990L717>. The (TRIS)- and (253I )-isomeis of the substituted azetidine-2-carboxylic acids 3 (R = COjH) are obtained in several steps from the corresponding 3 (R = CHjOSiMejBu ) which, in turn, is produced in high yield by photochemical intramolecular cyclization <98HCA1803>. 

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