Hydroxy acids from aromatic compounds

With the exception of isochorismic acid the above mentioned acids are aromatic compounds, derived from benzoic acid by an additional hydroxy or amino group in o- or p-position. 

The hydroxamic acid function in most alicyclic and aromatic compounds is stable to hot dilute acid or alkali, and derivatives cannot undergo normal base-catalyzed Lessen rearrangement. Di Maio and Tardella," however, have shown that some alicyclic hydroxamic acids when treated with polyphosphoric acid (PPA) at 176°-195° undergo loss of CO, CO.2, or H2O, in a series of reactions which must involve earlj fission of the N—0 bond, presumably in a phosphoryl-ated intermediate. Thus, l-hydroxy-2- piperidone(108) gave carbon monoxide, 1-pyrroline (119), and the lactams (120 and 121). The saturated lactam is believed to be derived from disproportionation of the unsaturated lactam. 

The diazeniumdiolate functional group is a monobasic acid (Scheme 3.13), which is also unstable in acidic solutions. This has created some difficulties in measuring its properties. The aromatic compounds (cupferron analogs) have pKa values between 3.5 and 4.4 in water solutions [146], while the piG values of aliphatic derivatives range from 5.1 for nitrosofungin [147] to 6.4 for fragin (20) [148]. N-Hydroxy-N-... 

Elforts have been made to characterize the nature and content of individual components that are present in the low-molecular-mass fraction of the total mill effluents, which include the spent chlorination and alkali extraction stage liquors [2,4]. Approximately 456 types of compounds have been detected in the conventional bleach effluents, of which 330 are chlorinated organic compounds [22]. The compounds may be lumped into three main groups, namely, acidic, phenolic, and neutral (Table 2). Acidic compounds are further divided into the five categories of acids fatty, resin, hydroxy, dibasic, and aromatic acids. The most important fatty acids are formic and acetic acids. The dominant resin acids are abietic and dehydroabietic acids. Among the hydroxy acids identified, glyceric acid predominates. Dibasic acids such as oxalic, malonic, succinic, and mafic acids are derived from the lignin and carbohydrate fraction... 

Collie s hypothesis that aromatic compounds are made biologically from ethanoic acid was greatly expanded by A. J. Birch to include an extraordinary number of diverse compounds. The generic name acetogenin has been suggested as a convenient classification for ethanoate (acetate)-derived natural products, but the name polyketides also is used. Naturally occurring aromatic compounds and quinones are largely made in this way. An example is 2-hydroxy-6-methylbenzoic acid formed as a metabolite of the mold Penicillium urticae ... 

Free amino acids are further catabolized into several volatile flavor compounds. However, the pathways involved are not fully known. A detailed summary of the various studies on the role of the catabolism of amino acids in cheese flavor development was published by Curtin and McSweeney (2004). Two major pathways have been suggested (1) aminotransferase or lyase activity and (2) deamination or decarboxylation. Aminotransferase activity results in the formation of a-ketoacids and glutamic acid. The a-ketoacids are further degraded to flavor compounds such as hydroxy acids, aldehydes, and carboxylic acids. a-Ketoacids from methionine, branched-chain amino acids (leucine, isoleucine, and valine), or aromatic amino acids (phenylalanine, tyrosine, and tryptophan) serve as the precursors to volatile flavor compounds (Yvon and Rijnen, 2001). Volatile sulfur compounds are primarily formed from methionine. Methanethiol, which at low concentrations, contributes to the characteristic flavor of Cheddar cheese, is formed from the catabolism of methionine (Curtin and McSweeney, 2004 Weimer et al., 1999). Furthermore, bacterial lyases also metabolize methionine to a-ketobutyrate, methanethiol, and ammonia (Tanaka et al., 1985). On catabolism by aminotransferase, aromatic amino acids yield volatile flavor compounds such as benzalde-hyde, phenylacetate, phenylethanol, phenyllactate, etc. Deamination reactions also result in a-ketoacids and ammonia, which add to the flavor of... 

Phenols.—The ring hydroxyl compounds take the class name of phenols from the simplest member, hydroxy benzene or phenol. These are true aromatic compounds and in methods of formation, reactions and properties are distinctly different from aliphatic hydroxyl compounds or alcohols. Their outstanding distinction is their marked acid character, the alcohols being neutral (p. 103). This is attributed to the influence of the phenyl radical (CeHs—). The same influence is present in the amino derivatives, for the ring amines, CeHs— NH2, /CH3... 

N03)j, a newcomer to the arena of oxidants, is useful for the acetoxylation of aromatic side chains in benzylic positions [415, 416] and for the oxidation of methylene or methyl groups that are adjacent to aromatic rings to carbonyl groups [238, 415, 417]. The reagent also oxidizes alcohols to aldehydes [418, 419, 420, 421] and phenols to quinones [422, 423], cleaves vicinal diols to ketones and a-hydroxy ketones to acids [424, 425], and converts diaryl sulfides into sulfoxides [426]. A specialty of ammonium cerium nitrate is the oxidative recovery of carbonyl compounds from their oximes and semicarbazones [422, 427] and of carboxylic acids from their hydrazides [428] under mild conditions. 

In addition to these reactions in which the carbanions are supplied from carbonyl compounds, we will discuss in this chapter Grignard reactions, the benzilic acid rearrangement, the benzoin condensation, and the Kolbe synthesis of hydroxy aromatic acids. These reactions illustrate the addition of other kinds of carbanions to carbonyl groups. The benzilic acid rearrangement is an example of the intramolecular addition of a group with its pair of electrons to a carbonyl carbon atom. 

In tMs approach, conjugate addition of the anion from an isocyano-acetate to an a,p-unsaturated nitrocompound with evenmal loss of nitrous acid, produces 5-unsubstituted pyrrole-2-esters. The example below shows a mechanistic sequence that can be seen to parallel that in the van Leusen synthesis. The most useful route to the a,P-unsaturated nitro-compound involves the base-catalysed condensation of an aldehyde with a nitroalkane giving an a-hydroxy-nitroalkane it can alternatively be generated in situ, in the presence of the isonitrile, using diazabicycloundecane (DBU) as base on the 0-acetate of the a-hydroxy-nitroalkane (for an example see 16.16.2.1). The process works even when the unsaturated nitro unit is a component of a polycyclic aromatic compound. ... 

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