Carboxylic acids anion

Figure 15. Disproved isokinetic relationship for the proton transfer from nitro-methane to various carboxylic acid anions (156). Symbols as in Figure 13.

Besides fragmentation or rearrangement, the carboxylic acid anions, formed by an enzymatic hydrolysis, can also act as nucleophiles. Kuhn and Tamm used the asymmetric hydrolysis of meso-epoxy diester 8-28 with PLE to synthesize y-lactone... 

The manifestation of noncovalent catalysis as a microsolvent effect is illustrated by cycloamylose-catalyzed decarboxylations of activated carboxylic acid anions. Anionic decarboxylations, as illustrated in scheme VII, are generally assumed to proceed by a rate-determining heterolytic... 

This enzyme [EC 3.1.1.8] (also known as cholinesterase, pseudocholinesterase, acylcholine acylhydrolase, nonspecific cholinesterase, and benzoylcholinesterase) catalyzes the hydrolysis of an acylcholine to generate choline and a carboxylic acid anion. A variety of choline esters and a few other compounds can serve as substrates. 

Oxidation of the aldehyde group of an aldose to form a carboxylic acid or carboxylic acid anion is often used analytically to determine the amount of reducing sugar. The Benedict and Fehling methods measure the amount of reducing sugar present in a fluid. In these reactions, the oxidant, Cu2+, is reduced to Cu+. Cu+ precipitates as Cu20, which can be measured in a variety of ways. In the Tollens test, Ag+ is reduced to Ag°. 

Complexes of carbonic or carboxylic acid anions have been used as hydroformylation catalysts for various alkenes. The bicarbonate complex [Rh(H)2(02COH)(PPr 3)2] as catalyst enabled 1-hexene to be converted to aldehydes using paraformaldehyde as source of hydrogen and carbon monoxide in place of the more usual gas mixture.338 The acetate complex [Rh(OAc)CO(PPh3)2] (74) has been shown to effect the selective hydroformylation of cyclic dienes. The cyclohexadienes gave predominantly dialdehydes, whereas 1,3- and 1,5-cyclooctadiene gave the saturated monoaldehydes.339... 

The conjugate addition of unstabilized enolates to various acceptors was conceptually recognized by early researchers however, complications were encountered depending on the enolates and acceptors employed. Reexamination of this strategy was made possible by the development of techniques for kinetic enolate formation. This discussion is divided into three enolate classes (a) aldehyde and ketone enolates, azaenolates or equivalents, (b) ester and amide enolates, dithioenolates and dienolates and (c) a,0-carboxylic dianions and a-nitrile anions, in order to emphasize the differential reactivity of various enolates with various acceptors."7 The a-nitrile anions are included because of their equivalence to the hypothetical a-carboxylic acid anion. 

These processes are applied to organic compounds including phenols, aromatic amines, halogenated compounds, nitrated derivatives, fecal wastes, dyes, aldehydes, carboxylic acid anions, and others. The inorganic substance that has probably been the most commonly treated through the electrochemical route is cyanide its main product is the much less toxic cyanate ion. 

Active Figure 20.4 MECHANISM Mechanism of the basic hydrolysis of a nitrile to yield an amide, which is subsequently hydrolyzed further to a carboxylic acid anion. Sign in at www.thomsonedu.com to see a simulation based on this figure and to take a short quiz. 

MacGowan D. B. and Surdam R. C. (1988) Difunctional carboxylic acid anions in oilfield waters. Org. Geochem. 12, 245 - 259. 

The limitations to the preparation of U(III) complexes in aqueous solutions can be judged from the observation that the addition of phosphate, carbonate, nitrate, nitrite, sulphite, thiosulphate, or carboxylic acid anions to a U(III) sulphate solution all lead to rapid oxidation of the uranium, though color changes that suggest complex formation may occur (57). 

Voltammetric data for ester reductions are available for several aromatic esters [51-54], and in particular cyclic voltammetry shows clearly that in the absence of proton donors reversible formation of anion radical occurs [51]. In dimethylfonnamide (DMF) solution the peak potential for reduction of methyl benzoate is —2.29 V (versus SCE) for comparison dimethyl terephthalate reduces at —1.68 V and phthalic anhydride at —1.25 V [4]. Half-wave potentials for reduction of aromatic carboxylate esters in an unbuffered solution of pH 7.2 are linearly correlated with cr values [51] electron-withdrawing substituents in the ring or alkoxy group shift Ei/o toward less negative potentials. Generally, esters seem to be more easily reducible than the parent carboxylic acids. Anion radicals of methyl, ethyl, and isopropyl benzoate have been detected by electron paramagnetic resonance (epr) spectroscopy upon cathodic reduction of these esters in acetonitrile-tetrapro-pylammonium perchlorate [52]. The anion radicals of several anhydrides, including phthalic anhydride, have similarly been studied [55]. 

In a similar manner, carboxylic acid anions, phenolates, etc. can be separated from other organic matter by retention on a small anion exchanger in the OH form. 

At temperatures greater than a 100°C, thermal degradation of carboxylic acids produces methane and carbon dioxide (Surdam et ai, 1984). As the carboxylic acid anions are consumed due to increasing temperature, the carbonate system becomes internally buffered, and thus the pH may decrease due to increased in the system, leading to carbonate dissolution and the enhancement of secondary porosity (Surdam et ai, 1984). Factors influencing the thermal destruction rate of organic acids include coupled sulphate reduction and hydrocarbon oxidation, and the mineralogy of host sediments (Bell, 1991) the presence of hematite causes rapid rates of acetic acid decomposition. 

Over the temperature interval 120-160°C the carboxylic acid anions completely decarboxylate and the alkalinity is dominated by the carbonate system. Consequently, any increase in Pco, will cause further dissolution. 

MacGowan, D.B. Surdam, R.C. (1990) Carboxylic acid anions in formation waters, San Joaquin Basin and Lousiana Gulf Coast, USA—implications for clastic diagenesis. Appl. Geochem., 5, 687-701. 

We see that only complexes with formation constants of the order of 106 M-1 or more will lead to titration curves with a sufficiently steep change in pL near the equivalence point (at CM VM / CL VL = 1) to be useful for volumetric analysis. None of the common monodentate ligands, such as the halide anions (Cl-, Br , I-) or the pseudohalides (CN , SCN-, N3 ), form such strong complexes, nor do the carboxylic acid anions (such as acetate) or ammonia (NH3). However, in section 5.2 we will encounter special ligands, the chelates, that do form sufficiently strong 1 1 complexes. 

Dissolved organic species have been known to exist in sedimentary basin formation waters since before the turn of the century (5.6.71. A host of aqueous organic species have been identified in sedimentary formation waters including hydrocarbons, mono-, di- and tri-carboxylic acid anions, keto and hydroxy-acids, amino acids, phenols, cresols, and hydroxybenzoic acids (8.9.10.11.121. 

Table I. MAXIMUM REPORTED CONCENTRATIONS OF CARBOXYLIC ACID ANIONS IN PRODUCED FORMATION WATERS...

Controls on Concentration and Distribution of Carboxylic Acid Anions in Formation Waters... 

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