In carboxylic acids

Longer bond in carboxylic acids and esters (HCOOH, 131.2) 135.8(5)... 

The latter is an exttemely reactive species. Trifluoroacetate is a good leaving group and facilitates cleavage of the O—Br bond. The acyl hypohalites are also the active halogenating species in solutions of the hypohalous acids in carboxylic acids, where they exist in equilibrium. 

Section 19.3 Hydrogen bonding in carboxylic acids raises their- melting points and boiling points above those of comparably constituted alkanes, alcohols, aldehydes, and ketones. 

FIGURE 20.1 Structure, reactivity, and carbonyl-group stabilization in carboxylic acid derivatives. Acyl chlorides are the most reactive, amides the least reactive. Acyl chlorides have the least stabilized carbonyl group, amides the most. Conversion of one class of compounds to another is feasible only in the direction that leads to a more stabilized carbonyl group that is, from more reactive to less reactive. 

The negatively charged oxygen substituent is a powerful electron donor to the carbonyl group. Resonance in carboxylate anions is more effective than resonance in carboxylic acids, acyl chlorides, anhydrides, thioesters, esters, and amides. 

Correlations with o in carboxylic acid derivative reactions have been most successful for variations in the acyl portion, R in RCOX. Variation in the alkyl portion of esters, R in RCOOR, has not led to many good correlations, although use of relative rates of alkaline and acidic reactions, as in the defining relation, can generate linear correlations. The failure to achieve satisfactory correlations with cr for such substrates may be a consequence of the different steric effects of substituents in the acyl and alkyl locations. It has been shown that solvolysis rates of some acetates are related to the pA", of the leaving group, that is, of the parent alcohol. The pK of alcohols has been correlated with but this relationship... 

Phosphoric acid anhydride (Section 29.1) A substance that contains P02P0 link, analogous to the C02CO link in carboxylic acid anhydrides. 

A subsequent investigation using spectrophotometric and titration techniques indicated that the reaction order in carboxylic acid was approximately three and that first-order rate coefficients were, in fact, independent of the initial concentration of mercury compound606. The reaction mechanism was proposed as... 

In carboxylic acids with an aromatic group or a double bond the ii-systems can be oxidized to radical cations that react with the carboxyl group to lactones (Eqs. 7, 42) [142, 351]. 

For a review of hydrogen bonding in carboxylic acids and acid derivatives, see Hadzi, D. Detoni, S. in Patai The Chemistry of Acid Derivatives, pt. 1 Wiley NY, 1979, p. 213. 

Complementary to the work with aqueous acidic media is the study of the homolytic decompositions of Co(III) carboxylates in carboxylic acid media by Lande and Kochi . For example, Co(III) is reduced in pivalic acid media with first-order kinetics with E = 30.6 kcal.mole , AS = 8 eu and k ko = 1.28+0.10 (69 °C). The main oxidation products were found to be isobutylene and tert-butyl pivalate, which suggests that (CH3)3C- is an intermediate. Oxidative decarboxylation is the probable course in the analogous oxidations of n-butyric and isobutyric acids, in view of the production of propane and CO2 under normal... 

Y. Ohwaki and H. Hirata, Differences in carboxylic acid exudation among P-starved leguminous crops in relation to carboxylic acid contents in plant tissues and phospholipid levels in roots. Soil Sci. Plant Nutr. 38 2 i5 (1992). 

For long chains of these reactions, each step must be exothermic. Typical examples include Cl2 in carboxylic acids, and BrCCl3 in alkyl aromatics. The products are variable substitution and side chain substitution compounds, respectively. 

Peroxyl radicals attack all groups of acid Me(CH2) COOH and preferencially the a-CH2 group. The more the number of CH2 groups in carboxylic acid, the higher is the rate constant (see Table 8.20). 

Solutions of Ru3(CO)i2 in carboxylic acids are active catalysts for hydrogenation of carbon monoxide at low pressures (below 340 atm). Methanol is the major product (obtained as its ester), and smaller amounts of ethylene glycol diester are also formed. At 340 atm and 260°C a combined rate to these products of 8.3 x 10 3 turnovers s-1 was observed in acetic acid solvent. Similar rates to methanol are obtainable in other polar solvents, but ethylene glycol is not observed under these conditions except in the presence of carboxylic acids. Studies of this reaction, including infrared measurements under reaction conditions, were carried out to determine the nature of the catalyst and the mechanism of glycol formation. A reaction scheme is proposed in which the function of the carboxylic acid is to assist in converting a coordinated formaldehyde intermediate into a glycol precursor. 

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