Reactions of the carboxyl groups

Ester formation is a typical reaction of the carboxyl group... 

Reactions of the Carboxyl Groups. Carboxyl groups in the ortho position spontaneously form a strainless ftve-membered ring when heated to give anhydrides as shown for (8). Salts and esters (4) are readily formed as shown for (4) and (5), respectively. 

Esterification, Amidation, and Acid Chloride Formation. Amino acids undergo these common reactions of the carboxyl group with due regard for the need for A/-protection. 

Carboxylic Acid Group. Reactions of the carboxyl group include decarboxylation, reduction to alcohols, and the formation of salts, acyl hahdes, amides, and esters. 

In its chemical behavior benzoic acid shows few exceptional properties the reactions of the carboxyl group are normal, and ring substitutions take place as would be predicted. 

The alkanoic acids, with the exception of formic acid, undergo typical reactions of the carboxyl group. Formic acid has reducing properties and does not form an acid chloride or an anhydride. The hydrocarbon chain of alkanoic acids undergoes the usual reactions of hydrocarbons except that the carboxyl group exerts considerable influence on the site and ease of reaction. The alkenoic acids in which the double bond is not conjugated with the carboxyl group show typical reactions of internal olefins. All three types of reactions are industrially important. 

Reactions of the carboxyl group include salt and acid chloride formation, esterification, pyrolysis, reduction, and amide, nitrile, and amine formation. Salt formation occurs when the carboxyUc acid reacts with an alkaline substance (22)... 

Reaction of the carboxylic group with the epoxy group (Figure 26.7). 

Reactants of the A—A (or B—B) type are not likely to undergo direct cyclization instead of linear polymerization. A groups do not react with each other and B groups do not react with each other under the conditions of step polymerization. Thus there is usually no possibility of anhydride formation from reaction of the carboxyl groups of a diacid reactant under the reaction conditions of a polyesterification. Similarly, cyclization does not occur between hydroxyl groups of a diol, amine groups of a diamine, isocyanate groups of a diisocyanate, and so on. 

Even an oligopeptide has been attached to (Table 4.3, compound 130) [111]. This was achieved by a coupling reaction of the carboxylic group in the side chain of the cyclopropane ring as well. First, the tert-butylcarboxylate 129 was synthesized by the reaction of the corresponding diazomethylbenzoate with Cgg. After hydrolysis with trifluoromethanesulfonic acid, the acyl chloride was generated by treatment with oxalyl chloride. Finally, in a one-step procedure the fullerene peptide 130 was obtained by the reaction with the N-deprotected pentapeptide H-(L-Ala-Aib)2-L-Ala-OMe. 

The application of lipases in synthetic biotransformations encompasses a wide range of solvolytic reactions of the carboxyl group, such as esterification, transesterification (alcoholysis), perhydrolysis, and aminolysis (amide synthesis) [103]. Transesterification and amide synthesis are preferably performed in an anhydrous medium, often in the presence of activated zeolite, to suppress unwanted hydrolytic side reactions. CaLB (which readily tolerates such conditions [104,105]), PsL, and PcL are often used as the biocatalyst [106]. 

R and S isomers of HDT]acetic acid were synthesized by chemical and enzymatic methods that yield products of known stereochemistry.1819 The two isomers were then distinguished by using the following ingenious enzymatic assays. The acetic acid was first converted to acetyl-coenzyme A (by a reaction of the carboxyl group—and not the methyl—of acetic acid). The acetyl-coenzyme A was then condensed with glyoxylate to form malate in an essentially irreversible reaction catalyzed by malate synthase (equation 8.27). The crucial feature of this reaction is that it is subject to a normal kinetic isotope effect, so that more H than D... 

Intermediate 23b can be obtained by a direct nucleophilic attack of the uncharged amino group (present at low equilibrium concentration at pH 7) but the mechanism of this step may be more complex as shown by the observation of a catalytic effect of CO2 in amidations using CDI [191]. Moreover, the reaction of the carboxylate group followed by an intramolecular acyl transfer is also a possibility. CDI-promoted peptide formation was shown to display... 

The carboxyl groups introduced into wood by Reaction (13) are reactive with epoxy groups. Mastuda et al. 181,82] obtained epoxide-adducted esterified woods by the addition reaction of the carboxyl group-bearing esterified wood meal with epoxides as follows [Reaction (14)] ... 

Blends of polyurethane with [NP(0C6H4C02H)2] have been prepared under conditions which enable reactions of the carboxylic group with the isocyanate group. Loadings of 20 wt% phosphazene or more induce a significant increase in flame resistance.This finding corresponds with the... 

C1 (HJNCH2C00H), which is the fully protonated form of the amino acid. In this form, the molecule contains two acidic functional groups therefore, two equivalents of base are required to completely titrate 1 mol of glycine hydrochloride. There are two pK values pKj due to reaction of the carboxyl group and pKj due to reaction of the ammonium group. Addition of 0.5 eq of base to 1 mol of glycine hydrochloride raises the pH 2.34 (pK,), whereas addition of 1.5 eq further increases the pH to 9.66 (pK ). At low pH values (e.g., 0.4), the molecules are... 

The distinction between these groups can be made by reaction of the carboxylic group with HCl [25]... 

An interesting transformation of various 4-methylnicotinic acids, in which the activated 4-methyl group enters into the reaction of the carboxyl group with thionyl chloride, leads to a l,3-dioxo-l,3-dihydrothienol 3,4-clpyridine74 [Eq. (22)1. 

Amino acids can undergo reactions characteristic of any functional group in the molecule. This includes reactions of the carboxylate group, the amino group, and any other functional groups attached to the R side chain. However, two reactions are of special interest because of their influence in determining protein structure. 

Fatty acids can also act as the hydrophobic component of a surface-active substance by reaction of the carboxylic group with OH- or NH-containing molecules. One example of this is the class of so-called protein fatty acid condensates, which are soft to the skin and are therefore used in cosmetic products. The fatty acid esters or acid chlorides are converted to amides or esters of amino acids or sulfonic acids containing an OH-group. In this way taurates are formed by the reactions of 2-aminoethane sulfonic acid with fatty acids such as lauric, myristic or stearic acid. 

Peptides are short chains of two or more amino acid units linked by the covalent peptide bond, formed by the reaction of the carboxyl group of... 

The long-chain hardener segments are built up by a simple condensation reaction between a moles of a dicarboxylic acid and a-1 moles of a glycol, as shown in Fig. 5. Further reaction of the carboxylic groups with diepoxide groups then produces long-chain, flexible epoxide compounds, which require the use of corresponding hardeners. The best results have been obtained with anhydride hardeners. 

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