Formation of Carboxylic Acid Esters

Carbohydrates are polyhydroxy aldehydes or ketones. Therefore, one of their primary chemical properties is that of a polyalcohol. It is natural then that one of the first types of derivatives to be formed was esters. The formation of a completely acetylated carbohydrate can be obtained by the reaction with acetic anhydride in the presence of either a basic or an acidic catalyst. When reducing carbohydrates react with acetic anhydride in the presence of sodium acetate at 4°C, the (3-anomer is favored (reactions 4.1 and 4.2). 

Nonreducing carbohydrates react to give acetylation of all of the hydroxyl groups as shown by the acetylation of sucrose (reaction 4.3). 

Starting with a mixture of a- and P-D-glucose, reaction in acetic anhydride with an acid catalyst, such as zinc chloride, at 24°C favors the formation of a-D-glucose pentaacetate (reaction 4.6). 

Another common carbohydrate ester is benzoylate that is formed when benzoyl chloride is added to a pyridine solution of the carbohydrate (reaction 4.7). 

The formation of acetate or benzoate esters produces crystalline carbohydrate derivatives that were much sought by the organic chemists of the late nineteenth century. Because of their facile formation and easy removal under basic conditions (see discussion later), acetate and benzoate esters can be used to protect carbohydrate alcohol groups from undergoing reaction in synthetic procedures. Furthermore, the acetate derivatives are often volatile, especially the alditol acetates, permitting their use in gas chromatographic analyses of carbohydrates. 

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Sulfuric acid can form ester derivatives with alcohols, though since it is a dibasic acid (pAla — 3, 2) it can form both mono- and di-esters. Thus, acid-catalysed reaction of methanol with sulfuric acid gives initially methyl hydrogen sulfate, and with a second mole of alcohol the diester dimethyl sulfate. Though not shown here, the mechanism will be analogous to the acid-catalysed formation of carboxylic acid esters (see Section 7.9). 

Addition of halogen fluorosulfates XOS02F (X=C1, Br, I) to fluoroolefins is considered an electrophilic reaction [8]. However, the question of whether this process is concerted or the reaction proceeds via an independent carbocationic intermediate (Eqs. 2 and 3) is still open. Formation of carboxylic acid esters as byproducts in the reaction of HFP with C10S02F, which was carried out in trifluoroacetic or heptafluorobutyric acids as solvents, could not be a solid proof of conjugate addition, since formation of esters may be a result of addition of C10C(0)Rf to olefin. These materials are known to be formed in the reaction of ClOS02F with fluorinated carboxylic acids, even at low temperature [99]. 

Reaction with diazoalkanes. Catalytic amounts of nickel carbonyl decompose diazoalkanes to products evidently formed from an intermediate carbene. Use of a large excess of reagent in the presence of ethanol leads to formation of carboxylic acid esters in yields of 20-25%. 

NMR spectroscopy has proved to be a powerful technique to quantify the formation of carboxylic acid esters and sulfonate esters to polymer-... 

It should be emphasized that the reaction scheme of Eq. (49) is unlikely if hydroperoxides are distributed homogeneously over the whole sample. Owing to restricted mobility below Tm, the oxidation products carmot diffuse away. Locally, hydroperoxides can reach sufficiently high concentrations for secondary reactions to occur at a significant rate. In a similar fashion, the formation of carboxylic acids, esters and y-lactones proceeds through a complex series of oxidation reactions of alcohols and ketones. 

Formation of carboxylic acids ami their derivatives. Aryl and alkenyl halides undergo Pd-catalyzed carbonylation under mild conditions, offering useful synthetic methods for carbonyl compounds. The facile CO insertion into aryl- or alkenylpalladium complexes, followed by the nucleophilic attack of alcohol or water affords esters or carboxylic acids. Aromatic and a,/ -unsaturated carboxylic acids or esters are prepared by the carbonylation of aryl and alkenyl halides in water or alcohols[30l-305]. 

HNO3 leading to the formation of carboxyl acids, nitric acid ester, and nitro and nitroso compounds. Rate parameters for chemical degradation under different conditions have been investigated [106,107], The reaction of -dodecane with HNO3 is quite slow. 

The carbonylation of alcohols can proceed with formation of carboxylic acid by catalytic insertion of CO into the carbon-oxygen bond. An alternative reaction gives rise to oxalate or formate esters, when the CO is inserted into the oxygen-hydrogen bond. The members of the nickel triad carbonylate alcohols to give each of these products, and they will be discussed separately. 

Hundreds of impressive examples of enantioselective lipase-catalysed reactions are known, including industrial processes as in the case of the BASF method of chiral amine production (Collins et al. 1997 Breuer et al. 2004 Schmid and Verger 1998). However, the classical problem of substrate acceptance or lack of enantioselectivity (or both) persists. We were able to meet this challenge in model studies regarding the hydrolytic kinetic resolution of the ester rac-1 with formation of carboxylic acid 2, catalysed by the lipase from Pseudomonas aeruginosa. The wild-type (WT) lipase is only slightly (S )-selective, the selectivity factor amounting to a mere E = 1.1 (Scheme 1). 

Adducts (6) and (7) from amides and chlorophosphoric acid aiyl esters or dichlorophosphoric acid aryl esters respectively are well known. - The adducts are formed in a 1 1 ratio. They have been applied to the synthesis of mixed anhydrides from diarylphosphoric acids and carboxylic acids, as well as mixed substituted esters of pyrophosphoric acid. The adduct formation between primary or secondary carboxamides and dichlorophosphates has been used to prepare nitriles and isonitriles respectively. The adduct from DMF and phenyldichlorophosphate is a useful reagent for the preparation of carboxylic acid esters from the corresponding acids and alcohols, 3-lactams from imines and carboxylic acids," carboxylic acid anhydrides, carboxylic acid esters and thiol esters. Adducts of amides with ester amides or diamides of chlorophosphoric acid have been studied. ... 

The first step is the formation of H-bonded intermediate 49, in which Ccarbene takes on substantial cationic character. Next, termolecular attack by the amine in the presence of Y provides tetrahedral intermediate 50, which then breaks down into products. The reaction is sensitive to steric hindrance, with ammonia and primary amines reacting rapidly (several orders of magnitude faster than aminolysis of carboxylic acid esters) and secondary amines reacting much more sluggishly. The actual kinetic order associated with the amine is also a function of the solvent. Aprotic solvents such as hexane require a rate law with a third-order contribution from the amine pro tic solvents such as methanol show a mixed first- and second-order contribution from the amine. 

Formation of Carboxylic Acid Derivatives 28-7 Hydrolysis of Esters... 

Acylphosphonic acids (1-oxoalkylphosphonic acids) and their dialkyl esters undergo acid-catalyzed fission with the formation of carboxylic acids (or their alkyl esters) using a suiphonic acid as the catalyst the formation of an alkyl carboxylace is accompanied by that of an alkyl sulphonate. The reaction may be visualized as occurring through protonation on the carbonyl oxygen and migration of an alkoxy group from phosphorus... 

Esterification of amino acids is a difficult reaction because amino acids exist as zwitterions (dipolar ions) and carboxyl group is not a free group (but an anion). Since the esterification reaction is an equilibriiun process, factors that shift the reaction toward the products will benefit the formation of amino acid ester. 

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