Esters, carboxylic acid physical properties

Table 1.13, on the next page, describes some of the physical properties of esters. As you will see, esters have different physical properties than carboxylic acids, even though esters and carboxylic acids are isomers of each other. 

To overcome these drawbacks, in recent years much attention has been paid to the development of resins which cem be f2d ricated with the same processes as those for conventional polyester resins, but having superior properties. Vinyl ester resins are the result of such development efforts (4-6). Vinyl ester resins are addition products of Vcurious epoxide resins and ethylenically unsaturated mono-carboxylic acids ( ). It condsines the excellent mechcuiical, chemical cuid solvent resistemce of epoxy resins with the properties found in the unsaturated polyester resins. In general, the cured vinyl ester resin has physical properties superior to the cured conventional ester resin, particulcurly corrosion resistcuice. This arises from the differences in the number and arremgement of polar groups such as ester and hydroxyl groups eind ccurbon-to-ccirbon double bonds present in the polymer chains. 

Esters are usually prepared by esterification of carboxylic acids with alcohols. Industrial procedures depend on the physical properties of the esters concerned. Biosynthetic methods may be applied to produce natural esters for flavor purposes [24]. 

The physical properties of cyanoacetic acid [372-09-8] and two of its ester derivatives are listed in Table 11 (82). The parent acid is a strong organic acid with a dissociation constant at 25°C of 3.36 x 103. It is prepared by the reaction of chloroacetic acid with sodium cyanide. It is hygroscopic and highly soluble in alcohols and diethyl ether but insoluble in both aromatic and aliphatic hydrocarbons. It undergoes typical nitrile and acid reactions but the presence of the nitrile and the carboxylic acid on the same carbon cause the hydrogens on C-2 to be readily replaced. The resulting malonic acid derivative decarboxylates to a substituted acrylonitrile ... 

The solubilizing capacity of the choline residue is so pronounced that even substrates combining two hydrophobic amino acids are homogeneously soluble in aqueous buffer without any additional cosolvent. These favorable physical properties were also used in the enzymatic formation of peptide bonds. The amino acid choline ester 38 acts as the carboxyl component in kinetically controlled peptide syntheses with the amino acid amides 39 and 40 [52] (Fig. 11). The fully protected peptides 41 and 42 were built up by means of chymotrypsin in good yields. Other proteases like papain accept choline esters as substrates also, and even butyrylcholine esterase itself is able to generate peptides from these electrophiles. 

Wiley, New York. Each volume deals with the preparation, reactions, and physical and chemical properties of compounds containing a given functional group. Volumes covering >20 functional groups have appeared so far, including books on alkenes, cyano compounds, amines, carboxylic acids and esters, and quinones. 

Once characterized as a carboxylic acid, an unknown is identified as a particular acid on the usual basis of its physical properties and the physical properties of derivatives. The derivatives commonly used are amides (Secs. 20.11 and 23.6) and esters (Sec. 20.15). 

In keeping with this method, several approaches have been developed to document methods and dose-response relationships for irritation in humans. This work suggests that, at least for nonreactive compounds such esters, aldehydes, ketones, alcohols, carboxylic acids, aromatic hydrocarbons, and pyridine, the percentage of vapor pressure saturation of a compound is a reasonable predictor of its irritant potency. Specific physical properties of molecules predict overall irritation potential. This work is based on the identification of irritant thresholds for homologous series of specific agents. Quantitative structure-activity relationships derived from such work suggests a reasonable model to explain mucosal irritation. 

Table 1 Physical properties of selected mercapto carboxylic acids, esters, and derivatives... 

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