Properties of Esters

Second-order rate constants have been determined for the alkaline hydrolysis of 2-methoxycarbonylpyrazine in methanol-water (80%w/w) at 10° as 5.2x10 l/mol sec (1263) and for 2-ethoxycarbonylpyrazine at 30° in 50 and 60% dimethyl sulfoxide-water and 60, 70, and 80% ethanol-water as 95.9, 199, 12.4, 10.2, and 8.86x10 1/mol sec (1359). The failure of 2,5-dimethoxycarbonyl-pyrazine to undergo the Schmidt reaction has been accounted for in terms of its normal ionization, and I values in 100% sulfuric acid gave an average of 2.55 (1176). 

Some tetraalkoxycarbonylpyrazines have good heat stability and are claimed to be useful as lubricants and plasticizers (1321). 

All phosphate esters are subject to hydrolysis (5.340) - a fact of great importance in biological systems. Most biological hydrolyses are enzyme-catalysed (Chapter 11). 

Neutral triesters of the type (RO)3PO, where R is simple alkyl or aryl, are very similar to esters of organic acids in that they can usually be distilled at reduced pressure without much decomposition, and they are non-ionic and soluble in a large number of organic solvents. The lower alkyl derivatives are liquids (Table 5.26). When all groups R are different, the molecule is asymmetric and optical isomers are possible (13.2). 

Although these esters are stable at room temperature, some decomposition will occur if kept at say 15°C for 24 h. This thermal decomposition is acid-catalysed for alkyl derivatives, and proceeds by splitting off an unsaturated hydrocarbon, indicating that 0-C is the weakest link at raised temperatures (5.341). Such a process cannot take place with triaryl derivatives which are decomposed 

Salts of long-chain monoesters of type (5.342a) have surfactant properties (Chapter 12.5). Diesters of type (5.342b) have also been prepared [18]. 

When all three groups on the P atom are different, the molecule is asymmetric and optical isomers are possible (Chapter 13.2). 

---

The reactions of esters have been reviewed (11—15). Because of the large number of possible acid and alcohol moieties, the chemical properties of esters may differ considerably. Only typical reactions appHcable to the majority of esters are described in the following sections. 

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. 

Table V. Lithographic Properties of Ester Derivatives of Methacrylate — Based Electron Resists... 

Properties of esters Properties commonly associated with esters include ... 

Although metal ynoiates are equivalents of metallated ketenes, direct metallation of ketenes is often troublesome. Metallation of the precursors of ketenes, followed by transformation into the metallated ketenes, would be a better route to metal ynoiates. Based on this concept, an efficient method for the synthesis of lithium ynoiates has been developed, taking advantage of the properties of ester enoiates, which are easily converted into ketenes by elimination of alkoxides (equation 11) . The synthetic methods for lithium ynoiates via the cleavage of ester dianions are both convenient and quite general, because alkyl-, aryl- and sQyl-substimted lithium ynoiates can be synthesized in good yields. 

Summary of physical properties of esters and phthalate esters... 

Gramatica, P., Battaini, F. and Papa, F. (2004) QSAR prediction of physico-chemical properties of esters. Fresen. Environ. Bull., 13, 1258—1262. 

---