Esters and carboxyl acids

Alcohols are among the most versatile of all organic compounds. They occur widely in nature, are important industrial 7, and have an unusually rich chemistry. The most widely used methods of alcohol synthesis start with carbonyl compounds. Aldehydes, ketones, esters, and carboxylic acids are reduced by reaction with LiAlH4. Aldehydes, esters, and carboxylic acids yield primary alcohols (RCH2OH) on reduction ketones yield secondary alcohols (R2CHOH). 

D. Miller, A. Vollmer, M. Feustel, and P. Klug. Synergistic mixtures of phosphoric acid esters and carboxylic acid derivatives as asphaltene dispersants (Synergistische Mischungen von Phosphorsaureestem mit Carbonsaurederivaten als Asphalten-Dispergatoren). Patent EP 967361, 1999. 

The palladium-catalyzed Heck carbonylation reaction is a powerful means of generating amides, esters, and carboxylic acids from aryl halides or pseudohalides [28]. The development of rapid, reliable, and convenient procedures for the introduction of carbonyl groups is important for the development of high throughput chemistry in general and high-speed microwave-mediated chemistry in particular. Unfortunately, the traditional method of introducing carbon monoxide into a reaction mixture via a balloon or gas tube is not practical because of the special requirements of microwave synthesis. 

Table 21.6 Diastereoselective hydrogenation of double bond in cyclic esters and carboxylic acids. 

Aromatic halides react with crown ether-complexed K02 by an electron-transfer mechanism and not by nucleophilic attack, as was shown by Frimer and Rosenthal (1976) using esr spectroscopy. The corresponding phenol is the main reaction product (Yamaguchi and Van der Plas, 1977). Esters are saponified by the K02/18-crown-6 complex in benzene, presumably by an addition-elimination pathway (San Fillippo et al., 1976). The same complex has been used to cleave cr-keto-, or-hydroxy-, and or-halo-ketones, -esters, and -carboxylic acids into the corresponding carboxylic acids in synthetically useful quantities (San Fillippo et al., 1976). 

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. 

Current interest in synthetic fuels production by Fischer-Tropsch (FT) reactions have created a need for removal of byproduct oxygenates, formed by the FT reaction. The oxygenates consist of primary and internal alcohols, aldehydes, ketones, esters and carboxylic acids. The hydrocarbon products derived from the FT reaction range from methane to high molecular weight paraffin waxes containing more than 50 carbon atoms. 

OXYGEN AND SULFUR AS NUCLEOPHILES ESTERS AND CARBOXYLIC ACIDS... 

Selection of appropriate hydroxamic esters and carboxylic acid salts has enabled synthesis of a wide range of A-acyloxy-Af-alkoxyamides in which and can be alkyl or aryl but, to date, only aUcoxyl or arylalkoxyl groups have been present at R". ... 

Monometallic ruthenium, bimetallic cobalt-ruthenium and rhodium-ruthenium catalysts coupled with iodide promoters have been recognized as the most active and selective systems for the hydrogenation steps of homologation processes (carbonylation + hydrogenation) of oxygenated substrates alcohols, ethers, esters and carboxylic acids (1,2). 

As described above and shown in Table XIV, the identity of the solvent may have significant effects on the rate of CO reduction. Alcohols, esters, and carboxylic acids appear to provide the highest rates, whereas THF and sulfolane are somewhat less effective. Heptane solvent has been reported to afford poor rates of CO reduction by this system (163). Differences in rates among these solvents appear small enough to be attributable to an effect such as the enhanced stabilization of a polar transition state by the more polar solvents. The presence of certain additives, such as boric acid and aluminum alkoxides, has also been found to increase the rate of CO reduction, perhaps for similar reasons (168). 

Sodium borohydride is the more selective and milder reagent of the two. It cannot reduce esters or carboxylic acids, whereas LiALH4 reduces esters and carboxylic acids to 1° alcohols (see Sections 5.7.20 and 5.7.22). These... 

The extremely stable and general sp conformation of esters and carboxylic acids (3a) is one of the remarkable features of stereochemistry. It was observed uniformly2 in all other molecules with the group O—C=0 and also with their heteroatom analogues with S, Se or Te. In contrast with the rigid conformation, the conjugation in the ester molecule, expressed by the formulas 69, is relatively weak and can be just detected in the dipole moment values164. 

Many functional groups can co-ordinate to the metal of a hydrogenation catalyst, thereby playing an important part in the directing of diastereoselective reductions of proximal double bonds61. Particularly effective groups in this respect are alcohols, amides, ester and carboxylic acids. Many of these processes have been studied in great detail. 

Palladium-catalyzed carbonylation reactions with aryl halides are powerful methods of generating aromatic amides, hydrazides, esters and carboxylic acids [25]. We have previously reported the exploitation of Mo(CO)6 as a robust carbon monoxide-releasing reagent in palladium-catalyzed carbonylation reactions [26-29]. This stable and inexpensive solid delivers a fixed amount of carbon monoxide upon heating or by the addition of a competing molybdenum coordinating ligand (for example DBU). This allows for direct liberation of carbon monoxide in the reaction mixture without the need for external devices. 

The reactions of ethanol, ethyl acetate, and acetic acid in the presence of hydrogen on silica-supported copper were chosen to illustrate kinetic analyses of reaction schemes leading to multiple reaction products. Copper-containing catalysts are extremely important for the reduction of oxygenated compounds, such as alcohols, esters, and carboxylic acids. Such materials... 

Copper atoms in these catalysts may be distributed between bulk metallic particles and oxide patches associated with the silica support. However, as mentioned previously, spectroscopic evidence suggests that little if any oxidized copper is present on a 5 wt% Cu/Si02 catalyst reduced at 573 K. Furthermore, the reduction of esters and carboxylic acids is believed to occur predominantly on metallic copper (74). Accordingly, the conjecture of these analyses is that the reaction occurs on metallic copper. 

Carboxylic amides, carboxylic esters, and carboxylic acids react with acid-stable heteroatom nucleophiles in a neutral solution much more slowly via the mechanism of Figure 6.2 than in an acidic solution via the mechanism of Figure 6.5. In an acidic solution, their car-boxonium ion derivatives, which result from the reversible protonation of the carboxyl oxygen, act as precursors of the tetrahedral intermediate. According to the discussion earlier in... 

Primary, secondary, and tertiary carboxylic amides, carboxylic esters, and carboxylic acids are protonated by mineral acids or sulfonic acids at the carboxyl oxygen to a small extent (Figure 6.9). This corresponds to the activation discussed in Section 6.2.3. This activation is used in acid hydrolyses of amides and esters, in esterifications of carboxylic acids and in Friedel-Crafts acylations of aromatic compounds with carboxylic acids. 

Antimony(m) ethoxide (Sb(OEt)3) promotes the intermolecular amidation of esters and carboxylic acids with amines under azeotropic conditions.47,48 When tetramino esters are used, the antimony(in)-templated intramolecular macrolactamization provides macrocyclic spermine alkaloids in good yields (Equation (14)). Under the same... 

This reaction would therefore produce a roughly 50 50 mixture of ester and carboxylic acid if this were the whole story. But it isn t because the carboxylic acid will be deprotonated in the basic solution adding a third equilibrium. 

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