Carboxylic acid esters carbonates

Benzaldehyde Carboxylic acid, esters, carbonates PhCHO 158.0 [133]... 

I2 or with a carbon tetrahalide. " Carboxylic acids, esters, and amides have been... 

The first synthetically useful reaction of titanium complexes of type 4, leading to the formation of two new carbon—carbon bonds, was developed by Kulinkovich et al. [55]. They found that treatment of a carboxylic acid ester with a mixture of one equivalent of titanium tetraisopropoxide and an excess of ethylmagnesium bromide at —78 to —40 °C affords 1-alkylcyclopropanols 9 in good to excellent yields (Scheme 11.2) [55,56], This efficient transformation can also be carried out with sub-stoichiometric amounts of Ti(OiPr)4 (5—10 mol%) [57,58]. In this case, an ethereal solution of two equivalents of EtMgBr is added at room temperature to a solution containing the ester and Ti(OiPr)4. Selected examples of this transformation are presented in Table 11.1 (for more examples, see ref. [26a]). 

The chemical diversity of carboxylic acid esters (R-CO-O-R ) originates in both moieties, i.e., the acyl group (R-CO-) and the alkoxy or aryloxy group (-OR7). Thus, the acyl group can be made up of aliphatic or aromatic carboxylic acids, carbamic acids, or carbonic acids, and the -OR7 moiety may be derived from an alcohol, an enol, or a phenol. When a thiol is involved, a thioester R-CO-S-R7 is formed. The model substrates to be discussed in Sect. 7.3 will, thus, be classified according to the chemical nature of the -OR7 (or -SR7) moiety, i.e., the alcohol, phenol, or thiol that is the first product to be released during the hydrolase-catalyzed reaction (see Chapt. 3). Diesters represent substrates of special interest and will be presented separately. 

Apart from aryl esters and amides of carboxylic acids, aryl carbonates, and carbamates, other types of organic compound have been reported to undergo PFR. They include oxalates, formiates, sulfonates, sulfonamides, thioesters, selenoesters, and telluroesters. 

Condensation of the 5-methyl group in (80) (R = Me, Et, Ph, SMe) with aromatic aldehydes leads to 5-styrylthiadiazoles (79). The action of carboxylic acid esters gives ethoxalyl derivatives (81) and that of isoamyl nitrite produces the oxime (82) (Scheme 20) <82AHC(32)285>. These reactions are restricted exclusively to the 5-methyl group in (80) (R = Me), reflecting the greater reactivity of substituents in the 5-position compared to the 3-position in 1,2,4-thiadiazoles. This point is further illustrated when (80) (R = Me) is selectively converted into the carboxylic acid (83) on treatment with n-butyllithium and carbon dioxide (Scheme 20) <84CHEC-I(6)463). 

If a carboxylic acid ester side chain is introduced at the 3-position of a thiazine with a free NH group, lactam formation may occur <1987J(P1)1027>. Compound 78 is a result of lactam formation, and the synthesis of similar compounds is shown in Scheme 44 (Section 8.09.7). Reactions where the nitrogen reacts with a side chain introduced by a nucleophilic attack at the 3-carbon of 277-dihydrothiazines are shown in Schemes 6 and 27. 

In terms of A -substitution, Hartwig reported improved conditions for the Pd(0) catalyzed N-arylation of indoles and pyrrole <99JOC5575>. It was found that when commercially available P(<-Bu)3 was employed as ligand and cesium carbonate as base, the reaction between indoles 95 and unhindered aryl bromides 96 or chlorides occurred under milder conditions than the Pd(OAc)2/DPPF system previously reported yielding the A/-arylated products 97. Alternatively, it has been found that pyrrole- and indole-2-carboxylic acid esters can be selectively 7V-arylated with phenylboronic acids in the presence of cupric acetate and either tiiethylamine or pyridine <99T12757>. 

The root name is based on the longest continuous chain of carbon atoms bearing the carhoxyl group. The -e is replaced by -oic acid. The chain is numbered starting with the carhoxyl carbon atom. The carboxyl group takes priority over any other functional groups as follows carboxylic acid > ester > amide > nitrile > aldehyde > ketone > alcohol > amine > alkene > alkyne. 

A number of other methods exist for the a halogenation of carboxylic acids or their derivatives.134 The acids or their chlorides or anhydrides can be a chlorinated by treatment with CuCl in polar inert solvents (e.g., sulfolane).135 Acyl halides can be a brominated or chlorinated by use of N-bromo- or N-chlorosuccinimide and HBr or HC1.136 The latter is an ionic, not a free-radical halogenation (see 4-2). Direct iodination of carboxylic acids has been achieved with L-Cu(II) acetate in HO Ac.137 Acyl chlorides can be a iodinated with L and a trace of HI.138 Carboxylic esters can be a halogenated by conversion to their enolate ions with lithium N-isopropylcyclohexylamide in THF and treatment of this solution at - 78° with I2138 or with a carbon tetrahalide.139 Carboxylic acids, esters, and amides have been a fluorinated at -78°C with F2 diluted in Ni.,4°... 

Neutral Hydrolysis. We finish our discussion of the major hydrolysis mechanisms of carboxylic acid esters by looking at the neutral (pH independent) reaction at the carbonyl carbon. From the reaction scheme given in Fig. 13.12, we see that, very similar to what we have postulated for the base-catalyzed reaction, the dissociation... 

Solid Peroxygen Compounds. Hydrogen peroxide reacts with many compounds, such as borates, carbonates, pyrophosphates, sulfates, silicates, and a variety of oiganic carboxylic acids, esters, and anhydrides to give peroxy compounds or peroxyhydrates. A number of these compounds are stable solids that hydrolyze readily to give hydrogen peroxide in solution. 

An ester is an organic molecule similar to a carboxylic acid except that in the ester the hydroxyl hydrogen is replaced by a carbon. Unlike carboxylic acids, esters are not acidic because they lack the hydrogen of the hydroxyl group. Like aldehydes, many simple esters have notable fragrances and are used as flavorings. Some familiar ones are listed in Table 12.4. 

Lithium aluminum hydride usually reduces carbonyl groups without affecting carbon-carbon double bonds. It is, in addition, a good reducing agent for carbonyl groups of carboxylic acids, esters, and other acid derivatives, as will be described in Chapter 18. 

Confirmatory test for carboxylic acids. Ester formation. Warm a small amount of the acid with 2 parts of absolute ethanol and 1 part of concentrated sulphuric acid for 2 minutes. Cool, and pour cautiously into aqueous sodium carbonate solution contained in an evaporating dish, and smell immediately. An acid usually yields a sweet, fruity smell of an ester. (Acids of high molecular weight often give almost odourless esters, however.)... 

The first term, representing acid-"catalyzed" hydrolysis, is important in reactions of carboxylic acid esters but is relatively unimportant in loss of phosphate triesters and is totally absent for the halogenated alkanes and alkenes. Alkaline hydrolysis, the mechanism indicated by the third term in Equation (2), dominates degradation of pentachloroethane and 1,1,2,2-tetrachloroethane, even at pH 7. Carbon tetrachloride, TCA, 2,2-dichloropropane, and other "gem" haloalkanes hydrolyze only by the neutral mechanism (Fells and Molewyn-Hughes, 1958 Molewyn-Hughes, 1953). Monohaloalkanes show alkaline hydrolysis only in basic solutions as concentrated as 0.01-1.0 molar OH- (Mabey and Mill, 1978). In fact, the terms in Equation(2) can be even more complex both elimination and substitution pathways can operate, leading to different products, and a true unimolecular process can result from initial bond breaking in the reactant molecule. 

Log of the alkaline hydrolysis rate constant vs. difference in carbon-oxygen stretching frequency for 12 carboxylic acid esters. 

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