Esterification aromatic acids

Reaction with Organic Compounds. Many organic reactions are catalyzed by acids such as HCl. Typical examples of the use of HCl in these processes include conversion of HgnoceUulose to hexose and pentose, sucrose to inverted sugar, esterification of aromatic acids, transformation of acetaminochlorobenzene to chloroaruHdes, and inversion of methone [1074-95-9]. 

As a dibasic acid, malic acid forms the usual salts, esters, amides, and acyl chlorides. Monoesters can be prepared easily by refluxing malic acid, an alcohol, and boron trifluoride as a catalyst (9). With polyhydric alcohols and polycarboxyUc aromatic acids, malic acid yields alkyd polyester resins (10) (see Alcohols, polyhydric Alkyd resins). Complete esterification results from the reaction of the diester of maUc acid with an acid chloride, eg, acetyl or stearoyl chloride (11). 

Esterification of certain aromatic acids with p-aminoethanol and propanol derivatives frequently results in molecules that show local anesthetic... 

Although the ability of microwaves (MW) to heat water and other polar materials has been known for half a century or more, it was not until 1986 that two groups of researchers independently reported the application of MW heating to organic synthesis. Gedye et al. [1] found that several organic reactions in polar solvents could be performed rapidly and conveniently in closed Teflon vessels in a domestic MW oven. These reactions included the hydrolysis of amides and esters to carboxylic acids, esterification of carboxylic acids with alcohols, oxidation of alkyl benzenes to aromatic carboxylic acids and the conversion of alkyl halides to ethers. 

A few heterocyclic aromatic acids such as nicotinic acid and regioisom-ers have also been examined as pro-moieties for esterification of OH func-... 

It is apparent that the mode of reaction of the hyperbranched polyesteramides must be distinctively different from those of the known commercial crosslinkers. In order to explain these results, the hyperbranched polyesteramides should in our view not be regarded as simply multifunctional polymeric crosslinkers but rather as precondensed forms of two-functional crosslinkers (the addition product of diisopropanolamine and the cyclic anhydride), as depicted in Fig. 22, left. Bearing in mind the chemical fate of benzoic acid (2.2.1, Fig. 11) which was condensed with a polyesteramide resin and which appeared to transesterify at least as fast as it esterified, the mode of reaction of polyesters comprising aromatic acid end groups must be in accordance and comprised of both transesterification and esterification. 

It is known from the literature [12] that aliphatic acids are less reactive towards 2-hydroxyalkylamide groups than aromatic ones. Since the final network formation with the polyesteramides involves predominantly aliphatic acid groups, this could explain (in part) why the gel times found were longer than the commercial 2-hydroxyalkylamide crosslinkers, which react directly by esterification alone with the aromatic acid end groups of the polyester. 

The present procedure4 is an especially effective method for the synthesis of esters of aromatic acids and hindered tertiary alcohols or of acid-labile alcohols such as 2,2-diphenylethanol. The yields are excellent, and the reaction procedure is simple. The method is illustrated by the preparation of /-butyl p-toluate, a compound that could not be prepared by a conventional method0 of esterification involving the acid chloride and /-butanol in the presence of dimothylaniline. Examples of esters prepared by this method are illustrated in Table I. 

Substituents in the ortho positions of aromatic acids generally retard esterification. Such sterically hindered acids may be esterified by dissolving in 100% sulfuric acid and pouring the solutions into the desired alcohol. This reaction is limited to those acids which dissociate in sulfuric acid to give a positive acyl ion, RCO (cf. method 314). 

As was mentioned earlier, esterification using aromatic acid chlorides, ArCOCl, is often carried out in the presence of base (the Schotten-Baumann technique, Sec. 20.8). 

TMSCl, MeOH, 2,2-dimethoxypropane, rt, 95-99% yield. As with the above case, aromatic acids are not esterified by this method which generates HCl in situ In general, it is more difficult to prepare aromatic esters by acid catalyzed esterification than aliphatic esters because aromatic acids are not as easily protonated. BCI3 in MeOH has been used to prepare methyl esters and this combination of reagents also produces HCl. ... 

Lupane triterpenes are very common in the Celastraceae family. Esters of lupane triterpenes with aromatic acids have been isolated from others sources but in Celastraceae 0-caffeoyl esters are the most frequently found. C-3 position is the most common compromised with esterification and the stereochemistry of the ester moiety is usually p. 

The anomalies of ortho compounds are not restricted to their acidic strengths, but are found in all kinds of comparisons of the properties of related compounds. One of the first anomalies to be observed was the slower esterification of ortho substituted benzoic acids than of the corresponding meta and para acids This was attributed to the possibility of the physical interference of ortho groups, and was called steric hindrance. Fliirscheim, who early noted the anomalous strengths of ortho substituted aromatic acids, attributed the phenomenon to steric hindrance. He supposed that the ortho group... 

BE3 -OEt2 easy-to-handle and convenient source of BF3 Lewis acid catalyst promotes epoxide cleavage and rearrangement, control of stereoselectivity BF3 MeOH esterification of aliphatic and aromatic acids cleavage of trityl ethers)... 

Aromatic acid has serious steric hindrance. If there are both ortho-methyls, just as 2.46-trimethyl benzoic acid, the alcohol molecule is so difficult to access to carboxyl that the esterification cannot occur. However, if 2.4.6- trimethyl benzoic add is dissolved in the 100% sulfuric-acid solution, acylilum ion will be formed as shown in Figure 5. Then the added alcohol with the acylilum ion produced ester. The reaction will conduct smoothly (Streitwieser et al., 1985). 

Hydrogenation of quinuclidon-3, or of its derivatives, to the corresponding alcohols followed by esterification gave 3-hydroxyquinuclidine esters with ahphatic, arylaliphatic and aromatic acids of great pharmacological interest [74, 79, 80, 106, 107]. 

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