Carboxylic acids unsaturated, esterification

Other Condensation Reactions. BF3-MeOH and BF3 OEt2 with ethanol are widely used in the esterification of various kinds of aliphatic, aromatic, and carhoxyhc acids the reaction is mild, and no rearrangement of double bonds occurs. This esterification is used routinely for stable acids prior to GLC analysis. Heterocyclic carboxylic acids, unsaturated organic acids, biphenyl-4,4 -dicarboxylic acid, 4-aminobenzoic acid, and the very sensitive 1,4-dihydrobenzoic acid are esterified directly. 

In studies directed towards the synthesis of pseurotin A, the unsaturated acetal 3 has been used as a common starting material to prepare two different C-2-branched intermediates. In one route, 3 was 0-benzylated, the aldehyde im-masked with hydrochloric acid and oxidized to its carboxylic acid derivative. Esterification, dihydroxylation of the alkene then dimethylsulfoxide-thionyl chloride oxidation, addition of ethylmagnesium chloride and removal of the isopropylidene group gave compounds 4. In an alternative route, 3 was first epoxidized then treated sequentially with hydroxide, benzyl bromide-base and hydrochloric acid to give compounds 5. ... 

Schemes are available, however, that start from the free carboxylic acid, plus an activator . Dicyclohexylcarbodiimide, DCC, has been extensively employed as a promoter in esterification reactions, and in protein chemistry for peptide bond formation [187]. Although the reagent is toxic, and a stoichiometric concentration or more is necessary, this procedure is very useful, especially when a new derivative is targeted. The reaction usually proceeds at room temperature, is not subject to steric hindrance, and the conditions are mild, so that several types of functional groups can be employed, including acid-sensitive unsaturated acyl groups. In combination with 4-pyrrolidinonepyridine, this reagent has been employed for the preparation of long-chain fatty esters of cellulose from carboxylic acids, as depicted in Fig. 5 [166,185,188] ...

Unsaturated polyesters are prepared through a classical esterification process. Typically, a dihydroxy compound, or mixtures of dihydroxy compounds, are treated with maleic anhydride and/or together with other dicarboxylic acids such as aromatic or aliphatic dicarboxylic acids under elevated temperature to remove the water produced during esterification process. Although various catalysts will catalyze this esterification reaction, there is enough carboxylic acid in the mixture so that it is not necessary to add extra catalyst. 

Nakagami, T. (1978). Esterification of wood with unsaturated carboxylic acids. V. Effect of deUg-nification treatments on dissolution of wood esterified by the TEAA method. Mokuzai Gakkaishi, 24(5), 318-323. 

Schreiber and co-workers (436) prepared a library calculated to contain 2.18 million polycyclic compounds through the 1,3-dipolar cycloaddition of a number of nitrones with alkenes supported on TentaGel S NH2 resin (Scheme 1.83). (—)-Shikimic acid was converted into the polymer bound epoxycyclohexenol carboxylic acid 376 (or its enantiomer), coupled to the resin via a photolabile linker developed by Geysen and co-workers (437) to allow release of the products from the resin in the presence of live cells by ultraviolet (UV)-irradiation. A range of iodoaromatic nitrones (377) was then reacted with the ot,p-unsaturation of the polymer-bound amide in the presence of an organotin catalyst, using the tandem esterification/ dipolar cycloaddition methodology developed by Tamura et al. (84,85) Simultaneous cyclization by PyBrop-mediated condensation of the acid with the alcohol... 

Esters are most commonly prepared by the reaction of a carboxylic acid and an alcohol with the elimination of water. Esters are also formed by a number of other reactions utilizing acid anhydrides, acid chlorides, amides, nitriles, unsaturated hydrocarbons, ethers, aldehydes, ketones, alcohols, and esters (via ester interchange). Detailed reviews of esterification are given in References 1—9. 

Hydrogels prepared via homogeneous esterification of dextran with unsaturated carboxylic acids are advanced polysaccharide-based products useful for drug delivery systems and protective encapsulants, e.g. of viruses used in gene therapy [173]. Very promising in this regard is the dextran maleic acid monoester [174], which can be obtained by conversion of dextran in DMF/LiCl with the maleic anhydride in the presence of TEA. The DS of the products can be easily controlled with the amount of anhydride applied but... 

T. Nakagami, H. Amimoto, and T. Yokota, Esterification of wood with unsaturated carboxylic acids. I. Bull. Kyoto Univ. Forest 46 217-224 (1974). 

Kinetic Resolution by Direct Esterification. This is the least common strategy for kinetic resolution and is most commonly executed on racemic alcohols with carboxylic acids in organic solvents. Reports include several alicyclic secondary alcohols such as menthol and various aliphatic secondary alcohols. Kinetic resolution of a variety of racemic saturated, unsaturated, and a-substituted carboxylic acids has also been effected by direct esterification with various alcohols. ... 

Esterification. Boron thfluoride etherale in combination with a large excess of an alcohol is an elTeclive reagent for the esterification of 4-aminobenzoic acid. The combination is particularly useful for esterification of unsaturated carboxylic acids. The boron trifluoridc etherate alcohol reaction is particularly useful for esterification of heterocyclic carboxylic adds. ... 

Catalytic hydrocarboxylations and related esterifications as well as amidations of alkenes belong to a family of carbonylation reactions which has attracted considerable industrial interest. Minor changes in the catalyst system as well as in reaction conditions can lead to simple carboxylic acids, diacids, polyketones, or unsaturated acids as products (Scheme 1). Most importantly, these methods provide routes to monocarboxylic acids, e.g., ethylene to propanoic acid (see Section 2.1.2.2), or 1-olefins (readily available from the oligomerization of ethylene discussed in Section 2.3.1.3) to higher carboxylic acids. 

Fatty acids are saturated and unsaturated carboxylic acids containing between twelve and twenty-four carbon atoms. Fatty acids with even numbers of carbon atoms occur most frequently in nature. The reactions of fatty acids are identical to those of carboxylic acids. They include esterification, production by acid hydrolysis of esters, saponification, and addition at the double bond. Prostaglandins, thromboxanes, and leukotrienes are derivatives of twenty-carbon fatty acids that have a variety of physiological effects. 

Menthol [(—)-l] has been used as a chiral ligand for aluminum in Lewis acid catalyzed Diels-Alder reactions with surprising success2 (Section D.l.6.1.1.1.2.2.1). The major part of its application is as a chiral auxiliary, by the formation of esters or ethers. Esters with carboxylic acids may be formed by any convenient esterification technique. Esters with saturated carboxylic acids have been used for the formation of enolates by deprotonation and subsequent addition or alkylation reactions (Sections D.l.1.1.3.1. and D.l.5.2.3.), and with unsaturated acids as chiral dienes or dienophiles in Diels-Alder reactions (Section D. 1.6.1.1.1.), as chiral dipolarophiles in 1,3-dipolar cycloadditions (Section D.l.6.1.2.1.), as chiral partners in /(-lactam formation by [2 + 2] cycloaddition with chlorosulfonyl isocyanate (SectionD.l.6.1.3.), as sources for chiral alkenes in cyclopropanations (Section D.l.6.1.5.). and in the synthesis of chiral allenes (Section B.I.). Several esters have also been prepared by indirect techniques, e.g.,... 

Although the combined additive phosphonylation and esterification of an a,j5-unsatu-rated carboxylic acid by a trialkyl phosphite can thus easily, although not necessarily accurately, be envisaged, that of a similarly unsaturated ester, nitrile, or amide is perhaps not so readily apparent. Harvey showed that successful reaction between triethyl phosphite and such a substrate (Scheme 43) occurs in a protic medium. In this respect, the reactions proceed faster in methanol than in ethanol, but reactions are, in general, (including those of structurally analogous unsaturated ketones) much cleaner and faster when carried out in phenol, and also afford much higher yields in this solvent. It has also been shown that ammonium salts will also act as a proton source to allow completion of addition without alkylation. The later Russian workers used acetic acid with successful results ... 

The rates of the esterification and hydrolysis are much faster than that of condensation reaction. To increase the amount of esters in the product with respect to that of acid, the reaction is usually performed in the presence of a large excess of methanol with respect to the amount of HCHO. Naturally, unsaturated esters can also be obtained by the reaction of HCHO with carboxylic acids in the presence of methanol. 

The esterification of cyclic olefins with carboxylic acids, such as dicyclopentadiene or naturally occurring terpenes, yields compounds of industrial value. For instance, the esterification of dicyclopentadiene with saturated carboxylic acids, such as acetic acid, leads to a starting material for the flavour and fragrance industry, as well as the resulting alcohols in consecutive hydrolysis. By using unsaturated carboxylic acids as nucleophiles, the resulting esters are also useful compounds in the manufacture of binders for polymer concrete (Scheme 1). ... 

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