Carboxylic acids, esterification

FIGURE 15.3 PLC separation of carboxylic acids from soluble organic matter with the use of carboxylic acids esterification based on experimental data given in Reference 36, Reference 67 to Reference 69, and Reference 102 to Reference 104. 

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. 

Cobalt catalysts completely dominated industrial hydroformylation rmtil the early 1970s, when rhodium catalysts were commercialized. Most aldehydes produced are hydrogenated to alcohols or oxidized to carboxylic acids. Esterification of the alcohols with phthalic anhydride produces dialkyl phtha-late plasticizers that are primarily used for polyvinyl chloride plastics - the largest single end-use. Detergents and surfactants make up the next largest category, followed by solvents, lubricants, and chemical intermediates. 

Alvaro, M., Corma, A., Das, D., Fomes, V., and Garda, H. 2005. "Nafion"-functionalized mesoporous MCM-41 silica shows high activity and selectivity for carboxylic acid esterification and Friedel-Crafts acylation reactions. 7. Catal. 231 48-55. 

The 8-parameter was used with good results in structure-activity correlations for modeling the acid-catalyzed carboxylic acid esterification and ester hydrolysis, and bimolecular substitution reactions (Chiriac et al. 1996). 

Synthesis of Esters from Carboxylic Acids, Esterification (eq 1) proceeds by activation of the carboxyl component using a 2-halopyridinium salt (2 X = Cl, Y = I or X = F, Y = OTs) and (1) (2,4 equiv) in the presence of an alcohol. The best solvents for this process are CH2CI2 or MeCN, but a range of other solvents may also be used. 

List [86] and Jorgensen [87] have recently independently described a novel application of L-proline (107) for catalysis of enantioselective hydrazidation of aldehydes [88]. For example, when aldehyde 106 is allowed to react with di-tert-butyl azodicarboxylate (95) in the presence of 10 mol% 107, adduct 108 is isolated in > 90% yield and 93% ee (Scheme 10.18) [87]. The product hydra-zides can be transformed into protected amino acid derivatives through a sequence that involves oxidation of the aldehyde to the corresponding carboxylic acid, esterification, deprotection, and N-N bond cleavage with Raney-Ni [86, 87]. The observed selectivity has been attributed to the intervention of transition state 111 [86]. This structure incorporates a hydrogen bond between proline s carboxyl group and the azodicarboxylate as a key organizing feature. The transition state structure has parallels to that proposed for the proline-cata-lyzed aldol addition reactions and is supported by quantum mechanical studies by Houk [89]. 

---