Esterification reagents

Good selectivity was always obtained when the esterification reactions were done in a more polar solvent (Scheme 10). The reason is likely due to decreased reactivity of the esterification reagent from solvent-induced destabilization of the stannylene intermediates. If the experiments were performed in polar solvents, higher yields of 15 and 38 would be acquired. 

Reichert and Linckens [83] have reviewed gas chromatographic methods for the determination of nitriloacetic acid in potable waters. They point out that esterification of the nitriloacetic acid is required to enable it to be volatilised in the gas-liquid chromatographic column, and they compared a range of esterification reagents and conditions for simplicity and speed of operation. The method chosen involved treatment of a concentrated sample with a mixture of -propanol-acctyl chloride (10 1) and the resulting nitroacetic acid-propyl ester injected into a column, which was fitted with a nitrogen-sensitive detector. The detection limit for nitriloacetic acid in potable water is about lpgL-1. 

The above esterification reagent, however, decomposes Trp considerably (up to 75% after 1 h) and therefore it is essential not to exceed the optimal time in order to obtain reproducible yields. 

Silylation reagents Esterification reagents Other derivatizing reagents Various reaction (micro)vials and other accessories... 

A number of ligands bears hydroxy groups which are ostensibly capable of reaction with various esterification reagents. The studies of the reactions of amino alcohols which have been directed toward the detection of reactions of free donor groups have produced rather discordant results which make any generalization impossible. 

The simplest esterification reagents are the corresponding alcohols ROH themselves. Different esters have been used as the analytical derivatives of carboxylic adds Me, Et, Pr, iso-Pr, isomeric Bu (excluding tert-B i esters, owing to their poorer synthetic yields), and so forth. This method requires the use of excess of dry alcohol and acid catalysis by BCI3, BF3, CH3COCI, SOCI2,... 

Other classes of esterification reagents are halo-genated compounds (alkyl iodides, substituted benzyl and phenacyl bromides, etc.), which need basic media... 

The use of graphite bisulphate, C24,HS04,2H2S04, as an esterification reagent in organic synthesis has been considered.It is very efficient for the production of formates and acetates, reaction times being less than one hour esterification of other acids is slower, but in most cases the yields are very high. 

Studies on kinetics are also important in the development of new derivatization reagents. For example, Campana Filho and Goissis [81] proposed a new esterification reagent for the derivatization of amino acids, and they studied the kinetics of the esterification reaction. Sixteen amino acids were esterified with yields higher than 95% using SMthionyl chloride in -propanol at 100°C for 60 min. The results were reproducible, thus offering an approach for the synthesis of 0-n-propyl esters of amino acids. 

Die synthesis of enantiomerically pure inteimediates and active products is a major requiiement for the pharmaceutical industry. Hydrolytic biocatalysts such as esterases, lipases and proteases aie employed for the preparation of enantiopure compounds from racemic precursors, prochiral compounds, and diastereomeric mixtures. Hydrolytic enzymes alsocatalyze reverse hydrolysis and thus offer access to both enantiomers of a specific compound. Examples aie the use of enol esters as trani-esterification reagents and the combination of hydi olytic enzymes with racemization catalysts. 

The acidity of tropolones derives from their being extended or vinylogous carboxylic acids, as mentioned earlier in this chapter, and other facets of the chemistry of the hydroxyl group resemble carboxylic acids. Thus conversion of a tropolone into its alkyl ether corresponds to an esterification reaction and it may be brought about by means of the usual esterification reagents, e.g. with alcohols and mineral acid [278], alkyl sulphates [279], or diazomethane [245,274, etc.] or by treating a metal salt of tropolone with an alkyl halide [245,280]. (9-Alkylation of unsymmetric-ally substitut ed tropolones leads to two isomeric alkoxytropolones ... 

The technique used in our laboratory is an adaptation of Pappin s method [124], Briefly, the esterification reagent is obtained by addition of thionyl chloride to dry methanol at -80°C to form a 1% solution. Fresh reagent (lOlll) is added to an Eppendorf tube containing the dried peptide sample After incubation at 55°C for 20 minutes, the excess reagent is removed by vacuum centrifugation. The modified peptides are re-suspended in 5 pi of acetonitrile/water/TFA solution (50 49 1 v v v). Two pi of the sample are loaded on the MALDI sample plate prior to matrix addition andMALDI-MS analysis [120]. 

Shimizu et al. [18] have further examined the effects of esterification of the carboxylic acids in an MAA/EGDMA matrix imprinted with ethyl adenine-9-acetate (EA9A) (Fig. 2). Consistent with the results of Sellergren and Shea, esterification of the matrix led to a loss of affinity and selectivity. Both diazomethane and phenyldia-zomethane were examined, yielding similar results, suggesting that the difference in size between the two esterification reagents was insufficient to change the selectivity of the reaction. 

Uses Intermediate for procaine hydrochloride, dyestuffs esterification reagent Manuf./Disthb. Aldrich http //www.sigma-aidrich.com, Biddle Sawyer http //www.biddiesawyer.com, ChemFirst http //www.chemfirst.com, Fluka http //www.sigma-aidrich.com, Jiangsu Eternal Union http //www.Jeu-cn.com Nordic Synthesis AB Sigma... 

A very recent investigation called upon trifluoroacetic anhydride as the esterification reagent for the surface of cellulose fibres. The reaction was carried out both in the gas [40, 41] and the liquid phase [42], The presence of the CF3 groups on the cellulose surface gave rise to very hydrophobic and lipophobic properties [42]. Given the... 

Another class of esterification reagents are halogenated compounds (alkyl iodides, substituted benzyl, and phena-cyl bromides), which need basic media for their reaction [K2CO3 or DMFA (dimethyl formamide) is normally used for the neutralization of HHal as acid by-product]. For methy-lation of carboxylic acids, some tetra-substituted ammonium hydroxides or halides can be used, e.g., tetramethylammo-nium hydroxide (in aqueous solutions) or trimethylanilinium hydroxide (in methanol solution). The intermediate ammonium carboxylates are thermally unstable and produce methyl alkanoates when the reaction mixtures are heated or when the carboxylates are introduced into the hot injector of the gas chromatograph (flash or on-column methylation) ... 

Excessive amounts of water in the sample interfere by destruction of the esterification reagent and contribution to a high unreal hydroxyl number value. If the water content of the sample exceeds 0-2%, it is recommended that the sample be dried. Primary and secondary amines and higher fatty acids also interfere since they react with the reagent to form stable compounds and would be included in the analysis. 

The butyl esterification reagent that is added to the dried metabolites extracted from the blood spot is comprised of 3 N HCl in n-butanol. Due to the significant water content of concentrated HCl, this reagent cannot be prepared in a laboratory by simply mixing concen-... 

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