Esterification of Carboxyl Groups

Acetylation of hydroxyl groups and esterification of carboxyl groups have been observed ia a limited number of cases but, ia geaeral, have ao preparative advantage over chemical methods. By comparison, phosphorylation has been useful ia the preparatioa of modified purine and pyrimidine mononucleotides from their corresponding nucleosides, eg, 6-thioguanosiae [85-31-4] (51) (97). 

Sequential Methylation Technique. A sequential methylation-extraction technique has been devised primarily to separate phenolics from aromatic and aliphatic acids. The procedure, outlined below, allows quantitative conversion of phenolic hydroxyls to methyl ethers in one step and esterification of carboxyl groups in another. 

Thus, according to Scheme 28, (-)-shikimic acid 169 was converted to cyclohexadiene derivative 170 via esterification of carboxyl group, protection of the m-disposed hydroxyls, and elimination of the remaining carbinol moiety. Catalytic dihydroxylation of 170 gave unsaturated esters 171 and 172 as a separable 1 1 mixture. The 5,5a-unsaturated isomer 171 was finally elaborated into the desired (-)-MK7607 (174) via simple protection-reduction-deprotection sequence. 

Polyesters can be prepared by the direct esterification of carboxyl groups with alcoholic hydroxyl groups in the same or different compounds. Similarly, polyesters can be prepared from the reaction of carboxylic esters and alcoholic hydroxyl groups in the same or different... 

Linear polyesters prepared by direct esterification of carboxyl groups with hydroxyl groups can be derived from one compound, viz. 

The esterification of carboxylic acids can be provided, also, by synthetic equivalents of alcanols acetals RCH(0R )2 (with acid catalysis), ortho-esters RC(0R )3 (acid catalysis), and dialkylcarbonates C0(0R)2 (base catalysis). The series of bifunctional reagents of this type [dimethylformamide dialkylac-etals (CH3)2N-CH(0R)2] is commercially available. Besides the esterification of carboxyl groups, these compounds react with primary amino groups and, thus, are used for GC analysis of amino acids (see the entry Derivatization of Amines, Amino Acids, and Related Compounds for GC Analysis ) ... 

The alkoxylation of these structures, having carboxyl groups and hydroxyl groups, is a self catalysis process, catalysed by the acidic -COOH groups. Two simultaneous reactions take place the esterification of carboxyl groups with PO (reaction 16.14) and the etherification of hydroxyl groups (reaction 16.15) [34]. 

The protein methylases which add methyl groups to lysine, arginine, and histidine residues of proteins may be too specific to have potential application in food protein modification. Protein O-methyltransferase appears to methylate the carboxyl groups of numerous proteins and could have broad enough specificity to be important for increasing the hydro-phobic properties of proteins through esterification of carboxyl groups. 

When m-phenylenediamine (mPDA) or other aromatic primary amine is used as curing agent, the reaction (b), which leads to cross-linking of the resin, is catalyzed by carboxyl group as shown by the substantial reduction of the gel time (see Table 1). On the other hand, the esterification of carboxyl group is less accelerated by primary amines. As a result, only a small part of the... 

Imidazoles are very effective catalysts for the esterification of carboxyl group. The reaction between carboxyl group and epoxy group can be effected before gelation of the system by incorporation of 2 phr EMI when epoxy resin is cured by mPDA, or by incorporation of 1 phr EMI when 4,4 -diaminodiphenylsulfone was used as curing agent. 

Reactions at carboxyl groups are generally carried out using solution procedures. Esterification of carboxyl groups are achieved in order to increase the reactivity or to block some chemical functions. 

It is evident that the elimination of adsorption is essential for the full utilization of zone electrophoresis. When the supporting medium has a charge opposite to that of the substances, it is probable that electrostatic forces are in part responsible for the adsorption. In this institute an attempt has been made to reduce the number of charged groups in paper by esterification of carboxyl groups with diazomethane (Porath and... 

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