Derivatization of carboxylic acids

The current literature is replete with accounts of the determination of one fatty acid or another in numerous natural samples. It seems that the most common way to render fatty acids amenable to GC analysis is to use the time-honored method of acid-catalyzed direct esterification. The traditional acid catalysts H2SO4 and HCl are still used, but one also notes considerable reference to boron trifluoride and trichloride for BFj, in particular, the shorter time (relative to the mineral acids) needed to effect complete esterification has been noted [207]. 

Methyl esters can be obtained directly from triglycerides by transesterification with methanol traditional catalysts in transesterification to form methyl esters have been acids (e.g., sulfuric) and sodium methoxide. However, if the sodium methoxide contains any sodium hydroxide, some of the triglyceride will be hydrolyzed to the carboxylate salt, which cannot be esterified. On this account, we/o-trifluoromethyl-phenyltrimethylammonium hydroxide (w-CF3-QH4NMe3 OH ) was offered as a transesterification catalyst [208] methanolysis is reported to occur rapidly at room temperature. 

The selection of this reagent was based partly on the observation [209] that, because various quaternary ammonium carboxylates undergo thermal decomposition to methyl esters, such esters could be formed in situ in good yield by the simple injection of a methanolic solution of the quaternary ammonium carboxylate above 250°C. Thus, the use of the quaternary ammonium hydroxide in the transesterification scheme described above permits the simultaneous conversion of both glycerides and fatty acids to methyl esters. 

In a modification of the above method, methyl propionate is added as a scavenger for excess hydroxide ion which might cause degradation of any polyunsaturation in the fatty acid chain [210]. 

The reaction RCOO +R l- RCOOR + I has also been employed [211]. Quantitative results in less than 10 min under mild, non-acidic conditions are claimed for the conversion of any acidic compound to a primary alkyl ester when the tetramethylammonium salt is treated with the alkyl iodide in a highly polar solvent system such as anhydrous methanolic N, A -dimethylacetamide. 

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Methyl-3,4-dihydro-2tf-pyrido[l,2-a]pyrimidin-2-one is used in fluorescence (chiral) derivatization of carboxylic acids in HPLC with different 2-substituted 2H-benzotriazoles 688 in the presence of 2-bromo-1-ethylpyridinium tetrafluoroborate at room temperature (89MI2, 89MI15). This sensitive method has proved useful for the determination of carboxylic acids (e.g., ibuprofen) in small amounts of biological samples (89MI2). 

Davis, B., Crown ether catalyzed derivatization of carboxylic acids and phenols with pentafluorobenzyl bromide for electron capture gas chromatography, Anal. Chem., 49, 832, 1977. 

Used in the derivatization of carboxylic acids, phenols, mercaptans, and sulfamides lachrymator potentially unstable high sensitivity for electron capture detection not usable for formic acid... 

The most common fluorotags (fluorescent reagents) are dansyl chloride and o-phthalaldehyde (OPA). Chromotags include p-bromophenacyl bromide (PBPB) for derivatization of carboxylic acids (K-salts) with a crown ether catalyst, ninhydiin for primary amines forming complexes that have their adsorption maxima at about 570 nm, and dansyl chloride for primary and secondary... 

Decarboxylative hydroxylation of acids. After derivatization of carboxylic acids... 

Solid-phase extraction and TBDMS derivatization of carboxylic acids [298, 299] To 1 ml of aqueous sample or biological sample (e.g. saliva or urine) was added 100/rg/ml of internal standard (frons-cinnamic acid dissolved in methanol) and the solution was made basic by saturation with solid sodium bicarbonate. 

Derivatization of carboxylic acids Although the carboxyl group can also be transformed to the silyl... 

The reagents containing hydroxy group have been developed for FL derivatization of carboxylic acid or other activated acids. 1-Pyrenemethanol (1-PM), 4-hydroxymethyl-7-methoxycoumarin (HMC), and 5-(4-pyridyl)-2-thiophenemethanol (PTM) have been applied to carboxylic acids with LC-FL detection. 

Two-stage single-pot derivatization of carboxylic acids (with intermediate formation of chloroanhydrides with thionyl chloride followed by their conversion into amides) was recommended preferably for HPLC analysis, but the simplest dialkylamides and even anilides ° are volatile enough for GC analysis also (the mixture of PhaP and CCLt, instead of SOCI2, can be used in this reaction). Moreover, the same procedure is used for the synthesis of diastereomeric derivatives of enantiomeric carboxylic acids (see below) ... 

Cartwright AJ, Jones P, Wolf JC, Evans EH. Derivatization of carboxylic acid groups in pharmaceuticals for enhanced detection using liquid chromatography with electrospray ionization tandem mass spectrometry. Rapid Commun Mass Spectrom 2005 19 1058-62. 

Sasamoto, K. Ushijima, T. Saito, M. Ohkura, Y. Precolumn fluorescence derivatization of carboxylic acids using 4-aminomethyl-6,7-dimethoxycomnarin in a two-phase medium, Anal.Sci., 1996, 12, 189-193. [serum column temp 40 LOD 20-50 fmol linoleic acid palmitic acid oleic acid lauric add ... 

Knauer, A. Wintersteiger, R. Markl, R. Sametz, W. Juan, H. Derivatization of carboxylic acids with fluorescent reagents. J. Planar Chromatogr.-Mod. TLC1999, 72,211-214. 

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