Quantitative analysis carboxylic acids

Pentafluorobenzyl bromide has been used in the derivatization of mercaptans [55] and phenols [36], m the analysis of prostaglandins [37], and in quantitative GC-MS [5S] 1,3 Dichlorotetrafluoroacetone is used for the derivatization of amino acids to the corresponding cyclic oxazolidinones and allows the rapid analysis of all 20 protein ammo acids [d] Pentafluorophenyldialkylchlorosilane derivatives have facilitated the gas chromatographic analysis of a wide range of functionally substituted organic compounds, including steroids, alcohols, phenols, amines, carboxylic acids, and chlorohydrms [4]... 

Biological and Analytical Applications. - Phosphorus-31 n.m.r. continues to expand its application in the medical and biological fields20 and is now being applied to soil analysis.21 The problems involved in the use of FT 31P n.m.r. for quantitative determinations have been discussed.22 Samples of phosphinic carboxylic acids were cooled to -40°Cfor quantitative estimations.23... 

More than just a few parameters have to be considered when modelling chemical reactivity in a broader perspective than for the well-defined but restricted reaction sets of the preceding section. Here, however, not enough statistically well-balanced, quantitative, experimental data are available to allow multilinear regression analysis (MLRA). An additional complicating factor derives from comparison of various reactions, where data of quite different types are encountered. For example, how can product distributions for electrophilic aromatic substitutions be compared with acidity constants of aliphatic carboxylic acids And on the side of the parameters how can the influence on chemical reactivity of both bond dissociation energies and bond polarities be simultaneously handled when only limited data are available ... 

Both HPLC and GC-MS were employed for the separation, identification and quantitation of the decomposition products of indigo and indigo carmine. The chemical structures of the dyes are shown in Fig. 3.73. Carboxylic acids were preconcentrated before HPLC analysis either by ion-exchange SPE or by solid-phase microextraction. HPLC measurements were performed in a Sarasep column (300 X 7.8 mm i.d.) using 5 mM H2S04 at a flow rate of 0.7 ml/min. Analytes were detected at 215 nm. The main intermediates formed during the photocatalytic decomposition are compiled in Table 3.26. The results demonstrated that... 

Synthetic operations involving ozonolysis lead to formation of aldehydes, ketones or carboxylic acids, as shown in Scheme 16, or to various peroxide compounds, as depicted in Scheme 7 (Section V.B.5), depending on the nature of the R to R substituents and the prevalent conditions of reaction no effort is usually made to isolate either type of ozonide, but only the final products. This notwithstanding, intermediates 276 and 278 are prone to qualitative, quantitative and structural analysis. The appearance of a red-brown discoloration during ozonization of an olefin below — 180°C was postulated as due to formation of an olefin-ozone complex, in analogy to the jr-complexes formed with aromatic compounds however, this contention was contested (see also Section V1I.C.2). 

This reaction can be used for quantitative analysis of malonic acid by heating a sample in 4 M 11CI04 with excess standard Ce41 and back-titrating unreacted Ce4+ with Fe2+. Analogous procedures are available for many alcohols, aldehydes, ketones, and carboxylic acids. 

By adjusting the exposure time, quantitative conversion of carboxylic acid groups (followed near 1710 cm 1) can be obtained (fig. 5). Typical bands at 1836, 1796 and 1555 cm 1 correspond to acid fluorides, acid chlorides and ammonium carboxylates groups respectively. In the case of EMA (Ethylene-Methacrylic acid) some sodium carboxylate groups were initially present. FTIR analysis showed that these functions (1559 cm 1) were also converted into acid fluorides ... 

Another technique which has much potential in analysis, but which to date has had only limited use, is the formation of radioactive derivatives of non-radioactive compounds for quantitation by radiocounting. A radiolabeled reagent is used to form the derivative. This approach has been of use in combination with chromatography. The advantage of this technique is that it avoids problems of sample background which are often associated with spectrophotometric methods. The 14C-methylation of carboxylic acids and the 14 C-acetylation of hydroxyl groups have been studied [39,40]. These methods are quantitative and the sensitivity is dependent on the activity of the radioactive group added to the molecules. The radioactive derivatization of lipids has been reviewed [41]. 

For carboxylic acids, AG > 30 kj mol-1, so ApFCa < 2-5. The catalytic rate constants of the reaction, however, are often between 102 and 105 s Through analysis of known and well estimated p.Ka data, electrophilic catalysis can be demonstrated with a cycle process (Figure 16.12) to suffice as a quantitative explanation for the observed rates. 

Solutions of triethylamine (Et3N) 14 (1.0M), premixed carboxylic acid/alkyl chloroformate (1.0 M respectively), and 4-dimethylaminopyri-dine 15 (0.5 M) in MeCN were introduced into the reactor from separate inlets and the reaction products collected at the outlet in MeCN, prior to analysis by gas chromatography-mass spectrometry (GC-MS). Under optimized reaction conditions, the authors were able to synthesize the methyl 16, ethyl 17, and benzyl 18 esters in quantitative conversion, with no anhydride or deprotection by-products detected (as observed in conventional batch reactions). In addition to the Boc-glycine derivatives illustrated in Scheme 4, the authors also esterified a series of aromatic carboxylic acids with yields ranging from 91 to 100%, depending on the additional functional groups present. 

It is noteworthy that in practice even the reverse of the above may occur. Often it is necessary to analyse compounds that are too volatile. Significant losses during the preliminary treatment of the sample (e.g., extraction, removal of the solvent), due to this volatility, may introduce errors into the quantitative evaluation. Analysis of volatile carboxylic acids in biological samples is an example. Conversion of these compounds into less volatile derivatives is therefore advantageous from the viewpoint of both GC proper and preliminary isolation of the compounds and sample treatment. 

An example of the separation of the anilides of the eight lowest straight-chain carboxylic acids on sodium dodecylbenzene sulphonate is shown in Fig. 5.14. The problem of the procedure described above consists in that formanilide cannot be prepared as CO, SO2 and HC1 are produced by the action of thionyl chloride on formic acid. Formanilide must, therefore, be prepared in an aqueous medium, the other acids must be extracted into a non-aqueous medium. The yield of the extraction varies considerably depending on the type of the acid, and the presence of water in the reaction medium may affect the reaction yield significantly, which makes quantitative analysis difficult. Condensates with toluidine, which were used for the determination of formic acid by GC, are prepared by an analogous procedure. As other toluidine isomers may serve as the reagents, formyl derivatives have been suggested for the separation of these substances [181]. 

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