Carboxylic acids measurement

Jaffrezo, J. L., N. Calas, and M. Bouchet, Carboxylic Acids Measurements with Ionic Chromatography, Atmos. Environ., 32, 2705-2708 (1998). 

As previously described for aromatic carboxylic acids, measurements of the line-widths of the CH3 resonance in methanol give the rate of exchange of hydroxylic protons on methanol, and measurements of the line-widths of the OH resonance give the rate of exchange of protons on phenol. Values of ft, k2 and k3 have been determined for p-bromo-phenol and p-nitrophenol [67], and are tabulated in Table 11. 

Few good methods exist for determination of phenolic groups in humic substances. Their concentration is usually assessed by the difference between total acidity measured by titration and carboxyl acidity measured by calcium acetate... 

Jaffrezo, J.L., Galas, N., and Bouchet, M., Carboxylic acid measurements with ionic chromatography, Atmos. Environ., 32, 2705,1998. 

Fig. 5.5 Evolution of the RAS signal during increasing coverage by 3-thiophene carboxylic acid measured for three photon energies. Reprinted with permission from (Frederick et ai. 1998). Copyright 1998, American Physical Society.

In a previous study of HALS additives in y-irradiated PP, we have shown that, at the bend failure point, IR indicates that carboxylic acids are a major product in failure in contrast to the very low level in additive free or weakly stabilized samples (6). In unstabilized samples, ketonic and hydroperoxide products dominate. This same importance of carboxylic acids (measured as acid fluorides after SF4 treatment) was found at the failure point of samples containing phenols FV and V (reaction scheme 1). The detected carboxylic acid... 

It is also possible to measure microwave spectra of some more strongly bound Van der Waals complexes in a gas cell ratlier tlian a molecular beam. Indeed, tire first microwave studies on molecular clusters were of this type, on carboxylic acid dimers [jd]. The resolution tliat can be achieved is not as high as in a molecular beam, but bulk gas studies have tire advantage tliat vibrational satellites, due to pure rotational transitions in complexes witli intennolecular bending and stretching modes excited, can often be identified. The frequencies of tire vibrational satellites contain infonnation on how the vibrationally averaged stmcture changes in tire excited states, while their intensities allow tire vibrational frequencies to be estimated. 

Esters can participate m hydrogen bonds with substances that contain hydroxyl groups (water alcohols carboxylic acids) This confers some measure of water solubil ity on low molecular weight esters methyl acetate for example dissolves m water to the extent of 33 g/100 mL Water solubility decreases as the carbon content of the ester increases Fats and oils the glycerol esters of long chain carboxylic acids are practically insoluble m water... 

The structure was established on the basis of substitution at the 3-position (11CB2409), optical investigations (26LA(437)162), dipole moment (3.06 D) (44MI41600) and IR measurements (57MI41600, 66DIS(B)102). The first 2,1-benzisoxazole to be synthesized was 5,6-dimethoxy-2,l-benzisoxazole-4-carboxylic acid in 1881 (1881JPR353). 

Naphthenic acid is a collective name for organic acids present in some but not all crude oils. In addition to true naphthenic acids (naphthenic carboxylic acids represented by the formula X-COOH in which X is a cycloparaffin radical), the total acidity of a crude may include various amounts of other organic acids and sometimes mineral acids. Thus the total neutralization number of a stock, which is a measure of its total acidity, includes (but does not necessaiily represent) the level of naphthenic acids present. The neutralization number is the number of milligrams of potassium hydroxide required to neutralize one gram of stock as determined by titration using phenolphthalein as an indicator, or as determined by potentiometric titration. It may be as high as 10 mg KOH/gr. for some crudes. The neutralization number does not usually become important as a corrosion factor, however, unless it is at least 0.5 mg KOH/gm. 

In the discussion of the relative acidity of carboxylic acids in Chapter 1, the thermodynamic acidity, expressed as the acid dissociation constant, was taken as the measure of acidity. It is straightforward to determine dissociation constants of such adds in aqueous solution by measurement of the titration curve with a pH-sensitive electrode (pH meter). Determination of the acidity of carbon acids is more difficult. Because most are very weak acids, very strong bases are required to cause deprotonation. Water and alcohols are far more acidic than most hydrocarbons and are unsuitable solvents for generation of hydrocarbon anions. Any strong base will deprotonate the solvent rather than the hydrocarbon. For synthetic purposes, aprotic solvents such as ether, tetrahydrofuran (THF), and dimethoxyethane (DME) are used, but for equilibrium measurements solvents that promote dissociation of ion pairs and ion clusters are preferred. Weakly acidic solvents such as DMSO and cyclohexylamine are used in the preparation of strongly basic carbanions. The high polarity and cation-solvating ability of DMSO facilitate dissociation... 

Acids require vigorous conditions for successful reductions on a synthetic scale, but they can be reduced to the alcohol in small yield over rhodium even at ambient conditions. This fractional reduction is without utility but it is sufficient to cause errors in absorption measurements when a carboxylic acid is used as a solvent. At 150 C and 2000 psig, RhjOj becomes a useful catalyst for carboxylic acid hydrogenation 13). 

By simply hydrolyzing the easily accessible 2-hydroxy-2-methylalkanenitriles with concentrated acid, 2-hydroxy-2-methylalkanoic acids are obtained without measurable racemization (Table 3). The reaction sequence from the starting ketone to the carboxylic acid can be carried out in one pot without isolation of the cyanohydrin. The enantiomeric excesses of the (/ )-cyanohydrins and the (ft)-2-hydroxyalkanoic acids are determined from the ( + )-(/T)-Mosher ester derivatives and as methyl alkanoates by capillary GC, respectively. The most efficient catalysis by (R)-oxynitrilase is observed for the reaction of hydrocyanic acid with 2-alkanoncs. 3-Alkanoncs are also substrates for (ft)-oxynitrilase, to give the corresponding (/ )-cyanohydrins32. 

In the course of this study, the authors determined /Lvalues for dibenzyl, methyl phenyl, methyl p-nitrophenyl, di-p-tolyl, di-isopropyl and tetramethylene sulphoxides and for diethyl, dipropyl and dibutyl sulphites. The /Lscales are applied to the various reactions or the spectral measurements. The /Lscales have been divided into either family-dependent (FD) types, which means two or more compounds can share the same /Lscale, family-independent (FI) types. Consequently, a variety of /Lscales are now available for various families of the bases, including 29 aldehydes and ketones, 17 carboxylic amides and ureas, 14 carboxylic acids esters, 4 acyl halides, 5 nitriles, 10 ethers, 16 phosphine oxides, 12 sulphinyl compounds, 15 pyridines and pyrimidines, 16 sp3 hybridized amines and 10 alcohols. The enthalpies of formation of the hydrogen bond of 4-fluorophenol with both sulphoxides and phosphine oxides and related derivatives fit the empirical equation 18, where the standard deviation is y = 0.983. Several averaged scales are shown in Table 1588. 

Aalbers [49,50] calculated pKa-values from pH and conductivity measurements and concluded that the CMC increases with the EO degree and that the micelles of ether carboxylic acids are somewhat uncharged. 

Masparov [53] and coworkers measured with lauryl alcohol ethoxylated with 6 mol EO a better detergency and wetting effect than with the corresponding polyoxyethylene ether carboxylic acid. 

Flocculation values achieved from turbidity measurements using the light scattering technique showed improvement with nonylphenol ether carboxylic acid (4 mol EO) in particular. The oil solubilization rate has been found to be proportional to the surfactant micellar size [190]. 

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