Carboxylic acids determinations

Solutions of different carboxylic acids (fiimaric acid [FA], maleic acid, acrylic acid, succinic acid, and malonic acid) in ethanol have been effectively used as primers to increase the adhesion of synthetic vulcanized SBRs. The increase in the adhesion properties of SBR treated with carboxylic acid is attributed to the elimination of zinc stearate moieties and the deposition of acid on the rubber which migrates into the solvent-borne polyurethane adhesive layer once the adhesive joint is formed. The nature of the carboxylic acid determines the rate of diffusion into the adhesive and the extent of rubber-adhesive interfacial interaction. 

To examine this peculiar behavior, we have converted the elastic compressibility modulus, per unit area, Y (Fig. 12a), to the modulus per chain, Y = F/10 F (Fig. 12b). The elastic compressibility modulus per chain is practically constant, 0.6 0.1 pN/chain, at high densities and jumps to another constant value, 4.4 0.7 pN/chain, when the density decreases below the critical value. The ionization degree, a, of the carboxylic acid determined by FTIR spectroscopy gradually decreases with increasing chain density due to the charge regulation mechanism (also plotted in Fig. 12b). This shows that a does not account for the abrupt change in the elastic compressibihty modulus. 

Spectra are given for three compounds. Each compound has one or more of the following functional groups alcohol, amine, ketone, aldehyde, and carboxylic acid. Determine the functional group(s) in each compound, and assign the major peaks above 1600 cm-1. 

Table 7.5. Hydrogen-bond lengths in the carboxylic acids, determined by neutron diffraction...

The dimerization constants of carboxylic acids determined by the partition method are usually lower than the values obtained by IR spectroscopy, cryoscopy, or dielectric measurements (100). The correction for hydration gives dimerization constants expected from values in dry solvents by spectroscopic or dielectric measurements (29, 30). 

Dopamine and 3,4-dihydroxyphenylpyruvic acid were added to this cell-free extract, and the formation of labelled (67), (68), and (69) was observed (carrier compounds were added at the end of the incubation). It was stated that no norlaudanosoline-1-carboxylic acid was formed under the incubation conditions when boiled enzyme was used. In none of these experiments was the chirality of the norlaudanosoline-l-carboxylic acid determined. If the reaction yielding this compound is controlled by an enz3une, one would expect this amino-acid to be optically active. The enz3une isolated by Zenk and his co-workers failed to catalyze a reaction between dopamine and 3,4-dihydroxyphenylpyruvic acid. 4-Hydroxy-phenylacetaldehyde did serve as a substrate for the enzyme. To summarize, I believe that the evidence favoring the intermediacy of norlaudanosoline-l-carboxylic acid is somewhat flimsy. It is of course possible that there are two independent routes to nor-laudanosoline, and this is the most charitable explanation of these conflicting results. 

Benzene. Pure benzene (free in particular from toluene) must be used, otherwise the freezing-point is too low, and crystallisation may not occur with ice-water cooling alone. On the other hand, this benzene should not be specially dried immediately before use, as it then becomes slightly hygroscopic and does not give a steady freezing-point until it has been exposed to the air for 2-3 hours. Many compounds (particularly the carboxylic acids) associate in benzene, and molecular weights determined in this solvent should therefore be otherwise confirmed. 

Ozonolysis is sometimes used as a tool m structure determination By identifying the carboxylic acids produced we can deduce the structure of the alkyne As with many... 

As discussed earlier in Section lOC.l, ultraviolet, visible and infrared absorption bands result from the absorption of electromagnetic radiation by specific valence electrons or bonds. The energy at which the absorption occurs, as well as the intensity of the absorption, is determined by the chemical environment of the absorbing moiety. Eor example, benzene has several ultraviolet absorption bands due to 7t —> 71 transitions. The position and intensity of two of these bands, 203.5 nm (8 = 7400) and 254 nm (8 = 204), are very sensitive to substitution. Eor benzoic acid, in which a carboxylic acid group replaces one of the aromatic hydrogens, the... 

Until now we have been discussing the kinetics of catalyzed reactions. Losses due to volatility and side reactions also raise questions as to the validity of assuming a constant concentration of catalyst. Of course, one way of avoiding this issue is to omit an outside catalyst reactions involving carboxylic acids can be catalyzed by these compounds themselves. Experiments conducted under these conditions are informative in their own right and not merely as means of eliminating errors in the catalyzed case. As noted in connection with the discussion of reaction (5.G), the intermediate is stabilized by coordination with a proton from the catalyst. In the case of autoprotolysis by the carboxylic acid reactant, the rate-determining step is probably the slow reaction of intermediate [1] ... 

The absolute configuration of naturally occurring 5(-)-azetidine-2-carboxylic acid has been established (73CL5), and the DL form has been resolved (69JHC993). ORD and CD curves have been determined for 2-methylazetidine and an octant rule has been proposed for the N-chloro- and N-cyano-2-methylazetidines (74T39). 

In this work we studied the interaction of the ion pair Bromothymol Blue (BTB-trinonyloctadecylammonium (TNODA) with organic acids in toluene and its mixtures with different solvents and proposed the method for determination of carboxylic acids in solvents, oils, and other chemicals. 

A prototype of such phenomena can be seen in even the simplest carboxylic acid, acetic acid (CH3CHOOH). Acidity is determined by the energy or free energy difference between the dissociated and nondissociated forms, whose energetics usually depend significantly on their conformation, e.g., the syn/anti conformational change of the carboxyl-ate group in the compound substantially affects the acid-base equilibrium. The coupled conformation and solvent effects on acidity is treated in Ref. 20. 

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... 

A number of studies of the acid-catalyzed mechanism of enolization have been done. The case of cyclohexanone is illustrative. The reaction is catalyzed by various carboxylic acids and substituted ammonium ions. The effectiveness of these proton donors as catalysts correlates with their pK values. When plotted according to the Bronsted catalysis law (Section 4.8), the value of the slope a is 0.74. When deuterium or tritium is introduced in the a position, there is a marked decrease in the rate of acid-catalyzed enolization h/ d 5. This kinetic isotope effect indicates that the C—H bond cleavage is part of the rate-determining step. The generally accepted mechanism for acid-catalyzed enolization pictures the rate-determining step as deprotonation of the protonated ketone ... 

Plasticizers can be classified according to their chemical nature. The most important classes of plasticizers used in rubber adhesives are phthalates, polymeric plasticizers, and esters. The group phthalate plasticizers constitutes the biggest and most widely used plasticizers. The linear alkyl phthalates impart improved low-temperature performance and have reduced volatility. Most of the polymeric plasticizers are saturated polyesters obtained by reaction of a diol with a dicarboxylic acid. The most common diols are propanediol, 1,3- and 1,4-butanediol, and 1,6-hexanediol. Adipic, phthalic and sebacic acids are common carboxylic acids used in the manufacture of polymeric plasticizers. Some poly-hydroxybutyrates are used in rubber adhesive formulations. Both the molecular weight and the chemical nature determine the performance of the polymeric plasticizers. Increasing the molecular weight reduces the volatility of the plasticizer but reduces the plasticizing efficiency and low-temperature properties. Typical esters used as plasticizers are n-butyl acetate and cellulose acetobutyrate. 

The former passes into the second on further oxidation with hydrogen peroxide, indicating that it is an a-keto-carboxylic acid. Acid (b) loses carbon dioxide on fusion and gives a neutral substance, CjaHj OgN, m.p. 238°, which was shown to be 6 7-methylenedioxy-A-methylphenanthri-done (I), by comparison with a synthetic specimen. The position of the carboxyl group in (b) could not be determined by synthetic methods but is probably at since dihydrolycorineanhydromethine, Cl 7 7 2 ) m.p. 87-5° [picrate, m.p. 174° (dec.) methiodide, m.p. 236° (dec.)] on distillation with zinc dust yields a mixture of phenanthridine, 1-methyl-phenanthridine and 6 7-methylenedioxyphenanthridine, m.p. 142° [picrate, m.p. 257° (dec.)], the identity of the two latter being established by comparison with the synthetic products. These results indicate for lycorineanhydromethine formula (II). 

Acylation of various oxygen functions by use of common and commercially available fluonnated carboxylic acid denvatives such as trifluoroacetic anhydride or the corresponding acyl halides have already been discussed sufficiently in the first edition [10] Therefore only exceptional observations will be described in this section In the past 15 years, many denvatizations of various nonfluonnated oxygen compounds by fluoroacylation were made for analytical purposes. Thus Mosher s acid chlorides for example became ready-to-use reagents for the determination of the enantiomeric purity of alcohols and amines by NMR or gas-liquid chromatographic (GLC) techniques [//] (equation 1)... 

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