Basicity of carboxylic acids

At a first glance it may appear eccentric to show interest in the basicities of carboxylic acids. However, this is not as curious as it seems, since protonated carboxylic acids and their derivatives play the role as important intermediates during acid-catalysed reactions of these compounds. As a matter of fact, Scheele showed as early as in 1782 that addition of sulphuric acid to a mixture of acetic acid and ethanol accelerated esterification [192]. In this respect it is a key point that carboxylic acids, esters and anhydrides possess two oxygens which are po-... 

These reactions were studied in terms of steric effect, acidity and basicity of carboxylic acids, amines, and tertiary amines (e.g. pyridine) by using phosphorous acid and its mono-, di-, and tri-esters, as proposed in Scheme 1 for the case of the reaction with diesters. These N-phosphonium salts (i-4) were separated and characterized on the bases of the IR spectra, acid-base titration, and their reactions. 

Acidity and Basicity of Carboxylic Acids An analysis of rc.sonance and inductive elfects. 

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... 

Considering functional group complementarity, other commodity monomers may also be used. Thus for templates containing acid groups, basic functional monomers are preferably chosen. The 2- or 4-vinylpyridines (VPY) are particularly well-suited for the imprinting of carboxylic acid templates and provide selectivities of the same... 

Photolabile linkers play an important role in solid-phase organic synthesis (SPOS) due to their stability under both acidic and basic conditions. The ONb photolabile linker was modified to improve cleavage rates and yields Fmoc-Tos-OFI was released in 87% yield after 23 h (Scheme 4) [24]. Specifically, the primary alcohol was changed to a secondary benzylic alcohol and the attachment to the resin was through an alkyl chain as opposed to an amide function. Linker 20 was used for the production of carboxylic acids or carbohydrates. A second example... 

Alkenes with monosubstituted carbon atoms are oxidatively cleaved to salts of carboxylic acids by hot basic permangnate solutions. 

Esters ofN,N-dialkylhydroxylamines ((acyloxy)amines) appear to be possible candidates for prodrugs of carboxylic acids, but more studies must be published before any firm conclusion can be drawn. First, there are indications of low acute toxicity for N,N-(1 al ky I hydroxy Iambics [87], Whether the same applies (acutely and chronically) to the pro-moieties after their release from the prodrugs is not known. A second argument is the low basicity of hydroxylamines (the pKa of Ar,AT-dimethylhydroxylamine is 5.2), and the expected lower basicity of O-acylatcd hydroxylamines. As a result, esters of hydroxylamines will be in the unprotonated, more lipophilic form at physiological pH and should be absorbed more readily than the corresponding carboxylic acid [88]. 

It is particularly interesting, that some titanium and tantalum carbene complexes olefinate derivatives of carboxylic acids. These reagents are, moreover, much less basic than phosphorus ylides, and thus enable the olefination of strongly C-H acidic carbonyl compounds. 

For a basic coverage of carboxylic acids, visit www. brightredbooks.net... 

The synthesis of carboxylic acids by the oxidation of alkenes is a two-step process. In the first step, a hot basic potassium permanganate (KMnO ) solution oxidizes an alkene, and in the second step, the oxidized alkene is acidified. The process cleaves the Ccirbon backbone at the carbon-carbon double bond to produce two smaller carboxylic acid molecules. For example, oleic acid (CH3(CH2)yCH=CI-l(CI-l2)yCOOH) yields of mixture of nonanoic acid (CH3(CH2)7C00H) and nonadioic acid (HOOC(CH2)7COOH). 

Bruice and Schmir (3) have shown that for a series of imidazole derivatives, klm depends on the base strength of the catalyst and since pKA is an approximate measure of base strength, the value of klm should increase with increase in pKA. Table I shows that this is indeed the case. Imidazole, pKA = 7.08, has a catalytic constant eight times larger than that of benzimidazole, pKA = 5.53. Bronsted and Guggenheim (2) have obtained a linear relationship between log k/ and pKA for a series of carboxylic acids in the pKA range of 2 to 5, where kB is the carboxvlate anion basic catalytic constant for the mutarotation of glucose and Ka is the acid dissociation constant of the acid. Our results for imidazole and benzimidazole fit fairly well into the Bronsted plot. 

BASICITIES OF CARBOXYLIC SULPHURIC ACIDS AND ACID ESTERS 1 N ... 

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