Carboxylic acid basicity

Basic hydrolysis occurs by nucleophilic addition of OH- to the amide carbonyl group, followed by elimination of amide ion (-NH2) and subsequent deprotonation of the initially formed carboxylic acid by amide ion. The steps are reversible, with the equilibrium shifted toward product by the final deprotonation of the carboxylic acid. Basic hydrolysis is substantially more difficult than the analogous acid-catalyzed reaction because amide ion is a very poor leaving group, making the elimination step difficult. 

Room temperature conditions affected only the conversion, the reaction rate being smaller (entry 6). Noticeably, cyclization of 2-prop-2-ynyl-malonic acid monomethyl ester le and 2-phenyl-pent-4-ynoic acid If, also occurred with very good results (entries 7, 8). The obtained results may be ascribed to the LDH support, which exhibits enough basic properties to activate the unsubtituted acetylenic carboxylic acids. Basically, the composition of the LDH exhibits only a very minor influence in these reactions. 

Extraction by chemically active solvents. Not infrequently the crude organic product from a reaction may contain a mixture of acidic (phenols and carboxylic acids), basic and neutral components in various combinations. Some of these components may of course be impurities, but none the less, whether as a preliminary purification stage or as a means of separating the mixture, a carefully planned solvent extraction procedure may be adopted using acidic and basic reagents which react chemically with the basic and acidic components of the mixture respectively. The following full account of a typical procedure may be abbreviated in practice according to the complexity of the mixture to be handled. 

Acidic hydrolysis of an ester is a reversible reaction because the products are an alcohol and a carboxylic acid. Basic hydrolysis of an ester is irreversible because its products are an alcohol and a carboxylate anion, which has a negative charge and does not react with nucleophiles. 

An aqueous sluny of acidic alumina will have a pH of approx 4.0 and is most useful for the separation of acidic compounds such as carboxylic acids. Basic alumina (pH approx 10.0) is useful for the separation of such basic compounds as alkaloids. Neutral alumina (pH approx 7.0) is most often used for the separation of relatively nonpolar compounds such as steroids. 

Occasionally, phenols may be present in a reaction mixture as impurities, and removing them by extraction may be desired. Because phenols, although they are acidic, are about 10 times less acidic than carboxylic acids, basic extractions may be used to separate phenols from carboxylic acids by a careful selection of the base. If sodium bicarbonate is used as a base, carboxylic acids are extracted into the aqueous base, but phenols are not. Phenols are not sufficiently acidic to be deprotonated by the weak base bicarbonate. Extraction with sodium hydroxide, on the other hand, extracts both carboxylic acids and phenols into the aqueous basic solution because hydroxide ion is a sufficiently strong base to deprotonate phenols. 

Earlier experiments with Dowex-50 in 0.05N hydrochloric acid [16] had shown that aspartic acid, serine and threonine are hberated very rapidly but valine and isoleucine more slowly in comparison to hydrolysis in 6N hydrochloric acid. Peptide bonds with cystine and cysteic acid are said to be very resistant to this type of hydrolysis. About 25% of the glutamic acid present is converted into pyrrolidone carboxylic acid. Basic amino acids are only incompletely removed from the ion exchange resins by means of dilute ammonium hydroxide solution. 

Chem. Descrip. Polymeric carboxylic acid basic salt Uses Dispersant for filler/pigmeni dispersions in aq. tems vise, reducer for pigment paste deflocculani... 

Various basic substances, such as aromatic amines (naphthyl-amines dissolve with difficulty in dil. HCl, diphenylamine only in cone. HCl, triphenylamine insoluble) nitro-anilines some amino-carboxylic acids. 

The presence of certain substituents e.g., the amino group) may markedly affect the solubibty and other properties of the sulphonic acid or carboxylic acid. Thus such sulphonic acids as the aminobenzenesul-phonic acids, pyridine- and quinoline-sulphonic acids exist in the form of inner salts or zwitter-ions that result from the interaction of the basic amino group and the acidic sulphonic acid. Sulphanilic acid, for example, is more accurately represented by formula (I) than by formula (II) ... 

Section 19 5 Although carboxylic acids dissociate to only a small extent in water they are deprotonated almost completely m basic solution... 

Ester hydrolysis in base is called saponification, which means soap making Over 2000 years ago the Phoenicians made soap by heating animal fat with wood ashes Animal fat is rich m glycerol triesters and wood ashes are a source of potassium car bonate Basic hydrolysis of the fats produced a mixture of long chain carboxylic acids as their potassium salts... 

In base the tetrahedral intermediate is formed m a manner analogous to that pro posed for ester saponification Steps 1 and 2 m Figure 20 8 show the formation of the tetrahedral intermediate m the basic hydrolysis of amides In step 3 the basic ammo group of the tetrahedral intermediate abstracts a proton from water and m step 4 the derived ammonium ion dissociates Conversion of the carboxylic acid to its corresponding carboxylate anion m step 5 completes the process and renders the overall reaction irreversible... 

Section 20 11 Ester hydrolysis m basic solution is called saponification and proceeds through the same tetrahedral intermediate (Figure 20 5) as m acid catalyzed hydrolysis Unlike acid catalyzed hydrolysis saponification is irreversible because the carboxylic acid is deprotonated under the reac tion conditions... 

Section 20 19 The hydrolysis of nitriles to carboxylic acids is irreversible m both acidic and basic solution... 

These derivatives are prepared to protect a-hydroxy carboxylic acids they are cleaved by acidic hydrolysis of the acetal structure (HCl, DMF, 50°, 7 h, 71% yield), or basic hydrolysis of the lactone. ... 

Liquid carboxylic acids are first freed from neutral and basic impurities by dissolving them in aqueous alkali and extracting with diethyl ether. (The pH of the solution should be at least three units above the pKg of the acid, see pK in Chapter 1). The aqueous phase is then acidified to a pH at least three units below the pK of the acid and again extracted with ether. The extract is dried with magnesium sulfate or sodium sulfate and the ether is distilled off The acid is fractionally distilled through an efficient column. It can be further purified by... 

In September 1964 the Du Pont company announced materials that had characteristics of both thermoplastics and thermosetting materials. These materials, known as ionomers, are prepared by copolymerising ethylene with a small amount (1-10 % in the basic patent) of an unsaturated carboxylic acid such as acrylic acid using the high-pressure process. Such copolymers are then treated... 

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... 

Nickel peroxide is a solid, insoluble oxidant prepared by reaction of nickel (II) salts with hypochlorite or ozone in aqueous alkaline solution. This reagent when used in nonpolar medium is similar to, but more reactive than, activated manganese dioxide in selectively oxidizing allylic or acetylenic alcohols. It also reacts rapidly with amines, phenols, hydrazones and sulfides so that selective oxidation of allylic alcohols in the presence of these functionalities may not be possible. In basic media the oxidizing power of nickel peroxide is increased and saturated primary alcohols can be oxidized directly to carboxylic acids. In the presence of ammonia at —20°, primary allylic alcohols give amides while at elevated temperatures nitriles are formed. At elevated temperatures efficient cleavage of a-glycols, a-ketols... 

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