Classes of Organic Acids

The semi-empirical Yasuda-Shedlovsky technique of extrapolating a series of apparent pKa values obtained in several ratios of water/solvent to obtain an aqueous value is well established [32, 33], but three or more experiments are required and this adds significantly to assay times. A method of calculating aqueous pKas for various classes of organic acids and bases from single apparent pKa values obtained in water/solvent mixtures has been reported [34], and shows promise as a means of further speeding pKa measurement. 

Another important class of organic acids are the carboxylic acids. Since the pif0 s of these substances fall in the range 4—5, their acidities can be determined with... 

Many other relations between -AH and Av (many of which are valid for separate classes of organic acids and bases) and a relation between -AH and the Vxh band intensity enhancement (AA 2) ave been proposed [34]. A more detailed and thorough analysis of the experimental spectral characteristics and enthalpies for various organic acid ase H-complexes was provided by logansen on the basis of several methods (chromatography, calorimetry and so on). The author suggested an universal proportionality relationship which was named the intensity rule [34] (equation 7), where AA / =... 

Carboxylic acids are an important class of organic acids, but there is another important class known as the sulfonic acids. Sulfonic acids have the general structure shown in 77, and R may be any alkyl groups (methyl, ethyl, butyl, etc.). (Sulfonic acids were introduced in Chapter 6, Section 6.2.4.) Aliphatic sulfonic acids are named by using the name for the hydrocarbon unit R, with the suffix sulfonic acid. Examples include the one-carbon sulfonic acid 78. The one-carbon hydrocarbon is methane, and the one-carbon sulfonic acid 78 is named methane-sulfonic acid. Similarly, 79 is a three-carbon sulfonic acid named propane sulfonic acid. Substituents are handled much like carboxylic acids, in that the SO3H unit... 

Thus far, the chapter has been devoted to the chemistry of carboxylic acid derivatives. Another important class of organic acids is the sulfonic acids (see 175 X = OH). In principle, sulfonic acids should give the same t3rpes of derivatives as the carboxylic acids acid chlorides, esters, and amides. This section will explore some of these common sulfonic acid derivatives sulfonyl chlorides (175 ... 

GC methods tend to be more time consmning due to necessary sample preparation steps (e.g., concentration and derivatization) and are therefore less frequently utilized in recent years. Methods have been developed for specific classes of organic acids such as dicarboxylic and ketoacids [14—16]. Advantages of GC methods are their low detection limits (low pg/L) and their high separation efficiencies, which coupled with MS detection allows for imequivocal peak identification. 

Picrates, Many aromatic hydrocarbons (and other classes of organic compounds) form molecular compounds with picric acid, for example, naphthalene picrate CioHg.CgH2(N02)30H. Some picrates, e.g., anthracene picrate, are so unstable as to be decomposed by many, particularly hydroxylic, solvents they therefore cannot be easily recrystaUised. Their preparation may be accomplished in such non-hydroxylic solvents as chloroform, benzene or ether. The picrates of hydrocarbons can be readily separated into their constituents by warming with dilute ammonia solution and filtering (if the hydrocarbon is a solid) through a moist filter paper. The filtrate contains the picric acid as the ammonium salt, and the hydrocarbon is left on the filter paper. 

Study of the solubility behaviour of the compound. A semi-quantitative study of the solubility of the substance in a hmited number of solvents (water, ether, dilute sodium hydroxide solution, dilute hydrochloric acid, sodium bicarbonate solution, concentrated sulphuric and phosphoric acid) will, if intelligently apphed, provide valuable information as to the presence or absence of certain classes of organic compounds. 

The major classes of organic compounds common to living systems are lipids pro terns nucleic acids and carbohydrates Carbohydrates are very familiar to us— we call many of them sugars They make up a substantial portion of the food we eat and provide most of the energy that keeps the human engine running Carbohy drates are structural components of the walls of plant cells and the wood of trees Genetic information is stored and transferred by way of nucleic acids specialized derivatives of carbohydrates which we 11 examine m more detail m Chapter 28... 

There are two broad classes of organic peroxyacids peroxycarboxyUc acids, R[C(0)00H], where R is an alkyl, aralkyl, cycloalkyl, aryl, or heterocycHc group and n = 1 or 2, and organoperoxysulfonic acids, RSO2—OOH. PeroxycarboxyUc acids are commonly named by adding the prefix peroxy to the parent acid as in peroxypropionic acid. The prefix per- is accepted only for the weU-estabHshed products, ie, performic, peracetic, and perbenzoic acids. 

Diaziridines, discovered in 1958, six years after the oxaziridines, were almost immediately realized to be structural analogs of oxaziridines. Like these they showed oxidizing properties unexpected for other classes of organic nitrogen compound. Properties in common with oxaziridines include the rearrangement to open chain isomers on heating above 100 °C (for several diaziridines), and their hydrolytic behavior in acidic media, which leads to carbonyl compounds with conservation of the hetero-hetero bond. 

The hydrocarbons are the basic framework for all organic compounds. Different classes of organic compounds have one or more of the hydrogen atoms replaced by other atoms or groups of atoms. All we need to be aware of at this stage are the three classes of compounds known as alcohols, carboxylic acids, and haloalkanes ... 

Several dozens of aldolases have been identified so far in nature [23,24], and many of these enzymes are commercially available at a scale sufficient for preparative applications. Enzyme catalysis is more attractive for the synthesis and modification of biologically relevant classes of organic compounds that are typically complex, multifunctional, and water soluble. Typical examples are those structurally related to amino acids [5-10] or carbohydrates [25-28], which are difficult to prepare and to handle by conventional methods of chemical synthesis and mandate the laborious manipulation of protective groups. 

Carboxylic acids with one acid group are known as monobasic acids while those with two acid groups are dibasic acids. All acids with more than one acid group are in the class of polybasic acids. The simplest organic acid, formic acid, is responsible for the irritation of bee and ant stings. Vinegar is a 5% solution of acetic acid in water. The acetic acid is responsible for the characteristic sour taste. Citric acid, found in citrus fruits and used in soft drinks, is a tribasic acid with three carboxylic acid groups. The dibasic acid, adipic acid, is a major component of nylon. 

For successful DKR two reactions an in situ racemization (krac) and kinetic resolution [k(R) k(S)] must be carefully chosen. The detailed description of all parameters can be found in the literature [26], but in all cases, the racemization reaction must be much faster than the kinetic resolution. It is also important to note that both reactions must proceed under identical conditions. This methodology is highly attractive because the enantiomeric excess of the product is often higher than in the original kinetic resolution. Moreover, the work-up of the reaction is simpler since in an ideal case only the desired enantiomeric product is present in the reaction mixture. This concept is used for preparation of many important classes of organic compounds like natural and nonnatural a-amino acids, a-substituted nitriles and esters, cyanohydrins, 5-alkyl hydantoins, and thiazoUn-5-ones. 

Acetylsalicylic acid is an example of an ester, a class of organic compounds with the general formula RCOOR. Esters contain an ester linkage consisting of a carbonyl group to which an alkyl group (R) and an alkoxy group (OR ) are bonded (Fig. 13.4.1). Under either acidic or basic conditions or in the presence... 

Salicylic acid (Fig. 13.4.2) is an example of a carboxylic acid with the general formula R-COOH. In this class of organic compounds the carbonyl functionality... 

The designation of certain classes of organic materials as humic and fulvic acids unfortunately implies a certainty and regularity of structure which... 

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