Sulphonic acids basicity

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) ... 

A number of basic materials such as hydroxides, hydrides and amides of alkaline and alkaline earth metals and metal oxides such as zinc oxide and antimony oxide are useful catalysts for the reaction. Acid ester-exchange catalysts such as boric acid, p-toluene sulphonic acid and zinc chloride are less... 

Basic compound To neutralise strong mineral acids (from fuels) Barium or basic calcium salts of sulphonic acids and alkylsalicylic acid. Superbasic and hyperbasic additives are basic salts with a large excess of base... 

Cation units usually contain a sulphonic acid resin whilst anion resins fall into the two main categories of strongly basic, with quaternary ammonium groupings and weakly basic, with tertiary amine groups. The final unit is the mixed bed in which, by a mixture of cation and anion resins in the same vessel, the effect is achieved of a multiplicity of separate cation and anion units. Resin separation is necessary for regeneration purposes. Considerable improvements in water quality are obtainable by these means. 

An alternative approach to the synthesis of 1,3-dienes is by elimination of benzene-sulphinic acid from homoallylic sulphones under basic conditions. This method has been used for the synthesis of a pheromone constituent of the codling moth (equation 67)109. 

The presence of at least two sulphonic acid groups in the triarylmethane ring system permits the derivatives to be applied as acid dyes. Although sulphonic acid groups are often present in the intermediates used, acid dyes can also be obtained by direct sulphonation of the basic dye itself or at the leuco stage. 

The azo-dyes derived from phenols are called acid dyes, those derived from amines basic dyes. But since, in industry, the starting materials, not only diazo-components (diazotised amines), but also azocomponents (coupled phenols or amines), are nearly always sulphonic acids, this distinction is pointless. The vast majority of the azo-dyes... 

Synthetic colours are materials based around azo-sulphonic acids. They are water soluble and provide strong stable colours. There is an interesting chapter by Wadds (1984) that discusses some of the basic methods, including thin-layer, paper and high-performance liquid chromatography, which have been used in the past and are still used today to analyse for these colours. 

Deprotection is effected in the case of methyl or ethyl esters by hydrolysis, usually under basic conditions (Section 9.6.17, p. 1266). t-Butyl esters are de-protected by mild acidic conditions, for example, formic acid at room temperature,159 toluene-p-sulphonic acid in benzene solution, or hydrogen bromide in acetic acid at 10°C.160... 

The sulphonic acids, it will be recalled, are strong acids, their acid character being due to the remaining acid hydroxyl left in the compound. Sulphuric acid is di-basic and only one of the two hydroxyls is eliminated by the substitution in the ring. Nitric acid, however, is mono-basic and possesses only one acid hydroxyl. 

As both nitration and sulphonation take place with comparative ease, with either hydrocarbons or acids, and as the nitro compounds yield amino compounds and these yield diazo compounds, with their numerous reactions, in particular the Sandmeyer reaction for obtaining nitriles and as sulphonic acids are easily converted into phenols or nitriles it will be seen that by a combination of these synthetic reactions practically any desired ring-substituted mono-basic or poly-basic ring-carboxy acid may be obtained. 

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