Sulphonic acids, purification

The crude product contains isomers other than that required and also nitrated phenolic compounds resulting from side reactions. The usual method of purification is to treat the crude product with sodium sulphite, which converts asymmetric trinitro compounds to sulphonic acid derivatives, and to wash out the resulting soluble products with alkaline water. The purity of the product is determined by the melting point, the minimum value for Grade I TNT commonly being 80-2°C. Unless adequate purity is achieved, slow exudation of impurities can occur during storage and the TNT then becomes insensitive. 

In all the above sequences, single isomers are produced by careful control of the reaction conditions combined with purification by selective isolation at various points in the synthesis. Occasionally two isomers are produced which give dyestuffs that have very similar properties in these cases it is often quite acceptable and economically beneficial not to separate the individual components but to use the total mixture in dye preparation. An example is the mixture of l-naphthylamine-6- and 7-sulphonic acids (4.46 mixed Cleve s acids), which arises by nitration and reduction of naphthalene-2 Sulphonic acid (Scheme 4.30). 

A related series of 5-substituted-2-amino-oxadiazole compounds have also been prepared in a one-pot procedure using a microwave-assisted cyclisation procedure (Scheme 6.26)164. Rapid preparation of the pre-requisite ureas from the mono acyl hydrazines and various isocyanates (or the isothiocyanate) was easily achieved by simple mixing. The resulting products were then cyclo dehydrated by one of the two procedures either by the addition of polymer-supported DMAP and tosyl chloride or alternatively with an immobilised carbodiimide and catalytic sulphonic acid. Purity in most cases was excellent after only filtration through a small plug of silica but an SCX-2 cartridge (sulphonic acid functionalised - catch and release) could be used in the cases where reactions required additional purification. 

Unless the reagent has been recently purchased it may contain substantial amounts of toluene-p-sulphonic acid. The most satisfactory procedure for the purification of the chloride involves dissolving it in the minimum amount of chloroform (about 2.5 ml per g) and diluting with 5 volumes of light petroleum (b.p. 40-60 °C), which precipitates impurities. The filtered solution is treated with decolourising charcoal, filtered and concentrated to small volume when colourless crystals of the pure reagent, m.p. 68 °C, are obtained these should be washed with chilled light petroleum (b.p. 40-60 °C). 

Pyridine is a tertiary amine its aqueous solution shows an alkaline reaction and precipitates the hydroxides of metals, some of which are soluble in an excess of the amine. Salts of pyridine like those of other amines form characteristic double salts with metallic halides. The ferrocyanide of pyridine and the addition-product of pyridine and mercuric chloride are difficultly soluble in water these compounds are used in the purification of the base. Pyridine is a very stable compound it can be heated with nitric acid or chromic acid without undergoing change but at 330° it is converted by a mixture of nitric acid and fuming sulphuric acid into nitropyridine, a colorless compound that melts at 41° and boils at 216°. At a high temperature pyridine is converted into a sulphonic acid by sulphuric acid. Chlorine and bromine form addition-products, e.g., C5H5N.CI2, at the ordinary temperature when these are heated to above 200°, substitution-products are formed. The hydroxyl derivative of pyridine is made by fusing the sulphonic acid with sodium hydroxide it resembles phenol in chemical properties. The three possible carboxyl derivatives of pyridine are known. The a-acid is called picolinic acid, the jS-acid nicotinic acid (664), and the 7-acid isonicotinic acid. 

This compound is not well known till now it was only mentioned in a patent C58). We managed to prepare it in an analogous way to compound /3/ in good yield (46). After careful purification, colourless crystals witH a melting point of 23,5°C are yielded (b.p. 51°C,lo 3 torr H-NMR CCDCI3) S = 4,70(s 2H) 3,73 (s 8H) 3,63 (s 8H). This cyclic formal is also readily polymerizable by several initiators (as e.g. boron trifluoride etherate, tin tetrachloride, trifluoroacetic acid etc.) (59). At the solution polymerization in methylene cHToride ( [mJ = 2-3 Mole/1) at 0 C with trifluoro-methane sulphonic acid (0,5 mole ) waxlike polymers are obtained (molecular weights 20,000 - 30,000), which are easily soluble in water and in organic solvents. 

Some particular advantages of this protection method arise from the polar nature of the sulphonic acid group, which should allow the derivatives to be dissolved in polar reaction media, and should also aid their purification. 

PPy films were prepared by electropolymerization in distilled water. Pyrrole monomer was distilled under nitrogen. The polymerization solution contained fireshly distilled pyrrole (O.IM) and dopant (O.IM). Sodium dode l sulphate (98% purity, Aldrich), sodium p-toluene sulphonate (p-TS) (98% purity, MerclO and p-chlorobenzene sulphonic acid (CBS) (98% purity, Tokyo Kasei) were used as dopants without further purification. Electrodeposition was performed at a constant current of 2.8 mA cm using horizontal stainless steel electrodes under a nitrogen blanket. The film was removed firom the electrode and washed with a mbcture of water and acetonitrile to remove excess dopant. Dedoped films were obtained by reversing the polarity of the galvanostat. All films were stored in a vacuum desiccator before evaluation. 

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