Phenoldisulphonic acid

According to Urbanski (Ref 35) At room temperature the conversion proceeds slowly, whereas it occurs rapidly on heating. The higher the temperature, the more p-isomers are formed. At 90—100°C phenoldisulphonic acid is also formed ... 

Theory First and foremost the active ingredient i.e., glyceryl trinitrate is extracted completely from the tables by shaking with glacial acetic acid. To an aliquot of the resulting acetic acid solution an excess of phenoldisulphonic acid is added to produce a yellow colour which is subsequently intensified by adding an excess of ammonia. The following reactions take place ... 

Materials Required Glyceryl trinitrate tablets 20 glacial acetic acid (90% v/v) 5 ml phenoldisulphonic acid solution (heat 3 g of phenol with 20 ml of sulphuric acid on a water-bath for 6 hours, and transfer the resulting liquid to a stoppered vessel) 2 ml strong ammonia solution 20 ml potassium nitrate (previously dried at 105 °C) 1 g ... 

Dissolve 133.5 mg of potassium nitrate, in sufficient DW to produce 100 ml to 10 ml add sufficient glacial acetic acid to produce 100 ml. Taking 2 ml of this solution, just repeat the assay beginning the procedure at add 2 ml of phenoldisulphonic acid solution. . 

Cognate Assays The following two pharmaceutical products, namely Pentaerythritol tetranitrate Tablets and Diluted Isosorbide dinitrate are assayed by using a solution of phenoldisulphonic acid as detailed below ... 

Sulphophenol , which is the name of the starting material for the second stage, is a mixture of 1,4-phenolsulphonic and 1,2,4-phenoldisulphonic acids. 

Thus, when heating l-hydroxy-2,4,6-trisulphonic acid with 61% nitric acid at 110°C, picric acid is produced in a yield amounting to 90% of the theoretical (220 parts of picric acid per 100 parts of phenol), whereas from 1,2,4-phenoldisulphonic acid under analogous conditions, the yield of picric acid is 86% of the theoretical (208-210 parts of picric acid per 100 parts of phenol). 

To 400 parts of 30% oleum 94 parts (1 mole) of phenol is added with stirring, the temperature being maintained below 90°C. The mixture is heated to 90-100°C during a period of 5 hr. As a result phenoldisulphonic acid is formed. 

The phenoldisulphonic acid thus prepared is then nitrated in conventional iron nitrators with a jacket and a stirrer. 1000-2000 kg of sulphophenol may be nitrated at a time. From 100 parts of phenol 205 parts of picric acid can be obtained. 

Most spectrophotometric methods for determining nitrate are based either on I), nitration or oxidation of appropriate organic reagents to form coloured compounds or on, 2), reduction of NO.i to NO2 or NH3 with subsequent determination of this species. Prevalent among the methods belonging to the first group are those using phenoldisulphonic acid, and xylenols. 

Phenoldisulphonic acid, solution in cone. H2SO4. Dissolve 12.5 g of phenol in 75 ml of cone. H2SO4, add 37.5 ml of 13% oleum, and stir well. Heat the solution in a 250-ml conical flask for 2 hr on a boiling water-bath with occasional stirring. 

Neutralize the solution (containing not more than 100 )4g of NO3 ) in a small evaporating dish, add 1 ml of the CaCO suspension, and evaporate to dryness on a water-bath. Treat the cooled residue with 1 ml of phenoldisulphonic acid reagent and stir well. After 5 min, dilute with 10 ml of water, and transfer the solution quantitatively to a 25-ml standard flask. Add cone, ammonia solution until the solution becomes intensely yellow, then add 5 ml more, and dilute the solution with water to the mark. Measure the absorbance of the yellow solution at 410 nm against water or a reagent blank solution. 

Complete disintegration of the tablets is essential. Hora and Webber found that in the presence of amounts of ammonium ion comparable with the amount of nitrate-nitrogen present, serious losses of nitrate-nitrogen occurred in the phenoldisulphonic acid method but prevented these by a preliminary evaporation of sample solution after adding one or more drops... 

Small quantities of nitrate may be estimated colorimetrically either with (a) phenoldisulphonic acid or ( ) 2,4-xylenol. Reduction with Devarda alloy or aluminium foil can also be used (see under Determination of Nitrogen) and the ammonia produced determined with Nessler s reagent. 

In the phenoldisulphonic acid method chlorides must be eliminated. 

To a quantity of sample containing 0 05 mg or less of nitrogen, add a 0 44 per cent solution of silver sulphate (1 ml = 1 mg Cl) to precipitate all but about 0 5 mg of chloride. Heat to boiling, allow to settle and filter. Evaporate the filtrate to dryness in a porcelain dish, cool, treat with 2 ml of phenoldisulphonic acid solution (prepared by dissolving 25 g of phenol in 150 ml of concentrated sulphuric acid, adding 75 ml of fuming... 

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