Sodium, benzenesulphonate

Preparation of Sodium Benzenesulphonate (SECTION 470).—In a 250-cc. flask place 50 grams of fuming sulphuric acid which contains 8 to 10 per cent of sulphur trioxide (sp. gr. 1.90), connect the flask with a reflux condenser, and add, drop by drop, from a separatory funnel suspended in the condenser, 20 grams of benzene. During the addition of the benzene, which should take from 10 to 15 minutes, the flask should be shaken vigorously every minute or two. If all the benzene does not dissolve after continuous shaking for a few minutes, heat the mixture on a water-bath until solution is complete. 

The sulphonic acid formed can be separated in the form of a salt by either of the methods described below. In the first method (a), which in the case of benzenesulphonic acid is simpler, advantage is taken of the fact that sodium benzenesulphonate is insoluble in a solution of sodium chloride. The second method (.b) is the one commonly used to isolate sulphonic acids. It is 

Potassium benzenesulphonate crystallizes in lustrous plates, which effloresce in the air. The salt is very soluble in water, and melts above 300° with decomposition. 

—(b) The free sulphonic acid can be obtained from the calcium salt by adding to its solution just enough sulphuric acid to precipitate the calcium as sulphate, evaporating the solution to a small volume, and placing it in a desiccator to evaporate over sulphuric acid. In the preparation of free sulphonic acids in this way it is better to prepare the barium salt, as barium sulphate is less soluble in water than calcium sulphate, and the free add is not contaminated with a small amount of sulphate. 

Identification of a Sulphonic Acid by Conversion into a Phenol (SECTION 477).—Melt about 1 gram of sodium hydroxide in a small iron or porcelain crucible, and add to the fused mass about 0.5 gram of sodium benzenesulphonate. Keep the mixture just above its melting-point, and do not let it char. Stir occasionally during 5 minutes. Cool, dissolve in water, acidify with dilute hydrochloric acid, and note the odor produced. Filter and add bromine water, drop by drop. Write equations for all the reactions involved in the test. 

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The high sodium ion concentration results in facile crystallisation of the sodium salt. This process of salting out with common salt may be used for recrystallisation, but sodium benzenesulphonate (and salts of other acids of comparable molecular weight) is so very soluble in water that the solution must be almost saturated with sodium chloride and consequently the product is likely to be contaminated with it. In such a case a pure product may be obtained by crystallisation from, or Soxhlet extraction with, absolute alcohol the sul-phonate is slightly soluble but the inorganic salts are almost insoluble. Very small amounts of sulphones are formed as by-products, but since these are insoluble in water, they separate when the reaction mixture is poured into water ... 

Method 2. Place 90 g. of sodium benzenesulphonate (Section IV,29) (previously dried at 130-140° for 3 hours) and 50 g. of powdered phosphorus pentachloride (1) in a 500 ml. round-bottomed flask furnished with a reflux condenser heat the mixture in an oil bath at 170-180° for 12-15 hours. Every 3 hours remove the flask from the oil bath, allow to cool for 15-20 minutes, stopper and shake thoroughly until the mass becomes pasty. At the end of the heating period, allow the reaction mixture to cool. Pour on to 1 kilo of crushed ice. Extract the crude benzenesulphonyl chloride with 150 ml. of carbon tetrachloride and the aqueous layer with 75 ml. of the same solvent. Remove the solvent under atmospheric pressure and proceed as in Method 1. The yield is about 170 g., but depends upon the purity of the original sodium benzenesulphonate. 

Alternatively a mixture of 90 g. of sodium benzenesulphonate and 60 g. (36 ml.) of phosphorus oxychloride may be used. The experimental procedure is identical with that for phosphorus pentachloride, but the yield is slightly better. 

Method 2. The procedure described under Benzenesulphonyl Chloride, Method 2 (Section IV,206) may be used with suitable adjustment for the difierence in molecular weights between sodium p-toluenesulphonate (Section IV,30) and sodium benzenesulphonate. When the reaction product is poured on to ice, the p-toluenesulphonyl chloride separates as a sohd. This is filtered with suction it may be recrystaUised from hght petroleum (b.p. 40-60°) and then melts at 69°. 

Salts. Sodium benzoate Sodium benzenesulphonate Aniline hydrochloride Methylamine hydrochloride. 

Sodium benzenesulphonate [144-42-4] M 150.1. Crystd from EtOH or aqueous 70-100% MeOH, and dried under vacuum at 80-100°. 

Sodium azide, 918, 919 Sodium benzenesulphonate, 548,549 Sodium bicarbonate solution test, 360, 1071 ... 

The high sodium ion concentration results in crystallisation of the sodium salt. This process of salting out with common salt may be used for recrystallisation, but, for example, sodium benzenesulphonate (and salts of other acids of comparable molecular weight) is so very soluble in water that the solution... 

Hargis and Rogers [106] who studied foam separation of NaDoS/NaDoBS and NaDoS/NaBS mixtures (NaBS is sodium benzenesulphonate) have noted that the accumulation ratio in these surfactants remains constant over a wide concentration range regardless of the presence of the other component. 

One of such toxic compounds is diphenylsulphone (DPS) formed in the reaction of sodium benzenesulphonate with sodium hydroxide. 

In order to obtain pure sodium benzenesulphonate, 5 grammes of die crude product is crystallised from absolute alcohol, upon which it is noticed that the sodium chloride mixed with it is insoluble in alcohol. 

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