Sulpho benzoic acids

Sulpho Benzoic Acid.— When toluene is sulphonated with concentrated sulphuric acid a mixture of ortho and para toluene sulphonic acid is obtained. 

On oxidation of these compounds the products are the corresponding sulpho benzoic acids. 

Saccharin.—When ortho-sulpho benzoic acid is treated with phosphorus pentachloride the sulphonic acid group yields the stdphon chloride group and this with ammonia yields the sulphamine group. 

From Sulpho Benzoic Acid.— The most common method of preparing phenols is by the alkali fusion of the sulphonic acids, Sulpho benzoic acids will thus yield hydroxy benzoic acids. In case the sulpho benzoic acid has been made by direct sulphonation of benzoic acid the meta compound will result. If, however, we start with tolmne and sulphonate it we will obtain the ortho and para compounds. 

Benzoic acid — Thio-benzoic acid — Sulpho-benzoic acid — Phthalic acid—Ethyl-potassium phthalate—Phenyl-acetic acid—Cinnamic acid—Benzyl-malonic acid.56-58... 

Sulpho-benzoic Acid.—This acid is not changed by the current according to the statements of the same investigator. 

Phenolsulphonephthalein (phenol red). Mix 10 g. of o-sulpho-benzoic anhydride (Section VIII,9), 14 g. of pure phenol and 10 g. of freshly fused zinc chloride in a small conical flask. Place a glass rod in the flask and heat gently over a flame to melt the phenol. Then heat the flask containing the well-stirred mixture in an oil bath at 135-140° for 4 hours. Stir from time to time, but more frequently during the first hour if the mixture froths unduly, remove the flask from the bath, cool and then resume the heating. When the reaction is complete, add 50 ml. of water, allow the water to boil and stir to disintegrate the product. Filter the crude dye with suction and wash it well with hot water. Dissolve the residue in the minimum volume of warm (60°) 20 per cent, sodium hydroxide solution, filter, and just acidify the filtrate with warm dilute hydrochloric acid (1 1). Filter the warm solution, wash with water, and dry upon filter paper. The yield of phenol red (a brilliant red powder) is 11 g. 

Zincon (o-[l-(2-hydroxy-5-sulpho)-3-phenyl-5-formazono]-benzoic acid) [J35-52-4] M... 

Zincon disodium salt (< -[l-(2-hydroxy-5-sulpho)-3-phenyl-5-formazono]-benzoic acid disodium salt) [56484-13-0] M 484.4, m -250-260° (dec). Zincon soln is prepared by dissolving 0.13g of the powder in aqueous N NaOH (2ml diluted to 100ml with H2O). This gives a deep red colour which is stable for one week. It is a good reagent for zinc ions but also forms stable complexes with transition metal ions. [UV-VIS Bush and Yoe AC 26 1345 1954 Hunter and Roberts JCS 820 1941 Platte and Marcy AC 31 1226 7959) The free acid has been recrystd from dilute H2SO4. [Fichter and Scheiss B 33 751 1900]. 

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