Sodium Hydroxide → 4-Sulfothiophene-3-carboxylic acid

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Reaction Conditions

Reaction Steps

In a glass autoclave, 8.6 g of 4-chlorothiophene-3-carboxylic acid are dissolved in 23 ml of water containing 2.1 g of sodium hydroxide, whereupon a solution of 5.6 g of sodium bisulphite in 16 ml of water is added and the solution made just alkaline with a 30% sodium hydroxide solution. The solution is treated with 0.43 g of copper (I) chloride and heated at 143° C. for 16 hours. After cooling, the red copper oxide is filtered off under suction. The filtrate is acidified with 7 ml of concentrated hydrochloric acid and the unreacted starting material precipitates out, the latter being removed by shaking out with ether. The acidic solution is treated with 12 g of potassium chloride while warming and, after cooling to 0° C., the potassium salt of 4-sulphothiophene-3-carboxylic acid separates as colourless crystals. The crystals are dissolved in 50 ml of water and the solution passed through an ion-exchange column which is charged with protons, after which the column is rinsed with water until the solution flowing out has a pH value of 5. The eluate is evaporated to dryness in vacuo. There is obtained 4-sulphothiophene-3-carboxylic acid as a crystalline residue of melting point 154° C. (recrystallisation from water).

Provenance & Evidence