Hydrochloric Acid → 5-Fluoro-2-mercaptobenzoic acid

Beteiligte Stoffe

Reaktionsbedingungen

Reaktionsschritte

A mixture of crystallized sodium sulfide (1.8 g, 0.01 mole) and powdered sulfur (0.24 g) was dissolved by heating and stirring in 2 cc of boiled water. A solution of 0.3 g of sodium hydroxide in 1 cc of water was then added and the mixture was cooled stepwise as detailed above. Four cc of water, 1 g (0.007 mole) of 5-fluoro-anthranilic acid and 1.4 cc of concentrated hydrochloric acid were added to a separate beaker which was set by a freezing mixture to 0° C. The mixture was stirred and cooled to about 6° C. Meanwhile, 0.48 g (0.007 mole) of sodium nitrite were dissolved in 2 cc of hot water and the solution was cooled on ice. When the temperature dropped to 5° C., the nitrite solution was run through a separatory funnel into the anthranilic solution. About 3.5 g of cracked ice were added at a rate that kept temperature below 5° C. The diazo solution was then added to the alkaline sulfide solution (which was kept at a temperature of 2°-4° C.) along with 10 g of ice and temperature was kept below 5° C. The mixture was allowed to warm up to room temperature, and when evolution of nitrogen ceased (about 2 h), concentrated hydrochloric acid (˜1.5 cc) was added until the solution was acid to Congo red paper. The precipitate of disulfide was filtered and washed with water. To remove the excess sulfur, the precipitate was dissolved by boiling with a solution of 0.5 g of anhydrous sodium carbonate in 15 cc of water and the mixture was filtered while hot. The solution was then acidified with hydrochloric acid, the precipitate was filtered and the cake was sucked to dryness. The cake was dried by addition of toluene followed by azeothropic evaporation. This procedure was repeated twice. The cake was mixed with 0.2 g of zinc dust and 2 cc of glacial acetic acid, and the mixture was refluxed for overnight. The mixture was cooled and filtered with suction. The filter cake was washed once with water and transferred to a 10 cc beaker. The cake was suspended in 2 cc of water and the suspension was heated to boiling. The hot solution was made strongly alkaline by the addition of about 0.3 cc of a 33% sodium hydroxide solution. The alkaline solution was boiled about 20 min. and the insoluble material was filtered. The product was then precipitated by the addition of concentrated hydrochloric acid to make the solution acid to Congo red paper. The product was filtered with suction, washed once with water, and dried in an oven at 100°-130° C.; mp was 185° C.

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