Process for purifying crude 4-aminophenol

Details Process for purifying crude 4-aminophenol Process for purifying crude 4-aminophenol

C - Chemistry, Metallurgy

07

C

260/612.3

C07C 213/10 (2006.01) C07C 215/76 (2006.01)

Patent

CA 1309109

ABSTRACT A process for the purification of crude 4-aminophenol which was prepared by the catalytic hydrogenation of nitrobenzene in aqueous sulfuric acid is described involving: adjusting the pH of an aqueous solution of crude 4-aminophenol to pH 4.0-5.0 at a temperature between 75°C and 85°C; mixing the aforesaid solution with toluene as the solvent, in order to extract various impurities and the dissolved nitrobenzene starting material; adjusting the pH of the resultant solution as required to maintain it at pH 4.0-5.0; allowing the resultant mixture to settle thereby forming a top organic layer and a bottom aqueous raffinate layer which raffinate contains 4-aminophenol and the by-product material, ortho-aminophenol; separating the two layers and repeatedly extracting the raffinate layer with toluene at pH 4.0-5.0 at a temperature of 75-85°C until most impurities have been removed from the resultant final raffinate; adding to the resultant raffinate, a charcoal decolorizing agent and a sodium sulfite type salt, which are then removed, leaving a filtrate which contains the 4-aminophenol and also the by-product ortho-aminophenol; adjusting the pH of said filtrate to pH 6.5-8.0 and cooling it to a temperature below 10°C; separating the precipitated pure 4-aminophenol from the by-product ortho-aminophenol which remains in the solution.

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