| abstract |
The invention relates to a process for the isolation of p-hydroxybenzaldehyde from the reaction mixture obtained by oxidizing p-cresol with oxygen or oxygen-containing gases in methanol in the presence of Na or K hydroxide and an Mn, Ni, Cr or Co salt. The procedure in this process is optionally to add water to the reaction mixture, to heat the resulting solution and to filter off the precipitated Mn, Ni, Cr or Co oxide-hydrate, to remove the methanol from the filtrate by distillation, to cool the residual aqueous solution and thus to allow the p-hydroxybenzaldehyde to crystallize out in the form of the Na or K salt. n Alternatively, the reaction mixture is first dried by atomization, the soluble constituents of the dry substance are then dissolved in hot water, the undissolved Mn, Ni, Cr or Co oxide-hydrate is filtered off and the salt of p-hydroxybenzaldehyde is again allowed to crystallize out by cooling the filtrate. n A further method consists in diluting the reaction mixture with methanol, filtering off the undissolved Mn, Ni, Cr or Co oxide-hydrate, drying the filtrate by atomization, dissolving the resulting dry substance in hot water, and again allowing the p-hydroxybenzaldehyde to crystallize out as the Na or K salt by cooling the solution. |