| Abstract: | Synthesis of vanillin and 4-hydroxybenzaldehyde from guaiacol and phenol, respectively, was investigated. The condensation of guaiacol and phenol with glyoxylic acid in an aqueous alkaline medium resulted in the formation of 3-methoxy-4-hydroxymandelic and 4-hydroxymandelic acid respectively. A process version for the condensation of the phenol with glyoxylic acid, wherein it was found advisable to add an aqueous solution of glyoxylic acid and part of alkali to a batch of the phenol in aqueous alkali, was found to give 77% yield of the mandelic acid based on glyoxylic acid. The oxidation of the mandelic acid could be more suitably carried out at 95°C using 0.51 mol of copper (II) hydroxide for every mole of the mandelic acid in a process where air is simultaneously passed. Taking 3-methoxy-4-hydroxymandelic acid as an example, 88% conversion to vanillin could be obtained. The reaction was found to be second order with respect to the mandelic acid. |
