Salicylicaldehyde : Borate/Formol  process (EP0667331A1 Rhodia Chimie SAS Worldwide applications 1994

In a 250 ml three-necked flask provided with a stirring device, a thermometric sheath and a column equipped with a retrogradator for operating at solvent reflux and separating the reaction water, the following are charged:

    47 g of phenol (0.5 mole),
    31 g of boric acid (0.5 mole),
    15 g of toluene.

Distill for 3 hours with return from the entrainer (toluene) until separation of the theoretical amount of water.

Then, diluted with 75 g of toluene, added 16 g of trioxymethylene suspended in 25 g of toluene and maintained at 80 ° C until the end of reaction of formaldehyde (about 3 h).

The toluene solution of saligenin borate obtained is hydrolyzed at room temperature with a sodium hydroxide solution prepared by adding 200 g of water to 152 g of a sodium hydroxide solution at 30% by weight, then allowed to settle, and the solution is separated. aqueous containing the sodium salts of saligenol and boric acid.

This aqueous solution is then directly subjected to oxidation according to the same process as in Example 4, except that it is unnecessary to add boric acid.

    0,8 g de noir à 2 % de platine (16 mg de platine)
    0,035 g d'oxyde de bismuth (31 mg de bismuth)


until the volume of oxygen absorbed corresponds to the quantity theoretically necessary to transform saligenol into salicylic aldehyde, which requires approximately 1 hour.

The catalyst is then separated from the reaction mass, then the salicylic aldehyde formed from its sodium salt is released by the addition of 200 ml of 5N sulfuric acid, then the operations of entrainment in steam or water are carried out. extraction with a suitable solvent to isolate the salicylic aldehyde.

43 g of salicylic aldehyde are thus obtained, which represents a yield of 68% relative to the phenol used.