Process for preparing high-purity, halogen-free o-phthaladehyde
View Patent ↗Improved process for preparing high-purity, halogen-free o-phthalaldehyde, in which a) tetrahalo-o-xylene is hydrolyzed at a temperature of 155-160° C. and a pressure of from 2 to 5 bar, where appropriate in the presence of a phase-transfer catalyst, to o-phthalaldehyde, which b) is converted in an acidic alcoholic solution at a temperature of from 0 to the reflux temperature into the corresponding dialkoxyphthalane and, subsequently, c) an acetal cleavage is effected by acid hydrolysis at a pH >1.5 to pH 7, resulting in high-purity, halogen-free o-phthalaldehyde.
1. A process for preparing high-purity, halogen-free o-phthalaldehyde, which comprises:
a) hydrolyzing tetrahalo-o-xylene at a temperature of 155-160° C. and a pressure of from 2 to 5 bar, optionally in the presence of a phase-transfer catalyst, to o-phthalaldehyde,
b) converting the o-phthalaldehyde in an acidic alcoholic solution at a temperature of from 0 to the reflux temperature into the corresponding dialkoxyphthalane and, subsequently,
c) cleaving acetals by acid hydrolysis at a pH between 1.5 to 7, resulting in high-purity, halogen-free o-phthalaldehyde.
2. The process as claimed in claim 1 , wherein step a) is carried out in a C 1 -C 4 carboxylic acid in the presence of a base and water.
3. The process as claimed in claim 2 , wherein the amount of carboxylic acid employed is between 4 to 20 mole equivalents based on tetrahalo-o-xylene.
4. The process as claimed in claim 1 , wherein step b) takes place at a pH of between 0 and 3.
5. The process as claimed in claim 1 , wherein step c) takes place at a pH of between 1.6 and 2.5.