Process for synthesizing azo compounds
A process for synthesizing an azo compound by oxidation of a hydrogen compound in the presence of a catalyst and a compound of formula (I) is described in which R 1 , R 2 and R 3 (R 1 )(R 2 )C(PO 3 (R 3 ) 2 ) 2 (I) are as defined. The use of a compound of formula (I) as complexing agent for a catalyst is also described.
1. A process for synthesizing an azo compound, the process comprising the steps of:
a) reacting an oxidizing agent with a hydrazo compound, at least one catalyst comprising a water-soluble compound chosen from alkali metal or ammonium salts of molybdenum, alkali metal or ammonium salts of tungsten, phosphomolybdic acid and alkali metal or ammonium salts thereof, phosphotungstic acid and alkali metal or ammonium salts thereof, molybdosulfates and mixtures thereof, and at least one compound of formula (I):
(R 1 )(R 2 )C(PO 3 (R 3 ) 2 ) 2 (I)
so as to form a solution containing an azo compound,
wherein:
R 1 and R 2 , which may be identical or different, are chosen independently of each other from a hydrogen atom, a saturated or unsaturated, linear, branched or cyclic, optionally substituted hydrocarbon chain, —OH and —O-alkyl, where “alkyl” represents a saturated, optionally substituted, linear or branched hydrocarbon chain comprising from 1 to 6 carbon atoms; and
R 3 is chosen from a hydrogen atom and metal or ammonium ions;
b) recovering all or part of the reaction mixture obtained in step a);
c) separating the reaction mixture recovered into a fraction containing the azo compound and a fraction of residual aqueous liquors; and
d) recovering, and optionally washing and drying, the azo compound obtained.
2. The process as claimed in claim 1 , wherein the compound of formula (I) is chosen from [1-hydroxy-1-(H-imidazol-1-yl)ethane-1,1-diyl]diphosphonic acid or one of its salts, hydroxymethylenediphosphonic acid, 1-hydroxylethylidene-1,1-diphosphonic acid (HEDP) and 1-hydroxybutanediphosphonic acid, in their acid form or in the form of their salts.
3. The process as claimed in claim 1 , wherein the hydrazo compound is chosen from symmetrical hydrazo compounds bearing nitrogen-based functional groups.
4. The process as claimed in claim 1 , wherein the oxidizing agent is chosen from inorganic peroxide derivatives.
5. The process as claimed in claim 1 , wherein at least one reducing agent is added to the aqueous solution obtained in step a).
6. The process as claimed in claim 1 , wherein at least one reducing agent is added to the fraction of residual aqueous liquors.
7. The process as claimed in claim 5 , wherein the reducing agent is chosen from hydrazine, sodium sulfite, sodium bisulfite and mixtures thereof.