Process for synthesizing azo compounds

Abstract

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.sub.1, R.sub.2 and R.sub.3
(R.sub.1)(R.sub.2)C(PO.sub.3(R.sub.3).sub.2).sub.2  (I)
are as defined. The use of a compound of formula (I) as complexing agent for a catalyst is also described.

Claims

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.sub.1)(R.sub.2)C(PO.sub.3(R.sub.3).sub.2).sub.2  (I) so as to form a solution containing an azo compound, wherein: R.sub.1 and R.sub.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.sub.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.

Description

EXAMPLES

(1) In the examples which follow: DHC denotes hydrazobisisobutyronitrile, a hydrazo compound obtained industrially by reaction of acetone cyanohydrin with hydrazine hydrate, filtration and then washing with water, and stored in a refrigerator (T<10° C.). Its moisture content is 12.7% and its purity is greater than 99% by analysis. the phosphomolybdic acid used is a product sold by Aldrich which corresponds to the formula H.sub.3[P(Mo.sub.3O.sub.10).sub.4].xH.sub.2O and is used as is (molar mass 1825.25 g/mol in anhydrous form). The product used has a molybdenum content of 50%. DOSS denotes di(2-ethylhexyl) sulfosuccinate. AZDN (or AIBN) denotes azobisisobutyronitrile.
Method for Sampling and Assaying the Content of Residual Peroxide

(2) In the following examples the contents of residual peroxide are measured as follows.

(3) About 3 ml to 5 ml of the reaction medium in suspension is withdrawn and is filtered in order to remove DHC and solid AZDN present. About exactly 1 gram of the filtered solution is weighed out and introduced into a 250 ml flask, and to this are added 50 ml of distilled water, 15 ml of 30% by weight sulfuric acid and 15 ml of a 30% KI solution. The flask is stoppered and left in the dark for 15 min. It is then titrated with a solution of sodium thiosulfate having a normality of 0.1 N until the yellow coloration disappears. The content of residual hydrogen peroxide (H.sub.2O.sub.2) is calculated as follows:

(4) $\%H_2{O}_2\mathrm{résiduel}=\frac{\mathrm{Volume}\mathrm{de}\mathrm{thiosulfate}\mathrm{de}\mathrm{sodium}0.1N\left(\mathrm{en}\mathrm{mL}\right)}{2\times 100\times \mathrm{masse}\mathrm{de}\mathrm{filtrat}\left(\mathrm{en}\mathrm{grammes}\right)}$

(5) The assaying of the residual molybdenum is carried out by the optical ICP (or inductively coupled plasma) technique. The particle size measurement is carried out using a Mastersizer® S device. The measurement is performed on wet crystals using as dispersant water and a drop of Igepal® (ethoxylated nonylphenol) surfactant, after 10 minutes of circulation in the measurement cell.

Example 1: Complexing Agent Test

(6) A mixture is prepared containing 100 ml of a 5% by mass aqueous hydrogen bromide solution, 1.5 g of Phosphomolybdic acid (catalyst) and 1 g of complexing agent.

(7) After 30 minutes, a first observation is made on the solubility of the Phosphomolybdic acid in the absence of ammonium bromide (NH.sub.4Br).

(8) 10 ml of a 37.5% aqueous ammonium bromide solution is then added. After 30 minutes, a second observation is made on the solubility of the phosphomolybdic acid in the presence of ammonium bromide.

(9) The results are collated in table 1 below:

(10) TABLE-US-00001 TABLE 1 Presence of Presence of precipitate precipitate (without (with Complexing agent NH.sub.4Br) NH.sub.4Br) 1-Hydroxyethylidene-1,1-diphosphonic acid NO NO (Dequest ® 2010) Aminotris(methylenephosphonic acid) YES YES (Dequest ® 2000) Diethylenetriaminepenta(methylene- YES YES phosphonic acid) (Dequest ® 2060) 2,2′-Ethylenebis(nitrilomethylidene)diphenol YES YES N,N′-ethylenebis(salicylimine) (Salen) Glycerol NO YES 2-Amino-3-(1H-imidazol-4-yl)propanoic acid YES YES (DL Histidine) 2-Amino-3-mercaptopropanoic acid NO YES (DL Cysteine) Methionine NO YES 1,10-Phenanthroline YES YES Blank NO YES

(11) The tests show that the compounds other than those corresponding to formula (I) do not make it possible to prevent the appearance of a precipitate in the presence of ammonium ions. On the other hand, when the complexing agent corresponds to the definition of formula (I), no precipitate is observed. This absence of precipitate reflects the stability of the phosphomolybdic acid in the presence of the complexing agent in a medium containing ammonium ions. The complexing agent of formula (I), for example Dequest® 2010, makes it possible to prevent the precipitation of the phosphomolybdic acid in the presence of ammonium ions.

(12) Another test, performed under the same operating conditions as above, was carried out in order to determine the amount of compound of formula (I) which is sufficient to prevent the precipitation of the phosphomolybdic acid in the presence of NH.sub.4Br the amount of complexing agent of formula (I) was gradually reduced until the formation of a precipitate was observed.

(13) This series of tests made it possible to demonstrate that, in a solution comprising containing 100 ml of a 5% by mass aqueous hydrogen bromide solution, 1.5 g of phosphomolybdic acid (catalyst) and 5 ml of a 37.5% by mass NH.sub.4Br solution, an amount of 0.35 g of complexing agent of formula (I), such as Dequest® 2010, is sufficient for inhibiting the precipitation of the phosphomolybdic acid, i.e. a complexing agent/phosphomolybdic acid molar ratio of 0.2.

Example 2: Counter Example (Process in the Absence of Complexing Agent)

(14) 126 g of AZDN (0.77 mol), 128 g of DHC (hydrazobisisobutyronitrile) (0.77 mol), an aqueous solution composed of 635 g of water, 35 g of HBr, 7 g of phosphomolybdic acid (50% Mo content, i.e. 0.036 mol of molybdenum), and 0.1 g of DOSS (di(2-ethylhexyl) sulfosuccinate) are introduced into a 1.5 l capacity reactor equipped with a stirring system allowing the mixing of a suspension. After starting the stirring and the jacketed cooling system, stabilization of the temperature at around 10° C. is awaited.

(15) Once a temperature of 10° C. has been reached, 78.05 g of 35% H.sub.2O.sub.2 (i.e. 0.80 mol of H.sub.2O.sub.2) are introduced continuously over 4 h. During the reaction, the medium is maintained at a temperature of between 10° C. and 12° C. The reaction is stopped about 20 to 30 minutes after having introduced the entire amount of H.sub.2O.sub.2. The end of the reaction is made visible by the formation of bromine and by the increase in the redox potential (before the introduction of H.sub.2O.sub.2 the potential is about 400 mV and at the end of the reaction, that is to say after the introduction of the entirety of the H.sub.2O.sub.2, the potential is about 800 mV). The redox potential is measured using a platinum redox probe.

(16) The suspension from the reactor is then completely filtered. 290 g of crude AZDN containing 15% moisture is obtained, i.e. a yield of 95%. In addition, 20 ml of water are also used to rinse the filter and are added to the residual aqueous liquors.

(17) The obtained residual aqueous filtration liquors, i.e. 740 g, are neutralized by hydrazine hydrate in order to remove the peroxide excess and the bromine formed (assaying found 0.1% of residual H.sub.2O.sub.2 equivalent). The redox electrode is utilized to bring the potential back to its initial value, i.e. about 300 mV to 400 mV.

(18) Half of the residual aqueous liquors, i.e. 374 g, is put aside to be reused directly in the following test, whereas the other half undergoes a step of concentration under vacuum aiming to remove about 60% to 65% of the water from this fraction of residual aqueous liquors. This is carried out under a vacuum of 250 millibar (25 kPa) between 55° C. and 60° C. For 325 g of residual aqueous liquors employed, 235 g of an aqueous distillate fraction and 90 g of resulting concentrated solution are thus obtained. This resulting concentrated fraction, containing the catalytic system, may thus be reused with the fraction of untreated residual aqueous liquors for the following cycle.

(19) Half of the AZDN obtained is washed four times with water using 200 ml of water each time. The other half of the crude AZDN is kept as is (with the fraction of residual aqueous mother liquors present in the crystals) to be recycled during the following cycle in the following example.

(20) Thus, practically all of the components of the catalytic system are recycled, except for the fraction which is inherent to the losses in transfer and sampling for assays and also the fraction of residual aqueous liquors retained in the crystals of the washed AZDN produced.

Example 3: Counterexample (Process without Complexing Agent and with Recycling)

(21) 145 g of the crude unwashed AZDN obtained previously (i.e. 0.78 mol of AZDN containing about 15 g of residual aqueous liquors in the crystals), 128 g of DHC (hydrazobisisobutyronitrile) (0.78 mol), 0.05 g of DOSS (di(2-ethylhexyl) sulfosuccinate), 374 g of residual aqueous liquors resulting from the filtration of the reaction medium during the previous test and also the residual aqueous liquors concentrated during the previous test are introduced into the reactor of the previous example. The bromides present in the recycled fractions of residual aqueous liquors are assayed in order to determine the supplement of catalytic system required. In order to maintain a reaction medium of the same composition as that of the previous example, 4 g of HBr, 0.78 g of phosphomolybdic acid and 150 g of water are typically added, this feedstock of water being calculated according to the water contents of the reactants used (aqueous HBr solution, moisture content of the DHC) in order to return to the initial composition of the previous test.

(22) This water, 150 g, will make it possible, in an industrial process, to more easily feed the solid DHC in the form of an aqueous suspension from a holding tank, for example.

(23) The reaction is then conducted as in the previous example by continuously pouring 78.05 g of 35% H.sub.2O.sub.2 over a period of 4 hours into the reaction medium maintained between 10° C. and 12° C.

(24) The process is thus carried out by recycling into test n+1 half of the AZDN and of the residual aqueous liquors obtained and concentrating the other half of the residual aqueous liquors in test n.

(25) The three first recycling operations lead to the obtaining of white products with a purity of greater than 95% by NMR analysis. During the fourth recycling operation the formation of a significant deposit with a yellow color is noted. This deposit contaminates the AZDN obtained, washing operations with water do not make it possible to remove this deposit.

(26) It is also noted that the deposit forms again over time in the residual aqueous liquors obtained after filtration.

(27) The following concentration step was conducted on these residual aqueous liquors, after filtration to remove these crystals. At the end of the concentration, it is noted that these crystals have reformed at the bottom of the boiler and hence contaminate the concentrated solution of the residual aqueous liquors.

(28) Analysis of this deposit, by X-ray fluorescence and X-ray diffraction, shows that it is a crystalline compound of ammonium phosphomolybdate, these compounds being known for being very insoluble in acidic media.

(29) The formation of ammonium ions in the medium seems to be attributable to the hydrolysis of the cyano by-products. The ammonium ions thus accumulate over the course of the operations of recycling into the reaction medium, causing the precipitation of the catalyst.

Example 4: Process in the Presence of Dequest® 2010 (According to the Invention)

(30) The process of the invention is carried out according to the same procedure as that described in counterexample 2, but with addition of 20.7 g of a 60% aqueous solution of Dequest® 2010 (i.e. 1.65 mol of Dequest® 2010 per mole of molybdenum) to the reaction medium before the introduction of the hydrogen peroxide solution.

(31) A series of recycling operations is carried out as described in counterexample 3. In this example, 12 recycling operations are thus carried out, without noting formation of precipitate contaminating the AZDN obtained or precipitating in the aqueous mother liquors or during the concentration operations.

(32) The supplements of catalytic system are carried out throughout the process as indicated in counterexample 3, but in this example, for an addition of 4 g of HBr; 1.4 g of Dequest® 2010 (i.e: 2.35 g of 60% aqueous solution of Dequest® 2010) are also added.

(33) On the twelfth recycling operation, the yields of washed AZDN remain above 95%, the residual bromide content of the washed AZDN is from 80 ppm to 90 ppm and the purity by NMR analysis is greater than 98%. The particle size remains constant and is between 110 μm and 130 μm (number-average diameter).

Example 5: Recrystallization of the AZDN Obtained by the Process

(34) The AZDN obtained according to example 4 at the end of the twelfth recycling operation is washed 3 times with 200 ml of water and then dried at ambient temperature (residual moisture content 1% to 2% by weight). 20 g of this AZDN are then dissolved in 250 ml of methanol at 35° C. When the crystals have dissolved, the temperature is lowered to 2° C. to recrystallize the AZDN. The mixture is then filtered under cold conditions; the methanol solvent fraction recovered is put aside to be reused in the next recrystallization. The AZDN crystals recovered on the filter are washed with a 50 ml portion of water and then dried.

(35) The operation is started again by once more taking 20 g of the AZDN obtained at the end of the twelfth recycling operation and using the methanol fraction previously recovered, and possibly supplementing it to compensate for losses of solvent or to completely dissolve the 20 g of AZDN employed.

(36) Five successive recrystallization operations were thus carried out each time re-employing the fraction of recovered methanol. The search for traces of molybdenum by the optical ICP method on an ICAP 6500 spectrometer device shows that all of the AZDN thus obtained is free of traces of residual molybdenum (detection limit of 1 ppm).