The present invention relates to a process for the preparation of the alkoxyamine 2-methy1-2-[N-(diethoxy-phosphory1-2,2-dimethyIpropy1)aminoxyJpropionic acid of formula (I):
(Figure remove)
or of its salts from an azo compound and from a
^-phosphorated nitroxide. *
WO 2004/014926 discloses the synthesis of the alkoxyamine 2-methyl-2-[N-(diethoxyphosphoryl-2,2-
dimethyIpropy1)aminoxy]prppionic acid according to an ATRA (Atom Transfer Radical Addition) reaction which uses a metal complex, in particular a copper complex. This process requires expensive purification stages to remove the metal compounds, such as washing operations with aqueous solutions, and generates large amounts of metal-comprising effluents.
US 4 581 429 discloses the synthesis of an alkoxyamine other than the alkoxyamine of formula (I) by photolysis of an azo compound (4,4'-azobis(4-cy-ano-n-pentanol)) in the presence of di(t-butyl) nitroxide. However, the yield is low (43%) and the alkoxyamine obtained has to be purified by chromatography on a silica column, which cannot be extrapolated to the industrial scale.-
The process for the preparation, of the alkoxyamine (I) developed by the Applicant Company does not exhibit the disadvantages of the processes of the prior art:
^ the yield of alkoxyamine (I) is high: it is possible to
obtain a quantitative yield with respect to the
(i-phosphorated nitroxide;
^ the process can operate at low temperature (< 30°C),
which makes it possible in particular to retain the
stability of the alkoxyamine (I) in solution, and proves to
be more economical than the prior processes;
*i> the purification of the alkoxyamine (I) is easy: by
simple precipitation from the reaction mixture, the
alkoxyamine (I) is obtained with a purity of greater .than
99%;
^ the process is a 2- or 3-stage process, which stages
can follow on successively from, one another in the same
reactor (one pot) when the solvent used in the 3 stages is
the same and the intermediates do not require purification;
*i> the process generates • very little in the way of
effluents and in particular -no metal-comprising effluents;
^ the process can be ' adapted to a semicontinuous or
continuous process.
The process according to the invention takes place in 2 or 3 stages according to the reaction scheme detailed below:
(Figure remove)
The first stage consists in saponifying the ester functional group of the az;o compound of dialkyl azobisisobutyrate type, preferably dimethyl or diethyl azobisisobutyrate, in the presence of a base.
The dialkyl azobisisobutyrates can be prepared from azobisisobutyronitrile according to the process disclosed in WO 2000/042000. In the process according to the invention, it will not be departing from the scope of the invention to start from azobisisobutyronitrile and an alcohol (methanol, ethanol, and the like), as disclosed in WO 2000/042000, the dialkyl azobisisobutyrates thus being prepared in situ.
Preferably, the base of MOH type is sodium hydroxide, potassium hydroxide or ammonium hydroxide (M represents Na+7 K* or NH4+).
The base/azo compound molar ratio is generally between 2 and 3 and the reaction is generally carried out at a temperature of between 0 and 40°C in 'the presence of a solvent. The solvents which can be used can be mixtures of alcohols and water, acetonitrile and water or tetra-hydrofuran and water and preferably, methanol/water or ethanol/water mixtures. The salt of the azo compound can be isolated by evaporation of the solvent or used as is in solution for the 2nd stage.
The 2nd stage consists in photolysing the salt of the azo compound in the presence of N-(tert-butyl)-!-diethylphosphono-2,2-dimethylprqpyl nitroxide of . formula (II):
(EtO)j P CH N O'
I
. C(CH3)3
The nitroxide of formula (II) (abbreviated to SGI) can be prepared, for example, according to the processes disclosed in WO 2000/040526 or WO 2000/040550 or alternatively in WO 2002/048159.
The nitroxide (II)/azo compound molar ratio is generally between 0.5 and 5 and preferably between 1 and 2.5.
Irradiation can, for example, be carried out using one or more mercury vapour lamps emitting radiation with a wavelength of between 200 and 600 nm. The reaction is generally carried out at a temperature of between 0 and 40°C in the presence of a solvent. The solvents which can be used can be, as in the 1st stage, mixtures of alcohols and water, acetonitrile and water or tetrahydrofuran and water and preferably methanol/water or ethanol/water mixtures. Preferably, the solvents of the 1st and 2nd stages are identical.
It is preferable to carry out the reaction under an inert atmosphere (nitrogen, argon, and the like) and with vigorous stirring, either by sparging nitrogen via an atomizer head or using a recirculating pump. It is possible either to isolate the alkoxyamine in the' salt form, by precipitation or by evaporation of the solvent, or to precipitate it in the acid form from the reaction mixture according to the 3rd stage.
The 3rd stage consists in acidifying the alkoxyamine salt in order to recover the alkoxyamine in the acid form. Preferably, the acid used is hydrochloric acid (in the gaseous or aqueous solution form) or sulphuric acid. Acidification is generally carried out at a temperature of between 0 and 30°C. The use of a solvent of alcohol(s) and water type, such as methanol/water or ethanol/water, as in the 1st and 2nd stages, is also preferred as it makes possible the precipitation of the alkoxyamine (I), which can be recovered by simple filtration.
The process of the present invention can be carried out batchwise, semicontinuously or continuously. In the case of a batch process, the three stages described above can follow on in succession, the solvent used being the same and the intermediates not requiring a purification stage.
The reaction mixture resulting from the 2nd stage can also be drawn off continuously and then subjected to
acidification with a strong acid to precipitate the alkoxyamine (I), which can then be recovered, for example by
filtration.
The alkoxyamine (I) thus prepared can be used as radical polymerization initiator, in particular as initiator for controlled radical polymerization; see, for example, US 4 581 429, WO 2000/49027 and WO 2004/014926.
The following examples illustrate the invention without limiting it.
Example 1
a- Preparation of the sodium salt of DEAB
Diethyl azobisisobutyrate (DEAB) is prepared according to
WO 00/42000.
25 g of DEAB (96.8 mmol) and 125 ml of methanol are introduced into a 500 ml glass reactor. 9.7 g of sodium hydroxide (242 mmol) are dissolved in 250 ml of water in a dropping funnel. The sodium hydroxide solution is run into the DEAB solution while maintaining the temperature at 25°C and then reaction is allowed to take place at ambient temperature for 1 h.
b - Synthesis of the alkoxyamine (I)
The nitroxide SGI of formula (II) is prepared according to
the example of WO .02/48159.
The photochemical reactor used is a jacketed glass reactor with a working volume of 1 1 equipped with a jacketed lamp holder made of quartz. The lamp used is a high pressure mercury vapour lamp having a power of 700 W and emitting between 240 nm and 580 nm with a radiation maximum at 366 nm (reference TQ718 from Heraeus). Stirring is provided by sparging with nitrogen via an atomizer head.
The DEAB sodium salt solution prepared above is introduced into the photochemical reactor described above and then
9.5 g of nitroxide SGI (32.3 mmol), dissolved in 125 ml of methanol, are added. The reaction mixture is brought to 10°C and degassed by sparging with nitrogen for 15 min, and then irradiation is begun. The reaction is maintained at 10°C under nitrogen sparging for 5 h (until the reaction mixture has discoloured).
The reaction mixture is then poured into 2.5 1 of water comprising 20 ml of 37% hydrochloric acid (647 mmol). The white powder formed is filtered off, washed with pentane and then dried under vacuum. 11.5 g of alkoxyamine (I) are obtained in the form of a white solid (yield = 93%).

31,
13,
The product is characterized by XH, 1JC and J1P NMR. The results are in agreement with those given in WO 2004/014926 (Example 1) .
The elemental analysis (empirical formula the following results:
(Table remove)Example 2
The preparation is carried out as in Example 1, except for the modification of the sodium hydroxide/DEAB ratio (3 instead of 2.5), of the DEAB/nitroxide SGI ratio. (2.3 instead of 3) and of the photolysis temperature (20 °C instead of 10°C).

(Table remove)15.6 g of alkoxyamine (I) are then recovered, i.e. a yield of 97%.

1. Process for the preparation of the alkoxyamine 2-methyl-2-[N-(diethoxyphosphoryl-2,2-dimethylpropyl)-aminoxyjpropionic acid of formula (I):
(Figure remove) or of its salts, comprising:
• a stage of saponification of an azo compound of dialkyl
azobisisobutyrate type, preferably dimethyl or diethyl
azobislsobutyrate, in the presence of a base preferably
chosen from sodium hydroxide, potassium hydroxide or
ammonium hydroxide,
• a stage of photolysis of the azo compound salt
resulting from the saponification stage in the presence of
N-(tert-butyl)-l-diethylphosphono-2,2-dimethylpropyl
nitroxide,
• optionally a stage of acidification of the salt of the
alkoxyamine obtained on conclusion of the photolysis stage,
preferably with hydrochloric acid (in the gaseous or aqueous
solution form) or sulphuric acid,
• and recovery of the alkoxyamine or of its salts.

2. Process according to Claim 1, characterized in that, in
the saponification stage, the base MOH/azo compound molar
ratio is between 2 and 3, the temperature is between 0 and
40°C and use is made of a solvent which is preferably chosen
from mixtures of alcohols and water, acetonitrile and water
or tetrahydrofuran and water and which is advantageously a
methanol/water or ethanol/water mixture.
3. Process according to Claim 1 or 2, characterized in
that, in the photolysis stage, the nitroxide/azo compound
molar ratio is between 0.5 and 5 and preferably between 1
and 2.5, irradiation is carried out using one or more lamps emitting radiation with a wavelength of between 200 and 600 run, the temperature is between 0 and 40°C and use is made of a solvent which is preferably chosen from mixtures of alcohols and water, acetonitrile and water or tetrahydrofuran and water, which is advantageously a methanol/water or ethanol/water mixture and which is preferably identical to the solvent of the saponification stage, under an inert atmosphere and with stirring.
4. Process according to any one of Claims 1 to 3,
characterized in that, in the acidification stage, the
temperature is between 0 and 30 °C and use is made of a
solvent preferably chosen from mixtures of alcohols and
water, such as methanol/water or ethanol/water, a solvent
» 4
identical to that of the saponification and photolysis
stages advantageously being preferred.
5. Process according to any one of Claims 1 to 4,
characterized in that it .is carried out batchwise,
semicontinuouslv or continuously.
6. Process fro the preparation of the alkoxyamine 2-methyl-2-[N-(diethoxyphosphoryl-2, 2-dimethylpropyl)-arninoxy] propionic acid of formulat (I), substantiall as hereinbefore described with reference to the foregoing examples.