Organic compounds -- part of the class 532-570 series – Organic compounds – Azo
Reexamination Certificate
2001-09-28
2002-06-18
Powers, Fiona T. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Azo
C534S599000, C534S738000, C534S838000, C534S886000
Reexamination Certificate
active
06407219
ABSTRACT:
A subject matter of the present invention is a process for the preparation of azoiminoethers (in the hydrochloride form) and their hydrolysis to azocarboxylic acid esters, these esters thus prepared being of use as free radical initiator in polymerization reactions. Another subject matter of the present invention is the mixed azoiminoethers thus prepared and the mixed esters of azocarboxylic acids deriving therefrom.
The preparation of azocarboxylic acid esters is conventionally carried out by a two-stage process comprising a first stage of conversion of the azonitrile by reaction with an alcohol in the presence of HCl according to the Pinner reaction, resulting in the corresponding azoiminoether hydrochloride, and a second stage of hydrolysis in the presence of water of the hydrochloride thus obtained.
This process exhibits a number of disadvantages which render it entirely unsuitable for production on an industrial scale. This is because it is too expensive, it is difficult to control, the purification of the final product is difficult and it requires a large excess of alcohol. Furthermore, it results in an inadequate yield and in a final product of unsatisfactory purity. Such a process is described, for example, by G. A. Mortimer in the Journal de chimie organique, page 1632-33 (1965), for the preparation of dimethyl azobisisobutyrate, used as intermediate in the synthesis of a polymerization initiator: azobisisobutyl diacetate.
Several solutions have been provided for solving some of these problems and thus allowing industrial scale production of the process for the preparation of azocarboxylic acid esters.
A process as described above, resulting in an increase in the yield and simultaneously in a significant reduction in the duration of the reaction and in a much better and much faster separation of the phases between the azodiisobutyric ester and the aqueous phase, is disclosed in DE 2 254 572. According to this patent, such improvements can be obtained by carrying out the Pinner conversion in the presence of a water-soluble cyclic ether and/or of a water-soluble diol of low MW and/or of an etherdiol or of a polyetherdiol, which is linear, of low MW ranging up to 1 800, in an amount of 0.001 to 11.0% by weight with respect to the aliphatic C
1
-C
6
alcohol.
EP 80 275 dicloses that 2,2′-azobis(2-methylpropio-nitrile) and the related compounds can be converted using the Pinner reaction with an excellent yield with only the stoichiometric amount of the alcohol if the reaction is carried out in the presence of a compound comprising an ether group. It is disclosed that a faster conversion (and not a higher yield and/or a higher selectivity) can be obtained by increasing the concentration of HCl in the reaction mixture. However, the presence of ether presents problems, in particular with regard to the subsequent separation and treatment.
EP 230 586 has demonstrated that the preparation of azoiminoethers can be carried out in a single stage in a single receptacle according to a very easily controllable reaction, during which halogenation/oxidation of the hydrazonitrile and iminoetherification of the azonitrile take place. The preparation process according to EP 230 586 thus comprises the reaction of a hydrazonitrile with chlorine in the presence of an alcohol capable of converting the cyano group to an iminoether group in the presence of HCl (which is formed in situ). This reaction is carried out in a nonaqueous system in the presence of a solvent used in the halogenation/oxidation and iminoetherification, such as aromatic hydrocarbons, halogenated hydrocarbons and some other solvents. The amount of alcohol used varies between the theoretical amount required and 1.2 times this amount and the amount of chlorine varies between the theoretical amount and a slight excess. The final reaction product, corresponding to the azoiminoether hydrochloride, can be converted to an azoester by hydrolysis.
However, none of the above documents provides a process which can be used on an industrial scale, with a high yield and with a satisfactory purity, which makes it possible to dispense with awkward separation techniques.
The applicant company has demonstrated, surprisingly, a novel process for the preparation of azoiminoether salts and of the corresponding azocarboxylic acid esters which achieves the above aims. The present invention thus relates to a process for the preparation of azoiminoether salts by conversion of the azonitrile according to the Pinner reaction, in which invention the reaction is carried out in an aromatic solvent and in the presence of a large excess of HCl.
A subject matter of the present invention is thus a process for the preparation of an azoiminoether hydrochloride comprising the reaction of an azonitrile with an alcohol and hydrochloric acid in an aromatic solvent, in which process the molar ratio R=HCl/azonitrile is >2 when the alcohol is methanol and >3 when the alcohol is ethanol or a higher alcohol.
According to a specific embodiment, the azonitrile is formed in situ by reaction of the corresponding hydrazonitrile with chlorine.
According to another embodiment, the solvent is selected from the group consisting of toluene, chlorobenzene, xylene and benzene; chlorobenzene preferably being used when the azonitrile is formed in situ.
According to another embodiment, the alcohol is ethanol.
According to one embodiment, the alcohol used is composed of a mixture of alcohols, in particular a mixture comprising methanol, or methanol and ethanol.
According to one embodiment of the preparation process according to the invention, the azoiminoether hydrochloride corresponds to the formula (II)
in which:
R1, R2, R3 and R4, which are identical or different, are independently selected from the group consisting of: linear or branched C
1
-C
9
(preferably C
1
-C
4
) alkyls which are unsubstituted or substituted by one or more substituents selected from hydroxyl, C
1
-C
6
alkoxy or halogen substituents;
C
3
-C
6
cycloalkyls which are unsubstituted or substituted by one or more substituents selected from C
1
-C
6
alkyl, C
1
-C
6
alkoxy, hydroxyl or halogen;
C
7
-C
12
aralkyls which are unsubstituted or substituted by one or more substituents selected from C
1
-C
6
alkyl, C
1
-C
6
alkoxy, hydroxyl or halogen;
C
7
-C
12
aryls which are unsubstituted or substituted by one or more substituents selected from C
1
-C
6
alkyl, C
1
-C
6
alkoxy, hydroxyl or halogen;
it being possible for at least one of the R1-R2 and R3-R4 combinations optionally to form an aliphatic ring,
R and R′, which are identical or different, are independently selected from the group consisting of linear or branched C
1
-C
10
, preferably C
1
-C
4
, aliphatic radicals.
According to another embodiment of the present invention, in the formula (II), R and R′ are different from one another and are selected from linear C
1
-C
4
aliphatic radicals.
According to a specific embodiment, R1, R2, R3 and R4 are C
1
-C
4
alkyl groups.
Another subject matter of the invention is a process for the preparation of an azocarboxylic acid ester comprising the synthesis of an azoiminoether hydrochloride by the process as defined above and the hydrolysis in the presence of water of the azoiminoether hydrochloride thus obtained.
According to one embodiment, the hydrolysis is carried out by successive addition of water to the reaction mixture or by running the reaction mixture into water, at a temperature of between 15° C. and 50° C., preferably approximately 30° C.
According to a specific embodiment of the process for the preparation of an azocarboxylic acid ester, after the synthesis stage, the azoiminoether hydrochloride is filtered off and washed with an organic solvent, and then the hydrolysis is carried out by gradual addition of the filtration cake to water at a temperature of between 15° C. and 50° C., preferably between 25° C. and 35° C.
An additional subject matter of the invention is a process for the preparation of a liquid composition of azocarboxylic acid esters comprising the synt
Atofina
Blank Rome LLP
Powers Fiona T.
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