Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2001-09-24
2003-03-25
Rotman, Alan L. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C546S184000, C546S186000, C544S106000, C564S015000, C564S297000, C564S298000
Reexamination Certificate
active
06538141
ABSTRACT:
The present invention relates to a process for preparing secondary amine N-oxide radicals by oxidizing the corresponding secondary amines.
Secondary amine N-oxide radicals, referred to hereinbelow as nitroxides, are free radicals containing an unpaired electron. These nitroxide radicals may be used as stabilizers for organic polymers, in particular to inhibit the thermal and light-mediated degradation of polyolefins (U.S. Pat. No. 3,431,233) and of PVC (U.S. Pat. No. 3,547,874). They are also used as spin labels for studying biological compounds and as free-radical polymerization regulators (Georges, M. K. et al. Macromolecules 1993, 26, 2987).
The main methods for preparing nitroxides are the oxidation of hydroxylamines and the oxidation of secondary amines, this second method being the one which is most commonly used industrially.
The methods for obtaining nitroxide radicals by oxidizing the corresponding secondary amines have been widely described.
Among these methods, mention will be made of those which use aqueous hydrogen peroxide solution in the presence of catalysts such as phosphotungstic acid (Briére R. et al., Bulletin de la Société Chimique de France, 1965, pages 3273-3282), alkaline-earth metal salts (EP 0 574 607), NaHCO
3
or Na
2
CO
3
(Levina et al., Dokl. Akad. Nauk. SSSR 1981, 261(1), 109-110), EDTA combined with WO
4
Na
2
(Zakizewski J., J. Prakt. Chem. 1985, 327(6), 1011-1014).
In all these methods, the oxidation reaction takes place in water or a water/alcohol mixture at temperatures of between 60 and 100° C.
Although they use an inexpensive oxidizing agent—H
2
0
2
—these methods are applicable only to amine
itroxide couples that are sufficiently water-soluble. They also have drawbacks residing especially in long reaction times and in the impossibility of recycling the catalytic system, thus making it necessary to wash the product and treat the effluents before removing them.
In addition, these methods are not general since the temperatures used, generally high, make it difficult, if not impossible, to isolate certain nitroxides that are readily overoxidizable.
Other methods for oxidizing secondary amines to nitroxides have been proposed.
Thus, patent U.S. Pat. No. 4,665,185 discloses a process for oxidizing cyclic secondary amine, which consists in reacting said amine in an inert organic solvent, with an organic hydroperoxide such as tert-butyl hydroperoxide, in the presence of catalytic amounts of a metal carbonyl (Mo(CO)
6
), a metal oxide (MoO
3
), a metal acetylacetonate or a metal alkoxide (Ti(OiPr)
4
), the metal of which belongs to one of the groups IVB, VB, VIB, VIB and VIII of the Periodic Table, at a temperature ranging from 0° C. to 200° C.
The reaction times are shorter, but the problem of recovering the catalyst still remains. The products must be purified and the effluents treated.
Another method for oxidizing secondary amine consists in reacting said secondary amine with dimethyldioxirane (DMD) in the absence of catalysts (U.S. Pat. No. 5 087 752).
DMD, which is not commercially available, is prepared by oxidizing acetone either with Oxone® which is a potassium monoperoxysulsulfate, or more rarely with Caro's acid which is an H
2
SO4/H
2
SO
5
mixture.
This powerful oxidizing agent gives high yields of nitroxides. However, its highly explosive nature makes its preparation very random and is unacceptable for industrial use.
Furthermore, to obtain DMD, it is necessary to use the Oxone® in excess in basic medium, which generates a large amount of sulfate as effluent.
Perbenzoic acids such as meta-chloroperbenzoic acid (Journal of American Chemical Society, 1967, 89(12) 3055-3056) or para-nitropebenzoic acid (Rassat A. et al. Bulletin de la Société Chimique de France, 1965, 3283-3290) dissolved in organic solvents such as methylene chloride, allow many secondary amines to be oxidized efficiently to nitroxides.
However, the cost and the benzoic acids they generate make them unsuitable for use on an industrial scale.
It has now been found that nitroxides can be obtained according to a process which avoids the abovementioned drawbacks, which consists in oxidizing secondary amines using aliphatic peracids in an organic solvent/water two-phase medium in which the aqueous phase is maintained at a pH ranging from 4 to 12.
One subject of the present invention is thus a process for preparing secondary amine N-oxide radicals (nitroxide radicals) from the corresponding secondary amines, characterized in that the following steps are carried out:
a/ the secondary amine is dissolved with a water-immiscible organic solvent, and water is then added,
b/ an amount of aliphatic peracid in a peracid/secondary amine molar ratio ranging from 1.5 to 2.5 and preferably ranging from 1.5 to 2, and an amount of an aqueous basic solution sufficient to give the aqueous phase or the two-phase medium a pH ranging from 4 to 12, are then added simultaneously and with vigorous stirring to the two-phase medium thus obtained, at a temperature of between −10° C. and +40° C., until conversion of the secondary amine is complete, and then
c/ the organic phase is recovered by simple separation of the phases by settling, and the nitroxide is isolated by evaporating the organic solvent under reduced pressure.
According to the present invention, the organic solvent must be water-immiscible, inert towards the reagents and products and must have good solvent power for the reagents and products obtained.
By way of illustration of such organic solvents which may be used according to the present invention, mention will be made of aliphatic or cycloaliphatic hydrocarbons such as pentane, hexane, heptane, decane, cyclohexane and cyclododecane; aromatic hydrocarbons such as benzene, toluene and xylenes; chlorinated hydrocarbons such as methylene chloride, 1,2-dichloroethane, chloroform and chlorobenzene; aliphatic acid esters such as ethyl acetate, ethyl propionate or a mixture of at least two of the abovementioned solvents.
By way of illustration of aliphatic peracids which may be used according to the present invention, mention will be made of peracetic acid, perpropionic acid and perbutanoic acid.
Peracetic acid or perpropionic acid will preferably be used.
The process of the present invention thus consists in dissolving, with stirring, the secondary amnine in water-immiscible organic solvent which is inert towards said secondary amine and the reagents used.
The amount of organic solvent used depends on the solubility of said secondary amine in said solvent.
This amount of organic solvent is not critical and may vary within a wide range. However, for economic reasons and out of concern for the environment, a person skilled in the art will make efforts to select an organic solvent (or a mixture of solvents) so as to use only minimum amounts to dissolve the secondary amine.
Water is added to the organic solution, with stirring, followed by simultaneous addition to the two-phase medium obtained, with vigorous stirring, of the aliphatic peracid, generally dissolved in the corresponding aliphatic acid, in a peracid/secondary amine molar ratio as defined above and a sufficient amount of an aqueous basic solution of a carbonate or hydrogen carbonate of an alkali metal or of an alkaline-earth metal so that the pH of the aqueous solution of the two-phase medium is maintained at a value ranging from 4 to 12 and preferably ranging from 5 to 9.
According to the present invention, an aqueous basic solution of an alkali metal carbonate or hydrogen carbonate will preferably be used.
By way of illustration of alkali metal carbonates or hydrogen carbonates which may be used according to the present invention, mention will be made of NaHCO
3
, KHC0
3
, K
2
CO
3
and Na
2
CO
3
.
Ammoniacal solutions may also be used.
The weight concentration of the aqueous solutions of alkali metal or alkaline-earth metal carbonates or hydrogen carbonates is set by the solubility limit of these species in water. Efforts will be made to use solutions that are as concentrated as possible.
The oxidation reacti
Gillet Jean-Philippe
Guerret Olivier
Lascombe Jean-Pierre
Atofina
Desai Rita
Millen White Zelano & Branigan P.C.
Rotman Alan L.
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