Organic compounds -- part of the class 532-570 series – Organic compounds – Azo
Reexamination Certificate
2001-01-10
2002-01-01
Powers, Fiona T. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Azo
C534S887000, C526S219000, C526S341000
Reexamination Certificate
active
06335431
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates to a safe and an efficient method for separately recovering a racemic isomer and a meso isomer of azo compounds showing activity at low temperature from an isomeric mixture of the racemic isomer and the meso isomer.
In a field of polymer compounds, study has recently been conducted on increase of polymerization speed in order to improve polymerization degree.
On the other hand, azo compounds showing activity at low temperature, which have been useful polymerization initiators, exist as an isomeric mixture of a racemic isomer and a meso isomer and usually use has been made of the mixture as it is, but it has been known that a racemic isomer has high solubility in organic solvents as compared with a meso isomer.
Therefore, if a racemic isomer is separately recovered from an isomeric mixture of this kind of azo compound and the racemic isomer is used as a polymerization initiator, a concentration of the polymerization initiator in a reaction solvent could be increased because the racemic isomer has high solubility in organic solvents and thus a polymerization speed can be increased.
Further, the above azo compound has been useful as an initiator for radical reactions and it can specifically proceed a radical addition reaction at room temperature, and thus it could be utilized as an initiator in a field wherein a radical reaction is to be applied in place of a photo reaction. A racemic isomer has been known as preferable also for this purpose, and this has been considered to be caused by difference in a stereo structure such as isomerization of the trans-cis isomer of the azo compound, though details have not yet been clarified.
For instance, when bromomalononitrile (BrCH(CN)
2
) and 2,3-dimethyl-2-butene are subjected to a radical addition reaction with the use of a racemic isomer of the above azo compound as an initiator of the radical reaction, the object addition product is obtained at a yield of 95%, while use of a meso isomer as an initiator of the radical reaction under the same conditions gives the object addition product only at a yield of 7%.
Thus, effective separation of a racemic isomer and a meso isomer from an isomeric mixture of a racemic isomer and a meso isomer of an azo compound showing activity at low temperature and use of only the separated racemic isomer as a polymerization initiator or an initiator for radical addition reactions have now strongly been demanded.
As methods for separation of a racemic isomer from an isomeric mixture of a racemic isomer and a meso isomer of the azo compound, there has been known a method comprising extracting a racemic isomer from an isomeric mixture of the azo compound with an ether utilizing higher solubility of a racemic isomer of azo compounds showing activity at low temperature in organic solvents as compared with a meso isomer, removing a remaining meso isomer by filtration and removing ether under concentration from a filtrate wherein a racemic isomer is dissolved, whereby the object racemic isomer is obtained (Chim.Ind. (Milan) 1970, 52(11), 1116-20(Ital)), etc.
However, this method is accompanied with such drawbacks that an azo compound showing activity at low temperature which is unstable at room temperature is decomposed because of the heat treatment required and so the use of the azo compound is not preferable in a safe side and there exists risk of fire and explosion because of use of a flammable ether. Therefore, development of a method for separating safely and efficiently the racemic isomer at low temperature without using highly flammable ether has strongly been desired.
SUMMARY OF INVENTION
The present invention has been accomplished under the circumstance as mentioned above and the object is to provide a method for recovering separately a racemic isomer and a meso isomer safely and efficiently from an isomeric mixture of a racemic isomer and a meso isomer of an azo compound showing activity at low temperature.
The present invention relates to a method for separation of a racemic isomer and a meso isomer from an isomeric mixture of a racemic isomer and a meso isomer of a compound shown by the general formula [1]
(wherein R
1
and R
2
are each independently a lower alkyl group or a cyano group, which are different from each other, R
3
and R
4
are each independently a lower alkyl group, and R
5
is a hydrogen atom or a lower alkoxy group), which comprises treating the mixture with a water soluble organic solvent.
Further, the present invention relates to a method for recovering a racemic isomer of a compound shown by the general formula [1]
(wherein R
1
and R
2
are each independently a lower alkyl group or a cyano group, which are different from each other, R
3
and R
4
are each independently a lower alkyl group, and R
5
is a hydrogen atom or a lower alkoxy group), which comprises treating a mixture of a racemic isomer and a meso isomer of the compound shown by the above general formula [1] with a water soluble organic solvent.
Still further, the present invention relates to a polymerization initiator comprising a racemic isomer of the compound shown by the general formula [1].
Further, the present invention relates to a method for polymerizing a polymerizable monomer, which comprises using, as a polymerization initiator, a racemic isomer of the compound shown by the general formula [1].
Namely, the present inventors have extensively conducted study for realizing the above object to arrive at the finding that the said racemic isomer and the meso isomer can safely and efficiently be separated from each other by subjecting an isomeric mixture of a racemic isomer and a meso isomer of the azo compound, which has activity at low temperature and is unstable at room temperature, shown by the general formula [1] to a treatment with a water soluble organic solvent, and the present invention has been completed on the basis of this finding.
PREFERRED EMBODIMENTS OF INVENTION
In the general formula [1], the lower alkyl group shown by R
1
to R
4
may be straight chained, branched or cyclic and includes one having generally 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, which is specifically exemplified by a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a sec-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a sec-pentyl group, a 2-methylbutyl group, a 1-ethylpropyl group, a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, etc.
The lower alkoxy group shown by R
5
may be straight chained, branched or cyclic and includes one having generally 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, which is specifically exemplified by a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, an n-pentyloxy group, an isopentyloxy group, a sec-pentyloxy group, a tert-pentyloxy group, a neopentyloxy group, an n-hexyloxy group, a cyclopropoxy group, a cyclobutoxy group, a cyclopentyloxy group, a cyclohexyloxy group, etc.
Specific examples of the azo amide compound shown by the general formula [1] are 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (mfd. by Wako Pure Chemical Industries, LTd.: Trade name V-70) shown by the following formula
and 2,2′-azobis(2,4-dimethylvaleronitrile) (mfd. by Wako Pure Chemical Industries, Ltd.: Trade name V-65) shown by the following formula
among which 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile) is preferable.
The method of the present invention concerning recovering separately the racemic isomer and the meso isomer from a mixture of the racemic isomer and the meso isomer of the azo compound showing activity at low temperature is specifically conducted as follows.
Namely, there is conducted a process step comprising allowing an isomeric mixture of the racemic isomer and the meso isome
Armstrong Westerman Hattori McLeland & Naughton LLP
Powers Fiona T.
Wako Pure Chemical Industries Ltd.
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