Bromo-functionalized benzotriazole UV absorbers

Details Bromo-functionalized benzotriazole UV absorbers Bromo-functionalized benzotriazole UV absorbers

2000-12-27

2001-09-04

Higel, Floyd D. (Department: 1626)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C548S259000

Reexamination Certificate

active

06284895

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to bromo functionalised benzotriazole UV absorbers. More particularly the present invention relates to bromo-derivatives of benzotriazole UV absorbers having general formula 1
wherein R
1
is hydrogen, tert-butyl; X
1
is selected the group consisting of hydrogen, halogen, tert-butyl and C
1
to C
12
alkoxy. Still more particularly, the invention concerns the synthesis of intermediate compounds which are the bromo derivatives of conventional UV absorbers and useful for the synthesis of many other functional UV absorbers and a method for the preparation thereof.
Our copending application Ser. No. 09/749,277 filed on the same day as this application relates to a process for the preparaton of novel bromo functionalised benzotriazole UV absorbers of this invention.
BACKGROUND OF THE INVENTION
Most thermoplastic polymers and coating compositions are unstable to extended exposure to ultraviolet light source in atmosphere. Thermoplastics and coatings tend to demonstrate unwanted colour changes and reduced mechanical strength upon exposure to UV radiation. The preliminary effect of ultraviolet radiation on polymers is the formation of free radicals on the polymer chain, which react with atmospheric oxygen. This results in the formation of peroxide groups. Furthermore, decomposition of peroxide groups causes formation of carbonyl groups and chain scission. Irradiation in absence of oxygen causes the increase in crosslinking. Ultimately, this reflects on the mechanical properties and the colour of the polymeric materials. In order to prevent or at least retard the damage caused by these factors, stabilizers are added to the plastics.
UV absorbers are compounds that upon addition to the polymers are capable of preventing or retarding the reactions of degradation caused by light energy. 2-Hydroxyphenyl benzotriazoles are one of the most important UV absorbers, which are used commercially. The preparation and use of functional UV absorber in polymers and coatings is well documented.
In order to meet the need for the different UV absorbers for different systems, the reactive intermediates for the synthesis of novel UV absorber are very essential.
Side chain bromination in UV absorbers in the prior art is a three step reaction as reported in the literature [S. Yoshida & O. Vogl, Makromol.Chem., 183, 259(1982); S. Yoshida, C. P. Lillya & O. Vogl, Monatshefte Chem., 113, 603(1982); S. Yoshida, C. P. Lillya & O. Vogl, J.Polym.Sci., Polym.Chem.Ed., 20, 2215(1982)]. Literature reports the similar process via three-step reaction, which includes protection of hydroxyl group, bromination, and then deprotection reaction. However, there is no report of bromination of benzotriazole UV absorbers in the art.
Hydroxyphenyl benzotriazole monomers may be prepared by any method known in the art including those disclosed in U.S. Pat. Nos., 5,104,992; 4,943,637; and 5,097,041. 2-Aryl-2H-benzotriazoles monomers may be prepared by reducing o-nitroazobenzenes through a 2-phenylbenzotriazole-N-oxide intermediate. Reduction of o-nitroazobenzenes to 2-phenylbenzotriazole by zinc in presence of sodium hydroxide is disclosed in U.S. Pat. Nos. 3,018,269; 3,773,751; 4,041,044; and 4,224,451. Aldehyde reducing agents and aromatic ketone catalysts are disclosed in U.S. Pat. No. 4,835,284. All of these patents are incorporated herein by reference.
It is therefore important to obtain bromo functionalized UV absorber is highly reactive and can be used for the synthesis of various functional UV absorbers.
OBJECTS OF THE INVENTION
The object of the present invention is therefore to provide a process for the preparation of bromo-functionalized benzotriazole UV absorbers.
SUMMARY OF THE INVENTION
Accordingly the present invention provides bromo-functionalized benzotriazole UV absorbers having a general formula 1
wherein R
1
is selected from hydrogen and tert-butyl; X
1
is selected the group consisting of hydrogen, halogen, tert-butyl and C
1
to C
12
alkoxy.
The present invention also provides a process for preparation of bromo-functionalized benzotriazole UV absorbers having a general formula 1
wherein R
1
is selected from hydrogen and tert-butyl; X
1
is selected the group consisting of hydrogen, halogen, tert-butyl and C
1
to C
12
alkoxy, by reacting a benzotriazole of the formula
wherein R
1
is selected from hydrogen and tert-butyl; X
1
is selected the group consisting of hydrogen, halogen, tert-butyl and C
1
to C
12
alkoxy, with bromine in presence of a non-polar solvent and a free radical initiator at a temperature ranging between 45 to 52° C. for a period of 4 to 10 hours, bringing the reaction mixture to ambient temperature, separating the solvent and purifying the product by recrystallization to obtain the pure product.
In one embodiment of the invention, the non-polar solvent used is selected from the group consisting of carbon tetrachloride, benzene, n-pentane, 1,2-dichloroethane, 1,2-dibromoethane, chloro and bromo substituted benzenes.
In another embodiment of the invention, the free radical initiator is selected from the group consisting of 2,2′-azobisisobutyronitrile, 1,1′-azobis-2-cyclopropylpropionitrile, 2,2′-azobis-2-cyclopropylpropionitrile, 2,2′-azobis-2,4,4-trimethylvalaronitrile, 1,1′-azobis-1-cyclooctanenitrile, azo-bis-(1-carbomethoxy-3-methylpropane).
In another embodiment of the invention the recrystallisation is carried out using solvents such as acetone, methyl ethyl ketone, chloroform.
DETAILED DESCRIPTION OF THE INVENTION
The process of the present invention begins with a benzotriazole monomer of the formula 2:
wherein R
1
is hydrogen, tert-butyl; X
1
is selected the group consisting of hydrogen, halogen, tert-butyl and C
1
to C
12
alkoxy.
Hydroxyphenyl benzotriazole monomers may be prepared by any method known in the art including those disclosed in U.S. Pat. Nos., 5,104,992; 4,943,637, and 5,097,041. 2-Aryl-2H-benzotriazoles monomers may be prepared by reducing o-nitroazobenzenes through a 2-phenylbenzotriazole-N-oxide intermediate. Reduction of o-nitroazobenzenes to 2-phenylbenzotriazole by zinc in presence of sodium hydroxide is disclosed in U.S. Pat. Nos. 3,018,269; 3,773,751; 4,041,044; and 4,224,451. Aldehyde reducing agents and aromatic ketone catalysts are disclosed in U.S. Pat. No. 4,835,284. All of these patents are incorporated herein by reference.
Bromination of p-cresol in the same condition did not proceed whereas in the case of benzotriazole UV absorbers, same reaction gives the brominated product with bromination at methyl side chain in very high yield.
In the present invention bromo-functionalized benzotriazole UV absorbers of general formula 1
wherein R
1
is selected from hydrogen and tert-butyl; X
1
is selected the group consisting of hydrogen, halogen, tert-butyl and C
1
to C
12
alkoxy, are prepared by reacting a benzotriazole of the formula 2
wherein R
1
is selected from hydrogen and tert-butyl; X
1
is selected the group consisting of hydrogen, halogen, tert-butyl and C
1
to C
12
alkoxy, with bromine in presence of a non-polar solvent and a free radical initiator at a temperature ranging between 45 to 52° C. for a period of 4 to 10 hours, bringing the reaction mixture to ambient temperature, separating the solvent and purifying the product by recrystallization to obtain the pure product.
The process of the present invention is described hereinbelow with reference to examples, which are illustrative only and should not be construed to limit the scope of the present invention in any manner.


REFERENCES:
patent: 4780541 (1988-10-01), Senio et al.
patent: 4943637 (1990-07-01), Senio et al.
patent: 5097041 (1992-03-01), Higel et al.
patent: 5104992 (1992-04-01), Fukuoka et al.
patent: 5488112 (1996-01-01), Reinehr et al.
patent: 5554759 (1996-09-01), Vishwakarama et al.
patent: 5637726 (1997-06-01), Collins et al.

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