Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
1999-08-18
2001-09-04
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
Reexamination Certificate
active
06284935
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention concerns an improved process for the production of hexabromocyclododecane. The process produces a low-melting, highly pure hexabromocyclododecane product.
Hexabromocyclododecane (1,2,5,6,9,10-hexabromocyclododecane) is a well established flame retardant for use in various thermoplastics. This compound is usually produced as a mix of its three stereoisomers, the alpha, beta and gamma isomers. It is preferred that the gamma isomer comprise about 70 wt % of the mix. Hexabromocyclododecane is commercially available as a product which contains principally hexabromocyclododecane and lesser amount of impurities. A principal impurity is the underbrominated species, tetrabromocyclododecene. The tetrabromocyclododecene impurities can comprise up to 10 wt % of the hexabromocyclododecane product. Lesser impurities include the side-reaction products formed by the reaction of the brominating agent with cyclododecatriene, brominated cyclododecane and reactive solvents, e.g., alcohols.
The product is produced by the bromination of cyclododecatriene in the presence of a solvent, generally an alcohol, e.g., isobutanol. The alcohol can be used alone or in combination with a wide variety of co-solvents, e.g., halogenated hydrocarbons, dioxane, etc. The main drawbacks with using alcohol-based solvents are that (i) a significant amount of the reaction intermediate, tetrabromocyclododecene, precipitates out of the reaction solution before the intermediate has an opportunity to be hexabrominated, and (ii) alcohols readily react with the brominating reagent to produce undesirable side-reaction products and to consume brominating reagent. If the so-consumed brominating agent is not replaced, increased formation of underbrominated species, e.g., tetrabromocyclododecene, is likely to occur. The industry has responded to these drawbacks by suggesting that the reaction mass could be heated, in a finishing step, to redissolve the tetrabromocyclododecenes and then further brominating the tetrabromocyclododecenes to form the hexabromocyclododecane. However, heating of the reaction mass exacerbates the formation of undesirable side-reaction products derived from the solvent. To increase the purity of the finished hexabromocyclododecane product, the crude process product is repeatedly washed with solvents, such as toluene, which will remove tetrabromocyclododecene and other impurities. Unfortunately, such washing will also remove significant amounts of the alpha and beta isomers which reduces the total yield of hexabromocyclododecane product. In addition, since the alpha and beta isomer content is reduced without a concomitant reduction in the gamma content, the melting point of the hexabromocyclodecane product will be high, say between 185 to 200° C. Such high-melting products are commercially viable, however, the more commercially significant hexabromocyclododecane products are those having a melting point between 175 to 195° C., which products are referred to by the industry as low-melt products. Low-melt products generally contain 10 to 12 wt % alpha isomer, 4 to 9 wt % beta isomer and 71 to 78 wt % gamma isomer. But the problem with most low-melt products is that they have a high impurity content since they have not undergone the washing steps, indeed they contain up to about 10 wt % tetrabromocyclododecene. With a high impurity content, comes a less than desirable thermal stability.
It is an object of this invention to provide a process for the production of low-melt hexabromocyclododecane products having good thermal stability. This and other objects will be more fully understood from the following description of various processes and products which are claimed herein.
THE INVENTION
This invention provides a process which comprises brominating cyclododecatriene in a 1,4-dioxane and water solvent and in the presence of from about 0.5 to about 30 wt % bromide ion (Br
−
), the wt % being based on the total weight of the liquid portion of the reaction mass.
Other embodiments, advantages, and features of this invention will be further apparent from the ensuing description and appended claims.
It has been discovered that by using a 1,4-dioxane-water solvent there is obtained, at reaction end, a reduction in the amount, i.e., to less than about 1.5 wt %, of tetrabromocyclododecene in the recovered hexabromocyclododecane product. (Unless otherwise stated, the wt % of the tetrabromocyclododecane, the isomers of hexabromocylododecane, by-product impurities, etc., which are recited herein are all based on the total weight of the recovered hexabromocyclododecane product of which they are a constituent.) Also achieved is good utilization of the brominating agent, e.g., bromine. Both of these benefits are the result of the aqueous 1,4-dioxane being relatively inert in the reaction while having good solubility for tetrabromocyclododecenes at the reaction temperature, e.g., 20 to 50° C. By keeping most of the tetrabromocyclododecenes in solution during the reaction, it is more likely, over time and in some cases under heat, that the underbrominated species will be brominated to hexabromocyclododecane. Further, since aqueous 1,4-dioxane is relatively unreactive with the brominating agent, there are less by-product impurities formed and thus more brominating agent present in the reaction to promote the hexabromination of the tetrabromocyclododecenes. In addition, hexabromocyclododecane is relatively insoluble in the aqueous 1,4-dioxane solvents of this invention, thus very little is lost to the residual mother liquor after recovery of the precipitate. This, along with the perbromination of the tetrabromocyclododecene, promotes high yields.
While the aqueous 1,4-dioxane solvent system attenuates the formation of impurities and promotes the perbromination of tetrabromocyclododecene, this system does not produce a high gamma content. Generally, the gamma content will be about 50 wt %, the wt % being based on the total weight of brominated cyclododecatriene in the reaction mass. It has been discovered, however, that if the liquid portion of the reaction mass contains from about 0.5 to 30 wt %, and preferably from about 3 to about 30 wt %, bromide ion (Br
−
), then the gamma content will be enhanced to 65 to 75 wt % on the same basis. Most preferred amounts of bromide ion are in the range of from about 4 to about 13 wt %. The wt % values for the bromide ion are based on the total weight of the liquid portion of the reaction mass. It is theorized, though this invention is not to be limited to any one theory, that the bromide ion complexes with the brominating agent, e.g., bromine, and that the resulting complex selectively assists bromination of the sterically hindered intermediates which leads to the gamma isomer. Thus, the formation of the gamma isomer is facilitated.
The process of this invention is similar to prior art processes in its operation and equipment used except for the aqueous 1,4-dioxane solvent system and the use of a high bromide ion content in the liquid portion of the reaction mass.
The brominating agent is preferably liquid bromine which is added as such to the reactor. It is within the scope of this invention, however, to produce the bromine in situ. For example, HBr can be fed to the reactor along with a oxidant such as H
2
O
2
which will convert HBr to Br
2
. Since HBr is a good source for the bromide ion feature of this invention, this mode of operation may be attractive as the HBr can be provided in an amount which fulfills both the Br
2
and the bromide ion needs. The Br
2
and HBr used should both be of good quality and essentially free of impurities. Commercially available grades of either of these two compounds are generally suitable.
The cyclododecatriene should also have a good quality and can be provided by most commercial grades of this compound. The usual molecular configuration of the cyclododecatriene corresponds to 1,5,9-cis,trans,trans-cyclododecatriene. However, the actual isomeric configuration of the cyclododecatriene is not deemed
Aplin Jeffrey T.
Kendall John K.
Albemarle Corporation
Siegel Alan
Spielman, Jr. E. E.
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