Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
2001-10-18
2003-01-14
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
Reexamination Certificate
active
06506952
ABSTRACT:
TECHNICAL FIELD
This invention concerns an improved process for the production of hexabromocyclododecane. The process enables production of a hexabromocyclododecane product with increased gamma isomer content.
BACKGROUND
Hexabromocyclododecane (1,2,5,6,9,10-hexabromocyclododecane, HBCD) is a well established flame retardant for use in various thermoplastics. HBCD is composed of three isomers conventionally referred to as alpha, beta, and gamma. Of the three isomers, pure gamma has the highest melting point. Mixtures of the three isomers exhibit extended melt point regime, but generally it may be said that increasing the gamma isomer content of an HBCD product increases that product's initial melt point. HBCD products with higher initial melting points are the most desirable in the industry, and numerous methods have been sought to boost the gamma isomer content of HBCD. One such method involves washing, triturating, or recrystallizing the crude HBCD to not only increase gamma content, but to also increase product purity. For example, the crude process product may be repeatedly washed with solvents, such as toluene or alcohol, which will remove tetrabromocyclododecenes and other impurities. Such washing will also remove significant amounts of the alpha and beta isomers which, undesirably, reduces the total yield of hexabromocyclododecane product. It is preferred that the gamma isomer comprise at least 70 wt % of the mix to obtain an acceptable melting point regime.
A principal impurity of hexabromocyclododecane (HBCD) 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, viz., brominated cyclododecane and reactive solvent coproducts, e.g., alcohols.
The prior art lists a variety of solvents for HBCD production with the goal of producing an HBCD product with high purity, acceptable gamma isomer content, and good yields. One method to achieving a higher purity/higher yielding HBCD is to increase the proportion of HBCD that exists as the gamma isomer. The gamma isomer has the lowest solubility and highest melting point of the three HBCD isomers. Therefore, enhancing the production of the gamma isomer, and lessening the production of the alpha and beta isomers, is very desirable.
Heretofore HBCD has been produced by the bromination of cyclododecatriene in the presence of a solvent, generally an alcohol, e.g., isobutyl alcohol. 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, generating large amounts of HBr in the process. Indeed, U.S. Pat. No. 5,292,450 reports that in isobutyl alcohol, for every mole of CDT fed to a reaction, 0.4 moles of HBr are generated. The generation of HBr in HBCD production is generally viewed as a nuisance and numerous neutralizing agents are listed in the prior art. U.S. Pat. No.4,918,253 lists many of these neutralizing agents. Thus, the art teaches that HBr presence in the HBCD solvent is undesirable.
DE 1,147,574 and DE 1,222,049 teach the use of alcoholic (ethanol) or amide (dimethylacetamide) solvents for HBCD in the presence of “halogen carriers” such as aluminum chloride, aluminum bromide, iodine, chlorineiodide, and lithium bromide. The purpose of the halogen carriers is to boost yields. For example it is indicated that addition of aluminum chloride increases the yield of HBCD from 63% to 86%. DE 1,222,049 mentions how polar solvents such as acetonitrile, dioxane, and THF have been proven particularly ineffective as HBCD solvents. Additionally, FR 1,553,410 criticizes the use of such systems represented by DE 1,147,574 and DE 1,222,049. The French patent teaches that such a halogen carrier system generates a “resineux non cristallins” (i.e., a non-crystalline resin). EP 429,059 agrees with the French patent and reports an “insoluble resinous matter” results from such systems. Apparently, addition of the halide salts decrease the solubility of HBCD in the solvent due to the well known salting-out effect.
As for water usage in the solvent medium, it appears that water has been suggested for use as a co-solvent only with alcoholic and organic acid solvents, and then only as an aid to boost yields. Thus, U.S. Pat. No. 5,043,492 teaches the addition of 2-5% water to the alcoholic solvent to boost yields, but then further mentions that water levels greater than 5% forms a “gummy product”. FR 1,553,410 allows for additions of 10% water to an acetic acid or propionic acid solvent to boost yields, but the yields are boosted by only a few percent. Thus, the art demonstrates addition of water only for slight yield increases by driving the HBCD out of the organic solvent.
It is an object of this invention to provide a process enabling the production of hexabromocyclododecane products in which the proportion of gamma isomer produced is increased relative to alpha and beta isomers. Another object is to provide process technology which makes possible the production of a highly pure hexabromocyclododecane product. A further object is to achieve at least one of the foregoing objects without forming gummy or resinous non-crystalline product. Still other objects may be seen from the following description.
SUMMARY OF THE INVENTION
Pursuant to this invention, it is now possible to achieve one or more of the foregoing objects efficiently and in a practical manner by producing hexabromocyclododecane in certain novel liquid reaction media or solvent systems which are comprised of a one or more particular types of organic solvents, water, and a suitable quantity of bromide ion.
Thus in one of its embodiments this invention provides a process which comprises brominating cyclododecatriene in a liquid medium comprised of (1) at least 50 wt % of at least one liquid inert organic solvent other than 1,4-dioxane having a solubility in water of at least 1 wt % at 25° C., and (2) water in an amount of up to about 40 wt %, in the presence of (3) about 0.5 to about 30 wt % of bromide ion (Br
−
), whereby hexabromocyclododecane is produced, each wt % being based on the total weight of the liquid portion of the liquid medium.
In another of its embodiments this invention provides a process which comprises brominating cyclododecatriene in a liquid medium comprised of (1) a predominate amount of (a) at least one halogen-free aprotic solvent other than 1,4-dioxane containing at least two oxygen atoms or at least one nitrogen atom (preferably one nitrogen atom) in the molecule, or (b) at least one liquid polyalkylene glycol in which the alkylene groups each contain two or three carbon atoms (preferably two carbon atoms) and in which the average molecular weight of the polyalkylene glycol is at least about 150 (preferably at least about 200, and more preferably in the range of about 200 to about 400) and/or at least one liquid monoalkyl ether thereof, or (c) a combination of (a) and (b), and (2) water in an amount of up to about 40 wt %, in the presence of (3) about 0.5 to about 30 wt % of bromide ion (Br
−
), each wt % being based on the total weight of the liquid portion of the liquid medium. For ease of reference, the components of (1) above, i.e., (a) at least one halogen-free aprotic solvent containing in the molecule at least two oxygen atoms (other than 1,4-dioxane) or at least one nitrogen atom (preferably one nitrogen atom), or (b) at least one liquid polyalkylene glycol in which the alkylene groups each contain two or three carbon atoms (preferably two carbon atoms) and
Albemarle Corporation
Siegel Alan
Spielman, Jr. Edgar E.
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