Process for preparing halogenated hydrocarbons

Details Process for preparing halogenated hydrocarbons Process for preparing halogenated hydrocarbons

1999-11-03

2002-12-31

Padmanabhan, Sreeni (Department: 1621)

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

Organic compounds

Halogen containing

C570S257000

Reexamination Certificate

active

06500993

ABSTRACT:

The present invention relates to a process for preparing halogenated hydrocarbons, comprising at least 3 carbon atoms, by catalytic reaction between a haloalkane and a olefin, in particular a halogenated olefin.
The addition of a haloalkane to an olefin is a well-known reaction, generally referred to as a telomerization reaction. Very often, copper derivatives are used to catalyse this addition reaction. For example, patent U.S. Pat. No. 3,651,019 describes the addition of carbon tetrachloride to olefins in the presence of catalysts containing copper or iron. That patent describes reactions in batches (non-continuous process) and, at the end of the reaction, the catalyst is not recovered. This makes the process economically unattractive. In the event of separation of the constituents of the reaction mixture by distillation, the catalyst would precipitate in the boiling vessel of the distillation column, thereby making its recycling difficult.
Patent application WO 97/07083 describes a process for preparing halogenated hydrocarbons by telomerization, preferably under the catalytic action of cuprous chloride in the presence of t-butylamine as co-catalyst, in which the mixture of products derived from the reaction step is separated in several steps. The mixture is first separated by a flash distillation into a first flow containing the unconverted reagents and the co-catalyst, and into a second flow comprising the halogenated hydrocarbon and the catalyst. The catalyst is then separated from this second flow by filtration, after which the halogenated hydrocarbon is purified by distillation. This process requires a filtration of the catalyst in solid form, which is always a difficult step to control in an industrial plant, in particular in a continuous synthetic process.
Patent application WO 97/05089 describes another process for preparing halogenated hydrocarbons by telomerization, under the catalytic action of a copper catalyst dissolved in a solvent which is immiscible with the desired halogenated hydrocarbon, thus making it possible to separate the catalyst/solvent system from the halogenated hydrocarbon by decantation. However, the production efficiency of this process remains very low.
A need consequently exists to provide a telomerization process which makes it possible to prepare halogenated hydrocarbons in excellent yield and excellent production efficiency, while at the same time also making it possible to recover the catalyst easily and return it to the reactor in a simple manner.
The present invention relates to a process for preparing a halogenated hydrocarbon, comprising the following steps:
(a) a reaction step between a haloalkane and an olefin in the presence of a catalyst and a co-catalyst under conditions which are suitable for producing the halogenated hydrocarbon, the co-catalyst being chosen from amines which are less volatile than the halogenated hydrocarbon;
(b) a separation step of the mixture of reaction products from step (a) wherein at least a first fraction comprising the halogenated hydrocarbon and a second fraction comprising the catalyst and the co-catalyst are obtained;
(c) optionally a recycling step of at least a part of the second fraction into step (a).
By “fraction” we relate to any part of the mixture enriched in certain of its constituents, obtained either in continous flow or in a discontinuous treatment. By “recycling” we relate to any operation of recovery and reuse indifferently in a continous or in a discontinuous mode.
In a specific mode of carrying out of the invention, in step (b) the mixture of reaction products from step, (a) is subjected to a separation by distillation, and, in addition to the first fraction comprising the halogenated hydrocarbon and the second fraction comprising the catalyst and the co-catalyst a third fraction comprising reagents not consumed is obtained, and in a step (c) also at least a part of the third fraction is recycled optionally to step (a).
The use, as co-catalyst, of an amine whose boiling point is higher than that of the halogenated hydrocarbon makes it possible to separate the halogenated hydrocarbon from the reagents not consumed and the catalyst/co-catalyst active complex by distillation. Since the catalyst remains soluble in the amine after the removal of the reagents not consumed and the halogenated hydrocarbon, it can thus be recovered easily.
In the reaction step (a) of the process according to the present invention, a haloalkane and a olefin, preferably a halogenated olefin are reacted in the presence of a catalyst and a co-catalyst to form a halogenated hydrocarbon, the co-catalyst being chosen from amines which are less volatile than the halogenated hydrocarbon produced.
Amines comprising from 8 to 25 carbon atoms, in particular aliphatic amines, may be suitable as co-catalysts in the process according to the invention. Aliphatic amines comprising from 10 to 22 carbon atoms are preferred. Very special preference is given to amines whose alkyl chain is branched, and more especially to tert-alkyl amines corresponding to the general formula (I)
in which R
1
, R
2
and R
3
represent C1-C8 alkyl groups. As non-limiting examples of amines with a high boiling point, in particular which are less volatile than 1,1,1,3,3pentachloropropane and 1,1,1,3,3pentachloro butane, mention may be made in particular of nonylamine, decylamine, undecylamine, dodecylamine and collidines. Amines corresponding to formula (I) are, in particular, the tert-alkyl amines Primene® 81-R and JM-T sold by Rohm & Haas Company. These latter amines are preferred. Mixtures of amines can also be used in the present process. The amines used as co-catalysts in the process according to the invention have also been found to be markedly more stable in the presence of the catalyst and the haloalkane than the amines used in the prior processes, such as isopropylamine and t-butylamine.
The haloalkanes used in the process according to the present invention are generally saturated organic compounds. They preferably contain from one to three carbon atoms and preferably at least 2 chlorine atoms. They can also comprise other substituents, such as other halogen atoms, alkyl groups or haloalkyl groups. As examples of haloalkanes according to the present invention, mention may be made of dichloromethane, chloroform, carbon tetrachloride, 1,1,1-trichloroethane or 1,1,2-trichloro-1,2,2-trifluoroethane. Carbon tetrachloride is most particularly preferred.
The olefins used in the process according to the present invention are, for example, linear or branched olefins comprising from 2 to 10 carbon atoms which may themselves be optionally substituted. They can be substituted, for example, with halogen atoms, alkyl or haloalkyl groups, nitrile (CN) groups or carboxylic acid (COOH) groups. Specific examples of such olefin are, amongst others, ethylene, propylene, butylene and the 1-olefines comprising from 2 to 10 carbon atoms. The olefin is preferably a halogenated olefin. The halogenated olefins are preferably derivatives of a haloethene or of a halopropene, which may themselves be optionally substituted. The halogenated olefins used in the process according to the present invention preferably correspond to the formula
Preferably, the halogenated olefin is a chlorinated olefin. As non-limiting examples of halogenated olefins, mention may be made of vinyl chloride, vinylidene chloride, trichloroethylene and the various chloropropene isomers, such as 1-chloro-1-propene, 2 -chloro-1-propene and 3-chloro-1-propene. Among these compounds, those in which X=Cl and R=H or CH
3
are preferred. Vinyl chloride and 2-chloro-1-propene are particularly suitable.
The halogenated hydrocarbons obtained according to the process of the present invention generally belong to the family of chlorinated hydrocarbons comprising from 3 to 12 carbon atoms. Often they belong to the family of chloropropanes, chlorobutanes or chloropentanes. The carbon atoms in the said chloropropanes, chlorobutanes and chloropentanes can also be substituted with other functional

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