CS202205B1 - Method of producing 2-brom-2-chlor-1,1,1-trifluorethane - Google Patents

Description

The present invention relates to a process for the preparation of 2-bromo-2-chloro-1,1,1-trifluoroethane (hereinafter referred to as "the compound")

I), a clinically used inhalation anesthetic.

One possible process for the preparation of the compound I is a two-step synthesis, the first step of which is the photochemically catalysed addition of hydrogen bromide to chlorotrifluoroethylene and the second step is the isomerization of the resulting

1-bromo-2-chloro-1,1,2-trifluoroethane (II) to I under the catalytic action of anhydrous aluminum chloride.

Methods for performing isomerization are described predominantly in the patent literature (DE Pat. No. 1,041,957; FR Pat. No. 1,200,540; AT Pat. No. 205 472; AT Pat. No. 205 472; SE Pat. No. 170 850; U.S. Pat. Nos. 107,661, 107,665, 107,890 and 110,151). All of the protected processes deal with isomerization in terms of the degree of conversion of II and the yield of crude I. However, they also do not address the isomerization side reactions which may substantially reduce the I content of the crude product and hence the overall synthesis yield or impurities resulting from the side reactions. which considerably hinder the purification of the raw material and thus deteriorate the quality of the final product.

In particular, the present invention is directed to a method of manufacturing to eliminate the adverse consequences of neglecting said aspect of the isomerization reaction.

2-bromo-2-chloro-1,1,1-trifluoroethane by isomerization of 1-bromo-2-chloro-1,1,2-trifluoroethane in the presence of aluminum chloride as a catalyst.

It is characterized in that the isomerization is carried out in the presence of 0.01 to 1.0% by weight, preferably 0.1 to 0.3% by weight. a hydrocarbon having a carbon number of 6 to 10 and containing at least one aromatic ring in the molecule, such as benzene, p-xylene, naphthalene or tetrahydronaphthalene, or halobenzene.

The invention is based on the surprising finding that the addition of a small amount of a compound as defined above to the starting material II significantly reduces side reactions. Experimentally, the inhibitory effect has been tested and demonstrated with benzene, toluene, p-xylene, chlorobenzene, naphthalene, tetrahydronaphthalene, etc. Of course, almost any of the aforementioned substances can be used for this purpose, but for practical reasons preference is given to those a high degree of conversion and a high content of substance I can be used in minimal quantities and which are most easily separated from the reaction mixture. Tetrahydronaphthalene added in an amount of 0.2 wt.

A practical consequence of carrying out the isomerization reaction according to the invention is to increase the yield of Compound (I), improve its quality and increase the rectification capacity of its final purification.

The details of the method according to the invention follow from the exemplary embodiments.

202 205

202 205

Examples

Example 1

Comparative experiment

To a 1.5 liter sulfonation flask with stirrer, reflux condenser and separating funnel, placed in a 58-60 ° C bath, was charged 11.2 g (0.084 mol) of anhydrous aluminum chloride to which it was added in 5 minutes 100 ml (187 g, 0.95 mol) of 1-bromo-2-chloro-1,1,2-trifluoroethane (II) having a purity of 99.99% by weight A characteristic feature of the isomerization was the intense reflux of the reaction mixture during the addition of the substance. The reaction mixture was further heated under stirring to reflux for 5 hours, at which time samples were taken from the vapor phase and the degree of conversion of the substance II was checked according to the author's certificate No. 156 228. The reaction was terminated by decomposing the aluminum chloride with water and in the crude reaction mixture, the conversion of II and the 2-bromo-2-chloro-1 content was determined by gas chromatography,

1,1-trifluoroethane, ie substance I, with the following result:

degree of conversion of substance II 99.999% of theory content of substance I 84.9% by weight

SUBJECT

Example 2

Isomerization in the presence of side reaction inhibitors

The isomerization was carried out as in Example 1 with the addition of a side reaction inhibitor. The following table shows the substances used, their concentration, degree of conversion of substance II and content of substance I:

t-l o

«^ H« 1-4—

<D

O ca t

D <D

U ΰ

O

Tetrahydronaftalen 0.1 99,999 91.5 Tetrahydronaftalen 0.2 99,999 96.4 Tetrahydronaftalen 0.3 99,999 96.3 Chlorobenzene 0.2 99,999 96.6 Naphthalene 0.2 99,999 96.3 Benzene 0.2 99,999 96.5 p-Xylene 0.2 99,999 95.8

Claims (1)

A process for the preparation of 2-bromo-2-chloro-1,1,1-trifluoroethane by isomerization of 1-bromo-2-chloro-1,1,2-trifluoroethane in the presence of aluminum chloride as catalyst, characterized in that the isomerization is carried out in the presence of 0, % To about 1.0 wt.%, Preferably 0.1 to 0.3 wt. a hydrocarbon having a carbon number of 6 to 10 and containing at least one aromatic ring in the molecule, such as benzene, p-xylene, naphthalene or tetrahydronaphthalene, or halobenzene.