Process for producing 2,2,3,3,-tetrafluorooxetane

The present application is a 35 U.S.C. 371 national stage filing of International Patent Application No. PCT/JP2005/002005, filed Feb. 10, 2005, through which and to which priority is claimed to Japanese Priority Patent Application No. 2004-047915, filed Feb. 24, 2004.

The present invention relates to a process for producing 2,2,3,3-tetrafluorooxethane, and more particularly to a process for producing 2,2,3,3-tetrafluorooxethane by reaction of tetrafluoroethylene with a compound of formaldehyde generation source in anhydrous hydrogen fluoride.

2,2,3,3-tetrafluorooxethane is a useful raw material compound for producing fluorine-containing rubber polymers, etc. For example, 2,2,3,3-tetrafluorooxethane can readily undergo polymerization reaction in the presence of an alkali metal halide, and fluorination of the hydrogen atoms of the resulting polyfluoropolyether polymer F(CH 2 CF 2 CF 2 O) n CH 2 CF 2 COF by a fluorine gas can give fluorine oil such as perfluoropolyether polymers F(CF 2 CF 2 CF 2 O) n CF 2 CF 2 COF or F(CF 2 CF 2 CF 2 O) n CF 2 CF 3 . React-ion with an alkali metal halide can give a 2,2-difluoropropionic acid derivative represented by the following general formula as raw materials for producing fluorine-containing rubber polymers:

XCH 2 CF 2 COF

(X: Cl, Br or I)

It is known that 2,2,3,3-tetrafluorooxethane having such effective uses can be produced by reaction of tetrafluoroethylene with a compound of formaldehyde generation source in anhydrous hydrogen fluoride.

Patent Literature 1: JP-B-2-37904

It is also reported that 2,2,3,3-tetrafluorooxethane can be obtained as a by-product in the production of 2,2,3,3,3-pentafluoropropanol CF 3 CF 2 CH 2 OH by reaction of tetrafluoroethylene with formaldehyde in anhydrous hydrogen fluoride, but only in a small amount because it is a by-product, and thus cannot be used as raw materials in the industrial scale.

Non-Patent Literature 1: J. Org. Chem. 28, 492-4(1963)

Problem to be Solved by the Invention

An object of the present invention is to provide a process for producing 2,2,3,3-tetrafluorooxethane by reaction of tetrafluoroethylene with a compound of formaldehyde generation source in anhydrous hydrogen fluoride in a high reaction yield.

Means for Solving the Problem

The object of the present invention can be attained by conducting above-mentioned process for producing 2,2,3,3-tetrafluorooxethane in the presence of polyfluoroalkylcarboxylic acid or polyfluoroalkyl ester thereof, represented by the following general formula:

RfCOORf′

(where Rf is a polyfluoroalkyl group having 1-5 carbon atoms, and Rf′ is a hydrogen atom or a polyfluoroalkyl group having 1-5 carbon atoms).

Effect of the Invention

In the process for producing 2,2,3,3-tetrafluorooxethane by reaction of tetrafluoroethylene with a compound of formaldehyde generation source in anhydrous hydrogen fluoride, the reaction is carried out in the presence of polyfluoroalkylcarboxylic acid or polyalkyl ester thereof, where-by the reaction yield can be enhanced to approximately twice or higher, amounting to nearly 40%.

2,2,3,3-tetrafluorooxethane can be produced by charging a compound of formaldehyde generation source and polyfluoroalkylcarboxylic acid or polyfluoroalkyl ester thereof into anhydrous hydrogen fluoride, and then adding tetrafluoroethylene thereto. As a compound of formaldehyde generation source, formaldehyde itself can be used, but owing to handling difficulty such as easy polymerizability of formaldehyde, etc., its polymers such as paraformaldehyde, trioxane, etc. can be preferably used. Generation of formaldehyde from the polymers can be carried out by acid decomposition, thermal decomposition etc. Since hydrogen fluoride is involved in the reaction system, acid decomposition based on hydrogen fluoride can be commonly used.

Anhydrous hydrogen fluoride for use in the reaction acts to conduct acid decomposition of the formaldehyde polymer and also as a solvent, and thus can be used in a proportion 1.0-20 equivalent weights, preferably 5-15 equivalent weights to number of moles in terms of HCHO of the formaldehyde polymer. Polyfluoroalkylcarboxylic acid or polyfluoroalkyl ester thereof can be used in a proportion of about 0.05 to about 10 equivalent weights, preferably about 0.2 to about 1.0 equivalent weight to number of moles in terms of HCHO of the formaldehyde polymer.

As the polyfluoroalkylcarboxcylic acid or polyfluoroalkyl ester thereof represented by the afore-mentioned general formula, trifluoroacetic acid CF 3 COOH, 2,2,3,3,3-pentafluoropropyltrifluoroacetic acid ester CF 3 COOCH 2 CF 2 CF 3 and 2,2,2-trifluoroethyltrifluoroacetic acid ester CF 3 COOCH 2 CF 3 can be preferably used. In addition thereto, the following compounds can be also used:

CF 3 CF 2 COOH

CF 3 CF 2 COOCH 2 CF 2 CF 3

CF 3 CF 2 COOCH 2 CF 3

CF 3 CF 2 CF 2 COOH

CF 3 CF 2 CF 2 COOCH 2 CF 2 CF 3

CF 3 CF 2 CF 2 COOCH 2 CF 3

CF 3 CF 2 CH 2 COOH

CF 3 CF 2 CH 2 COOCH 2 CF 3

The reaction can be carried out initially by charging anhydrous hydrogen fluoride, formaldehyde polymer and polyfluoroalkylcarboxylic acid or polyfluoroalkyl ester thereof, and then by adding tetrafluoroethylene thereto. The reaction can be carrier out either under the normal pressure of under super atmospheric pressure. In the case of the normal pressure, tetrafluoroethylene is discharged to the outside of the system, whereby the tetrafluoroethylene-based yield will be lowered. Thus, the flow rate of tetrafluoroethylene must be limited, and the reaction requires much time. The reaction is thus carried out under super atmospheric pressure, usually under about 0.1 to about 2MPa.

The lower the reaction temperature, the lower the reaction rate and the higher the amount of by-product, resulting in a decrease of the yield. On the other hand, the higher the reaction temperature, the more often the decomposition of the desired product, resulting in a decrease of the yield. Thus, it is appropriate to conduct the reaction at a temperature of usually about 0° to about 100° C., preferably about 30° to about 60° C.

The present invention will be described in detail below, referring to Examples.