DE1030336B - Process for the preparation of perfluorocyclohexenes - Google Patents

Description

GERMAN

PATENT OFFICE

M30563IVb / 12o REGISTRATION DATE: May 22nd, 1956

NOTICE
THE REGISTRATION
AND ISSUE OF THE
EDITORIAL: MAY 22, 1958

The invention relates to a novel process for the production of perfluorocyclohexene hydrocarbons.

The invention also relates to the production of perfhiorcyclohexene also the preparation of perfluoromethylcyclohexenes with one or more trifluoromethyl substituents on the ring.

These perfluorocyclohexenes are reactive and polymerizable; they can also be copolymerized. They are also valuable as chemical intermediates. They also enter into addition reactions and can, for. B. be oxidized by basic aqueous permanganate solution to form dibasic fluorocarboxylic acids. From perfluorocyclohexene z. B. Perfiuoradipic acid, (CF ₂ ) ₄ (COOH) ₂ , can be prepared.

It has been discovered that these perfluorocyclohexenes are very simple and in practically quantitative yields by pyrolysis of perfluorocyclohexane and perfluoromethylcyclohexane carboxylic acids can be produced. In these acids a carboxyl group is bound directly to a carbon atom of a perfluorocyclohexane ring. One or more trifluoromethyl groups can also be bonded to the carbon atoms of the ring, which occur during pyrolysis remain. The ring must, however, have a fluorine atom on the carbon atom that corresponds to the COOH group bearing carbon atom is adjacent, d. i.e. it must have at least one (5-position fluorine atom.

COOH

10 Process for the preparation of perfluorocyclohexenes

Applicant:

Minnesota Mining and Manufacturing Company, Saint Paul, Minn. (V. St. A.)

Representative: Dr.-Ing. H. Ruschke, Berlin-Friedenau, and Dipl.-Ing. K. Grentzenberg, Munich 27,

Pienzenauerstr. 2, patent attorneys

20th Thomas S. Reid, George H. Smith inventor been called St. A.), and Wilbur H. Pearlson, Saint Paul, Minn. (V. are as

Carboxyl group and ß-fluorine atom are formed a double bond in the ring is split off according to the following scheme:

CF CF

F ₂ C CF ₂ about_SSO ° _C_ F ₂ C CF

F ₂ C CF ₂ F ₂ C CF

C C

F ₉ F ₉ ,

CO ₂ + HF

The perfluorocyclohexanecarboxylic acid boils at b.p. ₇ 4 _O = 172 ° C and perfluorocyclohexene at _{b.p. 74O} = 52 ° C.

The starting acid is passed in the vapor state through a pipe which has ^{been heated to a temperature of about 550 °} C. and which is long enough to enable practically complete conversion. A catalyst is not required. The reaction tube can be a simple, unfilled tube lined with graphite or a similar material. CO ₂ and HF and unreacted starting acid, which are water-soluble and have an acidic reaction, can easily be separated from the water-insoluble and normally liquid perfluorocyclohexene, which can be further purified by fractional distillation.

Examples of starting acids for the preparation of perfluoromethylcyclohexenes with one or more Trifluoromethyl groups on the ring are the completely fluorinated 2 - methylcyclohexanecarboxylic acid, 3-methylcyclohexanecarboxylic acid, ^ Methylcyclohexanecarboxylic acid, 2,4-dimethylcyclohexanecarboxylic acid and 2,2,6-trimethylcyclohexanecarboxylic acid.

The present reaction is not an ordinary decarboxylation reaction according to the scheme

R-COOH → ■ R -H + CO ₂

because in addition to CO ₂ , HF is also split off.

The perfluorocyclohexanecarboxylic acids can be obtained from the corresponding cyclohexanecarboxylic acids by electrolysis in anhydrous liquid hydrogen fluoride using a 5 to 6 volt voltage at about 0 ° C working cell with steel cathode and nickel anode. The starting acid is converted into the

809. 527/481

corresponding fully fluorinated acid fluoride (Ry.COF, where Rf is the perfluorocyclohexane radical) converted, the settles along with by-products at the bottom of the cell. These products are used with the theoretically Hydrolysis of the perfluorocyclohexanecarboxylic acid fluoride required amount of water mixed and the formed Perfluorocyclohexanecarboxylic acid then obtained by fractional distillation.

Because the electrochemical fluorination causes unsaturated Compounds add fluorine, you can also use aromatic carboxylic acids as starting compounds for Use the preparation of the perfluorocyclohexanecarboxylic acids used as starting materials in the present process. So z. B. benzoic acid, o-, m- and p-toluic acid be used.

The above electrochemical process is described in detail in U.S. Patent 2,519,983. The preparation of the Pernuorcyclohexanarbonsäuren by this process is again extensive described in German Patent 836 796.

The perfluorocyclohexanecarboxylic acids used in the present process differ in behavior clearly from the non-cyclic perfluoroalkanecarboxylic acids. In contrast to these, they can be obtained by pyrolysis in almost quantitative yield even in the absence a catalyst can be converted into the perfluorocyclohexenes.

example

An unfilled steel tube lined with graphite or a similar material, with an inner diameter of about 2 cm and a suitable length and which was 33 cm long in an electric furnace, served as the reaction space. The temperature was measured with a thermocouple placed outside the tube. 70 g of evaporated perfluorocyclohexylcarboxylic acid were then passed through the tube, which had been heated to 550 ° C., over the course of 2 hours. To remove the HF, the emerging gas mixture was passed through an NaF tube and then successively through three receivers, which were filled _{with ice (0 ° C), a mixture of acetone and solid CO 2} ^{(-8O 0} C) and finally liquid air (- 18O ⁰ C) were cooled. The condensates from the first two templates were combined and the material boiling below room temperature was volatilized. The remainder was fractionally distilled in a laboratory distillation column filled with glass bodies, yielding 60 g of a colorless, water-insoluble liquid product that _{boiled at a boiling point of 74O} = 51 to 52 ° C and was identified as relatively pure perfluorocyclohexene. It had a maximum at 5740 ΐημ in the infrared absorption spectrum. The yield was almost 100 ° / ₀ pure. Undecafluorocyclohexane could not be detected. The composition was confirmed by analysis and examination of the reaction properties.

A particularly pure middle fraction had the refractive index # | ⁵ = 1.289 and the density D ²ⁱ = 1.665; Bp., ₄₀ = 52.0 to 52.5 ° C.

Claims (1)

PATENT CLAIM: Process for the preparation of perfluorocyclobexenes, characterized in that perfluorocyclohexanecarboxylic acid or perfluoromethylcyclohexanecarboxylic acids with at least one trifluoromethyl group in the ring and at least one fluorine atom in the vapor phase by a about 550 ° C heated tube and then the condensed perfluorocyclohexene in the usual way, such as by fractional distillation. © 809 527 / 4S1 5.58