Cyclic perfluoroketones and method of making

Provided are novel cyclic perfluoroketones which are thermally and chemically stable fluids. They are prepared by reacting perfluorodicarboxylic acid difluorides with carbonates in aprotic polar solvents.

This invention relates to novel cyclic perfluoroketones and a method for 
making the same. 
BACKGROUND OF THE INVENTION 
U.S. Pat. No. 4,067,884 assigned to Hoechst discloses perfluoroketones of 
formula (3): 
##STR1## 
wherein R.sup.1 and R.sup.2 are independently perfluoroalkyl groups, which 
may contain at least one oxygen atom as an ether bond, R.sup.1 and 
R.sup.2, taken together, have 10 to 80 carbon atoms, and R.sup.1 and 
R.sup.2 may be linear, branched or cyclic. The perfluoroketones are 
neutral liquids which are stable against acids and oxidizing agents and 
useful as heat transfer media when they are of low molecular weight and as 
lubricants when they are of high molecular weight. 
These perfluoroketones, however, have a boiling point as high as about 
100.degree. to 500.degree. C. which limits their use. There is a need for 
perfluoroketones having a lower boiling point or unique properties so that 
they may find a wider variety of applications. 
SUMMARY OF THE INVENTION 
Therefore, an object of the present invention is to provide novel cyclic 
perfluoroketones. Another object of the present invention is to provide a 
method for synthesizing cyclic perfluoroketones. 
The inventors have found that by reacting a perfluorodicarboxylic acid 
difluoride of formula (2) with a carbonate salt in an aprotic polar 
solvent, the acid fluorides at both ends are condensed into cyclic form 
through mild ionic reaction to form a novel cyclic perfluoroketone of 
formula (1). 
##STR2## 
In the formulae, x is an integer of from 2 to 10, and m and n each are an 
integer of from 0 to 2. 
The cyclic perfluoroketones of formula (1) are thermally and chemically 
very stable liquids and useful as reaction solvents in the chemical 
industry, heat transfer media, leak test fluids in the semiconductor 
industry, inert liquids for vapor phase soldering, and dielectric fluids 
in electric equipment. In particular, the cyclic perfluoroketone of 
formula (1) wherein both m and n are equal to 0 and x is equal to 2 has a 
lower boiling point of 84.degree. C. and will thus find a wider variety of 
applications than the conventional perfluoroketones, shown in U.S. Pat. 
No. 4,067,884. 
By utilizing the known photo decarbonylation as disclosed in Japanese 
Patent Application Kokai No. 10209/1977 by Hoechst, the cyclic 
perfluoroketones of formula (1) can be converted into cyclic 
perfluoroethers of formula (4) under moderate conditions in high yields 
according to the following scheme. The resulting cyclic perfluoroethers 
are more stable than the cyclic perfluoroketones and find use in the same 
applications as the cyclic perfluoroketones. 
##STR3## 
The cyclic perfluoroketones of formula (1) which have a carbonyl group are 
also used as precursors in synthesizing various compounds having a cyclic 
perfluoroether residue. 
U.S. Pat. No. 4,136,121 assigned to Hoechst discloses to react R.sup.1 
CO.sub.2 M wherein R.sup.1 is a perfluoroalkyl group having 2 to 50 carbon 
atoms which may contain at least one ether oxygen and M is a metal 
selected from the group consisting of Li, Na, K, Rb, Cs and Ag with 
R.sup.2 COF wherein R.sup.2 is a perfluoroalkyl group having 2 to 50 
carbon atoms which may contain at least one ether oxygen in an aprotic 
polar solvent at a temperature of 20.degree. to 200.degree. C. for 
synthesizing a perfluoroketone R.sup.2 COR.sup.3 wherein R.sup.3 is 
R.sup.1 or an isomer of R.sup.1. Also disclosed is to react R.sup.1 COF 
with M.sub.2 CO.sub.3 to form R.sup.1 CO.sub.2 M in situ which is further 
reacted with R.sup.1 COF coexisting in system for synthesizing R.sup.3 
COR.sup.3 wherein R.sup.1, M and R.sup.3 are as defined above. This 
patent, however, does not refer to perfluoroketones having a cyclic 
structure in the backbone. The inventors first discovered the cyclic 
perfluoroketones of formula (1).

DETAILED DESCRIPTION OF THE INVENTION 
The present invention provides novel cyclic perfluoroketones of formula 
(1). 
##STR4## 
wherein x is an integer of from 2 to 10, and m and n are independently an 
integer of from 0 to 2. (The definition of x, m and n are the same 
hereinafter.) They can be prepared by reacting perfluorodicarboxylic acid 
difluorides with carbonate salts in an aprotic polar solvent. 
The perfluorodicarboxylic acid difluorides used herein are represented by 
formula (2). 
##STR5## 
These perfluorodicarboxylic acid difluorides may be obtained by a well 
known technique (see U.S. Pat. No. 3,250,807) from a perfluorodicarboxylic 
acid difluoride free of an ether bond of the following formula (5) and 
hexafluoropropylene oxide of the following formula (6). 
##STR6## 
The carbonates used herein are represented by the general formula: M.sub.2 
CO.sub.3 wherein M is selected from the group consisting of Li, Na, K, Rb, 
Cs, and Ag, with Na.sub.2 CO.sub.3 and K.sub.2 CO.sub.3 being preferred. 
Use of anhydrous carbonate salts is preferred in order to control 
undesired side reaction. It is thus recommended to remove water from the 
carbonate salts by heating or vacuum drying prior to use. 
The aprotic polar solvents used herein include amides such as 
dimethylformamide, dimethylacetamide, and hexamethylphosphoric triamide; 
and ethers such as diethyl ether, tetrahydrofuran, dioxane, ethylene 
glycol dimethyl ether (glyme), diethylene glycol dimethyl ether (diglyme), 
triethylene glycol dimethyl ether (triglyme), and tetraethylene glycol 
dimethyl ether (tetraglyme), with the diglyme, triglyme and tetraglyme 
being preferred. It is also recommended to remove water from the solvents 
prior to use. 
Though not bound to the theory, it is believed that the conversion of the 
perfluorodicarboxylic acid difluorides of formula (2) into the cyclic 
perflurorketones of formula (1) proceeds through the process that the acid 
fluoride at one molecular end of the perfluorodicarboxylic acid difluoride 
first reacts with a carbonate to form a carboxylate which, in turn, reacts 
with the acid fluoride at the other end to form a cyclic ketone. This 
process is illustrated by the following chemical scheme. 
##STR7## 
The molar ratio of the carbonate to the perfluorodicarboxylic acid 
difluoride used is 1:1 from a stoichiometric aspect, but it is preferable 
in practice to use the carbonate in excess for reaction efficiency. For 
better results, the carbonate and the perfluorodicarboxylic acid 
difluoride are used in a molar ratio of from 1.2/1 to 5.0/1. If the amount 
of the carbonate used exceeds this range, there is the risk that 
undesirably both the ends of the molecule become carboxylates. The amount 
of the solvent used is not critical although it is often used in an amount 
of about 0.2 to 20 liters per mole of the perfluorodicarboxylic acid 
difluoride. 
Reaction may be effected by adding dropwise the perfluorodicarboxylic acid 
difluoride to a mixture of the carbonate and the solvent, preferably at a 
temperature of 20.degree. to 200.degree. C. At the end of addition, it is 
sometimes necessary to heat the reaction mixture to a temperature of 
100.degree. to 200.degree. C. for increasing the conversion rate of the 
reactant, preferably to a temperature of 150.degree. to 200.degree. C. for 
optimum reaction rates. The progress of reaction can be monitored by 
infrared spectroscopy wherein the absorption of acid fluoride appearing 
near 1890 cm.sup.-1 diminishes and eventually disappears. The reaction 
pressure is not critical and may be atmospheric or under pressure in an 
autoclave. Atmospheric pressure is convenient because reaction is 
accompanied by evolution of carbon dioxide gas. At the end of reaction, 
the product or cyclic perfluoroketone may be isolated by distillation. It 
is possible to sequentially distill out the product as it is produced 
during reaction. 
EXAMPLE 
Examples of the present invention are given below by way of illustration 
and not by way of limitation. 
EXAMPLE 
A 3-liter glass reactor equipped with a stirrer, a distillation head 
connected to a condenser and a cock for distilling out the product, a 
thermometer, and a heating bath was charged with 500 ml of dry diglyme and 
424 grams (4 mol) of dry sodium carbonate. Reaction was conducted in a 
nitrogen gas stream by adding dropwise 426 grams (1 mol) of 
perfluoro-2,7-dimethyl-3,6-dioxasuberic acid difluoride of the following 
formula to the reactor at a temperature of 80.degree. C. over one hour. 
##STR8## 
At the end of addition, the temperature was raised to 150.degree. C. and 
the reactor was maintained at the temperature for 3 hours while allowing 
the product to distill out. The crude product was distilled under 
atmospheric pressure, yielding 171 grams (0.48 mol) of 
perfluoro-2,7-dimethyl-3,6-dioxacycloheptanone of the following formula 
(5) having a boiling point of 84.degree. C. The following structure was 
established by the analytical data. 
##STR9## 
IR spectrum: 1790 cm.sup.-1 
.sup.19 F-NMR spectrum: The chemical shifts are relative to CF.sub.3 COOH. 
Two values were observed probably because two trifluoromethyl groups 
formed cis and trans isomers. 
##STR10## 
.sup.13 C-NMR spectrum: The chemical shifts are relative to TMS. Two values 
were observed for the same reason as above. 
##STR11## 
REFERENCE EXAMPLE 
A 100 ml glass reactor equipped with UVL-100HA high-pressure mercury lamp 
(manufactured by Riko Kagaku Sangyo K.K.) was charged with 175 grams (0.49 
mol) of the perfluoro-2,7-dimethyl-3,6-dioxacycloheptanone obtained in 
Example. The reactor was also equipped with a dry ice condenser and a 
magnetic stirrer, and argon gas was slowly passed therethrough. After 190 
hours of UV exposure, the disappearance of the reactant was observed by 
gas chromatography. There was obtained 146.5 grams (yield 81%) of a crude 
product having a purity of 89%. Distillation yielded 104.5 grams of a 
fraction having a boiling point of 65.degree. C. with a purity of higher 
than 97%. This product was identified to be 
perfluoro-2,3-dimethyl-1,4-dioxane of the following formula (6) by the 
analytical data. 
##STR12## 
IR spectrum: No absorption appeared at wave numbers higher than 1400 
cm.sup.-1, indicating the absence of ketone and other functional groups. 
.sup.19 F-NMR: -3 to -21 ppm 10F (CF.sub.3, --CF.sub.2 --) -49 to -51 ppm 
2F (--CF--) 
The chemical shifts are relative to CF.sub.3 COOH. 
Mass spectrum: 313 (M--F), 263 (M--CF.sub.3) 
______________________________________ 
Elemental analysis: 
Calcd. 
Found 
______________________________________ 
C: 21.7% 21.1% 
F: 68.7% 67.9% 
______________________________________ 
The cyclic perfluoroketones of the invention are thermally and chemically 
very stable liquids and useful as reaction solvents in the chemical 
industry, heat transfer media in various applications, leak test fluids in 
the semiconductor industry, inert liquids for vapor phase soldering, 
dielectric fluids in electric equipment, and the like. They can be 
converted into more stable cyclic perfluoroethers and used as precursors 
to various compounds having a cyclic perfluoroether residue. The method of 
the invention can produce such cyclic perfluoroketones with ease. 
Although some preferred embodiments have been described, many modifications 
and variations may be made thereto in the light of the above teachings. It 
is therefore to be understood that within the scope of the appended 
claims, the invention may be practiced otherwise than as specifically 
described.