Process for preparing perfluoroalkyl aryl sulfides and novel...

Details Process for preparing perfluoroalkyl aryl sulfides and novel... Process for preparing perfluoroalkyl aryl sulfides and novel...

1999-05-28

2001-01-16

Vollano, Jean F (Department: 1621)

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

Organic compounds

Amino nitrogen containing

C568S056000, C568S055000

Reexamination Certificate

active

06175042

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an improved process for preparing perfluoroalkyl aryl sulfides and to two novel perfluoroalkyl aryl sulfides.
Aromatic compounds carrying fluorine-containing substituents are intermediates for the synthesis of agrochemicals, pharmaceuticals, dyes, and polymers. The trifluoromethylthio group in particular is included in the development of novel biologically active compounds and novel dyes, since it has high chemical stability and is the most lipophilic known substituent E.g., R. E. Banks and K. C. Lowe, “Fluorine in Medicine in the 21
st
“Century”, Chemserve Ltd., Manchester (1994); S. B. Walker, “Fluorine Compounds as Agrochemicals”, Fluorochem Ltd., Old Glossop (U.K.) (1990); EP-A 374,061; J. H. Clark, D. Wails, and T. W. Bastock, “Aromatic Fluorination”, CRC Press, Boca Raton, Fla. (1996), page 119. 2-Hydroxyphenyl trifluoromethyl sulfide, for example, is required for preparing certain herbicides. E.g., U.S. Pat. No. 4,581,059. Chlorine-, nitro-, and amino-substituted phenyl trifluoromethyl sulfides are employed as intermediates for pesticides. E.g., DE-A 3,737,984 and DE-A 3,737,985.
Hitherto, a number of methods for preparing perfluoroalkyl aryl sulfides have been disclosed. Most of these methods require expensive and/or toxic reagents, which is a disadvantage for industrial production. Pentafluoroethyl and long-chain perfluoroalkyl radicals can be introduced into aromatic thiols by ion-radical and cationic reactions with perfluoroalkyl iodides. E.g.,
J. General Chem. USSR
, 53, 2254 (1983) and
J. Org. Chem. USSR
, 13, 1985 (1977). However, perfluoroalkyl iodides have the disadvantage that they must be prepared in a complicated manner and are therefore expensive.
A more recent method for preparing C
1
derivatives in which a thermally induced decarboxylation of potassium trifluoroacetate is carried out in the presence of aryl sulfides has been reported. E.g.,
Tetrahedron Lett
., 37, 9057 (1996). Although this process constitutes a considerable advance on the earlier methods, the yields—in most cases only about 50% of theory—are still unsatisfactory, and the process has hitherto been limited to introducing the trifluoromethyl group. Furthermore, this process is virtually impossible to carry out on an industrial scale, since the strongly exothernic reaction is virtually impossible to control. The entire reaction mixture is described as being heated rapidly by bringing it into contact with a hot heat exchange medium. A strongly exothermic reaction then results. No details about the pressure are given. Consequently, one skilled in the art must assume that the operation was carried out under atmospheric pressure.
SUMMARY OF THE INVENTION
This invention, accordingly, provides a process for preparing perfluoroalkyl aryl sulfides of the formula (I)
Ar—S—R
f
  (I),
in which
Ar represents optionally substituted phenyl, naphthyl, pyridyl, or pyrimidyl having a molecular weight, excluding any fluorine atoms that may optionally be present, of less than 200 g/mol, and
R
f
represents a perfluoroalkyl radical having 1 to 7 carbon atoms,
comprising
(1) reacting disulfides of formula (II)
 Ar—S—S—Ar  (II),
in which each Ar is defined as for formula (I),
with alkali metal salts of aliphatic perfluorocarboxylic acids of formula (III)
R
f
—COO
(−)
M(
+
)   (III),
in which
R
f
is defined as for formula (I), and
M represents an alkali metal,
in the presence of a high-boiling aprotic solvent at elevated temperature and reduced pressure, and
(2) distilling off the resultant perfluoroalkyl aryl sulfide of formula (I) at the rate at which it is formed.
Each Ar group preferably represents phenyl, naphthyl, pyridyl or pyrimidyl, each of which is optionally mono- or polysubstituted, independently, by balogen, nitro, cyano, C
1
-C
6
-alkyl that is optionally substituted with fluorine and/or chlorine, or C
1
-C
6
-alkoxy that is optionally substituted with fluorine and/or chlorine. Each Ar group more preferably represents phenyl, naphthyl or pyridyl, each of which is optionally mono- or polysubstituted, independently, by fluorine, chlorine, bromine, nitro, cyano, C
1
-C
4
-alkyl that is optionally substituted with fluorine and/or chlorine, or C
1
-C
4
-alkoxy that is optionally substituted with fluorine and/or chlorine. Each Ar group most preferably represents phenyl, naphthyl, 2-pyridyl, 3-pyridyl or 4-pyridyl, each of which is optionally mono- or disubstituted, independently, by fluorine, chlorine, bromine, nitro, cyano, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, trifluoromethoxy, difluoromethoxy, chlorodifluoromethoxy, 2-chloro-1,1,2-trifluoroethoxy, 1,1,2-trifluoroethoxy, 2,2,2-trifluoroethoxy, 1,1,2,2-tetrafluoroethoxy, 2,2,2-trichloro-1,1-difluoroetlioxy, 1,1-difluoroethoxy, trifluoro-methylthio, difluoromethyl, chlorodifluoromethyl, 2-chloro-1,1,2-trifluoroethyl, 1,1,2-trifluoroethyl, 1,1,2,2-tetrafluoroethyl, or pentafluoroethyl.
Group R
f
preferably represents a perfluoroalkyl radical having 1 to 5 carbon atoms. Group R
f
more preferably represents a perfluoroalkyl radical having 1 to 4 carbon atoms. Group R
f
most preferably represents trifluoromethyl, perfluoroethyl, or perfluoropropyl.
The present invention also relates to a process for preparing perfluoroalkyl aryl sulfides of the formula (I′)
Ar′—S—R
f
  (I′),
in which
Ar′ represents hydroxyl-, mercapto-, or amino-substituted phenyl, naphthyl, pyridyl, or pyrimidyl having a molecular weight of less than 200 g/mol, and
R
f
is defied as above for formula (I),
comprising
(1) reacting disulfides of the formula (II′)
Ar″—S—S—Ar″  (II′),
in which
each Ar″ independently represents methoxy-, methylthio-, or nitro-substituted phenyl, naphthyl, pyridyl, or pyrimidyl having a molecular weight of less than 200 g/mol,
with alkali metal salts of aliphatic perfluorocarboxylic acids of the formula (III)
in the presence of a high-boiling aprotic solvent at elevated temperature and reduced pressure,
(2) distilling off the resultant compound of formula (I″)
Ar″—S—R
f
  (I″)
in which
Ar″ is defined as for formula (II′), and
R
f
is defined as for formula (I);
at the rate at which it is formed, and
(3) forming the perfluoroalkyl aryl sulfides of the formula (I′) by (i) cleaving the methoxy or methylthio group of the compound of formula (I″) when Ar″ represents methoxy- or methylthio-substituted phenyl, naphthyl, pyridyl, or pyrimidyl and/or (ii) reducing the nitro group of the compound of formula (I″) when Ar″ represents nitro-substituted phenyl, naphthyl, pyridyl, or pyrimidyl.
The molecular weight of the aryl groups Ar, Ar′, and Ar″, excluding any fluorine atoms that may optionally be present, is preferably less than 180 g/mol (more preferably less than 160 g/mol).
DETAILED DESCRIPTION OF THE INVENTION
The aryl sulfides of formulas (II) and (II′) required for carrying out the process according to the invention are commercially available or can be prepared by known or analogous processes. See
Synth. Commun
., 25, 227 (1995);
Synth. Commun
., 26, 191 (1996);
Chem. Lett
., 12, 2269 (1990);
Khim. Geterots. Soed
., N9, 1276 (1992) [Engl. translation:
Chem Heteroc. Comp
., 28, 1084 (1992)]; and
Zh. Org. Khim
., 20, 202 (1984) [English translation.:
J. Org. Chem USSR
, 20, 181 (1984)].
The alkali metal salts of perfluorocarboxylic acids of formula (III) also required as starting materials are also commercially available or can be prepared in a known manner by neutralization from the corresponding perfluorocarboxylic acids. Preference is given to using the sodium or potassium salts (i.e., where M is Na or K), particularly the potassium salts.
In general, 1.0 to 5 mol (preferably 1.5 to 2.5 mol) of an alkali metal salt of a perfluorocarboxylic acid

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