Process for the manufacture of diphenyl ethers

Hydroquinone mono-phenyl ethers, and their alkali metal salts of the formula ##STR1## in which one of the radicals R.sub.1 and R.sub.2 denotes trifluoromethyl and the other denotes hydrogen or halogen and R.sub.3 represents hydrogen or an alkali metal cation or ammonium cation are prepared by reacting hydroquinone bis-phenyl ethers (bisphenoxybenzenes) of the formula ##STR2## with hydroquinone derivatives of the formula ##STR3## in which Cat denotes an alkali metal cation or ammonium cation and R.sub.4 denotes an alkali metal cation or ammonium cation or a (C.sub.1 -C.sub.4)-alkyl group, in a polar aprotic solvent at temperatures from 120.degree. to 280.degree. C., and optionally, an alkyl group present in the R.sub.4 -position is split off by treatment with an acid.

In the manufacture of hydroquinone mon-phenyl ethers by reacting alkali 
metal salts of hydroquinone with substituted halogenobenzenes, the 
corresponding bis-phenyl ethers are in general obtained as undesired 
by-products in varying amounts, depending on the reaction procedure. There 
is a need to convert by-products of this type into a form which can be 
used industrially. 
It has already been disclosed that diaryl ethers which carry, on one phenyl 
ring, a nitro group in the o-position or p-position relative to the other 
ether bond, can be trans-etherified or split using nucleophilic reagents, 
such as potassium phenolates, potassium alcoholates, potassium hydroxide 
or ammonia, in suitable solvents (Russian Patent Specification No. 
337,379; Z. Obsc. Chim. 34 (1964), 10, 3390; Z. Org. Chim. 1, (1965), 5, 
901; and Belgian Patent Specification No. 757,218). 
Corresponding trans-etherifications or splitting of diaryl ethers or 
bis-ethers which carry a trifluoromethyl group as a substituent in one 
phenyl ring have not hitherto been disclosed. 
The invention thus relates to a process for the manufacture of hydroquinone 
mono-phenyl ethers, and their alkali metal salts, of the general formula 
##STR4## 
in which one of the radicals R.sub.1 and R.sub.2 denotes trifluoromethyl 
and the other denotes hydrogen or halogen and R.sub.3 represents hydrogen 
or an alkali metal cation or ammonium cation, wherein hydroquinone 
bis-phenyl ethers (bisphenoxybenzenes) of the general formula 
##STR5## 
are reacted with hydroquinone derivatives of the general formula 
##STR6## 
in which Cat denotes an alkali metal cation or ammonium cation and R.sub.4 
denotes an alkali metal cation or ammonium cation or a 
(C.sub.1-C.sub.4)-alkyl group, in a polar aprotic solvent at temperatures 
from 120.degree. to 280.degree. C., and, optionally, an alkyl group 
present inthe R.sub.4 -position is split off by treatment with an acid. 
The reaction according to the invention formally proceeds according to the 
following overall equation: 
##STR7## 
A preferred radical R.sub.1 is --CF.sub.3 and preferred radicals R.sub.2 
are hydrogen and chlorine or bromine. A preferred radical R.sub.4 in 
formula III is R.sub.4 =Cat, potassium or sodium, in particular potassium, 
being preferred as the alkali metal. 
Aprotic polar solvents are used, such as, for example, dimethylsulfoxide, 
dimethylformamide, dimethylacetamide, diethylacetamide, 
hexamethyl-phosphoric acid tris-amide, tetramethylsulfone, 
tetramethylurea, N-methylpyrrolidone or nitriles, such as acetonitrile or 
propionitrile. Dimethylsulfoxide and N-methylpyrrolidone are preferred. It 
is advantageous to carry out the reactions as far as possible in the 
absence of water, so that water formed, for example in the manufacture of 
the alkali metal salts, should be removed in the customary manner, such 
as, for example, by azeotropic or simple distillation or by adding a 
water-binding substance. 
Possible reaction temperatures are those from 120.degree. to 280.degree. 
C., and temperatures from 160.degree. to 260.degree. C. are preferred. In 
order to achieve the desired reaction temperature, the reaction must be 
appropriately carried out under elevated (autogenous) pressure in a closed 
vessel. 
In general, the reactants are employed in approximately stoichiometric 
amounts, an excess of one or other of up to 50%, in particular of up to 
10%, being possible. 
The amount of solvent is chosen so that the reaction mixture remains easily 
stirrable. It can be, for example, between 2 and 10 parts by weight, 
relative to the compound of the formula II. 
After the reaction has ended, which in general requires between 2 and 20 
hours, the reaction product is isolated in the customary manner, for 
example by filtering off the resulting salt and/or distilling off the 
solvent or by pouring the mixture into water and ice and acidifying the 
aqueous phase and then extracting it with an organic solvent. 
The compounds of formula I obtained from them are valuable precursors for 
the manufacture of selective grass herbicides. 
It is a particular advantage of the process according to the invention that 
two molecules of the formula I are formed from one molecule of the 
symmetric bis-ether of the formula II, and at the same time the part split 
off from the molecule II is also obtained in a form which can be used 
directly in the same manner as the main part.

The examples which follow are intended to illustrate the invention without 
limiting it. 
EXAMPLE 1 
4-Trifluoromethyl-4'-hydroxy-diphenyl ether 
11.2 g (0.2 mole) of KOH in 11.2 g of water are added to 11.0 g (0.1 mole) 
of hydroquinone in 200 g of dimethylsulfoxide. The water is distilled off 
in vacuo. Thereafter, 39.8 g (0.1 mole) of 
1,4-bis-(4-trifluoromethyl-phenoxy)-benzene are added and the reaction 
mixture is stirred at a temperature of 170.degree. C. for 8 hours. The 
solvent is distilled off in vacuo, water is added to the residue and the 
mixture is acidified with 30 ml of concentrated HCl. The organic phase is 
separated off, the aqueous phase is extracted with methylene chloride and 
the combined organic phases are dried over Na.sub.2 So.sub.4 and 
distilled. 
34.2 g (0.134 mole) of 4-trifluoromethyl-4'-hydroxydiphenyl ether of 
melting point 46.degree.-49.degree. C. are obtained, corresponding to a 
yield of 67% of theory. 
##STR8## 
EXAMPLE 2 
4-Trifluoromethyl-4'-hydroxy-diphenyl ether 
If the solvent of Example (1) is replaced by N-methylpyrrolidone, 22.3 g of 
4-trifluoromethyl-4'-hydroxy-diphenyl ether of melting point 
46.degree.-49.degree. C. are obtained, corresponding to a yield of 44% of 
theory. 
##STR9## 
EXAMPLE 3 
4-Trifluoromethyl-4'-hydroxy-diphenyl ether 
81.5 g (0.2 mole) of NaOH in 8.15 g of water are added to 11.0 g (0.1 mole) 
of hydroquinone in 200 g of dimethylsulfoxide. The water is distilled off 
in vacuo. Thereafter, 39.8 g of 
1,4-bis-(4-trifluoromethyl-phenoxy)-benzene are added and the reaction 
mixture is stirred at a temperature of 170.degree. C. for 8 hours. Working 
up is carried out as in Example (1). 
23.1 g (0.091 mole) of 4-trifluoromethyl-4'-hydroxydiphenyl ether of 
melting point 46.degree.-49.degree. C. are obtained, corresponding to a 
yield of 45% of theory. 
##STR10## 
EXAMPLE 4 
2-Chloro-4-trifluoromethyl-4'-hydroxy-diphenyl ether 
11.2 g (0.2 mole) of KOH in 11.2 g of water are added to 11.0 g (0.1 mole) 
of hydroquinone in 200 g of dimethylsulfoxide. The water is distilled off 
in vacuo. Thereafter, 46.7 g (0.1 mole) of 
1,4-bis-(2-chloro-4-trifluoromethylphenoxy)-benzene are added and the 
reaction mixture is stirred at a temperature of 167.degree. C. for 8 
hours. Working up is carried out as in Example (1). 31.9 g (0.111 mole) of 
2-chloro-4-trifluoromethyl-4'-hydroxy-diphenyl ether of melting point 
42.degree.-46.degree. C. are obtained, corresponding to a yield of 55% of 
theory. 
##STR11## 
EXAMPLE 5 
2-Trifluoromethyl-4'-hydroxy-diphenyl ether 
11.2 g (0.2 mole) of KOH in 11.2 g of water are added to 11.0 g (0.1 mole) 
of hydroquinone in 200 g of dimethylsulfoxide. The water is distilled off 
in vacuo. Thereafter, 39.8 g (0.1 mole) of 
1,4-bis-(2-trifluoromethyl-phenoxy)-benzene are added and the reaction 
mixture is stirred at a temperature of 170.degree. C. for 14 hours. 
Working up is carried out as in Example (1). 23.4 g (0.092 mole) of 
boiling point 0.15 122.degree. C. are obtained, corresponding to a yield 
of 46% of theory. 
##STR12## 
EXAMPLE 6 
4-Trifluoromethyl-4'-methoxy-diphenyl ether and 
4-trifluoromethyl-4'-hydroxy-diphenyl ether 
5.6 g (0.1 mole) of KOH in 5.6 g of water are added to 12.4 g (0.1 mole) of 
4-hydroxyanisole in 200 g of dimethylsulfoxide. The water is distilled off 
in vacuo. Thereafter, 39.8 g of 
1,4-bis-(4-trifluoromethyl-phenoxy)-benzene are added and the reaction 
mixture is stirred at a temperature of 166.degree. C. for 20 hours. The 
solvent is distilled off in vacuo. Water is added to the residue, and 
(a) the aqueous phase is extracted with methylene chloride. The organic 
phase is dried with Na.sub.2 SO.sub.4 and distilled. 14 g (0.052 mole) of 
4-trifluoromethyl-4'-methoxy-diphenyl ether of melting point 
37.degree.-38.degree. C. are obtained, corresponding to 52% of theory. 
##STR13## 
(b) the aqueous phase is acidified with 30 ml of concentrated HCl and 
extracted with methylene chloride. The organic phase is dried with 
Na.sub.2 SO.sub.4 and distilled. 15 g of 
4-trifluoromethyl-4'-hydroxy-diphenyl ether of melting point 
46.degree.-49.degree. C. are obtained, corresponding to 59% of theory. 
##STR14## 
EXAMPLE 7 
4-Trifluoromethyl-4'-hydroxy-diphenyl ether 
39.8 g (0.1 mole) of 1,4-bis-(4-trifluoromethyl-phenoxy)-benzene are added 
to 6.2 g (0.11 mole) of sodium methylate in 200 g of dimethylsulfoxide and 
the mixture is stirred at a temperature of 180.degree. C. for 12 hours. 
The solvent is distilled off in vacuo. Water is added to the residue and 
the mixture is acidified with 30 ml of concentrated hydrochloric acid. The 
organic phase is separated off, the aqueous phase is extracted with 
methylene chloride and the combined organic phases are dried with Na.sub.2 
SO.sub.4 and distilled. 6.3 g (0.025 mole) of 
4-trifluoromethyl-4'-hydroxy-dipenyl ether of melting point 
46.degree.-49.degree. C. are obtained, corresponding to a yield of 25% of 
theory.