Process for the preparation of 1,2-bis-(2-nitrophenoxy)-ethane

The present invention relates to a process for the preparation of 1,2-bis-(2-nitrophenoxy)-ethane, by reacting 1 mole of ethylene glycol with about 190 to about 250 mol % of 2-chloronitrobenzene at temperatures of about 40.degree. to about 100.degree. C. with the addition of an alkali metal hydroxide in dimethylacetamide.

The invention relates to an improved process for the preparation of 
1,2-bis-(2-nitrophenoxy)-ethane in high yield and very good technical 
purity by etherification of ethylene glycol with 2-chloronitrobenzene, the 
solvent for etherification being N,N-dimethylacetamide and the base 
required for etherification being introduced into the dimethylacetamide as 
a solid or as a suspension. The product obtained in this way may be 
reduced to 1,2-bis-(2-aminophenoxy)-ethane and further processed without 
purification. 
1,2-bis-(2-nitrophenoxy)-ethane may be used as a fungicide (JP 48-010527). 
1,2-bis-(2-nitrophenoxy)-ethane is also an important intermediate in the 
preparation of pigments. Thus, reduction to the corresponding diamine, 
tetraazotization and subsequent coupling thereof with 
5-acetoacetylaminobenzimidazolones leads to valuable yellow pigments 
(EP-PS 0 024 702). 
It is known that 1,2-bis-(2-nitrophenoxy)-ethane may be prepared by the 
reaction of potassium 2-nitrophenolate with 1,2-dichloroethane or 
1,2-dibromoethane in alcohol (A. C. Cope, J. Am. Chem. Soc. 57 [1935] 572) 
or of sodium 2-nitrophenolate with 1,2-dichloroethane (A. Weddige, J. 
Prakt. Chem 21 [1880] 127) or with 1,2-dibromoethane in alcohol (R. 
Jaunin, R. Holl, Helv. Chim. Acta 41 [1958] 1783, 1789). 
The application of these known processes on an industrial scale is 
impossible from the current standpoint. Thus, etherification with 
1,2-dibromoethane is uneconomic due to the high cost of 1,2-dibromoethane. 
Furthermore, 1,2-dibromoethane, the 1,2-dichloroethane, is extremely 
harmful to health, so this compound must definitely be avoided in an 
industrial process, for occupational hygiene reasons. Furthermore, 
emissions of ethylene halides, which have a very high vapor pressure even 
at room temperature, cannot be avoided without the use of expensive 
apparatus. Also prohibitive for the reaction on an industrial scale is the 
formation of carcinogenic side products, such as vinyl chloride and vinyl 
bromide, which are produced under the previously mentioned reaction 
conditions of the disclosed processes. Finally, the above mentioned 
disclosed processes are also uneconomic from the point of view of yields 
(between 30 and 85%). 
A well-known alternative to the previously mentioned disclosed processes 
for the preparation of 1,2-bis-(2-nitrophenoxy)-ethane is to react 63 
parts of ethylene glycol with 315 parts of 2-chloronitrobenzene and 480 
parts of a 50% strength aqueous sodium hydroxide solution at 90.degree. C. 
in the presence of 80 parts of a 50% strength aqueous solution of 
benzyldimethyllaurylammonium chloride as phase transfer catalyst (DE 26 34 
419 Al). The dropwise addition of sodium hydroxide solution takes place 
over 3 hours and the final reaction requires 16 hours, which greatly 
reduces the economic viability of the process. The reaction mixture is 
added to 750 parts of water to precipitate the product, which is 
collected. 
The purification of the crude product which is obtained by this process is 
unfavorable. The filter cake has to be slurried in 500 parts of water and 
adjusted to pH 3-4 with hydrochloric acid. The solid is then collected 
again and finally washed, first with 350 parts and then with 80 parts of 
acetone, and dried. 
The disadvantages of the preparation variant mentioned are on the one hand 
the 400 mol % excess (relative to the ethylene glycol used) of sodium 
hydroxide, and on the other hand, and much more serious, the fact that an 
extremely alkaline effluent with a high concentration of salts, polluted 
with 2-nitrophenol (side product) and phase transfer catalyst which cannot 
be recycled, is produced. 
There was therefore a need for an improved industrial process for the 
preparation of 1,2-bis-(2-nitrophenoxy)-ethane, which gives, in one 
process step, a product which can be separated as far as possible by 
simple filtration and avoids the disadvantages described above of known 
processes, in good yield and high purity. 
Surprisingly, it has now been found that 1,2-bis-(2-nitrophenoxy)-ethane 
may be prepared in very good yield and high purity in a one-stage process 
by reacting 1 mole of ethylene glycol with about 190 to about 260 mol %, 
preferably with about 200 to about 250 mol %, in particular with about 210 
to about 220 mol %, of 2-chloronitrobenzene at temperatures of about 
40.degree. to about 100.degree. C., preferably of about 50.degree. to 
about 80.degree. C., in particular of about 55.degree. to about 65.degree. 
C., in the presence of an alkali metal hydroxide in dimethylacetamide 
(called "DMAc" in the following). 
The alkali metal hydroxide is expediently used in an amount of about 200 to 
about 300 mol %, preferably of about 230 to about 260 mol %, in particular 
of about 240 to about 250 mol %, relative to the ethylene glycol. Although 
in principle all alkali metal hydroxides, such as lithium, sodium, 
potassium, rubidium or caesium hydroxide and mixtures thereof may be used, 
sodium hydroxide and/or potassium hydroxide are used for preference. The 
alkali metal hydroxides, such as preferably potassium hydroxide or sodium 
hydroxide, are introduced into the reaction mixture continuously or in 
portions, either as a solid or suspended in DMAc. The use of a suspension 
of sodium hydroxide in DMAc is particularly preferred. 
Introduction of the alkali metal hydroxide generally takes between 2 and 4 
hours. When the addition has finished, the mixture is stirred for about 
another 2 to 3 hours. 
Finally, the reaction mixture, at the selected reaction temperature and 
with the aid of a pH electrode, is adjusted to a pH of 7.0 to about 5.5, 
preferably of about 6.5 to about 6.0, with a concentrated mineral acid. 
Suitable mineral acids are for example highly concentrated hydrochloric, 
hydrobromic, hydroiodic, sulfuric or phosphoric acid . The inorganic salts 
are filtered out of the hot reaction mixture and washed with DMAc. The 
product which has been produced is precipitated in the filtrate by adding 
water or lower aliphatic alcohols. It is collected and washed with water 
or alcohol. The water or alcohol and the DMAc are recovered from the 
filtrate by distillation and recycled to the production process. 
The process according to the invention is expediently performed at 
atmospheric pressure. It may, however, also be carried out at elevated or 
reduced pressure (vacuum). 
The process according to the invention is explained in more detail by the 
following example, but this does not represent a limitation.

EXAMPLE 
700 parts of DMAc, 362 parts of 2-chloronitrobenzene and 68 parts of 
ethylene glycol are initially introduced into a 2 l Witt jar with stirrer, 
flow-breaker and internal thermometer and heated to 55.degree. C. Then, at 
55.degree. C., a suspension of 108 parts of sodium hydroxide in 100 parts 
of DMAc is pumped in over the course of 4 hours at such a rate that the 
reaction temperature does not exceed 60.degree. C. It is then stirred for 
a further 2.5 hours at 60.degree. C. Then the reaction mixture is adjusted 
to pH 6.5 using 69 parts of 30% strength hydrochloric acid. After heating 
to 110.degree. C., salt is filtered out of the reaction mixture under 
suction and this is then washed with 100 parts of DMAc. To crystallise the 
product, 300 parts of water are stirred into the filtrate at 90.degree. C. 
The filtrate is cooled to 10.degree. C. and the 
1,2-bis-(nitrophenoxy)-ethane is filtered off under suction and washed 
with 100 parts of water. Water and DMAc are recovered from the filtrate by 
distillation and recycled to the production process. The moist, pale 
brown, crystalline product may be dried if necessary. The dried product, 
with a melting point of 167.degree.-168.degree. C., is obtained in a yield 
of 93% of theory and with a purity of 98.5%, according to HPLC. 
If 151 parts of potassium hydroxide are used instead of 108 parts of sodium 
hydroxide, in 100 parts of DMAc, and if the reaction mixture is acidified 
to pH 6.5 with 58 parts of 96% strength sulfuric acid instead of 69 parts 
of 30% strength hydrochloric acid, the same result is obtained.