CS229193B1 - Method of preparing 2,5-dialkoxy-4-chloro-nitrobenzene - Google Patents

Description

The present invention provides a process for the preparation of 2,5-dialkoxy-4-chloro-nitroben-

(I) wherein R is alkyl of 1 to 5 carbon atoms, by nitration of 2,5 " dialkoxy " -chlorobenzenes of formula II,

wherein R is as defined above, with dilute nitric acid and measured for a technically advantageous method of manufacture from unrefined

2,5-dialkoxy-chlorobenzenes *

2,5-Dialkoxy-4-chloro »nitrobenzenes are valuable semi-finished products used for the production of photosensitive compounds, especially for diazography ·

The preparation of these compounds has not been separately described in the literature so far. Only US patent j 028 240 discloses that 2.5 »

Dialkoxy-4-chloro-nitrobenzenes can be prepared by nitro-2,529,229,193

-Dialkoxy-chlorobenzenes diluted with nitric acid without mentioning the specific preparation and yields. The technical feasibility and economic advantageousness of the production of these substances depend greatly on the price and purity of the starting 2,5-dialkoxy-chlorobenzenes, the choice of working conditions during nitration and further processing into products of technical purity. The preparation of 2,5-dialkoxy-chlorobenzenes as pure substances is a difficult technical problem, it is carried out by chlorination of 1,4-dialkoxybenzenes, which always produces a mixture of the desired 2,5-dialkoxy-chlorobenzene-unreacted

1,4-dialkoxybenzene and higher chlorinated 2,5-dialkoxy-1,4-dihlorobenzene, of which the desired monochloro derivative can only be obtained by high-vacuum rectification, which results in significant decomposition of the substances and is associated with considerable corrosion problems in the production equipment. During nitration, a suitable initial nitric acid concentration must be selected so that during the nitration the reaction mixture is well stirrable and the reaction is well controlled by cooling. Also, the nitration temperature has a significant effect on its course and further on the yield and purity of the resulting product. At nitration temperatures below 40 ° C and at appropriate nitric acid concentrations, the reaction rate is very slow and conversely at nitration temperatures above 65 degrees to side oxidation reactions.

It has already been found that it is advantageous to carry out nitration of 2,5-dialkoxy-chlorobenzenes, in particular of their lower purity, containing as main impurities 1,4-dialkoxybenzene and 2,5-dialkoxy-1,4-dichlorobenzene, with an aqueous solution of nitric acid. with an initial concentration of 36 to 50, preferably 40% by weight, with an amount of 2 to 5, preferably 3 moles of nitric acid per mole of 2,5-dialkoxy-chlorobenzene starting material, and at an initial temperature of 30 to 50, preferably 40 to 50 ° C and terminate the nitration at 60-70 ° C. It is advantageous to dispense 2,5-dialkoxy-chlorobenzenes, which are mostly liquids at normal temperature, especially if they are less pure products, into the nitric acid solution with good stirring and maintaining the temperature by cooling, since good miscibility and re-reaction as well as internal product is excreted in good crystalline form. In the temperature range of 40 to 65 ° C, the nitration time is 1.5 to 3 hours with almost complete reaction of 2,5-dialkoxy-chlorobenzenes, and its course can be easily controlled, for example, by chromatographic methods.

-4 229 193

It has been found that in the nitration of technical unrefined 2,5-dialkoxy-chlorobenzenes, 1,4-dialkoxybenzenes are easily nitrated from the accompanying substances to the corresponding mononitro compounds, which are liquid under the reaction conditions,

2,5-Dialkoxy-1,4-dichlorohenzenes are not titrated. These changes in the physical properties of the accompanying substances after nitration make it easier to isolate 2,5-dialkoxy-4-chloro-nitrobenzenes in a pure state than is the case when refining technical 2,5-dialkoxy-chloro-benzene to a pure product.

The most preferred way of separating 2,5-dialkoxy-4-chloro-nitrobenzenes from the reaction mixture after nitration is by separating them at a temperature above the melting point by separating two immiscible liquids, wherein the separated product liquid is still scrubbed with aqueous sodium carbonate and freed from acid residues nitric. In order to avoid undesired oxidation reactions, it is advantageous to dilute the reaction product after nitration with water before separation so that the concentration of nitric acid in the aqueous layer does not exceed 20% by weight. If the melting point of some 2,5-dialkoxy-4-chlorobenzenes is above 85 ° C, for example, as is the case with 2,5-diethoxy-4-chloronitrobenzene, it is necessary to separate the product in solid form, eg by filtration and also washed with aqueous alkaline solutions and water ·

After separation and scrubbing, the products obtained - 2,5-dialkoxy-4-chloro-nitrobenzenes - are predominantly contaminated to a lesser extent with resinous substances, followed by 2,5-dialkoxy-1,4-dichlorohenzenes and possibly 2,5-dialkoxy-nitrobenzenes . It has been found that crystallization from organic solvents such as aliphatic alcohols, petroleum ether, benzene, toluene is the most suitable method of refining, especially crystallization from ethanol or its aqueous solutions containing above 90% by weight of ethanol is preferred due to the steep solubility curve of these · The refining effect can be further enhanced by filtering the activated carbon solutions before crystallization. Taking into account the minimum solvent consumption, suspension density of the crystallized product, final purity and yield, it is preferable to isolate the product in two

- 5,229,193 degrees, at higher and lower crystallization temperatures and, if necessary, the less pure product obtained from the second isolation step refine the crystallization once more. the isolated crystallization products must be freed of solvent residues by conventional drying methods. '

The process for preparing the 2,5-dialkoxy-4-chloro-nitrobenzenes of the present invention has many technical and economic advantages. It is simple, takes place under mild temperature conditions, and production can be carried out on a simple conventional production equipment. It provides the possibility of processing unrefined 2,5-dialkoxy-chlorobenzenes obtained after chlorination of 1,4-dialkoxybenzenes of at least 70% purity. 90 to 98% yields of 2,5-dialkoxy-4-chloro-nitrobenzenes according to theory are obtained to a starting amount of 2,5-dialkoxy-chlorobenzenes of good purity suitable for further processing e.g.

Further details of the process are given in the following examples, where parts denote parts by weight, percentages by weight.

Example 1

358 parts of 2,5-dibutoxy-chlorobenzene (81.8%), 2,5-dibutoxy-chlorobenzene, 12.8%, are metered in with stirring over a period of 0.5 hours to 659 parts of a 40% nitric acid aqueous solution at 40 ° C. % Of 2,5-dibutoxy-1,4-dichlorobenzene and 6.2% of 1,4-dibutoxybenzene. During dosing, the temperature is maintained by cooling to rise from the initial 40 ° C to 50 ° C at the end of the dosing, the reaction mixture is maintained at 50 ° C for 0.5 h with stirring and then raised to 60 ° C and allowed to cool. To the reaction product thus obtained, 423 parts of water are added, the mixture is heated to 82 ° C and allowed to settle, then layered over two liquid layers. The lower organic layer was separated and further processed at 82 ° C by shaking with 537 parts of a 2% aqueous sodium carbonate solution and then twice more with 537 parts of water. After the last wash, the aqueous extract having a pH of between 6 and 7.5, the separated organic layer is dissolved in 345 parts of 96% ethanol by heating to 65 ° C with stirring, cooled to 25 ° C over 1 hour, thereby crystallizing

229 193 major portion of 2,5-dibutoxy-4-chloro-nitrobenzene to be filtered · After washing the filtered portion with 32 parts of 96% ethanol, 391 parts of the filter cake are obtained and dried to 50 ° C.

328.5 parts of dry product 2,5-dibutoxy-4-chloro-nitrobenzene 96.4% pure, yellow crystalline powder with melting point 77 to 79 ° C according to Kofler, ie in 92.9% yield to the starting amount 2 5-dibutoxy-chlorobenzene, which is only contaminated

2,5-dibutoxy-1,4-dichlorobenzene. From the filtrate after filtering off the major portion of the crystallized product, after cooling to 0 ° C, further crystallization is isolated by filtration and after washing with 20 parts 96% ethanol 22.55 parts filter cake, from which after drying to 30 ° C 21.6 parts are obtained. of the product 2,5-dibutoxy-4-chloro-nitrobenzene 49.4% pure, yellow crystalline powder, m.p. 47-52 ° C, i.e. in a yield of 3.1% of theory to the starting amount of 2,5-dibutoxy -chlorobenzene, whose main impurity is 2,5-dibutoxy-1,4-dichlorobenzene

Example 2

The same procedure as in Example 1 was followed except that the technical 2,5-dibutoxy-chlorobenzene was used in a different amount and composition, 144.2 parts of 76.4% 2,5-dibutoxy- chlorobenzene, 19.7% 2,5-dibutoxy-1,4-dichlorobenzene, 3.2% 1,4-dibutoxybenzene and 0.7% other impurities of unidentified substances · After crystallization from 96% ethanol at 25 ° C 138 parts of dry 2,5-dibutoxy-4-chloro-nitrobenzene 88.4% purity and a melting point of 72-76 ° C are obtained, i.e. in a yield of 94.2% of theory, starting from 2,5-dibutoxy-chlorobenzene. Further crystallization from the mother liquors at 0 ° C yielded 6.7 parts of dry product

2,5-dibutoxy-4-chloro-nitrobenzene 62,6% Purity, melting point 43-54 ° C according to Kofler, contaminated with 2,5-dibutoxy-1,4-dichlorobenzene, ie · in a yield of 3,2% of theory 2 5-dibutoxy-chlorobenzene.

Example 3

To 180 parts of an aqueous solution of 40% nitric acid 3e after the heat ^Q 40 C dosed during 1 h with cooling and stirring, 109 parts of commercial 2,5-diethoxy-chlorobenzene containing 18% 1,4-dietho7 _

229 193 xybenzene and 2,5-diethoxy-1,4-dichlorobenzene as impurities. Then the temperature of the reaction mixture is raised to 50 ° C for 0.5 h and further to 60 ° C for 1 h to complete the nitration. After nitration, the reaction mixture is diluted with 92 parts of water, heated to 80 ° C, filtered and the filter cake washed with 115 parts of 2% aqueous sodium carbonate solution and 115 parts of water. After drying the filter cake, 133 parts of crude 2,5-diethoxy are obtained. 94-104 ° C according to Kofler, which is contaminated mainly with 2,5-diethoxynitrobenzene · Crystallization of the crude product from 175 parts of 96% ethanol, after cooling to 22 ° C by filtration, 116 parts of filtration after drying, 104 parts of pure 2,5-diethoxy-4-chloro-nitrobenzene, melting at 107-108 ° C according to Kofler, i.e. in a yield of 95% of theory. By cooling the mother liquors from the crystallization to a temperature of -3 ° C, a further crop of product crystallized, the amount of which after filtration and drying was 2.1 parts and was only 50% pure.

According to similar procedures, 2,5-dimethoxy-4-chloro-nitrobenzene, 2,5-dipropoxy-4-chloro-nitrobenzene and 2,5-diisoamyl-4-chloro-nitrobenzene can be prepared from the corresponding 2,5-dialkoxy-chlorobenzenes.

Claims (5)

SCOPE OF THE INVENTION 229 193 A process for the preparation of 2,5-dialkoxy-4-chloronitrobenzenes of the formula I, wherein R is C 1 -C 5 alkyl, characterized in that: Of 2,5-dialkoxy-4-chloro-nitrobenzenes having a melting point above 85 ° C, separation is effected by isolation of the crude product in solid form · 2,5-dialkoxy-1,4-dichlorobenzene 2,5-dialkoxy-chlorobenzene either a pure or technical product of at least 70% * purity obtained after the chlorination of 1,4-dialkoxybenzenes in which 1,4-dialkoxybenzene is present as impurities; and 2. The process according to claim 1, wherein the starting material is The 2,5-dialkoxy-chlorobenzenes of formula II, wherein R is as defined above, are treated with an aqueous solution of nitric acid at a concentration of 36 to 50% by weight in an amount of 2 to 5 moles of nitric acid per mole of 2,5-dialkoxy-chlorobenzene at a temperature of 30 to 70 ° C, the crude 2,5-dialkoxy-4-chloro-nitrobenzene is separated from the obtained nitration product, which is refined by crystallization · 3. The process of claim 1, wherein 2,5-dialkoxy-chlorobenzene is sequentially metered into the nitric acid solution. The method according to claim 1, characterized in that the separation is carried out At a temperature above the melting point of 2,5-dialkoxy-4-chlorobenzene by the principle of separation of two immiscible liquids, the residual acidity in the product liquid is washed with aqueous solutions of alkali or alkaline, carbonates and water, or Process according to claim 1, characterized in that the crystallization is carried out using organic solvents which are aliphatic alcohols having 1 to 6 carbons, petroleum ether, benzene, toluene, preferably ethanol and its solutions with water containing at least 90 wt. ethanol.