Description:FIELD OF THE INVENTION

The present invention relates to continuous process of preparation of m-dichlorobenzene comprising denitration of m-nitrochlorobenzene and chlorinating the same to obtain m-dichlorobenzene without catalyst.

BACKGROUND OF THE INVENTION

Meta Dichlorobenzene is colourless liquid, irritant smell. Water insoluble, be dissolved in alcohol, ether. Can carry out chlorination, nitrated, sulfonation, hydrolysis reaction, meet reactive aluminum violent, for organic synthesis. Meta Dichlorobenzene is basic Organic Chemicals, and as one of important source material of agricultural chemicals, medicine and dyestuff intermediate, its market outlook are quite wide. Meta Dichlorobenzene under the condition that has iron(ic) chloride or aluminium mercury, carry out chlorination reaction, mainly generate 1,2,4-trichlorobenzene as an important intermediate used in dyes and pharmaceuticals preparations. Further Meta Dichlorobenzene is also useful for the preparation of m-Chlorophenol and Resorcinol in presences of catalyzer, at 550-850? of hydrolysis.

From U.S. Pat. No. 4,089,909, a process is known for the separation of dichlorobenzene isomers in which, in a dichlorobenzene mixture, m-dichlorobenzene is preferentially chlorinated to 1,2,4-trichlorobenzene and higher poly-chlorobenzenes with elemental chlorine in the liquid phase in the presence of Friedel-Crafts catalysts. The residual o-/p-dichlorobenzene can then be separated from higher chlorinated chlorobenzenes by conventional fractional distillation and crystallization.

In this separation process, it is disadvantageous that not only the m-dichlorobenzene in the mixture is chlorinated, but also, to a significant degree, the valuable o- and p-dichlorobenzene, as the tables in the U.S. Pat. No. 4,089,909 mentioned.

Thus, significant losses of the desired o- and p-dichlorobenzene are unavoidable during the separation and purification of the dichlorobenzene isomers according to the process described in U.S. Pat. No. 4,089,909. The economics of this process are therefore poor.

Halogenated aromatic compounds can be obtained by replacing nitro groups in the nucleus by halogen atoms. This reaction of exchange generally takes place at high temperatures (cf. Houben-Weyl 1, page 880). In industry use is made of this reaction in the manufacture of m-dichlorobenzene (BIOS, volume 986 1, page 151) wherein gaseous chlorine is introduced into molten m-dinitrobenzene. The formed m-dichlorobenzene together with rather considerable amounts of m-chloronitrobenzene, starting product, chlorine, hydrogen chloride and nitrous gases are distilled off from the reaction vessel over a small column. Although this chlorinating denitration starts at about 180?, a reaction temperature of about 220? is chosen so that the formed m-dichlorobenzene having a boiling point of 172? can distil off immediately.

Existing manufacturing technique mainly comprises: benzene chlorination wherein benzene and chlorine is main raw material, chlorination under certain conditions, contain in the product that generates: chlorobenzene (monochlor(in)ate benzene), orthodichlorobenzene, Meta Dichlorobenzene and a small amount of trichlorobenzene, in fact the dichlorobenzene that obtains of benzene chlorination is mainly orthodichlorobenzene and Meta Dichlorobenzene is a by product, generally accounts to about 3% only. The Meta Dichlorobenzene that obtains by this method can't satisfy the growing market requirement.

There is a need at the present time for an improved economical process of preparation m-dichlorobenzene.

SUMMARY OF THE INVENTION

The primary objective of the present invention is to provide continuous process of preparation of m-dichlorobenzene comprising denitration of m-nitrochlorobenzene and chlorinating the same to obtain m-dichlorobenzene without catalyst.

It is the object of the present invention to carry out the chlorinating denitration of m-nitrochlorobenzene to m-dichlorobenzene which is isolated as the main product.

It is the object of the present invention a continuous process for the manufacture of m-dichlorobenzene comprises: chlorinating and denitration of m-nitrochlorobenzene, with continuously introducing chlorine into a reaction kettle equipped with chlorine sparger and assembly set as continuous distillation; chlorine reacts with m-nitrochlorobenzene under atmospheric pressure and high temperature and continuously separating the reaction products, which contain 80% m-dichlorobenzene and 20% m-nitrochlorobenzene; and continuously introducing m-nitrochlorobenzene and maintain 50% volume of reaction mass in reaction kettle.

It is the object of the present invention provide improved process of preparation of m-dichlorobenzene comprising denitration and chlorinating of m-nitrochlorobenzene with continuous addition of m-nitro chlorobenzene at temperature of about 190-250? and formation of m-chloronitrobenzene, wherein the chlorination reaction kettle, m-nitrochlorobenzene is continuous maintain upto 50% volume of reaction mass. It has been observed that at high temperature in the continuous denitration and chlorinating of m-nitrochlorobenzene the final reaction mass contain 80% m-dichlorobenzene and 20% m-nitro chlorobenzene which is collected from the reaction kettle continuous. The collected m-dichlorobenzene and m-nitrochlorobenzene neutralized and taken for vacuum distillation for recovery of m-dichlorobenzene. The distilled by-product is recycled to reaction kettle continuously. The yield of m-dichlorobenzene is quantitatively, purity is 99%. During the process there no catalyst is used. This surprising temperature effect could also be ascertained at reduced pressure.

It has also been found that with continuous introduction of chlorine into the m-nitrochlorobenzene and with continuous separation of the reaction products by distillation under an atmospheric pressure the chlorinating of m-nitrochlorobenzene yields m-chloronitrobenzene as the principal reaction product provided that at the respective temperature.

These and other objects of the invention will be apparent from the following detailed description thereof.

DETAILED DESCRIPTION OF THE INVENTION
In the process according to the invention, provide continuous process of preparation of m-dichlorobenzene comprising denitration of m-nitrochlorobenzene and chlorinating the same to obtain m-dichlorobenzene without catalyst. m-dichlorobenzene as obtained in the denitration and chlorination of m-nitrochlorobenzene, for example, in an continuous process. Such m-dichlorobenzene mixtures contain, depending on the preparative method, about 15 to 20% by weight of m-nitrochlorobenzene and about 80 to 85% by weight of m-dichlorobenzene.

This process according to the invention comprises reaction and separation processes, described chlorination reaction with entering preheating of raw material to 190-250? in the chlorination reaction of nitro-chlorobenzene. The boiling point of product meta dichlorobenzene is 173?, so under chlorination reaction temperature, the product Meta Dichlorobenzene is distilled out of with the by product m- Dichlorobenzene is condensed and collects, and by product overflows and removed.

An embodiment present invention of the present invention continuous process for the manufacture of m-dichlorobenzene comprises:
a) chlorinating of m-nitrochlorobenzene, with continuously introducing chlorine into a reaction kettle consisting of bubble-cap equipped sparger and assembly set with a reflux condenser as continuous distillation;
b) chlorine reacts with m-nitrochlorobenzene under atmospheric pressure and high temperature;
c) continuously distillation and separating the reaction products, which contain 80% m-dichlorobenzene and 20% m-nitrochlorobenzene; and
d) continuously introducing m-nitrochlorobenzene and maintain 50% volume of reaction mass in reaction kettle.
wherein chlorination of chlorobenzene to m-dichlorobenzene with a gaseous chlorinating agent to m-dichlorobenzene when halogenated in the liquid phase which comprises feeding said gaseous halogenating agent to a liquid phase containing said organic compound at a temperature of 0° to 250° C. in the form of a gas jet with bubble-cap equipped sparger at the point said chlorination enters the reaction vessel whereby the formation of bubbles is prevented.

An embodiment present invention of the present invention provide improved process of preparation of m-dichlorobenzene comprising denitration and chlorinating of m-nitrochlorobenzene with continuous addition of m-nitro chlorobenzene at temperature of about 190-250? and formation of m-chloronitrobenzene, wherein the chlorination reaction kettle, m-nitrochlorobenzene is continuous maintain upto 50% volume of reaction mass. It has been observed that at high temperature in the continuous denitration and chlorinating of m-nitrochlorobenzene the final reaction mass contain 80% M-dichlorobenzene and 20% M-nitro chlorobenzene which is collected from the reaction kettle continuous. The collected m-dichlorobenzene and m-nitrochlorobenzene neutralized and taken for vacuum distillation for recovery of m-dichlorobenzene. The distilled by-product is recycled to reaction kettle continuously. The yield of m-dichlorobenzene is quantitatively, purity is 99%. During the process there no catalyst is used. This surprising temperature effect could also be ascertained at reduced pressure.

It has also been found that with continuous introduction of chlorine into the melt of m-nitrochlorobenzene and with continuous separation of the reaction products by distillation under a pressure of from about 250 torr to atmospheric pressure the chlorinating denitration of m-nitrochlorobenzene yields m-dichlorobenzene as the principal reaction product provided that the pressure of the system is inferior to the vapor pressure of m-dichlorobenzene but superior to the vapor pressure of m-nitrochlorobenzene at the respective temperature.

A temperature increase of 10? in the continuous chlorinating denitration corresponds to an increase in the m-dichlorobenzene content in the distillate, but simultaneously a greater amount of unreacted chlorine leaves the reaction mixture. Thus, at a reaction temperature of 280? the distillate contains 80% of m-dichlorobenzene. At atmospheric pressure the process is preferably carried out at a temperature of from 235 to 280?, more preferably 260 to 275?.

It is likewise possible to perform the process at elevated pressure: in this case, however. the apparatus used must be pressure resistant. Moreover, with increasing pressure higher and higher temperatures are required for the distillation of the m-dichlorobenzene. Besides a better degree of utilization of chlorine no other advantage is achieved.

During chlorination the reaction products are best separated over a column in order that a small amount only of starting product distills over. The design of the column is critical. With a low separating effect or when the reaction is carried out without using a column, the proportion of starting product in the distillate will increase.

chlorination reaction kettle consisting of a stirring flask, a bubble-cap equipped sparger and assembly set for chlorine inlet tube reaching down to the bottom and a reflux condenser, an air bath heating, a heatable dropping funnel, a fractionating column with mirror coated inner surface (about theoretical plates) with distillation bridge and reflux condenser and a collecting vessel. chlorination kettle equipped with bubble-cap equipped sparger and assembly set with a reflux condenser for continuous distillation, wherein at an entry of Chlorine is metered into a kettle with velocity of 15 to 25 m/second, through an inlet tube into bubble-cap column equipped sparger and assembly set. The solution of molten m-nitrochlorobenzene is introduced with contuse inlet of Chlorine gas with bubble-cap equipped sparger and assembly set at the temperature about 190? to 250?. When the quantity of chlorine and m-nitrochlorobenzene has been introduced at temperature about 190? to 250? corresponding to the desired degree of conversion of to m-dichlorobenzene, which is removed by distillation and the residue at the bottom product of the reaction remained substantially constant in its composition consisted of 80 to 95 % of m-nitrochlorobenzene and 5 to 10 % of m-dichlorobenzene, wherein m-nitrochlorobenzene is continuously chlorinated with Chlorine gas.

In accordance with process continuous process, the molten m-nitrochlorobenzene and the chlorine are, for example, metered simultaneously in the ratio corresponding to the desired degree of conversion into a single-stage reaction kettle consisting of bubble-cap equipped sparger and assembly set with a reflux condenser. The entry velocity of the chlorine gas is approx. 20 m/second. In the course of this, the reaction mixture is heated to the boil by the heat liberated in the reaction. The heat is removed by evaporative cooling caused by the refluxing solvent. The mixture of products, which flows straight out of the reactor into a distillation column, is freed from the rector by distillation. The crude m-dichlorobenzene is worked up by vacuum distillation into the pure components in a known manner.

The process according to the invention makes it possible to improve appreciably the selectivity of conversion of m-nitrochlorobenzene reactions which take place in the gas/liquid phase. The high degree of selectivity at which the chlorinating m-nitrochlorobenzene reaction takes place also leads to a number of further advantages, such as, say, a higher yield in respect of the m-dichlorobenzene product, less undesirable by-products, which is associated with a reduced incidence of costs in the removal of the by-products, and the possibility of carrying out chlorination reactions at higher temperatures, as a result of which it becomes possible to remove the heat of reaction more simply by means of cooling water instead of cooling by brine, which is expensive. In addition, the chlorination reaction can be carried out in a considerably more concentrated solution without the production of more by-products in comparison with the conventional process. As a result, a markedly better space/time yield can be achieved, which is an important factor in considering the profitability of an industrial plant.

The reaction can be carried out with advantage also under reduced pressure provided that the temperature is sufficiently high for the starting of the reaction and the vacuum is such that the starting product does not yet boil. It is necessary, of course, to adapt temperature and vacuum to each other in such a manner that the formed m-dichlorobenzene can distill off.

A further limitation of the vacuum to be applied. which is of economic nature. is the fact that a reduction in pressure reduces the conversion of chlorine. i.e. increases the portion of unreacted chlorine. In practice, the lower limit of the vacuum to be applied is, therefore, about 250 torr. The range within which the continuous chlorinating denitration is suitably carried out is between 250 torr and atmospheric pressure, however the pressure of the system should be smaller than the vapor pressure of m-dichlorobenzene but higher than the vapour pressure of m-nitrochlorobenzene at the respective temperature.

An embodiment present invention in the process, the atmospheric pressure and higher temperature increase in the continuous chlorinating denitration favours the formation of the m-nitrochlorobenzene. This surprising temperature effect could also be ascertained at reduced pressure.

It has also been found that with continuous introduction of chlorine into the melt of m-dinitrobenzene and with continuous separation of the reaction products by distillation the chlorinating denitration of m-nitrochlorobenzene yields m-chloronitrobenzene as the principal reaction product provided that the pressure of the system is inferior to the vapor pressure of m-chloronitrobenzene but superior to the vapor pressure of m-dinitrobenzene at the respective temperature.

A temperature increase in the continuous chlorinating denitration corresponds to an increase in the m-chloronitrobenzene content in the distillate, but simultaneously a greater amount of unreacted chlorine leaves the reaction mixture. Thus, at a reaction temperature of 250? the distillate contains 80% of m-chloronitrobenzene. At atmospheric pressure the process is preferably carried out at a temperature of from 190 to 250?, more preferably 210 to 220?.

It is likewise possible to perform the process at elevated pressure: in this case, however. the apparatus used must be pressure resistant. Moreover, with increasing pressure higher and higher temperatures are required for the distillation of the m-chloronitrobenzene.

During chlorination the reaction products are best separated in a vacuum distillation and a small amount of distilled by-product is recycled to reaction kettle continuously. The design of the vacuum distillation to reaction kettle. Optionally the separation of the reaction is carried out using a column, the proportion of starting product in the distillate will increase. this influences the ratio of m-chloronitrobenzene to m-dichlorobenzene in vacuum distillation.

An embodiment present invention the reaction can be carried out with advantage also under reduced pressure provided that the temperature is sufficiently high for the starting of the reaction and the vacuum is such that the starting product does not boil. It is necessary, of course, to adapt an optimum temperature and vacuum to each other in such a manner that the formed m-chloronitrobenzene can distill off.

A further limitation of the vacuum to be applied. which is of economic nature. is the fact that a reduction in pressure reduces the conversion of chlorine. i.e. increases the portion of unreacted chlorine. In practice, the lower limit of the vacuum is applied with higher temperature. The range within which the continuous chlorinating denitration is suitably carried out is between 190-250? of temperature and atmospheric pressure, however the pressure of the system should be smaller than the vapor pressure of m-chloronitrobenzene but higher than the vapor pressure of m-dinitrobenzene at the respective temperature.

The reaction temperature should advantageously not exceed 220? as at higher temperature (from about 250-300? onward) the danger exists that M-dichlorobenzene decomposes. Furthermore the degree of conversion of the introduced chlorine will reduce.

EXAMPLE A: Working example reaction in conventional reactor.
The reaction vessel without bubble-cap equipped sparger and assembly set with a reflux condenser, with stirrer was charged up with m-dinitrobenzene and after heating to 230C. 0.40 mole/hour of chlorine (about 15.0 l/min of gaseous chlorine) was introduced and simultaneously 10.0 g/hour of molten m-dinitrobenzene were dropped in. With this amount of addition the volume in the reaction vessel remained constant and 10.5 g of chlorination mixture distilled off per hour. After about 45 minutes the transition temperature of 168 to 170? was reached and the reaction product distilled over continuously. The distillate was washed until neutral to 4 eliminate acid constituents. Over a duration of the experiment of 60 hours the neutral distillate had the following composition:
65.0 % of m-dichlorobenzene and 34.0% of m-chloronitrobenzene and higher chlorinated constituents.

The following examples illustrate the invention.

EXAMPLE 1: Process for preparation of m-dichlorobenzene
A reaction kettle consisting of a stirring flask, a bubble-cap equipped sparger and assembly set for chlorine inlet tube reaching down to the bottom and a reflux condenser, an air bath heating, a heatable dropping funnel, a fractionating column with mirror coated inner surface (about theoretical plates) with distillation bridge and reflux condenser and a collecting vessel, was filled with m-nitrochlorobenzene up to the marking (1000 ml).
After heating to 275?, 0.67 mole /hour of chlorine (about 25.0 l/minute) were introduced and simultaneously 15 kg/h of molten m-nitrochlorobenzene were dropped in. With this rate of addition the volume in the reaction vessel remained constant and 12.5 Kg of M-dichlorobenzene distilled off per hour. The temperature in the bottom was maintained at to 210 +2?. The beginning of the reaction was recognized by the development of nitrous gases which passed, together with the unreacted portions of gaseous chlorine, through the reflux condenser into an absorption device. The collecting distillate (boiling point 205 to 220C) was washed
Yield: 80 % of M-dichlorobenzene;
20 % of M-nitrochlorobenzene

80 % of M-dichlorobenzene and 20 % of M-nitrochlorobenzene of the constituents is distilled by single fractionation the distillate and separated into m-chloronitrobenzene and m-dichlorobenzene having a purity of over 99 %. Wherein m-chloronitrobenzene is reintroduced into reaction kettle consisting of bubble-cap equipped sparger and assembly set with a reflux condenser for chlorination of m-chloronitrobenzene.

The bottom product of the reaction remained substantially constant in its composition and on the average it consisted of
91.5 % of m-nitrochlorobenzene
7.5 % of m-dichlorobenzene and
about 1 of higher chlorinated constituents.

Example 2
Process for preparation of m-dichlorobenzene

Take 500 gm of M-nitro chlorobenzene in chlorination kettle equipped with chlorine sparger and assembly set as continuous distillation of m-dichlorobenzene. Raised the temperature upto 210? start chlorination with continuous addition of m-nitro chlorobenzene. As temp reached to 210? M-dichlorobenzene collection start in receiver flask. It contain 80% M-dichlorobenzene and 20% M-nitro chlorobenzene. Maintain 50% volume of reaction mass in reaction kettle. The collected M-dichlorobenzene and m-nitro chlorobenzene neutralized and taken for vacuum distillation for recovery of m-dichlorobenzene. The distillation bottom product recycles to reaction kettle continuously. The yield of m-dichlorobenzene is quantitatively, purity is 99%. During the process there no catalyst is used.

Example 3 : Process for preparation of m-dichloro benzene
Take 500 gm of M-nitro chlorobenzene in chlorination kettle equipped with chlorine sparger and assembly set as continuous distillation of m-dichlorobenzene. Raised the temperature upto 210? start chlorination with continuous addition of m-nitro chlorobenzene. As temp reached to 210? M-dichlorobenzene collection start in receiver flask. It contain 80% M-dichlorobenzene and 20% M-nitro chlorobenzene. Maintain 50% volume of reaction mass in reaction kettle. The collected M-dichlorobenzene and m-nitro chlorobenzene neutralized and taken for vacuum distillation for recovery of m-dichlorobenzene. The distillation bottom product recycle to reaction kettle continuously. The yield of m-dichlorobenzene is quantitatively, purity is 99%. During the process there no catalyst is used.
, C , Claims:CLAIM
We Claim,
1. A continuous process for the manufacture of m-dichlorobenzene comprises:
e) chlorinating of m-nitrochlorobenzene, with continuously introducing chlorine into a reaction kettle consisting of bubble-cap equipped sparger and assembly set with a reflux condenser as continuous distillation;
f) chlorine reacts with m-nitrochlorobenzene under atmospheric pressure and high temperature;
g) continuously distillation and separating the reaction products, which contain 80% m-dichlorobenzene and 20% m-nitrochlorobenzene; and
h) continuously introducing m-nitrochlorobenzene and maintain 50% volume of reaction mass in reaction kettle.
wherein chlorination of chlorobenzene to m-dichlorobenzene with a gaseous chlorinating agent to m-dichlorobenzene when halogenated in the liquid phase which comprises feeding said gaseous halogenating agent to a liquid phase containing said organic compound at a temperature of 0° to 250° C. in the form of a gas jet with bubble-cap equipped sparger at the point said chlorination enters the reaction vessel whereby the formation of bubbles is prevented.

2. The continuous process of preparation of m-dichlorobenzene as claimed in claim 1 wherein chlorination of m-nitrochlorobenzene to obtain m-dichlorobenzene is without catalyst.

3. The continuous process of preparation of m-dichlorobenzene as claimed in claim 1 wherein process for the manufacture of m-dichlorobenzene comprises: chlorinating of m-nitrochlorobenzene, with continuously introducing chlorine into a reaction kettle equipped with chlorine sparger and assembly set as continuous distillation; chlorine reacts with m-nitrochlorobenzene under atmospheric pressure and high temperature and continuously separating the reaction products, which contain 80% m-dichlorobenzene and 20% m-nitrochlorobenzene; and continuously introducing m-nitrochlorobenzene and maintain 50% volume of reaction mass in reaction kettle.

4. The continuous process of preparation of m-dichlorobenzene as claimed in claim 1 wherein reaction temperature of about 190-250? and formation of m-chloronitrobenzene.

5. The continuous process of preparation of m-dichlorobenzene as claimed in claim 1 wherein m-nitrochlorobenzene is continuous maintain upto 50% volume of reaction mass.

6. The continuous process of preparation of m-dichlorobenzene as claimed in claim 1 wherein distilled by-product m-nitrochlorobenzene is recycled to reaction kettle continuously.

7. The continuous process of preparation of m-dichlorobenzene as claimed in claim 1 wherein continuous introduction of chlorine into the m-nitrochlorobenzene and with continuous separation of the reaction products by distillation under a atmospheric pressure the chlorinating of m-nitrochlorobenzene to m-dichlorobenzene at the temperature of about 190-250?.

8. The continuous process of preparation of m-dichlorobenzene as claimed in claim 1 wherein chlorination reaction kettle consisting of a stirring flask, a bubble-cap equipped sparger and assembly set for chlorine inlet tube reaching down to the bottom and a reflux condenser, an air bath heating, a heatable dropping funnel, a fractionating column with mirror coated inner surface (about theoretical plates) with distillation bridge and reflux condenser and a collecting vessel.

Dated this 21st Day of Dec 2023