WO2023242867A1

WO2023242867A1 - A process for hydrodechlorination of dichlorotoluenes

Info

Publication number: WO2023242867A1
Application number: PCT/IN2023/050559
Authority: WO
Inventors: Prashant POTNIS; Ankit Mittal; Sandip GADGE
Original assignee: Aarti Industries Limited
Priority date: 2022-06-15
Filing date: 2023-06-14
Publication date: 2023-12-21

Abstract

The present invention discloses a process for hydrodechlorination of 2,5-dichlorotoluenes to obtain toluene and monochlorotoluenes. Particularly, the present invention discloses a process for hydrodechlorination of dichlorotoluenes, wherein the selectivity for toluene and 3-chlorotoluene is higher.

Description

A PROCESS FOR HYDRODECHLORINATION OF DICHLOROTOLUENES

FIELD OF THE INVENTION:

The present invention relates to a novel process for hydrodechlorination of dichlorotoluenes to obtain toluene and monochlorotoluenes. More particularly, the present invention relates to hydrodechlorination of dichlorotoluenes to obtain a mixture of toluene, 2-chlorotoluene and 3- chlorotoluene.

BACKGROUND OF THE INVENTION:

Dichlorotoluenes are very important and useful molecules with many industrial applications. Certain dichlorotoluenes are desirable and need to be produced to meet the market demands. During the production of specific desirable dichlorotoluenes for example 2,6-dichlorotoluene and 2,4-dichlorotoluene the comparatively undesirable dichlorotoluenes for example 2,3- dichlorotoluene, 3,4-dichlorotoluene and 2,5-dichlorotoluene are inevitable produced. 2,3- dichlorotoluene, 3,4-dichlorotoluene and 2,5-dichlorotoluene are undesirable for the reason that their market demand is comparatively lesser than the market supply. The undesirable dichlorotoluenes production cannot be avoided as the production of desirable dichlorotoluenes is required. In industry, it is a common practice to incinerate, photo degrade, oxidize, electrolyse or catalytically reduce undesirable or overproduced dichlorotoluenes while producing desired dichlorotoluenes. All of these practices make the operations uneconomical and the industry has to bear the additional cost of carrying out such operations to make the production of desirable dichlorotoluenes sustainable.

Therefore, to avoid additional cost and make the production of desired dichlorotoluenes sustainable there is a need to provide alternatives for better utility of oversupplied dichlorotoluenes. One of the ways to meet this need is to convert oversupplied dichlorotoluenes to monochlorotoluenes or toluene by hydrodechlorination process. Monochlorotoluenes or toluene then can be reused and recycled in pharmaceuticals, chemicals, dyes, rubbers, insecticides, bactericide, paints, coatings, synthetic fragrances, adhesives, inks, and cleaning applications.

Several synthetic methods have been reported in the prior art for hydrodechlorination of dichlorotoluenes. For example, CN108586192 discloses the hydrodechlorination of a mixture of 2,3- dichlorotoluene, 2,4-dichlorotoluene and 2,5-dichlorotoluene using Pd/C catalyst without using a base in a fixed-bed continuous reactor at 200°C temperature and 0.5 atm pressure. The resulting products are toluene, 2- chlorotoluene, 3 -chlorotoluene and 4-chlorotoluene with a conversion rate of 57%, wherein almost 80% of the reaction product is 2- chlorotoluene, the selectivity for toluene is in the range of 8 % to 11 % and the selectivity of 3 -chlorotoluene is in the range of 4 to 8%.

CN108863708 discloses the hydrodechlorination of a mixture of 2,3-dichlorotoluene, 2,4- dichlorotoluene and 2,5-dichlorotoluene using palladium supported on silicon carbide as a catalyst in a fixed-bed continuous reactor at temperature 120-250 °C and pressure 0.01 to 00.10 MPa, wherein the selectivity for toluene is in the range of 38 % to 53 % and the selectivity of 3- chlorotoluene is in the range of 1 to 2%.

The drawback associated with the processes as disclosed in CN’ 192 and CN’708 are that both the processes fail to provide toluene and 3 -chlorotoluene in good yields at the same time, further in these documents when the selectivity for 3 -chlorotoluene is higher the toluene selectivity is lower and vice versa.

The article by Hironao Sajiki et al. titled “Complete and truly catalytic degradation method of PCBs using Pd/C-Et3N system under ambient pressure and temperature” discloses hydrodechlorination of polychlorinated biphenyls using the Pd/C as a catalyst and triethylamine as a reagent in methanol at ambient temperature and pressure with high conversion.

Another article by Hironao Sajiki et al. titled “Mild and general procedure for Pd/C-catalyzed hydrodechlorination of aromatic chlorides” also discloses a mild and one-pot method for the hydrodechlorination of aromatic chlorides using a Pd/C-triethylamine at room temperature.

However, there is no process reported in the literature that discloses or teaches hydrodechlorination of dichlorotoluenes in a batch reactor. Further, none of the processes disclose hydrodechlorination of di chlorotoluenes to obtain 3 -chlorotoluene in relatively higher yields which is also a key starting material in several downstream products but can not be obtained by chlorination reaction of toluene as easily as 2-chlorotoluene and 4-chlorotoluene. Also, none of the prior art processes discloses the hydrodechlorination of dichlorotoluenes wherein 3-chlorotoluene and toluene are simultaneously obtained in higher selectivities and good yields.

Thus, there is a need for the process that addresses at least one unmet need. In order to address the need, the inventors of the present invention envisaged a process for hydrodechlorination of dichlorotoluenes.

The inventors of the present invention also envisaged a process for hydrodechlorination of dichlorotoluenes wherein toluene and 3-chlorotoluene are obtained in comparatively higher yields.

OBJECTIVE OF THE INVENTION:

Some of the objects of the present invention are described herein below:

It is an object of the present invention to ameliorate at least one drawback of the prior art or to provide an alternative path.

Another object of the present invention is to provide a process for hydrodechlorination of dichlorotoluenes which is simple, requires non-expensive assets and is industrially amenable.

Yet another object of the present invention is to provide a process for hydrodechlorination of dichlorotoluenes which employs a batch reactor.

Yet another object of the present invention is to provide a process for hydrodechlorination of dichlorotoluenes in which the selectivity for 3-chlorotoluene and toluene is higher.

Other objects and advantages of the present invention will be more apparent from the following description which is not intended to limit the scope of the present invention.

SUMMARY OF THE INVENTION:

Accordingly, the present invention provides a process for the hydrodechlorination of 2,5- dichlorotoluene comprising reacting 2,5-dichlorotoluene with a hydrogen in the presence of a suitable organic amine reagent, a metal catalyst and a suitable solvent at a suitable temperature and pressure to obtain a mixture of toluene, 2-chlorotoluene and 3-chlorotoluene. In an embodiment, the selectivity for 3 -chlorotoluene is in the range of 7 to 12 % and the selectivity for toluene is in the range of 30 to 55 %.

Non-limiting examples of the organic amine reagent suitable for the reaction include pyridine, Ci to C4 alkyl pyridine, triethylamine, isopropylamine, diisopropylamine, N,N- Diisopropylethylamine, piperidine, morpholine, /V-methylpiperidine, piperazine, pyrrolidine, imidazole, benzimidazole, Ci to C4 alkyl imidazole and mixtures thereof.

The molar ratio of 2,5-dichlorotoluene and the organic amine reagent for the reaction is in the range of 1:1 to 1:3.

Non-limiting examples of solvent suitable for the reaction include methanol, acetonitrile, water, ethanol, isopropyl alcohol or mixtures thereof.

Non-limiting examples of the metal catalyst suitable for the reaction include platinum (Pt) or palladium (Pd) optionally supported on a carrier selected from silicon carbide or carbon.

DETAILED DESCRIPTION OF THE INVENTION:

The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

The terms“comprise(s),”“include(s), ’’“having, ’’“has, ’’“can, ”“contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures.

The singular forms “a,”“an” and“the” include plural references unless the context clearly dictates otherwise. The present disclosure also contemplates other embodiments“comprising, ’’“consisting of and “consisting essentially of,” the embodiments or elements presented herein, whether explicitly set forth or not. The present invention relates to a novel, efficient and industrially advantageous process for the hydrodechlorination of 2,5-dichlorotoluene into a product toluene, 2-chlorotoluene and 3- chlorotoluene, wherein the selectivity for 3 -chlorotoluene is in the range of 7 to 12 % and the selectivity for toluene is in the range of 30 to 55 %.

In an embodiment, the present invention provides a process for the hydrodechlorination of 2,5- dichlorotoluene comprising reacting 2,5-dichlorotoluene with a hydrogen at a suitable temperature and pressure in the presence of a suitable organic amine reagent, a metal catalyst and a suitable solvent to obtain a mixture of toluene, 2-chlorotoluene and 3 -chlorotoluene; wherein the selectivity for 3 -chlorotoluene is in the range of 7 to 12 % and the selectivity for toluene is in the range of 30 to 55 %.

Typically, 2,5-dichlorotoluene is reacted with hydrogen in the presence of an organic amine reagent, a metal catalyst, and a suitable solvent to obtain a mixture of toluene, 2-chlorotoluene and 3 -chlorotoluene.

Non-limiting examples of the metal catalyst suitable for the reaction include platinum (Pt) or palladium (Pd) supported on carbon.

The percentage of metal in the catalyst is in the range of 2.5 % or 5.0 % and the loading of the metal catalyst ranges from 0.01 to 5.0 w/w% with respect to 2,5-dichlorotoluene.

The molar ratio of 2,5-dichlorotoluene and the organic amine reagent for the reaction is in the range of 1:1 to 1:3. The weight ratio of reactant to catalyst is in the range of 1 : 0.001 to 1 : 0.1.

The reaction is carried out at a pressure ranging from 10 Kg/cm² to 40 Kg/cm².

The reaction is carried out at a temperature ranging from 80 °C to 200 °C.

In one embodiment, the reaction is carried out at a temperature ranging from 80 °C to 150 °C.

In an exemplary embodiment, 2,5-dichlorotoluene is mixed with a metal catalyst in the presence of organic amine reagent and a suitable solvent to obtain a mixture. The mixture thus obtained is flushed with an inert gas followed by passing hydrogen gas at a temperature in the range of 80 °C- 200 °C to obtain a mixture of toluene, 2- chlorotoluene and 3 -chlorotoluene.

After completion of the reaction, the resulting mixture is cooled to 20 °C to 35 °C. The metal catalyst is filtered and recovered. The layers are separated. The composition and the selectivity therein for a particular product can be measured by chromatographic techniques such as high pressure liquid chromatography (HPLC) or by gas chromatography (GC).

In one embodiment, toluene is formed in the range of 30 % to 55 % when the total conversion of 2,5-dichlorotoluene is in the range of 40 % to 75 %.

In yet another embodiment, 3-chlorotoluene is formed in the range of 7 % to 12 % when the total conversion of 2,5-dichlorotoluene is 40 % to 75%.

The advantage of the present invention is that it provides improved selectivity towards 3- chlorotoluene and toluene simultaneously.

An advantage of the process of the invention is that the catalyst can easily be separated from the reaction mixture by industrial separation operations and can be reused without a loss of activity.

Further, the advantages of the present invention are effective utilization of side reaction product 2,5-dichlorotoluene and its recycling can make full use of raw materials. Further, the process of the present invention reduces the waste generation which makes the process environmentally benign. New economic value can be realized because of the high m-chlorotoluene selectivity which is an important chemical for the production of various intermediates. Various features and embodiments of the present invention are illustrated in the following representative examples, which are intended to be illustrative and non-limiting.

EXAMPLES

Example 1: Hydrodechlorination of 2,5-dichlorotoluene

To a dry and clean hydrogenation reactor, 50 gm of 2,5-dichlorotoluene, 0.25 gm of 5.0% Pd/C catalyst and triethylamine solution were added. The reactor was flushed with nitrogen and hydrogen gas was then passed to the resulting mixture at a pressure of 10-30 Kg/cm² and the temperature was increased to 150°C-190°C till the consumption of hydrogen stopped. After completion of the reaction, the resulting mixture was cooled to room temperature and the vent valve was opened to discharge the gas. The catalyst was filtered under nitrogen and the layers were then separated to obtain the products, toluene, 2- chlorotoluene and 3 -chlorotoluene.

3 -chlorotoluene selectivity is in the range of 7% to 12%, 2-chlorotoluene selectivity is in the range of 50% to 60% and toluene selectivity is in the range of 30% to 45% when the total conversion of 2,5-dichlorotoluene is in the range of 60%-75%.

Example 2: Hydrodechlorination of 2,5-dichlorotoluene

To a dry and clean hydrogenation reactor, 50 gm of 2,5-dichlorotoluene, 0.025 gm of 5.0% Pd/C catalyst and triethylamine solution were added. The reactor was flushed with nitrogen and hydrogen gas was then passed to the resulting mixture at a pressure of 10-30 Kg/cm² and the temperature was increased to 150°C-190°C till the consumption of hydrogen stopped. After completion of the reaction, the resulting mixture was cooled to room temperature and the vent valve was opened to discharge the gas. The catalyst was filtered under nitrogen and the layers were then separated to obtain the products, toluene, 2- chlorotoluene and 3 -chlorotoluene.

3 -chlorotoluene selectivity is in the range of 7% to 12%, 2-chlorotoluene and toluene selectivity are in the range of 35% to 50% when the total conversion of 2,5-dichlorotoluene is -50%.

Example 3: Hydrodechlorination of 2,5-dichlorotoluene

To a dry and clean hydrogenation reactor, 50 gm of 2,5-dichlorotoluene, 1 gm of 5.0% Pd/C catalyst and triethylamine solution were added. The reactor was flushed with nitrogen and hydrogen gas was then passed to the resulting mixture at a pressure of 10-30 Kg/cm² and the temperature was increased to 80°C-150°C till the consumption of hydrogen stopped. After completion of the reaction, the resulting mixture was cooled to room temperature and the vent valve was opened to discharge the gas. The catalyst was filtered under nitrogen and the layers were then separated to obtain the products, toluene, 2-chlorotoluene and 3 -chlorotoluene.

3 -chlorotoluene selectivity is in the range of 7% to 12%, 2-chlorotoluene selectivity is in the range of 45% to 55%, toluene selectivity are in the range of 45% to 55% when the total conversion of 2,5-dichlorotoluene is -75%.

Example 4: Hydrodechlorination of 2,5-dichlorotoluene

To a dry and clean hydrogenation reactor, 50 gm of 2,5-dichlorotoluene, 0.05 gm of 5.0% Pd/C catalyst and triethylamine solution were added. The reactor was flushed with nitrogen and hydrogen gas was then passed to the resulting mixture at a pressure of 10-30 Kg/cm² and the temperature was increased to 150°C-190°C till the consumption of hydrogen stopped. After completion of the reaction, the resulting mixture was cooled to room temperature and the vent valve was opened to discharge the gas. The catalyst was filtered under nitrogen and the layers were then separated to obtain the products, toluene, 2-chlorotoluene and 3 -chlorotoluene.

3 -chlorotoluene selectivity is in the range of 7% to 12%, 2-chlorotoluene selectivity is in the range of 40% to 50%, toluene selectivity are in the range of 30% to 40% when the total conversion of 2,5-dichlorotoluene is -58%.

Example 5: Hydrodechlorination of 2,5-dichlorotoluene To a dry and clean hydrogenation reactor, 50 gm of 2, 5 -di chlorotoluene, 0.05 gm of 5.0% Pd/C catalyst and diisopropylamine solution were added. The reactor was flushed with nitrogen and hydrogen gas was then passed to the resulting mixture at a pressure of 10-30 Kg/cm² and the temperature was increased to 150°C-190°C till the consumption of hydrogen stopped. After completion of the reaction, the resulting mixture was cooled to room temperature and the vent valve was opened to discharge the gas. The catalyst was filtered under nitrogen and the layers were then separated to obtain the products, toluene, 2- chlorotoluene and 3 -chlorotoluene.

3 -chlorotoluene selectivity is in the range of 7% to 11%, 2-chlorotoluene selectivity is in the range of 35% to 45%, toluene selectivity are in the range of 30% to 35% when the total conversion of 2,5-dichlorotoluene is -53%.

Example 6: Hydrodechlorination of 2,5-dichlorotoluene

To a dry and clean hydrogenation reactor, 50 gm of 2,5-dichlorotoluene, 0.05 gm of 5.0% Pd/C catalyst and N,N-Diisopropylethylamine solution were added. The reactor was flushed with nitrogen and hydrogen gas was then passed to the resulting mixture at a pressure of 10-30 Kg/cm² and the temperature was increased to 150°C-190°C till the consumption of hydrogen stopped. After completion of the reaction, the resulting mixture was cooled to room temperature and the vent valve was opened to discharge the gas. The catalyst was filtered under nitrogen and the layers were then separated to obtain the products, toluene, 2-chlorotoluene and 3 -chlorotoluene.

3 -chlorotoluene selectivity is in the range of 9% to 12%, 2-chlorotoluene selectivity is in the range of 38% to 47%, toluene selectivity are in the range of 30% to 40% when the total conversion of 2,5-dichlorotoluene is -50%.

Example 7: Hydrodechlorination of 2,5-dichlorotoluene

To a dry and clean hydrogenation reactor, 50 gm of 2,5-dichlorotoluene, 0.05 gm of 5.0% Pd/C catalyst and piperidine solution were added. The reactor was flushed with nitrogen and hydrogen gas was then passed to the resulting mixture at a pressure of 10-30 Kg/cm² and the temperature was increased to 150°C-190°C till the consumption of hydrogen stopped. After completion of the reaction, the resulting mixture was cooled to room temperature and the vent valve was opened to discharge the gas. The catalyst was filtered under nitrogen and the layers were then separated to obtain the products, toluene, 2-chlorotoluene and 3-chlorotoluene.

3 -chlorotoluene selectivity is in the range of 7% to 11%, 2-chlorotoluene selectivity is in the range of 33% to 43%, toluene selectivity are in the range of 30% to 36% when the total conversion of 2,5-dichlorotoluene is -54%.

Example 8: Hydrodechlorination of 2,5-dichlorotoluene

To a dry and clean hydrogenation reactor, 50 gm of 2,5-dichlorotoluene, 0.05 gm of 5.0% Pd/C catalyst and morpholine solution were added. The reactor was flushed with nitrogen and hydrogen gas was then passed to the resulting mixture at a pressure of 10-30 Kg/cm² and the temperature was increased to 150°C-190°C till the consumption of hydrogen stopped. After completion of the reaction, the resulting mixture was cooled to room temperature and the vent valve was opened to discharge the gas. The catalyst was filtered under nitrogen and the layers were then separated to obtain the products, toluene, 2-chlorotoluene and 3-chlorotoluene.

3-chlorotoluene selectivity is in the range of 9% to 12%, 2-chlorotoluene selectivity is in the range of 40% to 45%, toluene selectivity are in the range of 32% to 42% when the total conversion of 2,5-dichlorotoluene is -57%.

Comparative Example 1: Hydrodechlorination of 2,5-dichlorotoluene

To a dry and clean hydrogenation reactor, 50 gm of 2,5-dichlorotoluene, 2.0 gm of 5.0% Pd/C catalyst and triethylamine were added. The reactor was flushed with nitrogen and hydrogen gas was then passed to the resulting mixture at a pressure of 10-30 Kg/cm² and the temperature was increased to 150°C-190°C till the consumption of hydrogen stopped. After completion of the reaction, the resulting mixture was cooled to room temperature and the vent valve was opened to discharge the gas. The catalyst was filtered under nitrogen and the layers were then separated to obtain the products, toluene, 2-chlorotoluene and 3-chlorotoluene.

3-chlorotoluene selectivity is in the range of 32%, 2-chlorotoluene selectivity is in the range of 64%, toluene selectivity are in the range of 3% when the total conversion of 2,5-dichlorotoluene is -15%. Comparative Example 2: Hydrodechlorination of 2,5-dichlorotoluene

To a dry and clean hydrogenation reactor, 50 gm of 2,5-dichlorotoluene, 1.0 gm of 5.0% Pd/C catalyst and sodium hydroxide solution were added. The reactor was flushed with nitrogen and hydrogen gas was then passed to the resulting mixture at a pressure of 10-30 Kg/cm² and the temperature was increased to 150°C-190°C till the consumption of hydrogen stopped. After completion of the reaction, the resulting mixture was cooled to room temperature and the vent valve was opened to discharge the gas. The catalyst was filtered under nitrogen and the layers were then separated to obtain the products, toluene, 2- chlorotoluene and 3 -chlorotoluene.

2-chlorotoluene selectivity is in the range of 4% to 6%, toluene selectivity is in the range of 80% to 85% when the total conversion of 2,5-dichlorotoluene is -84%. No selectivity for 3- chlorotoluene was observed.

The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

The description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

While considerable emphasis has been placed herein on the particular features of this invention, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the invention. These and other modifications in the nature of the invention or the preferred embodiments will be apparent to those skilled in the art from the invention herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

Claims

CLAIMS:

1) A process for hydrodechlorination of 2, 5 -dichlorotoluene comprising reacting 2,5- dichlorotoluene with hydrogen in the presence of a suitable organic amine reagent, a metal catalyst and a suitable solvent at a suitable temperature and pressure to obtain a mixture of toluene, 2-chlorotoluene and 3 -chlorotoluene; wherein the selectivity for 3 -chlorotoluene is in the range of 7 to 12 % and the selectivity for toluene is in the range of 30 to 55 %.

2) The process as claimed in claim 1, wherein said suitable temperature is in the range of 80 °C to 200 °C.

3) The process as claimed in claim 1, wherein said suitable pressure is in the range of 10 to 40 kg/cm²

4) The process as claimed in claim 1, wherein said organic amine reagent is selected from the group consisting of pyridine, Ci to C4 alkyl pyridine, triethylamine, isopropylamine, diisopropylamine, N,N-Diisopropylethylamine, piperidine, morpholine N- methylpiperidine, piperazine, pyrrolidine, imidazole, benzimidazole, Ci to C4 alkyl imidazole and mixture thereof.

5) The process as claimed in claim 1, wherein the molar ratio of 2,5-dichlorotoluene and the organic amine reagent is in the range of 1 : 1 to 1:3.

6) The process as claimed in claim 1, wherein said metal catalyst is selected from the group consisting of platinum (Pt) or palladium (Pd) optionally supported on a carrier selected from silicon carbide or carbon.

7) The process as claimed in claim 1, wherein the weight ratio of reactant to catalyst is in the range of 1 : 0.001 to 1 : 0.1.

8) The process as claimed in claim 1, wherein loading of the metal catalyst is in the range of 0.01 to 5.0 w/w% with respect to 2,5-dichlorotoluene.

9) The process as claimed in claim 1, wherein said suitable solvent is selected from the group of methanol, acetone, acetonitrile, water, ethanol, isopropyl alcohol and mixtures thereof.

10) The process as claimed in claim 1, wherein the conversion of di chlorotoluene is in the range of 40 to 75 %.