WO2007017900A2

WO2007017900A2 - Preparation of para dichlorobenzene from benzene or mono chlorobenzene

Info

Publication number: WO2007017900A2
Application number: PCT/IN2006/000185
Authority: WO
Inventors: Sisir Kumar Mandal; Suleman Mohammad Shafi Inamdar
Original assignee: Sisir Kumar Mandal; Suleman Mohammad Shafi Inamdar
Priority date: 2005-05-26
Filing date: 2006-05-25
Publication date: 2007-02-15
Also published as: WO2007017900A3

Abstract

The invention herein relates to a process for the selective preparation of Para dichlorobenzene, comprising reacting benzene or monochlorobenzene with chlorine in presence of Lewis acid catalyst, at least one inorganic modifier and at least one organic modifier in a reactor. In particular, a process provided in which the para dichlorobenzene is obtained with a selectivity >72% by reacting benzene and chlorine under normal pressure in presence of a new catalyst technology in solution phase with ortho dichlorobenzene <25%, Meta dichlorobenzene <0.025 and trichlorobenzene <2%.

Description

Preparation of para dichlorobenzene from benzene or mono chlorobenzene

FIELD OF INVENTION

The invention relates to the selective preparation of para dichlorobenzene from benzene or mono chlorobenzene.

The invention envisages the selective preparation of para dichlorobenzene from benzene or monochlorobenzene by reacting with chlorine in presence of a Lewis acid catalyst or in combination of Lewis acid catalysts and in presence of organic modifier or in combination of organic and inorganic modifier with or without activating the catalyst by hydrochloric acid gas or in combination of chlorine and hydrochloric acid gas.

INTRODUCTION

Dichlorobenzene specially para dichlorobenzene (PDCB) is an important monomer building block as a drug precursor in the pharmaceutical and agrochemical intermediates, insecticides, deodorants, dyestuffs, plastics, polyphenylene sulfide molding resins, moth propellant, germicide. A high purity of the p-dichlorobenzene is important especially for its use as a drug precursor and as a raw material for polyphenylene sulfide. In particular, it should contain the isomeric dichlorobenzenes, o- dichlorobenzene and m-dichlorobenzene, in only very small amounts.

The scope for ortho dichlorobenzene (ODCB) is limited and it is mainly used as a solvent (Low value application) though some value added products of high value for example DCFA and 4-fluoro-3-chloroaniline etc. are produced in recent years.

Due to the low demand of ODCB and higher chlorinated products, there was significant focus on the selective production of para dichlorobenzene starting from benzene or monochlorobenzene by chlorination in presence of catalyst. Additionally, the formation of ODCB and higher chlorinated products are undesirable due to the difficulty in purifying PDCB from the mixture. This process engages the manufacturer to convert large amount of higher chlorinated products to a lower chlorinated product by using an expensive process. As a result the process becomes economically unattractive.

Dichlorobenzenes are typically manufactured by reacting benzene and chlorine in the presence of Lewis acids by nucleophilic substitution reaction' where there is a substitution of hydrogen atoms of the benzene initially gives monochlorobenzene, which can be further chlorinated to give a mixture of the three isomeric dichlorobenzene for example para dichlorobenzene, orthodichlorobenzene and meta dichlorobenzene. Chlorobenzene can also be used as the starting substance for the preparation of dichlorobenzene. See Scheme 1 for the reactions and further chlorination to dichlorobenzenes. Some quantities of trichlorobenzene are also formed in the reaction. (Chlorine ion behaves as an electrophile)

This chlorination is conveniently carried out at ordinary temperature in the presence of a Lewis acid e.g. the chlorides of Al, Fe, Sb, i.e. AICI₃. AIBr₃, SbCI₅, SbBr₅.

Iron is commonly used, being converted to Lewis acid (FeCI3) or other Friedel-Crafts catalysts for halogenations.

The extent of the substitution depends on the amount of halogen used, e.g. chlorobenzene is formed when benzene is treated with chlorine (one molecule) in the presence of Iron:

FeCI3+AICI3 + modifier

C6H6 ^C6H5CI + HCI

CI2

If two molecule of chlorine are used, then a mixture of o- and p- dichlorobenzene is obtained, the latter predominating.

C6H6 +CI2 --^« _* --» C6H4CI2 (orthodichloro) + C6H4CI2 (para dichloro,

Major) Some amount of Meta dichlorobenzene and trichlorobenzene is also formed in the reaction.

Catalyst and the reaction conditions play important role in the selectivity of chlorinated products of benzene. The normal chlorination of benzene in presence of ferric chloride catalysts leads to the formation of PDCB (50- 61%), ODCB (30-36%) and higher chlorinated products (4-13%) under normal pressure of chlorine.

BACKGROUND OF THE INVENTION

A process of making PDCB is known with high selectivity by chlorinating monochlorobenzene in the presence of a solid catalyst system in gas phase [US-5,001,290]. The disadvantage of this process is that monochlorobenzene is used as a feed stock which needs to be prepared separately. The catalyst gets deactivated significantly. The regenerated catalyst showed lower selectivity thereby making the cycles inconsistent.

Zeolites are known [EP-118,851, EP-195514, EP-225723, EP-231133, EP- 273736, and US-4777305] to give PDCB from monochlorobenzene in high selectivity. Zeolites in combination with co-catalysts are also known [EP- 154236, EP-231662, DE- 3720 391, EP-248931] to give similar or better selectivity to PDCB formation. The major issues with the Zeolite are low conversion of the starting material and the cost of the catalyst. Because of the low activity unreacted chlorine is liberated from the reaction, particularly at the later part of the reaction. In addition, Zeolite gets slowly deactivated over a period of time due to carbon deposition. As a result, reactivation of the Zeolite becomes important in order to make it viable. Moreover, Zeolite produces detectable amounts of m- dichlorobenzene as impurity having very close boiling point with PDCB, thereby making the process difficult for separation.

Lewis acids in combination with organic co-catalyst improve the PDCB selectivity beyond 70% [EP1535890, EP126669, EP474074, WO97/43041, EP-126,669, and US-5210343]. The organic co-catalysts are chosen from the group of phenothiazines that are expensive. The reaction requires more quantities of catalyst in order to get significant conversion of benzenes. A significant quantity of unreacted chlorobenzene remains in the product mixture. Driving the reaction further results in the formation of trichlorobenzene as the major by product. Therefore, reaction efficiency is hard to achieve maintaining very low level of trichlorobenzene. Reduction of catalyst level results in the low conversion and high batch cycle time. Moreover, the major issue with phenothiazine series of co- catalyst is the formation of detectable amount of Meta dichlorobenzene, a problematic by-product.

Most chlorination catalysts yield dichlorobenzene with poor selectivity to PDCB which is <70% with normal Friedel craft catalysts. Extensive conversion of monochlorobenzene to dichlorobenzene leads to the formation of higher chlorinated products.- Sulfur and sulfur related inorganic co-catalyst along with Friedel Craft catalyst are not very selective with respect to dichlorobenzene [see comparative example I]. Para dichlorobenzene to dichlorobenzene ration is less than 3.

Therefore, manufacturer of dichlorobenzene requires a process by which PDCB selectivity preferably goes >70% with highly efficient ~ (100%) conversion of benzene to monochlorobenzene to dichlorobenzene with significantly low level of unreacted monochlorobenzene, trichlorobenzene and undetectable amounts of Meta dichlorobenzene.

OBJECT OF THE INVENTION

The object of the invention is to provide a process for the selective preparation of Para dichlorobenzene, comprising reacting benzene or monochlorobenzene with chlorine in presence of Lewis acid catalyst, at least one inorganic modifier and at least one organic modifier in a reactor. Another object of the invention is to provide a selective and viable process and manufacturing technology for dichlorobenzenes from benzene with an efficiency of benzene conversion of 100% and monochlorobenzene conversion >95% with para dichlorobenzene (PDCB) as a major product with significantly less amounts of trichlorobenzene. Another object of this invention is to provide a process in which the PDCB is obtained with a selectivity >72% by reacting benzene and chlorine under normal pressure in presence of a new catalyst technology in solution phase with ODCB <25%, Meta dichlorobenzene <0.015 and trichlorobenzene <2%.

Yet another object of the invention is to provide a process which does not require dehydration of benzene/special purification of chlorine gas.

Still another object of the invention is to provide a catalyst system that tolerates impurities in chlorine and benzene to a greater level than tolerated by the existing catalyst systems.

Another object of this invention is to provide a process in which the PDCB is obtained with a selectivity >74% by reacting benzene and chlorine under normal pressure in presence of a new catalyst in batch reactor with monochlorobenzene conversion efficiency ranging 90-95% with trichlorobenzene <2% and undetectable amounts of Meta dichlorobenzene <0.025%.

SUMMARY OF THE INVENTION

According to this invention, therefore there is provided a process for the selective preparation of Para dichlorobenzene, comprising reacting benzene or monochlorobenzene with chlorine in presence of Lewis acid catalyst, at least one inorganic modifier and at least one organic modifier in a reactor.

Typically, the reaction is carried out at temperature ranging from 5-10O⁰C. Typically, the reaction is carried out at temperature preferably ranging from 50-70⁰C.

Typically, the reaction is completed in the period ranging from 4-36 hrs. Typically, the reaction is completed in the period preferably ranging from 3-7 hrs.

In accordance with one embodiment of the invention, gaseous chlorine at atmospheric pressure is used for chlorination.

Typically, rate of chlorination is ranging from about 1.5 % w/w to 30% w/w of benzene.

Typically, the moisture content of gaseous chlorine ranges from about 250 to 700 ppm.

Typically, the chlorination of benzene is performed in batch or in continuous mode.

Typically, the degree of chlorination preferably ranges from about 1.5 to 2.05.

In accordance with another embodiment of the invention, Lewis acid catalyst is at least one compound selected from a group of compounds consisting of Organometals, halides of Iron, Aluminum, Antimony, Manganese, Zinc, Copper, Tin, Ti, Lanthanides and Actinides.

In accordance with another embodiment of the invention, Organometal is at least one compound selected from a group of compounds consisting of phenoxides, thiophenoxides, sulfonates, borates, phosphonates, Aluminum phenoxides, aluminum thiophenoxides, aluminum sulfonate, aluminum thiosulfonate, aluminum boronate, aluminum phosphonate, Iron acetate, iron phenoxide, iron thio phenoxide, iron boronate, iron thioboronate, iron phosphonate, iron thiophosphonate and Iron amides. In accordance with another embodiment of the invention, halide is at least one compound selected from a group of compounds consisting of chloride, bromide, iodides and fluoride, FeCI₃, AIQ₃, ZnCI₂, CuCI₂, LaCI₃, YbCI₃ and ScCI₃.

Typically, halide is preferably a compound of Ferric chloride (FeCI₃) complex catalyst.

In accordance with another embodiment of the invention, FeCI₃ complex catalyst is a compound prepared by reacting FeCI₃ and the amines of following formulas in a mole ratio of FeCI₃:amine as 1 : (0.1-6).

Formula

Wherein

Rl, = H, Cl, Br, F, NO₂, R', OR'

R2 = H, Cl, Br, F, NO₂, R', OR' R2-R3, can be a part or aromatic or aliphatic ring.

R3, = H, Cl, Br, F, NO₂, R', OR' R6-R7, can be a part of the aliphatic or aromatic ring

R4, = H, Cl, Br, F, NO₂, R', OR'

R5, = H, Cl, Br, F, NO₂, R', OR'

R6, = H, Cl, Br, F, NO₂, R', OR'

R7, = H, Cl, Br, F, NO₂, R', OR'

R8, = H, Cl, Br, F, NO₂, R', OR'

Rl, = H, Cl, Br, F, NO₂, R', OR'

R'= hydrocarbon radical starting from C1-C18. Typically, Lewis acid catalyst is hydrated or dehydrated.

Typically, the mass of Lewis acid catalyst ranges from about 0.01% to 10% w/w of the total mass of the reactants.

Typically, the mass of Lewis acid catalyst preferably ranges from about 0.2 to 0.5% w/w of the total mass of the reactants.

Typically, the reaction was performed in presence of Lewis acid catalyst without activation of catalyst.

In accordance with another embodiment of the invention, the reaction is performed with activation of catalyst in benzene by passing a small amount of chlorine for a period in the range of about 15 min to 30 min. and at temperature in the range of 5°C-50°C.

In accordance with another embodiment of the invention, the organic modifier is at least one compound selected from a group of compounds consisting of compounds of the following structures,

wherein

R'= hydrocarbon radical starting from C1-C18,

wherein

Y = O, S, S-S;

R' = 1°, 2° or 3° hydrocarbon radical,

wherein

X = H, Cl, Br, F, R', OR', NR'2, R' = 1°, 2° or 3° hydrocarbon radical from C1-C18,

Rl = H, Cl, Br, F, NO2, R', OR',

R2-R3, can be a part or aromatic or aliphatic ring,

R2 = H, Cl, Br, F, NO2, R', OR',

R6-R7, can be a part of the aliphatic or aromatic ring,

R3, = H, Cl, Br, F, NO₂, R', OR',

R4 = H, Cl, Br, F, NO2, R', OR',

R5 = H, Cl, Br, F, NO2, R', OR',

R6, = H, Cl, Br, F, NO₂, R', OR',

R7, = H, Cl, Br, F, NO₂, R', OR',

R8, = H, Cl, Br, F, NO₂, R', OR'.

In accordance with another embodiment of the invention, the organic modifier is used without inorganic modifier when Y= S or S-S.

Typically, the mass of the organic modifier is ranges from about 0.01% to 10% w/w of the total mass of the reactants. Typically, the mass of the organic modifier preferably ranges from about 0.2% to 0.5% w/w of the total mass of the reactants.

In accordance with another embodiment of the invention, the inorganic modifier is at least one compound selected from a group of compounds consisting of elemental sulfur, sulfur halides, sulfur oxyhalides, alkyl sulfides of the type dimethyl sulfide, ethyl methyl sulfide, methyl phenyl sulfide, ethyl phenyl sulfide, organo sulfoxides, organo sulfone, aliphatic or aromatic sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, methyl phenyl sulfone, ethylphenylsulfone dialkyl, diaryl sulfoxides, dimethyl sulfoxide, diphenyl sulfoxides, alkyl and aryl sulfoxides like methyl phenyl sulfoxides, ethyl phenyl sulfoxides, S₂CI₂, SCI₂ and SO₂CI₂.

Typically, the mass of the inorganic modifier ranges from about 0.01% to 10% w/w of the total mass of the reactants.

Typically, the mass of the inorganic modifier preferably ranges from about 0.2 to 0.5% w/w of the total mass of the reactants.

In accordance with another embodiment of the invention, therefore there is provided a process for the selective preparation of Para dichlorobenzene, comprising reacting benzene or monochlorobenzene with chlorine in presence of a Lewis acid catalyst and a modifier in a reactor.

In accordance with another embodiment of the invention, wherein the modifier is at least one compound selected from a group of compounds consisting of an organic modifier and an inorganic modifier.

Typically, the modifier is preferably an organic modifier.

In accordance with another embodiment of the invention, the Lewis acid catalyst is at least one compound selected from a group of compounds consisting of halides and sulfides of iron, aluminum, zinc, Aηtimony, titanium, copper, tin, Manganese, lanthanides and actinides. Typically, halide is at least one compound selected from a group of compounds consisting of chlorides, bromides and iodides.

Typically, wherein halide is preferably a chloride.

Typically, the Lewis acid catalyst is a mixture of compounds of which at least one compound is FeCI₃.

Typically, the ratio of FeCI₃ and other Lewis acid catalyst preferably ranges from about 1: 0.15 to 1 : 1.25.

Typically, Lewis acid catalyst is hydrated or dehydrated and preferably Lewis acid catalyst is dehydrated.

Typically, the mass of the Lewis acid catalyst ranges from about 0.01- 10% w/w of the total mass of the reactants.

Typically, the mass of the Lewis acid catalyst preferably ranges from about 0.01% to 0.35% w/w of the total mass of the reactants.

In accordance with another embodiment of the invention, the Lewis acid catalyst is activated by at least one compound selected from a group of compounds consisting of chlorine gas and HCI gas.

Typically, the water content of HCL gas is in the range of about 1 to 100 ppm.

Typically, the water content of Chlorine gas is in the range of about 1 to 700 ppm.

Typically, the water content of Chlorine gas is preferably in the range of about 1 to 500 ppm.

Typically, activation of the catalyst mixture by HCI gas is done at temperature in the range of about 30 to 80⁰C. Typically, activation of the catalyst mixture by HCI gas is done for a period in the range of about 4 to 12 hrs.

Typically, the catalyst mixture is activated in situ by reaction generated HCI gas or by supplying HCI gas from external sources.

In accordance with another embodiment of the invention, reactor is a series of two column reactors in line; the catalyst mixture is not activated by external supply of HCL gas.

Typically, the water content of benzene or monochlorobenzene preferably ranges from about 5 to 650ppm of the total mass of the reactants.

Typically, moisture content of chlorine preferably ranges from about 5 to 650ppm of the total mass of the reactants.

Typically, the reaction is performed in batch mode or continuous mode.

Typically, the reactor is at least one reactor selected from a group of reactors consisting of batch reactor, column, tubular reactor and multi- reactors connected in series.

Typically, the reactor is preferably column reactor.

Typically, the reactor is fabricated from at least one material selected from a group of materials consisting of MS steel, SS steel, glass lined, PTFE lined and quartz tube.

Typically, reactor is preferably a series of two column reactors in line.

In accordance with another embodiment of the invention, the organic modifier is at least one compound selected from a group of compounds consisting of quaternary alkyl ammonium halide, quaternary aryl ammonium halide and quaternary alkyl phosphonium halide, quaternary aryl phosphonium halide compounds, organic sulfides, organic disulfides, organic sulfones, organic sulfoxides, organic bisulfides, organic nitrates, organic sulfates, tetra alkyl -onium radicals, tetra aryl -onium radicals and Amines.

Typically, the organic Sulfides is at least one compound selected from a group of compounds consisting of dialkyl Sulfides, aryl sulfides, dimethyl sulfide, diphenyl sulfide and methyl phenyl sulfides.

Typically, the organic sulfone is at least one compound selected from a group of compounds consisting of aryl sulfones, alkyl sulfones, dimethyl sulfone, diphenyl sulfone and methyl phenyl sulfone.

Typically, the amines is at least one compound selected from a group of compounds consisting of aromatic amines, tertiary aromatic amines, dimethylphenyl amine, methyl ethyl phenyl amine and diethyl phenyl amines.

Typically, the quaternary ammonium halide is at least one compound selected from a group of compounds consisting of tetra butyl ammonium chloride and tetra butyl ammonium bromide.

Typically, the mass of the organic modifier preferably ranges from about 0.1% to 0.3% w/w of the total mass of the reactants.

Typically, reaction temperature is in the range of 5 to 100⁰C.

Typically, reaction temperature is preferably in the range of 30 to 7O⁰C.

Typically, the degree of chlorination preferably ranges from about 1.5 to 2.05.

Typically, rate of chlorination is ranging from 1.5 % w/w to 60% w/w of benzene per hour. DETAILED DESCRIPTION OF THE INVENTION

This invention relates to two processes of producing dichlorobenzene comprising reacting chlorine or a mixture of chlorine and hydrochloric acid with benzene with or without drying, at a temperature between 5-100⁰C in the presence of a mixture of catalysts and a modifier or a combination of modifiers, to convert the benzene to mono chlorobenzene and finally to dichlorobenzenes, the significantly major product being the Para dichlorobenzene in the resulting chlorination products with low levels of trichlorobenzene and meta dichlorobenzene.

Process 1:

This invention provides a process of producing dichlorobenzene comprising reacting chlorine or a mixture of chlorine and hydrochloric acid with benzene with or without drying, at a temperature between 5-100⁰C in the presence of a Lewis acid catalyst and a modifier or a combination of modifiers, to convert the benzene to mono chlorobenzene and finally to dichlorobenzenes, the significantly major product being the Para dichlorobenzene >72% in the resulting chlorination products with low levels of trichlorobenzene (<2%) and meta dichlorobenzene ( <0.025%).

A feature of the invention is to use a catalyst system which can be extracted with water for recovery. The products of chlorobenzene and benzene can be handled carefully without VOC issues.

The invention envisages the following reaction.

Sulfur + organic modifier

Benzene + FeCI3 + modifiers + CI2 - -> Para + orthodichlorobenzene.

The invention is further illustrated in example 1.

The process comprises reacting benzene and chlorine in presence of one Lewis acid catalyst (FeCI3 alone), inorganic modifier and an organic modifier at temperature 5-7O⁰C provided by exothermic heat of the reaction to give dichlorobenzene predominantly Para dichlorobenzene with very low level of trichlorobenzene and undetectable amounts of meta dichlorobenzene with efficiency of nearly 100% and a chlorination degree of 1.95 to 2.05.

Efficiency means the % conversion of monochlorobenzene to dichlorobenzenes.

A typical and technologically important specification that obtained is as follows.

Monochlorobenzene <5%

Dichlorobenzenes >95%

PDCB >72%

ODCB <25%

Trichlorobenzene < 2%

Meta dichlorobenzene <0.01

Monochlorobenzene conversion efficiency is >95%.

No unreacted chlorine liberated from the reactor till the end of the reaction.

The reaction is carried out in the invention at temperature ranging from 5- 100⁰C under normal pressure of chlorine. The preferred temperature is 50-70⁰C.

The batch time of the reaction may vary from 4-36 hrs depending on the removal of exothermic heat. The reaction can be performed in less than 7 hrs.

The chlorine addition rate can be chosen from 1.5% w/w of benzene to 60% w/w depending on the exothermic condition. Normally chlorine addition rate kept moderate to reduce evaporation of benzene from the reaction mixture at temperature <50oC. The chlorine addition rate is increased when at least 30% of monochlorobenzene is formed. Temperature is then increased >60oC The reaction can be performed in batch mode or in continuous mode using batch or column or tubular reactor. The preferred reactor is column reactor.

The material of the reactor can be of different types for example MS steel, SS steel, glass lined, PTFE lined or quartz tube.

The Lewis acid catalyst can be chosen from the group consisting of halides of Iron, Aluminum, Antimony, Zinc, Copper, Tin, Ti, Lanthanides and Actinides or a mixture thereof. The preferred catalyst is chosen from one group. The metal organic compounds of the Lewis acid metal can also be used. The level of the catalyst may vary from 0.01% to 10%, preferably, 0.2 to 0.5% by weight of the starting material.

The purity of Lewis acid catalyst is >98%. This can be hydrated or dehydrated.

Halides of Lewis acid metal can be chosen from chloride, bromide, iodides and fluoride for example, FeCI₃, AIQ₃, ZnCI₂, CuCI₂, LaCl₃, YbCI₃, ScCI₃ etc. or a mixture thereof. The preferred catalyst is FeCI3 and halide is chloride.

Organometals of phenoxides, thiophenoxides, sulfonates, borates, phosphonates are also useful for example, Aluminum phenoxides, aluminum thiophenoxides, aluminum sulfonate, aluminum thiosulfonate, aluminum boronate, aluminum phosphonate and at least one such organic group attached with the metal. The catalyst of the iron series can be chosen from Iron acetate, iron phenoxide, iron thio phenoxide, iron boronate, iron thioboronate, iron phosphonate, iron thiophosphonate, Iron amides are of aromatic nature. At least one organic group is attached with the metal.

Iron complex for example amine or amide complex can be chosen from aromatic secondary or tertiary amines or amine derivatives for example iron diphenylamide, iron alkyl phenylamide in which case at least one substituent is aromatic. The benzene ring of the amine group can be substituted or unsubstituted, for example,

Figure 1.

Rl, = H, Cl, Br, F, NO₂, R', OR'

R4, = H, Cl, Br, F, NO₂, R', OR'

R5, = H, Cl, Br, F, NO₂, R', OR'

R6, = H, Cl, Br, F, NO₂, R', OR'

R7, = H, Cl, Br, F, NO₂, R', OR'

R8, = H, Cl, Br, F, NO₂, R', OR'

Rl, = H, Cl, Br, F, NO₂, R', OR'

R'= hydrocarbon radical starting from C1-C18.

Organometal compounds or complexes of Friedel Craft catalysts can be used as such or can be prepared in situ by the addition of Friedel Craft catalyst and amines. The catalyst system could be a single complex or a mixture of complexes with varying stoichiometry of amine ligands. The amount of organic amines/amides forming the complex may vary from 1 equivalent to 6 mole equivalent of metal.

Fe+++ + amine/or amide = [Iron-amine/ or amide] ⁿ⁺ complex where n= 3 or less.

Organic modifier often called co-catalysts for Friedel craft catalysts can be chosen from the different group of amine derivatives of the following structural formula,

X = H, Cl, Br, F, R', OR', NR"2; R' = 1°, 2° or 3° hydrocarbon radical from C1-C18.

Rl = H, Cl, Br, F, NO2, R', OR' R2-R3, can be a part or aromatic or aliphatic ring.

R2 = H, Cl, Br, F, NO2, R', OR' R6-R7, can be a part of the aliphatic or aromatic ring

R3, = H, Cl, Br, F, NO₂, R', OR'

R4 = H, Cl, Br, F, NO2, R', OR'

R5 = H, Cl, Br, F, NO2, R', OR'

R6, = H, Cl, Br, F, NO₂, R', OR'

R7, = H, Cl, Br, F, NO₂, R', OR'

R8, = H, Cl, Br, F, NO₂, R', OR'

The level of the modifier may vary from 0.01% to 10% and the preferable concentration of the modifier is 0.2%-0.5% w/w. The inorganic modifier can be chosen from the group of sulfur or sulfur halides or sulfur oxyhalides. The preferred modifier is sulfur or sulfur halides. The level of inorganic modifier may vary from 0.01 to 10% by weight of the starting material. Preferably is 0.2 to 0.5%.

The inorganic modifier is used along with organic modifier or their complex with Friedel craft catalyst.

Inorganic modifier for example sulfur is chosen from elementary sulfur, S₂CI₂, SCI₂, S₂Br₂ and SOCI₂, SO₂CI₂ or a mixture thereof. The purity of sulfur compounds is >98%%.

Inorganic and organic modifiers can be chosen singly or a mixture there from.

Organosulfur compounds for example alkyl sulfides of the type dimethyl sulfide, ethyl methyl sulfide, mixed sulfides of the type methyl phenyl sulfide, ethyl phenyl sulfide also are used as co-catalyst. The level of the sulfur compound may vary from 0.1-10%. Preferably is in the range of 0.2%-0.5%.

Organodiphenyl compounds of the following formula are also used as organic modifier.

Y = O, S, S-S and

Rl = H, Cl, Br, F, NO₂, R', OR' R2-R3, can be a part or aromatic or aliphatic ring. R2, = H, Cl, Br, F, NO₂, R', OR' R6-R7, can be a part of the aliphatic or aromatic ring

R3, = H, Cl, Br, F, NO₂, R', OR'

R4, = H, Cl, Br, F, NO₂, R', OR'

R5, = H, Cl, Br, F, NO₂, R', OR'

R6, = H, Cl, Br, F, NO₂, R', OR'

R7, = H, Cl, Br, F, NO₂, R', OR'

R8, = H, Cl, Br, F, NO₂, R', OR'

R' = 1°, 2° or 3° hydrocarbon radical.

The level of the organic modifier is chosen from 0.1%- 10% by weight of the starting material, preferably, 0.2-0.5%.

In addition, organo sulfoxides and sulfone can be included in the sulfur compound series which can be added sole or in addition with above organic modifiers. The level may vary from 0.0-5% w/w.

Organo sulfoxide can be chosen from the group consisting of dialkyl and diaryl sulfoxides of the type dimethyl sulfoxide, diphenyl sulfoxides or mixed alkyl and aryl sulfoxides like methyl phenyl sulfoxides, ethyl phenyl sulfoxides and a mixture thereof.

Organic sulfone can be chosen from aliphatic or aromatic sulfone. Aliphatic sulfone can be chosen from dimethyl sulfone, diethyl sulfone. Among the mixed sulfones, methyl ethyl sulfone, methyl phenyl sulfone, ethylphenylsulfone can be included in the series. The level may vary from 0-5%, preferable, 0.01-0.2% w/w.

The catalyst can be optionally activated by a small amount of chlorine for 15-30 minutes starting at 5-30oC during which time the entire catalyst mixture becomes a homogeneous phase. The reaction can be done in one reactor system or two reactor systems in series with the same or different starting composition both in batch or continuous mode.

The moisture content of the chlorine content or the chlorine can be from 0-700 ppm and moisture content in starter benzene or monochlorobenzene can be 0-650ppm.

The para dichlorobenzene and ortho dichlorobenzene ratio can vary from 2.9-3.25.

The process in accordance with this invention gives significantly low percent of trichlorobenzene with no detectable amounts of Meta dichlorobenzene. The trichlorobenzene level is <2% and often <0.6%.

The dichlorobenzene content may vary from 94-99% after removal of trace amount of monochlorobenzene with a monochlorobenzene conversion efficiency of >95%.

The invention of above type is further illustrated by examples. A comparative example has been produced as reference.

Process 2:

The invention provides a process of producing dichlorobenzene comprising reacting chlorine or a mixture of chlorine and hydrochloric acid with benzene with or without drying, at a temperature between 5-100⁰C in the presence of a mixture of activated Lewis acid catalysts and modifier or a combination of modifiers, to convert the benzene to mono chlorobenzene and finally to dichlorobenzene, the significantly major product being the para dichlorobenzene in the resulting chlorination products containing meta dichlorobenzene <0.025% and trichlorobenzene <2.5%.

A feature of the invention is to use a catalyst system which can be extracted with water for recovery. The products of chlorobenzene and benzene can be handled carefully without VOC issues. The invention envisage the following reaction.

Benzene + Lewis acid catalysts + modifier + Cl₂ Activated by HCI gas. -- > para + orthodichlorobenzene

The above reaction mixture contains small amount of monochlorobenzene, trichlorobenzene and nearly undetectable amount of Meta dichlorobenzene.

The starter for chlorination in accordance with this invention can be selected from the group consisting of benzene or monochlorobenzene or a mixture thereof.

The reaction can be carried out in batch reactor or column reactor. The operation can be done either in batch mode or in continuous mode irrespective of the material of construction of the reactor. The preferred reactor is mild steel column reactor. The reaction can be carried out in one reactor or multi-reactors connected in series.

The reaction is carried out at a temperature in the range 5-lOOoC, preferably 30-70oC.

The ratio of FeCI3 and other Lewis acid catalyst may vary from 1 : 0.15 to 1: 1.25.

The Lewis acid catalyst were obtained from commercial sources where the purity of the Lewis acid was >98%.

The Lewis acid catalyst can be hydrated or dehydrated. The preferred catalyst is dehydrated.

The chlorination was aimed to obtain dichlorobenzene in which case the chlorination degree was in the range of 1.5 to 2.05. The rate of chlorine addition can vary from 1.5% of benzene to 60% depending on the exothermic condition. Initial rate is low due to the loss of benzene evaporation. The rate of chlorine addition is significantly increased when 30% of monochlorobenzene is formed.

The temperature of the reaction can be set from 5-8O⁰C, preferably 30- 70oC.

The temperature of the initial reaction is maintained <50oC due to the loss of benzene and the temperature is increased when >30% of monochlorobenzene is formed.

The catalyst activation can be done in situ by reaction generated HCI gas or by supplying HCI gas from external sources. External activation is not required when two connecting reactors in series are chosen.

The catalyst can be activated in situ or can be used from an activated master match. The activation is preferred in second reactor in a series of two reactors.

The catalyst composition of the two reactors may be of same type and same concentration or of different composition.

The temperature of the two reactors can be kept same or different but not increased beyond 8O⁰C. At higher temperature there is a chance of formation of higher chlorinated products, especially, when catalyst is not fully activated.

Catalyst activation in this art is very important, failing which the reaction becomes less selective to para dichlorobenzene.

The Lewis acid catalyst can be selected from the group consisting of halides or sulfides of iron, aluminum, zinc, Antimony, titanium, copper, tin, Manganese, lanthanides, actinides or a mixture thereof. The preferred metals in the invention were chosen from the group consisting of Iron and Aluminum halides. The preferable Lewis acids are Fe and Al.

The metal halides can be chosen from metal chlorides, bromides or iodides or a mixture thereof. The preferred halides are chlorides.

The Lewis acids is a mixture of Lewis acids in which at least one component is ferric chloride. Another component can be chosen from the group consisting of AICI₃, ZnCI₂, TiCI₂ or a mixture thereof as an example, preferably AICI3. The catalyst mixture forms an intractable solid complex dispersed in the reaction medium.

The concentration of the Lewis acid catalysts may vary from 0.01% to 10.0% by weight of the aromatics. The preferred concentration of the catalysts is 0.01% to 0.35% depending on the type of reactors.

The Lewis acid catalyst can be added as dispersion in starter or as solid. The metal Lewis acid can be least hydrated or dehydrated.

The catalyst activation is done by dry HCI gas (water <100 ppm) and at temperature ranging from 30-80⁰C. The amount of HCI required may vary from one mole equivalent of starting material to two mole equivalent of starting material. The HCI can be passed for 4 hr to 12 hours for catalyst activation. A mixture of chlorine and HCI can also be used for activation. The water present in benzene can vary 0-700ppm. Preferably below 500 ppm.

The moisture content in the chlorine can vary from 0-700 ppm. Preferably <500 ppm.

The reaction is controlled by the addition of a modifier preferably by organic modifier. The modifier controls the kinetics of dichlorobenzene formation from monochlorobenzene. The modifier can be added in the beginning of the reaction or in the middle of the reaction. Excess addition of the modifier may kill the reaction. So the formation of trichlorobenzene can be controlled by adjusting the concentration of the modifier.

The type of modifier can be selected from a group consisting of both inorganic and organic compounds. The preferred modifiers are chosen from organic compounds.

The inorganic modifier can be chosen from the group consisting of metal compounds such as ZnCI₃-, SnCI₃-, and SbCI5- etc.

The concentration of the modifier can vary from 0.01% to 5% by weight of starting material. The preferred concentration is 0.15-0.25%. The modifier can be added as solids or liquids or a solution/dispersion in a solvent. The solvent for adding modifier can be inert or benzene or monochlorobenzene.

The organic modifiers play major role in the selectivity of the para dichlorobenzene formation. The preferred modifier is organic modifier. The modifier forms a complex with the metal ion preferably on iron during the reaction. The crowding of iron metal by the ligand provides structural direction. As a result there is preferential formation of para dichlorobenzene since the ortho position is more crowded.

The organic modifiers can be chosen from the group consisting of quaternary ammonium salt, quaternary phosphonium salts or a mixed onium salts with mixed substituents. The salts can be chosen from halides. Preferably chloride or bromide. Salts can be of other types for example Sulfide, bisulfides, nitrates, sulfates etc. Quaternary ammonium or phosphonium may be composed of alkyl, aryl or with mixed substituents. Preferable are tetra alkyl or aryl -onium radicals.

The level of the modifier can vary from 0.01%-10%. The preferred level of modifier is 0.02% to 0.5%. The modifier can be added in the beginning of the reaction or in the middle of the reaction.

Other modifiers for example organic sulfides, disulfides, sulfones sulfoxides can also be used in small quantities.

Sulfides can be chosen from dialkyl or aryl sulfides for example dimethyl sulfide, diphenyl sulfide, methyl phenyl sulfides. Preferably aryl sulfide.

Like wise, sulfones can be of aryl or alkyl type for example dimethyl sulfone, diphenyl sulfone, methyl phenyl sulfone. Preferably diphenyl sulfone.

Amine can also be used as organic modifying agent. Among the amines aromatic amines particularly tertiary aromatic amines for example dimethylphenyl amine, methyl ethyl phenyl amine, diethyl phenyl amines are preferred. Amines can also be used along with quaternary compounds.

Thus it is apparent that there has been provided, in accordance with the invention, a product and process that fully satisfy the objects, aims, and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.

The invention is further illustrated in the following examples.

EXAMPLES Example 1:

To a 250 ml glass reactor equipped with a stirrer, a condenser, a thermocouple and a chlorine spurger was added 152 gm of benzene (1.94 mols), anhydrous FeCI3 0.076 gm (0.00466mols) and sulfur 0.020 gm( 0.00062 mols) followed by chlorine ( 34.5 gm/hr) purging at room temperature of 30oC. As the temperature of the reaction mixture reached 40-50oC the cooling was started to maintain the temperature. After 80% conversion of benzene to monochlorobenzene the cooling was stopped and the temperature was allowed to rise to 60-70⁰C and held constant till the reaction completed. (Total batch time 6-8 hrs). The GC of the product mixture shows the following composition in two different time intervals.

PDCB/ODCB ratio 2.61

Example 2. Preparation of dichlorobenzene by the use of FeCI3, sulfur and organic modifier.

To a 250 ml glass reactor equipped with a stirrer, a condenser, a thermocouple and a chlorine spurger was added 152 gm of benzene (1.94 mols), anhydrous FeCI3 0.152 gm ( 0.00093), sulfur 0.089 gm (0.0028 mols) and diphenylamine 0.47 gm (0.0028 mol). Followed by this, chlorine gas (34.5 gm/hr) purging was started at 30oC. As the temperature of the reaction mixture reached 40-50⁰C the cooling was started to maintain the temperature. After complete conversion of benzene to monochlorobenzene the cooling was stopped and the temperature was allowed to rise to 60-7O⁰C and held constant till the reaction completed (total batch time 8 hrs). The GC of the product mixture shows the following composition. Monochlorobenzene 3.49%

Para dichlorobenzene 72.42%

Ortho dichlorobenzene 23.48% 1, 2, 4-trichlorobenzene 0.59% Meta dichlorobenzene ND P/O ratio 3.09

Example 3:

To a 250 ml glass reactor equipped with stirrer, a condenser, a thermocouple and a chlorination spurger was added 300 gm of benzene (3.85mols), anhydrous FeCI3 0.150 gm (0.00046), sulfur 0.177 gm (0.0028 mols) and diphenyl amine 0.93 gm (0.0028 mols). Followed by this, chlorine gas (65 gm/hr) purging was started at room temperature. As the temperature of the reaction mixture reaches 45-50oC the cooling was stated to maintain the temperature. After complete conversion of benzene to monochlorobenzene the cooling was stopped and the temperature was allowed to rise to 60-70oC and held constant till the reaction complete (total batch time 8 hrs). The GC of the product mixture shows the following composition.

Monochlorobenzene <2%

Para dichlorobenzene 74.31%

Ortho dichlorobenzene 23.22% Meta dichlorobenzene ND Tri-chlorobenzene 0.46%

P/O ratio 3.2

Example 4:

To a 1 lit. glass reactor equipped with stirrer, a condenser, a thermocouple and a chlorination Spurger was added 600 gm of benzene (7.69 mols), anhydrous FeCI3 0.300 gm (0.00046 mols), sulfur 0.44 gm (0.0035 mols) and diphenyl amine 2.23 gm (0.0035 mols). Followed by this, chlorine gas (110 gm/hr) purging was started at room temperature. As the temperature of the reaction mixture reaches 45-50oC the cooling was stated to maintain the temperature. After complete conversion of benzene to monochlorobenzene the cooling was stopped and the temperature was allowed to rise to 60-70oC and held constant till the reaction complete (total batch time 10 hrs). The GC of the product mixture shows the following composition.

Monochlorobenzene 2.43%

Para dichlorobenzene 73.26%

Ortho dichlorobenzene 23.83%

Tri-chlorobenzene 0.45% Meta dichlorobenzene ND P/O ratio 3.13

Example 5:

To a 250 ml glass reactor equipped with stirrer, a condenser, a thermocouple and a chlorination Spurger was added 152 gm of benzene (1.94mols), anhydrous FeCI3 0.076 gm (0.00046), sulfur 0.089 gm (0.0028 mols) and diphenyl amine 0.47 gm (0.0028 mols). Followed by this, chlorine gas (20 gm/hr) purging was started at room temperature. As the temperature of the reaction mixture reaches 40-50oC the cooling was stated to maintain the temperature. After complete conversion of benzene to monochlorobenzene the cooling was stopped and the temperature was allowed to rise to 55-70oC and held constant till the reaction complete (total batch time 12 hrs). The GC of the product mixture shows the following composition.

Monochlorobenzene 3.16%

Para dichlorobenzene 72.75%

Ortho dichlorobenzene 23.35% Tri-chlorobenzene 0.72%

Meta dichlorobenzene ND P/O ratio 3.12 Example 6. . FeCI₃ and AICI₃ system...

Impurities in Feed: The moisture level in benzene is 250-660 ppm and moisture level in chlorine in the range 400-660 ppm.

a) Preparation of a master batch of catalyst.

To a 250 ml glass reactor equipped with a overhead stirrer, a condenser and a gas spurger was added 8.1 gm of anhydrous FeCl3 (0.05 mols), AICI3 8.52 gm (0.062 mols) and benzene 70 ml. To the mixture, 140 gm dry HCI was purged with stirring for 12-15 hrs at 30-40oC and used the mixture as a master batch for the chlorination of subsequent batches.

b) Preparation of dichlorobenzene by using the catalyst from the master batch.

To a 250 ml glass reactor equipped with stirrer, a condenser, a thermocouple and a chlorine spurger was added 152 gm of benzene (1.94 mols) and 2.7 gm of catalyst from master batch with stirring at room temperature (25oC). The resulting mixture was purged with chlorine at the rate of ~ 25 gm/hr for a period of 11 hrs. As the reaction proceeds the temperature of the reaction mixture slowly increases due to exothermic nature of the reaction. The temperature of the reaction mixture was set to 45-55oC by controlling the chlorine flow and the reaction was monitored by GC with time till the entire benzene converts to monochlorobenzene. Then 0.22 gm (0.00068 mol) tetrabutyl ammonium bromide was added and monochlorobenzene was finally converted to dichlorobenzenes at 60- 65oC. The resulting reaction mixture was allowed to cool to room temperature and the said mixture was washed with sufficient amount of water in order to remove residual HCI, chlorine and catalysts. The GC result shows the following composition. Monochlorobenzene 9.96%

Para dichlorobenzene 68.59%

Ortho dichlorobenzene 19.95%

Trichlorobenzene 1.5%

P/O ratio 3.4

Example 7:

To a 250 ml glass reactor equipped with stirrer, a condenser, a thermocouple and a chlorination spurger was added 152 gm of benzene (1.94mols) with stirring at room temperature (25oC) and 0.9gm of the catalyst was added from master batch. The resulting mixture was purged with chlorination at the rate of ~ 9 gm/hr for a period of 28 hrs. As the reaction proceeds the temperature of the reaction mixture slowly increases due to exothermic nature of the reaction. The temperature of the reaction mixture was set to 50-55 by controlling the chlorine flow and reaction was monitored by GC with time till the entire benzene converts to monochlorobenzene. Then 0.11 gm (0.00034 mol) Tetrabutyl ammonium bromide was added and monochlorobenzene was finally converted to dichlorobenzene at 60-65oC. The resulting reaction was allowed to cool to room temperature and the said mixture was washed with sufficient amount of water in order to remove residual HCI, chlorine and catalysts. The GC result shows following composition.

Monochlorobenzene 11.34%

Para dichlorobenzene 66.23%

Ortho dichlorobenzene 20.85%

Tri-chlorobenzene 1.61%

P/O ratio 3.17

Example 8:

To a 500 ml glass reactor equipped with stirrer, a condenser, a thermocouple and a chlorination spurger was added 250 gm of benzene (3.2mols) with stirring at room temperature (25oC) and 2.5gm of the catalyst was added from master batch. The resulting mixture was purged with chlorination at the rate of ~ 23.3 gm/hr for a period of 13 hrs. As the reaction proceeds the temperature of the reaction mixture slowly increases due to exothermic nature of the reaction. The temperature of the reaction mixture was set to 40-50 by controlling the chlorine flow and reaction was monitored by GC with time till the entire benzene converts to monochlorobenzene. Then 0.2 gm (0.0006 mol) Tetrabutyl ammonium bromide was added and monochlorobenzene was finally converted to dichlorobenzene at 65-70oC. The resulting reaction was allowed to cool to room temperature and the said mixture was washed with sufficient amount of water in order to remove residual HCI, chlorine and catalysts. The GC result shows following composition.

Monochlorobenzene 08.95%

Para dichlorobenzene 69.09%

Ortho dichlorobenzene 20.63%

Tri-chlorobenzene 1.33%

P/O ratio 3.34

Example 9. In situ preparation of the catalyst and the preparation of dichlorobenzene.

To a 250 ml glass reactor equipped with a stirrer, a condenser and a gas spurger was added 0.076 gm of anhydrous FeCI3 ( 0.00046 mols), AICI3 0.079 gm ( 0.00058 mol) and benzene 152 gm. To the mixture, 140 gm dry HCI and 70 gm of chlorine was purged together with stirring for 99 hrs at 40-50⁰C. Hydrochloric acid stream was stopped and tetrabutylammonium bromide 0.22 gm (0.000068 mols) was added and chlorine purging was continued for four hours at the rate of 25 gm/hr at a temperature off 60-65⁰C The reaction was stopped and a sample of the product mixture was analyzed. The following composition was obtained from GC analysis.

Monochlorobenzene 52.16%

Para dichlorobenzene 38.46%

Ortho dichlorobenzene 9.37%

P/O ratio 4.1

Claims

Claims:

1. A process for the selective preparation of Para dichlorobenzene, comprising reacting benzene or monochlorobenzene with chlorine in presence of a Lewis acid catalyst, at least one inorganic modifier and at least one organic modifier in a reactor.

2. A process for the selective preparation of Para dichlorobenzene as claimed in claim 1, wherein the reaction is carried out at a temperature ranging from 5 ]to 100⁰C and preferably between 50 to 7O⁰C.

3. A process for the selective preparation of Para dichlorobenzene as claimed in claim 2, wherein the reaction is completed in the period ranging from 3 to 36 hrs and preferably between 3 to 7 hrs.

4. A process for the selective preparation of Para dichlorobenzene as claimed in claim 1, wherein gaseous chlorine at atmospheric pressure is used for chlorination.

5. A process for the selective preparation of Para dichlorobenzene as claimed in claim 4, wherein rate of chlorination ranges from about 1.5 % w/w to about 60% w/w of benzene.

6. A process for the selective preparation of Para dichlorobenzene as claimed in claim 5, wherein the moisture content of the gaseous chlorine ranges from about 100 ppm to about 700 ppm.

7. A process for the selective preparation of Para dichlorobenzene as claimed in claim 5, wherein the chlorination of benzene is performed in batch mode.

8. A process for the selective preparation of Para dichlorobenzene as claimed in claim 5, wherein the chlorination of benzene is performed in continuous mode.

9. A process for the selective preparation of Para dichlorobenzene as claimed in claim 5, wherein the degree of chlorination preferably ranges from about 1.5 to about 2.05.

10. A process for the selective preparation of Para dichlorobenzene as claimed in claim 1, wherein the Lewis acid catalyst is at least one compound selected from a group of compounds consisting of Organometals, halides of Iron, halides of Aluminum, halides of Antimony, halides of Manganese, halides of Zinc, halides of Copper, halides of Tin, halides of Titanium, halides of Lanthanides and halides of Actinides.

11. A process for the selective preparation of Para dichlorobenzene as claimed in claim 10, wherein Lewis acid catalyst is at least one Organometal compound selected from a group of compounds consisting of phenoxides, thiophenoxides, sulfonates, borates, phosphonates, Aluminum phenoxides, aluminum thiophenoxides, aluminum sulfonate, aluminum thiosulfonate, aluminum boronate, aluminum phosphonate, Iron acetate, iron phenoxide, iron thio phenoxide, iron boronate, iron thioboronate, iron phosphonate, iron thiophosphonate and Iron amides.

12. A process for the selective preparation of Para dichlorobenzene as claimed in claim 11, wherein Lewis acid catalyst is at least one halide selected from a group of compounds consisting of chlorides, bromides, iodides, fluorides, FeCI₃, AIC₃, ZnCI₂, CuCI₂, LaCI₃, YbCI₃ and ScCI₃.

13. A process for the selective preparation of Para dichlorobenzene as claimed in claim 12, wherein the halide is a Ferric chloride (FeCI₃) complex catalyst.

14. A process for the selective preparation of Para dichlorobenzene as claimed in claim 13, wherein the FeCI₃ complex catalyst is a compound prepared by reacting FeCI₃ with an amine of the following formula in a mole ratio of FeCI₃:amine as 1 : (0.1-6). formula

wherein

Rl, = H, Cl, Br, F, NO₂, R', OR' R2 = H, Cl, Br, F, NO₂, R', OR' R2-R3, can be a part or aromatic or aliphatic ring. R3 = H, Cl, Br, F, NO₂, R', OR' R6-R7, can be a part of the aliphatic or aromatic ring R4 = H, Cl, Br, F, NO₂, R', OR' R5 = H, Cl, Br, F, NO₂, R', OR' R6 = H, Cl, Br, F, NO₂, R', OR' R7 = H, Cl, Br, F, NO₂, R', OR' R8 = H, Cl, Br, F, NO₂, R', OR'.

15. A process for the selective preparation of Para dichlorobenzene as claimed in claim 13, wherein the FeCI₃ complex catalyst is a compound prepared by reacting FeCI₃ with an amine of following formula in a mole ratio of FeCI₃:amine as 1 : (0.1-6).

formula

wherein

Rl, = H, Cl, Br, F, NO₂, R', OR' R2 = H, Cl, Br, F, NO₂, R', OR' R2-R3, can be a part or aromatic or aliphatic ring. R3 = H, Cl, Br, F, NO₂, R', OR' R6-R7, can be a part of the aliphatic or aromatic ring

R4 = H, Cl, Br, F, NO₂, R', OR'

R5 = H, Cl, Br, F, NO₂, R', OR'

R6 = H, Cl, Br, F, NO₂, R', OR'

R7 = H, Cl, Br, F, NO₂, R', OR'

R8 = H, Cl, Br, F, NO₂, R', OR'

R'= hydrocarbon radical starting from C1-C18.

16. A process for the selective preparation of Para dichlorobenzene as claimed in claim 10, wherein the Lewis acid catalyst is hydrated.

17. A process for the selective preparation of Para dichlorobenzene as claimed in claim 10, wherein the Lewis acid catalyst is anhydrous.

18. A process for the selective preparation of Para dichlorobenzene as claimed in claim 10, wherein the mass of Lewis acid catalyst to the total mass of the reactants ranges from about 0.01% to about 10% w/w and preferably ranges from about 0.2 to about 0.5% w/w.

19. A process for the selective preparation of Para dichlorobenzene as claimed in claim 1, wherein the reaction is performed in the presence of Lewis acid catalyst without activation of catalyst.

20. A process for the selective preparation of Para dichlorobenzene as claimed in claim 1, wherein the reaction is performed with activation of catalyst in benzene by passing a small amount of chlorine for a period in the range of about 15 min to 30 min. and at temperature in the range of 5°C-50°C.

21. A process for the selective preparation of Para dichlorobenzene as claimed in claim 1, wherein the organic modifier is at least one compound selected from a group of compounds consisting of compounds of the following structure,

wherein

Rl = H, Cl, Br, F, NO2, R', OR',

R2-R3, can be a part or aromatic or aliphatic ring,

R2 = H, Cl, Br, F, NO2, R', OR',

R6-R7, can be a part of the aliphatic or aromatic ring,

R3 = H, Cl, Br, F, NO₂, R', OR',

R4 = H, Cl, Br, F, NO2, R', OR',

R5 = H, Cl, Br, F, NO2, R', OR',

R6 = H, Cl, Br, F, NO₂, R', OR',

R7 = H, Cl, Br, F, NO₂, R', OR',

R8 = H, Cl, Br, F, NO₂, R', OR',

R'= hydrocarbon radical starting from C1-C18.

22. A process for the selective preparation of Para dichlorobenzene as claimed in claim 1, wherein the organic modifier is at least one compound selected from a group of compounds consisting of compounds of the following structure,

wherein

R'= hydrocarbon radical starting from C1-C18,

Rl = H, Cl, Br, F, NO2, R', OR',

R2-R3, can be a part or aromatic or aliphatic ring,

R2 = H, Cl, Br, F, N02, R', OR',

R3 = H, Cl, Br, F, NO₂, R', OR',

R4 = H, Cl, Br, F, N02, R', OR',

R5 = H, Cl, Br, F, N02, R', OR'.

3. A process for the selective preparation of Para dichlorobeπzene as claimed in claim 1, wherein the organic modifier is at least one compound selected from a group of compounds consisting of compounds of the following structure,

wherein Y = O, S, S-S;

R' = 1°, 2° or 3° hydrocarbon radical, Rl = H, Cl, Br, F, NO2, R', OR', R2-R3, can be a part or aromatic or aliphatic ring, R2 = H, Cl, Br, F, NO2, R', OR', R6-R7, can be a part of the aliphatic or aromatic ring,

R3, = H, Cl, Br, F, NO₂, R', OR', R4 = H, Cl, Br, F, NO2, R', OR', R5 = H, Cl, Br, F, NO2, R', OR⁷, R6, = H, Cl, Br, F, NO₂, R', OR', R7, = H, Cl, Br, F, NO₂, R', OR', R8, = H, Cl, Br, F, NO₂, R', OR'.

24. A process for the selective preparation of Para dichlorobenzene as claimed in claim 1, wherein the organic modifier is at least one compound selected from a group of compounds consisting of compounds of the following structure,

wherein

X = H, Cl, Br, F, R', OR', NR'₂, R' = 1°, 2° or 3° hydrocarbon radical from C1-C18, Rl = H, Cl, Br, F, NO2, R', OR', R2-R3, can be a part or aromatic or aliphatic ring, R2 = H, Cl, Br, F, NO2, R', OR',

R6-R7, can be a part of the aliphatic or aromatic ring, R3, = H, Cl, Br, F, NO₂, R', OR', R4 = H, Cl, Br, F, NO2, R', OR', R5 = H, Cl, Br, F, NO2, R', OR', R6, = H, Cl, Br, F, NO₂, R', OR', R7, = H, Cl, Br, F, NO₂, R', OR', R8, = H, Cl, Br, F, NO₂, R', OR'.

25. A process for the selective preparation of Para dichlorobenzene as claimed in claim 23, wherein the organic modifier is used without inorganic modifier when Y= S or S-S.

26. A process for the selective preparation of Para dichlorobenzene as claimed in claim 21, wherein the mass of the organic modifier to the total mass of the reactants ranges from about 0.01% to about 10% w/w and preferably ranges from about 0.2% to about 0.5% w/w.

27. A process for the selective preparation of Para dichlorobenzene as claimed in claim 1, wherein the inorganic modifier is at least one compound selected from a group of compounds consisting of elemental sulfur, sulfur halides, sulfur oxyhalides, alkyl sulfides, dimethyl sulfide, ethyl methyl sulfide, methyl phenyl sulfide, ethyl phenyl sulfide, organo sulfoxides, organo sulfones, aliphatic sulfones, aromatic sulfones, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, methyl phenyl sulfone, ethylphenylsulfone dialkyl, diaryl sulfoxides, dimethyl sulfoxide, diphenyl sulfoxides, alkyl sulfoxides, aryl sulfoxides, methyl phenyl sulfoxides, ethyl phenyl sulfoxides, S₂CI₂, SCI₂ and SO₂CI₂.

28. A process for the selective preparation of Para dichlorobenzene as claimed in claim 27, wherein the mass of the inorganic modifier to the total mass of the reactants ranges from about 0.01% to about 10% w/w and preferably ranges from about 0.2 to about 0.5% w/w.

29. A process for the selective preparation of Para dichlorobenzene, comprising reacting benzene or monochlorobenzene with chlorine in presence of a Lewis acid catalyst and a modifier in a reactor.

30. A process for the selective preparation of Para dichlorobenzene as claimed in claim 29, wherein the Lewis acid catalyst is at least one compound selected from a group of compounds consisting of halides and sulfides of iron, aluminum, zinc, Antimony, titanium, copper, tin, Manganese, lanthanides and actinides.

31. A process for the selective preparation of Para dichlorobenzene as claimed in claim 30, wherein halide is at least one compound selected from a group of compounds consisting of chlorides, bromides and iodides.

32. A process for the selective preparation of Para dichlorobenzene as claimed in claim 31, wherein halide is preferably chloride.

33. A process for the selective preparation of Para dichlorobenzene as claimed in claim 29, wherein the Lewis acid catalyst is a mixture of compounds of which at least one compound is FeCI₃.

34. A process for the selective preparation of Para dichlorobenzene as claimed in claim 33, wherein the ratio of FeCI₃ and other Lewis acid catalyst preferably ranges from about 1: 0.15 to about 1: 1.25.

35. A process for the selective preparation of Para dichlorobenzene as claimed in claim 33, wherein Lewis acid catalyst is hydrated.

36. A process for the selective preparation of Para dichlorobenzene as claimed in claim 33, wherein Lewis acid catalyst is dehydrated.

37. A process for the selective preparation of Para dichlorobenzene as claimed in claim 33, wherein Lewis acid catalyst preferably is dehydrated.

38. A process for the selective preparation of Para dichlorobenzene as claimed in claim 33, wherein the mass of the Lewis acid catalyst to the total mass of the reactants ranges from about 0.01 to about 10% w/w and preferably ranges from about 0.01% to about 0.35% w/w.

39. A process for the selective preparation of Para dichlorobenzene as claimed in claim 33, wherein the Lewis acid catalyst is activated by at least one compound selected from a group of compounds consisting of chlorine gas and HCI gas.

40. A process for the selective preparation of Para dichlorobenzene as claimed in claim 39, wherein the water content of HCL gas is in the range of about 1 to about 100 ppm.

41. A process for the selective preparation of Para dichlorobenzene as claimed in claim 39, wherein the water content of Chlorine gas is in the range of about 1 to about 700 ppm and preferably in the range of about 1 to about 500 ppm.

42. A process for the selective preparation of Para dichlorobenzene as claimed in claim 39, wherein activation of the catalyst mixture by HCI gas is done at temperature in the range of about 30 to 80⁰C.

43. A process for the selective preparation of Para dichlorobenzene as claimed in claim 42, wherein activation of the catalyst mixture by HCI gas is done for a period in the range of about 4 to 12 hrs.

44. A process for the selective preparation of Para dichlorobenzene as claimed in claim 43, wherein the catalyst mixture is activated in situ by reaction generated HCI gas.

45. A process for the selective preparation of Para dichlorobenzene as claimed in claim 43, wherein the catalyst mixture is activated by supplying HCI gas from external sources.

46. A process for the selective preparation of Para dichlorobenzene as claimed in claim 29, wherein reactor is a series of two column reactors in line, the catalyst mixture is not activated by external supply of HCL gas.

47. A process for the selective preparation of Para dichlorobenzene as claimed in claim 1 and 29, wherein the water content of benzene or monochlorobenzene ranges from about 5 to 650ppm of the total mass of the reactants.

48. A process for the selective preparation of Para dichlorobenzene as claimed in claim 1 and 29, wherein the moisture content of chlorine ranges from about 5 to 650ppm of the total mass of the reactants.

49. A process for the selective preparation of Para dichlorobenzene as claimed in claim 1 and 29, wherein the reaction is performed in batch mode or continuous mode.

50. A process for the selective preparation of Para dichlorobenzene as claimed in claim 1 and 29, wherein the reactor is at least one reactor selected from a group of reactors consisting of batch reactor, column, tubular reactor and multi-reactors connected in series.

51. A process for the selective preparation of Para dichlorobenzene as claimed in claim 50, wherein the reactor is preferably a column reactor.

52. A process for the selective preparation of Para dichlorobenzene as claimed in claim 51, wherein the reactor is fabricated from at least one material selected from a group of materials consisting of MS steel, SS steel, glass lined, PTFE lined and quartz tube.

53. A process for the selective preparation of Para dichlorobenzene as claimed in claim 52, wherein reactor is preferably a series of two column reactors in line.

54. A process for the selective preparation of Para dichlorobenzene as claimed in claim 29, wherein the modifier is at least one compound selected from a group of compounds consisting of an organic modifier and an inorganic modifier.

55. A process for the selective preparation of Para dichlorobenzene as claimed in claim 55, wherein the inorganic modifier is at least one compound selected from a group of compounds consisting of ZnCI₃-, SnCI₃- and SbCI₅-.

56. A process for the selective preparation of Para dichlorobenzene as claimed in claim 55, wherein the mass of the inorganic- modifier to the total mass of the reactants ranges from about 0.01% to about 5% w/w and preferably ranges from about .15 to about 0.25% w/w.

57. A process for the selective preparation of Para dichlorobenzene as claimed in claim 54, wherein the modifier is preferably an organic modifier.

58. A process for the selective preparation of Para dichlorobenzene as claimed in claim 54, wherein the organic modifier is at least one compound selected from a group of compounds consisting of quaternary alkyl ammonium halide, quaternary aryl ammonium halide and quaternary alkyl phosphonium halide, quaternary aryl phosphonium halide compounds, organic sulfides, organic disulfides, organic sulfones, organic sulfoxides, organic bisulfides, organic nitrates, organic sulfates, tetra alkyl -onium radicals, tetra aryl - onium radicals and Amines.

59. A process for the selective preparation of Para dichlorobenzene as claimed in claim 58, wherein the organic Sulfides is at least one compound selected from a group of compounds consisting of dialkyl Sulfides, aryl sulfides, dimethyl sulfide, diphenyl sulfide and methyl phenyl sulfides.

60. A process for the selective preparation of Para dichlorobenzene as claimed in claim 58, wherein the organic sulfones is at least one compound selected from a group of compounds consisting of aryl sulfones, alkyl sulfones, dimethyl sulfone, diphenyl sulfone and methyl phenyl sulfone.

61. A process for the selective preparation of Para dichlorobenzene as claimed in claim 58, wherein the amines is at least one compound selected from a group of compounds consisting of aromatic amines, tertiary aromatic amines, dimethylphenyl amine, methyl ethyl phenyl amine and diethyl phenyl amines.

62. A process for the selective preparation of Para dichlorobenzene as claimed in claim 58, wherein the quaternary ammonium halide is at least one compound selected from a group of compounds consisting of tetra butyl ammonium chloride and tetra butyl ammonium bromide.

63. A process for the selective preparation of Para dichlorobenzene as claimed in claim 58, wherein the mass of the organic modifier to the total mass of the reactants ranges from about 0.1% to about 0.3% w/w. ,64. A process for the selective preparation of Para dichlorobenzene as claimed in claim 29, wherein reaction temperature is in the range of about 5 to about 100⁰C and preferably in the range of about 30 to about 70⁰C.

65. A process for the selective preparation of Para dichlorobenzene as claimed in claim 29, wherein the degree of chlorination preferably ranges from about 1.5 to about 1.95.

66. A process for the selective preparation of Para dichlorobenzene as claimed in claim 29, wherein rate of chlorination is ranging from about 1.5 % w/w to about 30% w/w of benzene.

67. A process for the selective preparation of Para dichlorobenzene substantially as herein described and illustrated with reference to the examples.