DESC:FORM – 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
(See section 10 and rule 13)

AN INTEGRATED PROCESS FOR CARBOXYLATION AND OXIDATION OF ALKYL SUBSTITUTED AROMATIC HYDROCARBONS

RELIANCE INDUSTRIES LIMITED
an Indian Company
of 3rd Floor, Maker Chamber-IV, 222,
Nariman Point, Mumbai - 400 021,
Maharashtra, India

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD:
The present disclosure relates to an integrated process for carboxylation and oxidation of aromatic compounds.
BACKGROUND:
Aromatic compounds such as phthalic acid and terephthalic acid are prepared by oxidation of ortho-xylene and para-xylene respectively.
Alternatively, phthalic acid or terephthalic acid is prepared by carboxylating toluene to obtain 2-methyl benzoic acid or 4-methyl benzoic acid followed by oxidation of the methyl group. Carboxylation of aromatic compounds such as toluene can be carried out using reactions such as Grignard carboxylation and Friedel-Crafts carboxylation.
US Patent 3138626 suggests carboxylation of toluene using aluminium chloride and carbon dioxide.
US7271286 suggests a method in which Lewis acid and CO2 are activated by incubation to produce aromatic carboxylic acids.
WO2001016072 suggests a method for producing aromatic acids and diacids by reacting aromatic hydrocarbons with carbonate containing salts such as K2CO3, Rb2CO3, Cs2CO3, and Na2CO3.
An article titled “Carboxylation of aromatic compound in a supercritical carbon dioxide medium” authored by Shlyakhtin et al., suggests the carboxylation of aromatic compounds using carbon dioxide in a supercritical form in the presence of Lewis acids such as AlCl3, FeCl3, ZrCl4 and ZnCl2.
The oxidation of alkyl group present in aromatic mono-carboxylic acid compounds generated by using some of the above suggested processes is carried out using oxidizing agents to generate aromatic dicarboxylic acids.
Therefore, for the preparation of aromatic dicarboxylic acids from aromatic hydrocarbons, a person skilled in the art has to separately employ two processes namely carboxylation and oxidation. Effluent generated in these two processes contains different catalysts and reagents which are later added to the effluent stream leading to environmental pollution.
Further, the final product prepared by these processes is more likely to contain impurities generated due to incomplete conversion of the intermediates and therefore requires further purification which increases the production cost.
Thus, there exists a need for a simple and efficient process to carry out carboxylation and oxidation of aromatic compounds in a single step with maximum conversion of all intermediate species into the desired product.
OBJECTS:
Some of the objects of the present disclosure are described herein below:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
It is another object of the present disclosure to provide an integrated process for carboxylation and oxidation of aromatic compounds in a continuous step.
It is yet another object of the present disclosure to provide an integrated process for the oxidation and carboxylation of aromatic compounds which is simple, eco-friendly and cost-efficient.
It is yet another object of the present disclosure to provide an integrated process for the preparation of aromatic di-carboxylic acids with maximum purity and with little contamination.
It is a further object of the present disclosure to provide a reagent for the integrated process of carboxylation and oxidation of substituted aromatic hydrocarbons.
It is still another object of the present disclosure to provide an integrated process for the preparation of terephthalic acid from toluene.
Other objects and advantages of the present disclosure will be more apparent from the following description which is not intended to limit the scope of the present disclosure.
DEFINITION:
The term “continuous step” in the context of the present disclosure means a single step comprising two sub-steps namely carboxylation and oxidation reactions taking place one after the other, respectively in a single reaction vessel.
Subcritical form of CO2 is defined as pressurised CO2 having the properties of both liquid as well as gas.
Toluic acid includes o-toluic acid, m-toluic acid and p-toluic acid.
Xylylic acid includes the isomeric products resulting from the carboxylation of xylenes. Such products include but are not limited to o-xylylic acid, m-xylylic acid and p-xylylic acid.
Benzene tricarboxylic acid includes but is not limited to 1,2,3-Benzenetricarboxylic acid; 1,2,4-Benzenetricarboxylic acid; 1,3,4-Benzenetricarboxylic acid; and 1,3,5-Benzenetricarboxylic acid.
SUMMARY:
The present disclosure relates to a process for carboxylating and oxidizing an aromatic compound substituted with at least one alkyl group in a continuous step. The catalyst used for the carboxylation reaction is converted during the carboxylation reaction into a reagent that is capable of in-situ oxidizing the alkyl group of the aromatic compound.
DESCRIPTION:
In accordance with one aspect of the present disclosure there is provided a process for carboxylating and oxidizing an aromatic compound in a continuous step. In the prior art, carboxylation reaction of an aromatic hydrocarbon to which at least one alkyl group is attached and oxidation reaction of the alkyl group attached to the aromatic hydrocarbon are carried out separately to obtain desired polyacids. The final product obtained by these conventional processes is often subjected to further purification processes to remove intermediate species trapped during different reactions.
However, in the process of the present disclosure the carboxylation reaction of aromatic ring with catalyst in-situ provides a reagent which oxidizes the alkyl group attached to the aromatic ring. Thus, both the reactions occur in a single reaction vessel almost simultaneously in one continuous step. Therefore, the process is termed as an integrated process.
In the process of the present invention carboxylation is carried out using carbon dioxide in the presence of a typical catalyst which during or after the carboxylation reaction is converted to a reagent or catalyst that is capable of inducing in-situ oxidation of the alkyl group attached to a carboxylated hydrocarbon obtained after the carboxylation reaction.
For illustration purpose, the carboxylation reaction and the oxidation reaction taking place in a continuous step is represented schematically herein below:

In the above reaction, nitric acid formed as a result of carboxylation reaction, in-situ initiates the oxidation of the methyl group of the p- toluic acid to produce terephthalic acid.
The process of the present invention is
- cost-effective as the two different reactions are carried out in a continuous step almost simultaneously and in a single pot , and
- eco-friendly as the effluent is reduced by at least 50 % as an optimum conversion of the aromatic compound into aromatic dicarboxylic acid is achieved by exhausting all the intermediate species and the catalyst.
The process of the present invention is simple and the product is obtained in an acceptable high yield with minimum impurities of possible intermediate species.
The carboxylation reaction is carried out using at least one carboxylating agent selected from the group consisting of carbon dioxide, organic carbonate such as diethyl or methyl carbonate, orthoformate, Cyanide(CN-).
Particularly, the carboxylation reaction is carried out by employing carbon dioxide in any form selected from the group consisting of gaseous, subcritical, solid and liquid. However, carbon dioxide in a subcritical form is preferably used for carboxylating at least one alkyl group substituted aromatic hydrocarbon. Further, the carboxylating reaction may be carried out using any suitable liquid medium capable of facilitating the reaction. Such liquid medium includes but is not limited to straight chain or branched chain alkanes, cycloalkanes, halogenated alkanes and mixtures thereof.
Care is needed to be taken to restrict the moisture content of the liquid medium used for the purpose of the present disclosure to be in the range of 1 to 100 ppm as a higher amount of moisture is likely to adversely affect the activity of the catalyst being used.
The catalyst useful for the purpose of the present disclosure is represented by a

Formula I;
(AxBy)
Formula I
‘A’ in the Formula I is a cation of a metal selected from group including but not limited to aluminium (Al), Iron (Fe), Galium (Ga), Antimony (Sb), Molybdenum (Mo) and Copper(Cu).
‘B’ in the Formula I is an anion selected from the group which includes but is not limited to sulphate (SO42-), nitrate(NO3-), chromate(CrO42-), dichromate (Cr2O72-), perchlorate(ClO4-), periodate(IO4-), perbromate(BrO4-), persulphate (S2O82-) and the like.
x and y are integers ranging from 1 to 2, indicating the number of cations and anions, respectively.
Particularly, aluminium nitrate (Al(NO3)3) is used as a catalyst for carrying out an integrated process of the present disclosure.
The cation part of the compound is typically, characterized as a Lewis acid or strong Lewis acid or super Lewis acid or any form of acidic or electron deficient species that is able to elevate the activity of CO2 and the site of carboxylation reaction.
The anion part of the compound is typically characterized by an electron-withdrawing character so that it can enhance Lewis acid character of the cation part and can also act as an oxidizing agent.
The anion part of the compound is typically an acid liberating reagent represented by a Formula II;
HxBy
Formula II
H in Formula II is hydrogen.
‘B’ in Formula II is an anion selected from the group the group consisting of sulphate (SO42-), nitrate (NO3-), chromate (CrO42-), dichromate (Cr2O72-), perchlorate (ClO4-), periodate (IO4-), perbromate (BrO4-) and persulphate (S2O82-).
x and y are integers ranging from 1 to 2.
It is observed that though any molar concentration of the catalyst with respect to the reactant may be used, for cost and reaction efficiency reasons the molar concentration of the catalyst in the range of 5 to 10 w/w% is used.
The oxidizing agent formed during carboxylation reaction of an aromatic ring is capable of carrying out oxidation reaction of the alkyl group attached to the carboxylated aromatic product. The said oxidising agent includes but is not limited to sulphuric acid, nitric acid, chromic acid, per-acetic acid and hypochlorous acid.
The carboxylation reaction and the oxidation reaction are carried out at temperatures ranging from 40oC to 100 oC; and at a pressure ranging from 500 to 900 psi.
For the reasons of adverse effect on the activity of the catalyst used in the process of the present disclosure, the process particularly, carboxylation reaction is carried out at moisture free conditions. A moisture free atmosphere can be maintained by employing inert gases.
The alkyl group in the aromatic compound to which at least one alkyl group is attached or alkyl substituted aromatic compound is C1 to C5 alkyl group. Particularly, the aromatic compound to which at least one alkyl group is attached is selected from the group consisting of toluene, ortho xylene, meta xylene, para xylene and C2-alkyl benzenes. Further, the carboxylated products obtained as a result of carboxylation reaction of these reactants is at least one compound selected from the group consisting of toluic acid, xylylic acid and mono carboxy aromatic ketone.
Still further, the oxidized products obtained as a result of oxidation reactions of intermediates acids is at least one compound selected from the group consisting of phthalic acid, terephthalic acid and benzene tricarboxylic acid.
In accordance with one of the exemplary embodiments of the present disclosure, there is provided an integrated process for carboxylation-oxidation of toluene in order to obtain terephthalic acid.
The invention of the present disclosure will now be explained with the help of the following non-limiting examples.
Comparative example 1:
10g of benzene was added to a high pressure reactor containing 2 g of anhydrous aluminium chloride. The reactor was pressurized at 700 psi by passing CO2 and heated at 100 °C. The reaction was allowed to continue for 4 h under stirring. At the end of the reaction, CO2 was released and the mass was extracted by ethyl acetate. The presence of benzoic acid was confirmed by FTIR peak at 1680 cm-1, including other characterizations as mentioned in Ind, Eng Chem Res, 2009, 48, 1059.
Comparative example 2:
This example was carried out in the same manner as that in comparative example 1, except that toluene was used instead of benzene to obtain toluic acid as a product.
Present invention example 3:
This example was carried out in the same manner as that in comparative example 2, except that 2.54 gm of aluminium nitrate was used to obtain benzene dicarboxylic acids i.e., terephthalic acid and phthalic acid. The ratio of terephthalic acid and phthalic acid was 97:3. The presence of terephthalic acid and phthalic acid was confirmed by FTIR.
TECHNICAL ADVANCEMENT:
The present disclosure relates to an integrated process for carboxylation and oxidation of organic compounds to prepare poly carboxylic acid in a continuous step obviating the use of a large number of reagents under cryogenic conditions, thereby making the process economical and environment friendly.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
Any discussion of documents, acts, materials, devices, articles or the like that has been comprised in this specification is solely for the purpose of providing a context for the invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the invention as it existed anywhere before the priority date of this application.
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 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 herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing 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.
“Whenever a range of values is specified, a value up to 10 % below and above the lowest and highest numerical value respectively, of the specified range, is comprised in the scope of the disclosure”.
While considerable emphasis has been placed herein on the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiments as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the forgoing descriptive matter to be implemented merely as illustrative of the disclosure and not as limitation.
,CLAIMS:WE CLAIM:

1. A process for carboxylating and oxidizing an aromatic hydrocarbon substituted with at least one alkyl group, said process comprising the following continuous sub-steps of carboxylating the aromatic hydrocarbon using carbon dioxide and at least one catalyst represented by formula I,
AxBy
Formula I
wherein,
‘A’ is a cation of a metal selected from the group consisting of Aluminium (Al), Iron (Fe), Galium (Ga), Antimony (Sb), Molybdenum (Mo) and Copper (Cu),
‘B’ is an anion selected from the group the group consisting of sulphate (SO42-), nitrate(NO3-), chromate(CrO42-), dichromate(Cr2O72-), perchlorate(ClO4-), periodate(IO4-), perbromate(BrO4-), and persulphate (S2O82-),
x is an integer ranging from 1 to 2 indicating the number of cations, and
y is an integer ranging from 1 to 2 indicating the number anions,

to generate a reaction mass comprising at least one oxidizing agent represented by a formula II, and a carboxylated product substituted with at least one alkyl group;
HxBy
Formula II
wherein,
H is hydrogen,
‘B’ is an anion selected from the group the group consisting of sulphate (SO42-), nitrate(NO3-), chromate(CrO42-), dichromate(Cr2O72-), perchlorate(ClO4-), periodate(IO4-), perbromate(BrO4-) and persulphate (S2O82-),
x is an integer ranging from 1 to 2, and
y is an integer ranging from 1 to 2; and

in-situ oxidizing the carboxylated product substituted with at least one alkyl group with the oxidizing agent represented by a formula II formed during the sub-step of carboxylating to obtain an oxidized product.

2. The process as claimed in claim 1, wherein the process is carried out in at least one liquid medium selected from the group consisting of straight or branched chained alkanes, cycloalkanes and halogenated alkanes.
3. The process as claimed in claim 1, wherein the alkyl group is C1 to C5
4. The process as claimed in claim 1, wherein the aromatic hydrocarbon substituted with at least one alkyl group is at least one compound selected from the group consisting of toluene, ortho xylene, meta xylene, para xylene, and C2-alkyl benzenes.
5. The process as claimed in claim 1, wherein the carboxylated product substituted with at least one alkyl group is at least one compound selected from the group consisting of toluic acid, xylylic acid, and mono carboxy aromatic ketone.
6. The process as claimed in claim 1, wherein the oxidized product is at least one compound selected from the group consisting of phthalic acid, terephthalic acid, benzene tricarboxylic acid.
7. The process as claimed in claim 1, wherein the carbon dioxide is in a subcritical form.
8. The process as claimed in claim 1, wherein the amount of the catalyst ranges from 5 to 10 % with respect to the total weight of the aromatic hydrocarbon substituted with at least one alkyl group .
9. The process as claimed in claim 1, wherein the sub-steps are carried out at a temperature ranging from 40 to 100 oC and at a pressure ranging from 500 to 900 psi.
10. The process as claimed in claim 1, wherein the aromatic hydrocarbon substituted with at least one alkyl group is toluene, the catalyst is aluminium nitrate and the oxidized product is terepthalic acid and phthalic acid.