FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULE, 2003
COMPLETE SPECIFICATION
(see section 10; rule 13)
HYDROLYSIS AND ESTERIFICATION WITH ACID CATALYSTS
RELIANCE INDUSTRIES LIMITED
an Indian Organization
of Reliance Industries Limited.
3rd Floor, Maker Chamber-IV
222, Nariman Point
Mumbai-400021
Inventors
1) Aduri Pavankumar
2) Uppara Parasu Veera
3) Ratnaparkhi Uday 4) Sakhalkar Mangesh
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF THE INVENTION:
The present invention relates to a process for inter-conversion between an organic carboxylic acid and an organic carboxylic acid ester in the presence of an acid catalyst & Ionic liquid
BACKGROUND:
lonic liquids are examples of viscous molten salts which are liquid at or below ambient temperatures. In the last two decades, ionic liquid systems have found profound use in a number of applications as solvents, co-solvents and catalysts because of the number of interesting and useful properties and utilities associated with them. Diversified areas including electrochemistry, synthesis of chemical compounds, dyes, batteries, fuel cells, photovoltaic devices, electro-deposition processes, semi-conductor cleaning, pyrolysis, gasification, and applications involving cellulose dissolution have observed successful implementation of ionic liquid systems in place of conventional molecular solvents.
The need to replace conventional molecular acid catalysts with ionic liquid arise from the urge to develop environmentally safe processes. Ionic liquids exhibit very low or zero vapor pressure and thus, in contrast to many conventional molecular solvents, do not produce any vapors.
EXISTING KNOWLEDGE:
United States Patent No. 5892124 discloses quaternary ammonium or phosphonium based ionic liquid having general formula of Q A' wherein A represents various anions including tetrachloroaluminate and trichlorozincate. The feasibility of ionic liquid system is disclosed for Dies-Alder reactions.

United States Patent No. 6573405 discloses quaternary ammonium based ionic compound formed by the reaction of a quaternary ammonium compound of formula R1R2R3R4+N+ X' or a mixture of two or more thereof, with a halide of zinc, tin or iron, or a mixture of two or more thereof. The preferred ionic compound derived from choline chloride and zinc chloride for electrochemical. electrodeposition, electrochromics and dissolution of metal oxides, battery and Dies-Alder reactions is disclosed.
Another United States Patent No. 7183433 discloses quaternary ammonium based ionic compound derived from the reaction of a quaternary ammonium compound of formula R1R2R3R4N+X" or mixture of two or more thereof and urea; for example choline chloride and urea. Similarly, attempts were also made to synthesize ion liquid of quaternary ammonium compound of the formula R1R2R3R4N+X" with specific hydrogen donor compounds chosen from carboxylic acids, amides, ethers, esters, aldehydes, ketones, alcohols, and carbohydrates. Anions of quaternary ammonium compound of the formula R1R2R3R4N+X' were chloride, nitrate and tetraborate. The aforementioned US Patent further discloses the effect of anion X" by varying anions with symmetric amine salts.
The hydrolysis of alkyl esters such as methyl, ethyl, propyl and n-butyl acetate is carried out with an ion exchange resin to produce methanol and acetic acid. These hydrolysis reactions are equilibrate reactions and they do not move forward without removal of alcohol formed in the reaction. The alcohol formed in the reaction is therefore continuously removed in the form of azeotrope along with the reactants. This limits the extent of conversion per mass. Furthermore, it also requires high temperature to continuously remove the alcohol formed during the reaction.

Reactions that employ ion exchange resins for the hydrolysis of alkyl esters have been reported in a number of Patent documents such as Chinese Patent No. 1343649; CN1377873, CN1380273, CN2536587, CN101130482, CN1927792, CN101012162, CN101306981, CN101348415, CN101186575, CN101209955, CN101244982, CN101704733, CN101481293 and Korean Patent No.100888065, Japan Patent No. 53031608, JP56007739, JP59036631, JP10139716, JP2007210980, GB687902, GB826240, US2511467, US2936321, US3239572, US3317593, US4352940, US5113015, US5235102, US5770770, US6518465, United States Patent Application No.2002/0183549, United States Patent Application No. 2008/0128262 and United States Patent Application No.2010/0041919. In all these foregoing patent/patent applications, alkyl esters are hydrolyzed with ion-exchange resins in reactors of various configurations such as fixed bed, reactive distillation column and at the temperatures in the range of 50-150 °C, so as to take the reaction forward by continuous rectification in the reflux mode.
The esterification of alcohols and carboxylic acids to produce respective alkyl esters is known to be carried out in the presence of acid catalysts. Employment of cation exchange resin is largely reported to facilitate esterification reactions. However there are few processes which use mineral acids, mostly sulfuric acid and organic catalyst such as phosphoric acid, para-toluenesulfonic acid (PTSA). Acidic inorganic catalysts are also employed in some instances. The prior-art methods for the esterification of alcohols are carried out at temperatures in the range of 50 to 150 °C. The esterification reactions are equilibrating reactions; therefore removal of one of the product is highly desirable to move the reaction forward thereby increasing the conversions.
Esterification reactions as reported in European Patent No.0087870, US2719166, US3014066, US4435595, US4481146, US4939294, US5430178, US5518699,

US5998658, US4939294, US5430178, US5518699, US5998658, US6028215, US6458992, US6693123 and United States Patent Application No.2006/0041162 include high temperature reactions to achieve acceptable per mass conversions. leading to large reflux ratio.
The hitherto reported reactions however suffer from numerous drawbacks which include requirement of high temperature conditions and being non-ecofriendly.
Therefore, there is felt the need for the development of a new acidic catalyst system for the hydrolysis of organic carboxylic acid esters, and for the esterification of alcohols and organic carboxylic acids which is cost-effective and environmentally friendly.

OBJECTS OF THE INVENTION:
It is an object of the present invention to provide a process for inter-conversion between an organic carboxylic acid and an organic carboxylic acid ester in the presence of an acid catalyst and Ionic liquid
Another object of the present invention is to provide a process for inter-conversion between an organic carboxylic acid and an organic carboxylic acid ester with a high conversion rate.
Still another object of the present invention is to provide a process for inter-conversion between an organic carboxylic acid and an organic carboxylic acid ester that is carried at a low temperature.
Yet another object of the present invention is to provide a cost efficient process for inter-conversion between an organic carboxylic acid and an organic carboxylic acid ester.
A further object of the present invention is to provide an environmentally safe process for inter-conversion between an organic carboxylic acid and an organic carboxylic acid ester.
DEFINITIONS:
As used in the present specification, the following words and phrases are generally intended to have the meanings as set forth below, except to the extent that the context in which they are used indicates otherwise.

The phrase "ionic fluid" is used herein to refer to a prepared solvate whereby an ionic compound formed in-situ by dissolving the mixture of a hydrogen donor compound and a quaternary ammonium salt.
SUMMARY OF THE INVENTION:
In accordance with the present invention, there is provided a process for inter-conversion between an organic carboxylic acid and an organic carboxylic acid ester, said process comprising:
dissolving equimolar quantities of a hydrogen donor compound and a quaternary ammonium salt in a medium comprised of at least one solvent selected from the group consisting of a first alcohol and water to obtain an ionic fluid containing an in-situ generated ionic compound; and performing at least one reaction step selected from the group consisting of:
a hydrolyzing an organic carboxylic acid ester by introducing the same to the ionic fluid, under constant stirring at a temperature in the range of20°C to l00°C;and
b esterifying an organic carboxylic acid compound with a second alcohol by introducing the same to the ionic fluid, under constant stirring at a temperature in the range of 20 °C to 50 °C.
Typically, the first alcohol and the second alcohol are same.
Typically, the second alcohol is not added to the ionic fluid in the method step (b).

However, the first alcohol and the second alcohols can be different.
Typically, the hydrogen donor compound is selected from the group consisting of para-toluene sulfonic acid, oxalic acid, maleic acid, methane sulfonic acid and tartaric acid.
Typically, the quaternary ammonium salt is choline chloride.
Typically, the alcohol is at least one selected from the group consisting of methyl alcohol, ethyl alcohol, iso-propyl alcohol, and n-butyl alcohol.
Typically, the organic carboxylic acid is at least one selected from the group consisting of acetic acid, propanoic acid, and butanoic acid.
Typically, the organic carboxylic acid ester is at least one selected from the group consisting of methyl acetate, ethyl acetate, iso-propyl acetate, n-butyl acetate, amyl acetate and hexyl acetate.
Typically, the proportion of organic carboxylic acid ester and water expressed in terms of molar ratio is in the range of 1:1 to 1:10.
Typically, the proportion of organic carboxylic acid and alcohol expressed in
terms of molar ratio is in the range of 0.1:2 to 2:0.1
Typically, the hydrolysis of organic carboxylic acid ester in the method step (a)
is carried out at azeotropic boiling temperature of the organic carboxylic acid
ester.

Typically, the esterification reaction in the method step (b) is carried out at a temperature in the range of 20°C to50 °C.
DETAIL DESCRIPTION OF THE INVENTION:
The present invention envisages a process for inter-conversion between an organic carboxylic acid and an organic carboxylic acid ester in the presence of acid catalysts wherein the acid catalyst is in the form of an ionic fluid.
The ionic compounds with cations and anions connected by hydrogen bond are reported to have supramolecular structural organization (ref.: Oliver-Bourbigou. H., et al., Applied Catalysis A: General, 373, 1-56, 2010; Deetlefs, m,, et al., J. Physical Chemistry B.110, 12055-12061; Canongia Lopez, J.N. and Padua. A.A.H., J. Physical Chemistry B.110, 3330-3335, 2006). The continuous micro domain structures formed due to the network of hydrogen bond seems to be favorable for acid catalytic reactions.
In the prior-art, preparation of deep eutectic ionic compound in larger quantities is found to be tedious. The resultant ionic compound being very viscous in nature, the process for making the ionic compound is time consuming and it also requires high temperature.
The ionic compounds used for the preparation of ionic fluids in the present invention are derived from a quaternary ammonium salt and a hydrogen donor compound.

In accordance with one aspect of the present invention, ionic compound as such is used as an acid catalyst. Typically, the ionic compound in the form of a deep eutectic mixture is synthesized by heating a hydrogen donor compound along with a quaternary ammonium compound.
In accordance with another aspect of the present invention there is provided a process for inter-conversion between an organic carboxylic acid and an organic carboxylic acid ester which employs an ionic fluid as an acid catalyst.
The ionic fluid which is used as an acid catalyst in accordance with the present invention is prepared by a simple process at a low temperature that overcomes the drawbacks associated with the preparation of ionic compounds as reported in the prior art.
Typically, the process for the preparation of ionic fluid and for inter-conversion between organic carboxylic acid and organic carboxylic acid ester in the presence of prepared ionic fluid is carried out as follows:
In a first aspect, the present invention provides a hydrolysis reaction of an organic carboxylic acid ester to a respective alkyl alcohol and carboxylic acid; and
In second aspect, the present invention provides an esterification of an organic carboxylic acid and an alkyl alcohol to a respective organic carboxylic acid ester.
The process of inter-conversion between an organic carboxylic acid and an organic carboxylic acid ester of the present invention is carried out in the presence an acid catalyst, wherein the acid catalyst is in-situ generated ionic fluid.

The equimolar quantities of a hydrogen donor compound and a quaternary ammonium salt is dissolved in a medium under constant stirring to obtain an ionic fluid containing in-situ generated ionic compound.
The medium in accordance with the present invention is comprised of at least one solvent selected from the group consisting of a first alcohol and water.
During hydrolysis of the organic carboxylic acid ester of the present invention, the medium for the dissolution of the hydrogen donor compound and the quaternary ammonium salt may be alcohol or water; preferably water.
To the obtained ionic fluid derived from the quaternary ammonium salt and the hydrogen donor compound, an organic carboxylic acid ester is introduced to obtain a reaction mixture.
In accordance with the present invention, the organic carboxylic acid ester is at least one ester selected from the group consisting of methyl acetate, ethyl acetate. isopropyl acetate, n-butyl acetate, amyl acetate and hexyl acetate.
The portion of organic carboxylic acid esters and water expressed in terms of molar ratio is in the range of 1:1 to 1:10.
The inventors of the present invention have studied the effect of temperature on the rate of hydrolysis of organic carboxylic acid esters carried out in the presence of in-situ generated ionic fluid.

In accordance with the present invention, the hydrolysis of organic carboxylic acid esters in the presence of in-situ generated ionic fluid is carried out at temperature in the range of 20 °C to 100 °C.
One set of experiments for the hydrolysis of organic carboxylic acid ester is carried out at a temperature in the range of 20-30 °C, whereas another set of experiment is carried out at azeotrope boiling temperature of respective organic carboxylic acid esters.
In accordance with one of the embodiment of the present invention, the hydrolysis of organic carboxylic acid ester is carried out at a temperature in the range of 20 °C to 50 °C.
In accordance with another embodiment of the present invention, the hydrolysis of organic carboxylic acid ester is carried out at azeotrope boiling temperature of the organic carboxylic acid esters.
Methyl acetate forms azeotrope with methanol and the boiling point of methyl acetate/methanol azeotrope is 53.4 °C. Therefore, one set of experiment for the hydrolysis of methyl acetate involves the hydrolysis at 26 °C, whereas another set of experiment involves the hydrolysis at 55 °C (azeotrope boiling temperature of methyl acetate) in the presence of in-situ generated ionic fluid.
Similar to the hydrolysis of methyl acetate, the hydrolysis of ethyl acetate, iso-propyl acetate and n-butyl acetate is also carried out at two different temperatures; one set of experiments at room temperature (preferably at 25 °C to 27 °C) whereas another set of experiments at azeotrope boiling temperature of respective organic carboxylic acid esters in the presence of in-situ generated ionic fluid.

Typically, the hydrolysis of ethyl acetate, isopropyl acetate and n-butyl acetate at their azeotrope boiling temperature is carried out at 70 °C, 80 °C and 100 °C
respectively.
Hydrolysis of n-butyl alcohol is carried out at its azeotrope boiling temperature only, because miscibility of n-butyl alcohol in water is negligible at room temperature which increases considerably at 100 °C temperature.
After the completion of the reaction, the reaction mixture is subjected for product analysis.
The hydrolysis of organic carboxylic acid esters carried out at room temperature (preferably 25 °C to 27 °C) and at azeotrope boiling temperature of organic carboxylic acid esters is tabulated in Table 1 to Table 11 of the present invention.
From the comparative data as provided in Table-1, Table-2 and Table-3 of the present, it is clearly evident that the rate of hydrolysis of methyl acetate carried out in the presence in-situ generated ionic-fluid is faster in comparison to the hydrolysis carried out in the presence of only acids (ref: Table-3).
The rate of hydrolysis of organic carboxylic acid esters carried out at room temperature (preferably 25 °C to 27 °C) in the presence of in-situ generated ionic fluid is faster in comparison to the hydrolysis carried out in the presence of only acid. However, in some instances, the final conversion is found to be reduced in the former case. At room temperature, both the reactants and the products are present in liquid phase and the presence of highly acidic ionic fluid favors the reversible reaction thereby reducing the final conversion (ref. Table-1 and Table-3 of the present invention).

In accordance with the present invention, the hydrolysis of methyl acetate at 55 °C (azeotrope boiling temperature of methyl acetate) in the presence of in-situ generated ionic-fluid derived from para-toluene sulfonic acid and choline chloride reaches equilibrium conversion in 30 minutes, whereas the hydrolysis of methyl acetate carried out in the presence of para-toluenesulfonic acid reaches equilibrium conversion in 60 minutes.
The rate of hydrolysis of organic carboxylic acid esters carried out at their respective azeotrope boiling temperature in the presence of in-situ generated ionic fluid is considerably higher in comparison to the hydrolysis carried out in the presence of only organic acids. At azeotrope boiling temperature, the lower boiling products remain in vapor phase by forming an azoetrope with the organic carboxylic acid ester; therefore the continuous removal of the products in the vapor form favors the forward reaction.
The hydrolysis of ethyl acetate, iso-propyl acetate and n-butyl acetate carried out in the presence of ionic fluid acid catalyst and only acids, at room temperature (preferably 25 °C to 27 °C) and azeotrope boiling temperature is tabulated in Table 4 to Table-11 of the present invention.
In accordance with second aspect of the preset invention, there is provided an esterification reaction of an organic carboxylic acid and an alcohol in the presence of an ionic fluid acid catalyst.
Similar to the method step of ionic fluid generation during hydrolysis of the organic carboxylic acid ester, the ionic fluid acid catalyst as employed for the esterification of the organic carboxylic acid and the alcohol is generated in-situ by

dissolving equimolar quantities of the hydrogen donor compound and the quaternary ammonium salt in a medium.
The medium in accordance with the present invention comprised of at least one solvent selected from the group consisting of water and first alcohol.
In accordance with the present invention, the medium in the method step of esterification is preferably first alcohol.
To the obtained ionic fluid, the organic carboxylic acid compound and a second alcohol is introduced under constant stirring at a temperature in the range of 20 °C to 30 °C and at atmospheric pressure.
In accordance with one of the embodiment of the present invention, the first alcohol and the second alcohol are same.
In accordance with another embodiment of the present invention, the first alcohol and the second alcohol can be different.
In accordance with the present invention, when the first alcohol used in the method step of dissolution and the second alcohol used in the method step of esterification are same, in that case, the second alcohol is not added to the ionic fluid in the method step of esterification.
In accordance with the present invention, the alcohol is at least one selected from the group consisting of methyl alcohol, ethyl alcohol, iso-propyl alcohol and n-butyl alcohol.

In accordance with the present invention, the organic carboxylic acid is at least one selected from the group consisting of acetic acid, propanoic acid and butanoic acid.
After introducing the organic carboxylic acid compound, the obtained reaction mixture is allowed to stand at the pre-defined temperature under continuous stirring until an equilibrium condition is achieved.
In accordance with one of the embodiment of the present invention, the method step of esterification reaction is preferably carried out at a temperature in the range of25°C to 27°C.
In accordance with the present invention, the proportion of organic carboxylic acid and alcohol expressed in terms of molar ratio is in the range of 0.1:2 to 2:0.1
The esterification of the organic carboxylic acid and the alcohol to respective organic carboxylic acid ester is also carried out in the presence of an organic acid alone at the same reaction condition of pressure and temperature as maintained during esterification of organic carboxylic acid and alcohol in the presence of ionic-fluid.
The analytical data for the esterification of organic carboxylic acid and alcohol in the presence of in-situ generated ionic fluid and in the presence of organic acid alone is tabulated in Table 12 to Table 19 of the present invention.
From the data as provided in Table 12 to Table 19. it is clearly evident that equilibrium conversion is higher in both the cases i.e. for the esterification carried out in the presence of in-situ generated ionic fluid and in the presence of organic acid alone.

However, in some instances the rate of esterification carried out in the presence of ionic fluid acid catalyst is faster; for example in the case of esterifi cation of an ethanol carried out in the presence of ionic fluid derived from oxalic acid, maleic acid and tartaric acid (ref: Table 14 and Table 15 of the present invention).
In case of an iso-propyl alcohol, considerably high rate of conversion is achieved in the presence of in-situ generated ionic fluids in comparison to the esterification carried out in the presence of only acid compounds (ref: Table 16 and Table 17 of the present invention).
The esterification of organic carboxylic acid and alcohol does not require high temperature conditions to achieve high conversion rates. The miscibility of the two reactants along with catalyst is one of the reasons to achieve the high equilibrium conversions at 26 °C.
In some instances, there is faster equilibrium in both the cases, nevertheless the presence of ionic fluid as an acid catalyst system obviates the drawbacks associated with use of conventional acid catalyst systems.
The equilibrium conversion achieved in the case of esterification of organic carboxylic acid and alcohol carried out in the presence of in-situ generated ionic fluid acid catalyst eliminates the need of complex reactive distillation columns thereby reducing capital and operational investments.
In accordance with the present invention, the hydrogen donor compounds are selected from the group consisting of methane sulfonic acid (MSA), para-toluenesulfonic acid (PTSA), oxalic acid, maleic acid and tartaric acid.

The quaternary ammonium salt as used herein the present invention is choline chloride.
The in-situ formation of ionic fluid in suitable medium in accordance with the present invention is confirmed by the enhanced solubility of hydrogen donor compound in a suitable medium. For example, solubility of oxalic acid in water at 25 °C is 14%, which is enhanced to 30 % in the presence of choline chloride. This phenomenon clearly indicates the formation of ionic compound through hydrogen bond enhancing the solubility of oxalic acid at 25 °C. Other wise, a water temperature of about 40-45 °C is required to solubilize 30 % of oxalic acid in water.
The inventors of the present invention have surprisingly found out that the product obtained by the process of the present invention remains completely free of any residual free acid. This obviates the need for neutralization of the reaction mixture before isolation of the product as is required in the known processes.
The present invention will be further described with reference to the following non-limiting examples:
Example 1:
Tolune-4-suIfonic acid monohydrate (PTSA), a hydrogen donor compound (5.7 gm) and choline chloride (4.2 gm) in equimolar ratio was added to 17 ml of water under constant stirring to prepare ionic fluid. To the prepared ionic fluid, 15 ml of methyl acetate was added to obtain reaction mixture and reaction was carried out at 26 °C. After the completion of the reaction, the reaction mixture was analyzed

for reaction products. Methyl acetate was converted to acetic acid and methanol and conversion was found to be 53.4 %,
Example 2-5:
The procedure of example 1 was followed with different hydrogen donors in lieu
of PTSA. Details are provided in Table-1.
Table 1: Hydrolysis of methyl acetate with ionic compound at 26 °C

Example 6-10:
The procedure of Example 2 was followed except the reaction temperature was maintained at 55 °C. The details are provided in Table-2.
Table 2: Hydrolysis of methyl acetate with ionic compound at 55°C


Example 11-20:
The procedure of above examples (1 to 10) was followed for different acids (no ionic compound was used). The details are provided in Table-3.
Table 3: Hydrolysis of methyl acetate with only acid catalyst

Example 21:
Procedure of example 1 was followed except, methyl acetate was replaced with ethyl acetate and reaction was carried out 26 °C. Ethyl acetate was converted to acetic acid and ethanol and conversion was found to be 24.4 %.

Example 22-25:
The procedure of Example 21 was followed with different hydrogen donors in lieu
of PTSA and the hydrolysis was carried out. The details are provided in Table-4.
Table 4: Hydrolysis of ethyl acetate with ionic compound at 26 °C

Example 26 -30:
The procedure of example 22 was followed except the reaction temperature was maintained at 70 °C. The details are provided in Table-5.
Table 5: Hydrolysis of ethyl acetate with ionic compound at 70 °C


Example 31-40:
The procedure of above examples 21 to 30 was followed for different acids only (no ionic compounds). Table-6 provides the details of reactions.
Table 6: Hydrolysis of ethyl acetate with only acid catalysts

Example 41:
Procedure of example 1 was followed except methyl acetate was replaced with iso-propyl acetate and reaction was carried out 26 °C. Iso-propyl acetate was converted to acetic acid and iso-propyl alcohol and conversion was found to be 21 %.
Example 42-45:
The procedure of example 41 was followed with different hydrogen donors in lieu of PTSA and the hydrolysis was carried out. The details are provided in Table-7.


Table 7: Hydrolysis of iso-propyl acetate with ionic compound at 26 °C
Example 46-50:
The procedure of example 42 was followed except the reaction temperature was maintained at 80 °C. The details are provided in Table-8.
Table 8: Hydrolysis of iso-propyl acetate with ionic compound at 80 °C

Example 51-60:
The procedure of examples 41 to 50 was followed for different acids only (no ionic compounds). The details are provided in Table-9.


Table 9: Hydrolysis of iso-propyl acetate with only acid catalyst
Example 61:
Procedure of example 1 was followed except, methyl acetate is replaced with n-butyl acetate and reaction was carried out at 100 °C, Butyl acetate was converted to acetic acid and n-butanol and conversion was found to be 49.3 %.
Example 62-65:
The procedure of example 61 was followed with different hydrogen donors in lieu of PTSA and the hydrolysis was carried out. Details are provided in Table-10.


Table 10: Hydrolysis of n-butyl acetate with ionic compound at 100 °C
Example 66-70:
The procedure of examples 61 to 65 was followed for different acids only (no ionic compounds). The details are provided in Table-11.
Table 11: Hydrolysis of n-butyl acetate with acid catalysts at 100 °C

Example 71:
Toluene-4-su]fonic acid monohydrate (PTSA), a hydrogen donor compound (5.7 gin) and choline chloride (4.2 gm) in equal molar ratio was added to 15 ml of methyl alcohol under constant stirring to obtain ionic fluid. To the prepared ionic fluid, 21.5 ml of acetic acid was added. The reaction was carried out at 26 °C.

Methyl alcohol was esterified to methyl acetate and water, and equilibrium conversion was found to be 78 %,
Example 72-75:
The procedure of example 71 was followed with different hydrogen donors in lieu
of PTSA and the esterification was carried out. The details are provided in Table-
12.
Table 12: Esterification of methanol at 26 °C with ionic compounds

Example 76-80:
The procedure of example 71 was followed for different acids only (no ionic
compounds). The details are provided in Table-13.
Table 13: Esterification of methanol at 26 °C with acid catalysts


Example 81-85:
The procedure of example 71 was followed except, methyl alcohol was replaced with ethyl alcohol. Ethyl alcohol was esterified to ethyl acetate and water. The conversion details are provided in Table-14.
Table 14: Esterifi cation of ethanol at 26 °C with ionic compounds

Example 86-90:
The procedure of example 81 was followed for different acids only (no ionic compounds). The details are provided in Table-15,
TabJe 15: Esterification of ethanol at 26 °C with acid catalysts


Example 91-95:
The procedure of example 71 was followed except, methyl alcohol was replaced with isopropyl alcohol. Iso-propyl alcohol was esterified to propyl acetate and water. The conversion details are provided in Table-16.
Table 16: Esterification of iso-propyl alcohol at 26 °C with ionic compounds

Example 96-100:
The procedure of example 91 was followed for different acids only (no ionic compounds). The details are provided in Table-17.
Table 17: Esterification of iso-propyl alcohol at 26 °C with acid catalysts


Example 101-105:
The procedure of example 91 was followed except, methyl alcohol was replaced with n-butyl alcohol, n-butyl alcohol was esterified to butyl acetate and water. The conversion details are provided in Table-18.
Table 18: Esterification of n-butanol at 26 °C with ionic compounds

Example 106-110:
The procedure of example 101 was followed for different acids only (no ionic compounds). The details are provided in Table-19.
Table 19: Esterification of n-butanol at 26 °C with acid catalysts


TECHNICAL ADVANTAGES:
Technical advantages of the present invention lie in providing a novel method for inter-conversion of an organic carboxylic acid and an organic carboxylic acid ester in the presence of an ionic fluid acid catalyst comprising:
1. in-situ generation of an ionic fluid, thereby eliminating a process step of synthesizing deep eutectic ionic compound separately;
2. time and energy saving process over conventional processes;
3. cost efficient, eco-friendly and safe processes over conventional processes.
"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 included in the scope of the invention".
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 invention. These and other changes in the preferred embodiments as well as other embodiments of the invention 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 invention and not as limitation.

We Claim:
1. A process for inter-conversion between an organic carboxylic acid and an organic carboxylic acid ester, said process comprising:
dissolving equimolar quantities of a hydrogen donor compound and a quaternary ammonium salt in a medium comprised of at least one solvent selected from the group consisting of a first alcohol and water to obtain an ionic fluid containing an in-situ generated ionic compound; and performing at least one reaction step selected from the group consisting of:
a hydrolyzing an organic carboxylic acid ester by introducing the same to the ionic fluid, under constant stirring at a temperature in the range of20°C to 100 °C; and
b esterifying an organic carboxylic acid compound with a second alcohol by introducing the same to the ionic fluid, under constant stirring at a temperature in the range of 20 °C to 50 °C.
2. The process as claimed in claim 1, wherein the first alcohol and the second alcohol are same.
3. The process as claimed in claim 1, wherein the first alcohol and the second alcohol are different.
4. The process as claimed in claims 1 and 2, wherein the second alcohol is not added to the ionic fluid in the method step (b).

5. The process as claimed in claim 1, wherein the hydrogen donor compound is selected from the group consisting of para-toluene sulfonic acid, oxalic acid, maleic acid, methane sulfonic acid and tartaric acid.
6. The process as claimed in claim 1. wherein the quaternary ammonium salt is choline chloride.
7. The process as claimed in claim 2 and claim 3, wherein the alcohol is at least one selected from the group consisting of methyl alcohol, ethyl alcohol, iso-propyl alcohol, and n-butyl alcohol.
8. The process as claimed in claim 1, wherein the organic carboxylic acid is at least one selected from the group consisting of acetic acid, propanoic acid, and butanoic acid.
9. The process as claimed in claim 1, wherein the organic carboxylic acid ester is at least one selected from the group consisting of methyl acetate, ethyl acetate, iso-propyl acetate, n-butyl acetate, amyl acetate and hexyl acetate.
10. The process as claimed in claim 1, wherein the proportion of organic carboxylic acid ester and water expressed in terms of molar ratio is in the range of 1:1 to 1:10.
11. The process as claimed in claim 1, wherein the proportion of organic carboxylic acid and alcohol expressed in terms of molar ratio is in the range of 0.1.-2 to 2:0.1

12. The process as claimed in claim 1, wherein the hydrolysis of organic carboxylic acid ester in the method step (a) is carried out at azeotropic boiling temperature of the organic carboxylic acid ester.
13. The process as claimed in claim 1, wherein the esterification reaction in the method step (b) is preferably carried out at a temperature in the range of 25 °C to 27 °C.