Title of Invention	"A PROCESS FOR THE SELECTIVE ESTERIFICATION OF TERTIARY ALCOHOL BY AN ACID ANHYDRIDE USING A REUSABLE SOLID CATALYST"
Abstract	A process for the selective esterification of a tertiary alcohol by contacting a mixture of tertiary alcohol and an organic acid anhydride optionally in presence of a non aqueous solvent with the fine particles of solid catalyst in a stirred batch reactor provided with a reflux water condenser at atmospheric pressure at the reaction conditions, the reaction temperature is below about 80°C; and the reaction period is in the range from about 0.1 h to about 50 h, removing the solid catalyst from the reaction mixture by filtration; and reusing the separated solid catalyst for subsequent batch of the process.

Title of Invention

"A PROCESS FOR THE SELECTIVE ESTERIFICATION OF TERTIARY ALCOHOL BY AN ACID ANHYDRIDE USING A REUSABLE SOLID CATALYST"

Abstract

A process for the selective esterification of a tertiary alcohol by contacting a mixture of tertiary alcohol and an organic acid anhydride optionally in presence of a non aqueous solvent with the fine particles of solid catalyst in a stirred batch reactor provided with a reflux water condenser at atmospheric pressure at the reaction conditions, the reaction temperature is below about 80°C; and the reaction period is in the range from about 0.1 h to about 50 h, removing the solid catalyst from the reaction mixture by filtration; and reusing the separated solid catalyst for subsequent batch of the process.

Full Text	This invention relates to a process for the selective esterification of a tertiary alcohol by an acid anhydride to corresponding tertiary ester using a solid catalyst. This process particularly relates to a process for the esterification of a tertiary alcohol by an acid anhydride to corresponding tertiary ester with very high selectivity at a high conversion using a reusable solid catalyst. The process of this invention can be used for the preparation of tertiary esters, which are speciality chemicals and/or chemical intermediates, used in the chemical industries for the production of perfumes and other fine chemicals. Process for the esterification of normal alcohols by carboxylic acids using homogeneous acid catalyst, such as concentrated sulfuric acid, are well known in the prior art [Encyclopedia of Chemical Technology, Editor: Mary Howe-Grant, 4th Edition, John Wiley and Sons,vol. 9, pp. 755-809]. However, this prior art processes can not be used for the esterification of tertiary alcohols because of the high rate of dehydration of tertiary alcohol to corresponding iso-olefin, for example, tertiary butanol is dehydrated to isobutylene in the presence of the acid catalyst. Moreover, the homogeneous acid catalyzed alcohol esterification process have following limitations: 1. The separation and recovery of the dissolved acid catalysts from the liquid reaction mixture is difficult. 2. The disposal of the used acid catalysts creates environmental pollution. 3. The homogeneous acid catalysts also pose several other problems such as high toxicity, corrosion, spent acid disposal, etc. The prior art information on the esterification of tertiary alcohols is scarce. There is no patent literature disclosing a process for the esterification of tertiary alcohol with carboxylic acid or acid anhydride. However, a few research papers disclosed the esterification of tertiary butyl alcohol with an acid halide, as follows: Nagasawa et. al., have reported the esterification of tert-butanol by an acid bromide or acid chloride, having formula RCOCl(or Br), wherein R is an organic group, to a tertiary ester having formula RCOOC(CH3)3, using activated basic alumina catalyst with catalyst to tert-butanol and acid bromide or chloride wt/wt ratio of above about 2.0 at room temperature for 9-15 h [Ref. Nagasawa, K. et. al., Chemistry Letters., year 1994, pp. 209-212; and Nagasawa, K. et. al., Synthetic Communications, vol. 20(13), year 1990, pp 2033-2040]. However, this process has number of limitations, as given below. 1) It produces in stoichiometric quantities gaseous HC1 or HBr as a by-product, which is highly corrosive and also environmentally unacceptable. 2) Tfie acid chloride or bromide, which is used as an esterification agent, is also corrosive in nature and hence difficult to handle. 3) This process requires a very large amount of catalyst per unit mass of the tertiary ester produced; the wt/wt ratio of catalyst to reactants is above about 2.0. Hence, the process of Nagasawa et. al., is not suitable for the commercial esterification of tertiary alcohols for producing tertiary esters. The prior art alcohol esterification processes, described above, are not suitable for the esterification of tertiary alcohol to corresponding tertiary ester and hence there is a need for the development of an environ-friendly and highly efficient process for the selective esterification of tertiary alcohol by using an esteriflcation agent, which leads to the formation of noncorrosive and environmentally acceptable by-product, and also using a reusable catalyst having high activity and selectivity for the esteriflcation at close to room temperature. This invention is made to develop a novel process for the esteriflcation of tertiary alcohol, meeting the above mentioned goals or conditions. 1 . The main object of this invention is to provide a novel liquid phase process for the esterification of tertiary alcohol to tertiary ester. 2. The another object is to provide a process for the estrification of tertiary alcohol to tertiary ester with high conversion,, and_ selectivity using a highly efficient solid catalyst, which is easily separable and which can be reused, at close to the room temperature. 3. Yet another object is to provide an environmentally clean process for the estrification of tertiary alcohol to tertiary ester. Accordingly, the present invention provides a process for the selective esterification of a tertiary alcohol (I) represented by a formula: (Formula Removed) by reacting an organic acid anhydride (II) represented by a formula: (R4CO)20 to produce an organic tertiary ester (III) represented by a formula: (Formula Removed) wherein, n is an integer having value greater than or equal to 1.0; R3 is H or a chemical group other than hydrogen; and R1, R2, and R4 are organic chemical groups, each comprising both carbon and hydrogen atoms selected from the group consisting of COOH, CnH2n+1, C6H5, substituted phenyl, OCn H2n+1, CnH2n-1, OCnH2n C6H5 & CnH2n C6H5 using a reusable solid catalyst(IV), represented by a formula: (Formula Removed) wherein, M is a chemical element selected from Ga (gallium), In (indium), Zn (zinc), Fe (iron) or a mixture of two or more thereof; Z is a halogen selected from Cl (chlorine), Br (bromine), I (iodine) and a mixture thereof; y is an integer having a value of 2 or 3, depending upon the valence requirement of M; S is a porous solid support on which MZy is deposited; and c is a loading of MZy on the support S expressed as the mmols of MZy deposited per gram of the support, S, in the range from about 0.01 mmol g"1 to about 10.0 mmol g-1; the process comprises: i) contacting a mixture of tertiary alcohol (I) and an organic acid anhydride (II) optionally in presence of a non aqueous solvent with the fine particles of solid catalyst (IV) in a stirred batch reactor provided with a reflux water condenser at atmospheric pressure at the reaction conditions, such that the mole ratio of (II) to (I) is in the range from about 0.1 to about 10.0; the weight ratio of (IV) to (I + II) is in the range from about 0.005 to about 0.5; the reaction temperature is below about 80°C; and the reaction period is in the range from about 0.1 h to about 50 h; ii) removing the solid catalyst(IV) from the reaction mixture by filtration; and iii) reusing the separated solid catalyst for subsequent batch of the process. In one embodiment of the invention, the catalyst support, S, used is a cationic clay or mesoporous zeolite-like crystalline material. In yet another embodiment, M in the solid catalyst(IV) is selected from In (indium), or Ga (gallium) and a mixture thereof. In yet another embodiment, Z in the solid catalyst(IV) is Cl (chlorine). In yet another embodiment, the catalyst loading, c, is in the range from about 0.02 mmol g-1 to about 2.5 mmol g-1. In yet another embodiment, each of the chemical groups R1, R2, and R4 is selected from the group consisting of methyl, ethyl, propyl, butyl and phenyl. In yet another embodiment, the mole ratio of acid anhydride(II) to tertiary alcohol(I) is preferably in the range from 0.5 to 2.0. In yet another embodiment, the weight ratio of solid catalyst(I V) to the reactants, » acid anhydride(II) and tertiary alcohol(I) is preferably in the range from 0.01 to 0.2. In yet another embodiment the reaction temperature is preferably in the range from 10°Cto50°C. In still another embodiment, the reaction period is preferably in the range from 0.2hto 10 h. In the process of this invention, the main product, by-product and side products are formed according to the following reactions: Esterification reaction (Formula Removed) Dehydration reaction (Formula Removed) The process of this invention can be carried out in a stirred batch reactor fitted with a reflux condenser. In the process of this invention, the role of reflux condenser fitted with the reactor is to condense reactants and solvent, if used, and to return them back to reaction mixture, and the role of stirring is to provide to a thorough mixing of the reactants and the catalysts in the reaction mixture, and thereby to provide a very efficient contact between the catalyst and the reactants. Said catalyst(IV), is in solid form, heterogeneous with respect to the reaction mixture, and hence it can be removed from the reaction mixture simply by filtration and the separated catalyst can be reused in said process for subsequent batches. The role of said catalyst(IV) in the process of this invention to activate both the reactants, tertiary alcohol(I) and acid anhydride(II) and thereby drastically reduced the activation energy of the esterification reaction between the reactants. The role of porous support, S, in said catalyst(IV) of this invention is to immobilise the active catalyst component MZy, defined above. The catalyst support, S, may also show activity for the conversion of tertiary alcohol(I) but it shows less selectivity for the formation of tertiary ester(III) in the absence of active catalyst component, MZy. The presence of MZy is essential for both high activity and high selectivity of the catalyst(IV) in the process of this invention. The catalyst support, S, for said catalyst(IV) of this invention is selected from various cationic clays and mesoporous zeolite-like materials and it may be acidic, non acidic or basic in nature. Example of the cationic clays are montmorillonite K-10, commonly called as Mont K-10, montmorillonite KSF, commonly called as Mont KSF, kaolin, kaolinites, serpentinites, nontronites, vermiculite and other clays in smectite group [Ref. Vaccari A., Catalysis Today, vol. 41, year, 1998, pp. 53-71], Examples of mesoporous zeolite-like crystalline material are MCM-41 type mesoporous materials, such as Si-MCM-41, Al-Si-MCM-41, Ga.Al-Si-MCM-41, etc. These cationic clays and mesoporous materials are well known in the prior art. The most preferred catalyst support, S, for said catalyst(IV) of this invention is Mont K-10 [Montmorillonite K-10]. Mesoporous materials have pore diameter above about 1.0 nm and below about 20.0 nm. By the process of this invention, tert-butanol can be esterified by acetic anhydride to tert-butyl acetate with a complete (100%) conversion of tert-butanol and above 95 % selectivity for tert-butyl acetate at room temperature (26-30 °C) using a very small amount of said solid catalyst(IV), InCl3 (1.1 mmol g-1) /Mont K-10, with a catalyst to reactants weight ratio of 0.03, for a short reaction period, 1.0 h. The present invention is described with respect to the following examples illustrating the process of this invention for the esterification of tertiary alcohols by different acid anhydrides to corresponding tertiary esters using said solid catalyst(IV) with different compositions. These examples are provided for illustrative purposes only and are nor to be construed as limitation on the process of this invention. Definition of terms used in the examples Conversion of tertiary alcohol (%) is defined as mole % of the tertiary alcohol converted to all products viz., tertiary ester and iso-olefin. The conversion of tertiary alcohol, selectivity for tertiary ester and selectivity for iso-olefm are estimated as follows: Conversion of tertiary alcohol (%) = [(XtA(i), - XtA(f))/ XtA(i)] x 100 Selectivity for tertiary ester (%) = [XtE/(X,A(i) - XtA(f))] x 100 Selectivity for iso-olefin = [Xio/(XtA(i) - XtA(f))] x 100 = 100 - [selectivity for tertiary ester (%)] wherein, XtA(i) = moles of tertiary alcohol in the reaction mixture before the reaction. XtA(f) = moles of tertiary alcohol in the reaction mixture after the reaction. XtE= moles of tertiary ester in the-reaction mixture after the reaction. XIO = moles of iso-olefin formed in the reaction. The following examples are given by the way of illustration and therefore should not be construed to limit the scope of the present invention EXAMPLES 1-14 These examples illustrate the process of this invention for the esterfication of tertiary alcohol(I) by an acid anhydride(II) to a tertiary ester(III) using a reusable solid catalyst(IV). The process of this invention was carried out in a magnetically stirred glass reactor of capacity 50 cm3 fitted with a reflux water condenser, the outlet of which was connected to a constant pressure (atmospheric pressure) gas collector, by contacting a reaction mixture containing tertiary alcohol(I) and acid anhydride(II) with the fine particles of said solid catalyst(IV) at reaction conditions given in Tables 1-3. The reaction temperature was measured by a mercury thermometer dipped in the reaction mixture and it was controlled by putting the glass reactor in a constant temperature water bath. After the reaction, the temperature of the reaction mixture was brought to room temperature and then the catalyst from the reaction mixture was separated by filtration. After the removal of the solid catalyst, the reaction mixture was subjected to the analysis of products and unconverted reactants. The iso-olefm formed in the reaction was measured quantitatively by collecting iso-olefm gas evolved, if any, during the reaction at atmospheric pressure and also by analyzing the reaction mixture for the iso-olefin by gas chromatographic analysis. The unconverted tertiary alcohol(I) and acid anhydride(II), tertiary ester(III) and carboxylic acid(V) in the reaction mixture were analyzed by gas chromatography or high pressure liquid chromatography. Results of the esterification of tertiary alcohol(I) by the process of this invention at different process conditions and using different tertiary alcohols, acid anhydrides and fresh catalysts or used catalysts are presented in Table 1-3. Before reusing the InCb (0.02 mmol g'^/Mont K-10 catalyst in Example-13 and the GaCl3 (0.5 mmol g'^/Mont K-10 catalyst in Example-14, both the used catalysts were washed with tert-butanol to remove any material adsorbed in the previous reaction. The catalysts given in Tables 1 - 3 were prepared as follows: The InCl3 (1.1 mmol g-1/Mont K-10 catalyst was prepared by depositing 2.43 g anhydrous InCl3 (Aldrich) from its acetonitrile solution on 10 g montmorillonite K-10 clay by incipient wetness technique followed by drying at 120 °C for 8 h. The ZnBr2 (1.1 mmol g-1/Mont K-10 catalyst was prepared by depositing 2.48 g anhydrous ZnBr2 (Aldrich) from its acetonitrile solution on 10 g montmorillonite K-10 clay by incipient wetness technique followed by drying at 120 °C for 8 h. The FeC13 (1.1 mmol g-1/Mont K-10 catalyst was prepared by depositing 1.78 g anhydrous FeCl3 (Aldrich) from its acetonitrile solution on 10 g montmorillonite K-10 clay by incipient wetness technique followed by drying at 120 °C for 8 h. The GaCl3 (4.6 mmol g"')/Mont K-10 catalyst was prepared by depositing 8.1 g anhydrous GaCl3 (Aldrich) from its acetonitrile solution on 10 g montmorillonite K-10 clay by incipient wetness technique followed by drying at 120 °C for 8 h. The InCl3 (2.3 'mmol g'VSi-MCM^l catalyst was prepared by depositing 5.09 g anhydrous InCl3 (Aldrich) from its acetonitrile solution on 10 g Si-MCM-41 by incipient wetness technique followed by drying at 120 °C for 8 h. The InCl3 (1.1 mmol g-1/Mont KSF catalyst was prepared by depositing 2.43 g anhydrous InCl3 (Aldrich) from its acetonitrile solution on 10 g montmorillonite KSF clay by incipient wetness technique followed by drying at 120 °C for 8 h. The InCl3 (0.5 mmol g'^/Mont K-10 catalyst was prepared by depositing 1.11 g anhydrous InCl3 (Aldrich) from its acetonitrile solution on 10 g montmorillonite K-10 clay by incipient wetness technique followed by drying at 120 °C for 8 h. The InCl3 (0.02 mmol g-1/Mont K-10 catalyst was prepared by depositing 0.044 g anhydrous InCl3 (Aldrich) from its acetonitrile solution on 10 g montmorillonite K-10 clay by incipient wetness technique followed by drying at 120 °C for 8 h. The GaCl3 (0.5 mmol g"')/Mont K-10 catalyst was prepared by depositing 0.9 g anhydrous InCl3 (Aldrich) from its acetonitrile solution on 10 g montmorillonite K-10 clay by incipient wetness technique followed by drying at 120 °C for 8 h. The InCl3 (0.5 mmol g"1) and GaCl3 (0.5 mmol g-1/Mont K-10 catalyst was prepared by depositing the mixture of 1.11 g anhydrous InCl3 (Aldrich) and 0.9 g anhydrous GaCl3 (Aldrich) from their acetonitrile solution on 10 g montmorillonite K-10 clay by incipient wetness technique followed by drying at 120 °C for 8 h. In the incipient wetness technique, the volume of impregnation solution is just sufficient to completely wet solid to be impregnated and there is no free solution in the impregnation mixture. The Mont K-10 (montmorillonite K-10), Mont KSF (montmorillonite KSF) and kaolin clays were obtained from Aldrich Chemicals Co, USA. The Si-MCM-41 mesoporous crystalline material was prepared by the procedure given by Mokaya et. al., [Ref. Mokaya, R. and Jones, W., Chemical Communication, year 1997, pp. 2185-2186]. Table 1: Results of the esterification of tertiary butanol with acetic anhydride at different reaction conditions. (Table Removed) Table 2: Results of the esterification of a tertiary alcohol with an acid anhydride at different reaction conditions. (Table Removed) Table 3: Results of the esterification of t-butyl alcohol with an acid anhydride at different reaction conditions. (Table Removed) Novel features and advantages of the process of this invention over the prior art processes for the esterification of tertiary alcohol 1) By the process of this invention, a tertiary alcohol can be esterified by an acid anhydride to a corresponding ester with very high conversion (upto 100 %) and high selectivity for the tertiary ester (above 95 %), without producing appreciable amounts of tertiary alcohol dehydration products and/or any environmentally unacceptable product, using a reusable solid catalyst for a short reaction period, as short as 1.0 h. 2) Unlike the prior art process, the process of this invention is environ-friendly process; no toxic/corrosive product, like gaseous hydrogen halide is formed as a by-product in the process of this invention. The by-product of the process of this invention, carboxylic acid, has a commercial value and it can be converted into an acid anhydride, and thereby, recycled in the process. 3) Unlike the prior art processes, the amount of solid catalyst used in the process of this invention is very small. The solid catalyst to reactants weight ratio in the process of this invention is very much lower than that used in the prior art processes. 4) Unlike the prior art processes, the reaction time require for completing the esterification reaction in the process of this invention is much shorter even though the amount of catalyst used is very much smaller. We claim: 1. A process for the selective esterification of a tertiary alcohol(l) represented by a formula: (Formula Removed) by reacting an organic acid anhydride (II) represented by a formula: (R4CO)20 to produce an organic tertiary ester (III) represented by a formula: (Formula Removed) wherein Rs is H or a chemical group other than hydrogen selected from the group consisting of halogen,NH2, NO2,OH,SO3H ; and R1, R2, and R4 are organic chemical groups, each comprising both carbon and hydrogen atoms selected from the group consisting of COOH, CnH2n+1, C6H5, substituted phenyl, OCn H2n+1, CnH2n-1, OCnH2n C6H5 & CnH2n C6H5 wherein, n is an integer having value greater than or equal to 1 using a reusable solid catalyst(IV), represented by a formula: MZy(c)/S wherein, M is a chemical element selected from Ga (gallium), In (indium), Zn (zinc), Fe (iron) or a mixture of two or more thereof; Z is a halogen selected from Cl (chlorine), Br (bromine), I (iodine) and a mixture thereof; y is an integer having a value of 2 or 3, depending upon the valence requirement of M; S is a porous solid support on which MZy is deposited; and c is a loading of MZy on the support S expressed as the mmols of MZy deposited per gram of the support, S, in the range from about 0.01 mmol g"1 to about 10.0 mmol g"1; the process comprises: i) contacting a mixture of tertiary alcohol (I) and an organic acid anhydride (II) optionally in presence of a non aqueous solvent with the fine particles of solid catalyst (IV) in a stirred batch reactor provided with a reflux water condenser at atmospheric pressure at the reaction conditions, such that the mole ratio of (II) to (I) is in the range from about 0.1 to about 10.0; the weight ratio of (IV) to (I + II) is in the range from about 0.005 to about 0.5; the reaction temperature is below about 80°C; and the reaction period is in the range from about 0.1 h to about 50 h; ii) removing the solid catalyst(IV) from the reaction mixture by filtration; and iv) reusing the separated solid catalyst for subsequent batch of the process. 2. A process as claimed in claim 1 wherein, the catalyst support, S, is cationic clay and mesoporous crystalline material. 3. A process as claim in claim 1 wherein, M in the solid catalyst(IV) is In (indium) or Ga (gallium) or a mixture thereof. 4. A process as claimed in claim 1 wherein, Z in the solid catalyst(IV) is Cl (chlorine). 5. A process as claimed in claim 1 wherein, the catalyst loading, c, is in the range from about 0.02 mmol g-1 to about 2.5 mmol g-1. 6. A process as claim in claim 1 wherein, each of the chemical groups R1, R2, and R4 is selected from methyl, ethyl, propyl, butyl and phenyl. 7. A process as claimed in claim 1 wherein, the mole ratio of acid anhydride(ll) to tertiary alcohol(l) is in the range from 0.5 to 2.0. 8. A process as claimed in claim 1 wherein, the weight ratio of solid catalyst(IV) to the reactants, acid anhydride(ll) and tertiary alcohol(l) is in the range from 0.01 to 0.2. 9. A process as claimed in claim 1 wherein, the reaction temperature is in the range from 10°Cto50°C. 10. A process as claimed in claim 1 wherein, the reaction period is in the range from 0.2h to 10 h. 11. A process for the selective esterification of tertiary alcohol by an acid anhydride using a reusable solid catalyst substantially as herein described with reference to the examples.

Full Text

This invention relates to a process for the selective esterification of a tertiary alcohol by an acid anhydride to corresponding tertiary ester using a solid catalyst. This process particularly relates to a process for the esterification of a tertiary alcohol by an acid anhydride to corresponding tertiary ester with very high selectivity at a high conversion using a reusable solid catalyst.
The process of this invention can be used for the preparation of tertiary esters, which are speciality chemicals and/or chemical intermediates, used in the chemical industries for the production of perfumes and other fine chemicals.
Process for the esterification of normal alcohols by carboxylic acids using homogeneous acid catalyst, such as concentrated sulfuric acid, are well known in the prior art [Encyclopedia of Chemical Technology, Editor: Mary Howe-Grant, 4th
Edition, John Wiley and Sons,vol. 9, pp. 755-809]. However, this prior art processes
can not be used for the esterification of tertiary alcohols because of the high rate of
dehydration of tertiary alcohol to corresponding iso-olefin, for example, tertiary butanol is dehydrated to isobutylene in the presence of the acid catalyst. Moreover, the homogeneous acid catalyzed alcohol esterification process have following limitations:
1. The separation and recovery of the dissolved acid catalysts from the liquid reaction
mixture is difficult.
2. The disposal of the used acid catalysts creates environmental pollution.
3. The homogeneous acid catalysts also pose several other problems such as high

toxicity, corrosion, spent acid disposal, etc.
The prior art information on the esterification of tertiary alcohols is scarce. There is no patent literature disclosing a process for the esterification of tertiary alcohol with carboxylic acid or acid anhydride. However, a few research papers disclosed the esterification of tertiary butyl alcohol with an acid halide, as follows:
Nagasawa et. al., have reported the esterification of tert-butanol by an acid bromide or acid chloride, having formula RCOCl(or Br), wherein R is an organic group, to a tertiary ester having formula RCOOC(CH3)3, using activated basic alumina catalyst with catalyst to tert-butanol and acid bromide or chloride wt/wt ratio of above about 2.0 at room temperature for 9-15 h [Ref. Nagasawa, K. et. al., Chemistry Letters., year 1994, pp. 209-212; and Nagasawa, K. et. al., Synthetic Communications, vol. 20(13), year 1990, pp 2033-2040]. However, this process has number of limitations, as given below.
1) It produces in stoichiometric quantities gaseous HC1 or HBr as a by-product,
which is highly corrosive and also environmentally unacceptable.
2) Tfie acid chloride or bromide, which is used as an esterification agent, is also
corrosive in nature and hence difficult to handle.
3) This process requires a very large amount of catalyst per unit mass of the tertiary
ester produced; the wt/wt ratio of catalyst to reactants is above about 2.0.
Hence, the process of Nagasawa et. al., is not suitable for the commercial esterification of tertiary alcohols for producing tertiary esters.
The prior art alcohol esterification processes, described above, are not suitable for the esterification of tertiary alcohol to corresponding tertiary ester and hence there is a need for the development of an environ-friendly and highly efficient process for the

selective esterification of tertiary alcohol by using an esteriflcation agent, which leads to the formation of noncorrosive and environmentally acceptable by-product, and also using a reusable catalyst having high activity and selectivity for the esteriflcation at close to room temperature. This invention is made to develop a novel process for the esteriflcation of tertiary alcohol, meeting the above mentioned goals or conditions.
1 . The main object of this invention is to provide a novel liquid phase process for the esterification of tertiary alcohol to tertiary ester.
2. The another object is to provide a process for the estrification of tertiary alcohol
to tertiary ester with high conversion,, and_ selectivity using a highly efficient solid
catalyst, which is easily separable and which can be reused, at close to the room
temperature.
3. Yet another object is to provide an environmentally clean process for the
estrification of tertiary alcohol to tertiary ester.

Accordingly, the present invention provides a process for the selective esterification of a tertiary alcohol (I) represented by a formula:
(Formula Removed)
by reacting an organic acid anhydride (II) represented by a formula: (R4CO)20
to produce an organic tertiary ester (III) represented by a formula:
(Formula Removed)
wherein, n is an integer having value greater than or equal to 1.0; R3 is H or a chemical group other than hydrogen; and R1, R2, and R4 are organic chemical groups, each comprising both carbon and hydrogen atoms selected from the group consisting of COOH, CnH2n+1, C6H5, substituted phenyl, OCn H2n+1, CnH2n-1, OCnH2n C6H5 & CnH2n C6H5 using a reusable solid catalyst(IV), represented by a formula:

(Formula Removed)
wherein, M is a chemical element selected from Ga (gallium), In (indium), Zn (zinc), Fe (iron) or a mixture of two or more thereof; Z is a halogen selected from Cl (chlorine), Br (bromine), I (iodine) and a mixture thereof; y is an integer having a value of 2 or 3, depending upon the valence requirement of M; S is a porous solid support on which MZy is deposited; and c is a loading of MZy on the support S expressed as the mmols of MZy deposited per gram of the support, S, in the range from about 0.01 mmol g"1 to about 10.0 mmol g-1; the process comprises:
i) contacting a mixture of tertiary alcohol (I) and an organic acid anhydride (II) optionally in presence of a non aqueous solvent with the fine particles of solid catalyst (IV) in a stirred batch reactor provided with a reflux water condenser at atmospheric pressure at the reaction conditions, such that the mole ratio of (II) to (I) is in the range from about 0.1 to about 10.0; the weight ratio of (IV) to (I + II) is in the range from about 0.005 to about 0.5; the reaction temperature is below about 80°C; and the reaction period is in the range from about 0.1 h to about 50 h; ii) removing the solid catalyst(IV) from the reaction mixture by filtration; and iii) reusing the separated solid catalyst for subsequent batch of the process.

In one embodiment of the invention, the catalyst support, S, used is a cationic clay or mesoporous zeolite-like crystalline material.
In yet another embodiment, M in the solid catalyst(IV) is selected from In (indium), or Ga (gallium) and a mixture thereof.
In yet another embodiment, Z in the solid catalyst(IV) is Cl (chlorine).
In yet another embodiment, the catalyst loading, c, is in the range from about 0.02 mmol g-1 to about 2.5 mmol g-1.
In yet another embodiment, each of the chemical groups R1, R2, and R4 is selected from the group consisting of methyl, ethyl, propyl, butyl and phenyl.
In yet another embodiment, the mole ratio of acid anhydride(II) to tertiary alcohol(I) is preferably in the range from 0.5 to 2.0.
In yet another embodiment, the weight ratio of solid catalyst(I V) to the reactants, » acid anhydride(II) and tertiary alcohol(I) is preferably in the range from 0.01 to 0.2.
In yet another embodiment the reaction temperature is preferably in the range from 10°Cto50°C.
In still another embodiment, the reaction period is preferably in the range from 0.2hto 10 h.
In the process of this invention, the main product, by-product and side products are formed according to the following reactions:
Esterification reaction
(Formula Removed)
Dehydration reaction
(Formula Removed)
The process of this invention can be carried out in a stirred batch reactor fitted with a reflux condenser.
In the process of this invention, the role of reflux condenser fitted with the reactor is to condense reactants and solvent, if used, and to return them back to reaction mixture, and the role of stirring is to provide to a thorough mixing of the reactants and the catalysts in the reaction mixture, and thereby to provide a very efficient contact between the catalyst and the reactants.
Said catalyst(IV), is in solid form, heterogeneous with respect to the reaction mixture, and hence it can be removed from the reaction mixture simply by filtration and the separated catalyst can be reused in said process for subsequent batches. The role of said catalyst(IV) in the process of this invention to activate both the reactants, tertiary alcohol(I) and acid anhydride(II) and thereby drastically reduced the activation energy of the esterification reaction between the reactants.
The role of porous support, S, in said catalyst(IV) of this invention is to immobilise the active catalyst component MZy, defined above. The catalyst support, S, may also show activity for the conversion of tertiary alcohol(I) but it shows less selectivity for the formation of tertiary ester(III) in the absence of active catalyst component, MZy. The presence of MZy is essential for both high activity and high selectivity of the catalyst(IV) in the process of this invention. The catalyst support, S, for said catalyst(IV) of this invention is selected from various cationic clays and
mesoporous zeolite-like materials and it may be acidic, non acidic or basic in nature. Example of the cationic clays are montmorillonite K-10, commonly called as Mont K-10, montmorillonite KSF, commonly called as Mont KSF, kaolin, kaolinites, serpentinites, nontronites, vermiculite and other clays in smectite group [Ref. Vaccari A., Catalysis Today, vol. 41, year, 1998, pp. 53-71], Examples of mesoporous zeolite-like crystalline material are MCM-41 type mesoporous materials, such as Si-MCM-41, Al-Si-MCM-41, Ga.Al-Si-MCM-41, etc. These cationic clays and mesoporous materials are well known in the prior art. The most preferred catalyst support, S, for said catalyst(IV) of this invention is Mont K-10 [Montmorillonite K-10]. Mesoporous materials have pore diameter above about 1.0 nm and below about 20.0 nm.
By the process of this invention, tert-butanol can be esterified by acetic anhydride to tert-butyl acetate with a complete (100%) conversion of tert-butanol and above 95 % selectivity for tert-butyl acetate at room temperature (26-30 °C) using a very small amount of said solid catalyst(IV), InCl3 (1.1 mmol g-1) /Mont K-10, with a catalyst to reactants weight ratio of 0.03, for a short reaction period, 1.0 h.
The present invention is described with respect to the following examples illustrating the process of this invention for the esterification of tertiary alcohols by different acid anhydrides to corresponding tertiary esters using said solid catalyst(IV) with different compositions. These examples are provided for illustrative purposes only and are nor to be construed as limitation on the process of this invention.
Definition of terms used in the examples
Conversion of tertiary alcohol (%) is defined as mole % of the tertiary alcohol converted to all products viz., tertiary ester and iso-olefin. The conversion of tertiary alcohol, selectivity for tertiary ester and selectivity for iso-olefm are estimated as

follows:
Conversion of tertiary alcohol (%) = [(XtA(i), - XtA(f))/ XtA(i)] x 100 Selectivity for tertiary ester (%) = [XtE/(X,A(i) - XtA(f))] x 100 Selectivity for iso-olefin = [Xio/(XtA(i) - XtA(f))] x 100
= 100 - [selectivity for tertiary ester (%)] wherein,
XtA(i) = moles of tertiary alcohol in the reaction mixture before the reaction. XtA(f) = moles of tertiary alcohol in the reaction mixture after the reaction. XtE= moles of tertiary ester in the-reaction mixture after the reaction. XIO = moles of iso-olefin formed in the reaction.
The following examples are given by the way of illustration and therefore should not be construed to limit the scope of the present invention
EXAMPLES 1-14
These examples illustrate the process of this invention for the esterfication of tertiary alcohol(I) by an acid anhydride(II) to a tertiary ester(III) using a reusable solid catalyst(IV).
The process of this invention was carried out in a magnetically stirred glass reactor of capacity 50 cm3 fitted with a reflux water condenser, the outlet of which was connected to a constant pressure (atmospheric pressure) gas collector, by contacting a reaction mixture containing tertiary alcohol(I) and acid anhydride(II) with the fine particles of said solid catalyst(IV) at reaction conditions given in Tables 1-3. The reaction temperature was measured by a mercury thermometer dipped in the reaction mixture and it was controlled by putting the glass reactor in a constant temperature

water bath. After the reaction, the temperature of the reaction mixture was brought to room temperature and then the catalyst from the reaction mixture was separated by filtration. After the removal of the solid catalyst, the reaction mixture was subjected to the analysis of products and unconverted reactants. The iso-olefm formed in the reaction was measured quantitatively by collecting iso-olefm gas evolved, if any, during the reaction at atmospheric pressure and also by analyzing the reaction mixture for the iso-olefin by gas chromatographic analysis. The unconverted tertiary alcohol(I) and acid anhydride(II), tertiary ester(III) and carboxylic acid(V) in the reaction mixture were analyzed by gas chromatography or high pressure liquid chromatography.
Results of the esterification of tertiary alcohol(I) by the process of this invention at different process conditions and using different tertiary alcohols, acid anhydrides and fresh catalysts or used catalysts are presented in Table 1-3. Before reusing the InCb (0.02 mmol g'^/Mont K-10 catalyst in Example-13 and the GaCl3 (0.5 mmol g'^/Mont K-10 catalyst in Example-14, both the used catalysts were washed with tert-butanol to remove any material adsorbed in the previous reaction.
The catalysts given in Tables 1 - 3 were prepared as follows:
The InCl3 (1.1 mmol g-1/Mont K-10 catalyst was prepared by depositing 2.43 g anhydrous InCl3 (Aldrich) from its acetonitrile solution on 10 g montmorillonite K-10 clay by incipient wetness technique followed by drying at 120 °C for 8 h.
The ZnBr2 (1.1 mmol g-1/Mont K-10 catalyst was prepared by depositing 2.48 g anhydrous ZnBr2 (Aldrich) from its acetonitrile solution on 10 g montmorillonite K-10 clay by incipient wetness technique followed by drying at 120 °C for 8 h.
The FeC13 (1.1 mmol g-1/Mont K-10 catalyst was prepared by depositing 1.78 g anhydrous FeCl3 (Aldrich) from its acetonitrile solution on 10 g montmorillonite K-10

clay by incipient wetness technique followed by drying at 120 °C for 8 h.
The GaCl3 (4.6 mmol g"')/Mont K-10 catalyst was prepared by depositing 8.1 g anhydrous GaCl3 (Aldrich) from its acetonitrile solution on 10 g montmorillonite K-10 clay by incipient wetness technique followed by drying at 120 °C for 8 h.
The InCl3 (2.3 'mmol g'VSi-MCM^l catalyst was prepared by depositing 5.09 g anhydrous InCl3 (Aldrich) from its acetonitrile solution on 10 g Si-MCM-41 by incipient wetness technique followed by drying at 120 °C for 8 h.
The InCl3 (1.1 mmol g-1/Mont KSF catalyst was prepared by depositing 2.43 g anhydrous InCl3 (Aldrich) from its acetonitrile solution on 10 g montmorillonite KSF clay by incipient wetness technique followed by drying at 120 °C for 8 h.
The InCl3 (0.5 mmol g'^/Mont K-10 catalyst was prepared by depositing 1.11 g anhydrous InCl3 (Aldrich) from its acetonitrile solution on 10 g montmorillonite K-10 clay by incipient wetness technique followed by drying at 120 °C for 8 h.
The InCl3 (0.02 mmol g-1/Mont K-10 catalyst was prepared by depositing 0.044 g anhydrous InCl3 (Aldrich) from its acetonitrile solution on 10 g montmorillonite K-10 clay by incipient wetness technique followed by drying at 120 °C for 8 h.
The GaCl3 (0.5 mmol g"')/Mont K-10 catalyst was prepared by depositing 0.9 g anhydrous InCl3 (Aldrich) from its acetonitrile solution on 10 g montmorillonite K-10 clay by incipient wetness technique followed by drying at 120 °C for 8 h.
The InCl3 (0.5 mmol g"1) and GaCl3 (0.5 mmol g-1/Mont K-10 catalyst was prepared by depositing the mixture of 1.11 g anhydrous InCl3 (Aldrich) and 0.9 g anhydrous GaCl3 (Aldrich) from their acetonitrile solution on 10 g montmorillonite K-10 clay by incipient wetness technique followed by drying at 120 °C for 8 h.

In the incipient wetness technique, the volume of impregnation solution is just sufficient to completely wet solid to be impregnated and there is no free solution in the impregnation mixture.
The Mont K-10 (montmorillonite K-10), Mont KSF (montmorillonite KSF) and kaolin clays were obtained from Aldrich Chemicals Co, USA. The Si-MCM-41 mesoporous crystalline material was prepared by the procedure given by Mokaya et. al., [Ref. Mokaya, R. and Jones, W., Chemical Communication, year 1997, pp. 2185-2186].
Table 1: Results of the esterification of tertiary butanol with acetic anhydride at different reaction conditions.
(Table Removed)
Table 2: Results of the esterification of a tertiary alcohol with an acid anhydride at different reaction conditions.
(Table Removed)
Table 3: Results of the esterification of t-butyl alcohol with an acid anhydride at different reaction conditions.
(Table Removed)
Novel features and advantages of the process of this invention over the prior art processes for the esterification of tertiary alcohol
1) By the process of this invention, a tertiary alcohol can be esterified by an acid
anhydride to a corresponding ester with very high conversion (upto 100 %) and
high selectivity for the tertiary ester (above 95 %), without producing appreciable
amounts of tertiary alcohol dehydration products and/or any environmentally
unacceptable product, using a reusable solid catalyst for a short reaction period,
as short as 1.0 h.
2) Unlike the prior art process, the process of this invention is environ-friendly
process; no toxic/corrosive product, like gaseous hydrogen halide is formed as a
by-product in the process of this invention. The by-product of the process of this
invention, carboxylic acid, has a commercial value and it can be converted into an
acid anhydride, and thereby, recycled in the process.
3) Unlike the prior art processes, the amount of solid catalyst used in the process of
this invention is very small. The solid catalyst to reactants weight ratio in the
process of this invention is very much lower than that used in the prior art
processes.
4) Unlike the prior art processes, the reaction time require for completing the
esterification reaction in the process of this invention is much shorter even though
the amount of catalyst used is very much smaller.

We claim:
1. A process for the selective esterification of a tertiary alcohol(l) represented by a formula:
(Formula Removed)
by reacting an organic acid anhydride (II) represented by a formula:
(R4CO)20
to produce an organic tertiary ester (III) represented by a formula:
(Formula Removed)

wherein Rs is H or a chemical group other than hydrogen selected from the group consisting of halogen,NH2, NO2,OH,SO3H ; and R1, R2, and R4 are organic chemical groups, each comprising both carbon and hydrogen atoms selected from the group consisting of COOH, CnH2n+1, C6H5, substituted phenyl, OCn H2n+1, CnH2n-1, OCnH2n C6H5 & CnH2n C6H5 wherein, n is an integer having value greater than or equal to 1 using a reusable solid catalyst(IV), represented by a formula: MZy(c)/S

wherein, M is a chemical element selected from Ga (gallium), In (indium), Zn (zinc), Fe (iron) or a mixture of two or more thereof; Z is a halogen selected from Cl (chlorine), Br (bromine), I (iodine) and a mixture thereof; y is an integer having a value of 2 or 3, depending upon the valence requirement of M; S is a porous solid support on which MZy is deposited; and c is a loading of MZy on the support S expressed as the mmols of MZy deposited per gram of the support, S, in the range from about 0.01 mmol g"1 to about 10.0 mmol g"1; the process comprises:
i) contacting a mixture of tertiary alcohol (I) and an organic acid anhydride (II) optionally in presence of a non aqueous solvent with the fine particles of solid catalyst (IV) in a stirred batch reactor provided with a reflux water condenser at atmospheric pressure at the reaction conditions, such that the mole ratio of (II) to (I) is in the range from about 0.1 to about 10.0; the weight ratio of (IV) to (I + II) is in the range from about 0.005 to about 0.5; the reaction temperature is below about 80°C; and the reaction period is in the range from about 0.1 h to about 50 h; ii) removing the solid catalyst(IV) from the reaction mixture by filtration; and iv) reusing the separated solid catalyst for subsequent batch of the process.
2. A process as claimed in claim 1 wherein, the catalyst support, S, is cationic clay and
mesoporous crystalline material.
3. A process as claim in claim 1 wherein, M in the solid catalyst(IV) is In (indium) or Ga
(gallium) or a mixture thereof.
4. A process as claimed in claim 1 wherein, Z in the solid catalyst(IV) is Cl (chlorine).
5. A process as claimed in claim 1 wherein, the catalyst loading, c, is in the range from
about 0.02 mmol g-1 to about 2.5 mmol g-1.

6. A process as claim in claim 1 wherein, each of the chemical groups R1, R2, and R4 is
selected from methyl, ethyl, propyl, butyl and phenyl.
7. A process as claimed in claim 1 wherein, the mole ratio of acid anhydride(ll) to tertiary
alcohol(l) is in the range from 0.5 to 2.0.
8. A process as claimed in claim 1 wherein, the weight ratio of solid catalyst(IV) to the
reactants, acid anhydride(ll) and tertiary alcohol(l) is in the range from 0.01 to 0.2.
9. A process as claimed in claim 1 wherein, the reaction temperature is in the range from
10°Cto50°C.
10. A process as claimed in claim 1 wherein, the reaction period is in the range from 0.2h to
10 h.
11. A process for the selective esterification of tertiary alcohol by an acid anhydride using a
reusable solid catalyst substantially as herein described with reference to the examples.

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Patent Number

232085

Indian Patent Application Number

1076/DEL/2000

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

15-Mar-2009

Date of Filing

29-Nov-2000

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110 001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	VASANT RAMCHANDRA CHOUDHARY	LABORATORY PUNE-411 008,MAHARASHTRA,INDIA.
2	KSHUDIRAM MANTRI	LABORATORY PUNE-411 008,MAHARASHTRA,INDIA
3	SUMAN KUMAR JAVA	LABORATORY PUNE-411 008,MAHARASHTRA,INDIA

PCT International Classification Number

C08F 69/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA