Field of the Invention:
The present invention relates to the field of chemical science and more particularly the invention provides the direct esterification of alcohols with carboxylic acids comprising of protic acids adsorbed over solid support as a catalytic system, and use of perchloric acid and fluroboric acid adsorbed on silica, monmorilonite clays.
Background of the Invention:
Simple and polymeric esters are major products of the chemical industry, and there are a wide variety of processes for their production. These include direct esterification by reactions of alcohols with carboxylic acids or anhydrides as well as various interchange reactions including alcoholysis, in which the alcohol moiety of an ester is exchanged by another alcohol, acidolysis, in which the carboxylic acid moiety is exchanged by another carboxylic acid, and transesterification in which the alcohol moieties of two different esters exchange with each other. These interchange reactions will be collectively referred to as transesterification reactions.
In the absence of some type of catalyst, esterification and transesterification reactions tend to be quite slow. For this reason reactions are almost always catalyzed. Acids, bases, and transition metal based catalysts are all used in various applications. However, there are a number of problems associated with the use of acidic and basic catalysts. These catalysts often promote undesirable side reactions which can make it difficult to isolate a pure product without employing extensive purification procedures. Furthermore, they also often require neutralization at the end of the reaction as well as removal from the product. This again may entail extensive purification procedures.
Esterification processes that manufacture pharmaceuticals and chemicals are typically run in the liquid phase using homogeneous catalysts. These catalysts must be removed from the effluent and this entails extra processing steps as well as creating waste water. Often even trace amounts of metallic impurities

introduced from homogenous catalyst system of transition and rare earth metal impurities in unacceptable for the pharmaceutical products and drug syntheses processes are intolerable and, therefore, complex steps are often needed to reduce metallic content to acceptable levels. This results in additional processing steps, waste, and/or yield losses. Furthermore, homogeneous catalysts are often destroyed during removal. This "once through" utilization of the catalyst can result in unacceptably high manufacturing costs.
US 5827939 disclose the use of heteropolyacids for direct esterification process, which contains transition metal based catalyst. The invention reports the reaction condition at a temperature of 20 to 200 °C, inert atmosphere and general is 4-20 h with overall yield of 25-95%.
US 5183930 disclose the use of transition metal alkoxide catalyst over support. The invention report the high amount of catalyst 20-100 mol%, time require for the reaction is 10-450 h with overall yield of 12-67%.
It is therefore a need to develop an improved, economical, and simple catalytic process for esterification of long chain aliphatic alcohol using stoichiometric amounts of long chain aliphatic carboxylic acids.
Hence, the present invention is to provide a heterogeneous catalyst system which is easily recovered and recycled to the next reaction batch and eliminate extra processing steps.
Objects of the Invention:
An object of the present invention is to provide a cost effective moisture resistant, non-toxic and eco-friendly heterogeneous catalyst system which can be used multiple times for esterification of aliphatic alcohols using stoichiometric amounts of aliphatic carboxylic acid.
Another objective of the present invention is to provide process for preparing aforesaid catalyst.

One another object of the present invention is to provide a method for direct esterification of alcohols with carboxylic acid.
Summary of the Invention:
The present invention provides an improved catalytic process esterification of aliphatic alcohols using stoichiometric amounts of aliphatic carboxylic acids in presence of protic acid absorbed on solid support and more particularly perchloric acid on silica and montmorillonite clay and zeolite as a catalyst system.
Detailed Description of the Invention:
Accordingly, the present invention describes the direct esterification of alcohols with carboxylic acids comprising of protic acids adsorbed over solid support as a catalytic system, and use of perchloric acid and fluroboric acid adsorbed on silica, monmorilonite clays.
For purposes of this invention, the term carboxylic acid includes mono- and dicarboxylic acids. Any carboxylic acid ester can be used in the process according to the invention. Any ester made by reacting a saturated or unsaturated aliphatic carboxylic acid, a saturated or unsaturated aliphatic dicarboxylic acid, an aromatic carboxylic acid or an aromatic dicarboxylic acid, heteroaromatic carboxylic acid, cyclic carboxylic acid with a saturated or unsaturated aliphatic alcohol or aromatic alcohol, cyclic alcohol can be used. Exemplary monocarboxylic acids finding use in the present invention include, for example, dodecanoic or lauric, hexadecanoic or palmitic, oleic, linoleic, linolenic and octadecanoic or stearic.
The process is most useful in the preparation of alkyl esters of saturated and unsaturated carboxylic acids having from 2 to 18 carbon atoms and mixtures of such saturated and unsaturated carboxylic acids. While the alkyl portion of the ester can be any alkyl group having from 1 to 18 carbon atoms, the preferred alkyl groups are those having from 1 to 18 carbon atoms. Thus, the preferred esters are methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, octyl and stearyl esters of saturated and unsaturated carboxylic acids having from 2 to 18 carbon atoms.

The main embodiment of the invention is directed to an improved catalytic process esterification of aliphatic alcohols using stoichiometric amounts of aliphatic carboxylic acids in presence protic acid adsorbed on solid support, and more particularly, the catalyst system useful for direct esterification of alcohol with carboxylic acid comprising 1 to 10 % by weight of protic acid, 90 to 99 % by weight of silica, 90 to 99 % by weight of clays, 90 to 99 % by weight of neutral and acidic alumina, and 90 to 99 % by weight of zeolites and heated to the temperature between 80 to 100 °C for activation.
Yet another embodiment of the invention is catalyst system comprising 5 to 8 % by weight of protic acid, 92 to 95 % by weight clay, and 92 to 95 % by weight zeolites.
Still another embodiment of the invention is clays are selected from the group comprising montmorillorate/semectite, zeolites, kalonite, illite, and chlorite.
Yet another embodiment of the invention is clays are selected from semectite group.
Still another embodiment of the invention is clay used is montmorillonite clay.
Yet another embodiment of the invention is catalytic system contain perchloric acid or fluoroboric acid as active sites, which acts by electrophilic activation mechanism in which the electrophiles (carboxylic acids) are activated by the catalyst through coordinate bond formation followed by attack by the nucleophiles (alcohols) on the carbonyl carbon atom of the carboxylic acid complexed with the catalysts and the elimination of water molecule.
Still another embodiment of the invention is catalyst is heat treated at a temperature in the range of 80 to 100 °C before use for activating the same.
Yet another embodiment of the invention is 0.05 to 0.25 gm of said catalyst chemisorbs 1 to 10 % of reaction mixture in one cycle.

Still another embodiment of the invention is spent catalyst system containing protic acids is regenerated by filtration from the reaction mixture, followed by washing with DCM and activation of the recovered catalyst by vacuum drying at 100°C for 72 hrs.
Yet another embodiment of the invention is the regenerated catalyst treats and use for direct esterification of alcohol with carboxylic acid.
Still another embodiment of the invention is catalyst used in at least three chemisorptions and regeneration cycle.
Yet another embodiment of the invention is catalyst used in fixed bed reactor or fluidized reactor.
Still another embodiment of the invention is catalyst divided into fine particles having particle size in the range of mesh # 230 to 400 for used in fixed bed reactor.
Yet another embodiment of the invention is catalyst palletized or granulated to obtained pellets/granules having diameter in the range of mesh # 230 to 400 for used in fixed bed reactor.
Still another embodiment of the invention is a process for preparing a catalyst system useful for direct esterification of alcohol with carboxylic acid comprising the following steps:
a) suspending petroleum ether washed and dried silica in DCM and
magnetically stirred
b) adding 70% aqueous protic acid solution dropwise to step(a) and
then mixture was magnetically stirred for 2 hrs
c) removal of solvent under rotary vacuum evaporation; and
d) drying the residue at 100°C for 72 hrsto afford the adsorbed
catalyst.

Yet another embodiment of the invention is 0.25 gm of catalyst system thus chemisorbs 300 to 1000 mg of reaction mixture.
Still another embodiment of the invention is catalyst thus obtained has pH value in the range of 5 to 6.
Yet another embodiment of the invention is catalyst thus obtained is used in fixed bed reactor.
Still another embodiment of the invention is catalyst thus obtained contain perchloric acid or fluoroboric acid as active sites.
Yet another embodiment of the invention is catalyst thus obtained is pulverized into fine particles for use in fixed bed reactors.
Still another embodiment of the invention is a method for direct esterification of alcohol with carboxylic acid using the catalyst system comprising the following steps:
a) adding alcohol, carboxylic acid and catalyst composition in a
round bottom flask and magnetically stirred at 80°C till complete
consumption of acid
b) diluting the mixture of step (a) with solvent and filtered to
remove the catalyst composition; and
c) concentrating the filtrate under rotary vacuum evaporation and
obtained product.
Yet another embodiment of the invention is directed to an improved catalytic process for esterification of aryl aliphatic alcohols using stoichiometric amounts of aryl aliphatic carboxylic acids in presence of HC1O4 on SiO2 as catalyst.
Still another embodiment of the invention is directed to an improved catalytic process for esterification of cyclic aliphatic alcohols using stoichiometric amounts of aryl aliphatic carboxylic acids in presence of HC1O4 on SiO2 as catalyst.

Yet another embodiment of the invention is directed to an improved catalytic process esterification of aliphatic alcohols using stoichiometrie amounts of aryl aliphatic carboxylic acids in presence of HC1O4 on SiO2 as catalyst.
Still another embodiment of the invention is directed to an improved catalytic process esterification of aliphatic alcohols using stoichiometrie amounts of aryl carboxylic acids in presence of HC1O4 on SiO2 as catalyst.
Yet another embodiment of the invention is directed to an improved catalytic process esterification of aliphatic alcohols using stoichiometrie amounts of hetero-aryl carboxylic acids in presence of HC1O4 on SiO2 as catalyst.
Still another embodiment of the invention is directed to an improved catalytic process esterification of allylic and propargyllic alcohols using stoichiometrie amounts of aryl aliphatic carboxylic acids in presence of HC1O4 on SiO2 as catalyst.
Yet another embodiment of the invention is directed to an improved catalytic process esterification of long chain aliphatic alcohols using stoichiometrie amounts of long chain aliphatic carboxylic acids in presence of HC1O4 on SiO2 as catalyst.
Still another embodiment of the invention is directed to an improved catalytic process for esterification of aliphatic alcohols using stoichiometrie amounts of aliphatic carboxylic acids in presence of HCIO4 on SiO2 as catalyst for preparing flavoring agents having ester functional group.
Yet another embodiment of the invention is directed to an improved catalytic process for esterification of polyethylene glycols (PEGs) of various lengths using stoichiometrie amounts of aliphatic carboxylic acids in presence of HC1O4 on SiO2 as catalyst.
Still another embodiment of the invention is directed to obtain a feasible reaction condition with different solvents in the presence of HC1O4 on SiO2 and HBF4 on
SiO2 as catalyst. The solvent for reaction is selected from a group consisting of aprotic polar solvents such as acetonitrile (CH3CN) and nitromethane (CH3NO2), aromatic solvents such as toluene, non-polar solvents like hexane and ethereal solvents such as diethyl ether, and THF (tetrahydrofuran).
Yet another embodiment of the invention is process of acylation of alcohols with carboxylic acids using catalytic amount of catalyst system derived under milder conditions preferably at higher temperature 40 to 90 °C and under solvent free conditions.
Still another embodiment of the invention is alcohols used are either a chiral saturated aliphatic or allylic, propagyllic or aromatic alcohols, long chain alcohols and chiral alcohols along with PEGs.
Yet another embodiment of the invention is carboxylic acids used are aromatic alkyl carboxylic acids, aromatic carboxylic acids, aliphatic acyclic carboxylic acids, aliphatic cyclic carboxylic acids, long chain carboxylic acids and dicarboxylic acids.
Still another embodiment of the invention is catalysts used are either HC1O4 and/or HBF4 adsorbed on silica gel and other supports.
Yet another embodiment of the invention is solid supports used are neutral and acidic alumina, clays like K-10 and zeolites.
Still another embodiment of the invention is catalyst used in the present reaction is in the range from 0.1 to 10 mol % overall concentration.
Yet another embodiment of the invention is the reaction temperature can be selected from 40°C to 90°C.
Still another embodiment of the invention is solvent is selected from a group consisting of chlorinated solvent such as methylene chloride (CH2Cl2), aprotic polar solvent such as acetonitrile (CH3CN) and nitromethane (CH3NO2), aromatic

solvent such as toluene and ethereal solvent such as diethyl ether, and THF (tetrahy dr ofuran).
The invention is illustrated by the following examples which are only meant to illustrate the invention and not act as limitations. All embodiments apparent to a process their in the art are deemed to fall within the scope of the present invention.
Examples: Example 1 PROCEDURE FOR PREPARATION OF CATALYTIC SYSTEM
Preparation of HClO4-SiO2: To a magnetically stirred suspension of 26.7 gm of silica gel (mesh # 230-400), previously washed with petroleum ether and dried, in 75 mL of DCM in a 250 mL rb flask was added 2.145 gm of 70% aqueous HC1O4 solution dropwise and the mixture was stirred magnetically for 2 h. The solvent was removed under rotary vacuum evaporation and the residue was subjected to vacuum drying at 100°C for 72 h to afford the adsorbed catalyst HClO4-SiO2 (0.5 mmol of HCIO4 gm-1). Following the same procedure, 0.5 mmol HC1O4 gm-1 adsorbed on different supports such as acidic alumina [(Al2O3 (A)], neutral alumina [(Al2O3 (N)], K-10, and titanium dioxide (TiO2) were prepared.
Preparation of HBF4-SiO2: To a magnetically stirred suspension of 26.7 gm of silica gel (mesh # 230-400), previously washed with petroleum ether and dried, in 75 mL of DCM in a 250 mL rb flask was added 3.3 gm of 40% aqueous HBF4 solution was added dropwise and the mixture was stirred magnetically for 2 h. The solvent was removed under rotary vacuum evaporation and the residue was subjected to vacuum drying at 100°C for 72 h to afford the adsorbed catalyst HBF4-SiO2 (0.5 mmol of HBF4 gm-1).
Example 2
GENERAL PROCEDURE FOR ESTERIFICATION REACTION
A mixture of octanol (0.65ml, 5 mmol), phenyl butyric acid (840 mg, 5 mmol, 1 equiv.) and HClO4:SiO2 (1 mol%, 250 mg) in a 25 mL round bottom flask was stirred magnetically at 80°C till complete consumption of phenyl butyric acid (3.5 h, Thin Layer Chromatography). The reaction mixture was diluted with EtOAc (25 ml) and filtered to remove the catalyst. The filtrate was concentrated under rotary vacuum evaporation and the residue was subjected to column chromatography (60-120 mesh silica gel, 2:98 EtOAc: Hexane) to afford the pure product (94 %).
Example 3
Aromatic Acids
Hydrocinnamic acid was chosen as a substrate since aryl alkyl acids are relatively
'easy' substrates for esterification. It is easy to monitor the course of the reaction
as the compound is visible in U.V. light. Also the standardization was done using
this substrate only as it has been previously reported many a times in the
literature.
Various kinds of alcohols were acylated using hydrocinnamic acid as an acylating agent (scheme 5). These included primary aliphatic alcohols like n-butanol and 1-octanol, unsaturated primary alcohols like allyl and propargyl alcohol, secondary alcohols like 2-octanol and cyclohexanol. Benzyl alcohol was taken as a representative for aromatic class of alcohols and esterified with this acid. Menthol as a chiral alcohol was also acylated using hydrocinnamic acid (table 7). The results obtained were highly encouraging to carry out the reactions with other substrates.
Scheme 1
(Scheme Removed)
Table 1
(Table Removed)
Removed)
Example 4
Following successful reactions with hydrocinnamic acid, it was decided to check the generallity of the reaction by using other aryl alkyl acids of increasing and decreasing carbon chain length. A few representative alcohols which were earlier acylated with hydrocinnamic acid were acylated with these acids. Allyl alcohol, 1-octanol and benzyl alcohol were successfully acylated with phenyl acetic acid.
Scheme 2

(Scheme Removed)
Table 2
(Table Removed)
Example 5
Similar reactions were carried out with phenyl butyric acid, an aryl alkyl alcohol
with increased carbon chain length (scheme 3). Propargyl alcohol and cyclphexanol along with allyl alcohol and octanol were successfully acylated with phenyl butyric acid. A reaction with phenethyl alcohol was also set up. In fact, the reaction times observed were even shorter than the ones with hydrocinnamic acid.
Scheme 3

(Scheme Removed)
Table 3

(Table Removed)

Example 6
Consequently, reactions were carried out using benzoic acid as acylating agent (scheme 4). Aryl car boxy lie acids are weak electrophiles and are not easily activated. This explains the longer duration of reactions in acylation of alcohols previously acylated with other acids. Longer reaction times were also observed for acylation of 2-octanol. However, the yields obtained were still good without any side product formation.
Scheme 4

(Scheme Removed)
Table 4

(Table Removed)
Example 7
Subsequently, substituted benzoic acid derivatives were used as acylating agents
for esterification of alcohols. Both electron donating (scheme 5) and electron
withdrawing substitutes (scheme 6) were used for this purpose. The results
obtained were encouraging. High yields were obtained with both the acylating
agents.
Scheme 5

(Scheme Removed)
Table 5

(Table Removed)
Scheme 6
(Scheme Removed)
Table 6
(Table Removed)

Example 8
Next, cinnamic acid, an unsaturated aryl aliphatic acid was also used for acylation of alcohols which were earlier successfully acylated with other acids (scheme 7). The accomplishment of complete acylation of alcohols with cinnamic acid is an indication of the mildness of the catalyst. Both the acylating agent, cinnamic acid in this case, as well as the alcohols, allyl alcohol and propargyl alcohol, are acid sensitive substrates which can easily undergo rearrangement reactions. But they were acylated without the formation of any side product. Scheme 7

(SchemeRemoved)
Table 7

(Table Removed)
Example 9
Subsequently, heterocyclic acids were investigated as acylating agents. Thiophene car boxy lic acid was first used as acylating agent (scheme 8). Although the yield obtained was not very high, still no side product formation was seen. The reaction times observed were also slightly long. Scheme 8

(SchemeRemoved)
Table 8

(Table Removed)
Furan carboxylic acid was next investigated (scheme 13). Allyl alcohol, propargyl alcohol and n-butanol were taken as substrates. The yields obtained were better than thiophene carboxylic acid and in shorter duration. Scheme 9

(SchemeRemoved)
Table 9

(Table Removed)
Example 10
Next, we investigated the efficiency of the developed protocol for acylation of alcohols with aliphatic carboxylic acids. Both open chain aliphatic acids like caproic acid (scheme 10) and cyclic carboxylic acids having 5, 6, 7 membered ring systems were investigated. All the reactions were successfully completed. Scheme 10
(SchemeRemoved)
Table 10

(Table Removed)

Scheme 11

(SchemeRemoved)
Table 11

(Table Removed)
Table 12

(Table Removed)
Table 14 Prodrugs
(Table Removed)
Table 15 Peglytion

(Table Removed)
3-Phenyl-propionic acid allyl ester:
Clear oily liquid, Yield 92 %; IR (Neat) v: 1739 cm-1; 1H NMR (CDCl3, 300 MHz) δ
ppm: 2.64 (t, / = Hz, 2H), 2.95 (t, / = Hz, 2H), 4.56 (d, / =5.24 Hz, 2H), 5.21 (q, / = 33.96 Hz, 2H), 5.94-5.81 (m,lH), 7.18-7.29 (m, 5H). MS (El): m/z 190 (M+).
3-Phenyl-propionic acid prop-2-ynyl ester:
Clear oily liquid, Yield 87 %; IR (Neat) v: 1743 cm-1; 1H NMR (CDCl3, 300 MHz) δ ppm: 2.48 (t, / = 2.47 Hz, 1H), 2.65 (q, / = 8.14 Hz, 2H), 2.94 (t, / = 2.29 Hz, 2H), 4.65 (d, / =2.52 Hz, 2H), 7.16-7.29 (m, 5H). 13C NMR (CDCl3, 75 MHz): 30.3, 31.3, 36.1, 52.5, 75.5, 77.3, 77.8, 78.1, 78.3,126.9,129.1,140.8,172.5. MS (El): m/z 188 (M+).
3-Phenyl-propionic acid butyl ester:
Clear oily liquid, Yield 94 %; IR (Neat) v: 1735 cm-1;1H NMR (CDCl3, 300 MHz)δ ppm: 0.91 (t, / = 7.80 Hz, 3H), 1.21-1.39 (m, 2H), 1.52-1.61 (m, 2H), 2.61 (t, / = 7.82 Hz, 2H), 2.94 (t, J = 7.79 Hz, 2H), 4.06 (t, / = 6.64 Hz, 2H), 7.16-7.29 (m, 5H). MS (El): m/z 206 (M+).
3-Phenyl-propionic acid octyl ester:
Clear oily liquid, Yield 92 %; IR (Neat) v: 1736 cm-1;1H NMR (CDCl3, 300 MHz)δ ppm: 0.88 (t, / =6.63 Hz, 3H), 1.27 (s,10H), 1.58 (t, / = 6.63 Hz, 2H), 2.61 (t, / = 7.80 Hz, 2H), 2.94 (t, / = 7.59 Hz, 2H), 4.05 (t, / = 6.57 Hz, 2H), 7.16-7.3 (m, 5H). MS (El): m/z 262 (M+).
Phenyl-acetic acid allyl ester:
Clear oily liquid, Yield 91 %; IR (Neat) v: 1738 cm-1; 1H NMR (CDCl3, 300 MHz)δ ppm: 3.87 (s, 2H), 4.80-4.89 (m, 2H), 5.41-5.52 (m, 2H), 6.06-6.19 (m, 1H), 7.44-7.57 (m, 5H). MS (El): m/z 216 (M+).
Phenyl-acetic acid octyl ester:
Clear oily liquid, Yield 89 %; IR (Neat) v: 1738 cm-1; 1H NMR (CDCl3, 300 MHz)δ ppm: 0.88 (t, / =6.70 Hz, 3H), 1.26 (s,10H), 1.55-1.65 (m, 2H), 3.60 (s, 2H), 4.07 (t, / = 6.70 Hz, 2H), 7.18-7.34 (m, 5H). MS (El): m/z 248 (M+).
Cyclohexanecarboxylic acid octyl ester:
Clear oily liquid, Yield 93 %; IR (Neat) v: 1723 cm-1; 1H NMR (CDCl3, 300 MHz)δ ppm: 0.88 (t, / =6.60 Hz, 3H), 1.2-1.5 (m, 15H), 1.61 (t, / =6.60 Hz, 3H), 1.72-1.76 (m, 2H),1.87-1.91 (m, 2H), 2.23-2.31 (m, 1H), 4.04 (t, / = 3.42 Hz, 2H); 13C NMR (CDCl3, 75 MHz): 14.5, 23.1, 26.0, 26.3, 26.4, 29.2, 29.5, 29.7, 32.3, 43.8, 64.7, 176.5. MS (El): m/z 240 (M+).
Hexanoic acid octyl ester:
Clear oily liquid, Yield 84 %; IR (Neat) v: 1733 cm-1; 1H NMR (CDCl3, 300 MHz)δ ppm: 0.86-0.92 (m, 6H), 1.28-1.31 ( m, 14 H), 1.58-1.67 (m, 4H), 2.29 (t, / = 7.50 Hz, 2H), 4.06 (t, / = 6.69 Hz, 2H). 13C NMR (CDCl3, 75 MHz)δ ppm: 14.5, 22.8, 23.1, 25.2, 26.4, 29.2, 29.7, 30.2, 31.8, 32.1,32.3,34.8, 64.8,174.3. MS (El): m/z 228 (M+).
3-Phenyl-propionic acid cyclohexyl ester:
Clear oily liquid, Yield 91 %; IR (Neat) v: 1730 cm-1; IH NMR (CDCl3, 300 MHz) δ ppm : 1.20-1.38 (m, 6H), 1.42-1.53 (m, IH), 1.66-1.80 (m, 4H), 2.58 (t, / = 7.26 Hz, 2H), 2.93 (t, / = 7.56 Hz, 2H), 4.71-4.78 (m,lH), 7.14-7.28 (m, 5H). 13C NMR (CDCl3, 75 MHz)δ ppm: 24.3, 25.0, 31.67, 32.2, 36.8, 73.2, 126.7, 128.9, 129.0,. 141.2, 172.9; MS (El): m/z 232 (M+).
Cycloheptanecarboxylic acid octyl ester:
Clear oily liquid, Yield 91 %; IR (Neat) v: 1733 crrr1; IH NMR (CDCl3, 300 MHz) δ ppm : 0.88 (t, / = 6.39 Hz, 3H), 1.28-1.31 ( m, 11 H), 1.47-1.71 (m, 11H), 1.82-1.96 (m, 2H), 2.43-2.49 (m, IH), 4.02-4.09 (m, 2H). 13C NMR (CDCl3, 75 MHz) δ ppm: 14.6, 21.5, 23.2, 26.5, 26.9, 28.8, 29.2, 29.7, 31.4, 32.3, 45.6, 64.8, 65.2,177.7. MS (El): m/z 255 (M+).
Cyclopentanecarboxylic acid octyl ester:
Clear oily liquid, Yield 89 %; IR (Neat) v: 1733 cm-1; IH NMR (CDCl3, 300 MHz) δ ppm: 0.88 (t, / = 6.89 Hz, 3H), 1.28-1.43 (m, 10 H), 1.57-1.72 (m, 6H), 1.76-1.89 (m, 4H), 2.66-2.74 (m, IH), 4.06 (t, / = 6.67 Hz, 2H). 13C NMR (CDCl3, 75 MHz) δppm: 14.6, 23.1, 26.3, 26.4,29.2, 29.7,30.5,32.3,44.4, 64.9,177.6. MS (El): m/z 227 (M+).
4-Phenyl-butyric acid allyl ester:
Clear oily liquid, Yield 93 %; IR (Neat) v: 1735 cm-1;IH NMR (CDCl3, 300 MHz) δ ppm : 1.91-2.01 (m, 2H), 2.35 (t, / = 7.45 Hz, 2H), 2.65 (t, / = 7.55 Hz, 2H), 4.56 (d, / = 5.66 Hz, 2H), 5.20-5.33 (m, 2H), 5.84-5.97 (m, IH), 7.16-7.30 (m, 5H). MS (El): m/z 204 (M+).
4-Phenyl-butyric acid octyl ester:
Clear oily liquid, Yield 94 %; IR (Neat) v: 1739 cm-1; IH NMR (CDCl3, 300 MHz) δ ppm: 0.88 (t, / =6.49 Hz, 3H), 1.28-1.43 ( m, 10 H), 1.56-1.63 (m, 2H), 1.90-2.02 (m, 2H), 2.31 (t,} = 7.44 Hz, 2H), 2.64 (t, / = 7.59 Hz, 2H), 4.05 (t, / = 6.7 Hz, 2H), 7.15-7.29 (m, 5H). 13C NMR (CDCl3 75 MHz)δ ppm : 14.7, 23.2, 26.5, 27.2, 29.2, 29.8, 34.2, 35.7, 65.06,126.5,128.9,129.1,142.0,174.1. MS (El): m/z 276 (M+).
4-Phenyl-butyric acid prop-2-ynyl ester:
Clear oily liquid, Yield 84 %; IR (Neat) v: 1742 cm-1;1H NMR (CDC13, 300 MHz)δ ppm: 1.96-2.03 (m, 2H), 2.40 (t, / = 7.44 Hz, 2H), 2.51 (t, / = 2.29 Hz, 1H), 2.69 (t, / = 7.27 Hz, 2H), 4.69 (d, / = 2.31 Hz, 2H), 7.20-7.34 (m, 5H); 13C NMR (CDCl3, 75 MHz) δ ppm : 27.0, 30.3, 33.8, 35.6, 52.4, 75.5, 126.6, 129.0, 129.1, 141.8, 173.1. MS (El): m/z 202 (M+).
4-Phenyl-butyric acid cyclohexyl ester
Clear oily liquid, Yield 91 %; IR (Neat) v: 1729 cm-1; 1H NMR (CDCk, 300 MHz) δ ppm: 1.26-1.54 (m, 6H), 1.70- 1.98 (m, 6H), 2.28 (t, / = 7.42 Hz, 2H), 2.63 (t, / = 7.67 Hz, 2H), 4.76 (t, / = 4.02 Hz, 1H), 7.15-7.28 (m, 5H). 13C NMR (CDCl3, 75 MHz) δ ppm: 24.4, 26.00, 27.3, 30.3, 32.3, 34.1, 34.6, 35.7, 73.00, 126.5, 129.0, 129.1, 142.1, 173.4. MS (El): m/z 246 (M+).
4-Phenyl-butyric acid phenethyl ester
Clear oily liquid, Yield 90 %; IR (Neat) v: 1733cm-1; 1H NMR (CDCl3), 300 MHz) δ
ppm: 2.18-2.27 (m, 2H), 2.60 (t, / = 7.32, 2H), 2.90 (t, / = 7.47, 2H), 3.22 (t, / = 6.93,
2H), 4.57- 4.61(m, 2H), 7.43-7.59 (m, 5H). 13C NMR (CDCk, 75 MHz):27.1, 34.2,
35.8, 65.4, 126.7, 127.2, 128.1, 129.1, 129.6, 138.5, 142.1, 174.0. MS (El) m/z: 268
(M+).
3-Phenyl-acrylic acid allyl ester
Clear oily liquid, Yield 91 %; IR (Neat) v: 1717 cm-1; 1H NMR (CDCl3, 300 MHz) δ ppm: 4.68-4.70 (m, 2H), 5.23-5.39 (m, 2H), 5.91-6.04 (m, 1H) 6.44 (d, / = 16.03 Hz, 1H), 7.32-7.34 (m, 3H), 7.46-7.50 (m, 2H), 7.70 (d, / = 16.04 Hz, 1H). 13C NMR (CDCk, 75 MHz) δ ppm: 65.7,118.4,128.7,129.4,130.9,132.9,134.9,145.6,167.0.). MS (El): m/z 188 (M+).
3-Phenyl-acrylic acid prop-2-ynyl ester:
Clear oily liquid, Yield 86 %; IR (Neat) v: 1724 cm-1; 1H NMR (CDCl3, 300 MHz) δ
ppm: 2.51 (t, / = 2.43 Hz, 1H), 4.80 (d, / = 2.52 Hz, 2H), 6.45 (d, / = 16.01 Hz, 1H),
7.36-7.38 (m, 3H), 7.50-7.53 (m, 2H), 7.73 (d, / = 16.03 Hz, 1H). MS (El): m/z 186
(M+).
3-Phenyl-acrylic acid butyl ester
Clear oily liquid, Yield 92 %; IR (Neat) v: 1713 cm-1;1H NMR (CDCl3, 300 MHz)δ ppm: 0.96 (t, / = 7.34 Hz, 3H), 1.38-1.5 (m, 2H), 1.64-1.74 (m, 2H), 4.21 (t, / = 6.68Hz, 2H), 6.44 (d, / = 16.04 Hz, 1H), 7.36-7.38 (m, 3H), 7.50-7.53 (m, 2H), 7.68 (d, / = 16.03 Hz, 1H). MS (El): m/z 204 (M+).
Benzole acid allyl ester
Clear oily liquid, Yield 92 %; IR (Neat) v: 1723 cm-1; 1H NMR (CDCl3, 300 MHz) δ ppm: 4.80 (d, / = 5.57 Hz, 2H), 5.25 (dd, J1,2= 0.90 Hz, J1,3 = 10.49 Hz, 1H), 5.38 (dd, J1/2= 1.31 Hz, J13= 17.24 Hz, 1H), 5.95-6.08 (m, 1H), 7.36-7.41 (m, 2H), 7.48-7.53 (m, 1H), 8.05(d, / = 8.49 Hz, 2H). 13C NMR (CDCl3, 75 MHz) δppm: 30.3, 66.0,118.6, 128.5,128.9,130.2,130.7,132.8,133.5,166.6. MS (El): m/z 162 (M+).
Benzoic acid prop-2-ynyl ester
Clear oily liquid, Yield 84 %; IR (Neat) v: 1725 cm-1; 1H NMR (CDCl3 300 MHz)δ ppm: 2.55 (t, / = 2.34 Hz, 1H), 4.89 (d, / = 2.33 Hz, 2H), 7.38-7.43 (m, 2H), 7.51-7.56 (m, 1H), 8.04 (d, / = 7.57 Hz, 2H);13C NMR (CDCl3 75 MHz)δ ppm: 52.9, 75.7, 78.4,129.0,130.0,130.3,133.8,166.2; MS (El): m/z 160 (M+).
Benzoic acid butyl ester:
Clear oily liquid, Yield 93 %; IR (Neat) v: 1721 cm-1; 1H NMR (CDCl3, 300 MHz) δ ppm: 0.97 (t, / =7.36 Hz, 3H), 1.41-1.53 (m, 2H), 1.69-1.79 (m, 2H), 4.32 (t, / = 6.59 Hz, 2H), 7.38-7.43 (m, 2H), 7.49-7.54 (m, 1H), 8.04 (d, / = 8.61 Hz, 2H). 13C NMR (CDCl3, 75 MHz) δ ppm: 14.3,19.8, 31.3, 65.3,128.8, 130.0,131.1,133.3,167.1. MS (El): m/z 178 (M+).
Benzoic acid octyl ester
Clear oily liquid, Yield 91 %; IR (Neat) v: 1720 cm-1; 1H NMR (CDCl3, 300 MHz) δ ppm: 0.88 (t, / =6.65 Hz, 3H), 1.28- 1.43 (m, 10 H), 1.71- 1.82 (m, 2H), 4.31 (t, / =6.57 Hz, 2H), 7.42 (t, / = 7.48 Hz, 2H), 7.5-7.55 (m, 1H), 8.04 (d, / = 8.6 Hz, 2H). 13C NMR (CDCl3, 75 MHz) δ ppm: 14.6, 23.2, 26.6, 29.3, 29.7, 29.8, 30.3, 32.3, 65.6, 128.8,130.1,131.1,133.3,167.2. MS (El): m/z 235 (M+)
Benzole acid 1-methyl-heptyl ester
Clear oily liquid, Yield 87 %; IR (Neat) v: 1721 cm-1; 1H NMR (CDCL3, 300 MHz) δ
ppm: 0.88(t, J = 6.66 Hz, 3H), 1.27-1.41 (m, 11H), 1.54-1.63 (m, 1H), 1.68-1.75 (m,
1H), 5.13-5.19 (m, 1H), 7.38-7.43 (m, 2H), 7.49-7.54 (m,lH), 8.05 (d, / = 7.60 Hz,
2H).
4-Methyl-benzoic acid allyl ester:
Clear oily liquid, Yield 92 %; IR (Neat) v: 1716 cm-1; 1H NMR (CDCL3, 300 MHz) δ ppm: 2.38 (s, 3H), 4.79-4.81 (m, 2H), 5.24-5.28 (m, 1H), 5.42-5.36 (m,lH), 5.98-6.09 (m, 1H), 7.22 (d, / = 8.17 Hz, 2H), 7.95 (d, / = 8.20 Hz, 2H). 13C NMR (CDCl3, 75 MHz) δ ppm: 22.2, 65.9,118.5,128.0,128.9,129.6,130.2,133.0,144.2,166.8. MS (El): m/z 176 (M+).
4-Methyl-benzoic acid butyl ester:
Clear oily liquid, Yield 94 %; IR (Neat) v: 1715 cm-1; 1H NMR (CDCl3, 300 MHz) δ ppm: 0.97 (t, / =7.37 Hz, 3H), 1.41-1.53 (m, 2H), 1.69-1.78 (m, 2H), 2.38 (s, 3H), 4.30 (t, / = 6.60 Hz, 2H), 7.21 (d, / = 8.06 Hz, 2H), 7.93 (d, / = 8.18 Hz, 2H). 13C NMR (CDCl3, 75 MHz)δ ppm: 14.3,19.8, 22.1, 31.4, 65.1,128.4,129.5,130.1,143.9,167.2. MS (El): m/z 192 (M+).
4-Chloro-benzoic acid prop-2-ynyl ester:
Clear oily liquid, Yield 62 %; IR (Neat) v: 1727 cm-1; 1H NMR (CDCl3, 300 MHz) δ ppm: 2.54 (t, / = 2.41 Hz, 1H), 4.92 (d, / = 2.47 Hz, 2H), 7.41 (d, / = 8.57 Hz, 2H), 7.99 (d, / = 8.56 Hz, 2H). MS (El): m/z 194 (M+).
4-Chloro-benzoic acid butyl ester:
Clear oily liquid, Yield 78 %; IR (Neat) v: 1716 cm-1; m NMR (CDCl3, 300 MHz)δ ppm: 0.98 (t, / =7.33 Hz, 3H), 1.41-1.53 (m, 2H), 1.69-1.79 (m, 2H), 4.30-4.40 (m, 2H), 7.39 (d, / = 8.52 Hz, 2H), 7.97 (d, / = 8.54 Hz, 2H). 13C NMR (CDCl3, 75 MHz) δppm: 14.3, 19.8, 31.3, 65.6, 124.0,129.2,129.5,131.2, 131.5, 139.8, 166.3. MS (El): m/z 212 (M+).
Thiophene-2-car boxy lie acid allyl ester:
Clear oily liquid, Yield 52 %; IR (Neat) v. 1712 cm-1; 1H NMR (CDCl3, 300 MHz) δ ppm: 4.78-4.80 (m, 2H), 5.26-5.30 (m, IH), 5.37-5.44(m,lH), 5.95-6.08 (m, IH), 7.08-7.11 (m, IH), 7.55-7.57 (m, IH), 7.81-7.83 (m, IH); MS (El): m/z 168 (M+).
Thiophene-2-carboxylic acid butyl ester
Clear oily liquid, Yield 73 %; IR (Neat) v: 1711 cm-1; 1H NMR (CDC13, 300 MHz) δ ppm: 0.97 (t, J =7.36 Hz, 3H), 1.39-1.51 (m, 2H), 1.67-1.77 (m, 2H), 4.29 (t,J = 6.6 Hz, 2H), 7.07 (t, J= 4.35 Hz, IH), 7.52 (d, / = 4.87 Hz, IH), 7.78 (d,J = 3.63 Hz, IH). MS (El): m/z 184 (M+).
Furan-2-carboxylic acid allyl ester
Clear oily liquid, Yield 84 %; IR (Neat) v: 1731 cm-1; 1H NMR (CDCl3, 300 MHz) δ ppm: 4.8 (d, J = 3.63 Hz, 2H), 5.27-5.43 (m, 2H), 5.95-6.08 (m, IH), 6.50-6.52 (m, IH), 7.20 (d, J = 3.46 Hz, IH), 7.58 (s, IH).
Furan-2-carboxylic acid butyl ester
Clear oily liquid, Yield 87 %; IR (Neat) v: 1729 cm-1; 1H NMR (CDCl3, 300 MHz) δ ppm: 0.97 (t, J =7.36 Hz, 3H), 1.39-1.51 (m, 2H), 1.69-1.78 (m, 2H), 4.31 (t, / = 6.65 Hz, 2H), 6.49-6.51 (m, IH), 7.16 (d, / = 3.38 Hz, IH), 7.57(s, IH). 13C NMR (CDCL3, 75 MHz) δ ppm: 14.2,19.6, 29.8, 65.2,112.2,118.1,145.4,146.6,159.3; MS (El) m/z : 168 (M+).
Furan-2-carboxylic acid prop-2-ynyl ester:
Clear oily liquid, Yield 69 %; IR (Neat) v: 1720 cm-1; 1H NMR (CDCL3, 300 MHz) δ ppm: 2.54 (t,J= 2.42 Hz, IH), 4.90 (d, / = 2.45 Hz, 2H), 6.50-6.54 (m, IH), 7.26 (d, / = 3.40 Hz, IH), 7.61 (s, IH); MS (El) m/z :150 (M+).
3-Phenyl-propionic acid 2-isopropyl-5-methyl-cyclohexyl ester: Clear oily liquid, Yield 69 %; IR (Neat) v: 1732 cm-1; 1H NMR (CDCL3, 300 MHz) δ ppm: 0.70 (d, J = 6.92 Hz, 2H), 0.83-0.93 (m, 14H), .097-1.01 (m,), 1.26-1.32 (m, 3H), 1.61-1.69 (m, 3H), 1.91-1.95 (m, IH), 2.60 (t, / = 7.73 Hz, 2H), 2.94 (t, / = 7.60 Hz, 2H), 4.63-4.71 (m, IH), 7.15-7.29 (m, 5H).
Acetic acid octyl ester
Clear oily liquid, Yield 90 %; IR (Neat) v: 1739 cm-1; 1H NMR (CDCl3), 300 MHz) δ ppm: 0.87 (t, / = 3.46, 3H), 1.28 (s, 10H), 1.60 (m, 2H), 2.04 (s, 3H), 4.02-4.07 (m, 2H). 13C NMR (CDCb, 75 MHz): 14.5, 21.4, 23.1, 26.4, 29.1, 29.7, 32.3, 65.1, 171.6. MS (El) m/z: 172 (M+).
3-Phenyl-acrylic acid methyl ester
Clear oily liquid, Yield 88 %; IR (Neat) v: 1718 cm-1;1H NMR (CDCl3), 300 MHz) δ ppm: 3.80 (s, 3H), 6.44 (d, J = 16.00,1H), 7.38 (t, / = 3.16, 3H), 7.51- 7.54 (m, 2H), 7.70 (d, J = 16.02,1H). MS (El) m/z: 162 (M+).
Phenyl-acetic acid phenethyl ester
Clear oily liquid, Yield 94 %; IR (Neat) v: 1737cm-1; 1H NMR (CDCl3), 300 MHz) δ ppm: 2.95-3.03 (m, 2H), 3.66-3.75 (m, 2H), 4.34-4.40 (m, 2H), 7.20-7.41 (m, 10H). MS (El) m/z: 240 (M+).
Acetic acid phenethyl ester
Clear oily liquid, Yield 92 %; IR (Neat) v: 1740 cm-1;1H NMR (CDCl3), 300 MHz) δ ppm: 1.99 (s, 3H), 2.90 (t, / = 7.07, 2H), 4.26 (t, / = 7.08, 2H), 7.17-7.30 (m, 5H). MS (El) m/z: 164 (M+).
Octadecanoic acid octadecyl ester
Low melting solid, Yield 92 %; IR (Neat) v: 1736 cm-1; 1H NMR (CDCl3), 300 MHz)
δppm: 0.81 (t, / = 6.46, 6H), 1.19 (s, 60 H), 1.52 (m, 4H), 2.22 (m, 2H), 3.98 (s, 2H). MS (El) m/z: 536 (M+).
Hexadecanoic acid octadecyl ester
Low melting solid, Yield 94 %; IR (Neat) v: 1732 cm-1;; 1H NMR (CDCl3), 300 MHz)
δ ppm: 0.87 (t, / = 6.46, 6H), 1.22 (s, 62 H), 1.56 (m, 4H), 2.27 (m, 2H), 4.04 (s, 2H).
MS (El) m/z: 508 (M+).
Octadecanoic acid hexadecyl ester
Low melting solid, Yield 91 %; IR (Neat) v: 1735 cm-1; ; 1H NMR (CDCl3), 300 MHz) δ ppm: 0.87 (t, / = 6.46, 6H), 1.25 (s, 54 H), 1.60 (m, 4H), 2.27 (m, 2H), 4.04 (s, 2H). MS (El) m/z: 508 (M+).
2-(4-Isobutyl-phenyl)-propionic acid isopropyl ester
Clear oily Uquid, Yield 92 %; IR (Neat) v: 1735 cm-1; 1H NMR (CDCl3), 300 MHz) δ ppm: 0.88 (d, J = 6.6, 6H), 1.11-1.22 (m, 6H), 1.46 (d, J = 7.1, 3H), 1.79 (m, IH), 2.43 (d, 7 = 7.2, 2H), 3.60-3.67 (m, IH), 4.94-5.02 (m, IH), 7.07 (d, J = 8.0, 2H), 7.19 (d, J = 8.0,2H). MS (El) ra/z: 248 (M+).
2-(4-Isobutyl-phenyl)-propionic acid butyl ester
Clear oily Uquid, Yield 92 %; IR (Neat) v: 1728 cm-1; 1H NMR (CDCl3), 300 MHz) δ ppm: 0.82-0.89 (m, 9H), 1.20-1.32 (m, 2H), 1.46-1.58 (m, 5H), 1.79-1.88 (m, IH), 2.44 (d, 7 = 7.1, 2H), 3.63-3.71 (m, IH), 4.05 (t, J = 6.6, 2H), 7.08 (d,} = 8.0, 2H), 7.19 (d, J = 8.0,2H). MS (El) m/z: 262 (M+).

WE CLAIM:
1. A catalyst system useful for direct esterification of alcohol with carboxylic
acid, the said catalyst system comprising 1 to 10 % by weight of protic acid,
90 to 99 % by weight of silica, 90 to 99 % by weight of clays, 90 to 99 % by
weight of neutral and acidic alumina, and 90 to 99 % by weight of zeolites
and heated to the temperature between 80 to 100 °C for activation.
2. A catalyst system as claimed in claim 1, wherein the said catalyst
comprising 5 to 8 % by weight of protic acid,92 to 95 % by weight clay, 92
to 95 % by weight zeolites.
3. A catalyst system as claimed in claim 1, wherein the clays are selected from
the group comprising montmorillonite/semectite, zeolites, kalonite, illite,
and chlorite.
4. A catalyst system as claimed in claim 3, wherein the clays are selected from
semectite group.
5. A catalyst system as claimed in claim 4, wherein clay used is
montmorillonite clay.
6. A catalyst system as claimed in claim 1, wherein the said catalytic system
contain perchloric acid or fluoroboric acid as active sites, which acts by
electrophilic activation mechanism in which the electrophiles (carboxylic
acids) are activated by the catalyst through coordinate bond formation
followed by attack by the nucleophiles (alcohols) on the carbonyl carbon
atom of the carboxylic acid complexed with the catalysts and the
elimination of water molecule.
7. A catalyst system as claimed in claim 1, wherein the said catalyst is heat
treated at a temperature in the range of 80 to 100 °C before use for
activating the same.
8. A catalyst system as claimed in claim 1, wherein the 0.05 to 0.25 gm of said
catalyst chemisorbs 1 to 10 % of reaction mixture in one cycle.
9. A catalyst system as claimed in claim 1, wherein said spent catalyst system
containing protic acids is regenerated by filtration from the reaction
mixture, followed by washing with DCM and activation of the recovered
catalyst by vacuum drying at 100°C for 72 hrs.
10. A catalyst system as claimed in claim 1, wherein the regenerated catalyst
treats and use for direct esterification of alcohol with carboxylic acid.
11. A catalyst system as claimed in claim 1, wherein the said catalyst is used in
at least three chemisorptions and regeneration cycle.
12. A catalyst system as claimed in claim 1, wherein the said catalyst is used in
fixed bed reactor or fluidized reactor.
13. A catalyst system as claimed in claim 1, wherein the said catalyst is divided
into fine particles having particle size in the range of mesh # 230 to 400 for
used in fixed bed reactor .
14. A catalyst system as claimed in claim 1, wherein the said catalyst is
palletized or granulated to obtained pellets/granules having diameter in
the range of mesh # 230 to 400 for used in fixed bed reactor.
15. A process for preparing a catalyst system useful for direct esterification of
alcohol with carboxylic acid as claimed in claim 1, wherein said process
comprising the following steps:

e) suspending petroleum ether washed and dried silica in DCM and
magnetically stirred
f) adding 70% aqueous protic acid solution dropwise to step(a) and
then mixture was magnetically stirred for 2 hrs
g) removal of solvent under rotary vacuum evaporation; and
h) drying the residue at 100°C for 72 hrsto afford the adsorbed catalyst.
16. A process as claimed in claim 15, wherein 0.25 gm of catalyst system thus
chemisorbs30O to 1000 mg of reaction mixture.

17. A process as claimed in claim 15, wherein the catalyst thus obtained has pH value in
the range of 5 to 6.
18. A process as claimed in claim 15, wherein the catalyst thus obtained is used in fixed
bed reactor.
19. A process as claimed in claim 15, wherein the catalyst thus obtained contain
perchloric acid or fluoroboric acid as active sites.
20. A process as claimed in claim 15, wherein the catalyst thus obtained is pulverized into
fine particles for use in fixed bed reactors.
21. A method for direct esterification of alcohol with carboxylic acid using the catalyst
system as claimed in claim 1, wherein the said method comprising the following
steps:
i) adding alcohol, carboxylic acid and catalyst composition in a round bottom flask and magnetically stirred at 80°C till complete consumption of acid
j) diluting the mixture of step (a) with solvent and filtered to remove the catalyst composition; and
k) concentrating the filtrate under rotary vacuum evaporation and obtained product.
22. A method as claimed in claim 21, wherein the carboxylic acid used are aromatic alkyl
carboxylic acids, aromatic carboxylic acids, aliphatic acyclic carboxylic acids, aliphatic
cyclic carboxylic acids, long chain carboxylic acids, and dicarboxylic acids.
23. A method as claimed in claim 21, wherein the alcohols used are achiral saturated
aliphatic, allylic, propagyllic, aromatic alcohols, long chain alcohols, chiral alcohols
along with PEGs.
24. A catalyst system and/or a process for preparing the said catalyst system and/or a
method for direct esterification substantially as herein described with reference to the
given examples.