Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2000-11-29
2002-07-16
Vollano, Jean F. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S190000, C560S103000, C558S260000, C558S275000, C554S213000, C554S215000, C554S220000
Reexamination Certificate
active
06420596
ABSTRACT:
FIELD OF THE INVENTION
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.
BACKGROUND OF THE INVENTION
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, 4
th
Edition, John Wiley and Sons, vol. 9, pp. 755-809]. However, such prior art processes cannot be commercially 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. To the applicants' knowledge, 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(CH
3
)
3
, using activated basic alumina catalyst with catalyst to tertbutanol 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 HCl or HBr as a by-product, which is highly corrosive and also environmentally unacceptable.
2) The 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 environmentally friendly and highly efficient process for the selective esterification of tertiary alcohol by using an esterification 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 esterification at close to room temperature. This invention is made to develop a novel process for the esterification of tertiary alcohol, meeting the above mentioned goals or conditions.
SUMMARY OF THE INVENTION
Accordingly, the main object of this invention is to provide a novel liquid phase process, which is an environmentally clean process, for the esterification 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.
This invention provides a process for the selective esterification of a tertiary alcohol(I) represented by a formula:
by its reaction with an organic acid anhydride (II) represented by a formula:
(R
4
CO)
2
O (II)
to produce an organic tertiary ester(III) represented by a formula:
wherein, n is an integer having value greater than or equal to 1; R
3
is H (hydrogen) or a chemical group selected from the group consisting of halogen, NH
2
, NO
2
, OH, SO
3
H, (preferably hydrogen); and R
1
, R
2
, and R
4
are organic chemical groups, each comprising both carbon and hydrogen atoms selected from the group consisting of COOH, C
n
H
2n+1
, C
6
H
5
, (phenyl), substituted phenyl, OC
n
H
2n+1
, C
n
H
2n−
, OC
n
H
2n
C
6
H
5
, C
n
H
2n
—C
6
H
5
, and the like, wherein n is an integer having a value equal to or greater than 1 (preferably selected from methyl, ethyl, propyl, butyl and phenyl groups) using a reusable solid catalyst (IV), represented by a formula:
Mz
y
(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 (preferably selected from Ga, In and mixture thereof); Z is a halogen selected from Cl (chlorine), Br (bromine), I (iodine) or a mixture thereof (preferably Cl); 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 MZ
y
is deposited; and c is a loading of MZ
y
on the support, S, expressed as the mmols of MZ
y
deposited per gram of the support, S, in the range from about 0.01 mmol g
−1
to about 10.0 mmol g
−1
(preferably from 0.02 mmol g
−1
to 2.5 mmol g
−1
); said process comprising:
contacting a mixture of (I) and (II) in the absence or presence of a non aqueous solvent with the fine particles of (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 (preferably from 0.5 to 2.0); the weight ratio of (IV) to (I+II) is in the range from about 0.005 to about 0.5 (preferably from 0.01 to 0.2); the reaction temperature is below about 80° C. (preferably between 10° C. and 50° C.); and the reaction period is in the range from about 0.1 h to about 50 h (preferably from 0.2 h to 10.0 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.
The main finding of this invention is that, by the process of this invention, a tertiary alcohol can be esterified by an acid anhydride to a corresponding tertiary ester with very high conversion and high selectivity or without producing appreciable amounts of tertiary alcohol dehydration products, such as iso-olefin and water, at room temperature and even when the catalyst to reactants weight ratio is very much less than 1.
Other important finding of this invention is that the solid catalyst used in the process of this invention can be separated from the reaction mixture easily, simply, by filtration, and it can be reused repeatedly in the process and hence, it does not create environmental problems.
Another important finding of this invention is that the catalyst for this process of this invention is highly efficient or highly active and selective and hence, the esterification reaction can be completed in a short period.
Yet, another important finding of this invention is that the by-product of the process of this invention, a carboxylic acid, is not corrosive and also does not cause environmental pollution or problems. Being a valuable by-product, it can be sold in the market or converted back to an acid anhydride
Choudhary Vasant Ramchandra
Jana Suman Kumar
Mantri Kshudiram
Council of Scientific and Industrial Research
Vollano Jean F.
Zucker Paul A.
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