Process for the preparation of saturated carboxylic acids...

Details Process for the preparation of saturated carboxylic acids... Process for the preparation of saturated carboxylic acids...

1999-12-30

2001-09-25

Padmanabhan, Sreeni (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acid esters

C560S233000, C562S406000

Reexamination Certificate

active

06294687

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an improved process for the preparation of saturated carboxylic acids and their esters. More particularly, this invention relates to a process for the conversion of olefinically unsaturated compounds to corresponding carboxylic acids and their esters of formula III
wherein R
1
, R
2
, R
3
and R
4
may independently be hydrogen, alkyl, aryl, arylalkyl, cycloaliphatic with or without substituents, R and R
5
may be H and COOR′ or vice versa wherein R′ may be H in the case of acids and may be alkyl, aryl, arylalkyl, cycloaliphatic with or without substituents, in the case of esters. More particularly, the present invention relates to a process for the preparation of saturated carboxylic acids and their esters using an efficient catalyst.
BACKGROUND OF THE INVENTION
The aryl and aliphatic carboxylic acids and esters have a variety of applications in industries as anti-inflammatory drugs, fine chemicals etc. The prior art describes catalyst systems for employment in processes for the preparation of esters of carboxylic acids. So far, the most preferred catalyst system has been homogeneous palladium catalysts. Generally, the various catalyst systems used for the hydrocarbonylation of olefins contains a palladium source, a phosphine ligand and a hydrogen halide promoter. Hydrocarbonylation of olefins using a catalyst system comprising PdCl
2
or PdCl
2
(PPh
3
)
2
, excess triphenyl phosphine and HCl has been found to occur only at drastic conditions such as 300-700 atm of CO pressure.
(Bittler et al., Agnew. Chem. Internat. Edit. 7, 1968, 329). Oi et al. (J. Mot. Cat. A. Chem., 115, 1997, 289) have reported hydroesterification of styrene using cationic palladium complexes which proceeds under mild conditions (20 atm, 80° C.) to give 91 to 94% product yield in four hours (TOF=11 h
−1
) with n: iso ratio of 60:40. Recently, Seayed et al (Ind. Eng. Chem. Res., 37, 1998, 2180) have shown enhanced reaction rates in the hydroesterification of styrene (TOF=41 l h
−1
) using a catalyst system comprising of Pd(OAc)
2
, PPh
3
and p-toluene sulphonic acid with an n: iso ratio of 35:64. Even though, a variety of palladium phosphine complexes have been used for olefin hydroesterification, metal complexes which contain N- containing ligands have never been attempted.
Most of these catalyst systems cause disadvantages during the course of their employment for the preparation of carboxylic acids and esters. These include the requirement of severe conditions, use of excess ligands and promoters. Also, most of the conventional catalyst systems lose their efficacy on recycling.
Thus, there is a need for an improved process for the manufacture of carboxylic acids and esters wherein the yield and selectivity are good and the catalyst system is stable even in the absence of excess ligands.
The applicants have observed that the new transition metal complex containing a semilabile anionic ligand, which is a chelating organic compound containing a N-donor and an O
−
group, described in their co-pending U.S. patent application Ser. No. 09/281, 929 now U.S. Pat. No. 6,069,253 is particularly suited for use as a catalyst for the preparation of saturated carboxylic acids and esters by the hydrocarbonylation of olefinically unsaturated compounds. This transition metal complex is prepared according to the process described in said co-pending application Ser. No. 09/281,929 now U.S. Pat. No. 6,069,253. The catalyst gives good yield and selectivity and the catalyst is stable even in the absence of excess ligands and can also be recycled efficiently.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide an improved process for the preparation of saturated carboxylic acids and their esters by the hydrocarbonylation of olefins.
It is another object of the invention to provide a process for the preparation of saturated carboxylic acids and esters using a novel catalyst system.
It is another object of the invention to provide a process for the preparation of saturated carboxylic acids and esters thereof with an improved yield and selectivity even in the absence of excess ligands in the catalyst.
It is yet another object of the present invention to provide a process for the preparation of saturated carboxylic acids and esters thereof with an improved yield and selectivity using a catalyst which contains a N donor and an O
−
group for the hydrocarbonylation of olefins.
It is a further object of the invention to provide a process for the preparation of saturated carboxylic acids and their esters wherein the catalyst system substantially retains its efficiency even on recycling.
SUMMARY OF THE INVENTION
The present invention relates to an improved process for the preparation of saturated carboxylic acids and esters thereof of the formula III
wherein R
1
, R
2
, R
3
and R
4
may independently be hydrogen, alkyl, aryl, arylalkyl, or cycloaliphatic group with or without substituents and R and R
5
may be H and COOR′ or vice versa wherein R′ may be H in the case of acids and may be alkyl, aryl, arylalkyl, or cycloaliphatic group with or without substituents in the case of esters, which comprises reacting an olefin of general formula II
wherein R
1
, R
2
, R
3
and R
4
may independently be hydrogen, alkyl, aryl, arylalkyl, or cycloaliphatic group with or without substituents, with a transition metal complex catalyst of formula I
wherein M is a group VIII metal; R
1
, R
2
, and R
3
are substituents on the phosphine ligand and are selected from hydrogen, alkyl, aryl, arylalkyl, or arylalkyl cycloaliphatic group; X is selected from aryl or alkyl sulphonato or aryl or alkyl carbonate or formato or halides such as Cl
−
, Br
−
or I
−
; NO is a semilabile anionic chelating ligand containing a N donor and an O
−
group, 1<n<10, and a protonic acid (or hydrogen gas) and a proton source, in an organic solvent, in a carbon monoxide atmosphere in a homogeneous medium, with or without excess phosphorus ligand, heating the mixture to a temperature between 30° C. to 120° C., for a period ranging between 30 to 180 minutes, at a pressure ranging between 1 to 40 atm, cooling the reaction mixture to ambient temperature, flushing the reaction vessel with inert gas, removing the solvent by conventional methods, separating the catalyst and isolating said compound of general formula III.
In one embodiment of the present invention, the catalyst of the formula I is prepared as described in allowed U.S. patent application Ser. No. 09/281,929 now U.S. Pat. No. 6,069,253.
In a further embodiment of the invention, the catalyst is of the general formula I
wherein M is a group VIII metal selected from palladium or platinum; R
1
, R
2
, and R
3
are substituents on the phosphine ligand and are selected from hydrogen, alkyl, aryl, arylalkyl, or arylalkyl cycloaliphatic; X is selected from aryl or alkyl sulphonato or aryl or alkyl carbonato or formato or halides such as Cl
−
, Br
−
or I
−
; NO is a semilabile anionic chelating ligand containing a N donor and an O
−
group such as 8-hydroxy quinoline, 2-hydroxy pyridine, 2-(2-hydroxyethyl) pyridine, pyridyl-2-, piperidyl-2-, quinolyl-2-, isoquinolyl-1- and isoquinolyl-3- carboxylates, particularly pyridyl-2- carboxylate, piperidyl-2-carboxylate, and 8-hydroxyquinoline; and 1<n<10.
In a preferred embodiment of the invention, in the above formula I, M is Pd
−
, R
1
, R
2
, and R
3
are phenyl; X is p-toluenesulphonato (OT's); NO is pyridyl-2-carboxylate and n is 3. The catalyst of this embodiment is referred to by the general formula Ia.
In another embodiment of the invention, the proton source used is selected from water, formic acid, acetic acid and propionic acid for the preparation of the saturated acids and any alcohol such as methanol, ethanol, and butanol and phenols are used for the preparation of the saturated esters. and any alcohol such as methanol, ethanol, butanol and phenols are

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