Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2003-01-14
2004-05-04
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S323000, C568S331000, C568S336000
Reexamination Certificate
active
06730814
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a clay based catalytic process for the preparation of acylated aromatic ethers. More particularly, the present invention relates to the catalyzed acylation of anisole (methoxybenzene) and veratrole (1,2- dimethoxybenzene) for the preparation of acylated aromatic ether, namely, p-methoxyacetophenone and 3,4-dimethoxyacetophenone respectively, using a series of lantanide cation exchanged clay based catalysts.
BACKGROUND OF THE INVENTION
Acylated aromatic ethers are of commercial importance in fine chemicals industries, as many synthetic fragrances and pharmaceuticals contains an acyl group, and these ethers are useful intermediates. Acylated anisole is used for synthesis of 2-(4-Methoxybenzoyl) benzoic acid, the sodium salt of which is used as sweetening agent. Similarly, acylated veratrole is a synthon for preparation of vesnarinone 1-(3,4-Dimethoxybenzoyl)-4(1,2,3,4-tetrahydro-2-oxo-6-quinolinyl) piperazine which is a cardiotonic drug.
Reference is made to U.S. Pat. No. 62747441 B1 (Aug. 14, 2001, B. M. Choudary et al.) wherein it is disclosed that acylation of heteroaromtic compounds like furan, thiophene, or pyrrole with the anhydride of C
2-5
carboxylic acid (e.g. acetic anhydride) was carried out using Fe
+3
exchanged Montmorillonite clay. The reaction was carried out in the temperature range of 0 to 130° C. for 1 to 24 hours and the 2-acylaromatic compound was separated by conventional methods to obtain 2-acetylpyrrole of high purity. The drawback of this process is the longer reaction time and high temperature.
Reference is made to the work of B. M. Choudary et al, Applied Catalysis A, General 171 (1998) 155-160 which describes the acylation of aromatic ethers with acid anhydrides in the presence of cation exchanged clays viz., Fe
+3
and Zn
+2
exchanged montmorillonite clays. The reaction mixture of 46 millimoles of anisole and 10 millimoles of acetic anhydride and 250 mg of catalysts was stirred under nitrogen atmosphere. After 10 hours it gives conversion in the range of 25 to 70 percent. The drawback of this process is long reaction time, and the catalyst shows loss in activity. Reference is made to U.S. Pat. No. 5,637,773 (1993: Jean-Roger Desmurs et al.) wherein it is disclosed that 40 millimoles of an aromatic substrates and 10 millimoles of acylating agents with excess amount of Bismuth halide as a catalyst, was mixed at room temperature and then refluxed the reaction mixture for 6 hours to gives 67% of 4-acylated anisole. The drawback of this process is that more than stochiometric amounts of bismuth chloride was used and also poses problem of post-reaction catalysts separation. Furthermore, the Lewis acid must be eliminated from the reaction medium by carrying out acidic or basic hydrolysis at the end of the reaction.
Reference is made to German Patent DE 3809260 (1989, Botta A., et al.) wherein anisole and acetic anhydride were stirred for 3 hours with Mordenite zeolite catalysts at 160° C. under 20 bar of nitrogen pressure to give 75% conversion with 98% selectivity for p-methoxyacetophenone. This process has disadvantage of operating at high temperature and very high pressure and also needs a solvent for uniform mixing. Reference is made to Japanese Patent 1993-317557 (19931217. C. A.124;8397 Myata, Akira et al.) wherein a mixture of veratrole and propionyl chloride, in the presence of Zeolite-&bgr; was refluxed for three hours to give ca, 70% of 3,4-dimethoxypropiophenone. The drawback of the process is that it uses propionyl chloride as an acylating agent, which generates toxic hydrochloric acid during acylation reaction
Reference is made to the work of C. Kuroda et al, (Sei. Papers Inst. Phys. Chem. Res. 18, pp 51-60 (1932)) which describes the preparation of methoxyacetophenones by the reaction of an aromatic compound carrying methoxy group with acetyl chloride in the presence of excess amount of AlCl
3
to obtain high conversions. This process has disadvantages like more than stochiometric amounts of aluminum chloride due to complexation with the ketone formed and also involved process of post reaction effluent treatment and use of corrosive and irritant AlCl
3
. The major drawback of the above stated process is separation of catalysts after completion of the reaction. This necessitates a long, expensive treatment following hydrolysis, extraction of the organic phase, separation of organic and aqueous phase and even drying of latter. Further, there are problems with aqueous saline effluent which has to be neutralized and which necessities additional operation. The Lewis acid cannot be recycled, as it has been hydrolyzed.
Reference is made to the work of H. Burton and P. F. G. Praill (Journal of Chemical Society, April-1950, pp-1203-1206) wherein it is reported that Acetyl perchlorate formed in-situ from silver perchlorates and acetyl chloride, is an effective acylating agent and will convert anisole into p-methoxyacetophenone in about 70% yield. However, this process has disadvantages of using perchlorates which is hazardous chemical. Reference is made to the work of E. J, Bourne, et al. (Journal of Chemical Society, March-1951, pp-718-720) wherein trifluoroacetic anhydride catalyst is shown to promote, the condensation between suitably activated aromatic compound and carboxylic acid or sulphonic acid to give ketones or sulphones, respectively. In this process, reaction was done at room temperature. Anisole was added to a mixture of trifluroacetic anhydride and acetic acid. After three hours the solution was poured into the excess of sodium hydrogen carbonate solution and then extracted by chloroform The extract were dried, filtered and evaporated to dry syrup. After crystallization it gave 78% of p-methoxyacetophenone.
The reported process is multi-step process wherein separation of the product with very high recovery is a limitation.
Reference is made to the work of Cullinane N. M. et al. (Journal of Chemical Society, Feb-952, pp-376-380) wherein acylation of benzene, toluene and anisole is reported using TiCl
4
as a catalyst. Acids, acid chlorides and anhydrides were used as the acylating agents. Acid is reported to be the least and anhydride the most effective towards the formation of acylated products. With anisole (0.15 g-mols) and acetic anhydride (0.1 g-mol) and titanium tetrachloride (0.22 g-mol), the yield of p-acylated product was reported 76% after 4 hours. With anisole (0.2 g-mols) and benzoic acid (0.2 g-mols) and titanium tetrachloride (0.4 g-mols) the yield of p-acylated product was 63% after 1.5 hours. The process has disadvantage of separation of product, as it requires more than one step, like hydrolysis, separation of organic layer and finally removal of solvent at reduced pressure.
OBJECTS OF THE INVENTION
The main object of the present invention is to provide clay based catalytic process for the preparation of acylated aromatic ethers, which obviates the drawbacks as detailed above.
Another object of the invention is to develop clay based acylation process for aromatic ethers, which operates at moderate conditions of pressure, temperature and without the requirement of any solvent and yields high conversions for veratrole and for anisole.
Another object of the invention is to provide a process using solid acid heterogeneous catalysts, which are environmentally friendly, safe in handling and the acylating agent does not generate any hazardous byproduct.
Another object of the invention is to provide a process wherein acylation of aromatic ether occurs selectively at para position.
Another object of the invention is to provide a process where acylation of aromatic ether is carried out catalytically with high atom efficiency without giving rise to byproducts.
SUMMARY OF THE INVENTION
Accordingly the present invention provides a process for the preparation of an acylated aromatic ether which comprises acylating the aromatic ether with an acylating agent in presence of a solid acid heterogeneous catalyst comprising a rare earth cation exchanged clay based catalys
Badheka Yogiraj Mansukhlal
Jasra Rakesh Vir
Sengodagounder Muthusamy
Council of Scientific and Industrial Research
Nixon & Vanderhye P.C.
Richter Johann
Witherspoon SiKarl A.
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