Title of Invention

AN IMPROVED PROCESS FOR THE PREPARATION OF SUBSTITUTED BENZALDEHYDES

Abstract

An improved process for the preparation of substituted benzaldehydes: The invention provides an improved a process for producing substituted benzaldehydes in greater yields by vapour phase oxidation over a novel mixed oxide supported vanadium oxide based catalyst. The catalyst used in this process consists of elements of vanadium, molybdenum and oxygen promoted with one of the elements from potassium, calcium, cobalt and antimony on a mixed oxide carrier such as titania-alumina, titania-zilica, titania-zirconia and titanium-gallium oxide.

Full Text

This invention relates to an improved process for the preparation of substituted benzaldehydes. The present invention particularly relates to a process for the preparation of p-methoxybenzaldehyde from 4-methylanisole via vapour phase selective oxidation using an improved catalyst. Para-methoxybenzaldehyde (p-anisaldehyde) is an important chemical and chemical intermediate having many potential applications. It is used as a perfumer, brightener in plating, and raw material for the preparation of Pharmaceuticals and agrochemicals. It is a well established fact in the literature that substituted benzaldehydes can be synthesized from the corresponding substituted toluenes in liquid phase in the presence of cobalt, cerium, and manganese salts in acetic acid medium or by electrochemical methods. However, these routes are not highly efficient for large-scale production. In principle, substituted toluenes can be converted into the corresponding substituted benzaldehydes by partial oxidation in vapour phase with the involvement of a suitable heterogeneous catalyst system. Partial oxidation is a reaction to get an intermediate product selectively on the way of complete oxidation. Very few processes are known for the preparation of substituted benzaldehydes from the corresponding substituted toluenes in the vapour phase by partial oxidation with air at elevated temperatures and pressures. A Japanese patent publication No: 85/100 582, discloses a process for obtaining benzaldehyde derivatives by vapour phase oxidation of the corresponding toluene derivatives. The catalyst comprising of a mixture of vanadium oxide and some of the elements like Na, K, and Rb from lA-group, and also one of the elements from EA-group like Mg, Ca, etc., was used for the conversion of 4-methylanisole to anisaldehyde. This process produces only limited yields of the benzaldehyde derivatives at 773 K operating temperature. Another Japanese patent publication No: 88/203 125, discloses a process for the preparation of methoxy benzaldehydes with 94.6 % conversion of 4-methyleanisole and 78.7 % selectivity of anisaldehyde over a catalyst consisting of the elements of vanadium and silver oxide, optionally containing other oxides selected from K, Cu, P, Sb, Bi, Sn, and Pb. In another method, Nippon Shokubai Kagaku Kogyo Company Limited, Japan (European patent No: EP 228, 275), reported a catalyst obtained by calcining a product from a dried mixture containing NH4VO3, CsNO3, cellulite, and Cu(NO3)4 compounds. Another patent assignes to Nippon Shokubai Kagaku Kogyo Company Limited, Japan (Japan patent application No: 84/198 698) a catalyst consisting of elements of vanadium, rubidium and/or cesium, and potassium and one or more other elements selected from Cu, Ag, P, Sb, and Bi were used for the reaction of 4-methylanisole to anisaldehyde. The conversion of the 4-methylanisole was about 93.7 mole% and selectivity to anisaldehyde was 76.9 mole%. Nevertheless, the processes mentioned above possess many disadvantages for industrial production point of view such as low yields of the desired product, low inputs of substituted toluenes per unit weight of catalyst, usage of large excess of air or high operating temperatures, etc. The main object of the present invention is to provide an improved process for the preparation of substituted benzaldehydes. The present invention, as a result of extensive research, could overcome the disadvantages such as mentioned above and provides a process for producing substituted benzaldehydes in greater yields by vapour phase oxidation over a novel mixed oxide supported vanadium oxide based catalyst. The process for the preparation of a novel selective oxidation catalyst has been made the subject matter of our copending patent application no: 809/DEL/99. The catalyst used in this process consists of elements of vanadium, molybdenum and oxygen promoted with one of the elements from potassium, calcium, cobalt and antimony on a mixed support carrier such as titania-alumina, titania-silica, titania-zirconia and titanium-gallium oxides. The compounds of vanadium and/or molybdenum are dissolved in water and the solution is impregnated on the support material up to 5 - 20 wt% by co-precipitation method and later dried at 393 K in oven. The promoter atoms are later on added to the dried impregnated catalyst and dried once again at 393 K and calcined finally at 773 K in pen-air furnace. Accordingly, the present invention provides an improved process for the preparation of substituted benzaldehydes such as herein described using an improved vanadium oxide based catalyst such as herein described, the said process comprises the steps of (i) passing mixture of gases consisting of the substituted toluene, air or oxygen and N2 over an improved catalyst as defined above , at a temperature in the range of 623 to 723K, under a pressure ranging 0.5 to 1.5 atm., in the presence of diluent such as water, benzene or mixtures thereof and (ii) recovering the substituted benzaldehydes from vapour phase by conventional method. The reaction may also be conducted under reduced or high pressures. Substituted toluene used may be such as 4-methyl anisole, p-methyl toluene, p-iso-propyl toluene, and p-tertiary-butyl toluene. The reaction is performed with fixed bed Pyrex glass reactor mounted in a vertical tubular furnace. Catalyst was secured between quartz wool plugs, preferably 100 to 150 mm above the bottom of the furnace. Empty portion of the reactor, 200 to 400 mm on top of the catalyst bed, was filled with quartz beads, which served as preheating zone. The reaction usually takes place in the vapour phase. The required oxygen is supplied as air, although direct from a pressure cylinder may be used. In the copending application number 809/DEL/99 we have described and claimed a process for the preparation of the novel catalyst used in the process of the present invention. The process of the present invention is illustrated by the Examples given below which should not however be considered to limit the scope of the invention. Conversions and yields used are calculated by the following equations: Conversion% = 100 x Number of moles of 4-methylanisole reacted/ Number of moles of 4-methylanisole fed. Yield % = 100 x Number of moles of p-anisaldehyde formed / Number of moles of 4-methylanisole fed. Example 1 A Pyrex glass reactor of 10 mm I.D. and 500 mm long is filled with V-Ti-Ga oxide ( Vide copending patent application No : 809/DEL/99) particles mixed with quartz beads in a total bed length of 500 mm. Above the catalyst bed, a preheated zone consisting of Pyrex glass beads in about 200 mm length are placed. The catalyst is preconditioned in a flow of dry air at 723 K for a period of 4 hours. Air was supplied to the reactor through cylinders. The liquid reactant (4-methylanisole) was fed at a rate of 2-5 ml hour-1 to the reactor through pre-calibrated liquid syringe pump. The reaction is carried out under normal atmospheric pressure at a temperature of 673 K and at a space velocity of 3000 hour-1. The reaction products were condensed through cold traps and were analyzed by gas chromatography. The overall conversion of 4-methylanisole was 94% and the anisaldehyde yield was 78%. EXAMPLE 2 The reaction was carried out in a Pyrex glass reactor of 10 mm I.D. and 500 mm long is filled with Mo-V-Ti-Ga oxide (Vide copending patent application No : 809/DEL/99) particles mixed with quartz beads in a total bed length of 500 mm. Above the catalyst bed, a preheated zone consisting of Pyrex glass beads in about 200 mm length are placed. Molybdenum salt ( 5 wt% ) , preferably ammonium heptamolybdate was dissolved I water and impregnated to the oven dried catalyst sample . The obtained catalyst sample was oven dried again and calcined at 773 K for 6 hours . The reaction was conducted at 673 K temperature , at a space velocity of 2700 hours -1 , and at 1.2 atmospheric pressure . Air (45ml/min) or a mixture of nitrogen and oxygen were supplied to the reactor through cylinders. The percentage conversion of 4-methylanisole and p-methoxybenzaldehyde yield were 95% and 80% respectively. EXAMPLES The reaction was carried out in the same manner as in examples 1 and 2, but the catalyst used was magnesium supported one. The support material was separately prepared by hydrolysis of magnesium and calcium salts. The obtained precipitates were washed thoroughly with deionized water until free from anion impurities and dried in oven for 24 hours at 393 K and calcined at 973 K for 8 hours. Vanadium oxide from ammonium metavanadated was impregnated on the support material and was subsequently dried at 393 K for 12 hours and finally calcined at 773 K for 6 hours. The reaction was conducted at 663 K temperature, at a space velocity of 3000 hour-1, and at atmospheric pressure. Air (50 ml/min) or a mixture of nitrogen and oxygen were supplied to the reactor through cylinders. The average conversion of 4-methylanisole was 86 % and the aldehyde product selectivity was 78 %. EXAMPLE 4 The catalyst preparation is similar to Examples 1 and 2, but the active vanadium oxide component and the promoter atoms are co-impregnated on the TiO2-Ga2O3 mixed oxide support. The impregnated sample was oven dried at 393 K and calcined at 773 K. The catalyst sample was further preactivated with dry air and oxygen for 6 hours. The reaction was conducted at 683 K temperature, at a space velocity of 2700 hour-1, and at normal atmospheric pressure. Air (45 ml/min) or a mixture of nitrogen and oxygen were supplied to the reactor through cylinders. The conversion of 4-methylanisole was 95% and thep-methoxybenzaldehyde product yield was 81%. EXAMPLES The catalyst preparation is similar to Examples 1 and 2, but the active vanadium oxide component and the promoter atoms are co-impregnated on the TiO2-Ga2O3 mixed oxide support. The impregnated sample was oven dried at 393 K and calcined at 773 K. The catalyst sample was further preactivated with dry air and oxygen for 6 hours. The reaction was conducted at 698 K temperature, at a space velocity of 3000 hour"1, and at normal atmospheric pressure. Air (50 ml/min) or a mixture of nitrogen and oxygen were supplied to the reactor through cylinders. The reactant 4-metyl toluene was fed at a rate of 2 ml hour"1. The conversion of 4-methyl toluene was 82% and the 4-methyl benzaldehyde product yield was 71%. The major advantages of the process are: 1. This process provides higher yields of substituted benzaldehydes. 2. Avoids usage of large excess of air or a mixture of nitrogen and oxygen. 3. Low operating temperatures. 4. Highly flexible pressure options. 5. High inputs of substituted toluenes per unit weight of the catalyst. We Claim: 1. An improved process for the preparation of substituted benzaldehydes such as herein described using an improved vanadium oxide based catalyst such as herein described , the said process comprises the steps of (i) passing mixture of gases consisting of the substituted toluene, air or oxygen and N2 over an improved catalyst as defined above , at a temperature in the range of 623 to 723K, under a pressure ranging 0.5 to 1.5 atm., in the presence of diluent such as water, benzene or mixtures thereof and (ii) recovering the substituted benzaldehydes from vapour phase by conventional method. 2. An improved process as claimed in claim 1 wherein the preferable range of reaction temperature is of 648 to 698K. 3. An improved process as claimed in claims 1 to 3 wherein substituted toluene used is selected from 4-methylanisole, 4-methyl toluene, 4 - methyl toluene. 4. An improved process for the preparation of substituted benzaldehydes substantially as herein described with reference to the examples.

Documents:

807-del-1999-abstract.pdf

807-del-1999-claims.pdf

807-del-1999-correspondence-others.pdf

807-del-1999-correspondence-po.pdf

807-del-1999-description (complete).pdf

807-del-1999-form-1.pdf

807-del-1999-form-19.pdf

807-del-1999-form-2.pdf