Title of Invention	"IMPROVED PROCESS FOR THE PRODUCTION OF 2-VINYL PYRIDINE AND 4-VINYL PYRIDINE"
Abstract	The present invention provides an improved process for the production of 2-vinyl pyridine and 4-vinyl pyridine by reacting 2-methyl pyridine and 4-methyl pyridine respectively with formaldehyde, to form corresponding 2-pyridyl ethanol and 4- pyridyl ethanol followed by subsequent dehydration to give the title product.

Full Text

Improved Process for the Production of 2-Vinyl Pyridine and 4-Vinyl Pyridine FIELD OF INVENTION The present invention relates to an improved process for the production of 2/4-vinyl pyridines where 2/4-methyl pyridines are reacted with formaldehyde in absence of any catalyst to form corresponding 2/4-pyridyl ethanol and its subsequent dehydration to give the title product. The present process has the advantage that it is commercially viable and can be easily implemented at commercial scale. BACKGROUND OF THE INVENTION Vinyl pyridines are an important class of polymers exhibiting interesting properties due to the presence of the nitrogen atom in the pyridine ring. The weakly basic nitrogen atom makes possible a variety of reactions on vinyl pyridine polymers e.g. reaction with acids, quaternization and complexation of metals. The hetero atom is also responsible for unique characteristics in the polymerization mechanism. Vinyl pyridine polymers are particularly important in applications as polyelectrolytes (qv.), polymeric reactants, and in electrical applications. A large number of vinyl pyridine monomers have been prepared & polymerised. Out of all, 2-Vinyl pyridine and 4-Vinyl pyridine are two most commercially significant monomers. Because of the importance of butadiene-vinyl pyridine copolymers as synthetic rubbers, the preparation of this vinyl pyridine derivative from 2-methyl pyridine has been the subject of considerable industrial research in recent years. The production of 2/4-vinyl pyridine by condensation of formaldehyde with 2/4-picoline followed by dehydration of the resulting 2/4-pyridyl ethanol is already known in the literature. The reaction proceeds in the following manner (Formula Removed) The reactions as presented are very simple. However, the processes to achieve these reactions are extremely demanding by virtue of a number of factors leading to complex side reactions Formaldehyde can undergo multiple condensations on 2-Methyl Pyridine until all the methyl hydrogens are replaced with methylol groups. Hence, the first reaction shown does not stop at 2-pyridyl ethanol but continues further to form di- and tri- condensates. Moreover, the condensates may further react to form unsaturated compounds under the reaction conditions, which polymerizes to resinous residues. Formaldehyde on its own can undergo self-condensations to form hexoses- form of primitive sugars and also acetal resins. All these reactions lead to wastage of 2-methyl pyridine or formaldehyde or both depending upon the nature of each such reaction. The complexities thus obtaining makes the choice of reaction condition an extremely exacting one for the development of process conditions. The prior art processes differ from each other in respect of reaction conditions. Batch and continuous both types of operations at condensation stage have been reported in the prior art processes. Also, use of catalyst is reported. A significant problem in the prior art processes for the preparation of 2/4-vinyl pyridines is that desired product yield at both condensation and dehydration stages are very low. Hence the process is not economically viable. In some literature references, higher yields are reported but reaction conditions are so severe that it can not be implemented at industrial scale. It is therefore important and essential to develop an economically viable process for the manufacture of 2/4- vinyl pyridines, which can easily be implemented at commercial scale. DESCRIPTION OF PRIOR ART Several processes for the preparation of 2/4- vinyl pyridine by reaction of 2/4-methyl pyridine with formaldehyde followed by dehydration of the resultant 2/4-pyridyl ethanol is reported in the prior art. British Patent No. 901654 discloses a process for the preparation of pyridine alcohols and their homologues for batch and continuous mode of operations. Although reported yields are high, Very high temperature 230-270° C for batch process and very high pressure upto 150 atm. makes the process unsuitable for the industrial production. British Patent No.632,661 and US Patent No. 2556845 describe the similar two step process for the preparation of 2/4-vinyl pyridines. In the condensation stage, rate of reaction is very slow. Also, yields are not satisfactory. Therefore, it will have a large adverse impact on productivity as well as cost economics, hence it is not commercially acceptable. According to a British Patent no. 850114. residence time at condensation stage has been substantially reduced to 1.5 hrs with slightly increase in product yield, upto 70 %. But, in order to avoid the secondary reaction between the 2/4-pyridyl ethanol formed in the first step with formaldehyde, an excess (6:1) of 2/4-methyl pyridine is used. Here again, the product yield is not satisfactory and also because of the use of large excess of 2/4-methyl pyridine, the total productivity is very less. German Patent No. 2002661 (1971), describes a one step continues process for the manufacture of 2/4-vinyl pyridine. The major disadvantage of the process is that the reaction is performed at very high temperature & pressure conditions and in the presence of strong acid. The yield is also not very high. US Patent No. 2848456 reveals a process for the second step i.e. dehydration of 2-pyridyl ethanol to 2-vinyl pyridine. In the given process, the reaction product obtained after the condensation stage is first distilled under high vacuum to isolate 2-pyridyl ethanol, which is further dehydrated in presence of caustic alkali to produced 2-vinyl pyridine. The major disadvantage in the process is that one additional step of distillation is involved which, adds to the product cost and secondly, because of the reaction of 2/4-pyridyl ethanol with compounds presents in the crude mixture, undesired products are formed under the given dehydration condition which, decreases the yield of 2/4-VP considerably. Also, one additional step for the drying of 2/4-W is to be added to eliminate water formed during the dehydration. Another US Patent No. 2534285 reveals the dehydration process, which comprises contacting 2-pyridyl ethanol in vapour phase with an aluminum oxide as dehydration catalyst. Again as there are number of additional steps involved & also the final product yield is unsatisfactory, this process is not industrially viable. As can be seen, prior art processes suffer from several problems such as severe process conditions, low yield, both at condensation and dehydration steps and additional process steps. OBJECTS OF THE INVENTION It is therefore an object of the present invention to provide an improved process for the production of 2/4-vinyl pyridines from 2/4-methyl pyridines, which ensures higher yield & selectively of desired products at each process steps. It is another object of the present invention to provide a process for the production of 2/4- vinyl pyridines from 2/4-methyl pyridines where reaction conditions are not very severe so that it can be easily translated at industrial scale. Another object of the present invention is to provide a process for production of 2/4-vinyl pyridines from 2/4-methyl pyridines where the complete production process involves less number of process steps. Another object of the present invention is to provide a process for the production of 2/4-vinyl pyridines from 2/4 -methyl pyridines where the purity of the final products are exceptionally high. It is another object of the present invention is to provide a process for the production of 2/4-vinyl pyridines from 2/4-methyl pyridines where generation of process effluents has been considerably minimised by recycling to make the process environment friendly. Also, in the process, 2-methyl pyridine- water cut which is used in the process after extraction & distillation is reduced & final distillation capacity is enhanced. DETAILED DISCRETION OF THE INVENTION After extensive research and analysis, the applicants have found that in the production of 2/4-vinyl pyridines from 2/4-methyl pyridines by using optimum process conditions, a highly cost effective, environment friendly process can be developed which is suitable for use on an industrial scale. Accordingly, the present invention provides a process for the preparation of 2/4-vinyl pyridines from 2/4-methyl pyridines where the first process step i.e. condensation of 2/4-methyl pyridine with formaldehyde can be performed in batch mode as well in continuous mode. In one embodiment of the present invention, reaction temperature at condensation stage is kept low, max up to 200° C, preferably in the range of 160-180° C. In another embodiment of the invention, the reactor pressure at condensation stage, both for batch as well as for continuous mode of operation is kept below 15 kg/cm2, preferably in the range of 10-14 kg/cm2. In another embodiment of the present invention, for batch mode of operation, reaction time is maintained such that only trace amount of formaldehyde is left in the reaction product. For continuous mode of operation, feed rates are adjusted accordingly to achieve trace amount of formaldehyde in the reaction product. In another embodiment of the invention, the mole ratio of 2/4-methyl pyridine to formaldehyde is kept preferably 4:1 and most preferably 2-3:1. In another embodiment of the present invention, feeds are heated to preferably 140-160° C, before introducing in the reactor. In yet another embodiment of the present invention, formalin is preferably charged after achieving the reaction temp by heating 2/4-methyl pyridines for batch mode of operation at condensation stage. In another embodiment of the present invention, the reaction product obtained at condensation stage is immediately cooled after the completion of the reaction. In yet another embodiment of the present invention, before dehydration, reaction mass is preferably distilled to isolate most of the water & 2-methyl pyridine. This will enhance the dehydrator capacity considerably. In another embodiment of the present invention reaction product at condensation stage is dehydrated in presence of caustic alkali without isolating 2/4-pyrdyl ethanol. In another embodiment of the present invention, caustic alkali is added at dehydration stage, preferably 10 - 20%, more preferably 14 - 16% of the 2/4-pyridyl ethanol in the reaction product. V In yet another embodiment of the present invention, the dehydration is performed under vacuum & the dehydrated product is simultaneously distilled as it is formed. In yet another embodiment of the present invention, the dehydration is carried out by maintaining the pot temperature preferably below 170° C. In yet another embodiment of the present invention, initially solid sodium hydroxide pellets, equivalent to required for dehydration, will be added in the dehydrated product to partially dry the dehydrated product. The aqueous caustic solution can be recycled during dehydration stage. This will substantially reduce the effluent quantity. Also the 2-methyl pyridine-water cut is minimised. This minimises the extraction and distillation cost and also enhances the final distillation capacity. In yet another embodiment of the present invention, the dehydrated product obtained after drying, is distilled employing fractionating column under vacuum to obtain high purity 2/4-vinyl pyridines. The 2/4-methyl pyridine-water azeotrope, obtained as initial distillation cut, can be extracted & distilled to get 2/4- methyl pyridines, which can be further, recycled back in the process. The present invention is illustrated below with reference to the following examples, which are not to be construed as limiting the scope of the present invention. It must be understood that variations are possibe without departing from the spirit & scope of the embodiments described below. EXAMPLE 1 4.25 mole of formaldehyde, as 37% aqueous solution and 9.67 mole of 2-methyl pyridine was charged in a 2.0 lit. stainless steel autoclave (Parr make) equipped with agitators, cooling and heating arrangements. It has a sample valve for periodic drawl of samples. The reactor is further equipped with accurate temp, measurement capabilities & pressure guage & is complete with rupture disc & pressure relief valve. The reactor was slowly heated to desired reaction temp, samples were collected at regular intervals to monitor the unreacted formaldehyde in the reaction product. After the completion of the reaction (formaldehyde in the reaction product is almost nil), the autoclave is rapidly cooled to room temperature and reaction mass is discharged. The reaction mass is analysed by GC. 89 mole % yield of 2-pyridyl ethanol based on 2-methyl pyridine consumed achieved. The reaction mixture was transferred to distilling flask having small fractionating coloumn and heated to a pot temperature of 140° C to remove water and most of the unreacted 2-methyl pyridines. The left over mass is dehydrated by distilling in presence of 15 % NaOH, based on 2-pyridyl ethanolin the reaction product, at 90-100mm Hg pressure. The maximum pot temperature is maintained to 160° C. The residue is deposed off in hot condition by adding methanol. The dehydrated mass is analysed by GC. The total yield of 2-vinyl pyridine based on 2-pyridyl ethanol consumed is 95.0 mole%. 50 gm sodium hydroxide flakes, equivalent to sodium hydroxide required at dehydration stage, is added to the dehydrated mass and is agitated for 2-3 hrs. Aqueous layer containing 46.63% caustic is separated which is recycled at next dehydration reaction. The Organic layer containing water,2-methyl pyridine & 2-vinyl pyridine with some other byproducts, is distilled under vacuum employing 2 meter long glass column packed with stainless steel wire mesh. The initial cut containing water,2-methyl pyridine is used in the next reaction after extraction with benzene & then isolating 2-methyl pyridine by fractional distillation. Pure 2-methyl pyridine obtained during distillation can be recycled as such in the process. Finally, 2-vinyl pyridine with 99.0% + assay is obtained. EXAMPLE 2 The reaction of example 1 was carried out on a considerably large scale. 20 lit working capacity high pressure reactor with required necessary arrangements was used for condensation reaction. Initially, 145.2 mole of 2-methyl pyridine was charged in the reactor and heating started. After achieving the desired temp., 64.0 mole formaldehyde, in the form of 37% aqueous solution was charged by high pressure dosing pump. After completion of the reaction, the reactor was rapidly cooled & reaction product was discharged and analysed by GC. 92.6 mole% yield of 2-pyridyl ethanol based on 2-methyl pyridine consumed, was achieved. The reaction mass was worked up as per example 1. 85-lit capacity stainless steel kettle mounted with SS column packed with sulzer make packings, was used for dehydration & distillation purposes.96 mole% yield of 2-vinyl pyridine, based on 2-pyridyl ethanol, is achieved. EXAMPLE 3 The reaction of example 1 was carried out in a continuous mode such as preffered on the commercial scale. The reaction was carried out on pilot scale using, a mixture of 2-methyl pyridine & 37% formaldehyde with the mole ratio of 2-methyl pyridine to formaldehyde =2.27:1, as raw material. The same mixture was fed by high pressure dosing pump through a preheater, heated by dowtherm where it acquired the desired temp., to a tubular metal coil reactor immersed in tank filled with dowtherm. The coil reactor was heated upto 180° C. A pressure of 12 kg/cm2 was maintained in the coil by means of compressed nitrogen. The feed ratio was adjusted in such a way that formaldehyde content in the reaction produced is almost nil. The product was discharged through a chilled water-cooled metal condenser to rapidly cool the reaction product. It was collected in a metallic storage tank. The reaction product was analysed by GC. 90.84 mole% yield of 2-pyridyl ethanol, based on 2-methyl pyridine consumed, achieved. The further processing of the reaction product which involves dehydration, drying & distillation steps were followed as per example 2, maximum 95.06 mole% yield of 2-vinyl pyridine based on 2-pyridyl ethanol charged achieved. EXAMPLE 4 Experimental protocol remains the same as described in the example 1. Except 1.73 mole of formaldehyde as 37.0% aqueous solution and 5.19 mole of 4-methyl pyridine was charged in 2.0-lit stainless steel autoclave. The molar ratio of picoline to formaldehyde works out to be 3:1 .The reaction temperature maintained was 170° C. fThe pressure achieved at this temperature is 11.6 kg/cm . The reaction time is 20min. Further work up of the reaction product, which involved dehydration, drying with caustic alkali & fractional distillation under high vacuum, remains same as followed in example 1. 96.1 mole% yield of 4-vinyl achieved at dehydration stage & after fractional distillation, 99.28% purity of 4-VP achieved. EXAMPLE 5 Experimental protocol remains the same as described in the example 3. Except 20.86 mole/hr of formaldehyde as 37.0% aqueous solution and 62.68 mole/hr of 4-methyl pyridine was fed by high pressure dosing pump in coil reactor. The molar ratio of 4-methyl pyridine to formaldehyde works out to be 3:1. The reactor temperature and pressure maintained was 170° C & 12 kg/cm2. The reaction time was 22 min.. Further processing of the reaction product which involved dehydration, drying with caustic soda & fractional distillation under higher vacuum remains same as followed in example 2. 95.60 mole% yield of 4-vinyl pyridine based on 4-pyridyl ethanol was achieved at dehydration stage and after final fractional distillation, 99.15.0% purity of 4-vinyl pyridine was achieved. We claim: 1. An improved process for the production of 2-vinyl pyridine and 4-vinyl pyridine comprising reacting at a temperature of up to 200°C and maximum reaction pressure of 15 kg/cm2, 2-methyl pyridine and 4-methyl pyridine respectively with formaldehyde, to form corresponding 2-pyridyl ethanol and 4- pyridyl ethanol, subjecting the products so obtained to dehydration to obtain 2-vinyl pyridine and 4- vinyl pyridine. 2. A process as claimed in claim 1 where in the molar ratio of 2/4-methyl pyridine to formaldehyde used is preferably between 4:1 and most preferably between 2-3:1. 3. A process as claimed in claim 1 or 2 wherein the reaction temperature is between 160-180°C. 4. A process as claimed in any preceding claim wherein the reaction pressure is preferably between 10-14 kg/cm2. 5. A process as claimed in any preceding claim wherein reaction time is maintained such that the reaction product contains trace of formaldehyde. 6. A process as claimed in any preceding claim wherein the feeds are preferably preheated to 140-160°C before introducing in the reactor. 7. A process as claimed in claim 6 wherein the reaction product is immediately cooled after the completion of reaction. 8. A process as claimed in any preceding claim wherein most of the water and 2-methyl pyridine is distilled before dehydration to increase the dehydration capacity. 9. A process as claimed in any preceding claim wherein the dehydration of the reaction product obtained is carried out as such and preferably after isolating most of water and 2-methyl pyridine, in presence of caustic alkali. 10. A process as claimed in any preceding claim wherein quantity of caustic alkali is kept preferably in the range of 10 - 20%, more preferably 14 - 16% of the total 2/4-pyridyl ethanol pyridine in the condensation product. 11. A process as claimed in any preceding claim wherein dehydration is performed under vacuum preferably at 80-120mm Hg and more preferably 90-110 mm Hg and the dehydrated product is simultaneously distilled. 12. A process claimed in claim 1 or 11 wherein dehydration is carried out in by maintaining the pot temperature to preferably below 170°C. 13. A process as claimed in claim 11 or 12 wherein sodium hydroxide pellets are added for drying equivalent to as required for dehydration in the next batch. 14. A process as claimed in claim 1 wherein reaction product obtained after dehydration and drying is distilled employing fractionating column under vacuum. 15. An improved process for the production of 2-vinyl pyridine and 4-vinyl pyridine substantially as herein described with reference to the foregoing Examples.

Documents:

818-del-2002-abstract.pdf

818-del-2002-claims.pdf

818-DEL-2002-Correspondence-Others-(17-03-2011).pdf

818-del-2002-correspondence-others.pdf

818-del-2002-correspondence-po.pdf

818-del-2002-description (complete).pdf

818-del-2002-form-2.pdf

818-DEL-2002-Form-27-(17-03-2011).pdf

818-del-2002-gpa.pdf