Title of Invention	"AN IMPROVED PROCESS FOR THE SYNTHESIS OF PYRIDINE -2-CARBOXALDEHYDE"
Abstract	An improved process for the preparation of pyridine-2-car- boxaldehyde which comprises: passing a liquid feed comprising of 2—picolyl alcohol and water in the ratio in the range of 1:5 to 1:30 in presence air over a novel silica alumino phosphate (SAPO) catalyst at a temperature in the range of 250-420 C, recovering the product by conventional fractional distillation methods.

Full Text

AN IMPROVED PROCESS FOR THE SYNTHESIS OF PYRIDINE-2-CARBOXALDE--HYDE More particularly this invention relates to a process for the preparation of pyridine-2-carboxaldehyde selectively from 2-pyridyl carbinol. The dehydrogenation of 2-pyridyl carbinol was carried out over modified and unmodified amorphous or crystalline silico-alumino phosphate catalysts. The silico-alumino phosphates, are mild and oxidation catalysts. Pyridine-2-carboxaldehyde is used in the preparation of pralidox-ime met;hiodide which is antidote for poisning by organophosphate acetylcholine sterase inhibitors. Pyridine-2-carboxaldehyde is also used in the production of bisacodyl a laxative. E.P.Papodopoulous et al in 1966 reported the synthesis of Pyridine -2 -carboxaldehyde from 2-pyridyl carbinol over manganese dioxide catalyst. In 1990 Subrahmanyam and Prasad also reported the synthesis of pyridine-2-carboxaldehyde over mixed oxide like V-Mo oxide catalyst, from 2-picolyl alcohol. In 1980|S.L.T.An-dersson and Jaras synthesised 2-pyridine carboxaldehyde from 2-picoline itself. The yield and selectivity of pyridine-2-carboxaldehyde is lower. The water in the feed is very large amount to avoid the side products like pyridine and coke in case of literature reports. The catalysts used in the present invention were the silico-alumino phosphates (SAPO) and modified siiico-aiumino phosphate catalysts. Different types of silico-alumino phosphates were used like SAPO-37, SAPO(TBA), SAPO(TripA) and SAPO(DPA). The bracketed letters indicate the template used for the synthesis of respective SAPO's The synthesis of these silico-alumino phosphate(s) has been reported in our copending patents, Indian Patent Appl. No. 963/Del/1995, 1459/Del/1995. The Organic templates used were tetrabutyl ammonium bromide (TBA), tetra propyl ammonium bromide (TPA), tripropyl amine (TriPA) and dipropyl amine (DPA) All these catalysts are synthesized hydrothermally. The object of the present invention is to provide an improved process for the synthesis of pyridine-2-carboxaldehyde using modified silico-alumino phosphate catalysts. Accordingly the present invention provides an improved process for the synthesis of pyridine-2-carboxaldehyde which comprises: passing a liquid feed comprising of 2-picolyl alcohol and water in the ratio in the range of 1:5 to 1:30 in presence of air over a catalyst novel silico alurniniophous-plate at a temperature in the range of 250 to 420° C, recovering the product by conventional practional distillation methods. Feed containing 2-picolyl alcohol and water having weight hourly space velocity may be in the range of 0.25 to 1.0 h -1. The catalyst used may be such as SAPO-37, SAPO(TBA), SAPO(TPA), SAPO(TriPA) and SAPO(DPA) water) was fed from top using a syringe pump(BeBraun). The product was cooled using ice-cooled water and collected at the bottom. The air was passed through the calibrated manometer. The products were analysed by GC using SE-30 (30%) column. The analysis was confirmed by mass spectrometry and GC-mass. The mass balance was >90%. The reaction of 2-picolylalcohol in the presence of water and air was carried out over various modified and unmodified silico- aluminophosphate catalysts. The reaction was carried out in the 0 temperature range of 300-420 C with WHSV 0.25 to 1. The reactions were carried out after the removal of template. The yields of pyridine-2-carboxaldehyde were 69.1, 65.4 and 53.2 wt% ove"r SAPO(DPA), SAPO(TriPA) and SAPO-37 catalysts respective- 0 -1 ly at >95% conversion at 400 C reaction temperature and 0.5 h WHSV. Over HZSM-5(Si/Al=30) and V-Ti-ZSM-5, 2.2% pyridine-2- carboxaldehyde was obtained and the major products were pyridine and 2-picoline. The dealkylation of picolylalcohol leads to pyridine and the acidic centres are responsible for the process. To enhance the selectivity of pyridine-2-carboxaldehyde, the amorphous silico-aluminophosphate(DPA) catalyst was further promoted by potassium (5 wt%) and antimony (1 wt%) to reduce the acidic centres. The yield of pyridine-2-carboxaldehyde was 81.9 wt% at 98.0 wt% conversion of 2-pyridyl carbinol over Sb-K- 0 SAPO(DPA) at 380 C. The reaction of 2-picolylalcohol was carried out over amorphous MSAPO catalysts. The yields of pyridine-2-carboxaldehyde were 31.4, 65.9, 38.6 and 68.4 % over amorphous VSAPO-37, MnSAPO-37 0 CoSAPO-37 and NiSAPO-37 at 380 C. The variation in the activity is due to the transition cations. The effect of water dilution on the dehydrogenation of picolylal-cohol over amorphous SAPO(TriPA) has been studied. The yield of pyridine-2-carboxaldehyde decreased with the increase of dilution of the feed. On the other hand the formation of pyridine increases. The effect of reaction temperature on the dehydrogenation of 2-picolylalcohol is also studied. The yield of pyridine-2-carbox- 0 aldehyde in the temperature range of 350-400 C was 63.0 to 69.1 % over amorphous SAPO(TriPA) catalyst. Over vanadium (>15%) modified catalysts, the formation of other side products like carbox- 2 ylic acid and CO were observed due to strong oxidising nature of the active centre. In our studies we have not observed >2% car- 2 boxylic acids, CO etc. As proposed in the literature, the redox system like vanadium is the active centre for the dehydrogena- 5+ 4 + tion. In case of V V system, the oxidation states are stable and with the various coordination states, for the formation of oxo and peroxo species. Thus an improved process for the preparation of pyridine-2-carboxaldehyde by the dehydrogenation of 2-picolylalcohol has been carried out over crystalline and amorphous modified silico-aluminophosphate catalysts with high yield and selectivity. The following examples are given by way of illustration.- should not construed to limit the scope of the present invpnt' Example 1 : 0.57 gm per hr of 2-picolylalcohol, 1.5 gm per hr of water and 60 ml per hr air was passed over amorphous silico- aluminophosphate (DPA) catalyst, the yield of pyridine-2- carboxaldehyde was 69.1 wt% at 99 wt% conversion of 2-picolyl 0 -i alcohol. The reaction was carried out at 400 C and 0.5 hr weight hourly space velocity (WHSV). The other major products were pyridine (13.5%) and 2-picoline (14.8%). The products were collected using ice-cooled water. The products may be separated by fractional -distillation or extractive fractional distillation. Example 2 : 0.57 gm per hr of 2-picolylalcohol, 1.5 gm per hr of water and 60 ml per hr air was passed over amorphous silico- aluminophosphate (TriPA) catalyst, the yield of pyridine-2- carboxaldehyde was 65.4 wt% at 95.1 wt% conversion of 2-picolyl 0 -i alcohol. The reaction was carried out at 400 C and 0.5 hr weight hourly space velocity (WHSV). The other major products were pyridine (10.3%) and 2-picoline (13.3%). The products were collected using ice-cooled water. The products may be separated by fractional distillation or extractive fractional distillation. Example 3 : 0.57 gm per hr of 2-picolylalcohol, 1.5 gm per hr of water and 60 ml per hr air was passed over amorphous silico-aluminophosphate-37 catalyst, the yield of pyridine-2- carboxaldehyde was 53.2 wt% at 100 wt% conversion of 2-picolyl alcohol. The reaction was carried out at 400 C and 0.5 hr weight hourly space velocity (WHSV). The other major products were pyridine (19.2%) and 2-picoline (25.9%). The products were collected using ice-cooled water. The products may be separated by fractional distillation or extractive fractional distillation. Example 4 : 0.57 gm per hr of 2-picolylalcohol, 1.5 gm per hr of water and 60 ml per hr air was passed over amorphous potassium silico-aluminophosphate (DPA) (where 5% k is present) catalyst, the yield of pyridine-2-carboxaldehyde was 70.6 wt% at 100 wt% conversion of 2-picolyl alcohol. The reaction was carried out at 0-1 400 C and 0.5 hr weight hourly space velocity (WHSV). The other major products were pyridine (14.7%) and 2-picoline (9.7%). The products were collected using ice-cooled water. The products may be separated by fractional distillation or extractive fractional distillation. Example 5 : 0.57 gm per hr of 2-picolylalcohol, 1.5 gm per hr of water and 60 ml per hr air was passed over amorphous Sb-K-silico- aluminophosphate (DPA) (where 1% Sb, 5% K is present) catalyst, the yield of pyridine-2-carboxaldehyde was 81.9 wt% at 98 wt% conversion of 2-picolyl alcohol. The reaction was carried out at 0 -1 400 C and 0.5 hr weight hourly space velocity (WHSV). The other major products were pyridine (7.2%) and 2-picoline (5.3%). The products were collected using ice-cooled water. The products may be separated by fractional distillation or extractive fractional distillation. Example 6 : 0.57 gm per hr of 2-picolylalcohol, 1.5 gm per hr of water and 60 ml per hr air was. passed over amorphous Manganese silico-aluminophosphate -37 catalyst, the yield of pyridine-2- carboxaldehyde was 65.9 wt% at 93.4 wt% conversion of 2-picolyl 0 -l alcohol. The reaction was carried out at 380 C and 0.5 hr weight hourly space velocity (WHSV). The other major products were pyridine (7.6%) and 2-picoline (12.0%). The products were collected using ice-cooled water. The products may be separated by fractional distillation or extractive fractional distillation. Example 7 : # 0.57 gm per hr of 2-picolylalcohol, 1.5 gm per hr of water and 60 ml per hr air was passed over amorphous Cobalt silico-aluminophosphate -37 catalyst, the yield of pyridine-2- carboxaldehyde was 38.6 wt% at 69.8 wt% conversion of 2-picolyl 0 -1 alcohol. The reaction was carried out at 380 C and 0.5 hr weight hourly space velocity (WHSV). The other major products were pyridine (5.7%) and 2-picoline (13.3%). The products were collected using ice-cooled water. The products may be separated by fractional distillation or extractive fractional distillation. Example 8 : 0.57 gm perhr of 2-picolylalcohol, 1.5 gm per hr of water and 60 ml per hr air was passed over amorphous Nickel silico-alumi- collected using ice-cooled water. The products may be separated by fractional distillatiion or extractive fractional distillation. Advantages of the process 1. The yield and selectivity of 2-pyridine carboxaldehyde were higher in our process. 2. The amount of water in the feed was less in our process. 3. The dealkylation leading to pyridine and coking were less in our process. nophosphate -37 catalyst, the yield of pyridine-2-carboxaldehyde was 68.4 wt% at 97.8 wt% conversion of 2-picolyl alcohol. The reaction was carried out at 380 C and 0.5 hr weight hourly space velocity (WHSV). The other major products were pyridine (17.3%) and 2-picoline (11.7%). The products were collected using ice-cooled water. The products may be separated by fractional distillation or extractive fractional distillation. Example 9 : 0.57 gm per hr of 2-picolylalcohol, 1.5 gm per hr of water and 60 ml per hr air was passed over amorphous silico- aluminophosphate (TriPA) catalyst, the yield of pyridine-2- carboxaldehyde was 63.5 wt% at 90.5 wt% conversion of 2-picolyl alcohol. The reaction, was carried out at 350 C and 0.5 hr weight hourly space velocity (WHSV). The other major products were pyridine (14.6%) and 2-picoline (6.3%). The products were collected using ice-cooled water. The products may be separated by fractional distillation or extractive fractional distillation. Example 10 : 0.57 gm per hr of 2-picolylalcohol, 1.5 gm per hr of water and 60 ml per hr air was passed over amorphous silico- aluminophosphate (TriPA) catalyst, the yield of pyridine-2- carboxaldehyde was 64.4 wt% at 98.3 wt% conversion of 2-picolyl alcohol. The reaction was carried out at 380 C and 0.5 hr weight hourly space velocity (WHSV). The other major products were pyridine (20.1%) and 2-picoline (10.5%). The products were We Claim: 1. An improved process for the synthesis of pyridine-2 - carboxaldehyde which comprises: passing a liquid feed comprising of 2-picolyl alcohol and water in the ratio in the range of 1:5 to 1:30 in presence of novel silica alumina phosphate (SAPO) air over a catalyst at a temperature in the range of 250 to 420°C, recovering the product by conventional fractional distillation methods. 2. An improved process as claimed in claim 1 wherein the feed containing 2-picolylalcohol and water used is passed at weigh hourly space velocity in the range of 0.25 to 1.0. 3. An improved process as claimed in claim 1 and 2 wherein the silicoalumino phoshpate catalyst used is SAPO (ITA), SAPO (DPA), SAPO(TriPA) and SAPO-37. 4. An improved process for the preparation of pyridine-2-carboxaldehyde substantially as herein described with reference to the examples.

Documents:

2439-del-1997-abstract.pdf

2439-del-1997-claims.pdf

2439-del-1997-complete specification (granded).pdf

2439-del-1997-correspondence-others.pdf

2439-del-1997-correspondence-po.pdf

2439-del-1997-description (complete).pdf

2439-del-1997-form-1.pdf

2439-del-1997-form-2.pdf