Hydrolysis of Nitrile in Presence of NaY Zeolite under Microwave Irradiation

Introduction

Development of the simple and general synthetic routes for widely used organic compounds from the readily reagents is one of the major challenges  in organic synthesis. Zeolites have found many important industrial, agricultural applications due to their- High activity levels, regenerability, molecular shape selectivity^1-9. Zeolites are effective catalysts in organic chemistry and they have great utility in industry¹⁰ in Alkylation reaction, polymerisation, cyclization¹¹, photoreduction¹², or preparation of nitroalkenes¹³, occur in gas phase or with reactants sorbed within zeolite in inert solvent. NaY zeolites has been used as catalyst for number of organic reactions and offer several advantages over other classical catalysts i.e. non-corrosive properties, cheapness, mild reactions, high yields, high selectivity, ease of setting and work up. In the last few years a growing interest has also been shown in the use of microwave irradiation in organic synthesis.^14-15

The hydrolysis of nitriles under conventional heating methods is reported in literature¹⁶. But this method requires longer reaction time and tadius work up. So, we have the need of alternative technique for the hydrolysis of nitriles.

Now we want to explore our work for the hydrolysis of nitriles using NaY zeolite in presence of microwave irradiations(See scheme 1).. The organic reactions coupled with microwaves undergo completion with in a few minutes, results in an increase in the purity of the products besides enhancing the chemical yields.

Scheme 1 Click here to View scheme

 

We started our work by heating 2-Pyridylacetonitrile in presence of NaY zeolite as catalyst under microwave irradiations(See scheme-1) and we obtained corresponding amide in 76% yield in just 5-minutes(See table 1). The product was identified on the basis of their IR, ¹H-NMR and by comparison of their Rf values with those of the authentic samples prepared by standard routes.

The hydrolysis of cyanides to corresponding amides occurs on the surface of NaY zeolite catalyst having composition: crystallinity 100%; SiO₂ 63.80%; Al₂O₃ 22.90%; NaO 13.30%; molar ratio SiO₂ / Al₂O₃: 4.73; specific area (B.E.T) 850 m² / g; pore volume 0.32 cm³ / g; diameter of crystallite 3.5 mm; diameter of granulate 150 mm; pH of water suspension 10.05.

The hydrolysis of cyanides to corresponding amides most probably involves the co-ordination of cyanides to metal cations of NaY zeolite catalyst through the nitrogen atom which  become susceptible to nucleophilic attack at the carbon atom and thus results in enhancement of the rate of nucleophilic attack on nitriles co-ordinated to a metal ion is generally in the range 10⁶ to 10⁸(See scheme 2). The amide needs to be expelled from the co-ordination sphere and be replaced by a new nitrile molecule in order to make a more favourable catalytic system.

Scheme 2 Click here to View Scheme

 

In a similar ways, we have also  synthesized other amides in presence of NaY zeolite under microwave irradiations in high yield in shorter reaction time(See table 1).

Table 1 Click here to View table

 

Conclusions

In conclusion, we have shown that the hydrolysis of nitriles into corresponding amides  in presence of NaY zeolite as catalyst occurs in a few minutes with improved yield under microwave irradiation.

Experimental section

Typical Experimental Procedure

The suspension of a nitrile (200mg) in water (5ml) in presence of NaY zeolite (800mg) as catalyst is taken in the open erlenmyer flask. The flask was subjected to 70% irradiation level (560W) in the kenstar OM-9925 (800W) unmodified domestic microwave oven operating at 2450MHz for 5-7 minutes. The contents were allowed to cool and poured into water (30ml). The solid separated was filtered off and washed with ethanol (3ml) and recrystallised (from DMF).

2-Pyridylacetamide

Mp 120-122^oC. (colorless needles, water). IR (KBr) cm^-1: 3377, 3188, 3112, 3017, 1678, 1646, 1597, 1570, 1439, 1402. ¹H NMR (CD3OD, 200 MHz): 8.51-8.43 (m, ¹H, H-C(6′)), 7.78 (td, J = 7.8, 1.8, H-C(4′)), 7.40 (d, J = 8.0, H-C(3′)), 7.30 (ddd, J = 8, 5, 1, H-C(5′)), 3.75 (s, 2H-C(2)). ¹³C NMR (CD₃OD, 50 MHz): 174.97 (C1), 156.82 (C2′), 149.86 (C6′), 138.76 (C4′), 125.69 (C3′), 123.59 (C5′), 45.12 (C2). Anal. calc. for C₇H₈N₂O (136.06): C 61.75, H 5.92, N 20.57, found: C 62.08, H 5.57, N 20.83.

3-Cyanopropanamide

Mp 86-88^oC (colourless amorphous solid). IR (KBr) cm^-1: 3414, 3225, 2293, 2248, 1681, 1619,1421. ¹H NMR (D₂O, 200 MHz) : 2.80-2.65 (m, 4H, 2H-C(2), 2H-C(3)). ¹³C NMR (D₂O, 50 MHz) : 177.90 (C1), 123.04 (C4), 32.38 (C2), 15.12 (C3). MS (CI, isobutane): 197 (2 M++1). Anal. calc. for C₄H₆N₂O (98.11): C 48.97, H 6.16, found: C 49.34, H 6.08.

4-(5-Cyanopentoxy)benzamide

Colourless solid mp 97-101^oC. IR (KBr) cm^-1: 3466, 2140, 1614, 1566, 1401. ¹H NMR (CD₃OD,200 MHz): 7.84 (AA’BB’, J = 6.8, 2, H-C(2), H-C(6)), 6.98 (AA’BB’, J = 6.8, 2, H-C(3), H-C(5)), 4.06 (t, J = 6.2, 2H-C(1′)), 2.49 (t, J = 6.8, 2H-C(5′)), 1.90-1.57 (m, 6H). MS (EI, 70 eV): 232 (M+, 25), 137 (33), 121 (100), 96 (14), 55 (8), 41(5). Anal. calc. for C₁₃H₁₆N₂O₂ (232.12): C 67.22, H 6.94, N 12.06, found: C 67.54, H 6.90, N 12.

Acknowledgements

We thank Professor A.J.Bellamy (Swindon,UK) for inspiration.

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