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Reduction of Nitro to amine with iron and aqueous saturated sodium chloride; Ortho-toludine

SyntheticPage 829
Submitted Jul 15, 2017, published Aug 10, 2020
Ramesha Ramakrishna (ramesha63@hotmail.com)
A contribution from ramesha


			Reaction Scheme: Reduction of Nitro to amine with iron and aqueous saturated sodium chloride

Chemicals Used

2-Nitrotoluene (Commercial, Min 98%)
Iron powder (powder, lab grade)
Sodium chloride (commercial)
Methanol (commercial > 99%)
Toluene (commercial, >99%), Celite (hyflow supercel), commercial

Procedure

To a three necked 500 mL flask carrying a mechanical stirrer, thermometer pocket, reflux condenser was charged methanol (250 mL) followed by ortho nitro toluene (50 g, 0.36 mol). To this stirred solution, aqueous saturated sodium chloride solution (70 g sodium chloride in 70 mL water) was added all at once. Temperature raised to about 40°C. Iron powder (100 g, 1.79 equiv.) was added under stirring over a period of 15 min and then refluxed for 7h. Once TLC showed completion of the reaction (2:8, ethyl acetate: petroleum ether 40-60°C), the reaction mixture was cooled to about 40°C, water added (100 mL). It is very important to add water before distillation of methanol. If methanol is removed without addition of water, there is a possibility of runaway reaction. Iron sludge from the reaction is pyrophoric if dry. Approximately 90% methanol was removed under vacuum. The reaction was cooled to room temperature and extracted with toluene (200 mL x 2). The black toluene layer was filtered through a bed of celite. The celite was washed with toluene (50 mL). The combined filtrates were mixed and washed with water (150 mL). Toluene was removed under reduced pressure to give pale yellow to light brown liquid 36 g (92%). This crude product is pure by NMR.

 

 

Author's Comments

1. This reaction is milder compared to Iron-acid reduction.

2. This reaction can also be done in stainless steel vessel. This has been scaled upto 100 kg batches.

3. The product from this reduction is normally pure and does not require further purification.

4. Use of electrolytic grade iron reduces the reduction time from 7 to about 2-3 h.

5. This is a general method applicable to any nitro to amine reduction.

6. It is very important to add water before recovery of methanol to avoid exothermic reaction

 

Data

1H NMR (300 MHz): δ 2.09 (s, 3H), 3.47 (s, br, 2H), 6.58 (d, J = 7.6 Hz, 1H), 6.67 (t, J = 7.6 Hz, 1H), 6.98-7.01 (m, 2H).

13C NMR (100 MHz): δ 17.4, 115.0, 118.7, 122.4, 127.1, 130.6, 144.8.

 


Lead Reference

Krishnamurthy Ramadas & Natarajan Srinivasan, Synthetic Communications, 1992, 22(22), 3189–3195.

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Keywords: amine, amines, aromatics/arenes, Iron, Nitro, reduction, sodium chloride

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