Zinc-catalyzed ammonium formate reductions: rapid and selective reduction of aliphatic and aromatic nitro compounds
Gowda, D. Channe; Mahesh, B.; Gowda, Shankare.
Indian Journal of Chemistry, Section B: Organic Chemistry (2001), 40B(1), 75-77.
Abstract
Aliphatic and aromatic nitro compounds are selectively and rapidly reduced to their corresponding amino derivatives in good yields using Ammonium Formate and commetrial Zinc dust. This system is found to be compatible with several sensitive functionalities including halogens, -OH, -OCH3, -CHO, -COCH3, COC6H5, -COOH, -CO2C6H5, -CONH2, -CN, -CH:CHCOOH, -NHCOCH3. The reduction can be carried out not only with HCOONH4 but also with HCOOH.
In this communication we wish to report a selective, rapid and simple reduction of aliphatic and aromatic nitro compounds to the corresponding amino derivatives using commertial zinc dust and ammonium formate at room temperature. This new system reduced a wide variety of nitro compounds directly to the corresponding amines and many functional groups can bee tolerated. When ammonium formate is replace by formic acid the reduction proceeds effectively and the products were obtained in almost comparable yeilds.
The reduction of nitro group in the presence of activated zinc (pretreated with HCl and throughly washed with water and ether prior to use) and HCOONH4 or HCOOH was complete in 2 - 10 min. The course of this reaction was monitored by TLC and IR. The work-up and isolation of the products were easy. Thus all compounds reduced (Table 1) by this system were obtained in good yeild (90-95%). All products were characterized by comparison of their TLC, IR and melting points with authentic samples.
Typical Procedure
A suspension of an appropriate nitro compound (5 mmol) and Zn dust (6 mmol) in methanol or in any suitable solvent (5 ml) was stirred with ammonium formate (0.5 g) or 90% HCOOH (2.5 ml) at room temperature. After completion of the reaction (monitored by TLC), the mixture was filtered off. The organic layer was evaporated and the residue dissolved in CHCl3 or ether and washed with saturated NaCl to remove ammonium formate. The organic layer upon evaporation gave the desired amino derivatives.
Thus the reduction of nitro compounds can bee accomplished with commertial zinc dust instead of expensive Pt, Pd ect., without affecting the reduction of any reducible substituents includeing halogen and carbonyl compounds. The yeilds were virtually quantitative and analytically pure.
The obvious advantages of the proposed method over previous methods are: (i) selective reduction of nitro compounds in the presence of other reducible groups includeing halogen and carbonyl compounds, (ii) ready availabilty and easy to operate, (iii) rapid reaction, (iv) high yeilds of substituted anilines, (v) avoids strong acid media, (vi) no requirement for pressure apparatus, and (vii) LESS EXPENSIVE. This procedure will be of general use espically in cases where rapid, mild and selective reuction are required.
Table 1. Zinc catalyzed reduction of nitro compounds.
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-------------------------- Reaction Time in Min ---------Yeild (a)---
Nitro compound............ HCOONH4 ... HCOOH .......... (%) .......
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Nitromethane.........................2....................2...................45.....(b,c)
Nitroethane............................5....................7...................50.....(b,c)
1-Nitropropane......................5....................7...................55.....(c)
1-Nitrobutane........................2....................4....................60.....(c)
1-Nitroethylethanoate.............5....................5....................65.........
4-Nitromethylbutanoate..........5....................7...................80..........
Nitrobenzene..........................8...................10..................90......(d)
o,m,p-Nitrophenol................3-5.................3-5................92-93.......
2,4-Dinitrophenol...................5....................5....................92..........
o,m,p-Nitrotoluene................3-5.................3-5................89-91..(d)
2,4-Dinitrotoluene..................5....................5....................90..........
o,m-Dinitrobenzene...............4-6.................4-6................90-91.......
o,p-Nitrobenzaldehyde..........8-10.............10-15..............89-90.......
o,p-Nitroacetophenone.........8-10.............10-15..............92-93.......
p-Nitrobenzophenone............10..................10...................92.........
p-Nitrobenzamide...................8...................10...................90.........
p-Nitrophenylacetate...............5....................5...................91.....(e)
o,m,p-Nitrobenzoic acid........3-5................5-6................93-94.......
o,m,p-Nitrochlorobenzene.....5-6................5-6................94-95.......
o,m,p-Nitrobromobenzene.....5-6................5-6................91-92.......
p-Nitroiodobenzene................5...................5....................89.........
p-Nitrocinnamic acid...............5...................7....................90.........
p-Nitrobenzonitrile..................10.................15...................93.........
p-Nitrophenylacetonitrile........10.................15....................93.........
p-Nitrophenylethylalcohol.......15.................20...................90.........
3,5-Dinitrosalicylic acid...........6...................6...................89.........
p-Nitroacetanilide...................5....................5...................90.........
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(a) Isolated yeilds are based on a single experiment and not optimized
(b) The low yeild of aliphatic amines is due to their volitility
(c) Isolated as hydrochloride salts
(d) Isolated as benzoyl derivatives
(e) Isolated as acetyl derivative
(d) All nitro groups are transformed to their corresponding amine, with no other functional groups affected.