Chemical Reaction: Synthesis of m-Aminoacetophenone from m-Nitrocetophenone

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Research of synthesis of nitroaromatic compounds entails chemoselectivity because in many cases, there are two or more artificial reagents susceptible to reduction and consequently one of the functional group requires to be preferentially chosen to react. For instance, a solution containing nitro group (R-NO2) and a carbonyl team (RR’C=O). The nitro group can be converted into an amino crew while the carbonyl to alcohol but the usage of chemoselectivity, the nitro group can be reduced into the amino crew using Fe or Sn metal in the presence of hydrochloric acid except interfering with the carbonyl group (Wade). In the synthesis of m-aminoacetophenone from m-nitroacetophenone, chemoselectivity is applied whereby the nitro group is reduced to an amino group using tin metal in an acidic medium without interfering with the carbonyl group. An intermediate m-acetylanillinium is formed which after protonation, m-aminoacetophenone is formed. The end product is an essential ingredient in the industrial manufacture of drugs, dye, pesticides, active pharmaceutical ingredients (API), and fine chemicals (Carey).

Aim of the experiment

This experiment aims to synthesize m-Aminoacetophenone from m-Nitroacetophenone.

Procedure

1.00 g of m-nitroacetophenone, 1.20 g of granular tin metal, and 20 mL of 3M HCl were placed in a 100 mL round-bottomed flask.

A reflux condenser was attached and refluxing done until all the tin had dissolved.

20 mL of 6M NaOH was placed in a small beaker and cooled in an ice-water bath as refluxing continued.

After all the tin had dissolved, heating was discontinued, and the contents of the reaction were allowed to cool for 5 minutes.

The sodium hydroxide was carefully added dropwise to the reaction mixture while stirring. ( observations were recorded)

The resulting suspension was allowed to cool a little longer in the ice-water bath. The yellow precipitate was collected by suction filtration using Buchner funnel and washed with 10 mL of ice-cold water. The aqueous filtrate was put in in a waste container in the hood.

The product was allowed to air-dry with suction for a few more minutes.

The crude product was transferred to a 50 mL conical flask and recrystallized from 12 mL of a 3:1 water-ethanol mixture using a hot-plate in a hood. Hot filtration was performed to dissolve all the solids.

The hot solution was slowly cooled to room temperature and water added until cloudiness ensued. The flask was cooled in an ice-water bath to complete crystallization.

The crystals were collected via vacuum filtration, rinsed with a small amount of ice water, and allowed in suction for 30 minutes.

A few crystals of the product were collected and dissolved in acetone while awaiting completion of step 10. This solution and that of m-nitroacetophenone were spotted on a silica gel-coated TLC plate, and develop in dichloromethane. The formed plate was visualized with a UV lamp. Rf values for the starting material and product were calculated, TLC plate labeled clearly for future use. The results of the TLC analysis were discussed.

The product was weighed, and percent yield calculated. Melting point was also determined and recorded.

Results

Weight of m-Aminoacetophenone obtained: 0.66 grams

Percentage yield of the product: 66%

Melting point of the product: 61.9-68.20C

Response to Questions

It was not possible to get the IR spectra due to a time limit. However, three peaks are expected to be visible in m-aminoacetophenone. An arylamine should be indicated by two peaks in the region 3400-3250 cm-1. The other peak should indicate an aryl ketone peak at 1700-1680 cm-1. The aromatic C=C stretches should be found in parts, one at 1600cm-1 and the other at 1475cm-1.

M-Aminoacetophenone is more polar than m-Nitroacetophenone. The intermediate formed will be m-acetyanillium and will have a lower Rf than them-aminoacetophenone.

C6H5NO2 + 7H+ +6e- → C6H5NH3+ + 2H2O

In preparation for m-bromoaniline, the first step involves nitration of the benzene. The nitro group is then converted into an amine, and lastly, bromination is done. When the preparation of p-bromoaniline, bromination occurs first followed with nitration.

C7H6(NO2)2 + Sn + 4e- → C7H6(NH2)2 +Sn+4

Discussion

Use of tin and hydrochloric acid reagents allows the reduction in m-nitroacetophenone to occur selectively whereby reduction occurs only in the carbonyl group and not interfering with the nitro group. The metal tin dissolved in the hydrochloric acid donates electrons required to reduce the m-nitroacetophenone selectively. Refluxing is necessary after the nitro group is reduced to allow the formation of an amino cation solution. Cooling of the solution at 00C and alkalizing with sodium hydroxide deprotonates the cations to form a non-ionized amino group (Tibhe).

Conclusion

The objective of the experiment was achieved since the desired product was obtained in the end. It is necessary to be careful when handling the concentrated hydrochloric acid and concentrated sodium hydroxide since they are corrosive. Similarly, the m-Aminoacetophenone should be treated with care since it irritates in case of contact with the skin.

Works Cited

Carey, F.A. Organic Chemistry. 3rd ed. 916. New York: McGraw-Hill, 1996.

Tibhe, J., Sharma, Y., Joshi, R. A., Joshi, R. R., & Kulkarni, A. A. “Discontinuous two-step flow synthesis of m-aminoacetophenone.” Green Processing and Synthesis, 3(4) (2014): 279-285.

Wade, L. G., Jr. Organic Chemistry. 3rd ed. Englewood Cliffs, NJ: Prentice-Hall, 1995.

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