Experiment 4-Chemoselective_reductions_of_3-nitroacetophenone. final-final version

Experiment 4-Chemoselective_reductions_of_3-nitroacetophenone. final-final version

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Experiment 4 A. Reduction with tin and hydrochloric acid B. Reduction with sodium borohydride Lut Ming Cheng, 4957880, CHM2123, Section C Talal Zafar, 4827101, CHM2123, Section C TA: Wendy Campbell Due Date: October 20, 2008 1 – Theory and Mechanism In organic chemistry, reduction reaction involves a gain in hydrogen atoms as oxidation reaction involves a gain in oxygen atoms. In this experiment, the two functional groups on 3- nitroacetophenone are reduced using lewis acid and sodium borohydride (NaBH 4 ). Lewis acid is metals that donate electrons to reduce organic compounds. In the first part of the experiment, we use tin and hydrochloric acid as the reducing reagents. The metal provides its electron the organic compound, and the metals become oxidized to Sn 2+ . At the end of the experiment, the solution is basic and the tin becomes tin oxide, SnO. The reduction reaction with tin as the reduction agent involves three electrons transfer. The mechanism is shown below, C H 3 O N + O O - 2e - /2H + C H 3 O N O -H 2 O 2e - /2H + C H 3 O N OH H 2e - /2H + C H 3 O N H H -H 2 O Balanced eauation: C(CH 3 )OC 6 H 5 NO 2 + 3Sn + 7HCl C(CH 3 )OC 6 H 5 NH 3 + 7Cl - + 3Sn 2+ + 2H 2 O Sodium borohydride is used widely due to its less reactive nature comparing to another reducing agent, aluminum hydride (LiAlH 4 ). It can be used to reduce aldehyde and ketones whereas aluminum hydride can be used to reduce ester, carboxylic acid, etc. In the second part of the experiment, 3-Nitroacetophenone is reduced by sodium borohydride. The transfer of the hydride to the 3-nitroacetophenone reduces the ketone functional group to an alcohol branch. The mechanism is shown below, O C H 3 NO 2 H H B - H H O - C H 3 NO 2 H H OH OH C H 3 NO 2 H O H - + + + 3-Nitroacetophenone After the sodium borohydride is oxidized from the reduction reaction, it would have the form borate ester. At the end of reaction, addition of an acidic solution would turn the borate ester into a salt and boric acid, B(OH)3. The mechanism shown below, R OH BH 3 + B - (OR) 4 H 2 O B(OH) 3 R R OH +
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The purpose of this experiment is to identify the product from each reduction reaction. By measuring the melting point of each product from reactions, students would be able to identify which reducing agent selectively reduces one of the two functional groups on the benzene ring. 2 – Table of Reagents Part A. Reduction of 3-nitroacetophenone with tin and HCl Compound Molar Mass (g/mol) Quantity Density (g/mL) mmol equiv. 3-nitroacetophenone 165.20 0.50g - 3.02 1.00 Granular tin 118.71 1.00g 5.769 8.42 2.79 6M HCl 36.46 10.0mL 1.18 323.64 107.17 NaHCO 3 84.007 1.00mL 2.159 25.70 8.51 Ethyl acetate 88.105 1.00mL 0.897 10.18 3.37 10M NaOH 40.00 9.00mL - - - Water 18.015 7.00mL 1.00 388.57 128.67 Dichloromethane 84.93 15.00mL 1.325 234.02 77.49 Part B. Reduction of 3-nitroacetophenone with NaBH 4 Compound Molar Mass (g/mol) Quantity Density (g/mL) mmol equiv. 3-nitroacetophenone 165.20 0.50g - 3.02 1.00 Anhydrous ethanol 46.068 6.30mL 0.789 107.90 35.73 Sodium borohydride 37.83 0.175g 1.0740 4.626 1.532 Water 18.015 8.00mL 1.00 444.07 147.04 HCl 36.46 3.00mL 1.18 97.09 32.15 Dichloromethane 84.93 11.00mL 1.325 171.61 56.82 3 – Experimental procedure Ref: pages 32-35 of the Organic Chemistry II lab manual Modification B. Reduction of 3-nitroacetophenone with NaBH 4 13. Dry the dichloromethane solution with sodium sulfate for about 2 minutes. You can
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Experiment 4-Chemoselective_reductions_of_3-nitroacetophenone. final-final version

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