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Experiment 20

Experiment 20. SODIUM BOROHYDRIDE REDUCTION OF A KETONE. Objectives:. To synthesize a secondary alcohol from a ketone using a sodium borohydride reduction. To purify the product using fractional distillation. To analyze the purity of the product using GC.

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Experiment 20

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  1. Experiment 20 SODIUM BOROHYDRIDE REDUCTION OF A KETONE

  2. Objectives: • To synthesize a secondary alcohol from a ketone using a sodium borohydride reduction. • To purify the product using fractional distillation. • To analyzethe purity of the product using GC. • To characterize the reactants and products using NMR and IR spectroscopy.

  3. Before coming to lab… • Review these techniques: • Fractional distillation • Vacuum filtration • GC Analysis

  4. REDUCTION USING NaBH4 • NaBH4 (sodium borohydride) is a versatile and useful reducing agent in organic chemistry. • A reducing agent causes a reaction (a reduction) in which the product has more bonds from carbon to hydrogen (or fewer bond to oxygen)

  5. MECHANISM The oxygen anion eventually removes a proton from water. NaBH4 transfers a hydride ion to the carbonyl carbon.

  6. TODAY’S REACTION Pinacolone • Pinacolone is reduced using sodium borohydride. • Note that 1 mole of NaBH4 will reduce 4 moles of ketone.

  7. EXPERIMENTAL PROCEDURE(Synthesis) • Add 3,3-dimethyl-2-butanone and methanol to 100 mL beaker. • Place in ice water bath. • SLOWLY add NaBH4 while stirring with glass rod. • Continue to react at 0oC for 5min, then 10 min more at RT. • Add 6M HCl drop wise. • Suction filter to remove solid from liquid filtrate. • Transfer liquid filtrate to 50 mL round bottom flask. 100 mL 50 mL

  8. EXPERIMENTAL PROCEDURE(Purification and GC Analysis) • Set up fractional distillation apparatus. • Apply heat and collect distillate below 70oC in a small flask. • Switch to 25 mL round bottom flask and collect distillate between 70-85oC. • Cool 25 mL flask, reweigh. • Prepare GC sample. Keck clips 25mL PRODUCT! 50mL

  9. Table 20.1

  10. Table 20.2

  11. WASTE MANAGEMENT • Place the solid boric acid waste from the filtration into the container labeled “SOLID WASTE” located in the waste hood. • Place all liquid waste into the container labeled “LIQUID WASTE”.

  12. SAFETY CONCERNS • 3,3-dimethyl-2-butanone, 3,3-dimethyl-2-butanol, methanol and sodium borohydride are all FLAMMABLE materials. • Methanol and sodium borohydride are TOXIC in large concentrations. • Hydrochloric acid is CORROSIVE.

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