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Experiment 20 SODIUM BOROHYDRIDE REDUCTION OF A KETONE.

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Presentation on theme: "Experiment 20 SODIUM BOROHYDRIDE REDUCTION OF A KETONE."— Presentation transcript:

1 Experiment 20 SODIUM BOROHYDRIDE REDUCTION OF A KETONE

2 Objectives:  To synthesize a tertiary 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. c  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 NaBH 4  NaBH 4 (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 NaBH 4 transfers a hydride ion to the carbonyl carbon. The oxygen anion eventually removes a proton from water.

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

7 EXPERIMENTAL PROCEDURE (Synthesis)  Add 3,3-dimethyl-2-butanone and methanol to 100 mL beaker.  Place in ice water bath.  Add NaBH 4 while stirring with glass rod.  Continue to react at 0 o C for 5min, then 10 min more at RT.  Add 6M HCl dropwise.  Suction filter to remove separate solid from liquid filtrate.  Transfer 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 70 o C in a small flask.  Switch to 25 mL round bottom flask and collect distillate between o C.  Cool flask, reweigh.  Prepare GC sample.

9 Table 20.1 Theoretical yield (g)  Calculated based on limiting reactant Actual yield (g) Percent yield  (Actual yield/Theoretical yield) X 100 Distillation Range ( o C)  Give Ti-Tf of distillate collected in 25 mL round bottom flask Product Appearance  Give physical state and color of product

10 Table 20.2 Atom Economy (%)  Calculate based 3,3-dimethyl-2- butanone and sodium borohydride ONLY! Experimental Atom Economy (%) o Review Experiment 13 for calculations! “E product ” Cost per synthesis ($) Cost per gram ($/g)

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