Presentation on theme: "Experiment 20 SODIUM BOROHYDRIDE REDUCTION OF A KETONE."— Presentation transcript:
Experiment 20 SODIUM BOROHYDRIDE REDUCTION OF A KETONE
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.
Before coming to lab… Review these techniques: Fractional distillation Vacuum filtration GC Analysis
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)
MECHANISM NaBH 4 transfers a hydride ion to the carbonyl carbon. The oxygen anion eventually removes a proton from water.
TODAY’S REACTION Pinacolone is reduced using sodium borohydride. Note that 1 mole of NaBH 4 will reduce 4 moles of ketone. Pinacolone
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
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.
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
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)
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”.
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.