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Unformatted text preview: Experiment 4: Hydroboration-oxidation of an alkene Theory & Background: The hydroboration-oxidation of alkenes to alcohols has long fascinated organic chemists because of its synthetic usefulness and interesting mechanism. H. C. Brown shared the 1979 Nobel prize for developing this and other boron reactions. The reaction of borane with an unsymmetric alkene can give two regioisomeric products: boron at the most substituted carbon (Markovnikov addition) or at the least substituted carbon (anti-Markovnikov addition). The latter is heavily favored, providing for a regiose- lective reaction. As long as a B-H bond remains, addition reactions to alkenes continue, eventually affording a trialkylborane. Each addition reaction is a four-centered, four- electron process that is extremely rapid. And, each sequential reaction is slightly more regioselective. A GC will be taken of the product mixture at the conclusion of the ex- periment to determine the ratio of components. 1) BH 3 THF 2) NaOOH OH OH + Please regenerate this table in your notebook flling in any oF the blanks Reagent Values 1-octene (98%) ignore the 2% 1M borane in TH a stock solution HOOH 30% (w/w) active 3M sodium hydroxide 120g/l octanol Formula C 8 H 16 NA H 2 O 2 NaOH C 8 H 18 O equiv 1.0 0.37 (1.1H- equiv) 2.2 0.67 1.0 expected MW density volume mass mmol. boiling point Glassware Set-up: Procedure 1: Add 1-octene (150 mg, 1.0 equiv) to a dry 5.0 mL conical vial equipped with a spin vane. Attach a Claisen adapter and a CaCl 2 drying tube. Then chill the vial in an ice water bath (0 C) while stirring for 5 min- utes. Now add 1M BH 3 in THF (0.37 equiv; 1.1 hydride equiv) with a plastic syringe and needle dropwise over 5 minutes. Remove the ice bath and stir for 30 more min- utes. *Syringes for BH 3 additions may be shared. Work-Up: Remove the Claisen adapter and drying tube. Add H 2 O (5 drops) to the stirring solution slowly with a pipet to quench any unreacted borane. 18 Techniques Syringe use reagent transfer in air sensitive systems To help you preserve reagent quality, many Aldrich and luka air- and moisture-sensitive reagents are packaged under nitrogen or argon in crown-cap bottles, with a 6mm diameter hole in the crown-cap and a PTE Faced rubber liner under the crown-cap, For simple...
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This lab report was uploaded on 04/07/2008 for the course CHEM 6b taught by Professor Pettus during the Spring '07 term at UCSB.
- Spring '07