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Experiment 18: THE GRIGNARD REACTION
Objectives: • To synthesize a 3o alcohol from an alkyl halide and a ketone using a Grignard reaction. • To purify product using a liquid extraction method. • To determine purity using GC analysis. • To characterize starting materials and products using IR, 1H-NMR, and 13C-NMR spectra.
Before coming to lab… • Review the following techniques: • Extraction • Drying organic solvents with MgSO4 • Preparing GC samples • You will be expected to perform these will little review, as you learned these techniques in the first semester lab.
MAKING THE GRIGNARD REAGENT • Organic halides react with magnesium metal in diethyl ether or THF to yield an organomagnesium halide: RMgX DIETHYLETHER R-X + Mg-------------> R-Mg-X or THF Where R= 1o, 2o, or 3o alkyl, aryl or alkenyl X= Cl, Br, I • The C-Mg bond is a highly polar covalent bond. The carbon atom is both nucleophilic and basicmaking it very reactive with a wide variety of E+.
MECHANISM 3….which reacts with water when aqueous HCl is added, undergoing hydrolysis to form the product alcohol. 1. The Lewis acid Mg2+ forms an acid-base complex with the basic oxygen atom of the ketone, making the carbonyl group a better acceptor. 2. Nucleophilic addition of butyl group to acetone produces a tetrahedral intermediate…
WHEN THE GRIGNARD REAGENT MEETS WATER… • Since the carbon atom of a Grignard reagent is so nucleophilic and basic, it reacts with proton donors (Brönsted acids) such as H2O, ROH, RCOOH, RNH2 to yield hydrocarbons. • This makes it extremely important to keep the reaction flask and solvent completely dry of water.
OVERVIEW • Heat alkyl halide, magnesium turnings, and ketone in diethyl ether under reflux to synthesize intermediate. • Hydrolyze intermediate with HCl to produce neutral product. • Purify product by extraction. • Prepare GC sample. • Analyze product using GC to identify and determine purity.
EXPERIMENTAL PROCEDURE(Synthesis of Grignard reagent…) • Place Mg turnings in 50mL flask and place a CaSO4 tube in the top IMMEDIATELY! • Clamp flask to ring stand and set up remainder of reflux with addition apparatus. • Start reaction with a small amount of n-butylbromide and ether by scratching Mg surface and stirring with glass rod. • Add remaining n-butylbromide and ether to sep funnel. • Add to reaction mixture dropwise. CaSO4 drying tube in adapter Keck clips
EXPERIMENTAL PROCEDURE(Synthesis of alcohol product…) • Add acetone/ether to sep funnel. • Add to reaction mixture dropwise. • Cool reaction flask in water bath. • Transfer cooled liquid to 125 mL Erlenmeyer flask. • Add an ice cube and NH4Cl.
EXPERIMENTAL PROCEDURE(Purification…) • Set up an extraction apparatus. • Transfer the liquid from the flask to the funnel. • Extract with 5%HCl, 10% NaHCO3, and Sat. NaCl. • Transfer organic layer to a 50 mL flask and dry over MgSO4. • Transfer dried organic liquid to a beaker. • Submit a GC sample.
Table 18.1 Record retention times for ALL peaks in standard chromatogram! Record retention times and area % for ALL peaks present in sample chromatogram! Calculate AA% for REACTANTS AND PRODUCT only!
Table 18.2 • IR spectra available on p. 157, 158 of the lab manual! • In discussion, only refer to frequencies which indicate a CONVERSION to product!
Product Analysis(13C-NMR Spectroscopy) NMR solvent C1 29d NMR solvent
Table 18.3 n-butylbromide (reactant) 2-methyl-2-hexanol (product) • Enter chemical shifts ONLY based on the spectra on page 157, 158. • In discussion, only refer to signals which indicate a CONVERSION to product!
SAFETY CONCERNS • Diethyl Ether is EXTREMELY flammable. Use extreme caution at all times! • Be sure to wear goggles at ALL times during this experiment! • GLOVES are available upon request!
WASTE MANAGEMENT • RECOVERED MAGNESIUM WASTE: Unreacted magnesium & water rinse. • LIQUID AQUEOUS WASTE: • Aqueous extracts and washes. • LIQUID ORGANIC WASTE: • Crude Alcohol product. • MgSO4 WASTE: • Magnesium sulfate.
CLEANING • Rinse condenser and Claisen adapter with wash acetone only. • Clean all other glassware with soap, water, brush, and rinse with wash acetone. • Leave all ground glass jointware in lab hood for inspection. DO NOT place any in lab drawer. • DO NOT return any glassware to lab drawer dirty or wet.
LABORATORY NOTEBOOK(Pre-lab) • OBJECTIVE (Must clearly state…) • What compounds will be made and how • How the compounds will be purified • How the identity and purity of the product will be determined • CHEMICAL EQUATION • Include the balanced chemical equation from top of p.153. • TABLE OF PHYSICAL DATA (Complete the following table using a site listed on WWW Links ONLY. Wikipedia is unacceptable!) • REFERENCE TO PROCEDURE (Must include…) • full title including edition and authors • page numbers where actual procedure can be found
LABORATORY NOTEBOOK(In-lab) • DATA/CALCULATIONS • Physical state and color of product • Theoretical yield calculation • GC vial slot # • Give one example of an adjusted area % calculation • EXPERIMENTAL PROCEDURE • In paragraph form, describe the procedure that you actually followed during the lab. • Paragraph must be written in PAST TENSE, PASSIVE VOICE. • Include any volumes or weights of chemicals used during the experiment. • Include any mistakes, accidents or observations if applicable.