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Experiment 18:. THE GRIGNARD REACTION. Objectives:. To synthesize a 3 o 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.

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experiment 18

Experiment 18:

THE GRIGNARD REACTION

objectives
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
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
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
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
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
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.
slide9

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
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
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.
slide12

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
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 13 c nmr spectroscopy
Product Analysis(13C-NMR Spectroscopy)

NMR solvent

C1

29d

NMR solvent

table 18 3
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
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!
slide19

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
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
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
slide22

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.