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Experiment 11:. CONVERSION OF AN ALCOHOL TO AN ALKYL BROMIDE WITH REARRANGEMENT. Objectives. To synthesize isomeric alkyl halides from an alcohol using an S N 1 dehydration reaction. To determine product substitution based on reaction rate with AgNO 3.

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experiment 11

Experiment 11:

CONVERSION OF AN ALCOHOL TO AN ALKYL BROMIDE WITH REARRANGEMENT

objectives
Objectives
  • To synthesize isomeric alkyl halides from an alcohol using an SN1 dehydration reaction.
  • To determine product substitution based on reaction rate with AgNO3.
  • To characterize reactants and products using IR spectroscopy.
chemical equation
CHEMICAL EQUATION

2-methylcyclohexanol

1-bromo-1-methylcyclohexanol

(3o alkyl halide)

1-bromo-2-methylcyclohexanol

(2o alkyl halide)

s n 1 mechanism
SN1 MECHANISM

2. Forms new O-H bond, oxygen bears a positive charge (oxonium ion).

3. Water is eliminated-forms 2o carbocation.

1. hydroxyl oxygen attacks and removes a proton from hydrobromic acid.

4. Products may form from the 2o carbocation, but it is more likely that the 2o C+ will rearrange to a 3o C+.

5. Reaction of the carbocation with the bromide ion yields the alkyl halide.

5. Reaction of the carbocation with the bromide ion yields the alkyl halide.

overview
OVERVIEW
  • Heat alcohol and acid under reflux to synthesize product(s).
  • Purify product by extraction to remove unreacted starting materials.
  • Obtain final product mass and calculate % yield.
  • Analyze product with AgNO3 test to determine which product forms.
experimental procedure synthesis
EXPERIMENTAL PROCEDURE(Synthesis)

Leave open at top!

  • Add 2-methylcyclohexanol, 48% HBr and 3 boiling chips to flask.
  • Clamp flask to ring stand.
  • Attach clear hoses to condenser and place condenser on top of flask.
  • Begin water flow through condenser and apply heat.
  • Reflux the solution for 30 minutes.
  • Cool flask in beaker of tap water.
experimental procedure purification
EXPERIMENTAL PROCEDURE(Purification)
  • Transfer solution to separatory funnel.
  • Add concentrated sulfuric acid.
  • Stir solution gently with glass rod. Do NOT agitate.
  • Draw off bottom acidic layer into an Erlenmeyer flask.
  • Transfer the top layer to a preweighed beaker using a glass Pasteur pipet.
  • Reweigh beaker to obtain final mass.
  • Perform silver nitrate test.
experimental procedure silver nitrate test
EXPERIMENTAL PROCEDURE(Silver Nitrate Test)
  • When an alkyl halide is treated with a solution of alcoholic silver nitrate, a precipitate of silver halide forms.
  • The rate limiting step is the formation of the carbocation.
infrared spectroscopy ir how to answer the questions
Infrared Spectroscopy (IR)(How to answer the questions…)
  • How are you able to DIFFERENTIATE between reactant and product?
  • Discuss the appearance of certain types of absorptions, or the disappearance of others, which indicate that functional groups have changed.
  • Always answer like this: (fill in the blanks)
    • In the IR spectrum of the product, the appearance of the _____ (type of bond) absorption at _____ (actual frequency) indicates the conversion of the reactant to the product. The typical frequency for this type of absorption is _____ (base value frequency).
safety concerns
SAFETY CONCERNS
  • Sulfuric acid is very corrosive and must be used with EXTREME caution!
  • Silver nitrate will stain the skin! Use gloves at all times!
  • Alkyl bromides are lachrymators! Keep covered at all times to avoid inhalation!
waste management
WASTE MANAGEMENT
  • Place the acidic solution from extraction in bottle labeled “AQUEOUS ACIDIC WASTE”.
  • Place alkyl bromide product in the bottle labeled “ALKYL BROMIDE WASTE”.
  • Pour the contents of the test tubes used in the silver nitrate test in the container labeled “SILVER NITRATE WASTE”.
laboratory notebook pre lab
LABORATORY NOTEBOOK(Pre-lab)
  • OBJECTIVE(Must clearly state…)
    • What compounds you will make and how
    • How you will purify the compound
    • How you will determine the purity of your compound
  • CHEMICAL EQUATION
    • Include the general chemical equation from top of page 93.
  • TABLE OF PHYSICAL DATA (Complete the following table using MSDS sheets from a site 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
LABORATORY NOTEBOOK(In-lab)
  • DATA/CALCULATIONS
    • Initial weight of 2-methylcyclohexanol used
    • Initial 50 mL beaker weight
    • Final 50 mL beaker weight
    • Final product weight
    • Physical state and color of product
    • Theoretical yield calculation (not just the number!)
    • Percent yield calculation (not just the number!)
  • 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 ACTUAL volumes or weights of chemicals used during the experiment.
      • Include any mistakes, accidents, or observations if necessary.