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Experiment 11:

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:

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  1. Experiment 11: CONVERSION OF AN ALCOHOL TO AN ALKYL BROMIDE WITH REARRANGEMENT

  2. 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.

  3. CHEMICAL EQUATION 2-methylcyclohexanol 1-bromo-1-methylcyclohexanol (3o alkyl halide) 1-bromo-2-methylcyclohexanol (2o alkyl halide)

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Table 11.1

  9. 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.

  10. Table 11.2

  11. IR SPECTROSCOPY

  12. Table 11.3

  13. 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).

  14. 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!

  15. 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”.

  16. 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

  17. 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.

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