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

2. Objectives
To perform the dehydration of 2-methylcyclohexanol to form isomeric alkyl halides under SN1 conditions.
To purify the product using liquid extraction.
To analyze the product using a qualitative AgNO3 test in order to identify determine product substitution of products.
To characterize the reactant and major product 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.
Characterize reactant and major product with provided IR spectra.

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: Experimental Results
Theoretical Yield (g)
Must determine which reactant is your limiting reagent first, 48% HBr or
2-methylcyclohexanol.
Calculate the amount of product that can be formed based on the limiting reagent.
Actual Yield (g)
This mass will be obtained by weighing an empty small beaker, then reweighing after the product has been added. The difference in mass is the actual product yield.
% Yield
Actual yield (g) X 100
Theoretical yield (g)
Product Appearance
Physical state and color of product.

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: Silver Nitrate Test Results
Test Solution
Reaction Rate (min/sec)
1-bromobutane
You only need 3 drops of each of these! Get ONLY what you need!
2-bromobutane
2-bromo-2-methylpropane
Product sample

11. IR SPECTROSCOPY

12. Table 11.3: IR Spectral Analysis Results
Functional Group
Base Values
(cm-1)
2-methylcyclohexanol
Alkyl halide product
Frequency (cm-1)
OH stretch
N/A
C-O stretch
sp3 CH stretch
C-Br stretch

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 “LIQUID 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. CLEANING
Clean round bottom flask and separatory funnel with soap, water, brush, and wash acetone.
Rinse condenser with wash acetone only.
Clean all other glassware used with soap, water, brush, and final rinse with wash acetone.
Do not return any glassware to plastic box or lab drawer unless it is COMPLETELY DRY!

17. In-lab Question (The following question should be answered in laboratory notebook.)
There are two possible products from the reaction of
3-methyl-2-pentanol with aq. HBr.
Draw the products and a complete mechanism for their formation, including all intermediates.
Name both products based on the IUPAC system
circle the major product.

18. In-lab Question (The following question should be answered in laboratory notebook.)
Based on the reaction above:
Calculate the theoretical yield for the reaction based on 4.0 g of the alcohol and 20 mL of the 48% HBr.
Show calculations based on both reactants! The molecular weight of the alcohol is given, however the molecular weight of the product must be determined based on the structure.
Be sure to give units.