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 S N 1 dehydration reaction.  To determine product substitution based on reaction rate with AgNO 3.  To characterize reactants and products using IR spectroscopy.

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

4. S N 1 MECHANISM 1. hydroxyl oxygen attacks and removes a proton from hydrobromic acid. 3. Water is eliminated-forms 2 o carbocation. 2. Forms new O-H bond, oxygen bears a positive charge (oxonium ion). 4. Products may form from the 2 o carbocation, but it is more likely that the 2 o C + will rearrange to a 3 o C +. 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 AgNO 3 test to determine which product forms.

6. EXPERIMENTAL PROCEDURE (Synthesis) 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. Leave open at top !

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 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 Test SolutionReaction 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 Functional GroupBase Values (cm -1 ) 2-methylcyclohexanolAlkyl halide product Frequency (cm -1 ) OH stretch3200-3600 C-O stretch1000-1200 sp 3 CH stretch2850-3000 C-Br stretch500-700

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 CompoundMW (g/mol)bp (C o )d (g/mL)HAZARDS 2-methylcyclohexanol 48% Hydrobromic acid Sulfuric acid 1-bromobutane 2-bromobutane 2-bromo-2-methylpropane Silver nitrateXXX 1-bromo-1-methylcyclohexaneXXX 1-bromo-2-methylcyclohexaneXXX

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.