Preparation and Reactivity of Sn1 2-Bromobutane

Preparation and SN1 Reactivity of 2-Bromobutane Paul DeJong Department of Chemistry, Illinois State University, Normal, IL 61790-4160 Submitted: April 4, 2013 Introduction The purpose of part 1 of the lab is to prepare 2-Bromobutane using SN1 reactions. The purpose of part 2 of the lab is to determine the relative reactivity of alkyl halides under SN1 conditions. Results and Discussion The Overall Reaction The Proposed Mechanism Experimental Procedure To prepare 2-bromobutane in part one of the lab, you have to set up a flask apparatus with a thermowell and a Claisen adapter.Attached to the Claisen adapter is a thermometer measuring the temperature in the flask and a vertical condenser for reflux. Add in the reactants to the flask, sulfuric acid, 2-butanol, and ammonium bromide. Heat to 95OC and then maintain temperature for 30 minutes. Then, water was added and simple distillation began. The aqueous layer of the distillate was removed leaving the product, 2-bromobutane. For part 2, two drops of each of the following were placed in 3 different test tubes: 2-bromobutane, 1-bromoutane and 2-bromo-2-methylpropane.In each of the tubes an even amount of silver nitrate is added. Observations of the reactions precipitate are recorded. Same process is done with 2-chlorobutane, 2-iodobutane, and 2-bromobutane. Experimental Stoichiometry Compound| Molecularweight| Quantity| Moles| 2-butanol| 74. 12 g| 7. 4 mL (6. 0 g)| 0. 081| Sulfuric acid| 98. 08 g| 20 mL (12M)| 0. 24| Ammonium bromide| 97. 94 g| 8. 0 g| 0. 082| The limiting reactant is 2-butanol. Yield Data 2-bromobutane| | Molecular Weight| 137. 02 g|Theoretical Yield (moles)| 0. 081 mol| Theoretical Yield (grams)| 11. 10 g| Actual Yield| 10. 11 g| NMR Table Signal| Chemical Shift| Multiplicity| Integration| A| 4. 11| Multiplet| 1H| B| 1. 85| Pentet| 2H| C| 1. 60| Doublet| 3H| D| 1. 08| Triplet| 3H| Reactivity of Alkyl Halides Compound| Observations at Room Temp| Observations upon Heating| 1-bromobutane| Clear| Very little change but some white ppt| 2-bromobutane| Clear| Moderately cloudy white ppt| 2-bromo-2-methylpropane| Brown tint| Very milky white ppt|Compound| Observations at Room temp| Observations upon heating| 2-chlorobutane| Clear| No ppt at all| 2-bromobutane| Clear| Moderately white and some yellow ppt| 2-iodobutane| Dark brown| Thick, milky white and yellow ppt| Conclusion Overall, the first part of the lab produced 2-bromobutane using SN1 reactions. This product was then used in the second part of the experiment to determine the relative reactivities of alkyl halides. Reactivity increases as follows 1O < 2O < 3O and Cl- < Br- < I –