CHM$2201$ Summer$2011$ Department$of$C hemistry$Organic$Chemistry Lab I Villanova University Page 1 of 6 Nucleophilic Substitution of Alkyl Halides Period 7 – June 22, 2011 Bell, Clark & Taber, pgs. 188 – 191 (Expt 17A,B,C) Carry out this experiment in your hood. Alkyl halides are toxic; avoid breathing vapors and skin contact. You will be using warm water baths in this lab. A Styrofoam cup placed in a beaker (for stability) will be used as your water bath (see diagram on page 5), but you should immediately start to heat some water in another 400 mL beaker on your hotplate so that you have a supply of hot water ready to add to the Styrofoam cup to adjust the temperature as needed. You will also need a timing device of some kind. Experiment A. Structural Effects on SN1 and SN2 Reactivity Series 1, NaI/acetone (SN2 conditions) R X+acetoneR I+NaINaX(precip ita te)X = Chlorine, bromine 1. Label two groups of five clean dry test tubes with numerals 1 to 5. 2. In each group of test tubes add 0.2 mL (use a syringe) of the following alkyl halides to the labeled tubes 1. n-butyl chloride (1-chlorobutane)2. n-butyl bromide (1-bromobutane)3. sec-buty l chloride (2-chlorobutane)4. tert-butyl chloride (2-chloro-2-methylpropane)5. crotyl chloride (1-chloro-2-butene)ClBrClClCl 3. Keep the tubes stoppered with corks or parafilm and leave them covered at all times, before and after adding reagents. Carry out all experiments in your hood! 4. Obtain 15 mL of each of the following solutions: a. 15% NaI/acetone (for Series 1 of Experiment A) b. 1% ethanolic AgNO3 (for Series 2 of Experiment A) 5. Read/become familiar with steps 6-9 before continuing. 6. With one series of the tubes arranged in order, add in one portion 2 mL of 15% NaI/acetone solution to tube #1 and note the time of the addition on your table. NOTE: Record data/observations in your notebook in a table like that depicted on page 2. a. NOTE: after this and subsequent additions carefully watch each of the tubes for the formation (this may occur rapidly or slowly) of a precipitate (during your observations, periodically remove the test tubes from the testCHM$2201$ Summer$2011$ Department$of$C hemistry$Organic$Chemistry Lab I Villanova University Page 2 of 6 tube rack so you can look for solids on the bottom and/or sides of the test tube; turbidity or cloudiness is not precipitation) which indicates that the reaction has occurred. b. Record the time in your table if and when precipitation (NOTE: look for solids on the sides and/or bottom of the test tube) begins to occur in each of the test tubes. Cloudiness or a milky appearance is not precipitation. c. Remember to keep the tubes stoppered or covered (Parafilm) before and after adding the NaI. 7. After 2 to 3 minutes, add 2 mL of the NaI/acetone solution to tube #2 and note the time of the addition on your table; observe to see if or when a precipitate forms and note the time in your table. 8. Continue the process of adding 2 mL portions of the NaI/acetone solution to the remaining tubes in the series (#s 3, 4, and 5). 9. Allow this series of tubes to stand and observe them for precipitate formation periodically while the second series (Series 2) is run. Series 2, AgNO3/ethanol (SN1 conditions) R X+AgNO3, H2O, EtOH+X-AgX+RO H (and R OEt)+NO3-R 1. Arrange the second series of tubes and, in the same manner as above, add 2 mL portions of the 1% ethanolic AgNO3 to each tube at 2 to 3 minute intervals. 2. Note the time of each addition and, if possible, record the times (may be rapid or slow!) when the first appreciable turbidity (cloudiness) forms and then when a definite precipitate occurs. Be sure to record both times in your table. 3. If any tubes in the Series 1 NaI series still do not have a precipitate, unstopper the tubes and place them in a 50°C water bath for 10 -15 minutes, and note any changes that might occur. 4. When finished with all of these reactions, pour the contents into the organic waste container. 5. Explain your results from Series 1 and Series 2: Do your results correlate with what was expected theoretically? NaI/Acetone AgNO3/Ethanol Compound Time of addition Time of precipitate formation Time Elapsed Time of addition Time of turbidity appearance Time of definite precipitate formation Time elapsed n-butyl chloride DO NOT RECORD RESULTS IN THIS TABLE n-butyl bromide RECORD YOUR RESULTS DIRECTLY IN YOUR NOTE- BOOK sec-butyl chloride DO NOT RECORD RESULTS IN THIS TABLE tert-butyl chloride RECORD YOUR RESULTS DIRECTLY IN YOUR NOTE- BOOK crotyl DO NOT RECORD RESULTS IN THIS TABLECHM$2201$ Summer$2011$ Department$of$C hemistry$Organic$Chemistry Lab I Villanova University Page 3 of 6 chloride Experiment B. Effects of Solvent on SN1 Reactivity Acetone/water t-Bu—Cl + HOH ————————> t-BuOH + HCl (NaOH, phenolphthalein) 1. Label three clean dry test tubes with each of the acetone/water solvent mixtures that are available in the hood. The solvent mixtures available are: a. 55:45 acetone:water b. 60:40 acetone:water Solvent systems arranged in order of decreasing polarity c. 65:35 acetone:water 2. From the three acetone/water solvent mixtures, add one 2 mL portion of each mixture to the properly labeled test tube. 3. Using a Pasteur disposable pipet add exactly 2 drops of 0.5 M NaOH and then 2-3 drops of phenolphthalein solution to each of the above test tubes containing the solvent mixtures. 4. Cover the tubes with parafilm or corks and place them in a water bath at 35 + 1°C for 3 to 4 minutes to bring the solvent mixtures to the bath temperature. Use a Styrofoam cup in a beaker as an insulated container for your bath. 5. Using a disposable pipet add exactly 3 drops of tert-butyl chloride (2-chloro-2-methylpropane) to each test tube. 6. Note the time of the addition (record in your notebook in a table like that shown below); then briefly swirl the test tubes to mix and replace the tubes in the bath, swirling intermittently to insure good mixing. 7. Periodically add small amounts of hot water (obtained from the hot water in your 400 mL beaker) to the bath to maintain the temperature at 35 + 1°C. 8. Record the time for the pink color to disappear in each of the solvent mixtures. 9. Explain your results: Which solvent