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CHM 2201 Fall 2009 Department of Chemistry Organic Chemistry Lab I Villanova University Nucleophilic Substitution of Alkyl Halides Experimental Procedures amp Notes for Experiments 17 A B and C Chapter 17 in Bell Clark and Taber pgs 188 191 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 but you should immediately start to heat some water in a 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 SNl and SNZ Reactivity Seriesl M 1 3N2 Jquot acetone R X Nal gt R Nax i precipitate X Chlorine bromine 1 Label two groups of ve clean m test tubes with numerals 1 to 5 2 In each group of test tubes add 02 mL use a syringe of the following alkyl halides to the labeled tubes 1 nbutyl chloride lchlorobutane MCI 2 nbutyl bromide 1 39 39 MBr scobutylchloridc 2chlorobutanc gt rcl tenbutylohloridc 397 h 397 39 L 4 Ln crotyl chloride lchloroZbutonc Mel E Keep the tubes stoppered with corks or parafrlm and leave them covered at all times before and after adding reagents Car out all ex eriments in our hood Obtain 15 mL of each of the following solutions a 15 NaIacetone for Series 1 of Experiment A b 1 ethanolic AgNOg for Series 2 of Experiment A Readbecome familiar with steps 69 before continuing With one series of the tubes arranged in order add in one portion 2 mL of 15 NaIacetone 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 look for solids on the bottom andor sides of the test tube39 turbidity or cloudiness is not precipitation which indicates that the reaction has occurred 4 9939 Page 1 of 5 CHM 2201 Organic Chemistry Lab 1 9 Fall 2009 Department of Chemistry Villanova University b Record the time in your table if and when precipitation 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 0 after adding the NaI 7 After 2 to 3 minutes add 2 mL of the NaIacetone 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 remaining tubes in the series s 3 4 and 5 0 periodically while the second series Series 2 is run Series 2 AgNOQethanol S l conditions R X AgNO3 H20 EtOH R x39 gtAgxl ROHand ROEt Remember to keep the tubes stoppered or covered Para lm before and Continue the process of adding 2 mL portions of the NaI acetone solution to the Allow this series of tubes to stand and observe them for precipitate formation N03 Arrange the second series of tubes and in the same manner as above add 2 mL portions of the 1 ethanolic AgNOg to each tube at 2 to 3 minute intervals N 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 E If any tubes in the Series 1 NaI series are still clear unstopper the tubes and place them in a 50 C water bath for 10 15 minutes noting any changes that occur 4 When nished 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 NaIAcetone AgNO3Ethanol Time of compound Time of Time of Time Time of Time of definite Time addition precipitate Elapsed addition turbidity precipitate elapsed formation appearance formation DO NOT RECORD RESULTS IN THIS TABLE NOTE l fr m RECORD YOUR RESULTS DIRECTLY IN YOUR BOOK fr i DO NOT RECORD RESULTS IN THIS TABLE NOTE f i g RECORD YOUR RESULTS DIRECTLY IN YOUR BOOK DO NOT RECORD RESULTS IN THIS TABLE chloride Page 2 Of 5 CHM 2201 Organic Chemistry Labl Fall 2009 Department of Chemistry Villanova University Experiment B Effects of Solvent on SNl Reactivity N E 4 gt1 509 Acetonewater HOH gt NaOH phenolphthalein I Bu Cl I BuOH HCl Label three clean y test tubes with each of the acetonewater solvent mixtures that are available in the hood The solvent mixtures available are a 5545 acetonewater b 6040 acetonewater c 6535 acetonewater From the three acetonewater solvent mixtures add one 2 mL portion of each mixture to the properly labeled test tube Using a Pasteur disposable pipet add exactly 2 drops of 05 M NaOH and then 23 drops of phenolphthalein solution to each of the above test tubes containing the solvent mixtures Cover the tubes with para lm or corks and place them in a water bath at 35 i 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 Using a disposable pipet add exactly 3 drops of tert butyl chloride 2chloro2 methylpropane to each test tube Note the time of the addition record in your notebook in a table like that shown below then brie y swirl the test tubes to mix and replace the tubes in the bath swirling intermittently to insure good mixing 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 11 C Record the time for the pink color to disappear in each of the solvent mixtures Explain your results Which solvent mixture causes the fastest reaction Why Also using equations show why the pink phenolphthalein color disappears as the reaction progresses Solvent systems arranged in order of decreasing polarity Solvent mixture used Time of addition of ten Time pink color disappeared Time elapsed in seconds Bu 1 Chloride DO NOT RECORD RESULTS IN THIS TABLE 5545 Acetone Water RECORD YOUR RESULTS DIRECTLY IN YOUR NOTEBOOK DO NOT RECORD RESULTS IN THIS TABLE 6040 Acetone Water RECORD YOUR RESULTS DIRECTLY IN YOUR NOTEBOOK DO NOT RECORD RESULTS IN THIS TABLE 6535 Acetone Water RECORD YOUR RESULTS DIRECTLY IN YOUR NOTEBOOK Experiment C Effect of Temperature on Reaction Rates 1 From your results in Experiment B choose the solvent system for which the neutralization time at 35 C was closest to 5 minutes this usually should be the 5545 acetonewater solvent mixture Add 2 mL of this solvent mixture to a test tube and add exactly 2 drops of the 05 M NaOH and then 23 drops of the phenolphthalein solution Page 3 of 5 CHM 2201 Fall 2009 Department of Chemistry Organic Chemistry Lab I Villanova University E Place the test tube in a Styrofoam cup water bath at 25 i 1 C for 3 to 4 minutes to allow the solvent to come to the bath temperature Using a disposable pipet add exactly 3 drops of tert butyl chloride to the test tube and note the time of the addition in a table like that shown below Swirl the tube to mix place the tube in the water bath and note the time in your notebook table for the pink color to disappear at the 25 1 C temperature NOTE The time required for the color change may be as long as 20 25 minutes so be sure to start the next step step 6 while waiting Repeat this procedure with the same solvent system at 45 i 1 C and record the times for color disappearance NOTE Prepare a second water bath for this determination since the time required in Step 5 may take 20 7 25 minutes Use the times obtained for the samples at 25 C and 45 C and the time at 35 C from Exp B to make a plot oflog t time in seconds versus lT K From the slope in the above plot calculate the activation energy Ea for the solvolysis in the solvent used Note that a plot of log tvalues versus lT K should give a straight line with slope Ea23R R gas constant 199 calmole deg and Ea activation energy See your lab text for this equation 4 V39 05 gt1 9 0 em perature IN NOTEBOOK NOTEBOOK IN NOTEBOOK IN NOTEBOOK IN NOTEBOOK Example of plot of log versus 1T 310 300 290 quot x 280 270 E 2396 x Slope log t In seconds 2 50 23R 240 199 x10393 kcal 230 R 220 quot 210 39 200 K C273 mol K 000314 000325 000336 1Tin K Page 4 of 5 CHM 2201 Fall 2009 Department of Chemistry Organic Chemistry Lab I Villanova University Onestep to reactant RI gt RBr gt RC1 gt RF RCHZI gt RCHzBr gt RCHZCI gt RCHZF allyl 3 gt 2 gt 1 gt methyl Methyl allyl gt 1 gt 2 gt 3 3 Alkyl halides undergo only SNl Methyl halides and 1 alkyl halides 1 Alkyl and methyl halides do not undergo only SNZ rate rate reaction reaction if nucleophilic reactants isare TMBare 10262009 Page 5 of 5