The Finkelstein Reaction: Quantitative Reaction

3 downloads 0 Views 360KB Size Report
g/mol. Density, g/mL. BP,. oC. Health/Safety. 1-Bromobutane. 109-65-9 ..... the reaction is irreversible up to approximately 50% conversion. ..... manual will provide the procedure for determining the cell constant. .... Your Excel® worksheet.

The Finkelstein Reaction: Quantitative Reaction Kinetics of an SN2 Reaction Using Nonaqueous Conductivity

R. David Pace* and Yagya Regmi≠ Department of Science and Mathematics Lyon College Batesville, AR 72503 *[email protected]

Current Address: Pro-Dentec Therapeutics & Pro-Health 500 White Drive Batesville, AR 72501

Supplementary Material for Online Publication

1

I.

Instructor Information

II.

Potential Post Laboratory Questions

III.

Sample Student Data with Graphs

IV.

Student Laboratory Resource

V.

Master Data Sheet

I. Instructor Information: Note 1: Note 2: Note 3:

This is a two-part experiment that must be conducted over the course of two lab periods unless the instructor opts to provide students with the calibration data. All calibration curves are prepared in the first laboratory period. The kinetics experiments are conducted in the second laboratory period. If faced with limited availability of equipment, students may easily work in pairs to complete this exercise. The data presented in Section III were student-generated by the 2004 – 2005 Organic Chemistry Class at Lyon College unless otherwise stated.. R

R'

solvent

+ NaI

H R 1

I

20 - 40 o C

X

R

H

2

H

X I

R

+ NaX

R' 3

4

X = Cl, Br

Compound 1a 1b 1c

R'

1-bromobutane 2-bromobutane 1-chlorobutane

Solvent Acetone Acetonitrile

R

H -CH2CH2CH3 CH3 -CH2CH3 H -CH2CH2CH3

Table 1A. Required Chemicals* Chemical CAS Number 1-Bromobutane 109-65-9 2-Bromobutane 78-76-2 1-Chlorobutane 109-69-3 Sodium iodide 7681-82-5

MW, g/mol

Density, g/mL

BP, o C 100104

137.03

1.276

137.03

1.255

91

92.57

0.886

7778

149.89

--

--

Acetone 67-64-1

58.08

0.791

56

Acetonitrile 75-05-8

41.05

0.786

8182

1-Iodobutane 542-69-8

184.02

1.617

130131

2-Iodobutane 513-48-4

184.02

1.598

119120

Health/Safety Flammable. Harmful if inhaled or ingested. Skin and eye irritant. Flammable. Harmful if inhaled or ingested. Skin and eye irritant Flammable. Skin, eye, and respiratory tract irritant. Eye and skin irritant. Possible allergen. Possible teratogen. Flammable. Skin and eye irritant. Harmful if inhaled or ingested. Affects central nervous system. Unusual fire hazard. May cause skin and eye irritations/allergic reactions. May be absorbed in harmful amounts. Possible teratogen. Possible mutagen. Flammable. Severe irritant. Possible carcinogen. Flammable. Irritant. Light sensitive. Harmful by ingestion, skin contact, or inhalation. Possible carcinogen.

* Physical data were taken from The Aldrich Handbook, 2003-2004. Health and safety data were taken from the respective Material Safety Data Sheets (MSDS).

Instructors should thoroughly review the MSDS for each material prior to conducting this experiment in order to obtain a more complete understanding of the potential hazards and risks involved in handling these chemicals. However, it should be noted at this point that the MSDS for acetonitrile indicates that it is a teratogen and mutagen. The MSDS for 1-iodobutane indicates that it is a potential carcinogen. Appropriate caution should be taken when handling these materials, including the use of safety glasses, lab aprons, and butyl nitrile-type (not latex) gloves. Latex gloves are semi-permeable and provide only a temporary chemical barrier (3). Disposable butyl nitrile-type gloves may be purchased from a number of vendors. If 2

possible, students should work in approved fume hoods. All reaction mixtures should be disposed of in appropriate halogentated waste containers. The reactions may be run in a large test tube with magnetic stir bar for agitation (as detailed Table 1C). When the reaction tube and acetone/NaI solution equilibrate to the appropriate temperature, a calculated amount of a haloalkane is added at t0. Then, the conductivity probe is immersed in the reaction mixture and a section of Parafilm is used to seal the reaction tube for the duration of the experimental run. Table 1B provides some detail concerning the issue of solvent evaporation (namely, acetone at 40 oC) and Parafilm integrity. Table 1B. Solvent Evaporation Study Time, sec

0 60 300 600 1200 1800 2400 3000

Bath Temperature g NaI in 25.0 mL acetone µL 1-bromobutane Initial Mass Parafilm (g) Mass of empty reactor (g)

Mass of reaction (g)

Final Mass Parafilm (g) Change in Mass Parafilm (g)

21.9 oC 1.4582 1047 0.7265 127.59 22.39 22.41 22.39 22.41 22.39 22.41 22.40 22.40 0.7265 0

30.6 oC 1.4779 1061 0.4545 126.61 22.41 22.41 22.41 22.37 22.38 22.37 22.37 22.37 0.4570 +0.0025

40.1 oC 1.4953 1367 0.6163 121.00 22.36 22.36 22.34 22.31 22.33 22.32 ----0.5582 -0.0581

Clearly, Table 1B shows that the mass of the reaction remains fundamentally unchanged over the course of each run. Note that the run at 40.1 oC was stopped at 1800 sec (30 min) because all kinetic runs in this exercise at 40 oC do not proceed past 1500 sec (25 min). A small amount of a volatile liquid (0.0025g), presumably acetone, condensed on the interior surface of the Parafilm seal at 30.6 oC. It appears that at 40 o C a small decrease in mass is observed in the Parafilm seal. Again, it is presumed that acetone condensate/vapor may be partially compromising the Parafilm seal. However, the overall small effect on the Parafilm and little appreciable change in reaction mass in all cases suggest that Parafilm is an adequate material with which to seal the tube reactors. Additionally, there are two other points to consider with respect to evaporation of acetone (especially at 40 oC): 1) the surface area of acetone exposed to the vapor space within the reactor is small compared to the volume of the reaction; and, 2) the boiling point (a colligative property) of the reaction mass is something above the boiling point of pure acetone (56 oC). Table 1C. Equipment Requirements per Student/Group Quantity Description 1 Test tube (25mm x 200mm) 1 ½ inch magnetic stirring bar 1 Magnetic stirring platea 1 Constant temperature bath (reservoir and controller)a 1 2 Clamps and ring stand 1 Thermometer (monitoring room temperature/bath temperature) 1 1000 µL micropipette with appropriate tips 1 Conductivity meter with probeb (a) A large plexiglass constant temperature bath placed on two stirring plates makes an excellent setup that will easily serve two sets of students at a time. (b) Oakton® pH/CON 510 Benchtop Meter

3

Throughout the Student Data section, there are notes for the instructor concerning specific aspects of this laboratory exercise. We believed that it was more appropriate to include these notes at the point where relevant data are presented. II. Potential Post Laboratory Questions: (1) Were all the kinetic plots ([NaI] vs. time, ln[NaI] vs. time, and 1/[NaI] vs. time) straight lines? What does this say about the order of the Finkelstein reaction? (2) Consider the rate constants for 1-bromobutane at 20, 30, and 40 oC (k1a, k1b, and k1c). Is there a discernable trend in the magnitudes of these rate constants? Why? Draw a reaction energy diagram that clearly illustrates your answer. (3) Consider the rate constants of 1-bromobutane and 1-chlorobutane in acetone at 40 oC. How does leaving group ability affect the rate of the SN2 reaction? (4) Consider the rate constants of 1-bromobutane and 2-bromobutane in acetone at 30 oC. How does the structure of the reacting alkyl halide affect the rate of the SN2 reaction? (5) Consider the rate constants for 1-bromobutane in acetone at 40 oC and 1-bromobutane in acetonitrile at 40 oC. Look up the dielectric constants for the two solvents. How does solvent polarity affect the rate of the SN2 reaction? (6) Compare your rate constants with the published values. Assuming the published values are correct, what is your % error in each case? Please provide explanations for each case. In order to compare your experimental rate constant values to the published values (1), you must correct your values to compensate for the so-called negative salt effect (Table 4D Student Laboratory Resource) (2). A discussion of this phenomenon is beyond the scope of this laboratory exercise. Literature Cited: 1. a) Conant, J. B.; Hussey, R. E. J. Am. Chem. Soc. 1925, 47, 476. b) Hughes, E. D.; Ingold, C. K.; Mackie, J. D. H. J. Chem. Soc. 1955, 3177. c) Fowden, L.; Hughes, E. D.; Ingold, C. K. J. Chem. Soc. 1955, 3187. d) Le Roux, L.J.; Swart, E. R. J. Chem. Soc. 1955, 1475. 2. Epple, M.; Troger, L.; Hilbrandt, N. J. Chem. Soc., Faraday Trans., 1997, 93(17), 3035. 3. For example, see: (a) http://www.worksafesask.ca/files/ont_esao/handprotection.html; (b) Nierenberg, D. W.; Nordgren, R. E.; Chang, M. B.; Siegler, R. W.; Blayney, M. B.; Hochberg, F.; Toribara, T. Y.; Cernichiari, E.; Clarkson, T. N. Engl. J. Med. 1998, 338, 1672.

4

III. Sample Student Data and Graphs: A. Calibration Curves The following data were obtained using a simplified solution preparation protocol. The conventional preparation of a concentrated stock solution followed by volumetric dilutions to generate a series of solutions of certain concentrations may be insufficient for large classes given the requirement for many different sizes of micropipettes and volumetric pipettes. Therefore, we used a 50-mL buret to deliver specific volumes of the concentrated stock solution rapidly and efficiently in order to generate the series of required solutions for calibration purposes. In this case, the buret becomes a 50-mL Mohr-type pipette. Table 3A. Stock Solutions 50-mL Volumetric Stock Solutions Stock g NaI mol NaI [NaI] 3.7727 0.025170 0.5034 A 3.8193 0.025481 0.5096 B 3.7349 0.024918 0.4984 C 3.7950 0.025319 0.5064 D 3.8301 0.025553 0.5111 E 3.7302 0.024886 0.4977 F 3.7923 0.025301 0.5060 G 3.7245 0.024848 0.4970 H

Table 3B. Calibration Solutions Calibration Solution Stock Sol'n

Run 1

Run 2

5

1 2 3 4 5 6 7 Stock Sol'n

1 2 3 4 5 6 7

Acetone 20C

Acetone 30C

A Vol Stock , mL 0.135 0.207 0.845 1.55 6.95 13.4 20.7 Vol Stock, mL 0.135 0.207 0.845 1.55 6.95 13.5 20.4

Acetone 40C

B

Final [NaI], M 2.72×10-3 4.17×10-3 1.70×10-2 3.12×10-2 1.40×10-1 2.70×10-1 4.17×10-1 E Final [NaI], M 2.76×10-3 4.23×10-3 1.73×10-2 3.17×10-2 1.42×10-1 2.75×10-1 4.16×10-1

Vol Stock, mL 0.135 0.207 0.845 1.55 6.95 13.5 20.4 Vol Stock, mL 0.135 0.207 0.845 1.60 7.00 13.4 20.4

Acetonitrile 40C

C Final [NaI], M

2.75×10-3 4.22×10-3 1.72×10-2 3.16×10-2 1.42×10-1 2.74×10-1 4.15×10-1 F Final [NaI], M 2.69×10-3 4.12×10-3 1.68×10-2 3.19×10-2 1.39×10-1 2.67×10-1 4.05×10-1

Vol Stock, mL 0.135 0.207 0.845 1.55 6.95 13.5 20.4 Vol Stock, mL 0.135 0.207 0.845 1.6 6.9 13.5 20.3

D Final [NaI], M

2.69×10-3 4.13×10-3 1.68×10-2 3.09×10-2 1.39×10-1 2.68×10-1 4.06×10-1 G Final [NaI], M 2.73×10-3 4.19×10-3 1.71×10-2 3.24×10-2 1.40×10-1 2.73×10-1 4.11×10-1

Vol Stock, mL 0.135 0.135 0.845 1.6 6.95 13.5 20.4 Vol Stock, mL 0.135 0.207 0.845 1.55 6.9 13.5 20.4

Final [NaI], M 2.76×10-3 2.76×10-3 1.71×10-2 3.27×10-2 1.41×10-1 2.72×10-1 4.12×10-1 H Final [NaI], M 2.68×10-3 4.11×10-3 1.68×10-2 3.08×10-2 1.37×10-1 2.68×10-1 4.06×10-1

Table 3C. Calibration Data for Figures 1 – 4.

Run 1

Run 2

slope (m) σ(m) y-int (b) σ(b)

Acetone 20 oC κ, [NaI ] mS/cm 0.340 0.0521 0.456 0.065 1.57 0.130 2.72 0.177 8.22 0.374 12.6 0.519 16.3 0.646 0.338 0.0525 0.489 0.0650 1.66 0.131 2.72 0.178 8.34 0.376 12.7 0.524 16.3 0.644

Acetone 30 oC κ, [NaI ] mS/cm 0.532 0.0519 0.494 0.0642 1.61 0.130 2.74 0.176 8.2 0.372 12.3 0.518 16.4 0.637 0.528 0.0525 0.536 0.0525 1.71 0.131 2.91 0.181 9.07 0.375 12.8 0.522 16.6 0.642

Acetone 40 oC κ, [NaI ] mS/cm 0.422 0.0525 0.562 0.0651 1.65 0.131 2.96 0.178 8.23 0.377 13.0 0.524 16.6 0.645 0.543 0.0518 0.548 0.0642 1.65 0.130 2.81 0.179 8.18 0.373 12.8 0.517 16.5 0.637

Acetonitrile 40 oC κ, [NaI ] mS/cm 0.691 0.0523 0.736 0.0647 2.5 0.131 4.35 0.180 13.01 0.374 24.9 0.523 31.7 0.641 0.646 0.0518 0.692 0.0641 2.42 0.130 4.12 0.176 12.99 0.370 24.7 0.518 31.4 0.637

0.0365

0.0363

0.0360

0.0184

-4

6.58×10 0.0601 5.58×10-3

-4

8.14×10 0.0549 6.98×10-3

-4

7.78×10 0.0583 6.70×10-3

Table 3D. A Comparison of the Two Successive Dilution Methods. Calibration Buret method Volumetric pipette method Acetone [NaI ] = 0.0365κ+0.0601 [NaI ] = 0.0351κ+0.0591 20 oC 2 2 r = 0.996 r = 0.996 Acetone [NaI ] = 0.0363κ+0.0549 [NaI ] = 0.0336κ+0.0596 30 oC 2 2 r = 0.994 r = 0.995 Acetone [NaI ] = 0.0360κ+0.0583 [NaI ] = 0.0339κ+0.0579 40 oC 2 2 r = 0.994 r = 0.995 Acetonitrile [NaI ] = 0.0184κ+0.0761 [NaI ] = 0.0188κ+0.0701 40 oC 2 2 r = 0.981 r = 0.985

6

7.42×10-4 0.0761 1.19×10-2

III. Sample Student Data and Graphs, continued Figure 2. Calibration Curve of sqrt[NaI] vs κ in Acetone at 30C

0.3000 0.2000

18.00

17.00

16.00

15.00

14.00

13.00

11.00

10.00

9.00

8.00

7.00

6.00

5.00

4.00

3.00

2.00

1.00

12.00

y = 0.0360x + 0.0583 R2 = 0.994

0.1000 0.0000

sqrt[NaI]

0.5000 0.4000 0.3000 0.2000

0.00

18.00

17.00

15.00 16.00

14.00

8.00

Figure 4. Calibration Curve of sqrt[NaI] vs κ in Acetonitrile 40C

0.7000 0.6000 sqrt[NaI]

7.00

κ , mS/cm

Figure 3. Calibration Curve of sqrt[NaI] vs κ in Acetone 30C

κ , mS/cm

6.00

5.00

3.00 4.00

2.00

1.00

κ , mS/cm

13.00

sqrt[NaI] = 0.0363(κ) + 0.0549 R2 = 0.994

0.1000 0.0000

17.00 18.00

15.00 16.00

8.00 9.00 10.00

6.00 7.00

4.00 5.00

2.00 3.00

0.00 1.00

0.1000 0.0000

13.00 14.00

sqrt[NaI] = 0.0365(κ) + 0.0601 R2 = 0.996

0.00

0.3000 0.2000

12.00

0.5000 0.4000

11.00

0.5000 0.4000

9.00 10.00

0.7000 0.6000 sqrt[NaI]

0.7000 0.6000

11.00 12.00

sqrt[NaI]

Figure 1. Calibration Curve of sqrt[NaI] vs κ in Acetone at 20 deg. C

0.7000 0.6000 0.5000 0.4000 0.3000 0.2000 0.1000 0.0000

y = 0.0184x + 0.0761 R2 = 0.981 0

5

10

15

20

25

30

35

κ , mS/cm

Typical r2 values should lie in the 0.98 or greater region (this is an arbitrarily set minimum) for the calibration curves. A careful student (or, group of students) can easily obtain an r2 value exceeding 0.98 for a calibration curve. However, small errors in the physical handling and weighing out the sodium iodide are easily magnified when coupled with volumetric errors in successive dilutions. Additionally, it is difficult to have a student start completely over when they discover their error 15 minutes before class is over. Each instructor handles this issue differently. In the case of this lab, the precision and accuracy of the calibration curves are at a premium because so much is based upon the equations obtained from the curves.

7

III. Sample Student Data and Graphs, continued B. Student Kinetics Data Table 3E. The Kinetics Runs - Volumes and Masses of Reactants Sodium iodide Alkyl halide Initial Experiment/ Rate a o grams grams mMol µL [NaI] Temp C/ Const 1.4498 9.672 1.3254 1039 0.3715 1a 1.4805 9.877 1.3535 1061 0.3790 k1a 20 oC 1-Bromobutane 1.4622 9.755 1.3367 1048 0.3745 1.4500 9.674 1.3256 1039 0.3715 1b k1b 1.4330 9.560 1.3101 1027 0.3673 30 oC 1-Bromobutane 1.4631 9.761 1.3376 1048 0.3747 1.4730 9.827 1.3466 1055 0.3772 1c 1.4631 9.761 1.3376 1048 0.3747 k1c 40 oC 1-Bromobutane 1.4406 9.611 1.3170 1032 0.3692 1.4245 9.504 1.3023 1038 0.3650 2 k2 1.4555 9.710 1.3306 1060 0.3726 40 oC 2-Bromobutane 1.4575 9.724 1.3325 1062 0.3731 1.4678 9.793 0.9065 1023 0.3763 3 1.4769 9.853 0.9121 1029 0.3785 k3 40 oC 1-Chlorobutane --c ----1.4068 9.386 1.2861 1008 0.3609 4 k4 1.4604 9.743 1.3351 1046 0.3741 40 oC 1-Bromobutane 1.4611 9.748 1.3357 1047 0.3742 a) mMoles NaI = mMoles Alkyl halide. b) Two student groups used the same conductivity meter that had a sodium bromide fouled probe. These two rate constant values were excluded. c) Insufficient number of student groups to run this experiment.

In each experiment summarized in Table 3E, [RX]0 = [NaI]0. This condition allowed students to use the simplified rate expression for a 2nd order reaction with two different reactants. A more complete discussion of the mathematics for this case (where, [RX]0 = [NaI]0) as well as the more general case (where, [RX]0 ≠ [NaI]0) may be found on pages 14 and 15 of this Supplement (this section is in the Student Laboratory Resource). The more general case ([RX]0 ≠ [NaI]0) is operationally easier to handle in the laboratory, but the math to evaluate the rate constant is a bit more involved.

8

Table 3F. Average 1/[NaI] Versus Time for Figure 5 (1-Bromobutane in Aceteoneb) 20 deg. C a 1/[NaI] sd20

Time, sec 30 60 120 240 360 600 900 1200 1500 1800 2400 3000

3.08 3.10 3.13 3.21 3.29 3.47 3.72 3.97 4.23 4.50 5.06 5.64

Slope/10-4 y-Intercept r2 Rate Constant, k/10-4

0.088 0.076 0.085 0.093 0.102 0.129 0.149 0.172 0.165 0.172 0.238 0.311

7.99 ± 0.28 2.78 ± 0.04 0.997 k1 = 7.99 ± 0.28

30 deg. C a 1/[NaI] sd30 3.10 3.15 3.15 3.50 3.79 4.28 4.97 5.69 6.34 7.29 9.05 10.7

0.199 0.192 0.326 0.211 0.160 0.159 0.152 0.117 0.221 0.068 0.405 0.653

40 deg. Cc 1/[NaI] sd40 3.35 3.50 3.82 4.37 5.04 6.26 8.02 9.82 11.7 ----

23.2 ± 0.6 2.47 ± 0.08 0.994 k2 = 23.2 ± 0.6

0.303 0.331 0.414 0.423 0.435 0.433 0.533 0.659 0.783 ----

50.9 ± 1.7 2.78 ± 0.13 1.00 k3 = 50.9 ± 1.7

a)

Two student groups used the same conductivity meter that had a probe fouled with sodium bromide. Therefore, these values were excluded from the analysis. b) The dielectric constant (ε) for acetone is 20.7. c) Reactions all stopped at t=1500 seconds.

Figure 5. Kinetic Plots at 20, 30, and 40 deg. C (1Bromobutane in Acetone)

1/[NaI] (L/mol)

12.00 10.00 20 deg. C

8.00

30 deg. C 40 deg. C

6.00 4.00 2.00 0

500

1000

1500

2000

2500

3000

Time (sec) Note that if replicate runs are made for any reaction, then it is simplest if all data are taken at the same times. Of course, this makes plotting data with error bars much easier. The instructions for error analysis may be found on page 23 of the Student Resource. 9

III. Sample Student Data and Graphs, continued The y-intercepts of the curves in Figure 5 most probably represent the initial NaI concentrations at t = 0 seconds for each reaction. Indeed, the fact that they agree closely with one another is a good check of the calibration curves for each temperature. When NaI is the iodide source and an alkyl halide is the substrate, the reaction is irreversible up to approximately 50% conversion. Past this point, the by-product salt (NaX) concentration becomes significant enough to interfere with the forward reaction, and a change in the slope of the curve would be noted. Table 3G. 1/[NaI] Versus Time for Figure 6 (2-Bromobutane in Aceteone) Time (sec) 30 60 120 240 360 600 900 1214 1500 1800 2400 3000 Slope/10-4 y-Intercept r2 k2/10-4

2-Bromobutane 1/[NaI] sd 2.70 0.0823 2.71 0.0721 2.72 0.0699 2.73 0.0666 2.74 0.0630 2.76 0.0619 2.79 0.0573 2.81 0.0591 2.84 0.0627 2.87 0.0663 2.92 0.0712 2.97 0.0724 0.879 ± 0.115 2.71 ± 0.01 0.996 0.879 ± 0.115

Figure 6. Averaged Kinetic plot of 2-bromobutane in Acetone at 40C 3.10

1/[NaI] (L/mol)

3.00 2.90 2.80 2.70

1/[NaI] = 8.79x10-5t + 2.71 R2 = 0.996

2.60 2.50 0

500

1000

1500 Time (sec)

10

2000

2500

3000

III. Sample Student Data and Graphs, continued Table 3H. 1/[NaI] Versus Time for Figure 7 (4:1 [1-Chlorobutane]:[NaI] in Aceteone) 1-Chlorobutanea lnYb sd 60 0.985404 0.0510 120 0.989169 0.0457 240 0.992423 0.0467 420 0.995018 0.0468 600 0.997619 0.0469 1020 1.00291 0.0508 1200 1.006801 0.0491 1500 1.010779 0.0511 1800 1.014771 0.0532 2460 1.022716 0.0535 3120 1.037227 0.0446 0.155 ± 0.045 Slope/10-4 0.987 ± 0.010 y-Intercept 0.990 r2 -4 k3/10 0.155 ± 0.045 (a) Two students ran this reaction using a 1:1 [NaI]:[RCl]. This rate of this reaction is extremely slow. Less than 1% of the NaI reacted. The average student-determined rate constant was 2.17×10-5. (b) Y = ln([NaI]0[RCl]t/[NaI]t[RCl]0). Upon revision of the manuscript, we decided to include the data for the 1:4 reaction here given the greater extent of reaction. Time (sec)

11

Figure 7. Averaged Kinetic Plot of 1-Chlorobutane in Acetone at 40C

ln([RX]t[NaI]0 /[RX]0 [NaI]t)

1.1

1.05

1

0.95

0.9 0

500

1000

1500

2000

2500

3000

3500

Time (sec)

The regions of nonlinearity that may be seen in the early data points in the kinetics plots (Figures 6 and 7) are most likely an artifact of either the concentration dependence of the ionic velocity or the initial small temperature variation due to the injection of approximately 1000 µL of room temperature alkyl halide (or, a combination of both). Conductivity is a complex term that includes ion mobility as well as ion concentration. The mobility (u) of an ion (i) is independent of concentration but it is dependent upon several other solution/electronic parameters (1): zi e ui = 6πηRi where, zi = charge of ion e = elementary charge constant η = viscosity of solvent Ri= solvated radius of the ion In solution, there are three fundamental ionic environments: (1) cation-anion contact ion pair; (2) solvent separated ion pairs; and, (3) solvated, unpaired ions (3). Fundamentally, highly concentrated solutions behave differently than even moderately concentrated solutions because ionic velocity is concentration dependent. This is of some concern because more concentrated solutions exhibit an unexpectedly lower ∆κ/∆C (where, C is the concentration of the salt). The degree of this concern is electrolyte-dependent. Therefore, the slight departure from linearity at the onset of the reaction (high [NaI]) may be due to this effect. Since density is temperature dependent, it is not practical in an undergraduate organic laboratory to measure out the volume of several hundred microliters of the alkyl halide at any temperature other than room temperature. However, when this small volume of alkyl halide at room temperature is injected into the 12

solvent containing sodium halide that has equilibrated to 40 oC, a small variance in the ∆κ/∆C may be noted. Within 2 minutes the reaction temperature recovered in all cases. Table 3I. 1/[NaI] Versus Time for Figure 8 (Aceteone vs. Acetonitrile) Time, sec 30 60 120 240 360 600 900 1214 1500 1800 2400 3000

13

Acetone 1/[NaI] sd 3.35 0.303 3.50 0.331 3.82 0.414 4.37 0.423 5.04 0.435 6.26 0.433 8.02 0.533 9.82 0.659 11.7 0.783

ACN 1/[NaI] 2.81 2.88 2.97 3.05 3.15 3.37 3.63 3.88 4.13 4.39 4.87 5.23

sd 0.093 0.072 0.057 0.084 0.052 0.093 0.143 0.167 0.221 0.242 0.213 0.135

Slope/10-4 y-Intercept

50.9 ± 1.7 2.78 ± 0.13

8.24 ± 0.23 2.86 ± 0.03

r2 k/10-4

1.00 k1c = 50.9 ± 1.7

0.997 k4 = 8.24 ± 0.23

III. Sample Student Data and Graphs, continued Figure 8. Averaged Kinetic Data for 1-Bromobutane at 40C (Comparison of Solvent Polarity) 11.00 10.00 9.00 Acetone -1

1/[NaI] (M )

8.00 7.00 6.00 5.00 4.00 3.00

Acetonitrile

2.00 0

500

1000

1500

2000

2500

3000

Time (sec) 1/[NaI] = 8.24E-4(t) + 2.86

1/[NaI] = 5.09E-3(t) + 2.78

Table 3J. Arrhenius Data for Figure 9 Temperature T, K 1/T, K-1 293.15 0.00341 303.15 0.00330 313.15 0.00319

Rate Constants k lnk 7.99×10-4 -7.13 2.32×10-3 -6.07 -3 5.09×10 -5.28

Figure 9. Arrhenius Plot of 1-Bromobutane/NaI in Acetone -5

lnk

-5.5 -6 -6.5 -7

lnk = -8.51x103(1/T) + 21.9

R2 = 0.996 0.00342

0.0034

0.00338

0.00336

0.00334

0.00332

0.0033

0.00328

0.00326

0.00324

0.00322

0.0032

0.00318

-7.5

-1

1/T (K )

References Cited: 1. Coury, L. Current Separations 1999, 12(3), 91. 2. Shoemaker, D. P.; Garland, C. W.; Steinfield, J. I.; Nibler, J. W., Experiments in Physical Chemistry, 4th ed.; McGraw-Hill: New York, 1981; p 232. 3. Fuoss, R. M. J. Chem. Phys. 1978, 82, 2427. 14

IV. Student Laboratory Resource: Background R'

R'

+

C

H R

X

NaI

I

R'

C H

X R

C I

H

+

NaX

(1)

R

R, R' = alkyl, H X = Br, Cl

The objective of this laboratory exercise is to draw mechanistic conclusions based on differences in the rate data of the Finkelstein reaction (Equation 1) by making a series of empirical observations of the effects on rate by a multiplicity of factors. Reaction mechanism nomenclature rules define the Finkelstein reaction as an SN2 reaction (1). In the specific case shown in Equation 1, iodide ion (the nucleophile) approaches the alkyl halide from backside of the bound halogen (X) as shown in the transition state of Equation 1. This transition state shows that as the new bond begins to form between iodide and the central carbon, the C-X bond begins to break. As the reaction proceeds to completion, iodide is ultimately substituted for the initial halogen (X). Notice that an inversion of the stereochemistry of the central carbon has taken place. This is called the Walden inversion, and it is another piece of evidence used in conjunction with kinetics data to elucidate the mechanism of this reaction. Sodium iodide is soluble in acetone, and as the transhalogenation proceeds (the exchange of Cl or Br for I), acetone insoluble sodium halide (chloride or bromide) precipitates thus driving the reaction to completion (LeChâtelier’s principle). Since the concentration of the acetone soluble salt changes as the reaction proceeds, the ionic strength of the reaction mixture decreases as a function of time. An economical and commercially available conductivity meter is used to follow the change in concentration of sodium iodide as a function of time. The field of chemical kinetics provides chemists with the largest single body of mechanistic information on chemical transformations (2). Within the field of chemical kinetics, experimental determination of the rate expression for a given reaction is the central tool used to describe the molecularity and energetics of the rate limiting step as well as a numerical value for the rate constant. Therefore, a kinetics study of the Finkelstein reaction will show the sophomore organic student how empirical laboratory data are used to draw conclusion concerning the mechanism of a given reaction. In order to complete this exercise successfully, the student must understand three concepts: (1) the general scope and limitations of the SN2 mechanism; (2) basic mathematical concepts involved in describing simple second-order kinetics; and, (3) basic concepts of electrolytic conductivity theory and application. The SN2 Mechanism SN2 stands for Substitution Nucleophilic Bimolecular, and such reactions typically occur between charged nucleophiles and primary alkyl halides (tosylates, etc.). Equation 1 shows a wellknown example of an SN2 reaction called the Finkelstein reaction (3). The SN2 reaction is a one-step process involving two molecules and a single transition state. The rate expression for this process rate = k[RX][Nu]

(2)

(Equation 2) shows that the process is first order in each reactant. The overall process is second order (sum of concentration exponents). Reactant concentration is not the only factor influencing the rate of this reaction. Since the concentrations of NaI and the alkyl halide appear in the rate equation, it may be concluded that the transition state of the rate limiting step (RLS) of this reaction is 15

bimolecular. Factors including nucleophilicity of nucleophile, solvent polarity, leaving group ability, reaction temperature, and alkyl halide structure all influence the overall rate of reaction as evidenced by the magnitude of the rate constant, k. Indeed, it was through a multitude of extensive kinetic studies that chemists were able to elucidate unambiguously the SN2 mechanism by the effect of these factors on the reaction rate. This is the purpose of this laboratory exercise. In this laboratory, students will follow the kinetics of the Finkelstein reaction under various conditions. Then, all acquired data will be pooled and each student will determine the experimental rate constants and use them in subsequent analyses to draw conclusions concerning four rate determining factors: temperature, alkyl halide structure, leaving group, and solvent polarity. Simple Second-Order Kinetics There are two types of second-order reactions as shown in Equations 3 and 4 (4). The Finkelstein reaction actually fits the type summarized in Equation 4. However, in this experiment, 2A

P

(3)

A+B

P

(4)

the initial concentrations of [alkyl halide] and [sodium iodide] may be equal. Since the stoichiometry is obviously 1:1, the differential rate law for equation 3 may be used. rate =

− d[ A ] = k [ A][ B] dt

(5)

If x = [A]0 = [B]0, then Equation 3 may be reduced to the following form: rate =

− d[ x] = kx 2 dt

(6)

Equation 6 has the same form as the differential rate law for Equation 2. Therefore,



− dx = k ∫ dt x2

(7)

Integrating Equation 7 from t = 0, when x0 = [A]0, to time t, when xt = [A]t, gives the following general form of the second-order rate equation:

1 1 = + kt [ A] t [ A] 0

16

(8)

Alternatively, if [ A]0 ≠ [ B]0 , then Equation 6 must be rewritten to include [B]0 as follows: rate =

− dx = k ([ A]0 − x )([ B ]0 − x) dt

(9)

where, [ A]t = [ A]0 − x ; and, [ B]t = [ B ]0 − x Therefore, upon rearrangement, Equation 9 becomes:



− dx = k ∫ dt ([ A]0 − x )([ B ]0 − x )

(10)

Upon integrating from t = 0 when x0 = [A]0 to a time t when xt = [A]t gives the following more general form of the second-order rate equation when [ A]0 ≠ [ B]0 : ln

[ B]t [ A] 0 = ([ B] 0 − [ A]0 ) kt [ A]t [ B] 0

(11)

A comparison of Equations 6 and 9 reveals that the rate is concentration dependent but the rate constant is not. Therefore, the rate constants will be the same if this experiment is carried out with either [A]0≠[B]0 (which is often more convenient) or [A]0=[B]0. Finally, the second-order rate constants in this laboratory exercise have the units of L·mol-1·s-1. Basic Concepts of Conductivity

There is space here for only a general treatment of solution conductivity. However, there are many good references on the subject (5). Expressed simply, conductivity is a term used to express the overall effect of ion concentrations and ion mobilities as it relates to the ability of an electrolytic solution to act as an electrical conductor. Conductance (L) is simply the reciprocal of resistance (R)

L=

1 R

(12)

as shown in Equation 12. Resistance is expressed in ohms (Ω). Conductance is expressed in inverse ohms (Ω−1), or, in S.I. units, siemens (S). Historically, the units of Ω−1 were called mhos (ohms spelled backwards). Conductivity (κ) is related to conductance (L) as shown in Equation 13, where A is the surface

L=κ×

A = κ × k cell d

(13)

area of the electrode, and d is the distance between the electrodes. The ratio A/d is known as the cell constant (kcell), and each conductivity cell has its own cell constant. To simplify matters, modern conductivity probes usually have a cell constant of unity. Therefore, the conductivity (S/cm) of any solution may be read directly from the meter. 17

In this laboratory exercise, the concentration of iodide will be followed as a function of time by monitoring the rate of change of solution conductivity. To this end, Kohlrousch’s Law (Equation 14) must be applied (6): Λ = Λ0 − K c where, Λ=

(14)

κ

(molar conductivity) c Λ0 = limiting molar conductivity (conductivity at infinite dilution) K = coefficient for electrolyte type More generally, this laboratory exercise relies upon the fact (as shown in Equation 14) that solution conductivity (κ) is directly proportional to the square root of the ionic concentration as shown in Equation 15.

κ∝ c

(15)

At this point it must be noted that acetone is the typical Finkelstein solvent (although acetonitrile is also used in this laboratory exercise). A strong electrolyte dissolved in acetone or acetonitrile constitutes what is known as a nonaqueous electrolyte (7). A wide variety of factors influence the conductivity of nonaqueous electrolytic solutions including ion-solvent interactions, solvent-solvent interactions, ion-pairing, and solvent densities (8). This exercise simply relies on the linearity of the relation in Equation 15.

18

Hazards:

Table 4A. Required Chemicals* Chemical CAS Number 1-Bromobutane 109-65-9 2-Bromobutane 78-76-2 1-Chlorobutane 109-69-3 Sodium iodide 7681-82-5 Acetone 67-64-1 Acetonitrile 75-05-8 1-Iodobutane 542-69-8 2-Iodobutane 513-48-4

Health/Safety Flammable. Harmful if inhaled or ingested. Skin and eye irritant. Flammable. Harmful if inhaled or ingested. Skin and eye irritant Flammable. Skin, eye, and respiratory tract irritant. Eye and skin irritant. Possible allergen. Possible teratogen. Flammable. Skin and eye irritant. Harmful if inhaled or ingested. Affects central nervous system. Unusual fire hazard. May cause skin and eye irritations/allergic reactions. May be absorbed in harmful amounts. Possible teratogen. Possible mutagen. Flammable. Severe irritant. Possible carcinogen. Flammable. Irritant. Light sensitive. Harmful by ingestion, skin contact, or inhalation. Possible carcinogen.

*Physical data were taken from The 2003-2004 Aldrich Handbook 2003-2004. Health and safety data were taken from the respective Material Safety Data Sheets (MSDS).

Students should thoroughly review the MSDS for each material prior to conducting this experiment in order to obtain a more complete understanding of the potential hazards and risks involved in handling these chemicals. . However, it should be noted at this point that the MSDS for acetonitrile indicates that it is a teratogen and mutagen. The MSDS for 1-iodobutane indicates that it is a potential carcinogen. Appropriate caution should be taken when handling these materials, including the use of safety glasses, lab aprons, and butyl nitrile-type (not latex) gloves. Latex gloves are semi-permeable and provide only a temporary chemical barrier (9). Disposable butyl nitrile-type gloves may be purchased from a number of vendors. If possible, students should work in approved fume hoods. All reaction mixtures should be disposed of in appropriate halogentated waste containers.

19

The Finkelstein Reaction: Quantitative Reaction Kinetics of an SN2 Reaction Using Nonaqueous Conductivity

Name: _______________________________________________ Substrate: __________________________ Temp:_______________

Date: ______________ Solvent: ______________

Week I: Preparation of the Calibration Curves Note 1: Conductivity (κ) is reported in Siemens per cm (mS/cm or µS/cm). Note 2: Use Excel® (or equivalent) to manipulate data.

Each pair of students must prepare one calibration curve (instructor assigned) that provides a least squares fit to the plot of the square root [NaI] versus conductivity (κ, mS/cm). The following list details the four calibration curves required. (a) (b) (c) (d)

20 oC in acetone 30 oC in acetone 40 oC in acetone 40 oC in acetonitrile

Prepare a 50-mL volumetric solution of NaI (approximately 0.500M) in either acetone or acetonitrile: grams NaI = _____________ moles NaI = _____________ [NaI], mol/L = ____________ Use this stock solution and the successive dilution technique to prepare 25-mL volumetric solutions with the approximate concentrations listed in Table 4B. The laboratory instructor will instruct the student to use either the buret method or the transfer pipette method to prepare the solutions. Record the assigned calibration curve here: Temperature: __________oC Solvent:

Solutiona 1 2 3 4 5 6 7

______________________

Table 4B. Seven Volumetric NaI Solutions Volume of [NaI], Conductivity (κ), Stock Solution mol/Lb mS/cm Requiredc -3 2.70x10 M 4.14x10-3M 1.68x10-2M 3.06x10-2M 1.39x10-1M 2.69x10-1M 4.07x10-1M

(a) The volume of each solution is 25-mL. (b) The listed concentrations are approximate for guideline purposes. (c) The student must calculate the volume of stock solution required in each case using the following equation: M1V1=M2V2.

20

Obtain the conductivities of each solution in Table 4B at the specified temperature. Pool and average all student data. Prepare a plot of the square root of the NaI concentration versus conductivity. Use linear regression to determine the best fit line and correlation coefficient. A typical value for the correlation coefficient is at least 0.98. Week II: Laboratory Procedure Part I: Preparation of 25.0 mL (volumetric) ~0.394M NaI Solution

1. Determine number of moles of NaI required:

__________ moles NaI

2. Convert the moles in step 1 to grams:

__________ grams NaI

a) Weigh out the grams of NaI calculated in step 2 directly into 25-mL volumetric flask:

__________actual grams NaI

4. Calculate actual number of moles NaI from step 3 mass:

__________actual moles NaI

5. Calculate actual number of moles of RX required based on: (#equivalents)×(moles NaI from step 4):

__________actual moles RX

Part II: The Kinetics Experimental Procedure Note 3: Most modern conductivity meters directly read conductivity (mS/cm or µS/cm) because their cell constant is unity. If this is not the case with a given instrument, then the instruction manual will provide the procedure for determining the cell constant. This must be done first.

6. Submerge a large test tube equipped with a magnetic stirring bar in the appropriate bath (at least ¾ of test tube should be submerged). 7. Charge the test tube with 25-mL of the NaI solution prepared above. 8. Immerse conductivity probe (make sure the two metal bands are covered). Turn unit ON. 9. Place parafilm over opening of test tube and equilibrate for at least 5 minutes. Most conductivity probes are equipped with internal thermocouples. Watch for the temperature of the probe to equilibrate to the temperature of the bath. 10. While the NaI solution and conductivity probe are equilibrating to the bath temperature, perform the following calculations: (a) Record the number of moles of alkyl halide from step 5: _________moles alkyl halide (b) Calculate the grams of alkyl halide required based on step 10a: __________g alkyl halide (c) Calculate the µL of alkyl halide required based on step 10b: (use the density) __________µL alkyl halide 6 __________L (d) Calculate total vol., VTot = 0.025 + (µL step10c/1×10 ) (e) If, [NaI]0≠[Alkyl halide]0, calculate: [Alkyl halide]0 = (moles step 5)/VTot __________mol/L [NaI]0 = (moles step 4)/VTot __________mol/L 21

11. Record the following: (a) Initial conductivity reading: __________mS/cm (b) Temperature of the bath: __________oC (c) Temperature of the solution: __________oC 12. Do the following five steps rapidly!!! (less than 10 seconds) (a) Obtain the appropriate volume of alkyl halide (step 10c) using a 1000µL (or, larger) micropipet. (b) Remove conductivity probe. (c) Charge the alkyl halide (subsurface). (d) Start watch / replace probe. (e) Cover the top of the test tube with parafilm. 13. Record κ versus time in Table 4C. With each entry, include the internal reaction temperature. Note 4: The numbers in parentheses in the Time column are guideline times. Record the actual time each conductivity reading is taken.

Time, sec

(30) (60) (120) (240) (360) (600) (900) (1200) (1500) (1800) (2400) tfinal (3000)

Table 4C. Experimental Data Temp, oC Interpolated κ, mS/cm [NaI], M

Note 5: Reaction times are limited to a maximum of 50 minutes in all cases because the Finkelstein reaction is considered to be irreversible over the first 30 – 50 % of the reaction (22). This is due to the fact that the product sodium bromide is not completely insoluble in acetone. The sodium bromide concentration becomes appreciable past this point, and the kinetics become more involved because the reaction becomes reversible. During the development phase of this experiment, reaction times (tfinal) were adjusted according to the following equation such that the final sodium iodide concentration at tfinal was approximately 50 – 70 % (this corresponds to 30 – 50 % conversion to products) of the initial sodium iodide concentration: % NaI remaining at tfinal ≥

[ NaI ]t final [ NaI ]0

×100% ≥ 50 – 70 %

14. Upon completion of the experiment, dispose of the reaction mixture in the proper halogentated waste container.

22

Data Handling Students must pool and average all data. Convert all conductivities to [NaI] concentrations using the appropriate calibration curve prepared in Week 1. In order to accomplish this task two assumptions and a volume correction must be made. Assumption 1:

The initial addition of the alkyl halide does not appreciably affect the conductivity of the solution (step 12 of the procedure).

Assumption 2:

The reaction volume changes by the amount of alkyl halide such that the final reaction volume is the sum of 25.00 mL + X mL alkyl halide.

Record the total volume of the reaction: 25.00 mL + _________mL alkyl halide = __________mL total reaction volume Use the appropriate calibration curve to convert from conductivity to concentration of NaI at each time (last column of Table 4C). EXAMPLE: The reaction of 9.67 mmol (1039 µL) 1-bromobutane (1-BB) with 9.67 mmol NaI (25-mL solution) in acetone at 22 oC gave a conductivity reading at 60 seconds of 14.45mS/cm. Using the following calibration curve equation, the concentration of NaI may be calculated: [ NaI ] = 0.0360 × κ + 0.0583

r 2 = 0.995

[ NaI ]60 s = (0.0360 × 14.45 + 0.0583) 2 = 0.335M Remember, VTot = 25.00mL + 1.039mL = 26.04mL = 0.02604L Note 6: Use Excel® (or equivalent) to its fullest potential in order to simplify this step of the data handling process.

23

Entry 1a 1b 1c 2 3 4

Table 4D. Reaction Rate Constants Experimental Rate Constant Alkyl halide Temperature Solvent Abbreviation Value 20oC 30oC 40oC 40oC 40oC 40oC

1-bromobutane 1-bromobutane 1-bromobutane 1-chlorobutane 2-bromobutane 1-bromobutane

Acetone Acetone Acetone Acetone Acetone Acetonitrile

k1a k1b k1c k2 k3 k4

Obtain the rate constants from the slopes of the kinetic plots and record in Table 4D. If replicate runs were made for any given reaction, plot all replicate data on the same y by x plot. Then, for each time, calculate the standard deviation and add error bars to the plot. Your Excel® worksheet for each reaction should have columns labeled as follows: (x) Time, sec

κ, mS/cm

Stand dev.

x2

d

d2

Run

#1

Data







Run

#2

Data







Run

#3

Data

etc.





Σx 2

Σx

Σd2

The Excel® statistical operators “RSQ” and “STEYX” may be used to calculate the correlation coefficient (r2) and standard error (S), respectively. R2 is a measure that may be regarded as the percent of the total variation of y that is explained by the linear (in this case) relationship with x. The standard error (S) is an expression of the amount of error contained in the prediction of y for a given x (10c). The standard deviations for the slope (σm) and the y-intercept (σβ) may be calculated using the following equations (10a, 10b): D=

∑ (x ) ∑ x n ∑x 2 i

i

i

σ y ≈ sy =

24

∑ (d

2 i

n−2

)

Note 7: Recall:

a b = a×d −b×c c d

Where, d i = y i − (mxi + b)

Standard deviation of the slope: σ m =

σ y2 n D

Standard deviation of the y-intercept: σ b =

σ y2 ∑ ( xi2 ) D

Temperature Prepare a combined 2nd-order kinetic plot for all three temperatures and determine the rate constants at each temperature (k1a, k1b, and k1c) using one of the following integrated rate equations: 1 1 = + kt If , [NaI]0=[RX]0 then: [ NaI ] t [ NaI ] 0

If , [NaI]0≠[RX]0 then:

Note 8 : [ NaI ]0 =

mol NaI Vtot

ln

[ RX ]t [ NaI ] 0 = ([ RX ]0 − [ NaI ] 0 ) kt [ NaI ]t [ RX ] 0

(VTot obtained from step 10d)

[ RX ]t [ NaI ] 0 Plot either 1/[NaI]t versus time or ln [ NaI ] [ RX ] versus time for each temperature. The t 0 X − I, respectively. N slope of the best fit straight line is the rate constant k or R

Prepare an Arrhenius plot (lnk vs 1/T) and determine the Ea. Recall, the Arrhenius equation has the following linear form: ln k = ln A −

Ea 1 R T

Note 9: R = 8,315 J/K.mol = 1.987 cal/K.mol Note 10: T is in Kelvin (K)

Leaving Group Prepare a 2nd-order kinetic plot for 1-chlorobutane and determine the rate constant (k2) using the integrated rate equation described above. Substrate Structure Prepare a 2nd-order kinetic plot for 2-bromobutane and determine the rate constant (k3) using the integrated rate equation described above. Solvent Prepare a 2nd-order kinetic plot for 1-bromobutane in acetonitrile and determine the rate constant (k4) using the integrated rate equation described above. Optional: The rate constants determined in this experiment may be compared with published sources (11) using the following equation to compensate for the negative salt effect:

25

 c  log k corrected = log k exp + 0.37 log    0.024  where, kcorrected = the rate constant corrected for the difference in salt concentration kexp = the student’s experimental rate constant c = the student’s initial NaI concentration However, it must be stated that this is only an approximation due to the fact that this equation was originally derived based on lithium halide chemistry and it corrects back to the original Ingold, et al. work (11c). Specifically, this equation corrects for the effect of salt concentration on the rate constant. In their initial kinetics studies, the initial concentration of the metal halide was approximately 0.024M. Therefore, caution should be used in drawing conclusions based on this equation. Also, two rate constants taken at different temperatures may be compared using the following question:

ln

k 2 Ea  1 1   −  = k1 R  T1 T2 

Table 4E. Experimental Rate Constants versus Literature Values Experimental Rate Constant (kexp) Corrected Experimental % Entry Value Value Error Abbreviation Value 1a 1b 1c 2 3 4

k1a k1b k1c k2 k3 k4

References:

1. Smith, M. B. and March, J. March’s Advanced Organic Chemistry, 5th ed., Wiley-Interscience: New York, 2001, 274-277. 2. Sykes, Peter A Guidebook to Mechanism in Organic Chemistry, 6th ed.; Longman Scientific & Technical: Essex, England, 1987, p. 44. 3. Finkelstein, H. Chem. Ber. 1910, 43, 1528. 4. Houston, P. L. Chemical Kinetics and Reaction Dynamics, McGraw-Hill: New York, 2001, pp.40 – 44. 5. (a) Coury, L. Current Separations 1999, 12(3), 91; (b) Izonfuo, W-A. F.; Obunwo, C. C. Indian J. Chem. 1999, 38A, 939; (c) Fuoss, R. M. J. Phys. Chem. 1978, 82(22), 2427; (d) Krumgalz, B. S. J. Chem. Soc., Faraday Trans. 1 1983, 79, 571; (e) Fuoss, R. M. Proc. Natl. Acad. Sci. USA 1980, 77(1), 34. 26

6. As cited in ref. 5a: Bard, A. J.; Faulkner, L. R. Electrochemical Methods: Fundamentals and Applications, Wiley: New York, 1980, 64. 7. Izonfuo, W-A. F.; Obunwo, C. C.; Chukunda, G. O. Indian J. Chem. 2002, 41A, 746. 8. Gores, H. J.; Barthel, J. M. G. Pure & Appl. Chem. 1995, 67(6), 919. 9. For example, see: (a) http://www.worksafeask.ca/files/ont_esao/handprotection.html (accessed June 2005); (b) Nierenberg, D. W.; Nordgren, R. E.; Chang, M. B.; Siegler, R. W.; Blayney, M. B.; Hochberg, F.; Toribara, T. Y.; Cernichiari, E.; Clarkson, T. N. Engl. J. Med. 1998, 338, 1672. 10. (a) Pattengill, M. D.; Sands, D. E. J. Chem. Educ. 1979, 56, 244. (b) Heilbromer, E. J. Chem. Educ. 1979, 56, 240. (c) Walpole, R. E.; Meyers, R. H., Probability and Statistics for Engineers and Scientists, 3rd. ed.; MacMillan, Inc.: New York, 1985; pp 317 – 348. 11. (a) de la Mare, P. D. B. J. Chem. Soc. 1955, 3169. (b) Fowden, L.; Hughes, E. D.; Ingold, C. K. J. Chem. Soc. 1955, 3187. (c) Le Roux, L. J.; swart, E. R. J. Chem. Soc. 1955, 1475.

27

V. Master Data Sheets A. Calibration Data: Acetone, 20oC Solution

Student:____________________________ Actual Temp. ______ Run 2 ____oC Run 3 ____oC Run 1 ____oC [NaI] [NaI] [NaI] κ, mS/cm κ, mS/cm κ, mS/cm

1 2 3 4 5 6 7 Acetone, 30oC Solution

Student:____________________________ Actual Temp. ______ Run 2 ____oC Run 3 ____oC Run 1 ____oC [NaI] [NaI] [NaI] κ, mS/cm κ, mS/cm κ, mS/cm

1 2 3 4 5 6 7 Acetone, 40oC Solution

Student:____________________________ Actual Temp. ______ Run 2 ____oC Run 3 ____oC Run 1 ____oC [NaI] [NaI] [NaI] κ, mS/cm κ, mS/cm κ, mS/cm

1 2 3 4 5 6 7 Acetonitrile, 40oC Solution 1 2 3 4 5 6 7

28

Student:____________________________ Actual Temp. ______ Run 2 ____oC Run 3 ____oC Run 1 ____oC [NaI] [NaI] [NaI] κ, mS/cm κ, mS/cm κ, mS/cm

B. Kinetics Experiment Data Sheet

Alkyl halide: __________________

29

Solvent: ________________

Run 1 Student:__________________ Temp, oC Time, sec κ, mS/cm (30) (60) (120) (240) (360) (600) (900) (1200) (1500) (1800) (2400) tfinal (3000)

Comments on Run 1:

Run 2 Student:________________ Time, sec Temp, oC κ, mS/cm (30) (60) (120) (240) (360) (600) (900) (1200) (1500) (1800) (2400) tfinal (3000)

Comments on Run 2:

Run 3 Student:________________ Time, sec Temp, oC κ, mS/cm (30) (60) (120) (240) (360) (600) (900) (1200) (1500) (1800) (2400) tfinal (3000)

Comments on Run 3:

Temp: ___________

Suggest Documents