Chlorination of an Alchohol

Results
The final product was 2-chloro-2-methylbutane and its yield was 2.48 grams (MW: 106.5 grams).
Weight of 3-methyl-2-butanol: 3.92 grams (MW: 88.15 grams).
Theoretical yield:
3.92g alcohol x 1 mol alc. x 1 mol product x 106.59 g prod. = 4.74 grams product 88.15 g alc. 1 mol alc. 1 mol prod.
Percent yield:
2.48 grams product (experiment yield) x 100% = 52.3%
4.74 grams product (theoretical yield)

Discussion
The acid was put on ice because this reaction was exothermic. The acid, NaCl, and alcohol were put into an apparatus together. The acid protonated the alcohol to form a good leaving group, H2O. The heat was added to the reaction to catalyse the leaving group to leave and form the carbo cation (and H2O). The chlorine from NaCl added to the solution was the nucleophile and attacked the carbocation and yielded 2-chloro-3-methylbutane, which was the kinetic product. The thermodynamic product included a 1,2 hydride shift, and the Cl- yielded 2-chloro-2-methyl butane which completed the SN1 reaction. 2-chloro-2-methylbutane separated from the aqueous layer and creates an organic layer. The distillation apparatus was set up, and the product boiled at 24 deg. cel. And was collected in a second round bottom flask. The yield was quite low, coming in at 52.3% of the theoretical yield. This could have been due to some of the product evaporating, or more likely because our temperature never got past 67 degrees Celsius, some of the product may have remained behind in the aqueous solution during the distillation process.

Reaction mechanism

Intermediates
The starting material did not contain a good leaving group so the acid added turned the OH into H2O. The second step where the H2O left the main molecule was the rate determining step. The reaction was SN1, and the H2O left the molecule. The carbocation that was created was a secondary carbocation, so the positive charge was stabilized by neighboring electron densities. However, the 1,2 hydride shift allowed for the carbocation to become a tertiary carbocation, being stabilized by more electron densities than the secondary carbocation. The tertiary carbocation was a more stable molecule, and was therefore the thermodynamic intermediate

Compound | Lit NMR1 | Exp NMR | Fragment | H NMR | | | | | 1.764 | 1.8 | -CH2CH3 | | 1.556 | 1.5 | -C(CH3)2Cl | | 1.036 | 1.1 | -CH2CH3 | | | | | 13C NMR | | | | | 71.42 (1) | 71.59 | -C(CH3)2Cl | | 38.85 (2) | 38.31 | -CH2CH3 | | 32.00 (3) | 31.97 | -C(CH3)2Cl | | 9.52 (4) | 9.52 | -CH2CH3 |

Spectral analysis
The experimental proton NMR that was taken of the final product was very close to the literature values of 2-chloro-2-methylbutane1. A possible reason why they were not exactly matched up could have been due to the accuracy of the instrument used in the lab, or that the experimental product had some kinetic product remaining in it that did not convert to the more stable, thermodynamic product. The A peak of the proton NMR was the most deshielded, and therefore farthest downfield. It can be seen slightly farther downfield than B. This is because B and A peaks are connected to Cl, an electronegative atom, and B has more Hs shielding it than A. However the B peak shows up as a singlet because it is not coupling with any other protons, and it accounts for six hydrogens attached to two CH3s in symmetry which is why it has such a large single integration peak. The A peak accounts for the CH2 in 2-chloro-2-methylbutane, and its integration is two hydrogens, and it is a quartet because it neighbours with peak C which has three hydrogens for peak A to couple with. Peak C is the most shielded group hydrogens, it is the farthest away from Cl and its integration counts for three hydrogens. It is a triplet, which is because its hydrogens are J3 distance away from the hydrogens of CH2 and couple with them. The H NMR of the starting material is quite different from the product4. The similarities look like peak A and be switched sides, and that is all this could be due to the hydride shift during the thermodynamic step that produces the more stable product. The reaction was a success because the literature ppm and integration values match up closely1 to the experimental values, peaks B and C on the starting material4 1HNMR switched sides on the product’s proton NMR, and all of the other peaks disappeared other than the one at 1.1 ppm.

The values of the carbon 13 NMR was very close to the literature values1. The major difference in the experimental NMR is that you can see the triplet peak of the solvent of CDCl3 at around 77 ppm. On the 13C NMR, there are only four carbon environments that show up, but there are five carbons in the molecule, therefore it is known that there is symmetry in the molecule. The peak at 71.59 ppm is farthest downfield because it is the carbon that is connected to the Cl atom. The farthest upfield is the carbon of the methyl group farthest away from the chlorine atom, and peak 3 is the peak of the carbons 2 x CH3 which have the same environment and are there fore represented as one peak. The starting material 13C NMR is similar to the product 13C NMR in regards to it has symmetry, and that the ppm values stay below 80ppm4. Because of the hydride shift, the carbon signals moved on the product’s NMR, and that is how a successful result was determined, and that the values matched up with the literary values. Since the values of the 13 C NMR and 1H NMR of the experimental values and literature1 values matched up closely, it could be determined that the experiment yielded a pure product and that the experiment was a success.

Conclusion
Since the values of the 13 C NMR and 1H NMR of the experimental values and literature values matched up closely, it could be determined that the experiment yielded a pure product and that the experiment was a success.
Summary Box

Theoretical yield | Yield | % yield | purity | 4.74 grams 2-chloro-2-methylbutane | 2.48 grams 2-chloro-2-methylbutane | 52.3% | Values from experiment matched up closely to literary values, it could be determined that the experiment yielded a pure product |

References

(1) 2-chloro-2-methylbutane; SDBS [online]; National Institute of Advanced Industrial Schience and Technology (AIST). http://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi (accessed November 3, 2014). (2) 2-chloro-2-methylbutane; [online]; Sigma-Aldrich: Oakville, ON. http://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=CA&language=en&productNumber=44028&brand=FLUKA&PageToGoToURL=http%3A%2F%2Fwww.sigmaaldrich.com%2Fcatalog%2Fproduct%2Ffluka%2F44028%3Flang%3Den (November 3, 2014) (3) Neeland, E. Post-lab Report. Organic Chemistry: Lab Manual 2014/2015. 1996. 7-8. Print. (4) 2-chloro-3-methylbutane; SDBS [online]; National Institute of Advanced Industrial Schience and Technology (AIST). http://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi (accessed November 3, 2014). (5) 2-chloro-3-methylbutane; [online]; Sigma-Aldrich: Oakville, ON. http://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=CA&language=en&productNumber=44028&brand=FLUKA&PageToGoToURL=http%3A%2F%2Fwww.sigmaaldrich.com%2Fcatalog%2Fproduct%2Ffluka%2F44028%3Flang%3Den (accessed November 3, 2014) (6) Neeland, E. PSL 2:Identification of an Organic Unknown. Organic Chemistry: Lab Manual 2014/2015. 1996. 25-28. Print. (7) Zubrick, James W. The Organic Chem Lab Survival Manual: A Student’s Guide to Techniques. 9th ed. New York: Wiley, 2014. Print.