The Process of Alcohol Transforming into Alkyl Halides by IR and NMR Spectroscopy PDF

Preview

Summary

The Process of Alcohol Transforming into Alkyl Halides by IR and NMR Spectroscopy...

Description

The Process of Alcohol Transforming into Alkyl Halides by IR and NMR Spectroscopy Jessica Hilliker Section: M5

Results: Table 1: Table of Reagents Product Name Molecular Weight (g/mol) Sodium Bromide 102.29 9 M H2SO4 98.079 1-propanol 60.095 2-pentanol 88.148 Sodium Bicarbonate 84.007

Melting Point °C

Boiling Point °C

Density (g/cm3)

747 50 -176 -73 3000

1396 337 97 119.3 851

3.1 1.83 0.8 0.812 2.2

Percent yield was calculated by using the mass of the products. An example problem of this is shown below. This equation explains how the percent yield was calculated. Percent Yield = Actual Yield / Theoretical Yield * 100 Table 2: Percent yield Product 1-bromopropane 2-bromopentane and 3-bromopentane

Theoretical Yield (g) 4.133 3.478

Actual yield / product mass (g) 0.460 0.982

Percent Yield (%) 11.1 28.2

Equation 1: Percent Yield of 1-bromopropane 2.5 mL of 1-propanol * 0.804 g/ml * 1 mol/ 60.10g * 1 mol 1-bromopropane/ 1 mol 1-propanol * 122.99 g/mol = = 4.133 g 1-bromopropane The theoretical yield of the reaction as shown in Equation 1, was calculated to be around 4.133 grams of 1-bromopropane.

Equation 2: Percent Yield 2-bromopropane and 3-bromopropane 2.5 mL of 2-pentanol * 0.812 g/ml * 1 mol/ 88.15g * 1 mol 2-bromopropane or 3-bromopropane/ 1 mol 2-pentanol * 151.04 g/mol = = 3.478 g 2-bromopropane and 3-bromopropane

The theoretical yield of the reaction as shown in Equation 2, was calculated to be around 3.478 grams of 2-bromopropane and 3-bromopropane. The mass of the product was obtained and calculated by the precent yield of both sets of products. Table 2 above shows each of these products.

Figure 1: IR Spectrum for 1-propanol 1 1-propanol reacted with sodium bromide and sulfuric acid to produce 1-bromoproane. The signal that was produced has certain labeled peaks with functional groups.

1-propanol produced an IR signal of approximately 3300 cm-1 with a signal characteristic of a hydroxyl group through a peak at the fingertip region to show the C-O stretch. Triplet peaks were displayed around 2900 cm-1. This shows carbons as sp3 hybridized as above in Figure 1. Figure 2: IR Spectrum for 1-bromopropane 1

Figure 3: IR Spectrum for 2-pentanol 1 2-pentanol reacted with sodium bromide and sulfuric acid to produce 2-bromopropane and 3bromopropane. The IR signal that was produced has certain labeled peaks with functional groups.

1-propanol produced an IR signal of approximately 3300 cm-1 with a signal characteristic of a hydroxyl group through a peak at the fingertip region to show the C-O stretch. Triplet peaks were displayed around 2900 cm-1. This shows carbons as sp3 hybridized as above in Figure 3. Figure 4: NMR Spectrum for 1-bromopropane 1

Figure 4 above shows 1-bromopropane as the product of the reaction consisting of 1-propanol and NaBr.

Figure 5: IR Spectrum for 2-bromopropane and 3-bromopropane 1

The Figure 5 above has a peak around 2900 cm that shows a C-H stretch. The several peaks around 530 cm show a C-Br stretch. Figure 6: NMR Spectrum for 2-bromopropane and 3-bromopropane 1

The result of the reaction of 2-pentanol and NaBr is shown above. There are eight peaks with one major product and several minor products.

Table 2: NMR values of 2-bromopropane and 3-bromopropane 1 Product

Proton A

Chemical Shift 1.25

Splitting Pattern Doublet

Integration 0

B

4.2

Sexlet

1

C

1.83

quartet

0

D

1.6

Sexlet

0

E

1.1

triplet

0

F

1.02

triplet

0

G

1.85

quintet

0

H

3.95

quintet

0

A

3.42

triplet

2

B

1.9

Sexlet

2.03

C

1.1

triplet

3.05

2-bromopentane

2-bromopentane

2-bromopentane

2-bromopentane

2-bromopentane

3-bromopentane

3-bromopentane

3-bromopentane

1-bromopropane

1-bromopropane

1-bromopropane

Mechanism: Conversion of Alcohols to Alkyl Halides 1 Figure 1: Protonation of the alcohol to form a good leaving group.

Figure 2: Two mechanistic pathways 1

Top: SN2: the halide attacks the electrophilic carbon, kicking out water as a leaving group. Bottom: SN1: water leaves, forming a carbocation intermediate, that is attacked by the halide.

Figure 3: Reaction Mechanisms 1

Discussion: In this experiment, reflux, distillation, separation and drying are the four parts required. The first part, reflux, involves the reaction heating and cooling the vapor produced. Reflux was used to create an acid-catalyzed reaction. A condenser was used for a period of time to help. The second part, distillation is also necessary in separating the components while the vapors are condensed. Distillation separates the compounds based on their boiling points. Both of these steps are important in achieving an adequate product. Next, the apparatus must be set up and the distillation head should produce vapor that was collected in a flask. The third part, separation, releases the components of a mixture from each other and removes impurities. The organic layer will be separated from the distilled water. The last part, drying, uses evaporation to remove water from a mixture which will result in a mass transfer. With this step, a drying agent is used. Anhydrous sodium sulfate was used as the drying agent in this experiment. Simple distillation would be inadequate in condensing the vapor, and collecting the product compared to reflux because it has more product loss. There was a high yield of product in the distillation and the temperature was very similar to the products boiling points. Only a tiny amount of product was produced from the compounds. IR an

Conclusion:

The objective of this experiment was to use NMR and IR spectroscopy to identify compounds in the conversion of alcohols to alkyl halides. The reactions stretches and peaks could be inferred from the NMR and IR. When the reaction was complete, the O-H stretch was no longer present, suggesting that 1-bromopropane and 2-bromopentane were both seen in the product distribution. Error could have been present in the percent yield of the product. Adding too much or too little drying agent could affect the product.

References: UAB Central Authentication System - CAS – Central Authentication Service, uab.instructure.com/courses/1542566/pages/alcoholos-to-alkyl-halides-procedure-andprelab-information?module_item_id=16085018....