Archives for February 2008

I. Pre-Lab Report

A. Introduction

The purpose of this experiment is to convert benzoic acid to methyl benzoate via an acid catalyzed reaction with methanol. The reaction will be prepared by Fischer esterification, which involves the reaction reaching equilibrium after refluxing for a few hours. The purity of the benzoate will then be determined using infrared spectroscopy.

B. Main Reaction

Benzoic Acid + Methanol —> Methyl Benzoate + Water

C. Mechanism

Refer to the attached sheet.

D. Side Reactions

There are no side reactions.

E. Table of Reactants and Product(s)

II. Post-Lab Report

A. Experimental Procedure

The experimental procedure was followed pretty much as written. One change made was that an additional 15 mL of dichloromethane was added to the final dichloromethane solution because it was too concentrated. The one other change was that the IR spectrum of methyl benzoate was not taken.

B. Observed Yield of Product

Weight of benzoic acid: 10.008 g

Weight of distilled methyl benzoate: 6.274 g

Percent recovery: 62.69%

C. Calculations

(Weight of distilled methyl benzoate) / (Weight of benzoic acid) * 100 = Percent recovery

D. Conclusions

The percent recovery of methyl benzoate for the experiment was 62.69%. The theoretically yield for the experiment is 85%, so the percent recovery was low. Different factors could have contributed to this. First off, a small amount of the weighed benzoic acid did not make into the 100 mL round-bottomed flask. This means the actual starting amount was slightly lower than measured. While separating the layers, it gauge when to close the stopcock perfectly, so that led to a loss of eventual product. Also, while separating the layers, there was some emulsion during mixing, so again eventual product may have been lost because the layers did not completely separate. Lastly, if the concentration of methanol was higher, that would have also led to a higher percent yield.

If water was removed from the reaction mixture, it was cause equilibrium to shift towards methyl benzoate to make water and thus lead to an increased conversion of benzoic acid to methyl benzoate. When a compound on one side of the reaction is removed, equilibrium will shift towards the side it was removed from. If more of a compound is added to one side, then equilibrium will shift towards the other side.

I. Pre-Lab Report

A. Introduction

The purpose of this experiment is to investigate the influence of molecular structure on the reactivity of an alkane in free-radical chlorination using gas chromatography. The alkene to be used, 1-chlorobutane, will be reacted with sulfuryl chloride to produce four isomeric dichlorobutanes. The reaction will take place using a similar apparatus described in figure 18.1 of Williamson. The product will be washed and dried, then analyzed with a gas chromatograph.

B. Main Reaction

1-Chlorobutane + Sulfuryl Chloride –> 1,1-Dichlorobutane + 1,2-Dichlorobutane + 1,3-Dichlorobutane + 1,4-Dichlorobutane

C. Mechanism

The reaction proceeds with via free radical chlorination. Refer to the attached sheet to see the detailed mechanism.

D. Side Reactions

There are no side reactions.

E. Table of Reactants and Product(s)

II. Post-Lab Report

A. Experimental Procedure

The experimental procedure was followed exactly as written. The only minor difference was that 6 mg of AIBN was used instead of the recommended 4 mg. Also, it was noted that during washing, there was a bubble in the organic layer which may have caused error.

B. Observed Yield of Product

Tared vial: 11.568 g

Tared vial with organic product: 11.648 g

Organic product recovered: 0.080 g

C. Calculations

7.8% 1,1-dichlorobutane / 2 H = 3.9% per each primary H

22.7% 1,2-dichlorobutane / 2 H = 11.35% per each secondary H

44.4% 1,3-dichlorobutane / 2 H = 22.2% per each secondary H

25.1% 1,4-dichlorobutane / 3 H = 8.4% per each primary H

Ratio of reactivity per hydrogen at C1 : C2 : C3 : C4 = 1 : 2.9: 5.7 : 2.2

D. Conclusions

The mixture of isomeric dichlorobutanes contained 7.8% 1,1-dichlorobutane, 22.7% 1,2 dichlorobutane, 44.4% 1,3-dichlorobutane, and 25.1% 1,4-dicholorobutane. From this data, it was determined that the relative reactivities of the hydrogens found at C1, C2, C3, and C4 was 1 : 2.9 : 5.7 : 2.2. This seems to confirm that secondary hydrogens are more reactive than primary hydrogens. It also showed that the secondary hydrogens at C3, which were further away from the original chlorine found at C1, were more reactive then the hydrogens found at C2. The primary hydrogens found at C4 were more reactive than the primary hydrogens found at C1, which also suggests that the original chlorine at C1 lessened reactivity of the hydrogens near it.

Compared to the given ratio of 5.0 : 3.8 : 1.0 for the reactivity of tertiary to secondary to primary hydrogens of normal alkanes, the expected reactivity of the hydrogens on C1, C2, C3, and C4 of n-butane would be 3(1.0) : 2(3.8) : 2.(3.8) : 3(1.0), which simplifies to 1.0 : 2.5 : 2.5 : 1.0. Compared to the findings in the lab, the found ratio again hints that the original chlorine at C1 made the other primary hydrogens found at C1 and any hydrogens adjacent to it less reactive than expected.