Investigating the Oxidation Reaction of 2-Ethyl-1,3-Hexandiol with Sodium Hypochlorite

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18/05/20 Chemistry Reference this

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Investigating the Oxidation Reaction of 2-Ethyl-1,3-Hexandiol with Sodium Hypochlorite

 

Abstract: The purpose of this lab was to determine specifically how sodium hypochlorite acts as an oxidizing agent in the presence of a diol. To determine this, sodium hypochlorite was reacted with 2-ethyl-1,3-hexanediol with glacial acetic acid as the solvent. The product was isolated and purified via extraction, and ultimately an oily, clear liquid was observed to be the product. IR spectroscopy was used to identify the final product, and whether or not sodium hypochlorite is a selective oxidizing agent. The final product was determined to be 3-(hydroxymethyl)-4-heptanone, indicating that sodium hypochlorite is indeed a selective oxidizing agent. Percent yield for this experiment was 22.3%.

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Introduction: The purpose of this lab is to perform an experiment using a diol and an oxidizing agent to determine whether or not the oxidizing agent is selective. To do that, analysis of the final product using IR spectroscopy will be performed. The specific reaction used in this experiment is described in Scheme 1 below.

Scheme 1. Illustration of reaction with diol (2-ethyl-1,3-hexanediol) and oxidizing agent (sodium hypochlorite) in glacial acetic acid. Product not shown.

From this reaction scheme, there are three possible scenarios. If the oxidizing agent is not selective, both alcohol groups will be oxidized and an aldehyde and a ketone will be formed. If it is selective, it can either lead to the formation of an aldehyde by oxidizing the alcohol on the primary carbon or a ketone by oxidizing the alcohol on the secondary carbon. In both of these scenarios, an alcohol will still be left over. These three reactions are shown below in Schemes 2, 3, and 4.

Scheme 2. Proposed reaction of diol with non-selective oxidizing agent, forming both an aldehyde and ketone group.

Scheme 3. Proposed reaction of diol with selective oxidizing agent. In this illustration, only the primary alcohol is oxidized, resulting in the formation of an aldehyde.

Scheme 4. Proposed reaction of diol with selective oxidizing agent. In this illustration, only the secondary alcohol is oxidized, and therefore a ketone is formed.

While performing this experiment, it is important to react all of the diol in order to convert it to the final product so that the IR spectroscopy only measures the final product and not the starting reagent. In order to make sure that all of the starting diol reacts, an excess of sodium hypochlorite will be used. It is not known how much sodium hypochlorite will be needed in order to fully react with the diol, therefore a starch/iodine test will be used in order to determine when the reaction is fully completed by testing for excess sodium hypochlorite. If sodium hypochlorite is in excess, the starch/iodine test paper will change to a blue color. That indicates that there is no diol left for it to react with, meaning that the reaction is done. After the reaction takes place, extraction will be used to isolate and purify the product, which will then be characterized by IR spectroscopy.

Experimental: According to the procedure described in the Investigating of Oxidation Reactions lab packet (Arizona State University, 2018), 5 mL (0.46 g) of 2-ethyl-1,3-hexanediol was added to a pre weighed 25 erlenmeyer flask. Weight of reactant was recorded. 3 mL glacial acetic acid with magnetic stir bar was added to the flask. Flask was placed in an ice bath, 3 mL of 6% aqueous NaOCl solution was added and stirring began. Start time of reaction was recorded, flask was allowed to stir for 30 minutes. Starch/iodine test was used to check for excess NaOCl. An extra 1.0 mL of NaOCl was added in this experiment, the reaction continued for an extra ten minutes. End time of reaction was recorded. Reaction mixture was poured from the flask into beaker containing 10 mL of saturated NaCl with 0.5 grams of ice. Mixture was then transferred into 2 centrifuge tubes with screw caps with volumes being kept equal. 3 mL of diethyl ether was added to each tube and shaken. Aqueous layer was removed and put into waste beaker. 2 mL sodium carbonate was added to the centrifuge tubes and shaken, aqueous layer was removed and put into waste beaker. This step was performed twice. 2 mL of 5% sodium hydroxide was added to each tube and shaken, aqueous layer was removed and put into waste beaker. This step was also performed twice. Organic layers were combined into one centrifuge tube, then were dried using magnesium sulfate. Organic layer was then transferred to a pre weighed beaker and placed on hot bath until ether evaporated. Weight of final product was recorded, IR spectroscopy was taken of both the final product and the starting reagent.

Results:

 Masses of the starting reactant and the final product were taken during the experiment. Moles of the reactant and the product were calculated using the following formula.

Experimental Mass÷Molar Mass = Moles

Mass and mole values are shown below in Table 1.

Chemical

Experimental Mass

Molar Mass

Moles

2-ethyl-1,3-hexanediol

0.46 g

146.23 g

0.0031 moles

3-(hydroxymethyl)-4-

heptanone

0.099 g

144.214 g

0.00069 moles

Table 1. Masses and moles used of the reactant 2-ethyl-1,3-hexanediol and product 3-(hydroxymethyl)-4-heptanone.

In order to calculate the theoretical and actual yield of this experiment, moles of reactant and product are required. The formula for theoretical yield is as follows.

Theoretical Yield = # of moles limiting reagent

In short, the theoretical yield should be equal to the number of moles of limiting reagent. Since sodium hypochlorite was used in excess, 2-ethyl-1,3-hexanediol must be the limiting reactant. Therefore, the theoretical yield is equal to the moles of 2-ethyl-1,3-hexanediol. The theoretical yield must equal .0031 moles.

The formula to calculate percent yield is as follows.

% Yield = (Actual Yield/Theoretical Yield)×100

To find the actual yield, the number of moles of product was calculated using the moles formula above. Actual yield was calculated to be .00069 moles. Actual yield was then divided by the theoretical yield of .0031 moles, then multiplied by 100. Percent Yield was calculated to be 22.3%.

IR spectroscopy was taken of the final product. IR spectroscopy is shown below, as well as data.

Image 1. IR Spectroscopy of final product. Functional groups are indicated by the peaks on the chart and are drawn next to them. Functional groups indicate the presence of an alcohol and a ketone, demonstrating that the product is 3-(hydroxymethyl)-4-heptanone.

Frequency (cm-1)

Specific Bond Vibration

Functional Group

3351.02 cm-1

O-H

Alcohol

2874.24 cm-1

C-H

Alkane

2932.48 cm-1

C-H

Alkane

2959.28 cm-1

C-H

Alkane

1704.6 cm-1

C=O

Ketone

Table 2. Data from IR spectroscopy. Frequencies demonstrate presence of alcohol, alkane, and ketone functional groups in the product, indicating that the sodium hypochlorite only oxidized the secondary alcohol, creating 3-(hydroxymethyl)-4-heptanone. 

Discussion: The reaction that took place in the vessel involved the diol 2-ethyl-1,3-hexanediol and the oxidizing agent sodium hypochlorite. Sodium hypochlorite was used in excess, and therefore 2-ethyl-1,3-hexanediol was the limiting reagent. Sodium hypochlorite was determined to be in excess using a starch/iodine test, if the strip turned a blue color, then sodium hypochlorite was in excess and all of the starting diol had reacted. There were .0031 moles of 2-ethyl-1,3-hexanediol, so theoretical yield was .0031 moles of product. The final number of moles of product that this experiment produced was .00069 moles, so the actual percent yield was 22.3%.

Scheme 5. Reaction of 2-ethyl-1,3-hexanediol with sodium hypochlorite in glacial acetic acid. Sodium hypochlorite selectively oxidized the secondary alcohol, creating the product 3-(hydroxymethyl)-4-heptanone.

This experiment used a selective oxidizing agent, sodium hypochlorite. Sodium hypochlorite was determined to be a selective oxidizing agent based on the IR spectroscopy of the final product. The IR demonstrated the presence of both an alcohol and a ketone, indicating that only the secondary alcohol was oxidized in this reaction. Therefore, sodium hypochlorite selectively oxidized the secondary alcohol, and did not oxidize the primary alcohol.

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After the reaction took place, the product was then isolated and then purified via multiple extractions. These extractions were used to remove any impurities from the reaction mixture by exploiting the solubilities of different molecules. By creating a mixture that would separate into two layers, one aqueous and one organic, the product could effectively by isolated into the organic layer while the aqueous layer was discarded with a pipette. Different chemicals were added to the reaction mixture, such as sodium carbonate and sodium hydroxide, to help ‘wash’ more impurities into the aqueous layer for easy removal. Magnesium sulfate was used to draw out any remaining water from the organic layer as well, further isolating and purifying the 3-(hydroxymethyl)-4-heptanone product.

After the product was purified, an IR was taken. There are 5 major peaks >1500 cm-1, and each peak corresponds to a functional group. From these peaks, functional groups of the product were determined and ultimately the identity of the product was determined. The peak at 1704.6 cm-1 is indicative of the carbonyl bond of the ketone functional group. The three peaks between 2800 and 3000 cm-1 are indicative of C-H bonds of sp3 hybridized carbons. The broad peak at 3351.02 cm-1 indicates the O-H bond of an alcohol group. From these functional groups, it was determined that the identity of the final product was 3-(hydroxymethyl)-4-heptanone, because oxidation of the secondary alcohol will produce a ketone, while the primary alcohol does not get oxidized.

Possible sources of error for this experiment include mechanical errors during the extraction steps. Some of the organic layer may have been extracted along with the aqueous waste layer. Additionally, some impurities may not have been thoroughly washed and may have remained in the organic layer, despite efforts to wash them out. Some possible error could have also come from not all of the starting diol reacting with the oxidizing agent, even though an excess of oxidizing agent was used.

Conclusion

 In this experiment, an oxidation reaction was performed using 2-ethyl-1,3-hexanediol and sodium hypochlorite, with glacial acetic acid as the solvent. Sodium hypochlorite was the selective oxidizing agent, only oxidizing the secondary alcohol of the reactant and not the primary alcohol. An excess of sodium hypochlorite was used to ensure that all of the starting reactant would react and form product. After the reaction took place, the final product was isolated and purified through various extractions, which removed impurities. After extraction, an IR was taken of the final purified product, which indicated that the identity of the final product was 3-(hydroxymethyl)-4-heptanone. The final product was also weighted, and percent yield was calculated to be 22.3%.

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