Lab Report 9- pinacol rearrangement PDF

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Pinacol rearrangement...

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9 Lab$Report$Grading$Rubric$ Pinacol(Rearrangement( ( NAME: Rachel Totos

COURSE-SECTION TA: MW 12pm_ Xuan

Grading Rubric Fair

Poor

4 pts: The report begins with a statement of purpose. The introduction may miss some of the relevant chemical theory or diagrams, or have a small amount of theory incorrect, but overall demonstrates proficient knowledge about the background material. Final conclusions and overall findings & adequately presented 3 pts: Minor errors in the format or calculations exist, but all required components are present including diagram, quantities, and stoichiometry. The procedure is original and authentic. Some mistakes are present in calculation of rxn table.

2-3 pts: Report may be missing a statement of purpose. Chemical theory background is minimal, contains substantive errors, or lacks application of the theory to the current lab undertaken. Final conclusions and overall findings may bemissing, unclear, or lacking detail.

0-1 pt: The introduction does not connect the principles of the laboratory with the chemical theory. Very small amounts of material are presented and very little original thought is shown.

2 pts: The experimental procedure contains several errors and/or resembles almost exactly the procedure provided by the text with no thought behind the actual procedure followed. One to two components may be missing. Rxn table is incorrect. 3 -2 pt: Some data spectra, tables, calculations, or equations are missing or grossly incorrect.

1 pt: Two or more required components are missing. The procedure is unclear or mimics the text. The procedure lacks or presents incorrect details such as mols, equiv, conc, etc. Details may be missing.

Introduction & Reaction Tables

Good

5 pts: The introduction begins with a statement of the purpose of the lab undertaken and then presents a though, yet, concise, introduction to the chemical theory behind the lab, including a brief discussion of the mechanisms, analytical techniques, etc, At least one diagram supports the written word.

Experimental Procedure & Reaction Tables

Excellent

4 pts: Procedural details are written according to the examples provided with the correct format, including product name and reaction diagram. Math (mols, equivs, etc.) is correct. Procedure is original and authentic, and a diagram of the setup is included. Reaction tables are completed and correct.

Calculation

Performance Element

5 pts: Calculations/equations are shown and explained.

4 pts: Minor errors exist in titles, table presentation, or the description of acquisition method(s) Calculations are shown but have minor mistakes.

0-1 pts: Data section is incomplete. There are little to no spectra, tables, or calculations.

Earned Points

Conclusion & Data Analysis Post-Lab

6 pts: The conclusion accurately restates the purpose of the lab and concisely indicates whether the purpose and goals were achieved. The data collected is explained and used to verify and prove the concluded outcome. Insightful explanations are offered for unexpected results/procedures.

5 pts: The author accurately restates the purpose of the lab. Data are used to solidly verify and prove conclusions, but with some minor errors in theory and analysis. Explanations for unexpected results are offered.

4 pts: the purpose and conclusions of the lab may or may not be correct, but the author of the report makes gross errors in analyzing the data to arrive at any of these conclusions.

3-1pts: Little to no connections between the data acquired and the conclusions of the lab are presented. Data explained contains little thought and depth. 0 if conclusion is copied from a different source!

Points are assigned (0-10 pts)

Total Score (30 pts) à

Lab Report 9 Pinacol Rearrangement: Synthesis of Semicarbazone Derivative Rachel Totos TA: Xuan Duong 26 July 2021

Pinacol Rearrangement: Synthesis of Semicarbazone Derivative Introduction The purpose of this experiment is to oxidize an alcohol to a ketone via pinacol [1.2]rearrangement. Ketone is then transformed into its corresponding semicarbazone. See figure one for an illustration of this reaction. Finally, the ketone is analyzed using the haloform (iodoform) test and the cerium ammonium nitrate test and characterized by IR and melting point. Pinacol [1.2.]- rearrangement is a reaction of an acid catalyzed transformation of vicinal diols to ketones and aldehydes. The rearrangement proceeds in a stepwise fashion where an alphahydroxycarbenium ion is formed and then rearranged through a 1,2-alkyl shift and deprotonated to produce a carbonyl compound such as a ketone. See figure one for an illustration of this mechanism. This reaction can be a catalyzed by protic acids such as sulfuric acid, perchloric acid and phosphoric acid. This reaction is also highly stereo- and regioselective. Regioselectivity is determined by stereochemistry and general migratory aptitude. A substituent that is better at stabilizing a positive charge tends to migrate preferentially. For instance, the migratory aptitude for the following compounds are as follows: Aryl ~ Ph ~ H ~ alkenyl (vinyl) > t-Bu or 3° > 2° alkyl > 1° alkyl. Semicarbazide undergoes a condensation reaction with aldehydes and ketones in which water is eliminated. See figure two for the mechanism of this condensation reaction. In terms of carbocation stability, tertiary carbocations are the most stable intermediates and primary carbocations are the least stable intermediates. In this experiment, an Iodoform test and a Cerium Ammonium Nitrate (CAN) test are performed. See figure three for an illustration of the reactions taken place during these tests. The iodoform test is used to identity methyl (1°) ketones and will show a cloudy yellow test tube as a positive result. The CAN test performed is used to identify the presence of an alcohol functional

group. A positive result for the presence of an alcohol functional group will undergo a color change from yellow to red. Equations & Reactions Percent Yield = (Actual yield / Theoretical yield) x 100%

Figure 1. Mechanism of Pinacol [1.2]-rearrangement. This image is from the UIC Organic Chemistry Laboratory Manual, pg. 147.

Figure 2. Mechanism of the Condensation of Semicarbazide. This image is from the UIC Organic Chemistry Laboratory Manual, pg. 151.

Figure 3. Reactions taken place during the Haloform test and the CAN test. This image is from the UIC Organic Chemistry Laboratory Manual, pg. 236. Procedure Before beginning any experiment, safety precautions such as goggles, gloves and appropriate lab attire are required. To start, the alcohol and a boiling stone is added to a round bottom flask, also known as a “stillpot”. Using a graduated cylinder, 6M sulfuric acid was added to the flask. The flask was then clamped to a ring stand above a heating mantle and a simple distillation apparatus was assembled. See figure #, for an illustration of this setup. The receiving flask underneath the vacuum adapter was put on ice to prevent evaporation. Once assembled, the water and heat were turned on. Once all of the distillate has been collected, it is removed from the apparatus, while kept on ice, and is transferred to a separatory funnel. Since the product co-distills with water, we able to separate the layers and the aqueous layer (bottom layer) is put back into the separatory funnel and extracted with DCM. Once the DCM is added to the separatory funnel, the funnel is capped and shaken with intermittent venting. Once the layers have settled, the organic layer (bottom layer) is removed, while the aqueous layer remains in the separatory funnel. The aqueous layer is extracted once more with DCM by adding DCM to the separatory funnel, and the

funnel is shaken with intermittent venting. Once the layers have settled the organic layer (bottom layer) is removed and the aqueous layer is then removed and put into a separate flask. The collected organic layers are then transferred back into the empty separatory funnel. The organic layer is then washed with sodium bicarbonate, a base solution, to remove any residual acid. The separatory funnel is then capped and shaken with intermittent venting. Once the layers have settled, the organic layer (bottom layer) is removed. The organic layer is then dried using sodium sulfate until there is no new clumps forming. The dried solution is then decanted into a beaker to remove the sodium sulfate clumps. The solvent is then evaporated in a heating mantle. The pure product that is left behind in the beaker after evaporation will be used for the next part of the experiment, semicarbazone synthesis. To start the semicarbazone synthesis, semicarbazide hydrochloride and sodium acetate are added to a test tube and dissolved in water. Using a pipette, a small amount of the ketone is added to the pipette. The test tube is then capped and shaken vigorously to thoroughly mix the contents. The test tube is then uncapped and placed into a hot water bath placed on a hot plate. The heat was then turned off and the test tube is allowed to cool to room temperature. Once the test tube has cooled, it is placed on ice and the precipitate is vacuum filtered. The crude semicarbazone is then recrystallized using a minimal amount of hot ethanol. Once the crude semicarbazone has completely dissolved in the hot ethanol, it is allowed to cool to room temperature. Once it has cooled to room temperature it is put on ice to induce recrystallization. The formed crystals are then vacuum filtered and dried. In this experiment, two tests were carried out to analyze the reaction and help confirm the identity of the product, the Iodoform test and a Cerium Ammonium Nitrate (CAN) test. See figure three for an illustration of the reactions taken place during these tests.

To start the iodoform test, about 0.5g of iodine is added to a small beaker followed by water and mixed thoroughly with a stirring rod. Next, our product solution and the mixture of water and iodine from the beaker are added to a test tube. Next, sodium hydroxide (NaOH) solution is added to the test tube. The test tube is then heated to about 60°C. The iodoform test will form a cloudy yellow precipitate in the test tube as a positive result. To start the CAN test, about 1mL of the organic solution is added to a test tube, followed by a few drops of ceric ammonium nitration solution. A positive result for the presence of an alcohol functional group will undergo a color change from yellow to red. Next, the melting point of the recrystallized semicarbazone is measure by placing it into the capillary and then into the Melt Station apparatus. To obtain the melting point range, the temperature is recorded once the sample begins to melt and recorded again once the sample has completely melted. The obtained melting point range is then compared to the literature value. For IR comparison, an IR spectrum of the starting alcohol is taken for reference. Then, an IR spectrum for the ketone was taken and compared to the alcohol. Two major key differences that are to be expected between the IR spectra of pinacol and pinacolone are the -OH group around 3000 cm-1 for pinacol and a peak for the C=O around 1720 cm-1 for pinacolone.

Results

MW, g/mol

d (g/mL) or M (mmol/mL)

Rxn Weight or V (g or mL)

mmol

Equivalents

Pinacol (1)

118.18

-

6.73 g

56.9 mmol

1.00

6M H2SO4

98.08

6 mol/L

30 mL

180 mmol

3.16

Pinacolone (2)

100.16

-

0.50 g

4.99 mmol

1.11

semicarbazide HCl

111.53

-

0.50 g

4.48 mmol

1.00

NaOAc

82.03

-

0.80 g

9.75 mmol

2.18

Compound

Table 1. The table above represents the data from the two reactions occurred in this experiment.

Figure 4. Calculations for table one.

Figure 5. IR spectroscopy of pinacol.

Figure 6. 1H NMR of pinacol.

Figure 7. IR spectroscopy of pinacolone.

Figure 8. 1H NMR of pinacolone.

Data Analysis Referencing figure four, this image shows the calculations that were done to complete table one and find the percent yield. Given the actual yield of pinacolone isolated was 4.6 g, the theoretical yield (5.7 g) was calculated, and the percent yield was calculated using the equation shown in the equations section to result in an 80.7% yield of the product. IR and NMR spectrums were taken of pinacol (figures five and six) and pinacolone (figures seven and eight). The expected peaks for pinacol and pinacolone are shown in the given spectrums (see figure five and seven). Two major key differences between the IR spectra of pinacol and pinacolone are the -OH group around 3000 cm-1 for pinacol and a peak for the C=O around 1720 cm-1 for pinacolone. The literature value melting point of this semicarbazone derivative is 157°C. The obtained melting point in the experiment (159°C) is slightly higher than the literature melting point. Given that the obtain melting point is slightly higher than the literature value, this can be due to using an uncalibrated thermometer, using a too large of a sample or packing a sample too loosely in the capillary tube. In addition, measuring the melting point of a sample with significant quantities of impurities with a much higher melting point than the sample itself can cause the measured melting point to be higher than the literature value.

Conclusion The goals of this experiment were to oxidize an alcohol to a ketone via pinacol [1.2]rearrangement and convert the ketone into its corresponding semicarbazone. See figure one for an illustration of this reaction. Finally, the ketone was analyzed using the haloform (iodoform) test and the cerium ammonium nitrate test and characterized by IR and melting point.

The percent yield of the product was calculated to be 80.7%. In relation to the obtained melting point being slightly higher than the literature value, this percent yield could mean that the sample product was not pure enough. The characterization by melting point revealed that the measured melting point was higher than that of the literature value, meaning that the sample may have been too large or may have been packed too loosely in the capillary. The IR spectrums for both pinacol and pinacolone were both to be expected after analyzing the major peaks.

References 1. Gilbert, John C. Experimental Organic Chemistry: a Miniscale & Microscale Approach. 5th ed., Cengage Learning, 2015. 2. Landrie, Chad L., et al. Organic Chemistry: Laboratory I Lab Manual and Course Materials. 11th ed., Macmillan Learning Curriculum Solutions, 2021.

Post Lab Questions 1. (2 pts) The by-product for this experiment is 2,3-dimethylbutadiene. a) draw the structure of this product

b) based on your knowledge of elimination reactions, propose a detailed mechanism that

explains the formation of 2,3-dimethylbutadiene.

2. (1.5 pts) The boiling point of the by-product is 67-69 ºC. If a few drops of the final distillation

product are collected at 69 ºC, based on your previous experiments in this class what simple chemical test can you employ to identify that fraction as a diene or the 2,3-dimethyl-2,3butanediol? Briefly explain. I believe that the Lucas test can be used in this situation. Lucas test for alcohols allows us to distinguish between primary, secondary and tertiary alcohols via SN1 mechanism. Recall that with SN1 reactions, the rate of reactivity increases with increasing substitution

(3°>2°>>>1°). Primary alcohols are unreactive with the Lucas test. Tertiary alcohols show results almost immediately and secondary alcohols can take anywhere between 5-20minutes for results. 3. (1.5 pts) Briefly describe how would the IR spectra of pinacol, pinacolone, and the by-product

be different? Two major key differences between the IR spectra of pinacol and pinacolone are the -OH group around 3000 cm-1 for pinacol and a peak for the C=O around 1720 cm-1 for pinacolone. 4. (3 pts) Provide reasonable mechanisms for the reactions below.

5. (1 pt) What is the reason why semicarbazide was added as a hydrochloride salt in the

pinacolone semicarbazone derivative synthesis procedure? Semicarbazide hydrochloride (salt) is more water soluble, has a longer shelf life and is more crystalline than semicarbazide. 6. (1 pt) Why is the pH of the solution used to form the semicarbazone derivative important?

pH of the solution is important because a low pH slows the rate due to the nucleophile being protonated....