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Organic Chemistry Lab 654.02 2/16/20 Reaction of 2,3-Dimethyl-2,3-butanediol with an Acid Catalyst Laboratory Report Introduction The goal of this lab is to identify the product and struct of C6H12O. The reactions represented in figure 1 was what was expected to occur when 2,3-dimethyl-2,3-butanedoil reacted with sulfuric acid. It was expected to react like this because an alcohol in the presence of H2SO4 (an acid catalyst) undergoes an acid-catalyzed dehydration reaction that will result in an alkene forming.

Figure 1. Expected Acid-Catalyzed Dehydration of 2,3-Dimethyl-2,3-butanediol.1

1 Joiner, S. L. Reaction of 2,3-Dimethyl-2,3-butanediol with an Acid Catalyst Procedure, University of New Hampshire, Durham, NH, 2020

The reaction represented in Figure 2 is the reaction that occurred when 2,3-dimethyl-2,3butanedoil reacted with sulfuric acid. In order to determine the identity of this product several classification tests such as chromic acid, DNHP, potassium permanganate need to be done as well as IR and NMR spectroscopy. There were several techniques key to determining the identity of the product including simple distillation, IR spectroscopy, and NMR spectroscopy.

Figure 2. Observed Reaction of 2,3-Dimethyl-2,3-Butanediol with Sulfuric Acid Catalyst.2 Simple distillation is a technique used to boil out impurities from a compound. Simple distillation is often used to purify a substance that is already almost pure or one that has nonvolatile impurities. In a simple distillation the substance in the distillation flask will give rise to a vapor. The vapor will then come into contact with a thermometer and record the temperature. After that the vapor will pass through a condenser (a cold-water condenser was used for this experiment) and therefore will be re-liquified and deposited into an awaiting container. There can also be microscale distillations. When the glassware used during a distillation is large a certain volume of liquid is lost during the process. When working with large amounts of substances this is not usually a problem, but when working with small amounts of substances that can skew the results drastically. To reduce the loss of substance the condenser is made shorter. 3 2 Joiner, S. L. Reaction of 2,3-Dimethyl-2,3-butanediol with an Acid Catalyst Procedure, University of New Hampshire, Durham, NH, 2020. 3 Joiner, S. L. Distillation Power Point, University of New Hampshire, Durham, NH, 2020.

One of the techniques is known as IR spectroscopy. IR spectroscopy is used to measure which wavelengths of light pass through a certain substance. When a wavelength contains the same amount of energy as one of the vibrational modes of the bonds in a substance it causes a peak to show up on the spectra. If the energy does not match, it is transmitted through the substance and no peak is formed on the spectra. The importance of the type of bond in a substance depends on the intensity of the peak. Four important peak ranges are: 3200-3600 cm-1 (O-H bonds), 2500-3100 cm-1 (C-H bonds), 1630-1750 cm-1 (C=O bonds), 1000-1350 cm-1 (CO bonds). If peaks are formed in these bond regions it indicates that the particular bond is present. The information taken from an IR spectroscopy can be used to identify compounds with different functional groups.4 One of the most commonly used types of spectroscopy in organic chemistry is called nuclear magnetic resonance (NMR). It is so popular because it gives data that reveals the specific placement and connectivity of atoms. NMR spectroscopy can help with finding the exact location of functional groups and hydrogens. It also helps with information on the carbon skeleton and the molecule in general. NMR is used with any atom that has a nucleus with a nuclear spin, which is defined as any nucleus that has an odd mass number or an odd atomic number. There are two types of NMR hydrogen (1H NMR) and carbon (13C NMR). The proton is observed during 1H NMR which also happens to be the hydrogens nucleus. For the 13C NMR only the 13C isotope can be used since it has an odd number. The NMR spectroscopy gets its results by flipping the spin of the nucleus at hand to a high energy state and then the freeinduction decay (FID) is observed, which is the decay over a period of time. After the FID an oscillating signal occurs, which is then converted to an NMR spectrum using Fourier transform

4 Joiner, S. L. Infrared Spectroscopy, University of New Hampshire, Durham, NH, 2020.

so the data can be examined.5 The points in the 1H NMR spectrum can have multiple peaks. Having multiple peaks is defined as multiplicity and names such as singlet, doublet, triplet, etc. are used to describe the points depending on how many peaks they have. A simple rule is followed to determine the number of peaks for a given point and it is the n+1 rule. Based off the specific carbon atom and if the direct neighbors have any hydrogen bonds those are counted up (representative of n) and then 1 is added to determine the multiplicity.6 The DNHP test is used to test for aldehydes and ketones. A positive result would occur when a precipitate forms that is yellow, orange, or red as seen in figure 3.

Figure 3. Positive and negative DNHP test7

5 Joiner, S. L. NMR Spectroscopy-Background Info, University of New Hampshire, Durham, NH, 2020. 6 Joiner, S. L. NMR Spectroscopy-Chemical Shifts and Multiplicity, University of New Hampshire, Durham, NH, 2020. 7 Joiner, S. L. Classification Tests, University of New Hampshire, Durham, NH, 2020.

The chromic acid test is used to test for primary and secondary alcohols as well as aldehydes. A positive chromic acid test would result in the substance turning a blue/green color as shown in figure 4. The primary and secondary alcohol would form in 2 to 3 seconds while the aldehyde takes slightly long to show up at 10 or more seconds.

Figure 4. Positive and negative chromic acid test8 The potassium permanganate test is used to test for alkenes and alkynes. For this test a negative result can also mean that there are aromatics present, which would be when the solution stays purple. The positive result would result in a brown precipitate forming as shown in figure 6.

Figure 6. Positive and negative potassium permanganate test9 8 Joiner, S. L. Classification Tests, University of New Hampshire, Durham, NH, 2020. 9 Joiner, S. L. Classification Tests, University of New Hampshire, Durham, NH, 2020.

Results and Discussion There were multiple objectives of 2,3-Dimethyl-2,3-butanediol with an Acid Catalyst Lab. The first step was to use a microscale simple distillation to get an aqueous layer and an organic layer. The two layers were differentiated by using NaCl to wash the two layers as it helps create space between the organic layer and the aqueous layer. A drop test was used to identify the aqueous layer, which involved adding small amounts of water to see which layer it went to as well as force pipetting to ensure the water added did not get stuck in the organic layer and cause impurities. After identifying which layers was the organic the two layers were separated by pipetting the organic layer into a clean conical vial. Once the organic layer was separated it was purified with the simple distillation. During the purification process a boiling point was recorded (129 degrees Celsius). After purifying the sample a variety of tests were performed, IR spectroscopy, chromic acid test, 2,4-DNHP test, and the potassium permanganate test, in order to determine the structural makeup of the organic layer. The proposed structure for C6H12O is a 3,3-dimethyl-2-butanone molecule as shown in figure 7. This is the most likely structured based off all the tests run and data collected from them. The chromic acid test was run and it had a negative result. This fits with the proposed structure because chromic acids tests for primary or secondary alcohols and neither of those are present. The next test was a 2,4-DNHP test. This test was run, and a positive result came back which indicates that there was an aldehyde or ketone present. In the proposed structure there is also a ketone present which aligns with the result of the DNHP test. The last classification test run was the potassium permanganate test, which tests for a carbon-carbon unsaturation. The result was positive but based off of the IR spectra there were no C=C bonds present in the product. The IR spectra showed peaks at 2969.75 cm-1 indicating C-H bonds were present. Peaks

were also shown at 1705.75 cm-1 which indicates the there were C=O bonds present. The last peak of the IR spectra was at 1476.94 cm-1 indicating that C-C bonds were present. In the starting material (2,3-dimethyl-2,3-butanediol) IR spectra there were peaks at 3438.41 which show the O-H group in 2,3-dimethyl-2,3-butanediol. The IR spectra for 2,3-dimethyl-2,3-butanediol also lacked a C=O peak which indicates that that was gained during the sulfuric acid reaction. Both the 1H NMR and the 13C NMR were very helpful in determining the structure. The 1H NMR allowed the multiplicity to be determined, which helped with the positioning of the methyl groups. The 13C NMR indicated that there was a C=O bond in the structure because one of the points was 212 ppm and based of the correlation charts it indicated that there was a ketone with two R-groups present. After that big hint the data from the 1H NMR was able to fill in the rest of the structure.

Figure 7. Proposed structure of C6H12O10 The proposed mechanism for the reaction of 2,3-dimethyl-2,3-butanediol with sulfuric acid is a pinacol-pinacolone rearrangement. To start the mechanism the hydroxide group of sulfuric acid is protonated. Then the water is removed from the compound, which leaves a carbocation behind.

10 Pinacolone is. https://ww

020).

This carbocation is tertiary. One of the methyl groups shift to the positively charged carbocation which leaves a positive charge on the carbon connected to the OH group. One of the lone pair on oxygen will form a double bond to create a more stable molecule. And finally, the hydrogen left on the oxygen will be removed and give a new lone pair to the oxygen to remove the positive charge and create the final molecule of C6H12O. Figure 8. Proposed mechanism11 Experimental A microscale simple distillation apparatus was assembled. 2,3-dimethyl-2,3-butandiol (1.407g, 12.0 mmol) was distilled in sulfuric acid (4.0 mL, 3 M) in a 10mL round bottom flask with a stir bar. The reaction was then distilled until there was approximately 2.0-2.5mL of distillate. The temperature during the distillation ranged from 25-100 degrees Celsius. The distillate was collected in a conical vial. The aqueous layer was removed via pipet, and the remaining organic layer was washed twice with saturated aqueous sodium chloride (1mL x2) and was then forced mixed. A very small amount of sodium sulfate was then used to dry the organic layer. A clear colorless liquid was attained after the drying out process and the analysis resulted in this data: (0.595 g, 42.3% yield, IR: 2969, 1705, 1476 cm-1, 1H NMR (400 MHz, CDCl3) δ2.17 (s, 3 H), 1.09 (s, 9 H), 13C NMR (101 MHz, CDCl3) δ212, 43, 27, 24). A chromic acid test was then preformed and the test was a negative result based on the dark brown/orange color remaining. A 2,4-DNHP test was performed and the test result was positive because the tube had a yellow precipitate form. A potassium permanganate test was run and it was determined to be a positive result based off of the brown color, and slight precipitate.

11 Pinacolone. https://en.wikipedia.org/wiki/Pinacolone (accessed Feb. 16, 2020).

References 1.) Joiner, S. L. Reaction of 2,3-Dimethyl-2,3-butanediol with an Acid Catalyst Procedure, University of New Hampshire, Durham, NH, 2020 2.) Joiner, S. L. Reaction of 2,3-Dimethyl-2,3-butanediol with an Acid Catalyst Procedure, University of

New Hampshire, Durham, NH, 2020

3.) Joiner, S. L. Distillation Power Point, University of New Hampshire, Durham, NH, 2020. 4.) Joiner, S. L. Infrared Spectroscopy, University of New Hampshire, Durham, NH, 2020. 5.) Joiner, S. L. NMR Spectroscopy-Background Info, University of New Hampshire, Durham, NH, 2020. 6.) Joiner, S. L. NMR Spectroscopy-Chemical Shifts and Multiplicity, University of New Hampshire,

Durham, NH, 2020.

7.) Joiner, S. L. Classification Tests, University of New Hampshire, Durham, NH, 2020. 8.) Joiner, S. L. Classification Tests, University of New Hampshire, Durham, NH, 2020. 9.) Joiner, S. L. Classification Tests, University of New Hampshire, Durham, NH, 2020.

10.) Pinacolone is. https://www.toppr.com/ask/question/pinacolone-is/ (accessed Feb 16, 2020). 11.) Pinacolone. https://en.wikipedia.org/wiki/Pinacolone (accessed Feb. 16, 2020)....