Derivatization of Carboxylic Acid using Fisher Esterification PDF

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Ochem Lab...

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Derivatization of Carboxylic Acid using Fisher Esterification Introduction The purpose of this experiment is to generate a liquid ester product from excess unknown alcohol and carboxylic acid. Acetic acid is the carboxylic acid component and possible unknown alcohols are 1-propanol, 1-butanol, and Isopentanol. The possible unknown ester products are propyl acetate, butyl acetate, and isopentyl acetate. This condensation reaction between the alcohol and carboxylic acid is known as Fischer Esterification. This reaction is acid catalyzed where the unknown alcohol is the nucleophile and the carboxylic acid is the electrophile. To push the reaction to equilibrium, excess of the starting material is used. Also, 5% sodium bicarbonate is used to wash the ester layer and sodium sulfate is used to dry the ester layer. Brine is used for washing the ester while water is used to separate the organic layer from aqueous. This experiment utilizes five techniques including microwave reflux, liquid/liquid extraction, decanting, IR spectroscopy, and HNMR spectroscopy. Microwave reflux is a technique that uses internal heating with the ions present in the reaction mixture in order to reflux a reaction at a quicker rate than a normal reflux. Liquid/ liquid Extraction is a technique that is used to separate two immiscible liquids, typically an organic and aqueous layer. Solvent decanting is a technique that is used to separate mixtures by allowing the mixture to settle and be separated by gravity. Solvent removal by snorkel is a technique that removes the solvent by using the snorkels to extract the solvent fumes. IR spectroscopy is a technique used to find the functional groups in a molecule depending on the frequencies each functional group gives off. H NMR spectroscopy is a technique that makes the nuclei have a spin in the molecule and helps identify structures by seeing how many hydrogen signals are seen. Balanced Equation

Possible Unknown Alcohols

Reaction Mechanism

Table of Reagents Compoun d

Structure

MW (g/mol)

MP/BP (°C)

Densit y (g/cm3)

Glacial acetic acid

60.052

BP = 117.9

1.0446

Sulfuric acid

98.079

BP = 212

1.841

1-propanol

60.096

BP = 97.2

0.803

1-butanol

74.123

BP = 117.7

0.81

Isopentanol

88.15

BP = 132.5

0.81

Safety Highly flammable, exposure can harm skin or eyes. Exposure can cause severe burns if contacts skin, nose, or eyes. Highly flammable, exposure can cause headaches, dizziness, and nausea. Highly flammable, exposure can cause headaches, dizziness, and nausea. Highly flammable, exposure can cause headaches, dizziness, and nausea.

5% Sodium bicarbonate

84.006

MP = 50

-

Sodium sulfate

142.036

MP = 884

-

Brine

58.88

BP = 108

1.19

Water

18.015

BP = 100

1.00

If ingested, can cause loss of appetite. Can cause nausea or vomiting, nervousness and slow breathing. If ingested, causes diarrhea. Mild irritant to nose, throat & lungs Irritant to eyes and skin None

Propyl acetate

102.133

BP = 101.5

0.88

Butyl acetate

116.16

BP = 126.1

0.88

Isopentyl acetate

130.187

BP = 142

0.88

Flammable, exposure can cause irritation of the eyes, nose and throat. Weakness & drowsiness can occur Flammable liquid and vapor, repeated exposure can cause skin dryness or cracking Flammable, exposure can cause eye and skin irritant.

Safety        

Avoid sparks, flames, and hot surfaces. Avoid breathing any fumes as the chemicals are toxic. Use snorkels while working with boiling liquids. Make sure not to heat a sealed vessel. Report any vapor or liquid exposure to TA immediately. Dispose all organic solvent waste in appropriate labeled bottle in lab hood. Wear safety glasses, gloves, and lab coat at all times. Never seal a reflux apparatus airtight.

Procedure

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Each group was assigned a specific unknown alcohol by the TA. 5 mL of glacial acetic acid and 4 mL of an unknown alcohol were obtained and added to a microwave (MW) vessel. 1 mL of concentrated sulfuric acid was added carefully under the hood and a spin bar was added as well. MW vessel was sealed and placed in MW carousel and microwave reflux was carried out by TA for 10 minutes. Once the vessel was cooled, the contents were poured into a separatory funnel and 10 mL of water was added. The ester was separated from water and the aqueous layer was removed and washed with additional 10 mL of water. Then, the ester was washed again with 10 mL portions of 5% sodium bicarbonate until the resulting aqueous wash was basic according to the pH paper. Note: CO2 was formed during this step. Finally, the ester was washed with 5 mL of brine solution to remove residual water. The ester layer was dried with anhydrous Na2SO4 and swirled until the solution was clear and free of any remaining water droplets. The dried ester product was decanted into a clean dry beaker for characterization.

Characterization of the Product:    

Weight of the ester was measured and then it was transferred into an Eppendorf tube for HNMR analysis. The ID of the unknown ester must be determined and the ID of the unknown alcohol as well. Each proton of the compound was assigned with a signal from the obtained HNMR analysis. An IR spectrum was obtained using a little amount of product and data was compared with spectra of starting acid and alcohol.

Derivatization of Carboxylic Acid using Fisher Esterification Results

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Initial weight and volume of glacial acetic acid: 5.02 mL or 5.27 g Unknown code of the alcohol used: Q13762A Initial weight and volume of the alcohol used: 4.20 mL or 3.40 g Volume of concentrated sulfuric acid used to catalyze the reaction: 1 drop Volume of deionized water used to wash/extract the reaction mixture: 20 mL Volume of 5% sodium bicarbonate solution used to extract the reaction mixture: 20 mL Approximate amount of sodium sulfate used to dry the ester product: 1 scoop Final weight and volume of the purified product: 1.075 g or 1.22 mL

IR Spectrum

1

H NMR Spectrum

Calculations Limiting Reagent 5.02 mL glacial acetic acid x (1.04 g glacial acetic acid / 1 mL glacial acetic acid) x (1 mol glacial acetic acid / 60.052 g glacial acetic acid) x (1 mol Isopentyl acetate / 1 mol glacial acetic acid) x (130.187 g Isopentyl acetate / 1 mol Isopentyl acetate) = 11.42 g Isopentyl acetate 4.20 mL Isopentanol x (0.81 g Isopentanol / 1 mL Isopentanol) x (1 mol Isopentanol / 88.15 g Isopentanol) x (1 mol Isopentyl acetate / 1 mol Isopentanol) x (130.187 g Isopentyl acetate / 1 mol Isopentyl acetate) = 5.02 g Isopentyl acetate Isopentanol is the limiting reagent. Percent Yield (1.075 g / 5.02 g) x 100% = 21.41% Discussion The 1H NMR shows a triplet with a chemical shift around 4.0 ppm that has 2 protons and the singlet at approximately 2.0 ppm has 3 protons and the last carbon of the compound. Then, there seems to be a triplet with 2 protons and a multiplet with 1 proton combined around 1.5 ppm. Lastly, the doublet around 0.9 ppm has 6 protons. Altogether, the 1H NMR has 14 protons and the only product with 14 protons is Isopentyl acetate. Since the product is Isopentyl acetate, the identity of unknown alcohol is Isopentanol. The IR spectrum for the starting material acetic

acid has an OH stretch at 3040.3 cm-1 and a carbonyl (C=O) peak at 1704.3 cm-1. The IR spectrum of starting material Isopentanol has an OH stretch at 3317.1 cm-1 and C-H stretches at 2955.3 cm-1, 2928.4 cm-1, and 2870.8 cm-1. The IR spectrum of product Isopentyl acetate has CH stretches visible just below 3000 cm-1 and a carbonyl (C=O) peak at 1739.67 cm-1. Also, the IR of isopentyl acetate does not show the OH stretch but still has the C-H and C=O peaks visible. This shows that Fischer Esterification has taken place and an ester was formed successfully. The limiting reagents calculation determined Isopentanol as the limiting reagent. Excess of acetic acid was used in this reaction rather than 1:1 molar ratio, was to drive the reaction towards the formation of desired ester product and increase the amount of product produced. The percent yield of this reaction was 21.41% which is quite low. This low yield could possibly be the result of accidently losing ester product in the aqueous layer during the extractions.

Isopentyl acetate...