Lab #12 Isopentyl Acetate

Abstract

A 36.4% yield of isopentyl acetate was obtained via an acid catalyzed nucleophilic acyl substitution with 5 milliliters of isopentyl alcohol and 7 milliliters of acetic acid in the presence

of an acid catalyst. The solution was heated under reflux conditions and then transferred to a separatory funnel where three extractions were performed. The purified product was collected by simple distillation and a boiling point of 137°C was observed; an infrared spectrum analysis was also performed showing the expected absorptions but also indicated a slightly hydrated product.

Purpose

The purpose of this lab was to introduce students to heating under reflux and the reaction of acid catalyzed nucleophilic acyl substitution by synthesizing a sample of isopentyl acetate. Techniques such as extraction, use of a drying agent, separatory funnel use, simple distillation, and infrared analysis were revisited.

Isopentyl Acetate is more commonly known by the fragrance of banana oil. Many simple esters are pleasant smelling and are often used in food and beverage flavorings. More commonly referred to as essential oils these compounds are volatile and give off a strong scent. Unfortunately simple ester fragrances are easily hydrolyzed and thus unstable in the presence of aqueous or acidic solutions. 1

Reaction

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Mechanism

Competing Side Reaction

The competing side reaction for this experiment is the reverse reaction or hydrolysis of isopentyl acetate by the addition of water.

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Separation Scheme

5mL Isopentyl Alcohol

7mL Acetic Acid

Heat (reflux 1 hour)

Reaction mixture

10mL H2O

Aqueous Layer(discard)

Organic Layer

5mL 5% aq sodium bicarbonate

Aqueous Layer (discard)

Organic Layer +

Purified product

distill Distillate (discard)

Crude Product

H2O (discard)

Saturated MgSO4

Organic Layer

Anhydrous MgSO4

Aqueous Layer(discard)

5mL saturated NaCl

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Procedure

The procedure was conducted in accordance with experimental procedure 12 in the textbook, except that the drying tube packed with calcium chloride to be placed on top of the condenser was omitted. Anhydrous magnesium sulfate was used as a drying agent instead of anhydrous sodium sulfate .1

Physical Constants 1,2

Compound Molecular Formula MolecularWeight (g)

Density(g/ml) BoilingPoint (°C)

Isopentyl Alcohol

C5H12O 88.1 .81 131-132

Isopentyl Acetate

C7H14O2 130.2 .88 142

Glacial Acetic acid

C2H4O2 60.1 1.06 118

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Calculations

A. Limiting Reagent5 mL Isopentyl alcohol C5H12O .81 g C5H12O 1 mole C5H12O 1 mole C 7H14O2

1mL C5H12O 88.1 g C5H12O 1 mole C5H12O = .046 moles C5H12O

Isopentyl alcohol is the Limiting Reagent

B. Excess Reagent

7 mL Glacial Acetic Acid 1.06 g C 2H4O2 1 mole C 2H4O2 1 mole C 7H14O2 1mL C2H4O2 60.1 g C2H4O2 1 mole C2H4O2

= .123 moles C2H4O2 (Excess Reagent)

C. Theoretical Yield (Limiting moles)(Ratio)(Molecular Weight of Product)

(.046 moles C5H12O)(1:1)(130.2 g/mol C7H14O2)

= 5.99 grams C7H14O2

Actual Yield and Percent Yield

Crude Product Mass = 2.18 grams Percent Yield = (Actual/Theoretical) 100%

(2.18/5.99)100 = 36.4 % yield

D. Analytical Data

The lower percent yield of 36.4% was most likely due to the loss of product from the system during extractions, container transfers, and evaporation. The boiling point observed (137°C) is approaching that of pure isopentyl acetate literature value of 142°C which indicates with a few impurities present. The IR spectra analysis had the corresponding peaks (see printout for analysis), but also indicated a small amount of alcohol apparent due to the broad absorption at 3600-3400 cm-1. (Note* The Hydrogen NMR and Carbon NMR attached were given as a handout and not performed in the lab). 2

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Spectra 3

The above IR spectra indicates a small amount of alcohol present due to the medium broad absorption at 3600-3400 cm-1 but could also be the C=O overtones as well. The carboxyl group shows a strong absorption at 1740 cm-1 while the C-O shows as two bands from 1300-1000 cm-1. The aliphatic C-H bonding is seen as a strong absorption just below 3000 cm-1.

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O-H

C-HAliphatic

C=O C-OC-O

The above spectras are the expected NMR results for that of pure isopentyl acetate. The H NMR spectroscopy shows a doublet with an integration of six representing that of the terminal methyl groups which are equivalent being split by a single hydrogen. Subsequently that hydrogen shows up as a septet with an integration of one. The hydrogens of the alpha carbon show up close to 4 ppm due to the high deshielding of the ester group. In the C NMR we see the carbonyl carbon the furthest down field do the electronegative oxygen of the ester. The shifts of the subsequent carbons are shifted upfield in relation to their distance from the ester.

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Citations

1) D.L. Pavia, G. M. Lampman, G. S. Kriz, and R. G. Engel “Introduction to Organic Laboratory

Techniques: A Small Scale Approach, 3rd Ed.”, (2011) Brooks/Cole, pp.84-91

2) "Isopentyl Acetate." ChemicalBook---Chemical Search Engine. Chemical Book, n.d. Web. 24

Oct. 2012. <http://www.chemicalbook.com/ChemicalProductProperty_

EN_CB3158874.htm

3) D.L. Pavia, G. M. Lampman, G. S. Kriz, and R. G. Engel “Introduction to Organic Laboratory

Techniques: A Small Scale Approach, 3rd Ed.”, (2011) Brooks/Cole, pp.861-959

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Questions

1. Removal of water as it is formed will also direct the reaction to form the product of the ester.

2. Sodium bicarbonate acts to neutralize the acid in the crude product.

3. The acetic acid reacts with the sodium bicarbonate to produce a salt, water, and CO2 which is a gas.

4. The limiting reagent was determined to be the Isopentyl alcohol, while the limiting reagent was acetic acid. The molar excess of acetic acid was about 2.6 times greater than Isopentyl alcohol.

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8. Because upon freezing it forms crystals that look like needles, due the lack of water.

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