1. ESTERS: SYNTHESIS AND FRAGRANCE
Experiment 21:
ESTERS:
SYNTHESIS AND FRAGRANCE

2. Objectives:
To synthesize an ester from acetic acid with isoamyl alcohol under reflux.
To purify your product through acid-base extraction and simple distillation.
To identify and analyze the purity of your compound using GC analysis.
To identify your product by analyzing the NMR and IR spectra.

3. Before coming to lab… Review these techniques: Reflux
Acid-Base Extraction
Simple distillation
Drying over MgSO4
GC Analysis

4. FISCHER ESTERIFICATION
Fischer esterification is an acid catalyzed nucleophilic acyl substitution.
Net effect is the replacement of an –OH of a carboxylic acid with the –OR of an alcohol to produce an ester.
It is an equilibrium reaction with an unfavorable Keq, thus we can improve product yield in several ways:
Use an excess of the alcohol reactant.
Use an excess of the carboxylic acid reactant.
Remove water as it forms.

5. FISCHER ESTERIFICATION
Carboxylic acids are not reactive enough to undergo nucleophilic addition directly.
By using sulfuric acid as a catalyst, the carbonyl group oxygen is protonated to give the carboxylic acid a positive charge. This makes it more reactive.

6. MECHANISM
1. Protonation of the carbonyl oxygen activates the carboxylic acid… 1
2. …toward nucleophilic attack by the alcohol… 2
3. … yielding a tetrahedral intermediate. 3
4. Transfer of a proton from one oxygen to another yields a second tetrahedral intermediate… 4 5 6
5…and converts the OH group into a good leaving group.
6. Loss of a proton and expulsion of H2O regenerates the acid catalyst and gives the ester product.

7. OVERVIEW Synthesize product ester under reflux.
Neutralize acetic acid with 10% NaHCO3.
Extract in ether, then wash with 10% NaHCO3.
Dry organic layer.
Perform simple distillation to remove ether from product.
Obtain final product mass, calculate % yield, prepare GC sample.

8. EXPERIMENTAL PROCEDURE (SYNTHESIS)
Combine acetic acid, isoamyl alcohol and sulfuric acid in a 25 mL round bottom flask.
Clamp flask to ring stand and add 3 boiling chips.
Place water cooled condenser on top of flask, with a CaSO4 drying tube in the top.
Heat to reflux. Reflux 30 minutes.
Cool to room temp.
Add 10% NaHCO3 slowly to flask.
CaSO4 tube
25mL

9. EXPERIMENTAL PROCEDURE (PURIFICATION)
Transfer liquid to separatory funnel.
Rinse reaction flask with ether and transfer to separatory funnel.
Wash the organic layer with 10% NaHCO3.
Transfer the organic layer to a clean flask.
Dry over MgSO4.
Transfer liquid to a preweighed 50 mL round bottom flask.
Clamp flask to ring stand.
125 mL
50mL
50mL

10. EXPERIMENTAL PROCEDURE (PRODUCT ISOLATION)
Set up a simple distillation apparatus, using a 25 mL round bottom as the receiving flask.
Collect all distillate that boils under 40oC.
Record distillation range, Ti-Tf.
Allow reaction flask to cool to room temperature.
Reweigh 50 mL flask to determine final product mass (actual yield) and calculate % yield.
Prepare GC sample.
50mL PRODUCT!!!
25mL WASTE SOLVENT

11. Table 21.1 Theoretical yield (g)
Calculated value based on limiting reagent!
Actual yield (g)
(50mL RB flask + product) – (Empty 50mL RB flask)
% yield
ACTUAL YIELD X 100
THEORETICAL YIELD
Product Appearance
PHYSICAL STATE, COLOR

12. GC Retention Times (min)
Table 21.2
Compound
GC Retention Times (min)
Area Percent
Adjusted
Standard
Sample
methanol
SOLVENT
isoamyl alcohol
REACTANT
isoamyl acetate
PRODUCT

13. EXPERIMENTAL PROCEDURE (IR ANALYSIS)

14. Table 21.3 Functional Group Base Values Acetic acid Isoamyl alcohol
acetate
Frequency
(cm-1)
sp3 CH
stretch
C-O stretch
OH stretch
C=O stretch

15. EXPERIMENTAL PROCEDURE (NMR ANALYSIS)

16. SAFETY CONCERNS
CAUTION:
H2SO4
is a
STRONG ACID!

17. WASTE MANAGEMENT
All aqueous washes from the extraction can be flushed down the drain with plenty of water!
Ester product and distilled ether should be placed in the bottle labeled, “ORGANIC WASTE (Esters)”.

18. CLEANING
Clean round bottom flasks and distillation glassware with wash acetone only!
Separatory funnel and all other glassware should be cleaned with soap, water, and a brush if necessary, followed by a wash acetone.
DO NOT return any glassware to lab drawer dirty or wet!

19. LABORATORY NOTEBOOK (Pre-lab)
OBJECTIVE (Must clearly state…)
What compounds will be made and how
How the compounds will be purified
How the purity of the product will be determined
CHEMICAL EQUATION
Include the chemical equation from the top of page 177.
TABLE OF PHYSICAL DATA (Complete the following table using a site listed on WWW Links ONLY. Wikipedia is unacceptable!)
REFERENCE TO PROCEDURE (Must include…)
full title including edition and author names
page numbers where actual procedure can be found
Compound
MW (g/mol)
bp(oC)
d (g/mL)
HAZARDS
Isoamyl alcohol
Isoamyl acetate
Acetic acid
Sulfuric acid
Diethyl ether
methanol

20. LABORATORY NOTEBOOK (In-lab)
DATA/CALCULATIONS
Initial volumes of isoamyl alcohol and acetic acid used
Distillation range
Weight of 50 mL round bottom flask
Weight of 50 mL round bottom flask + product
Final product weight
Physical state and color of product
GC vial slot #
Theoretical yield calculation (not just value!)
% yield calculation (not just value!)
Example of an adjusted area % calculation (not just value!)
EXPERIMENTAL PROCEDURE
In paragraph form, BRIEFLY describe the procedure that you actually followed during the lab.
Paragraph must be written in PAST TENSE, PASSIVE VOICE.
Include any volumes or weights of chemicals used during the experiment.
Include any mistakes, accidents or observations if applicable.