Download ESTERIFICATION Ester Formation Important Vocabulary (review) O

ESTERIFICATION
Ester Formation
Important Vocabulary (review)
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Ester – generally an organic molecule containing the functional group R1-C-O-R2
Alcohol – generally an organic molecule containing the functional group R-O-H
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Carboxylic acid – generally an organic molecule containing the functional group //
R - C – O-H
Theory
Reactions between molecular species can be rather slow (especially when compared to the rates of
reaction, between ionic species). This lab may help show us this.
We know from our work on organic chemistry, that esters are organic molecules of the general form
where R1 and R2 are any carbon chain. Esters are unique in that many of them have strong, pleasant odors. As
such, they are often used in fragrances, and many artificial flavorings are in fact esters.
Esters are produced by the reaction between alcohols and carboxylic acids. For example, reacting ethanol with
acetic acid to give ethyl acetate is shown below.
+

+
In the case of ethyl acetate, R1 is a CH3 group and R2 is a CH2CH3 group, as you can see, by a careful analysis
of the diagrams.
The –OH group of the alcohol and the terminal “H” atom of the carboxylic acid group, break away from their
parent molecules and produce water. The unstable resulting species made from this “breakaway” group of
atoms, bond to each other, creating the ester. This is a classic example of a dehydration synthesis (the
formation of a larger species from two smaller species, due to the destabilizing loss of water)
Naming esters systematically requires naming the functional groups on both sides of the bridging oxygen. In
the example above, the right side of the ester as shown is a CH3CH2 group, or ethyl group. The left side is
CH3C=O, or acetate. The name of the ester is therefore ethyl acetate. Deriving the names of the side from the
carboxylic acid merely requires replacing the suffix –ic
Materials
1-Pentanol (n-amyl alcohol)
Ethanol (ethyl alcohol)
Methanol (methyl alcohol)
Butanol (butyl alcohol)
Glacial acetic acid
Methanoic acid (Formic acid)
Salicylic acid
Butanoic acid (Butyric acid)
18 M Sulfuric acid
5% by mass Sodium bicarbonate solution
Caution: Concentrated sulfuric acid is highly corrosive and should be stored in the hood. Glacial
acetic acid and formic acid are also corrosive.
Pentanol, ethanol, methanol, butanol, and glacial acetic acid are flammable.
And, let’s be clear here … NONE OF THEM ARE SAFE TO INGEST …as they are each toxic.
Methanol is particularly dangerous as it has such weak intermolecular forces, between its molecules, that it
easily and rapidly evaporates, mixing with the air. This makes for a hazardous fire ready to happen.
Great care should be used when handling these materials. Goggles, gloves, and aprons/lab coats should
be worn at all times.
Butanoic acid is um, how might one write this - Disgusting. It is the essence of vomit, old gym socks, a
primary odiferous component of catabolized perspiration, and the smell of rancid butter Need I urge you to
work under the hood… and not let it sit around unreacted at your lab station, even in a test tube?????
Procedure
1. Create a hot water bath using about 150 mL of tap water, in a 250 mL beaker. Use a hot plate as a heat
source … DO NOT use the burners. There are to be no open flames during this lab.
2. Using a graduated cylinder, add 2 mL alcohol and 2 mL carboxylic acid (or 2 scoops when the
carboxylic acid is the solid, salicylic acid), to a test tube. Get all of the mixtures together in separate test
tubes. Be sure you know what each test tube contains.
3. Call me over, and I will carefully add 6-8 drops of concentrated sulfuric acid
4. Put the test tubes in a hot water bath (50-60°C) for 5-10 minutes. The hot water bath should have
sufficient water, so that the level of hot water, is greater than the level of the materials in the test tube.
5. Try to identify the smell of the resulting product, using the absorbent/wafting technique taught to you.
If the smell of the sulfuric acid were too strong (giving it a “sour-smelling” odor), the excess acid can be
neutralized with a few drops of 5% NaHCO3.
Alcohol
Carboxylic
Acid
1-pentanol (n-amyl
Ester 1
acetic acid
alcohol)
Ester 2
ethanol (ethyl alcohol)
formic acid
Ester 3
methanol (methyl alcohol)
salicylic acid
Ester 4
ethanol (ethyl alcohol)
butyric acid
Ester 5
Ester 6
Ester 7
butanol (butyl alcohol)
not available in 1415
1-pentanol (n-amyl
alcohol)
methanol (methyl alcohol)
acetic acid
butyric acid
butyric acid
Ester name
Scent