How Do We Make Artificial Flavorings?
Introduction:
Organic chemistry is the study of compounds that are primarily composed of carbon atoms. The most basic
organic compound is a hydrocarbon, a compound of only hydrogen and carbon, and a common hydrocarbon
known as butane is shown below:
We can replace some of the hydrogen molecules with different molecules, known as functional groups, in
order to impact the overall reactivity of the compound. Esters are a class of organic compound functional
groups. An ester comprises an organic or inorganic acid in which one more hydroxy (OH) groups have been
replaced with alkoxy groups (O bound to carbon chain). A very simple ester molecule is shown below:
An ester
group
For example, the simplest ester, methyl formate (CHO – OCH3), is made up of formic acid (CHO – OH) in
which the hydroxy group has been replaced with a methoxy group (-OCH3). Similarly, ethyl acetate (CH3COOCH2CH3) is made up of acetic acid (CH3COOH) in which the hydroxy group has been replaced by an ethoxy
group (-OCH2CH3). This is the molecule that was pictured above.
Although esters can be produced by many mechanisms, the most commonly used method is a reaction known as
esterification, which is a condensation reaction between an alcohol and an acid, typically in the presence of a
strong acid catalyst, such as sulfuric acid. The most common way in which these reactions are ran is by using a
strong acid to catalyze the conversion from the original molecule to the new ester. Esters were traditionally
named by combining the name of the alcohol with the root name of the acid and adding “ate” as a suffix.
The flavoring industry is a multi-billion dollar industry that is responsible for millions of generated flavors that
allow us to artificially flavor our foods. Esters typically have strong, often pleasant, scents and tastes; so many
esters are used as flavoring and perfume agents, either individually or in combination. Some of the earliest
artificial flavors were discovered by chemists making common ester containing compounds. For example, the
scent and taste of strawberries is due to the presence of (among others) methyl cinnamate, ethyl formate, ethyl
butytate, ethyl carbonate, isobutyl acetate, and benzyl acetate.
In this lab session, we’ll synthesize methyl salicylate, whose common name is oil of wintergreen. The
wintergreen smell is constantly utilized in gums and other foods in order to substitute for the more expensive
wintergreen plant. We’ll synthesize methyl salicylaete by reacting methanol with aspirin, which is much easier
to come by than other organic compounds. The general reaction can be seen below:
The lab procedures that are utilized in organic chemistry are slightly more complex than the ones that we have
used in general chemistry. In particular, we often need to separate two or more mixtures by utilizing a
separatory funnel. If we have two solutions that are immiscible (unable to be mixed), then we can separate
these compounds based on their density. For example if I have a solution of oil and water, I can pour them into
the separatory funnel and they will separate from one another with the less dense oil rising to the top as shown
below:
We can then drain out the water and stop once we reach the water/oil line. By doing this basic procedure, we are
able to purify a mixture that was otherwise inseparable.
Pre-Lab
1. What are esters? Using the Internet, research into the basics of an esterification reaction and general
characterizations of this reaction. Include a general drawing of how the molecule is converted into an ester.
2. What are five common esters that are utilized in the flavoring industry? What are some common products
that we can find these flavorings in?
3. What is a separatory funnel? How is it used?
4. What is a reflux? How is it used in organic chemistry?
5. I have a solution with two immiscible substances. One solution has a density of 0.502 g/mL and one slightly
brown solution has a density of 1.234 g/mL. Design a procedure to separate these two solutions.
6. Calculate the theoretical yield (the number of grams of methyl salicylate that you expect to form) for the
reaction. You are starting with 13.0 g of aspirin. The molar mass of aspirin is 180.160 g/mol and the molar mass
of methyl salicylate is 152.1494 g/mol.
7. Using the theoretical yield in question 6, calculate the number of mL of product that you should form. The
density of methyl salicylate is 1.1825 g/mL.
Materials Available:
Materials
Balance
Test Tube
Beaker, 50 mL
Beaker, 250 mL
Beaker, 600 mL
Separatory Funnel
Erlenmeyer Flask, 250 mL
Graduated Cylinder, 10 mL
Graduated Cylinder, 100 mL
Pipet, 10.0 mL
Ring Stand
Thermometer
Aspirin
Methaonl
Sulfuric Acid, concentrated
Saturated sodium bicarbonate solution (3.9 g/50 mL)
Quantity
1
3
1
1
1
1
1
1
1
3
1
1
13.0 g
100 mL
10 mL
50 mL
Procedure:
Pre – Work: Formulating a Plan
1. Formulate a hypothesis about the amount of product that you expect to theoretically form (may use the prelab as reference.
Our Hypothesis: _____________________________________________
___________________________________________________________.
2. Read the procedure given below and note areas of confusion and at least 4 possible changes that you can
make in order to ensure that the procedure will lead to better results. Explain why each of the changes will lead
to better overall results.
Part I: Synthesize Methyl Salicylate
1. Mass and crush 13.0 g of aspirin into a fine powder
2. Transfer about 60 mL of methanol to the 125 mL Erlenmeyer flask. Add 13.00 g of aspirin to the flask and swirl or stir the
contents until the aspirin dissolves.
3. Add about 10.0 mL of concentrated sulfuric acid to the reaction vessel and swirl to mix the solutions.
4. Clamp the flask to the ring stand and partially immerse it in a hot water bath at about 60 oC.
5. Allow the reaction to proceed, stirring the reaction mixture occasionally for 60 minutes. As the methyl salicylate forms,
you’ll notice its distinct wintergreen odor. Keep the reaction at about 60 oC, adding water to the bath if necessary to keeps its
level up. The level of liquid in the reaction vessel will decrease as methanol evaporates from the flask. Add more methanol as
needed to keep the liquid in the reaction vessel near its original volume.
6. After 60 minutes, stop adding methanol to the flask. Increase heat slightly to bring the liquid in the reaction flask to a gentle
boil. Boil the solution long enough to vaporize most of its remaining methanol.
7. When enough methanol has boiled off to reduce the volume of liquid in the reaction vessel to about half its original volume,
remove the flask from the water bath and set it aside to cool.
Part II: Isolate and Purify the Product
The brown liquid in the reaction vessel is a complex solution that contains methanol, crude methyl salicylate, sulfuric acid,
unreacted aspirin, and other impurities. Methyl salicylate is freely soluble in methanol, but only slightly soluble in water. We’ll
take advantage of that differential solubility to extract most of the water-soluble impurities from the crude product.
1. Pour contents of the reaction flask into the separatory funnel
2. HAVE YOUR TEACHER HELP WITH THE NEXT 2 STEPS! Add about 50 mL of ice-cold tap water to the reaction
flask into the sep funnel, cap the funnel, and agitate the contents vigorously for 30 seconds.
3. Allow the contents of the sep funnel to separate into two layers. The aqueous layer contains nearly all of the sulfuric acid and
most of any other water-soluble impurities. Separate the two layers and transfer the aqueous layer to the 250 mL beaker.
4. Repeats steps 2 and 3 with two more washings.
5. Add about 50 mL of sodium bicarbonate solution to the sep funnel, cap the funnel, agitate the contents with continuous
venting for 30 seconds.
6. Allow the contents of the sep funnel to separate into two layers. The aqueous layer contains an excess of sodium bicarbonate
and a small amount of sodium sulfate produced by the neutralization of any sulfuric acid that remained in the organic layer.
Separate the two layers, and transfer the aqueous layer to the 250 mL beaker.
7. Neutralize the sulfuric acid solution in the 250 mL beaker with sodium bicarbonate and flush the neutralize solution down the
drain with plenty of water. Retain the organic layer in the sep funnel, which contains crude methyl salicylate.
Part III: Determine Density and Freezing Point of the Product
Our product is a few mL of semi-pure methyl salicylate. If we had the equipment needed for microscale distillations, we could
further purify our raw product by distillation. We don’t have that equipment, so we’ll test our product as is to determine its
density and freezing point.
We know the density of pure methyl salicylate is 1.1825 g/mL, so the density of our product will give us some idea of its purity.
That’s not sufficient however. Even if the density of our product is very close to 1.1825 g/mL, for all we know our product
might be a small amount of methyl salicylate mixed with a large amount of some impurity that has the same density. The
freezing point of our product will give us a better idea of its purity. Pure methyl salicylate freezes (or melts) at -8.3 oC.
Furthermore, the sharpness of the freezing point gives a good indication of a products purity. Pure substances tend to
freeze/melt very sharply, at one particular temperature. Impure substances freeze/melt more gradually over a range of a few
degrees.
1. Weigh a clean, dry, empty 50 mL beaker and record its mass to 0.01 g in your data table.
2. Draw up as much as possible of your product into the 10.0 mL pipette. Record the volume of product in your date table.
3. Transfer the measured product to the 50 mL beaker that you previously weighted. Reweigh the beaker and record the
combined mass of the beaker and methyl salicylate in your data table.
4. Calculate the mass of the methyl salicylate by doing a mass by difference calculations:
Mass of Methyl Salicylate = Mass of Beaker and Solution – Mass of Empty Beaker
5. Calculate the density by using the following equation. Place the result in your data table.
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑀𝑒𝑡ℎ𝑦𝑙 𝑆𝑎𝑙𝑖𝑐𝑦𝑙𝑎𝑡𝑒
𝐷𝑒𝑛𝑠𝑖𝑡𝑦 =
𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑀𝑒𝑡ℎ𝑦𝑙 𝑆𝑎𝑙𝑖𝑐𝑦𝑙𝑎𝑡𝑒
6. Transfer as much as possible of the sample to a clean test tube. Immerse the test tube in an ice bath and use a thermometer
(carefully) to stir the contents for the solution.
7. When the temperature of the sample falls to 0 oC, check the contents of the tube frequently to see whether solid crystals of
methyl salicylate have begun to form. If the solution does not freeze, then you may add salt to the ice bath in order to help drop
the temperature further. Record the temperature at the first sign of crystal formation. Record the temperature in your data table.
8. Continue cooling the contents of the test tube until the last portion of the solution freezes. Record the temperature where the
mixture stops freezing.
9. Remove the test tube from the ice bath and allow it to begin warming. Record the temperature at which the frozen sample
begins to liquefy.
10. Allow the test tube to continue warming. Stir gently and record the temperature at which all of the sample becomes a liquid
again.
Data Tables:
Discussion:
1. Does your data indicate that the initial hypothesis should be accepted or rejected? Cite specific data to support your
acceptance or rejection!
2. What were the inherent structural errors that were introduced as a result of your experimental design? How did these impact
your final data? How can this be fixed in order to improve your results should you repeat the lab?
3. What next steps could you take in order to further investigate this topic? Cite specific areas that you believe you could study
and how your data allows you to better study these areas.
4. How do your actual and theoretical yields compare? If the aspirin was older that expected and have some impurities, how do
you think the actual yield would have been impacted?