Kemian opetuksen keskeiset alueet II, spring 2012
Christian Franklin and Joonas Hippeläinen
11 April 2012
Lesson plan for teaching the Fischer–Speier
esterification using the historical approach
Contents
1
Time requirements 2
2
Teaching purpose 2
3
Epistemological issues 2
4
Lessons 3
4.1
Lesson 1 3
4.1.1 Part 1: Theory and history (35 minutes) 3
4.1.2 Part 2: Designing the practical experiments (30–40 minutes) 9
4.2
Lesson 2 9
4.2.1 Part 1: Quick review of the first lesson (5 minutes) 9
4.2.2 Part 2: Explaining the practical part, special focus on safety (5 minutes) 9
4.2.3 Part 3: Practical experiments (55 minutes) 10
4.2.4 Part 4: Review (10 minutes) 11
5
References 12
6
Links 13
A
Appendices 14
A.1
Appendix 1: Experiment instructions
A.2
Appendix 2: Product information given to students to design their synthesis
14
31
1
1
Time requirements
This plan is for two 75-minute lessons. The first lesson will probably not take a total of 75
minutes. Instead, 5 to 10 minutes at the beginning can be used to check the homework from
the previous lesson. The timing of the practical could be varied according to need by excluding
some of the design phases and experiments.
2
Teaching purpose
•
To teach an important reaction of organic chemistry synthesis within a historical context.
•
To show how science is a cumulative group endeavour.
•
To review the esterification mechanism, and provide the students with an opportunity to
try out several esterifications.
3
Epistemological issues
•
Scientific knowledge development as a process.
•
Science within a community of researchers.
•
Scientific approach in organic synthesis.
2
4
Lessons
4.1
Lesson 1
4.1.1 Part 1: Theory and history (35 minutes)
Introduction
•
Ask students to discuss what they know about esters. List the points. This helps the
students link the lesson to their previous knowledge.
•
Ask students to describe how they think science develops to make their preconceptions
clear.
•
History section: organic synthesis as a developmental process. Show Prezi (section 6)
which sketches development. Point out the links and influences. Then go through individual scientists and their work.
•
Fischer’s life story to link history to esterification (using Prezi).
•
Theory about esters: properties and esterification + mechanism (using Prezi).
Organic chemistry and synthesis history
The term ‘organic chemistry’ was first used by Berzelius in 1806. In its early days organic
chemistry was concerned with the isolation and purification of organic products, notably that
of ethanol distilled in Europe as early as the 12th century. Berzelius mentored Friedrich Wöhler
(Wikipedia, 2001a), who through an act of serendipity in 1828 synthesised urea while attempting to prepare ammonium cyanate from silver cyanate and ammonium chloride. Famously,
this is often given as the experiment that heralded the death of vitalism in chemistry, even
though Wöhler himself made no such claim. In any case, the cat was now out of the box and it
was apparent that organic compounds could be synthesised, from inorganic sources if need be.
(Hudson, 1992, pp. 104–105)
In 1860 Berthelot first used the word ‘synthesis’ and wrote a book on synthetic organic chemistry, which collected the means by which many compounds could be generated from their
elements. The field of organic synthesis grew, and in 1877 the Friedel–Crafts reaction was discovered whereby, in the presence of an aluminium chlorine catalyst, acyl or alkyl groups could
be added onto a benzene ring. (Hudson, 1992, p. 143)
Wöhler worked with Justus von Liebig, who was also involved in studying organic chemistry
(Wikipedia, 2001a) and developed the law of the minimum, an idea similar in principle to that
of limiting reagents. He also discovered nitrogen’s role as a fertiliser. The vapour condensation
device he popularised for his research is still known as a Liebig condenser (Wikipedia, 2001b).
3
In turn von Liebig had a major influence via his lectures on two other organic chemists, Emil
Erlenmeyer and August Kekulé. Erlenmeyer worked with alcohols and ketones as well as the
hydrolysis of ether to alcohol (Wikipedia, 2004a). Kekulé found out that tetravalent carbons
could link together. His most famous work was on the structure of benzene. In 1865 Kekulé
published a paper suggesting that the structure contained a six-membered ring of carbon atoms
with alternating single and double bonds (Wikipedia, 2002a). Robert Bunsen, the developer of
the Bunsen burner, was also influenced by von Liebig (Wikipedia, 2001c) and shared a doctoral
student with Kekulé called Baeyer who was involved in the synthesis of plant dyes. Baeyer in
turn had an assistant and doctoral student called Emil Fischer (Wikipedia, 2004b).
Emil Fischer was influential in organic synthesis during this period. In addition to working
on purines and proteins, he synthesised glucose from glycerol in 1890, producing a synthesis that involved isomerism. Fischer also worked on synthesis reactions to extend the carbon
chains of sugars (Hudson, 1992, p. 153) as well as the synthesis of caffeine (Wikipedia, 2004c).
Hermann Emil Fischer (1852–1919)
Fischer was always academically gifted, although his destiny was not always apparent to his
parents who tried to get him to join the family timber firm, calling him stupid when he failed
in the business. Fischer initially studied physics at the University of Bonn and was awarded his
doctorate from the University of Strasbourg, in time becoming a professor of chemistry. For his
work in organic chemistry Emil Fischer was awarded the Nobel Prize in chemistry. (Hudson,
1992, p. 153) Fischer was active during World War I and organised chemical production for the
Germans. Sadly he lost two of his sons in the war and was struck by depression, and unfortunately he also contracted cancer, possibly from the toxic effects of chemicals used during his
work. He ended up committing suicide. (McMurry, 2007, p. 795)
Emil Fischer and Arthur Speier first wrote about a new type of esterification reaction in 1895.
This was later named after them as the Fischer–Speier esterification. Their first esterifications
were carried out with methanol and ethanol in the presence of sulphuric acid or hydrochloric
acid. (Fischer and Speier, 1895) Fischer also developed a method for modelling carbohydrate
stereochemistry, which represented multiple chirality centers by projecting them onto a flat
surface. This process allowed for clearer identification of sugars, and carbohydrates modelled
in this fashion are called Fischer projections. (McMurry, 2007, pp. 975–978) Some Fischer
projections can be seen in Figure 4.1.
4
Figure 4.1: Fischer projections of D-glucose. A is the conventional Fischer projection, B is a
‘line structure’ variation without hydrogens and carbons, and C is the ‘zigzag’ style. (UC Davis
University of California)
Organic synthesis is concerned with the construction of organic compounds via organic reactions. Robert Burns Woodward is regarded as the father of modern organic synthesis. He received the 1965 Nobel Prize for Chemistry for a number of total syntheses. His 1954 synthesis
of strychnine (Figure 4.2), for example, had 29 steps in it. (Wikipedia, 2003b)
Figure 4.2: Woodward’s 1954 synthesis of strychnine. (Synarchive)
5
Woodward was an excellent student and went to Massachusetts Institute of Technology (MIT)
when he was sixteen years old. He did his PhD when he was twenty and spent the rest of his
academic life at Harvard, where he realised the power of spectroscopy. He solved many different structures using UV-absorption spectra. These included alpha and beta unsaturated ketones
as well as the structures of penicillin and strychnine. He also completed syntheses of quinine,
cholesterol, chlorophyll and vitamin B12 , and developed many new reactions and techniques
that are still used today. Impressively, his synthesis of vitamin B12 (C63 H90 CoN14 O14 P) was
carried out in partnership by teams in Harvard and Zürich, needing 100 chemists and taking 11
years. (Hudson, 1992. p. 156)
The design aspect is an important part of organic synthesis. When designing a synthesis, one
has to consider issues such as the price of the chemicals, toxicity of the chemicals and processes, amount of waste, time, equipment and yield. Later on strychnine was synthesised in
only 11 steps. The modern way to do synthesis design is through retrosynthetic analysis, for
which Elias James Corey won the Nobel Prize in Chemistry in 1990. The idea of retrosynthetic
analysis is to start the planning going backwards from the product to the reagents. (Wikipedia,
2005)
Esters: properties, esterification, mechanism
Esters are chemical compounds that are usually organic and most commonly formed by condensing an acid with an alcohol. The functional group of an ester is R-COO-R. Esters are
found everywhere. Most naturally occurring fats and oils are butyric acid esters of glycerol. Esters with a low molecular weight are commonly used as fragrances and found in fruits, essential
oils and pheromones. (Wikipedia, 2001d) Aspirin, or acetylsalicylic acid, is an example of a
generally known ester. It was first made in 1853. Aspirin is not the most typical ester, however,
since it is made starting from an acid and an acid anhydride. Another commonly used ester is
ethyl acetate, which is found in glues, nail polish removers and cigarettes.
Figure 4.3: Aspirin synthesis. (California State University, Stanislaus)
6
The Fischer–Speier esterification is an organic reaction. It is carried out by refluxing an alcohol and a carboxylic acid in the presence of an acid catalyst. The alcohol used in this reaction
can be primary or secondary, as usually tertiary alcohols are prone to elimination and phenols
are too unreactive. Typical reaction times vary from 1 to 10 hours at temperatures of 60–110
◦ C.
(Wikipedia, 2004d) Some of the commonly used acid catalysts are sulphuric acid and hy-
drochloric acid (McMurry, 2007, p. 796).
A nucleophile is a species that donates an electron pair to an electrophile to form a chemical
bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles.
(Wikipedia, 2002b) An electrophile (literally ‘electron-lover’, which can be used as a way
to memorise which way these work) is a reagent attracted to electrons that participates in a
chemical reaction by accepting an electron pair in order to bond to a nucleophile. (Wikipedia,
2004e)
The reaction is a nucleophilic acyl substitution, which is based on the electrophilicity of the
carbonyl carbon and the nucleophilicity of the alcohol. Direct acylations of alcohols with carboxylic acids are preferred over acylations with anhydrides and acid chlorides, which have poor
atom economy and are moisture sensitive respectively. (Wikipedia, 2004d)
In general carboxylic acids will not undergo the nucleophilic addition found in the first part of
the reaction due to low reactivity. In the presence of a strong acid, however, the reactivity is
increased. The reaction mechanism (Figure 4.4) begins when the acid catalyst protonates the
carbonyl group’s oxygen, which increases the electrophility of the carbonyl carbon. There are
three resonance structures at this point. (McMurry, 2007, pp. 795–796) The resonance structures are a way of describing delocalised electrons, which are not associated with a single atom
or one covalent bond (Wikipedia, 2003a). The middle one is the closest to ‘real life’ because the
positive charge is on the carbon atom. The carbonyl carbon is then attacked by the nucleophilic
oxygen atom of the alcohol. Next, another proton transfers from the oxonium ion to the alcohol,
giving an activated complex. The hydroxyl of the activated complex is then protonated, which
leads to a second oxonium ion. This oxonium ion is then eliminated as water and, lastly, after a
deprotonation, the acid catalyst is regenerated and the ester product is ready. (McMurry, 2007,
pp. 795–796)
7
Figure 4.4: Reaction mechanism of the Fischer–Speier esterification.
8
4.1.2 Part 2: Designing the practical experiments (30–40 minutes)
First, students should be divided into groups of three and told they will be designing the ester
synthesis in groups.
•
Give the groups the chemical formula of the first ester product: methyl salicylate.
•
They need to work out what reagents are required to produce the ester.
•
They need to draw the structures of the product (first one is already drawn) and the
reagents that are required and name them.
•
Once they think they have the answer ready, they should show it to you to confirm
whether it is correct or not. If it is not, give them additional instructions about what
went wrong. They should then try to correct it.
•
Once they have the correct answer, give them the next ester product information sheet
(Appendix A.2) for them to design that one too. All groups can make as many designs as
they have time for, ideally all seven.
4.2
Lesson 2
4.2.1 Part 1: Quick review of the first lesson (5 minutes)
History, theory, designing the experiments.
4.2.2 Part 2: Explaining the practical part, special focus on safety (5 minutes)
•
Explain how the experiments work and what the students need to do.
•
Clarify safety issues: Lab coats, goggles and rubber gloves are to be used at all times.
Everything must be done in the fume hoods, except when the students try to establish
the ester fragrances at the end. Extreme caution is needed when handling concentrated
sulphuric acid, and some of the other chemicals are dangerous too. Some (butyric acid,
acetic acid) will also smell very bad and must never be handled outside of a fume hood.
Additionally, point out that methanol is also dangerous and must not be inhaled.
•
Give the general instructions (first two pages of Appendix A.1) and tell the students that
they should read through them.
•
Tell the students to put on their safety gear.
9
4.2.3 Part 3: Practical experiments (55 minutes)
•
Divide the students into their previous groups of three.
•
Give the groups the first synthesis instructions (pages 3 and 4 of Appendix A.1)
•
Tell the groups to put around 4 cm water in a beaker and heat it until it boils.
•
During the first three-minute heating period, encourage them to study the reaction mechanism, which is found on the back of the instructions.
•
Once the heating is completed and distilled water added, tell the students to try and
identify the fragrance of the ester. The first one is oil of wintergreen, which will be
difficult to specifically identify.
•
After all the groups have finished the first esterification, give them brief practical information about oil of wintergreen.
Oil of wintergreen is naturally produced by many species of plants. Some of the plants which
produce it are called wintergreens (Figure 4.5), hence the common name. Methyl salicylate
may also be used by plants as a pheromone to warn other plants of pathogens as in the case
of the tobacco mosaic virus. It is also used as a mint flavour in some kinds of chewing gum
and candy as an alternative to the more common peppermint and spearmint oils as well as a
flavouring in root beer. (Wikipedia, 2004f)
Figure 4.5: Wintergreen plants (Gaultheria procumbens). (Wikipedia, 2004f)
It is probably worth mentioning to the students that the rest of the fragrances are easier to
recognise.
10
•
After the groups have done their first experiment, give the instructions (found in Appendix A.1) for one of the other esters they designed and tell them to synthesise it.
•
During the heating periods, instruct them to practise the reaction mechanism by filling
out incomplete reaction mechanisms found on the back of the instruction sheet.
•
Once they have heated the mixture for 3 minutes and added water, they will have the
product ready.
•
All the ester products apart from the first one have distinct identifiable fragrances, which
the students should be able to identify by smelling them, and their goal is to do so.
•
Groups should do as many esterifications as they can within the time reserved for the
experimental part.
•
At the end students should dispose of the waste safely and clean the lab equipment they
used. Some of the esters formed in the experiments are waxy and difficult to clean. It is
a good idea to use plastic test tubes and throw them away afterwards. If plastic test tubes
are used, take extra care when heating them in the water bath. If these test tubes come
into contact with the floor of the beaker they might melt. This problem can be solved by
balancing the test tubes in the water bath using, for example, wooden test tube holders.
•
In the end each group should have synthesised 2–7 products. If some groups have not
had time to do all of them, those groups can try to identify the fragrances of the products
other groups have made. This way all the groups would get to sample a fragrance of all
the different products that were made during the lesson and can express their opinions.
•
Lead a discussion to see what fragrances they came up with and discuss the correct answers. Relate this back to the product names, structures and starting chemicals (Appendix
A.1: Table A.1).
4.2.4 Part 4: Review (10 minutes)
•
Discuss the students’ previous knowledge and have them think about what they have
learned. Refer to the list about esters that the students made at the start of the first lesson.
Students can review their knowledge and think about their learning gains.
•
Go through the mechanism again. Finish by asking the students about the esterification
reaction in the context of Fischer and the scientific community. This could be parallelled
with their own experience in the lab working as a team. After the students have reflected
upon their experiences, they should fill in the questionnaire.
11
5
References
Athabasca University. Fischer Esterification: An ester from a carboxylic acid and an alcohol.
http://science.pc.athabascau.ca/chem360.nsf/f8ba9a4e31825f6f87256b6700619e85/
$FILE/360Exp10-02.doc, accessed 13.2.2012.
California State University, Stanislaus. The Synthesis and Characterization of Aspirin.
http://science.csustan.edu/stone/2090/The%20Synthesis%20and%
20Characterization%20of%20Aspirin.htm, accessed 13.2.2012.
Hudson, J. The history of chemistry, 1st edition, Macmillan, England, 1992, pp. 104, 105, 143,
153, and 156.
Johnson, K. Synthesis of Fragrant Esters. http://faculty.eicc.edu/kjohnson/labbook/
physicalscience/esters.pdf, accessed 13.2.2012.
McMurry, J.E. Organic Chemistry. 7th ed. Brooks Cole, 2007, pp. 795–796, 807 and 975–978.
Self determination theory. Intrinsic Motivation Inventory (IMI).
http://www.selfdeterminationtheory.org/questionnaires/10-questionnaires/
50, accessed 9.4.2012.
Synarchive. Synthesis of Strychnine by Robert B. Woodward in 1954. http://www.
synarchive.com/syn/10, accessed 4.3.2012.
UC Davis University of California. Fischer and Haworth projections.
http://chemwiki.ucdavis.edu/Organic_Chemistry/Organic_Chemistry_With_
a_Biological_Emphasis/Chapter__3%3A_Conformations_and_Stereochemistry/
Section_3.8%3A_Fischer_and_Haworth_projections, accessed 13.2.2012.
Wikipedia. Adolf von Baeyer, 2004b. http://en.wikipedia.org/wiki/Adolf_von_
Baeyer, modified 22.2.2012, accessed 11.3.2012.
Wikipedia. Electrophile, 2004e. http://en.wikipedia.org/wiki/Electrophile, modified
31.1.2012, accessed 4.3.2012.
Wikipedia. Emil Erlenmeyer, 2004a. http://en.wikipedia.org/wiki/Emil_Erlenmeyer,
modified 17.12.2011, accessed 11.3.2012.
Wikipedia. Ester, 2001d. http://en.wikipedia.org/wiki/Ester, modified 2.3.2012, accessed 4.3.2012.
12
Wikipedia,
Fischer–Speier
esterification,
2004d.
http://en.wikipedia.org/wiki/
Fischer%E2%80%93Speier_esterification, modified 22.1.2012, accessed 13.2.2012.
Wikipedia. August Kekulé, 2002a. http://en.wikipedia.org/wiki/Friedrich_August_
Kekul%C3%A9_von_Stradonitz, modified 14.3.2012, accessed 18.3.2012.
Wikipedia. Friedrich Wöhler, 2001a. http://en.wikipedia.org/wiki/Friedrich_W%C3%
B6hler, modified 10.3.2012, accessed 11.3.2012.
Wikipedia.
Emil
Fischer,
2004c.
http://en.wikipedia.org/wiki/Hermann_Emil_
Fischer, modified 8.3.2012, accessed 18.3.2012.
Wikipedia. Justus von Liebig, 2001b. http://en.wikipedia.org/wiki/Justus_von_
Liebig, modified 13.3.2012, accessed 18.3.2012.
Wikipedia.
Methyl
Salicylate,
2004f.
http://en.wikipedia.org/wiki/Methyl_
salicylate, modified 3.3.2012, accessed 4.3.2012.
Wikipedia. Nucleophile, 2002b. http://en.wikipedia.org/wiki/Nucleophile, modified
23.1.2012, accessed 4.3.2012.
Wikipedia.
Organic
synthesis,
2005.
http://en.wikipedia.org/wiki/Organic_
synthesis, modified 6.2.2012, accessed 4.3.2012.
Wikipedia. Resonance (chemistry), 2003a. http://en.wikipedia.org/wiki/Resonance_
%28chemistry%29, modified 30.12.2011, accessed 4.3.2012.
Wikipedia. Robert Bunsen, 2001c. http://en.wikipedia.org/wiki/Robert_Bunsen, modified 8.3.2012, accessed 11.3.2012.
Wikipedia. Robert Burns Woodward, 2003b. http://en.wikipedia.org/wiki/Robert_
Burns_Woodward, modified 9.2.3012, accessed 4.3.2012.
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6
Links
Link 1: Prezi
http://prezi.com/-t4lo4-4-aqt/copy-of-org-synth/
13
A
Appendices
A.1
Appendix 1: Experiment instructions
Synthesis of fragrant esters
using the Fischer–Speier esterification:
An ester from a carboxylic acid and an alcohol
with the help of an acid catalyst
Introduction
An ester is an organic compound that is formed when a carboxylic acid reacts with an alcohol
yielding water as a byproduct. The purpose of this experiment is to provide a practical example
of the synthesis of an ester using the acid catalysed using the Fischer–Speier esterification
method.
We are not going to use the exact method of the Fischer–Speier esterification as it would require
refluxing and purification and we do not have enough time for those. Instead, we will do a
simplified version.
Esters formed from carboxylic acids and alcohols often have fruity scents or flavours. These
synthetic esters produced in the laboratory are very similar to - or even the same as - the
molecules that give fruits their characteristic flavours. In this experiment you will first produce the esters and then try to identify their fragrances.
Safety
You will be using concentrated sulfuric acid (H2 SO4 ) as a catalyst. Sulfuric acid is very dangerous and can cause severe chemical burns when in contact with all human tissues.
•
Make sure you take extreme care when working with sulfuric acid. Some other dangerous
chemicals will also be used.
•
You must wear lab coats, safety goggles and rubber gloves at all times.
•
You must carry out the experiments in the fume hoods.
14
Experimental method
We will be using water baths for heating the experimental mixture.
•
Set up the water bath by measuring about 4 cm of hot water into a beaker and heating it
until it boils. Add water later if there is not enough.
•
Your group should do as many different syntheses as you can within the time reserved
for the experiment.
Every synthesis will begin with the design. You were given some information about the product
and you worked out the name of the ester and the chemicals that were needed to form the product during your previous session. Now you can use your designs and make the products. You
will be given the instructions for the experiments one at a time, starting with methyl salicylate.
15
1. Methyl salicylate
SAFETY ALERT: Remember to use concentrated sulfuric acid with extreme care. Make sure
it does not come into contact with your skin as it will vigorously attack tissue. If you get any
on your skin, immediately wash it off with plenty of cool water and tell the teacher.
1. Place 0.2 grams of salicylic acid into a clean, dry test tube.
2. Add 6 drops of methanol and agitate the tube until the contents are well mixed.
3. Then add 1 drop of concentrated sulfuric acid.
4. Agitate the tube contents and place the tube in a beaker of boiling water for 3 minutes.
5. After heating is complete, remove the tube from the bath and add 15 drops of distilled water
to the tube contents.
6. Cautiously note the fragrance of the products in the test tube by wafting the scent to your
nose. Do this until you can detect a fragrance. Write it down.
16
Study the reaction mechanism. Ignore the resonance structures on the left and right.
17
2. Propyl acetate
SAFETY ALERT: Remember to use concentrated sulfuric acid and glacial acetic acid with
extreme care. Make sure they do not come into contact with your skin as they will vigorously
attack tissue. If you get any on your skin, immediately wash it off with plenty of cool water and
tell the teacher.
1. Prepare propyl acetate by putting 6 drops of propanol in a clean, dry test tube.
2. Add 2 drops of glacial acetic acid.
3. Add 1 drop of concentrated sulfuric acid, agitate the tube to mix the contents, and place the
test tube in boiling water bath for 3 minutes.
4. When heating is completed, remove the test tube from the bath, and add 20 drops of distilled
water to the test tube contents. Agitate to mix.
5. Cautiously note the fragrance of the products in the test tube by wafting the scent to your
nose. Do this until you can detect a fragrance. Write it down.
18
Complete the reaction mechanism. Ignore the resonance structures on the left and right.
19
3. Isopentyl acetate
SAFETY ALERT: Remember to use concentrated sulfuric acid and glacial acetic acid with
extreme care. Make sure they do not come into contact with your skin as they will vigorously
attack tissue. If you get any on your skin, immediately wash it off with plenty of cool water and
tell the teacher.
1. Prepare isopentyl acetate by putting 6 drops of isopentyl alcohol in a clean, dry test tube.
2. Add 2 drops of glacial acetic acid.
3. Add 1 drop of concentrated sulfuric acid, agitate the tube to mix the contents, and place the
test tube in boiling water bath for 3 minutes.
4. When heating is completed, remove the test tube from the bath, and add 20 drops of distilled
water to the test tube contents. Agitate to mix.
5. Cautiously note the fragrance of the products in the test tube by wafting the scent to your
nose. Do this until you can detect a fragrance. Write it down.
20
Complete the reaction mechanism. Ignore the resonance structures on the left and right.
21
4. Octyl acetate
SAFETY ALERT: Remember to use concentrated sulfuric acid and glacial acetic acid with
extreme care. Make sure they do not come into contact with your skin as they will vigorously
attack tissue. If you get any on your skin, immediately wash it off with plenty of cool water and
tell the teacher.
1. Prepare octyl acetate by putting 6 drops of octanol in a clean, dry test tube.
2. Add 2 drops of glacial acetic acid.
3. Add 1 drop of concentrated sulfuric acid, agitate the tube to mix the contents, and place the
test tube in boiling water bath for 3 minutes.
4. When heating is completed, remove the test tube from the bath, and add 20 drops of distilled
water to the test tube contents. Agitate to mix.
5. Cautiously note the fragrance of the products in the test tube by wafting the scent to your
nose. Do this until you can detect a fragrance. Write it down.
22
Complete the reaction mechanism. Ignore the resonance structures on the left and right.
23
5. Benzyl acetate
SAFETY ALERT: Remember to use concentrated sulfuric acid and glacial acetic acid with
extreme care. Make sure they do not come into contact with your skin as they will vigorously
attack tissue. If you get any on your skin, immediately wash it off with plenty of cool water and
tell the teacher.
1. Prepare benzyl acetate by putting 6 drops of benzyl alcohol in a clean, dry test tube.
2. Add 2 drops of glacial acetic acid.
3. Add 1 drop of concentrated sulfuric acid, agitate the tube to mix the contents, and place the
test tube in boiling water bath for 3 minutes.
4. When heating is completed, remove the test tube from the bath, and add 20 drops of distilled
water to the test tube contents. Agitate to mix.
5. Cautiously note the fragrance of the products in the test tube by wafting the scent to your
nose. Do this until you can detect a fragrance. Write it down.
24
Complete the reaction mechanism. Ignore the resonance structures on the left and right.
25
6. Butyl butyrate
SAFETY ALERT: Remember to use concentrated sulfuric acid with extreme care. Make sure
it does not come into contact with your skin as it will vigorously attack tissue. If you get any
on your skin, immediately wash it off with plenty of cool water and tell the teacher. Because
butyric acid has a strong unpleasant odor, special attention must be paid when using it. DO
NOT handle it outside of a fume hood at all.
1. Prepare butyl butyrate by putting 6 drops of butanol in a clean, dry test tube.
2. Add 2 drops of butyric acid.
3. Add 1 drop of concentrated sulfuric acid, agitate the tube to mix the contents, and place the
test tube in boiling water bath for 3 minutes.
4. When heating is completed, remove the test tube from the bath, and add 20 drops of water to
the test tube contents. Agitate to mix.
5. Cautiously note the fragrance of the products in the test tube by wafting the scent to your
nose. Do this until you can detect a fragrance. Write it down.
26
Complete the reaction mechanism. Ignore the resonance structures on the left and right.
27
7. Ethyl butyrate
SAFETY ALERT: Remember to use concentrated sulfuric acid with extreme care. Make sure
it does not come into contact with your skin as it will vigorously attack tissue. If you get any
on your skin, immediately wash it off with plenty of cool water and tell the teacher. Because
butyric acid has a strong unpleasant odor, special attention must be paid when using it. DO
NOT handle it outside of a fume hood at all.
1. Prepare ethyl butyrate by putting 6 drops of ethanol in a clean, dry test tube.
2. Add 2 drops of butyric acid.
3. Add 1 drop of concentrated sulfuric acid, agitate the tube to mix the contents, and place the
test tube in boiling water bath for 3 minutes.
4. When heating is completed, remove the test tube from the bath, and add 20 drops of water to
the test tube contents. Agitate to mix.
5. Cautiously note the fragrance of the products in the test tube by wafting the scent to your
nose. Do this until you can detect a fragrance. Write it down.
28
Complete the reaction mechanism. Ignore the resonance structures on the left and right.
29
Table A.1: Reagents, products and fragrancies. (Johnson; Athabasca University)
number
alcohol
carboxylic acid ester (product)
fragrance
1
methanol
salicylic acid
methyl salicylate wintergreen
2
propanol
acetic acid
propyl acetate
pear
3
isopentyl alcohol
acetic acid
isopentyl acetate
banana
4
octanol
acetic acid
octyl acetate
orange
5
benzyl alcohol
acetic acid
benzyl acetate
peach
6
butanol
butyric acid
butyl butyrate
pineapple
7
ethanol
butyric acid
ethyl butyrate
strawberry
Concentrated sulphuric acid and distilled water are also needed.
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A.2
Appendix 2: Product information given to students to design their synthesis
1. Molecular formula: C8 H8 O3
Structure:
2. Molecular formula: C5 H10 O2
Both reagents are directly alkane-based structures. The alcohol has more carbons than the acid.
The acid is not methanoic acid.
3. Molecular formula: C7 H14 O2
The alcohol begins with ‘iso’. The acid has an icy feeling to it.
4. Molecular formula: C10 H20 O2
Both reagents are directly alkane-based structures. The alcohol has two more carbons than the
longest chain name that students learn in basic education.
5. Molecular formula: C9 H10 O2
The alcohol has an aromatic ring but it is not a phenol. The acid is not methanoic acid.
6. Molecular formula: C8 H16 O2
Both reagents are directly alkane-based structures. You cannot go wrong with a 4.
7. Molecular formula: C6 H12 O2
Both reagents are directly alkane-based structures. The acid, the alcohol, the answer to
everything (well at least the number of carbons). OR Both reagents are directly alkane-based
structures. The acid has more carbons than the alcohol. The alcohol is not methanol.
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