2004 Chem 2OB3 Lab Manual - Experiment 1. The Acid-Catalyzed Reaction of a Glycol.
Experiment 1. The Acid-Catalyzed Reaction of a Glycol.
References: Brown & Foote, Chapters 9 & 16
INTRODUCTION:
This experiment is a discovery oriented exercise where you need to determine the structure of the
starting material to understand the reaction. The IR and NMR spectra provided will reveal a
structure that will lead you to the correct reaction. The second part of this lab involves related
chemistry pertaining to reactions of amines (RNH2) or hydrazines (RNHNH2). Although
spectroscopic techniques (eg. IR) are becoming the norm for identifying organic compounds, it is
useful to use small scale reactions to characterize functional groups.
BACKGROUND:
The reaction mechanism for this experiment is a two step reaction starting from a glycol. The first
is a dehydration reaction followed by a 1,2-methyl shift. Below are the IR and NMR spectra of
the starting material. Once you have the correct IUPAC name and have looked up that structure
in the index of your textbook, you will know the reaction in this experiment.
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2004 Chem 2OB3 Lab Manual - Experiment 1. The Acid-Catalyzed Reaction of a Glycol.
Formation of Hydrazones
One common diagnostic test for the presence of a certain functional group (like in the compound
you just made) is to see if it will form a 2,4-dinitrophenylhydrazone. This is a simple test tube
reaction that generally leads to the formation of a solid. When this reaction leads to a solid
material, the determination of its melting point gives further confirmation of its structure.
PRE-LAB PREPARATION:
1. Using the above spectral data of a simple glycol, determine the structure and IUPAC name of
the starting material (C6H14O2). NMR integrations are 6 and 1 for the peaks at 1.3 and 2.4 ppm,
respectively.
2. Look up the name of the starting material in the index of your textbook. What is the proposed
reaction of this starting material when heated in H2SO4? Write the mechanism (curly arrows, etc.)
for the proposed reaction.
3. What peak should disappear in the IR spectrum of your final product (compared to the starting
material)? What peak should appear?
4. Draw a general reaction of 2,4-dinitrophenylhydrazine to form a hydrazone.
EXPERIMENTAL PROCEDURE:
This experiment is conducted using microscale equipment. You should review the procedures for
the use of this type of equipment which is contained in the Microscale Techniques section of the
lab manual.
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2004 Chem 2OB3 Lab Manual - Experiment 1. The Acid-Catalyzed Reaction of a Glycol.
1. Refluxing the Starting Material in H2SO4.
a) Weigh out 1g of the unknown glycol in a 10 mL cylindrical vial and add 5 mL of 20% H2SO4.
b) Equip the vial with a magnetic stir bar and a micro-condenser (with cooling water).
c) Heat the vial in a sand bath until the solution has refluxed for 10 minutes.
d) Remove the apparatus from heat and allow to cool.
e) Dismantle the refluxing apparatus and remove the stir bar using the micro-forceps.
b) Using a pipette, remove the aqueous layer (bottom layer) from the cylindrical vial. Try to
remove the entire aqueous layer.
2. Isolating the Final Product.
The crude product will be purified by simple distillation, using the
Hickman distillation head.
a) Transfer the remaining organic layer to a 3 mL conical vial. Check that
there is only one phase (no water drops in the bottom of the vial). If you
have less than 0.5 mL, check with your TA on whether to purify or not.
d) Equip the vial with a boiling chip and the distillation head.
e) Heat the solution in a sand bath until you've collected your product in
the distillation head. This is your distilled final product. Cover the sand
bath with aluminum foil to prevent the sand bath heat from reevaporating the final product in the distillation head.
f) Transfer your final product (using plastic pipettes) to a pre-weighed vial and obtain the mass of
your final product. Calculate the percent yield of your final product.
3. Formation of the Hydrazone.
a) To a small test tube containing 2 mL of a 0.1M solution of 2,4-dinitrophenylhydrazine (The
reagent is dissolved in a mixture of ethanol and hydrochloric acid.), add approximately 40 µL of
your product, using the syringe supplied by your TA.
b) Warm the tube for a few minutes, and then allow to cool until solid appears.
c) Collect the solid by vacuum filtration using the Hirsch funnel.
d) Record the colour of the hydrazone.
4. Characterization of the Final Product.
a) Obtain and label an IR spectrum of your final product.
b) Measure the melting point of your hydrazone and record it.
c) Based on your Melting Point (M.P.) and using the table below, determine which compound is
your final product.
Name of Compound M. P. of Derivative
Di-n-butyl ketone
41 °C
Butyroin
99 °C
Pinacolone
125 °C
Pulegone
142 °C
Iso-butyrophenone
163 °C
Carvone
193 °C
Furfural
229 °C
Note: The names in this table are their common names and NOT their IUPAC names.
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2004 Chem 2OB3 Lab Manual - Experiment 1. The Acid-Catalyzed Reaction of a Glycol.
d) Dispose your product in the ORGANIC WASTE jar provided.
5. Preparing for the Next Laboratory Experiment.
The glassware to be used in the next experiment is required to be scrupulously dry. To help
accomplish this, the glassware (10 mL cylindrical vial and micro-condenser) needs to be washed
with soap and water, then rinsed with acetone and allowed to dry for the next experiment.
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