Lab Report

LABORATORY MANUALFor
CHEMISTRY
204L
Fall 2022
Chemistry Department
Morgan State University
1
INTRODUCTION
Organic chemists have discovered and synthesized many useful, valuable
products. These include medicines, plastics, elastomers (rubber-like materials), fabrics,
dyes, food additives (e.g. preservatives, flavorings, vitamins) and cleaning products
(e.g. soaps, detergents, dry-cleaning solvents). In this organic chemistry laboratory
course you will study and use many of the methods that were instrumental in making
many of these important contributions to our welfare.
Research work in organic chemistry falls into these areas:
1. Separation and Purification
Most substances do not appear in their pure form in nature. Also, when we run
an organic reaction, the product usually does not “fall out” pure. Hence, organic
chemists must often separate mixtures to get pure substances. We learned several
techniques to accomplish this, such as distillation, crystallization, and several types of
chromatography.
2. Determination of Structure
After obtaining a pure substance, the chemist must determine its structure, i.e.
what atoms are present and how they are bonded to one another. There are many
physical and chemical methods known for accomplishing this. Several experiments this
semester will fall into this category.
3. Synthesis
Once the structure is known, the chemist needs to determine the best way to
prepare the substance. Most of the experiments in 204L fall into this category.
The principles used in the experiments follow the same sequence as the
principles in your textbook. The laboratory and lecture courses have been planned and
coordinated in order to give you the opportunity to gain a thorough understanding of the
principles of modern organic chemistry.
Good luck! We hope you enjoy the course and that you find it interesting and
valuable.
2
SAFETY
Like other activities, laboratory work can be safe or dangerous, depending on
how much care and common sense we use. We all want to prevent accidents and
injuries. These are some of the most important safety rules:
1.
Eye protection must be worn at all times; safety glasses will be provided for
students who don’t wear glasses. Use the eye bath AT ONCE in case
something does get into your eye.
2.
A laboratory coat or plastic apron must be worn at all times.
3.
No flames may be used in the laboratory.
4.
Wear plastic gloves when handling corrosive chemicals.
5.
If a chemical contacts your skin, wash IMMEDIATELY with a large amount of
water. Use the safety shower if a large area of skin is affected.
6.
Use the fume hood when an experiment involves noxious chemicals.
7.
No eating or smoking is permitted in the laboratory.
8.
Wipe up spills AT ONCE.
9.
Report injuries AT ONCE.
10.
Follow the instructors’ instructions regarding putting certain waste materials into
the proper containers.
LABORATORY COURTESY
Chemicals and some equipment items are shared by all students. Please you’re
your concern for your fellow students by leaving these items in good condition. For
example:
1.
2.
3.
4.
5.
6.
Do not contaminate reagents by putting contaminated spatulas, pipets etc. into
them.
Clean borrowed glassware before returning it.
Do not take reagent containers to your desk; transfer what you need to an
appropriate container.
Replace lids and stoppers on reagent bottles AT ONCE.
Clean your laboratory bench after each experiment.
Never place chemicals directly on the pan of a balance; use weighing paper.
3
LABORATORY NOTEBOOK
It is extremely important that clear, neat records be kept of all laboratory work. A
scientist often has to refer back to work that he/she did years before!
Sometimes a multimillion dollar lawsuit (who discovered something first?) can hinge on a
laboratory notebook. Your laboratory reports should be neat and well organized, and
they should use good sentence structure, grammar, spelling and punctuation.
A lab notebook dedicated to this course, no notes from other classes, is required; it can
be a simple spiral ring notebook.
The following items should be put into the notebook BEFORE YOU COME TO LAB:
1. Your name
2. Title of Experiment
3. Properties of Substances Involved in Experiment
List these in table form.
4. Diagram of Apparatus
5. Equations
6. Outline of the Procedure in “bullet” form.
The prelab will be checked and signed by instructor. A copy of the prelab must be
attached to your final lab report.
The following should be recorded in the notebook WHILE THE EXPERIMENT IS BEING
CONDUCTED:
7. Changes in Procedure
Describe any changes you may have made. If there were no changes, write “no
changes in procedure”.
8. Data and Observations
Record data you measure or observe while conducting the experiment, such as
weights, volumes, temperatures, times and color changes. Sometimes it is best to
list these in table form.
This data sheet will be checked and signed by instructor. A copy of this data sheet
must be attached to your final lab report.
The following should be included in your typed lab report; the lab report must include
your prelab sheets and the data sheet from the lab session:
Items 1 –5, 7, and 8 from above plus:
9. Calculations and Graphs
Include calculation of Rf values, per cent yields, rate constants, etc. as well as any
graphs called for in the experiment.
10. Conclusions
Write down the conclusions you drew. For example, if you analyzed an unknown, state
what the composition of the unknown is. THIS IS A CRITICAL PART OF THE LAB
REPORT. REPORTS WITHOUT CONCLUSIONS WILL NOT BE ACCEPTED.
4
11. Answers to Questions
Answer the questions at the end of the procedure.
At first, the manual will spell out clearly what you should include in your report. Later,
you will be asked to write reports with less and less guidance.
Here are some hints that will help you write good laboratory reports:
Units
1. Always attach the correct units to a measurement, e.g.
Weight of flask
Volume of methanol
Temperature of solution
38.33 g
6.3 mL
39o C
2. If you are listing measurements in a table, it’s OK to put the units at the top of each
column (usually in parentheses) and not after each number, e.g.
Substance
Weight (g)
Volume of
Temperature of
Solvent (mL)
Solution (oC)
Benzoic acid
4.13
17.9
25
Benzhydrol
15.11
99.8
23 38
Sucrose
5.88
40.0
28 25
3. Quantities that are calculated from measurements should also carry the correct
units. For example, if the weight of 5.00 mL of a liquid is 7.21 g, its density is
1.44 g/mL.
Significant Figures (SF)
1. Use significant figures to express how accurately the measurement was. For
example, if you measure a distance to the nearest 0.1 cm, it should be recorded
as 7.0 cm (not 7 cm) or 4.7 cm (not 4.66 cm).
2. Zeroes at the BEGINNING of a number DO NOT count as SF’s but zeroes at the end
of a number DO. For example, 0.00021 has 2 SF’s while 0.3000 has 4.
3. In multiplication and division, the answer should have the same number of SF’s as
the data with the lowest number. For example, if a sample has a volume of 5.6
mL (2 SF) and a mass of 4.293 g (4 SF), the density should be expressed as
0.77 g/mL (2 SF), even though the calculator reads 0.76661.
4. In addition and subtraction, the answer should have the same number of digits after
the decimal point as the data with the lowest number. Here are two examples:
Wt. of NaCl + paper
4.913 g
Wt. of beaker
17.12 g
Wt. of paper
0.403 g
Wt. of Mg
1.396 g
Wt. of NaCl
4.510 g
Wt. of beaker + Mg
18.52 g
(The zero is important!)
5
DEHYDRATION OF 2-METHYL-2-BUTANOL
Principles
2-Methyl-2-butanol will be dehydrated to give a mixture of two alkenes. The mixture
will be analyzed to determine (1) whether alkenes are indeed present and (2) the
percentage of each alkene that is formed.
Prelaboratory Preparation
Title of Experiment
Properties of Substances
Compound Boiling pt.
in oC
Density in
g/mL
Mol. Wt.
Volume in
mL
Weight in
g
Moles
2-methyl1-butene
———–
————–
————–
2-methyl2-butene
———–
————–
————–
2-methyl2-butanol
Diagram of Apparatus
Draw or paste in a diagram of a simple distillation with a heating mantle, NOT with
a Bunsen burner.
Equations
Write two equations for the dehydration of 2-methyl-2-butanol. One should show
the structures of both alkenes, and the other one should be balanced.
Procedure
USE GLOVES WHEN YOU HANDLE SULFURIC ACID! BE ABSOLUTELY
SURE YOUR SAFETY GLASSES ARE ON!
CAREFULLY put 19 mL of 47% sulfuric acid into a 50-mL round-bottomed flask.
Cool the flask in an ice bath while you add, SLOWLY AND CAREFULLY, WITH CONSTANT SWIRLING, 13.7 mL of 2-methyl-2-butanol. Dry the outside of the flask, clamp
it and lower it into a 50-mL heating mantle. Add a boiling chip and attach the glassware
needed for simple distillation. Use a 25-mL round-bottomed flask as the receiver.
Clamp the neck of the receiving flask and immerse it in an ice bath.
6
Set the voltage regulator at 4 (or 40). Collect distillate until dripping into the
receiver stops or the temperature reaches around 48oC, whichever occurs sooner.
Transfer the distillate to a small separatory funnel, which is held upright in a ring on
the ring stand. Add 10 mL of 0.1 M NaOH. Stopper the funnel, remove it from the ring
and shake it. Put it back into the ring, remove the stopper and drain the aqueous layer
into a flask. Pour the organic layer into a clean, dry 50-mL Erlenmeyer flask, add 2
g of calcium chloride (a drying agent), stopper the flask and let it stand, with
occasional swirling, for 10 minutes. Weigh a clean, dry, 50-mL Erlenmeyer flask
and stopper, decant your product into it, stopper the flask and weigh it.
Carry out the following experiments on your product:
1. Place 1 mL of methylene chloride (dichloromethane) into each of two small test
tubes. Add 3 drops of your product to the first test tube, and add 10 drops of 1% Br2 in
CCl4 to each. Compare the results in the two test tubes; the second one is a “blank”.
2. Place 1 mL of acetone into each of two small test tubes. Add 8 drops of your product
to the first tube, and then add 1 drop of 1% aqueous KMnO4 to each. Let the test tubes
stand for 10 minutes and observe the results.
3. A gas chromatogram of “your” product (“mixture”), of pure 2-methyl-1-butene and of
pure 2- methyl-2-butene is available on Canvas under Modules, Supplemental Spectra
for Dehydration.
Submit the remaining product to the instructor.
Gas Chromatography
This is a schematic diagram of a gas chromatograph:
The instrument contains two tubular metal columns, only one is shown in the
diagram. These contain the stationary phase, a high-boiling liquid. This liquid is supported
on a granular, inert solid. Both columns are in the column oven. The mobile phase is a
carrier gas such as helium. It enters the chromatograph and continuously flows through
both columns.
The sample is introduced through the injection port and goes through one of the
7
columns. As it does so, it is separated into its components. After going through the
columns, the gas streams flow through a detector. The detector causes the pen of the
recorder to draw a “base line” when only helium is going through it. When a
component of the sample goes through, the pen moves and draws a “peak”.
Data and Observations
1. Record all the weights and temperatures you measured during the experiment.
2. Describe the observations you made in the bromine and permanganate tests.
3. Include a copy of the gas chromatogram found on Canvas to your report.
Calculations and Graphs
1. Calculate the percent yield of alkenes in your dehydration.
2. Which peak in your chromatogram of your sample corresponds to 2-methyl-1butene? To 2-methyl-2-butene? (Consider the retention times of the various peaks.)
3. Calculate the percent of each alkene, either by comparing the heights of each peak
in the mixture, or by comparing the area under each peak in the mixture.
Conclusions
1. What conclusion can you draw from the results of the bromine and permanganate
tests? Are your conclusions consistent with the structures of the products?
Explain. Use equations for the reactions as a part of your explanation.
2. What is the major product of the dehydration reaction? Is this the one you would
expect on the basis of what is known about stabilities of alkenes? Explain your
answer, and give a proper literature reference for the information about
stabilities.
Questions to be Answered
1. Why should the temperature be kept below around 48oC during the distillation, and
not, say, allowed to rise to 100oC or more?
2. State LeChatelier’s principle (HINT: Refer to a General Chemistry text) and explain
how it helps us to get a good yield in this experiment.
3.
BrCH2CH2CH2CH2Br + 2 NaC≡N ——-> N≡CCH2CH2CH2CH2C≡N + 2 HBr
Dr. S. N. Too ran the above reaction using 60.00 g of 1,4-dibromobutane and 18.0 g
of NaCN. He obtained 8.00 g of the organic product. What was his per cent yield?
SHOW ALL YOUR WORK CLEARLY.
8
SPECTROSCOPY
Infrared (IR) Spectroscopy
A. Absorption of IR Radiation by Molecules
The bonds in a molecule are constantly vibrating, like springs. Usually, each
vibration is at the lowest vibrational energy level (the “ground state”). If the molecule is
struck by a quantum of IR radiation whose frequency equals the frequency of a bond
vibration, the quantum may be absorbed. As a result, the molecule moves to a higher
energy level (an “excited state”), in which the amplitude of vibration (the distance traveled
by the atoms during each cycle) is greater than the ground state. This absorption process
(represented by the vertical arrow) is shown for the stretching vibration of a C—H bond in
this diagram:
—————————excited state
C——–H
E = h = hc/
—————————-ground state
C——–H
1
In IR spectroscopy, tables list the wavenumber () at which absorption occurs, in cm This is equal to the frequency, in s-1, divided by the speed of light, in cm s-1.
B. Interpretation of IR Spectra
Fortunately, the wavenumber at which a certain bond or group absorbs is about
the same from one molecule to another. For example, the wavenumber for a C—H
stretching vibration is between 2850 and 2950 cm -1 if the carbon is sp3-hybridized. A
table showing absorption wavenumbers for a variety of bonds or groups is in your text.
Here are some hints to help you interpret your IR spectrum:
1. Absorption bands at 1350-4000 cm-1 are the most reliable. The others are difficult to
Interpret, so don’t worry if you can’t assign these to definite bonds or groups.
2. Negative evidence may be helpful. For example, if there is no band between 1680
and 1760 cm-1, the compound probably does not contain a C=O group.
9
1H NMR Spectroscopy
A. The Instrument
This is a diagram of our 1H NMR Spectrometer:
The sample, dissolved in a solvent (A), is placed between the poles of a magnet
(B) and spun. Radio waves of frequency 90 MHz (megahertz), generated by an
oscillator (C), go through a coil surrounding the sample. The strength of the magnetic field
increases as the spectrum is run, causing the protons in the sample to precess more
rapidly. When the precession frequency reaches 90 MHz, some protons absorb radio
waves from the coil. This is detected by the detector (D), causing a peak to appear
on the chart paper (E). The paper is marked off in  units, which relate the place where
each proton in the sample absorbs to the place where the reference substance, TMS,
absorbs (at  = 0).
B. Interpretation of 1H NMR Spectra
These four features of 1H NMR spectra are useful:
(1) There is a signal for each set of equivalent protons in the structure of the compound. In the 1H NMR spectrum of diethyl ether at the top of the next page, there are
two signals (a and b), which correspond to the two sets of equivalent protons (a and b)
in diethyl ether.
(2) The  values tell us something about the environment each set of protons is in.
There is a table relating to environment in your text. For example, the “b” protons in
diethyl ether are on carbons directly attached to an oxygen, so they give a  of 3-4. The
“a” protons are farther away from the oxygen, so they give a  of 1-2.
10
a
b
b
a
CH3CH2OCH2CH3
TMS
b
8
6
4
a
2
0
(3) The ratio of the heights of the signals, as measured by the integral curves, is
equal to the ratio of the numbers of protons responsible for the signals. For
example, the ratio of “a” protons to “b” protons in diethyl ether is 46 mm/31 mm,
which is close to 3:2. This is only a ratio; the actual numbers of protons are, of
course, 6 and 4.
(4) Splitting of signals is usually due to protons on the neighboring carbon(s). A set of n
equivalent protons split a signal into n + 1 peaks. In the diethyl ether spectrum, signal
“b” is split into 4 peaks (a quartet) because of the 3 neighboring protons “a”, and “a” is
split into 3 peaks (a triplet) because of the 2 neighboring protons “b”
Prelaboratory Preparation
Give structures for all the compounds listed under “Procedure”.
Procedure
You will be given the IR and 1H NMR spectra of one of the compounds listed below.
Use the information given above, your class notes and your text in order to figure out
exactly which of the listed compounds your unknown is.
11
Family
Hydrocarbons
Halides
“
“
“
“
“
“
“
“
“
Alcohols
“
“
“
Ethers
“
“
Aldehydes
Ketones
Esters
Nitriles
Name
Structure
Diphenylmethane
1,1-Diphenylethene
Toluene
Isopropylbenzene
Styrene
2-Bromopropane
1-Chloro-1-phenylethane
1-Chloro-2-phenylethane
1,3-Dichloropropane
1,4-Dichlorobutane
1-Bromopropane
p-Bromoethylbenzene
Iodoethane
2-Bromobutane
Chlorodiphenylmethane
2-Propanol
2-Phenylethanol
1-Phenylethanol
Ethanol
Ethoxybenzene
Diisopropyl ether
Benzyl ethyl ether
Propanal
Benzaldehyde
p-Methoxybenzaldehyde
2-Butanone
Acetophenone
2-Methyl-1-phenyl-1-propanone
1-Phenyl-1-propanone
Ethyl acetate
Diethyl succinate
Ethyl benzoate
Ethyl p-bromobenzoate
Benzonitrile
Benzyl cyanide
12
Data and Observations
Attach the spectra of your compound to your report.
Calculations and Graphs
None are needed for this experiment.
Conclusions
Give the structure of your compound and explain exactly how you reached this
conclusion.
Questions to be Answered
H
O
CH3O
CH(CH3)2
CH3CH2
CHO
H
CH3O
Br
O
For each of the above compounds, do the following:
1. List the wave numbers of all the IR bands in the 1350-4000 cm-1 region.
For each one, state what bond or group it represents.
2. Label equivalent sets of protons with lower-case letters. Then, for each 1H NMR
signal, give the  value, the type of splitting (singlet, doublet etc.), and the number of
protons it represents.
letter
δ value
splitting
# of protons
3. Redraw the compound and label equivalent sets of carbons with lower-case letters.
Then for each 13C NMR signal, give the δ value and # of carbons it represents.
letter
δ value
# of carbons
13
DIELS-ALDER REACTION
Principles
The Diels-Alder reaction is one of the most famous “name” reactions in Organic
Chemistry. It involves the heating (in the absence or presence of an inert solvent) of a
conjugated diene with a “dienophile”, which usually contains an alkene group (C=C)
conjugated with one or more carbonyl (C=O) or cyano (CN) groups:
O
+
O
Heat
The reaction forms a six-membered ring. Since six-membered rings are present
in many important compounds (e.g. steroids and other compounds that can affect our
metabolism), the Diels-Alder reaction is one of the most frequently used synthetic
reactions. It belongs to a class of reactions known as cycloadditions, since two molecules
are added together to give a new cyclic structure, or ring. The product is referred to as an
“adduct”; this is an abbreviation for addition product.
We will use 1,4-diphenyl-1,3-butadiene as the conjugated diene. The dienophile
is maleic anhydride (see structure below), in which the C=C is activated by two C=O
groups. The inert solvent is 2-methoxyethyl ether, commonly known as “diglyme”; its
structure is CH3OCH2CH2OCH2CH2OCH3.
O
O
O
Maleic anhydride
Our heat will be supplied by a microwave oven. Chemists have recently found
that this can often give shorter reaction times and higher yields than more conventional
methods of heating, such as refluxing using a heating mantle.
14
Prelaboratory Preparation
Properties of Substances Involved in Experiment
Compound
Weight in g
Mol. Wt.
Moles
Melting pt. in oC
——————-
210oC
1,4-diphenyl1,3-butadiene
Maleic
Anhydride
Adduct
—————–
Diagram of Apparatus
None is required for this experiment
Equations
Write a balanced equation for the reaction to be carried out.
Procedure
Place the following into a microwave tube:
0.42 g of 1,4-diphenyl-1,3-butadiene,
0.20 g of maleic anhydride, which has been freshly ground with a mortar and
pestle. Minimize exposure to the air; the moisture could hydrolyze some of it to maleic
acid, and
1.0 mL of 2-methoxyethyl ether.
Shake the microwave tube gently to mix the reactants, screw the cap on, and place it
into the microwave oven. Heat at 70% power for 3.50 minutes. Open the oven door and
wait 5 minutes for the beaker to cool. WEAR HAND PROTECTION and remove the
beaker from the oven. Let the tube stand at room temperature for 20 minutes. Add
3.0 mL of methanol, stir thoroughly and filter by vacuum, using a small Hirsch funnel. Use
another 3.0 mL of methanol to rinse the beaker and to wash the crystals. Air-dry for
5 minutes.
Transfer the product to a small, clean dry beaker and add 7.0 mL of toluene.
Heat to boiling on a hot plate. AS SOON AS BOILING STARTS, note whether all the solid
has dissolved. If not, add toluene slowly until you obtain a clear solution. WEAR HAND
PROTECTION and remove the beaker from the hot plate. Let it cool to room temperature
and then place it into an ice bath for 10 minutes. Filter by vacuum (small Hirsch funnel),
air-dry for 5 minutes and obtain the weight and melting range.
Data and Observations
Record the weight and melting range of the product.
15
Calculations and Graphs
Calculate your percent yield. Show all steps in the calculation clearly.
Conclusions
Is the product the expected one? Why? (HINT: Include the reported melting
points of reactants and products in your explanation.)
Questions to be answered
1. Give the structures of the products obtained when the following are heated. Include
stereochemistry where relevant.
A
+
N
C
O
H
B
H
+
O
O
O
C
O
+
O
2. Which compounds would you heat together in order to synthesize the
following?
16
NITRATION OF PHENOL
Principles
Nitration is an example of electrophilic aromatic substitution; this topic is covered
extensively in your text. In this experiment it is important to realize that an -OH group
attached to the aromatic ring acts as an activator and an ortho, para director.
Prelaboratory Preparation
Properties of Substances Involved in Experiment
List the melting points of the three (o, m, p) nitrophenols, and the densities of
o- and p- nitrophenol.
Diagram of Apparatus
None is needed for this experiment
Equations
Give two equations for the nitration of phenol:
a. An equation that shows the structures of the major organic products.
b. A balanced equation, to be used when calculating the percent yield.
Procedure
WEAR GLASSES AT ALL TIMES, AND WEAR GLOVES WHEN HANDLING
NITRIC ACID OR PHENOL!!
Into a 50-mL beaker put 20 mL of 3 M nitric acid. Rinse the graduated cylinder
thoroughly with water. Place a stir bar into the beaker and place the beaker on a
magnetic stirrer. Clamp a thermometer so that its bulb is below the surface of the liquid
but high enough so that the stir bar will not strike it.
Start the stirrer. Using a dropper, add 4.0 mL of liquefied phenol at a rate such
that the temperature rises to 45-55o and stays in this region. Stir for 5 minutes.
Transfer the mixture to a small separatory funnel, using a little water to aid the
transfer. Drain the organic layer into a 100-mL round-bottomed flask. (It may be easier
to see the line between the layers if you shine the light from your cell phone behind
the separatory funnel!) Clamp the flask into a heating mantle. Add 60 mL of water and
a boiling chip. Attach the glassware needed for simple distillation; remember to
GREASE JOINTS AND USE CLAMPS PROPERLY. As a receiver, use a 50-mL beaker
with a wax pencil mark at the 25-mL mark.
Turn on the heat; set the voltage regulator at 6. A yellow substance will co-distil
with water. If the substance solidifies in the condenser, turn the condenser water off till
the solid melts. When 25 mL has been collected, stop the distillation.
17
Collect the solid by vacuum filtration, wash it with 5 mL of water and recrystallize
it from petroleum ether. To do this, weigh the solid and place it into a 50-mL Erlenmeyer
flask. Add 10 mL of petroleum ether per gram of product. Clamp the flask and immerse
it in a water bath, heated to about 50o C, until the solid dissolves. Allow the mixture to
cool to room temperature and then immerse it in an ice bath. When crystallization is
complete, collect the product by vacuum filtration, air-dry it and obtain its weight and
melting point.
Show it to the instructor and place it into the proper container.
Data and Observations
Percent phenol in liquefied phenol (look at label on bottle):
Weight of product:
Melting point of product:
Calculations and Graphs
Calculate the percent yield. The density of liquefied phenol is 1.05 g mL -1.
Conclusions
What is the structure of the product? Explain how you arrived at this conclusion.
Questions to be answered
1. What volume of 1.50 M nitric acid is needed to convert 9.0 g of m-bromophenol to
3-bromo-4,6-dinitrophenol? (No excess of nitric acid is used.) Specify the units on the
volume.
2. In your experiment, you made quite a bit of another phenol, in addition to the one that
you isolated and purified. Read the information on the next page.
a. What is the structure of the product you did not isolate?
b. ON THE BASIS OF STRUCTURE, why did it stay behind during steam distillation?
Explain
c. ON THE BASIS OF STRUCTURE, why did the compound you isolated distil over?
3. What are two advantages of using steam distillation rather than simple distillation in
this particular experiment?
4. For each of the following, state whether it would undergo nitration faster, slower or at
the same rate as phenol. Explain each answer.
a) benzene
b) p-methoxyphenol
c) o-nitrophenol
18
Intra and Inter Molecular Hydrogen Bonding:
Intra-molecular hydrogen bonding is present in o-nitrophenol. This is due to the polar nature of the O-H bonds
which result in the formation of hydrogen bonds within the same molecule. This intramolecular H bonding
reduces water solubility and increases volatility. But in p-nitrophenol, inter molecular hydrogen bonding
(between H and O atoms of two different para-nitro phenol molecules) is possible. As a result of inter
molecular hydrogen bonding, p-nitrophenol undergoes association that increases the molecular weight,
whereby decreasing volatility. Thus o-nitrophenol is steam distillable while p-nitrophenol is not.
Para nitro phenol with inter molecular hydrogen bonding:
Ortho nitro phenol with inter molecular hydrogen bonding:
Reference: http://vlab.amrita.edu/?sub=2&brch=191&sim=1547&cnt=1
19
SODIUM BOROHYDRIDE REDUCTION
Principles
Metal hydrides are versatile reducing agents. Sodium borohydride, NaBH 4,
reduces aldehydes and ketones to primary and secondary alcohols, respectively.
Lithium aluminum hydride, LiAlH4, is more powerful; it can reduce esters and carboxylic
acids as well as aldehydes and ketones. We will study the reduction product of a diketone,
1,2-diphenyl-1,2-ethanedione (benzil) with sodium borohydride. By identifying the
product, we will be able to answer the following questions:
1. Were one or both of the carbonyl groups in benzil reduced?
2. If both were reduced, the product would contain two stereocenters (chiral
carbons). Thus, there could be several stereoisomers. Which stereoisomer(s) is
(are) actually formed?
Prelaboratory Preparation
Compound
Structure
Melting point
Color
1,2-diphenyl-1,2ethanediol, racemic
122-125oC
White
1,2-diphenyl-1,2ethanediol, meso
135-137oC
White
Benzil
Benzoin
Procedure
Place 0.50 g of benzil and 5.0 mL of 95% ethanol into a 50-mL Erlenmeyer flask.
Heat gently on a hot plate till the benzil dissolves, cool under running water with
swirling; a fine precipitate of benzil will probably form. Add 0.20 g of sodium borohydride
and SCREW THE CAP BACK ON THE JAR IMMEDIATELY. Swirl the flask, and record
any color and temperature changes. Let the mixture stand for 12 minutes.
Add 5.0 mL of distilled water and heat the mixture gently till it boils. Add 10.0 mL
of distilled water shake and let the mixture stand till crystallization is complete. Filter by
vacuum, using a small Hirsch funnel. Rinse with 3 mL of water, air-dry and oven-dry.
Weigh the product and determine its melting point.
Remove 0.10 g of the product, place it into a 100-mm test tube, add 2 mL of
chloroform and shake. Use this solution to obtain the IR spectrum.
20
Place another 0.10 g of the product into a test tube THAT IS FREE OF
ACETONE. Add 1.0 mL of 95% ethanol and warm in a water bath (a beaker containing
water on a hot plate) till the solid dissolves. Add 3.0 mL of 2,4-dinitrophenylhydrazine
reagent. The formation of a precipitate indicates that an aldehyde or ketone group was
present in your product.
Data and Observations
Record color and temperature changes that occurred during the reaction, as well
as the weight and melting point of the product. Attach the IR spectrum to your report,
and give the result of the 2,4-dinitrophenylhydrazine test.
Calculations and Graphs
Write a balanced equation for the reaction and calculate the per cent yield.
Conclusions
1. How many carbonyl groups in the benzil were reduced? Give the experimental
evidence for your answer. (HINTS: Refer to your melting point, 2,4dinitrophenylhydrazine test and IR spectrum. The discussion of IR spectroscopy in the
text will help you interpret the spectrum.)
2. What stereochemical form of the product did you get? Give your evidence.
3. Is the reaction exothermic or endothermic? Give your evidence.
4. Explain any color changes you observed when you added the sodium borohydride.
Questions to be Answered
1. Give stereochemical formulas (Fischer projections) for all (but no extras) the
stereoisomers that could theoretically form during the reduction of
a. the carbonyl group of 2-pentanone
b. both carbonyl groups of 2,3-butanedione
2. Predict the products of the reduction of O=CCH2CH2CH2C=O with
|
|
CH3
OCH3
a. LiAlH4
b. NaBH4
3. What starting material would you use to synthesize 5-hydroxypentanoic acid using a
NaBH4 reduction?
21
GRIGNARD SYNTHESIS OF TRIPHENYLMETHANOL
We will carry out this reaction:
When preparing and using Grignard reagents, anhydrous conditions must be
maintained, it is difficult to start the reaction between magnesium and an organic halide
in the presence of water. In addition, RMgX react with water to give RH + HOMgX, so
water could destroy the reagent before it has a chance to react with the ester.
Grignard reagents also react with aldehydes, ketones or epoxides to yield
alcohols; these syntheses are covered in class.
Pre-laboratory Preparation
Please include a diagram of the apparatus (see p. 25),
the equations for the reactions to be carried out (see above),
and the following table of “Properties of Substances Involved in Experiment”.
Substance
Magnesium
Mol.
Wt.
Density
In g/mL
——–
Volume
in mL
Weight in
g
Number
of moles
————–
Melting
pt in oC
——–
Bromobenzene
——–
Methyl benzoate
——–
Triphenylmethanol
——–
————
(expected) (expected)
22
Procedure
Clean and dry a 250-mL 3-necked flask, a condenser and a dropping funnel. Use
acetone for cleaning and drying and a gentle stream of air to evaporate the acetone.
Clamp the flask directly over a magnetic stirrer. Place a stirring bar and 1.3 g of
magnesium into the flask. Insert the condenser into the center neck (remember to
grease joints lightly), the dropping funnel into one of the other necks and a stopper into
the third. Stopper the funnel. Place an adapter into the top of the condenser and a
drying tube into the adapter. Use a hot air blower to dry the entire apparatus.
Place 5.3 mL of bromobenzene and 40 mL of anhydrous ether into the funnel
Stir with a glass rod to assure good mixing. Stopper the funnel and allow about 5 mL of
the solution to run into the flask. Start the stirrer. When the reaction starts, the mixture
becomes cloudy and brown, and the ether boils. If it doesn’t start in 5 minutes, try
(1) heating the mixture with a hot air blower and (2) starting a small reaction in a test tube
and pouring it into the flask. After the reaction has started, add the remaining etherbromobenzene solution at a rate such that a gentle reflux is maintained. Then continue
stirring for 10 minutes.
Place 2.8 mL of methyl benzoate and 25 mL of anhydrous ether into the funnel
then stir to assure good mixing. Add this slowly to the flask, and continue stirring for 10
minutes. REMOVE THE DRYING TUBE. Place 70 mL of 6 M hydrochloric acid into the
funnel and add this SLOWLY AND CAREFULLY, ONE DROP AT A TIME. This should
give two clear layers; add more hydrochloric acid if necessary. Pour the mixture into a
250-mL Erlenmeyer flask, stopper it, and wait ten minutes.
Pour the mixture into a separatory funnel. Draw off the aqueous layer and
discard it. Pour the ether layer into a clean, dry Erlenmeyer flask and dry it with 1 g of
sodium sulfate. Decant the liquid into a 100-mL round-bottomed flask and attach the
glassware needed for simple distillation. Use an adapter and receiving flask at the lower
end of the condenser, and cool this flask in an ice bath. Distil the ether using a water bath;
pour the distillate into the bottle labeled “RECOVERED ETHER”.
Carefully remove the distillation glassware from the flask containing the residue.
Add 10 mL of petroleum ether and a condenser. (This arrangement of glassware is called
a “reflux assembly”.) Bring the mixture to a boil using your water bath. Allow the mixture
to cool and collect the solid by vacuum filtration, using a small Hirsch funnel. Obtain the
weight and melting point.
If it melts well below the reported melting point of triphenylmethanol, place the solid
into a 50-mL Erlenmeyer flask. Add 6 mL of 95% ethanol per gram of solid. Warm on a
hot plate till the ethanol boils then let the mixture stand. If there is no solid after 15
minutes, induce crystallization by cooling in ice, scratching and/or seeding. Filter by
vacuum, air-dry, weigh and determine the melting point. Submit the product to the
instructor.
Data and Observations
As you conduct the experiment, please record all weights, the melting point(s) of
the product and observations such as color changes.
23
Calculations and Graphs
Calculate the per cent yield of triphenylmethanol. If you recrystallized from 95%
ethanol, calculate the yield before and after recrystallization. Show all steps in your
calculations clearly.
Conclusion
Is the product pure? On what basis did you reach this conclusion?
Questions to be Answered
1. Give two reasons why anhydrous conditions must be maintained during a Grignard
synthesis. Write chemical reactions to explain.
2. After the reaction mixture is transferred to a separatory funnel,
a. What substances (including solvent) make up the lower layer?
b. What substances (including solvent) make up the upper layer?
3. The procedure (paragraphs 2 and 3) states that the additions of bromobenzene,
methyl benzoate and hydrochloric acid must be done slowly. What might
happen if any of these were done too rapidly?
4. Give equations that show how each of the following can be prepared by a Grignard
synthesis:
a. 1-methylcyclohexanol
b. 1-pentanol
24
25
WILLIAMSON ETHER SYNTHESIS OF PHENACETIN
Principles
In the Williamson ether synthesis, an alcohol or phenol is converted to its conjugate
base, which carries out a nucleophilic substitution on an alkyl halide:
Base or Na
R’X
————————> RO- or ArO- ———-> ROR’ or ArOR’
ROH or ArOH
We will use this approach in order to convert p-hydroxyacetanilide (the active
ingredient in “Tylenol”) to p-ethoxyacetanilide (also known as “phenacetin”, which was
once used as an analgesic). The synthesis will be carried out in special microscale
equipment. We will use sodium hydroxide as the base and iodoethane as the alkyl halide.
We will use an actual “Tylenol” tablet to supply the p-hydroxyacetanilide.
Prelaboratory Preparation
Title of Experiment
Properties of Substances Involved in Experiment
Compound
Weight in g
phydroxyacetanilide
Mol. Wt.
Density in
g/mL
Moles
————
Iodoethane
pethoxyacetanilide
Melting pt.
in oC
————–(expected)
————
(expected)
Diagram of Apparatus
26
Equations
Procedure
Grind a “Tylenol” tablet using a mortar and pestle. Place a hard 50-mL heating
mantle on a magnetic stirrer. Clamp a vial and lower it into the mantle so that it makes
good contact. Put glass wool around the base of the vial. Place a small stir bar into the
vial, and add 7.00 mL of 0.25 M NaOH in 95% ethanol; measure this with a graduated
pipet and a pipetting pump. Add the amount of ground tablet that will supply 0.26 g of phydroxyacetanilide. (The tablets are 78% p-hydroxyacetanilide and 22% binder, which
holds the tablets together.) Add 0.25 mL or iodoethane (syringe) and attach a plastic
adapter and condenser (reflux assembly). Turn on the cooling water to the condenser.
Turn the voltage control to “4” and heat with stirring till the mixture has boiled for
20 minutes. Turn off the heat, raise the vial and attachments and let the mixture cool to
room temperature. Remove the stir bar with a magnetic retriever. Filter the mixture by
gravity, using a thick-stemmed funnel. Add 1.0 mL of 95% ethanol to the residue in the
vial and pour this through the funnel.
When filtration is complete, add 35 mL of distilled water stir and let it stand while
crystals form. When crystallization is complete, filter by vacuum using a large Hirsch
funnel then Air-dry the product and determine its weight and melting point.
Data and Observations
Record the weight and melting point of the product.
Calculations and Graphs
Calculate your percent yield.
Conclusions
Was your product pure and was it p-ethoxyacetanilide? Give reasons for your
answers.
Questions to be Answered
1. What is the purpose of each of these steps in the procedure?
a. Filtering by gravity (paragraph 2, lines 3-4)
b. Adding water to the filtrate (paragraph 3, line 1)
2. Starting with any alcohols, phenols or alkyl halides you wish, show the best way to
prepare each of these by the Williamson synthesis. (HINT: The second step goes by the
SN2 mechanism.)
a) t-butyl ethyl ether
b) phenyl propyl ether
3. List three advantages of microscale chemistry; look it up on the internet.
27
WITTIG REACTION
Principles
The Wittig reaction is discussed in the text. We will use benzyltriphenylphosphonium
chloride as the phosphonium salt, 9-anthraldehyde as the aldehyde or ketone, and
sodium hydroxide as the base.
Mixtures of the Z- and E-isomers of the alkene often form in Wittig reactions, but ours
should give only one isomer. We will use the melting point, IR spectrum and 1H NMR
spectrum of our product in order to determine its exact structure, including
stereochemistry.
Prelaboratory Preparation
No properties.
No diagram of apparatus.
Equations:
Procedure
Clamp a 25-mL Erlenmeyer flask atop a magnetic stirrer. Into the flask put a stir
bar, 0.40 g of benzyltriphenylphosphonium chloride, 0.23 g of 9-anthraldehyde and 1.0
mL of dimethylformamide (DMF). Stir as rapidly as possible without splashing. Add 0.5
mL of 50% aqueous sodium hydroxide (WEAR PLASTIC GLOVES) at a rate of 1 drop
every 7 seconds. If any solid is adhering to the walls of the flask, wash it off using a few
drops of DMF from a Pasteur pipette. Continue stirring for 30 minutes.
28
Add 8 mL of a 1:1 mixture of 1-propanol and water. Stir the mixture and collect
the solid by vacuum filtration. Transfer the solid to a clean 25-mL Erlenmeyer flask and
recrystallize it from 8 mL of 1-propanol, as follows. Add the 1-propanol, boil gently on a
hotplate, let the mixture cool to room temperature and immerse it in an ice bath. Filter
by vacuum, air-dry and obtain the weight and melting range. Take the IR spectrum.
(The 1H NMR spectrum is available on Canvas, under Modules, Supplemental Spectra.)
Show the product to the instructor and place it into the proper container.
Data and Observations
Weight of product:
Melting range of product:
Attach IR and proton NMR spectra to your laboratory report.
Calculations and Graphs
Calculate the percent yield. Keep in mind that the reagents may not be 100%
pure; refer to labels on the containers. The density of 50% aqueous sodium hydroxide
is 1.5 g mL-1.
Conclusions
1. Does your IR spectrum support the structure of the product? Explain; refer to the
exact IR band or bands you are using to reach this conclusion.
2. Is the product the Z- or E-isomer? Give the experimental evidence, using both of the
following:
a. The Z- isomer has been reported to melt at 107-108o, and the E- at 130-132o.
b. In the 1H NMR, vinylic protons that are cis to one another have a
coupling constant (J-value) of 6-15 Hz (Hertz), while those that are trans to one
another have J = 11-18 Hz.
Questions to be Answered
1. Why did you get the stereoisomer of the product that you did get rather than
the opposite one? Base your answer on the structures of the two isomers.
1. Outline syntheses of the following compounds, starting with triphenylphosphine,
an alkyl halide and an aldehyde or ketone.
a) 2-pentene
b) Trans 1,2-diphenylethene
c)
29
Solvent Free Reductive Amination
Objective
To conduct a reductive amination reaction between an aldehyde and an amine in solvent
free condition using an activator, p-toluenesulfonic acid monohydrate (PTSA) and a
reducing agent, sodium borohydride (NaBH4).
Background
Amines are of great importance not only in organic chemistry but also in the overall way
the world operates today. The simplest amine is ammonia (NH3). The worldwide
production of ammonia in the gas state is approximately 170 million tons each year, and
it is used in the fabrication of nylon, fertilizers, explosives and refrigeration. 1 Another
important characteristic of amines is their presence in different molecules that are vital to
the human body, such as the building block of proteins, amino acids and also nucleic
acids.2 Amines are also present in the development of pharmaceutical products, such as
amphetamines, used to decrease fatigue and increase focus.3
The synthesis of amines through reductive amination, is one of the preferred methods to
prepare amines in organic chemistry. This method involves the reaction between a
carbonyl compound (aldehyde or ketone) with ammonia or another primary or secondary
amine. An imine group (nitrogen double bonded to carbon) is formed and then reduced to
the final amine product with a source of H-.
30
The Experiment
You and your partner will prepare a 2o amine from an unknown aldehyde (A, B, C or D)
and a primary amine (#1 or #2) that will be selected for you. You will identify what the
two starting material components were, based on the melting point of the HCl salt of your
product dibenzylamine.
Safety
As with all laboratory experiments, the use of chemical splash goggles and gloves are
required at ALL TIMES.
Procedure
1. In a mortar and pestle place 0.58 mL (~5 mmol) of the aldehyde (if you have aldehyde
C, use 0.51 mL) and 0.58 mL (~5 mmol) of the amine you selected using a separate
1 mL syringe for each.
2. Take turns gently mixing the reaction for 15 minutes until a solid (“slushy
consistency”) is obtained. This indicates that you have formed the imine.
3. Weight 5 mmol of p-toluenesulfonic acid (PTSA) and 5 mmol of NaBH4 and mix them
together well in a watch glass with a glass rod. Add this solid mixture into the agate
mortar and take turns gently grinding for 25-30 minutes.
4. Transfer the mixture obtained into a 50 or 100 mL beaker with a spatula and wash
the remaining material on the mortar & pestle into the beaker with 20 mL of 5%
NaHCO3. Transfer the solution to a separatory funnel and add 20 mL of ethyl acetate.
5. Remove the aqueous layer and label the beaker with the aqueous layer for proper
disposal later.
6. Transfer the organic layer to a 50 mL Erlenmeyer and dry the solvent by placing 1-2
scoops of potassium carbonate into the organic layer and swirling the container. Filter
31
through a gravity filter by placing a filter paper and funnel into a previously weighed
50 mL round bottom flask.
7. Concentrate the product to dryness by placing the round bottom flask on the Rotovap
and evaporating the ethyl acetate. Get the mass of your round bottom flask containing
the product.
**********WASTE DISPOSAL**********
The condensed ethyl acetate from the rotary evaporator should be poured in the
bottle labeled “Ethyl Acetate” and located in the side hood. Be certain to reattach
the receiving flask from the rotary evaporator.
**********WASTE DISPOSAL**********
8. Add 5 mL of ethanol to your round bottom flask and transfer the product to a 25 mL
Erlenmeyer flask using a disposable pipette. DROPWISE, add 0.5 mL of
concentrated HCl (CAUTION: concentrated HCl is very corrosive).
9. At this point you should see some crystals forming in the flask. When this occurs,
collect the crystals by vacuum filtration using a Buchner or a Hirsh funnel and keep
the vacuum on for a few minutes until the crystalline salt is dry.
10. Transfer the solid to a 25 mL Erlenmeyer flask and recrystallize with 10 mL of hot
ethanol until the solid completely dissolves then let it cool to room temperature.
11. Collect the purified crystals by vacuum filtration using a Hirsch funnel, washing
them with 1-2 mL of ethanol and allow them to air dry for at least overnight. Make
sure you write down the initials of the group on the watch glass where you are
placing the product. Next day, obtain a melting point and weigh your final salt.
32
Melting points of the HCl salt of the reductive amination products
260-262°C 5
X
X
228-232°C
216-217°C 6
255-257°C
248-252°C
274-278°C 7
33
34
DETERMINATION OF STRUCTURE
There has been a flood in the stockroom, and the labels have washed off many of the
bottles. Your task is to identify the material in one of the bottles so it can be relabeled!
An inventory of the stockroom was done shortly before the flood, so we know what
compounds should be present. See Inventory List starting on p. 40.
Principles
You will receive a sample of the material in one of the bottles which is missing its
label. By applying various principles and laboratory techniques from Chemistry 203 and
204, you will be able to determine the identity of what’s in the bottle by doing the
following (items #1, #2, and #3 can be done in any order):
1. Determine the solubility in various solvents. Using the flow chart, place the
unknown into one of the Solubility Groups, I-VII.
2. If your unknown is a solid, determine its melting point using the melting point
apparatus.
If your unknown is a liquid, determine its boiling point by simple distillation.
3. Run the IR spectrum; note the presence or absence of important peaks.
4. Carry out any appropriate Functional Group Tests.
5. Receive an 1H NMR spectrum and a 13C NMR spectrum from the instructor. List
peaks and make preliminary assignments.
6. After completing steps 1-5, consult the Inventory List.
The solubility behavior of a substance narrows down the possible structures
considerably. Organic compound containing a polar group and < 5 carbons are soluble in water. Amines appear to dissolve in aqueous acid and acidic compounds appear to dissolve in aqueous base since they form water-soluble salts. Alkenes, alkynes, activated aromatic compounds and compounds containing oxygen and/or nitrogen appear to dissolve in concentrated sulfuric acid; they form soluble products by reacting with the acid. Solubility tests should be done systematically by following the flow chart. In some cases (e.g. water-insoluble amines) the solubility behavior alone tells us into which family of compounds the unknown falls. In other cases (e.g. Group I), solubility behavior only narrows down the list. In these cases, the exact family can be established by means of the IR spectrum and functional group tests. 35 Unknown Water Soluble Insoluble Group I 5% HCl Soluble Group I Group I: Alcohol, ether, aldehyde, ketone, carboxylic acid, ester, amide, nitrile, nitro compound or amine with 6 carbons Group II 5% NaOH Soluble Phenol or carbox ylic acid with >4
carbons
Insoluble
Other
5% NaHCO3
Usually soluble
Carboxylic acid III
H2SO4
Insoluble
Phenol GroupI IV
Soluble
a. Alkene
b. Alkyne
c. Aldehyde, ketone alcohol, ether,
ester, amide, nitrile or nitro compound with >4 carbons
d. Aromatic compound activated by
3 or more alkyl groups
Group V
Insoluble
a. Alkane
b. Alkyl or aryl
halide
c. Aromatic compound with no N
or O and