TCHEM 261 Clark Atlanta University Integrated Alkene Synthesis Distillation Lab Report

TCHEM 261 Organic Chemistry II
Problem Set H- Elimination Reactions
Name:
Instructions: Complete all problems prior to the deadline. Upload to the Problem Set H
assignment on Canvas. After the key posts, correct your problem set, and upload your
corrections as a second upload to the Problem Set H assignment.
Part 1: Smith Problems
Problems from “Organic Chemistry” 6 ed by Janice Smith.
1. Draw the structures of two different alkyl halides that yield the alkene as the only
product.
Alkyl Halide 1
Alkyl Halide 2
2. Draw all constitutional isomers formed in each elimination reaction. Label the
mechanism as E1 or E2.
E1 or
E2?
3. Taking into account stereochemistry, predict the major E2 product formed. Show
why.
4. Draw the structure, including stereochemistry, of an alkyl chloride that forms
each alkene as the exclusive E2 product.
5.
Draw the product(s) formed when treated with excess NaNH 2
.
6. Draw the structure of a dihalide that could be used to prepare the alkene. There
may be more than one possible.
7. Draw all of the substitution and elimination products formed when the alkyl
halide below is treated with a) CH3OH and b) KOH. Indicate stereochemistry of
products, as well as mechanisms of formation.
8. The following reactions do not afford the major product that is given. Explain why
and draw the structure of the major product actually formed.
9. Draw a detailed, stepwise mechanism for each reaction.
10. Draw a detailed, stepwise mechanism that illustrates how four organic products
are formed in the following reaction:
Product 1:
Product 2:
Product 3:
Product 4:
11. Draw all products formed by treatment of the dibromide (B) with one equivalent
of NaNH2. Label pairs of diastereomers and constitutional isomers.
Part 2: Klein Problems
Klein 10.27-10.38
Name: __________________________________________
Atomic #: __________
Pre-Lab Questions for Integrated Alkene-Distillation Lab – Part 1
1. In this lab you will separate a mixture of organic liquids by one of two methods:
simple or fractional distillation. Your partner group will do the alternate method. In
theory, which method should give the better separation? Briefly explain why.
2. A mixture of 10 mL of isoamyl acetate (MW=130.2 g/mol and density=0.88 g/mL)
and 15 mL of methyl benzoate (MW=136.2 g/mol and density=1.09 g/mL) is
distilled. Calculate the mole percent for each component.
3. Use the mole %’s from question 2 and the figure below to answer the following
questions.
a. What is the initial boiling point of this liquid mixture?
b. What is the composition of the vapor in equilibrium with the initial liquid?
c. What is the composition of the initial condensate (the condensate which
forms from condensation of the vapor in equilibrium with the initial liquid)?
Name: __________________________________________
Atomic #: __________
4. The distillation curves, one simple and one fractional, from a mixture of liquids is shown
below.
a) Which curve, solid or dashed line, is the simple distillation? Which is fractional? How could you
distinguish between them?
b) The possible liquids being distilled are in the table below. What are the actual identities of the two
liquids?
Liquid
2-methyl propane
butane
pentane
hexane
cyclohexane
Boiling point (degrees C)
27.8
30.2
36.1
69
80.8
Edit 1-5-2023 by Margaret Henderson
University of Washington – Tacoma
Organic Chemistry I (TCHEM 261)
Integrated Alkene Synthesis – Distillation Lab
Student Version
OVERALL INTRODUCTION
In this lab, you will first learn the technique of distillation, comparing the effectiveness of
simple versus fractional distillation by analyzing gc data. You will then use the distillation
technique to isolate the alkene products from an alcohol dehydration reaction. GC data will
allow students to determine whether this reaction proceeds according to Zaitsev’s rule.
PART 1 – DISTILLATION
INTRODUCTION
Distillation is an inexpensive and relatively simple technique used to purify mixtures of
liquids. Chemists often use this method to separate homogeneous solutions of two or more
liquids. In industry, distillation is used to separate the economically important components of
fossil fuels including natural gas, gasoline, kerosene, heating oil, and lubricants. In the food
industry, distillation is used to concentrate the alcohol in wines and other beverages obtained
from the natural fermentation of fruits and vegetables. Both of these economically important
processes separate liquids by differences in their boiling points.
Distillation can also be used to isolate a volatile product from a reaction mixture. For
reactions with an intermediate equilibrium constant, distillation can be used to shift the
equilibrium towards a greater yield as per Le Chatelier’s Principle.
In practice, liquids can be separated by simple or fractional distillation. A good Khan
Academy video explains this process: https://www.khanacademy.org/testprep/mcat/chemical-processes/separations-purifications/v/simple-and-fractional-distillations
and is required viewing in the preparation section. Basically, as a mixture of liquids is heated,
the vapors produced will be richer in the more volatile component, which is the one with the
higher vapor pressure. If these vapors rise and then re-condense, the condensed liquid will be
richer in the lower-boiling component. The phase diagram in Figure 1 shows this process.
Edit 1-5-2023 by Margaret Henderson
Figure 1: Change in Mole Fraction of Components During Distillation of a Mixture
In simple distillation, a liquid mixture is heated, travels up into a distillation head, then
condenses in a condenser. Figure 2, below left, shows a simple distillation set-up. Figure 3,
below right, shows a fractional distillation apparatus. In fractional distillation, the vapors
travel through a longer column which is usually packed with steel wool, glass beads, or some
other inert material designed to provide lots of surface area on which repeated cycles of
vaporization and condensation occur. Each time vaporization/condensation occurs, the
resulting liquid is further enriched in the component with the lower boiling point.
Fig. 2: Simple distillation apparatus
Fig. 3: Fractional Distillation Apparatus
As a mixture distills, the composition of the distillate changes, so the temperature of the
distillate also changes. A plot of the temperature as a function of the volume of distillate
collected is known as a distillation curve and can be used to determine what liquid is being
collected at different points in the distillation. Figure 4 shows typical distillation curves for
both simple and fractional distillations of a mixture of liquids.
Edit 1-5-2023 by Margaret Henderson
Fig. 4: Theoretical Distillation of a Mixture of Two Liquids
Distillation Curve
160
140
Temperature
120
100
80
60
40
20
0
0
1
2
3
4
5
6
7
8
Distillate Volume
Fig. 5: Actual Fractional Distillation Curve for a Curves for a Mixture of Two Liquids
In this experiment, you and a partner will be assigned one of the two distillation methods and
an unknown mixture of organic solvents. Using the semi-microscale glassware kit in your
organic drawer, you should separate the 8-ml unknown sample. You will share your data with
another group who will have distilled the same unknown using the other type of distillation.
After comparing the quality of the two methods by constructing a distillation curve, you will
also submit your samples for gas chromatography (GC) analysis. That, along with the boiling
points obtained from the distillation curves, should allow you to identify the pure unknowns.
Edit 1-5-2023 by Margaret Henderson
PREPARATION
1. Read the Whole Lab, especially the post-lab write-up instructions.
a. Watch the Khan Academy video online. https://www.khanacademy.org/testprep/mcat/chemical-processes/separations-purifications/v/simple-and-fractionaldistillations . Please note the following differences in procedure from the
video: I) We will use a hot plate and aluminum block to heat the distilling flask
instead of an oil bath or heating mantle. II) We will pack the fractional column
with steel wool instead of beads or stars.
b. In Section 14 the Nichols lab manual, read 14.2 on distillation theory (p. 756-759
and look at figure 14. 11 on p. 765. Read Section 15.1-15.3 (p. 768-773) and look
at figure 15.11.
c. Watch this video about Gas Chromatography: https://www.khanacademy.org/testprep/mcat/chemical-processes/separations-purifications/v/gas-chromatography
2. Learn or Review any concepts or skills you are not confident about applying during lab.
A suggested source to review the concepts of vapor pressure and boiling point is:
www.chem.umass.edu/~samal/269/distill.pdf
3. Prepare your lab notebook as described below.
LAB NOTEBOOK Set-Up
Clerical Information
• Title – Use the one given for this lab.
• Date work done
• Your Name
• Name of Lab Partner on that date/for that lab
• Be sure to also enter the lab in your Table of Contents.
Objective – After reading the entire Part 1 of this lab, identify and write down the objective of
the lab in your notebook. The objective is the question or questions your data will hopefully
allow you to answer.
Hypothesis – For this lab, please write a hypothesis about which type of distillation will be most
effective at separating your unknown.
Edit 1-5-2023 by Margaret Henderson
Physical & Chemical Properties Table – Use the format below. Be sure to include your
solvents and reagents. Think carefully about what physical properties are most relevant and ones
you might need to know during lab.
Possible unknown components of the liquid mixtures are acetone, cyclohexane,
ethylbenzene, hexane, heptane, octane, and toluene.
Chemical
Name
Use/Purpose Relevant Physical Properties
in THIS lab
?
?
Hazards
Response to
hazards
?
Chemical Reaction Equation – N/A for Part 1 of this lab.
Complete the Pre-Lab Worksheet on plain paper (NOT in your lab notebook)
Experimental Plan – Use the Experimental directions below to write a procedure for yourself in
your lab notebook.
• Bullet points or flowchart preferred
• Lab Guide not allowed in lab (but I will have a reference copy up front)
Data & Observations – Create pages in your notebook to record all the data you will collect.
Label spaces to remind you what you need to write down. Hint: Should you record your
unknown code?
After preparing your lab notebook, please take the on-line pre-lab quiz to ensure that you
have a solid background for the investigation you will carry out in this lab.
Experimental Directions
Set up either a simple or fractional distillation apparatus as assigned. Use a hot plate with the
aluminum heating block as the heat source. Place 2 boiling chips in the distilling flask, and add a
known volume of your unknown mixture. If you have been assigned fractional distillation,
loosely pack your air condenser with stainless steel cleaning pad material. You should also
insulate your column with the Tygon jacket material provided. Have tared and labeled collection
containers ready. Turn on the cooling water and begin heating. You will need to track
temperature and volume of condensate collected. It can be useful to note time as well. Record the
temperature and volume at frequent intervals. Collect different boiling fractions in separate
vials. Continue until 0.5-1.0 mL of liquid remain in the distilling flask. Do not boil the flask dry
– it will crack.
Edit 1-5-2023 by Margaret Henderson
Things to Watch Out For In Distillations:
(1) The thermometer is positioned incorrectly – this leads to observed temperatures which are
incorrect. The top of the thermometer bulb must be even with the bottom of the side arm on the
distilling head, or a little lower. It must not touch the metal packing or the glass apparatus.
(2) Be sure your water lines go IN the lower end of the condenser jacket and come OUT from the
higher connector.
(2) Distillation is too rapid due to excessive heating – this leads to a poor separation. Start over if
this occurs. If this happens with your unknown, do not dispose of the liquids. Simply recombine
all liquids and redistill the mixture.
(3) Not enough heating – this leads to reflux (a condition in which the vapors condense and
return to the distilling flask) instead of distillation. Supply enough heat so that the distillation
proceeds steadily at a rate of about one drop per 20 – 30 seconds.
(4) After the low-boiling fraction has distilled, the distillation may slow or stop and the
temperature may fluctuate or drop – this is because more heat is required to distill the higherboiling fraction. Increase the heat below the distilling flask so that the distillation proceeds at a
rate of one drop per 20 – 30 seconds. This is more likely to happen with the fractional distillation
because of the longer path. It is advisable, especially if the lab is drafty, to insulate the distilling
column in the fractional distillation.
(5) The distilling column is packed too tightly with metal sponge – this leads to a situation known
as flooding of the column, in which a plug of liquid collects in the column. Distillation will be
severely hampered in such a case.
(6) The distilling column is packed too loosely – a poor separation results.
(7) With this equipment, a measured BP may be considered to be reliable only after the
temperature has leveled off and the distillation rate is about 1 drop per 20-30 seconds. Even then
the measured BP may be a few degrees off.
(8) Liquid boils in the flask but none is collected in the vial. This may be due to a leaking
connection – check them.
Submitting Samples for GC
Small vials will be supplied for GC samples. You should submit two samples at a minimum.
The first should be the lower boiling component and the second the higher boiling component. If
you wish, you may submit one additional sample if you feel the need to analyze an additional
fraction of your distillation. A Gas Chromatogram of your original mixture will be provided..
Minimum sample volume to submit is 0.5 mL. Label samples clearly with lab section code (AA,
AB, BA, or BB, etc.), station number and atomic number, and part of distillation sample is from
(ie low temp, high temp, int. temp).
Submit Carbon copies of Pre-Lab and Data & Observation Lab NB pages before leaving
lab.
Edit 1-5-2023 by Margaret Henderson
PART 2 – ALKENE SYNTHESIS
INTRODUCTION
One method for preparing alkenes is dehydration of alcohols in the presence of strong acids and
heat. This is a -elimination reaction. In lecture, we were told that the reaction is both
regioselective and stereoselective. In this lab, we will be investigating to see if the reaction really
is regioselective and really follows Zaitsev’s Rule, producing the more highly substituted alkene
as the major product. The dehydration reaction is reversible, so the reaction equilibrium can be
pushed towards the product by distilling the low boiling point alkenes from the high boiling
point reaction mixture as the alkenes are formed. The distillation does not separate the alkenes.
The presence of the products will be verified and quantified by gas chromatography analysis.
The main reaction for this activity is shown below:
Figure 1. Reaction of tert-amyl alcohol (2-methyl-2-butanol) with sulfuric acid
producing a mixture of alkenes.
PREPARATION
1. Read the Whole Lab, especially the post-lab write-up instructions.
2. Learn or Review any concepts or skills you are not confident about applying during lab.
Review the alcohol dehydrogenation/elimination reaction from Smith if necessary. You should
be confident in doing a simple distillation (Part 1). Note that none of the pictures in various texts
and videos look exactly like our semi-microscale set-up. A better diagram of ours is shown
below.
3. Prepare your lab notebook as described below.
Edit 1-5-2023 by Margaret Henderson
LAB NOTEBOOK Set-Up
Clerical Information
• Title – Use the one given for this lab.
• Date work done
• Your Name
• Name of Lab Partner on that date/for that lab
• Be sure to also enter the lab in your Table of Contents.
Objective – After reading the entire Part 2 of this lab, identify and write down the objective of
the lab. The objective is the question or questions your data will hopefully allow you to answer.
Hypothesis – For this lab, please write a hypothesis about whether or not the reaction follows
Zaitsev’s rule. Explain what evidence will allow you to answer this question.
Physical & Chemical Properties Table – Use the format below. Think carefully about what
properties will be useful to have at hand when you are running this reaction.
Chemical
Name
Use/Purpose Relevant Physical Properties
in THIS lab
xx
xx
Hazards
Response to
hazards
xx
Complete the Pre-Lab Worksheet on plain paper (NOT in your lab notebook)
Experimental Plan – Use the Experimental directions below to write a procedure for yourself in
your lab notebook.
• Bullet points or flowchart preferred
• Lab Guide not allowed in lab (but I have a reference copy up front)
Data & Observations – Create pages in your notebook to record all the data you will collect.
Label spaces to remind you what you need to write down.
After preparing your lab notebook, please take the on-line pre-lab quiz to ensure that you
have a solid background for the investigation you will carry out in this lab.
Experimental Directions
Dehydration of t-amyl alcohol
The procedure was carried out in a semi-microscale distillation apparatus using the 10
mL round bottom distilling flask and the 5 mL vial as a receiving vessel. In a 10 mL
round bottom flask, t-amyl alcohol (2-methyl-2-butanol, 3.0 mL, __ moles) was
combined with H2SO4 (9M, 25 drops) and 2-3 boiling chips. The 10 mL round bottom
Edit 1-5-2023 by Margaret Henderson
flask was then attached to the distillation apparatus, and the reaction and distillation
were carried out.
Helpful Hints:
•
•
•
The product is very volatile, so pile the ice all around the receiving vial clear up to the
condenser.
Start with the hot plate set to 4-5, but be ready to adjust up or down as needed.
Be careful to think about what temperature the distillation must be stopped at!
After noting the volume of product collected, the product was transferred to a
reaction tube and washed twice with an equal volume of saturated NaHCO3. A clean,
dry pipet was used to transfer the alkene layer to a clean, dry test tube after the second
wash. (N.B. density of alkenes is 0.66 g/mL). Particular care was taken to NOT
transfer any of the aqueous layer into this dry test tube. The alkene layer was dried with
two pin-head-sized scoops of CaCl2. Care was taken to not shake the mixture enough
to mix any CaC2 into the liquid, or transfer any CaCl 2 with the alkene during decantation
into a clean, dry, labelled vial as this would clog the GC.
Bromine Test
The bromine test was carried out by placing 3 drops of a known alkene, 1-pentene or
cyclohexene, into one test tube and 3 drops of the supposed alkene layer into another
test tube. To each test tube, 1 drop of 5% Br 2/CH2Cl2 was added and color changes or
other evidence of a reaction was noted.
GC Sample Prep
The distillate was placed in a clean, dry GC vial and labelled as shown below.
How To Label the GC Vial
Lab station number
Brief lab title
5B
Alkenes
15, 23
Lab Section Code (A or B)
Each person’s atomic
number
When running the GC, it is often necessary to dilute the sample with a non-reactive
solvent with a clearly different GC retention time. Your lab instructor may give you
instructions about preparing a sample diluted in heptane.
Edit 1-5-2023 by Margaret Henderson
Clean-up
•
At the end of the experiment, dismantle, clean, dry and replace all equipment and
glassware in the appropriate drawer or cupboard.
• Discard the distillation residue (in the round bottom flask) and water washes in the
‘acid waste’ collector, CaCI2 solids in ‘spent drying agent’,
• Glassware that was used for acid or base must be rinsed with water first; acetone
does not dissolve acid or base.
• To remove non-polar chemicals or hasten the drying of wet glassware, rinse with a
minimal amount of acetone into the acetone waste collector.
Dry the acetone-rinsed glassware by blowing on it with a gentle stream of compressed
air.
PART 3 – GAS CHROMATOGRAPHY
Please read section 2.5 – gas chromatography – in your Nichols Organic
Chemistry lab manual.
https://chem.libretexts.org/bookshelves/organic_chemistry/organic_chemistry_lab_te
chniques_(nichols)/02:_chromatography/2.05:_gas_chromatography_(gc)
We will spend time learning about GC during the third lab session for this lab.
Gas Chromatography: Interpretation of Result
The area of each peak in the gas chromatogram is proportional to its concentration.
Since retention time is not absolute, a standard sample is injected at the start of every
run, and the retention time (in minutes) and peak area (in uV*sec.) for a standard sample
(usually 2%-5% concentration) of a known substance is used to identify peaks and
calculate the concentration of the unknown sample. In this experiment, overall
concentration of sample is irrelevant, because we are using the GC to determine the
relative concentrations of the two alkene isomers.
Edit 1-5-2023 by Margaret Henderson
Part 1 – Distillation Post Lab Write-Up
Post lab write-ups should be typed, double spaced, and submitted as a hardcopy.
DATA SUMMARY & PRESENTATION
1) Create a data table showing temperature, volume of distillate collected, and approximate
time using the simple distillation data you or your collaborating team collected. Include the
code of your unknown. Attach
2) Create a second data table showing temperature, volume of distillate collected, and
approximate time using the fractional distillation data you or your collaborating team
collected. Include the code of your unknown. Attach.
3) Using the data tables above, create separate graphs showing each type of distillation curve
using EXCEL. This should be a scatterplot of temperature as a function of total volume of
distillate collected. Plot the volume in 0.5 mL increments on the x-axis and the temperature on
the y-axis. Best fit lines should be added either using the line-fit function or by hand. ASK if
you don’t understand what kind of graphs are being requested. Attach.
4) Fill in tables below showing your GC results (retention times and peak areas). Attach your
chromatograms produced by the samples from your distillation of a mixture of liquids, with
peaks labelled, to this lab write-up.
Simple Distillation
Samples
Retention
Time for
Peak 1
Area
Under
Peak 1
Retention
Time for
Peak 2
Area
Under
Peak 2
% of this
component out of
total of both
components.
Retention
Time for
Peak 1
Area
Under
Peak 1
Retention
Time for
Peak 2
Area
Under
Peak 2
% Compositon of
Each Component
Initial Mixture
Lower Boiling
Component
Higher Boiling
Component
Mid-boiling sample?
Fractional Distillation
Samples
Initial Mixture
Lower Boiling
Component
Higher Boiling
Component
Edit 1-5-2023 by Margaret Henderson
POST-LAB QUESTIONS ABOUT DISTILLATION
5) Look at the graph you made for a simple distillation.
a. Can you identify a b.p. of the lower boiling component? If so, what is it?
b. Can you identify a b.p. of the higher boiling component? If so, what is it?
6) Look at the graph you made for fractional distillation.
a. Can you identify a b.p. of the lower boiling component? If so, what is it?
b. Can you identify a b.p. of the higher boiling component? If so, what is it?
7) Did your simple or fractional distillation give clearer temperature plateaus?
8) From your best distillation data, what would be reasonable identities of the components in
this mixture? Explain.
9) GC Data Analysis
a. Based on the retention times obtained from the GC, what do you think the
components of your mixture are? Explain.
b. Does this match the identities consistent with the boiling point data? If not, which
do you think is more reliable? Why?
Edit 1-5-2023 by Margaret Henderson
10) Composition of Fractions
a. Use your GC data from Question 4) to complete the following table.
Sample
% Component A
(lower boiling)
% Component B
(higher boiling)
Initial mixture
Simple Distillation
Low boiling sample
High boiling
sample
Fractional
Distillation
Low boiling sample
High boiling
sample
b. Based on these results, which type of distillation gave the best separation of
components? Was your hypothesis upheld or disproved? Explain your answer.
Edit 1-5-2023 by Margaret Henderson
Part 2 – Alkene Synthesis Post Lab Write-Up
Post lab write-ups should be typed, double spaced, and submitted as a hardcopy.
DATA SUMMARY
11. Your data submission consists of the following:
a. The carbon copies of the lab notebook pages on which you recorded data &
observations for this lab (turned in at end of lab session.)
b. Attach the GC chromatogram(s) generated from your product sample with peaks
labelled with the identity of each peak and its area.
c. Create a table giving the mass and volume of your reactant and your product mixture.
Attach.
DATA ANALYSIS
12. Using the GC data, calculate the relative concentrations of each type of alkene produced.
Show your calculations.
13. Calculate the percent yield of total product. Show your calculations.
14. Answer the following questions by giving evidence and the conclusion you reached based
on that evidence. Please note: always state the evidence before the conclusion so the reader
can follow your reasoning and anticipate your conclusions.
a. What do you believe is the identity of the compounds you isolated from the reaction
mixture?
Edit 1-5-2023 by Margaret Henderson
b. Were the products you obtained consistent with the reaction you expected to occur?
Include a chemical equation as part of your answer.
c. Was the ratio of alkenes you found consistent with Zaitsev’s Rule? Remember to give
data and explain how it led to your answer to this question.
d. Did your data include any conflicting or unexpected results? If so, explain and suggest
further work that could be done to answer the question posed in this hypothesis.
15. Was distillation a useful technique in the synthesis of alkenes?
a. Did it separate the products from the starting material well?
b. Did this method give a good yield of product?
c. If the alcohol and acid had been refluxed with no distillation, then the left-over starting
material and alkene products separated by another method such as liquid-liquid extraction,
how do you believe that might have affected the yield? Explain.
REFERENCES
Macroscale and Microscale Organic Experiments, by K.L. Williamson, 5th edition, Chapter 5
Edit 1-5-2023 by Margaret Henderson