CHEM2315 SDSU SEC10 Hydroboration and Oxidation of 1 Hexene Lab Report I need help with some things on my lab report. Directions are on pages 6-9 of the fi

CHEM2315 SDSU SEC10 Hydroboration and Oxidation of 1 Hexene Lab Report I need help with some things on my lab report. Directions are on pages 6-9 of the file. CHEM 2315 Fall 2019
HYDROBORATION/OXIDATION OF 1-HEXENE
Required Reading: Smith, Organic Chemistry –Section 10.16: Hydroboration – oxidation.
INTRODUCTION
The hydroboration-oxidation of alkenes is an important synthetic route to alcohols and
therefore receives considerable discussion in standard organic textbooks. Hydroboration of
substituted alkenes will exhibit regioselectivity via anti-Markovnikov addition and
steroselectivity via syn addition. In the present experiment, 1-hexene is first allowed to react
with borane-tetrahydrofuran (BH3-THF) complex to form a bis-alkylborane. In the second
reaction, oxidation replaces the borane group with retention of configuration to yield an
alcohol. In this experiment, you will attempt to characterize the major and minor products
using gas chromatography and infrared spectroscopy.
Figure 1. Hydroboration/oxidation of 1-hexene.
EXPERIMENTAL
Equipment
25 or 50 mL round bottom flask – dried in the oven for 24 hours prior to lab.
Magnetic stir bar
Stir plate
19/22 orange septum
Separatory funnel
Whatman filter paper & funnel
3 utility clamps
Disposable 1 mL syringe + needle
400-mL beaker (ice bath)
125-mL Erlenmeyer flask
Chemicals
Tetrahydrofuran, anhydrous__
1-hexene, 0.6 mL
Borane-THF (1 M in THF), 3.0 mL
3 M NaOH, 0.6 mL
30% hydrogen peroxide, H2O2, 0.6 mL
Waste Disposal
flammable, organic waste
flammable, organic waste
flammable, reactive, quench with
H2O before adding to organic waste
reactive, inorganic waste
reactive, inorganic waste
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CHEM 2315 Fall 2017
Potassium carbonate, 0.5 g
Dichloromethane, 10 m
Magnesium sulfate (anhydrous) ~1 g
_______
inorganic waste
flammable, halogenated waste
inorganic waste
Safety Notes
1. Borane-tetrahydrofuran complex (BH3-THF) is thermally unstable and must be kept cold.
BH3-THF is susceptible to hydrolysis, readily reacting with water to form hydrogen and boric
acid. It reacts readily with atmospheric moisture upon exposure to air resulting in a
decrease in purity.
2. 1-hexene: Flammable, keep away from heat. Keep away from sources of ignition. Do not
ingest. Do not breathe gas/fumes/ vapor/spray. Avoid contact with eyes and skin.
3. Tetrahydrofuran: Flammable, keep away from heat. Keep away from sources of ignition.
Always use fresh and do not store for long periods of time.
4. Hydrogen peroxide (30%) –strong oxidizer! Keep away from sources of heat. Causes severe
skin and eye burns. Handle with gloves. Wear your lab coat and goggles at all times. If any
peroxide comes into contact with your skin or eyes was with large amounts of water. It is
not uncommon for exposed areas to turn white. The color gradually will fade.
5. Sodium hydroxide is extremely corrosive. If you get it on your skin or eyes, wash with large
amounts of water.
Step 1 – Reaction set up
1. Collect together a magnetic stir bar and an orange septum then retrieve a clean/dry 25 or
50 mL round bottom flask from the oven. Handle with a glove or piece of folded up paper
towel as the glass will be extremely hot. Do not handle with your bare hands.
2. Add the magnetic stir bar to the round bottom flask then immediately cover with an orange
septum. Fold the septum over to hold in place.
3. When you return to the hood flush the flask with nitrogen by inserting the needle from the
nitrogen line through the center of the orange septum. It should not take much pressure to
pierce the septum. If it is too difficult move to a different position on the septum. Turn on
the nitrogen very slowly. Adjust the flow so that you observe slow bubbles in the glass
bubbler. Insert an open needle in the top of the septum to allow the nitrogen to replace any
air in the flask.
Step 2 – Hydroboration to form alkylborane
1. Measure 0.6 mL 1-hexene into a disposable 1 mL syringe fit with a needle. Inject the 1hexene into the round bottom flask by inserting the needle through the small center circle
of the septum. Immediately dispose of the entire syringe and needle in the sharps
container. You should NOT recap the needle or remove the needle from the syringe. Do
NOT dispose of the needles in the regular garbage.
2. Add 2 mL of anhydrous THF measured using a syringe fit with a needle.
3. Place the reaction mixture in an ice bath and begin to stir with the magnetic stir bar.
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CHEM 2315 Fall 2017
4. Notify your TA that you are ready for him/her to add 3.0 mL of 1 M borane-tetrahydrofuran
complex to your solution using a 5 mL disposable syringe.
5. After all of the BH3.THF has been added allow the mixture to stir for 5 min before removing
the ice bath. Allow the reaction mixture to stir for another 30 minutes at room
temperature. Anhydrous conditions are no longer necessary. You may remove the nitrogen
line and the rubber septum. Be sure to turn off the nitrogen and secure the needle from
your nitrogen line in the rubber stopper connected to the bubbler ring stand.
Step 3 – Oxidation to form alcohol
1. Add approximately 1 mL cold water slowly dropwise via a disposable plastic pipet. This
consumes any excess borane and creates H2 gas bubbles. If the bubbling becomes too
vigorous immerse the reaction mixture in an ice bath.
2. Add 0.6 mL 3 M NaOH via the disposable syringe (no needle necessary).
3. Add dropwise 0.6 mL of 30% hydrogen peroxide via disposable syringe, keeping the
temperature less than 40 °C. If the temperature is rising and approaching 40 oC then slow
the addition of peroxide and/or immerse the reaction in an ice/water bath. Important
Safety Note: The hydrogen peroxide you are using in today’s experiment is 10 times more
concentrated than the peroxide commonly used for disinfection (30% vs 3%). Wear gloves
and goggles! Avoid contact with skin and eyes! If you do get some on your skin rinse
thoroughly with water. Skin often turns white for a short time after exposure to peroxide.
4. After the addition of peroxide is complete stir for another 15 minutes.
Step 4 – Isolate the product
1. Cool the reaction mixture in an ice/water bath.
2. Add solid potassium carbonate until the solution is saturated (what does this mean?).
3. Pour the contents of the flask into a separatory funnel. Rinse with a few small (1-2 mL)
portions of diethyl ether to facilitate transfer of the product.
4. Extract with 3 x 2 mL of diethyl ether (Et2O). Recall: extract implies several separate actions:
First, add 2mL diethyl ether. You should observe two layers (look-up the density of diethyl
ether). Shake the separatory funnel, allow the layers to separate, drain the aqueous layer
into a labeled flask. Drain the organic layer into another dry labeled flask. Return the
aqueous layer to the separatory funnel and repeat this process two additional times.
5. Dry the combined organic layers with magnesium sulfate. Take care during this step to stir
well and allow the mixture to sit for 5-10 minutes to ensure that the solution is completely
dry. If you realize your sample is wet at a later stage you will be asked to repeat this drying
process.
6. Gravity filter into a pre-weighed round bottom flask. Your TA will demonstrate how to fold
the fluted filter paper used for a gravity filtration.
7. Concentrate the solution on the rotary evaporator. Be sure not to turn up the temperature
of the water bath too high too high. The ether boils at ~35 oC at atmospheric pressure.
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CHEM 2315 Fall 2017
8. Re-weigh the flask to determine the amount of product isolated. Calculate the percent
yield.
Step 5 – Characterize the product
1. Take an infrared spectrum of the product. What peaks would you expect to see that are
indicative of the product? Compare your product IR spectrum to that for the starting
material. Turn in a copy of your labeled IR spectrum with your report.
2. Prepare your sample for GC analysis by dissolving one drop of your product in 1 mL of
dichloromethane. Follow any additional instructions given by your TA. Note: your sample
must be COMPLETELY dry. Water destroys the GC columns. Analyze the GC to answer the
following questions: How many molecules are present in your product mixture? What is the
identity of these molecules? What is the ratio of the major products? Do you have any
starting material remaining in the product mixture? Turn in a copy of your GC trace with
your report.
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PRE-LAB INSTRUCTIONS
A. Title of the experiment.
B. Purpose/Goal of the experiment – this is a brief description of why you are performing the
experiment.
–
What is the purpose of a hydroboration/oxidation reaction and how does it work?
C. Provide a Hypothesis
–
Which one of the two possible alcohols do you predict will be the major product (refer
to figure 1)? Provide a brief explanation. Which product is the anti-Markovnikov
addition product?
D. Molecular structures and reactions:
–
Draw the reaction you will be performing along with the structures of all possible
products. Label products as a 1o, 2o or 3o alcohols.
Include the following in your notebook and record required exact amounts as you go:
1-hexene
BH3.THF
Hexanol isomers
MW (g/mol)
84.16
1M
102.17
d (g/mL)
0.67
NA
0.81
bp (oC)
63
NA
140-159
amount used/obtained (g or mL)
amount used/obtained (mol)
E. Mechanism – Provide a mechanism that accounts for the formation of both products shown
in Figure 1. Do your best, your effort, not accuracy, will be considered as part of the pre-lab
points.
F. Procedure – this should be the experiment written out in your own words. Diagrams can be
helpful to show what exactly you are trying to explain. Someone should be able to use your
procedure to complete the experiment without having the lab manual to follow.
G. Separation scheme – Begin with the 1-hexene + BH3 in THF and end with pure hexanol
isomers.
IN-LAB NOTEBOOK
§
§
Observations- record EXACT amounts of reagents used, observations, and any changes you
have made to the written procedure.
Calculations – calculate a percent yield for the conversion of hexane to the hexanol isomers.
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CHEM 2315 Fall 2017
POST-LAB REPORT
Students are encouraged to discuss results and conclusions to more fully understand the
experiment, however all written work should be done individually, even when working in
groups. This means that reports may contain similar ideas, but everything should be
presented in your own words and formatting.
After an experiment is complete and before the next lab-period, complete the exercise by
writing a 3-4 page typed laboratory report. The report should be a clear, concise reproduction
of your notebook entry. Reports must be written individually, even if the experiment is done
with a lab partner. Reports are due at least one week after the experiment and submitted to
your TA at the beginning of the next lab period.
The format should be as follows:
Formatting: 3-4 pages typed, 12pt font (Calibri, Times), double-spaced.
1. Title of the experiment. (2 pts)
2. Purpose/Goal of the Experiment and Your Hypothesis of the results. (3 pts)
a. Your hypothesis should be your honest opinion. Having the correct hypothesis will not
increase your grade. More often than not experimental hypotheses are wrong to some
extent. The goal is to explain your reasoning as why you predict what you do.
3. Brief Experimental Procedure and Observations. (10 pts)
a. This should be written in narrative format, avoiding personal pronouns such as. Explain
why you did certain important things in the reaction procedure (why was a catalyst or a
reflux necessary, why was it necessary to have anhydrous conditions, why was an
extraction or recrystallization or cooling necessary, etc).
4. Compiled Data and Relevant Calculations. (5 pt)
a. Report only relevant equations, final results, and any data in organized and labeled
tables.
5. Conclusion. (10 pts – 4pt for general conclusion, 6 pts for post–lab questions.)
a. The goal of the report and in general, the conclusions will (a) restate the goals of the
experiment, (b) briefly analyze the data obtained as it applies to the experiment, (d)
indicate any major problems or deviations from expected results, and (e) answers any
specific questions posed related to that experiment. What did some of your
observations indicate about the reactions that were occurring? How were impurities,
by-products, and unreacted starting materials removed during the work-up?
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CHEM 2315 Fall 2017
b. Specific instructions for each post-lab and for the reports will be included in the
experimental procedure posted on Canvas.
Chemical Structures: You may draw chemical structures by hand or use the wonderful chemical
drawing software, ChemDraw, available to you in HEB 1000 or via download through the
Marriott Library. The software is very easy to use, however a tutorial will be available on Canvas
under “Resources”. Chemistry majors are encouraged to familiarize themselves with ChemDraw
as it will be an invaluable tool throughout your academic and professional career.
Use your results as evidence to tell a story that culminates in your major conclusions. Be sure to
evaluate your confidence in the results. Important note here: any chemist can tell you that
following a written, published procedure is no guarantee that you will actually get the product
you set out to make. Therefore, treat all products isolated or synthesized as unknowns. Give
your percent yield and show how you did your calculation (indicating limiting reagent). Does
your data (mp, optical activity, IR, NMR) agree with the accepted (literature) values? Always be
sure to include the literature value and reference the source. Discuss the quantity and purity of
your product, and do an error analysis on your results if you had problems. Explain the possible
sources of a low yield or impurities and what you would do differently if you were to repeat the
experiment. You should emphasize concepts in your write-up that were emphasized in the lab
lecture. Your TA will also give you an indication each week of important concepts that you
should include in your write-up.
If you use a reference for your conclusion, be sure to indicate it.
The following items should be discussed in your report, try to include them in the narrative of
the report, with references to the specific question number. (feel free to include any additional
points you consider important):
1. Include the objective, reaction and correct mechanism. Label the products as the
“Markovnikov addition product” and the “Anti-Markovnikov addition product.
2. Draw the transition states leading to each of the two regioisomeric products of the
hydroboration reaction shown below:
3. Which of the two transition states is lower in energy and WHY? Be sure to include both an
electronic argument (optimal placement of partial charges) and a steric argument.
4. Treatment of 1-hexene with H2SO4 in H2O also forms an alcohol but the major product is 2hexanol. Provide a mechanism for this reaction and explain why 2-hexanol is the only
product formed. Identify the rate determining step in your mechanism and discuss the
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CHEM 2315 Fall 2017
stability of any intermediates formed. Provide an energy diagram for this reaction. Label
the axes, starting materials, product, intermediates, the Ea for each step and the ΔHo for the
overall reaction.
5. Which product did you isolate and how pure is it? Can you identify any of the impurities
that are present? Use your IR and GC results to back up your claim. Note – I am leaving out
specific instructions regarding the information you should include in this discussion. Use
what you have learned in previous experiments to determine which pieces of information
are useful. This should be a thorough discussion with claims backed up by evidence.
6. What was your percent yield? What could you do differently next time to improve on the
percent yield?
EXTRA CREDIT (2 pts): The oxidation of alkylboranes replaces with C-B bond with a C-O bond,
forming a new OH group with retention of configuration, that is, the OH group replaces the BR2
group in the same position relative to the other three groups on carbon. Provide a mechanism
for the oxidation of the trialkylborane below by alkaline hydrogen peroxide. You must show
the stereochemistry of the molecule in each step.
Table of Retention Times for the Dehydration of Methylcyclohexanol
Molecule
, 1-hexene
dichloromethane used to dilute your GC samples
diethyl ether, Residual from work up of your
product, not completely removed on the rotary
evaporator
Retention time, min.
0.605 (1st peak, often small, just to the
left of the large solvent peak)
0.616-0.666 (very large peak)
~1.4 – often quite large
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CHEM 2315 Fall 2017
2.66, 3.07
Some students have observed one or two peaks
that may correspond to the borate esters. These
species form after the addition of HOOH and NaOH
to the alkyl borane. They should be hydrolyzed to
the free alcohol and B(OH)3, but in some reactions
this hydrolysis appears to have been incomplete.
, 2-hexanol
3.32
3.80
, 1-hexanol
* Note: Your retention times will most likely not match exactly. Pay attention to the order with
which the peaks appear
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