Organic Chemistry I Lab 5&6

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Exp #
Date:
Lab Partner
Title: TLC and flash column chromatography
1. Abstract and Purpose: (2 point).
In this laboratory session, the reduction of fluorenone to fluorenol will be carried out, using
sodium borohydride as reducing agent. The reaction will be monitored by using thin-layer
chromatography with time reactions up to 180 seconds. The crude product will be purified
using flash column chromatography, comparing the Rf of the purified product to that of
the crude product.
2. Balanced equation: (2 point)
4 NaBH4
CH3OH
Fluorenol
Fluorenone
3. Reagent Table (Add more rows when needed) (3 points)
Name
M.W.
(g/mol)
Density*
(g/mL)
M.P.*
(°C)
B.P.*
(°C)
Amount
(grams
or mL)
Fluorenone
180.21
–
81-85
342
0.5 g
May cause severe eye
damage and irritation.
Toxic if swallowed.
May cause skin
irritation.
Moles
Hazards/Precautions
Sodium
borohydride
37.83
–
>300
>400
0.1 g
Methanol
32.04
0.792
–
65°C
10 mL
–
Flammable, volatile.
Dichloromethane
84.93
1.325
–
40
6 mL
–
Flammable, volatile.
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Exp #
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4. Calculations: Shown each calculation for moles of reagents, limiting reagent,
theoretical yield and percent yield. (4 points)
Calculating moles of reagents:
𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑓𝑙𝑢𝑜𝑟𝑒𝑛𝑜𝑛𝑒 = 0.5 𝑔 ×
1 𝑚𝑜𝑙
= 0.0028 𝑚𝑜𝑙𝑒𝑠
180.21 𝑔
𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑠𝑜𝑑𝑖𝑢𝑚 𝑏𝑜𝑟𝑜ℎ𝑦𝑑𝑟𝑖𝑑𝑒 = 0.1 𝑔 ×
1 𝑚𝑜𝑙
= 0.0026 𝑚𝑜𝑙𝑒𝑠
37.83 𝑔
Determining limiting reagent:
𝑚𝑜𝑙𝑒𝑠 𝑓𝑙𝑢𝑜𝑟𝑒𝑛𝑜𝑛𝑒 = 0.1 𝑔 ×
1 𝑚𝑜𝑙 𝑁𝑎𝐵𝐻4 4 𝑚𝑜𝑙𝑒𝑠 𝑓𝑙𝑢𝑜𝑟𝑒𝑛𝑜𝑛𝑒
×
= 0.011 𝑚𝑜𝑙𝑒𝑠
37.83 𝑔
1 𝑚𝑜𝑙 𝑁𝑎𝐵𝐻4
Excess reagent: sodium borohydride
The limiting reagent is fluorenone
Calculating theoretical yield:
𝑇ℎ𝑒𝑟𝑒𝑜𝑡𝑖𝑐𝑎𝑙 𝑦𝑖𝑒𝑙𝑑 = 0.0028 𝑚𝑜𝑙𝑒𝑠 𝑓𝑙𝑢𝑜𝑟𝑒𝑛𝑜𝑛𝑒 ×
1 𝑚𝑜𝑙 𝑓𝑙𝑢𝑜𝑟𝑒𝑛𝑜𝑙
182.22 𝑔
×
1 𝑚𝑜𝑙 𝑓𝑙𝑢𝑜𝑟𝑒𝑛𝑜𝑛𝑒
1 𝑚𝑜𝑙
𝑇ℎ𝑒𝑟𝑒𝑜𝑡𝑖𝑐𝑎𝑙 𝑦𝑖𝑒𝑙𝑑 = 0.51 𝑔 𝑓𝑙𝑢𝑜𝑟𝑒𝑛𝑜𝑙
The theoretical yield is 0.51 g fluorenol
The actual yield is
Calculating Percent yield:
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Exp #
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Lab Partner
Reaction percent yield is
5. Procedure, Observations and Data
•
Procedure (4 point)
Observations and Lab Data (4 point)
Six different premade TLC plates are
Report all observations and all data that you collect in the
prepared, drawing the spotting line about 5-7
lab here
mm from the bottom of the plate. Each plate
will be used to monitor the reaction at 0, 15,
30, 60, 120, and 180 s.
•
Each mark, in time, is separated by 5 mm.
The spot at time 0 corresponds to fluorenone.
•
0.5 g of fluorenone are weighed in a 50 mL
round-bottom flask and 10 mL of ethanol are
added, stirring until all of the solid dissolves.
•
Using a micropipette, this solution is
“spotted” into the TLC plate in the mark 0 s.
•
0.1 g of sodium borohydride are
weighed and added to the solution
above, under constant stirring.
•
At each of the designated time intervals
the solution is spotted into to the TLC
plate.
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Exp #
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Lab Partner
•
Once all of the solutions are spotted in
the plate, it is eluted using
dichloromethane in a developing
chamber. About 5 mL would suffice, as
long as it does not reach the spots.
•
Let the TLC develop and mark the
solvent front, to determine the Rf of
each spot afterwards.
•
The reaction mixture is transferred to a
50 mL Erlenmeyer flask and 5 mL of
water are added.
•
The solution is cool down in an ice bath
and the obtained solid vacuum filtered.
•
The crystals are weighed to determine
the actual yield of the reaction
For column chromatography:
•
15 g of silica gel are weighed and
transferred to a 50 mL Erlenmeyer
flask
•
15 mL of solvent mixture are
added, forming a slurry mixture.
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•
The slur is carefully added into the
column, using a funnel.
•
The excess silica on the walls of the
column is washed down with a
pipette and a little more of solvent.
•
The sides of the column are gently
tapped to remove air bubbles.
•
A thin layer of sand is added to the
top of the column, eluting a bit of
the solvent until the sand is dry but
not the silica gel.
•
0.2 g of the crude product is added
to the top of the column and the
walls of the column washed down
with a pipette and a bit more of
solvent.
•
5 mL of solvent mixture is carefully
added to the top of the column and
then slowly drained.
•
The fractions eluting from the
column are collected ach 8 mL of
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Exp #
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solution. Running TLC and
comparing it to the pure product.
6. Conclusions and discussions (4 points)
7. References: (1 point)
8. Image of your lab notebook. (3 point)
I reserve the right to modify points on this template at any time.