Magpie
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benzilic acid
Per Brewster 4g of benzil were converted to benzilic acid:
benzil rearrangement
4g of benzil, 5g of KOH, 10mL of ethanol, and 10 mL of water were added to a 100mL RBF and set up for reflux using a condenser and a heating mantle.
The reactants turned black and warmed up right away. However, I did cover the RBF with an insulation blanket. A crusty raft formed that remained
until the end of the 15 minute heating period. I didn't pulverize the benzil before adding it to the flask. I probably should have to facilitate
dissolution. However, I suspect this raft is some contaminant in the benzil.
apparatus
The hot products (minus the raft) were poured into a 250mL beaker and 100mL of water was added. Then 1g of activated charcoal was added to decolorize
the resulting carmel brown solution.
K benzilate before decolorization
This removed most of the color but a yellow tinge remained as can be seen below:
K benzilate decolorized
The yellow translucent filtrate was poured into 15mL of con HCl on 75mL of crushed ice in a second beaker. Off-white crystals formed right away as
can be seen below:
benzilic acid crystals
The crystals were retrieved by vacuum filtration using a 7cm Buchner funnel then spread on a porous plate to dry. The resulting solids were
off-white. Yield was 2.2g for a %yield of 42.8%.
A small portion was recrystallized from boiling water. A brown contaminant that did not dissolve formed while dissolving the small portion. This was
removed by filtration prior to the crystallization. The dried crystals were pure white. The melting point was determined to be 150C, in agreement
with my Lange's handbook for benzilic acid.
[Edited on 9-3-2012 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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bfesser
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Another nice writeup, Magpie. Thankyou for taking the time to compile it. Great work on the photographs, as well. It's nice to see other people
taking photos without using a flash. Time for me to find that bottle of benzil I've been saving with no particular reactions in mind.
[Edited on 3/9/12 by bfesser]
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Magpie
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Thank you, bfesser. Yes, I have a Canon PowerShot SD450 and I set it on "macro" and "no" flash. It seems that there is nearly always enough ambient
light that the camera does not call for the flash.
[Edited on 9-3-2012 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Endimion17
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Nicely done, and quite professionally looking, I might add. 
It seems to me that you've also managed to adjust white balance correctly.
There's nothing worse than a chemist taking closeup photos with no macro, a flash and bad white balance. Those things are mandatory basics for anyone
using a camera for documenting stuff and not just taking duckface photos for their myspace/facebook profiles. 
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Magpie
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Quote: Originally posted by Endimion17  | Nicely done, and quite professionally looking, I might add.
It seems to me that you've also managed to adjust white balance correctly.
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Thanks. I wouldn't even know how to adjust the "white balance." I'm just taking what the camera gives me.
The single most important condition for a successful synthesis is good mixing - Nicodem
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ScienceSquirrel
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Thread Pruned
13-3-2012 at 05:36 |
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