Rich_Insane
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Amides from Nitriles
The procedure I am referring to comes from the book "Vogel's Textbook of Practical Organic Chemistry, 5th edition"; The experiment number is
6.167, and the page number is 1080. This procedure details the preparation of an aromatic acid amide from an aromatic nitrile. Unfortunately,
my organic chemistry is rusty, and I've got a few unresolved questions before I undertake the procedure.
What I'm trying to do is recover the amide from a batch of "tar" that I had previously prepared via an (attempted) isomerization of the aldoxime to an
amide. Unfortunately, I was using an impure catalyst and my reaction conditions were less than ideal. I ended up with a brown, viscous goo that did
not resemble the amide at all (though I could see white crystalline shards forming in the tar). Recently, a friend of mine has been exploring the
synthesis of nitriles via "H. Veisi, Synthesis, 2010, 2631-2635" (preparation of nitriles from aldehyde using TCCA swimming tablets
and aq. NH3) and found that his "nitrile" was similar in appearance to my horrendous goo. Upon utilizing this procedure from Vogel, he was able to
recover a white precipitate that readily rearranged to an amine via Hofmann rearrangement. Unfortunately, his results have been inconsistent.
My questions are these: First off, I'd like to know what an appropriate molar equivalent of NaOH would be for this reaction. My friend uses 1 M NaOH,
but I fear that high concentrations of NaOH could push the nitrile all the way to the carboxylic acid (undesired). If I understand the reaction
mechanism correctly, what happens is that the OH- anion partakes in a nucleophilic attack on the cyano-carbon (which is slightly electronegative).
This leads to the formation of an imine, which readily reacts with water. The resulting intermediate is prone to forming the amide, because the
electronegative oxygen will tend to pull electrons and form the carbonyl double bond. I am confused how H2O2 proceeds to cease this reaction at the
amide step. Is it just a matter of [OH] concentration that determines whether there is a nucleophilic attack on the amide? Reviewing the mechanism, I
find that after this nucleophilic attack on the amide, the NH2 group is kicked off as an anion. The NH2 anion slowly (this is a slow stop) proceeds to
tear a proton off of the intermediate to form the carboxylic acid (and ammonia as a byproduct). Does this mean that I should use an excess of nitrile?
The ideal situation would be to perform an experiment with different NaOH concentrations, but I only have a little "nitrile." I don't even know for
sure if there is nitrile present.
My final question is less pressing. I don't have access to 30% H2O2, and I'd rather not work with it at the moment. I plan to perform this reaction on
the 10-50 mmol scale anyways. Will 3% H2O2 significantly impair the speed of the reaction? I have seen people slowly boiling off water from drug store
H2O2, so I think it might be possible for me to reach 6-9%, but my equipment (a cooking stove, essentially) is not suitable for boiling for a
prolonged period of time.
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solo
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Reference Information
THE TRANSFORMATION OF NITRILES INTO AMIDES
USING SODIUM PERCARBONATE
George W. Kabalka , Sunil M. Deshpande
SYNTHETIC COMMUNICATIONS
20(10), 1445-1451 (1990)
Abstract
The usefulness of sodium percarbonate, an inexpensive,
safe and easily handled reagent for the transformation
of nitriles into amides was investigated. Aromatic nitriles
lacking ortho-substituents and heteroaromatic nitriles were
efficiently transformed into amides; while ortho-substituted
aromatic nitriles and aliphatic nitriles gave moderate yields
of the corresponding amides.
Note:
Sodium percarbonate is produced industrially by reaction of sodium carbonate and hydrogen peroxide, followed by crystallization. Also, dry sodium
carbonate may be treated directly with concentrated hydrogen peroxide solution. World production capacity of this compound was estimated at several
hundred thousand tonnes for 2004.[3] It can be obtained in the laboratory by treating the two substances in aqueous solution with proper control of
the pH[4] or concentrations.
.....source,
http://en.wikipedia.org/wiki/Sodium_percarbonate
Attachment: THE TRANSFORMATION OF NITRILES INTO AMIDES USING SODIUM PERCARBONATE.pdf (216kB)
This file has been downloaded 1453 times
[Edited on 18-7-2013 by solo]
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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Rich_Insane
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Thanks solo! That is very interesting. I found another reference using K2CO3/DMSO. I'm not sure what journal it is from.
Here is the link: Efficient Conversion of Nitriles to Amides with Basic Hydrogen Peroxide in Dimethyl Sulfoxide
Is percarbonate commercially available (to the OTC experimenter)? I probably cannot prepare it myself because I do not have concentrated H2O2, but I
might be able to purchase it.
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watson.fawkes
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Many chlorine-free laundry bleaches use
percarbonates. Check the MSDS to see what else is in these formulations.
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solo
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.....as per watson.fawkes suggestion i found this,
Wood Deck Cleaner and Stain Remover
Sodium Percarbonate
80.0
Soda Ash
10.0
Sodium Tripolyphosphate
10.0
Total
100.0
Institutional Laundry Bleach
Sodium Percarbonate
80.0
Soda Ash
20.0
Total
100.0
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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Rich_Insane
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Wonderful. This means that I won't be needing that pesky conc. H2O2.
On another note, I boiled the infamous "goo" with water last night (it is water insoluble) to melt the goo and transfer it to a beaker... I am
noticing a huge population of colorless needle-like crystals. I can't be certain that this is the desired amide (the reaction that this batch came
from intended to produce amide from oxime, and previous trials demonstrated success albeit with low yield), but I need to separate it from the goo.
Normally, I'd just heat water to boiling and use the water as a solvent for the amide, which is soluble in hot water.
Unfortunately, this goo melts in boiling water, and it has a tendency to float on water. How should I go about isolating the crystalline material from
the suspect nitrile? I was thinking of boiling with water and decanting bit by bit the water (replacing water when it runs too low) and then purifying
the crude crystals via recrystallization from water... Any other suggestions?
Oh, and for those of you interested, I found that sodium percarbonate is readily available on Ebay for a relatively low price ($2.99 for 1/2 lb +
S&H).
[Edited on 19-7-2013 by Rich_Insane]
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solo
International Hazard
Posts: 3967
Registered: 9-12-2002
Location: Estados Unidos de La Republica Mexicana
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.....the oily stuff wont go through a filter as easily as hot water, do this and recover the water and allow to cool to get the amide....check the MP
to assure youself you have the amide desired.....solo
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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solo
International Hazard
Posts: 3967
Registered: 9-12-2002
Location: Estados Unidos de La Republica Mexicana
Member Is Offline
Mood: ....getting old and drowning in a sea of knowledge
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Reference Information
Direct Oxidative Conversion of Alcohols, Amines, Aldehydes, and Benzyl Halides into the Corresponding Nitriles with Trichloroisocyanuric Acid
in Aqueous Ammonia
H. Veisi
Synthesis
2010, 2631-2635.
Attachment: Direct Oxidative Conversion of Alcohols, Amines, Aldehydes, and Benzyl Halides into the Corresponding Nitriles with Tric (115kB)
This file has been downloaded 1981 times
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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