Hexavalent
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Acetic Acid
I've calculated that for a reaction I need 19.81g of glacial (99%) acetic acid, but I only have access to vinegar (5%) ATM. Can anyone please
enlighten me on how much I now need to use?
Many thanks.
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ScienceSquirrel
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Around 400ml but concentration may be an issue.
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Hexavalent
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Thanks, how did you do that calculation?
I've recently titrated my vinegar against a base standard and found it to be 5.07% BTW.
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Bot0nist
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You can not always just substitute GAA with distilled white vinegar. If you can provide a little more information on your intended reaction, perhaps
we can be of more help.
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Hexavalent
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I was intending to do a fischer esterification with IPA to make isopropyl acetate (smells like fruit) . . . but would the masses of water in the
vinegar inhibit the reaction?
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Bot0nist
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Let me check the literature, but often times esterifications need close to anhydrous conditions.
Maybe distill your vinegar, dry with heaps of Epson salt and then dilute with DCM, and re-distill and freeze out your GAA as per Sedits techniques.
This will be a bitch if starting from 5% AcOH though. Try and get some stronger acetic to start with. Try photography stores.
[Edited on 13-1-2012 by Bot0nist]
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ScienceSquirrel
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It would.
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Hexavalent
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Damn, perhaps I could use anhydrous sodium acetate instead?
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ScienceSquirrel
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That might work, with lots of sulphuric acid.
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Hexavalent
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How much, I know its catalytic (protonates the alcohol to make it electrophilic enough for the acetate to attack) would I need in this case?
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ScienceSquirrel
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Enough to convert the sodium acetate to acetic acid plus enough to catalyse the reaction.
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entropy51
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Quote: Originally posted by Bot0nist  | | Let me check the literature, but often times esterifications need close to anhydrous conditions.{Edited on 13-1-2012 by Bot0nist]
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Often, yes, but not always. Ethyl acetate, for example, can be made in aqueous reactions using ethanol,
sodium acetate, water and H2SO4. That one has been discussed on this forum and a variation using aqueous HCl is described in one of the organic lab
manuals in the forum library, either Norris or Noyes, I can't recall which. Esters of inorganic acids, such as ethyl chloride, are likely to require
anhydrous conditions however.
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UnintentionalChaos
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The fisher esterification is an equilibrium reaction. If you remove the product as it forms, you can increase the yield according to Le Chatlier's
principle. But without this "reactive distillation" technique, using aqueous acetic acid will do very little. The rate of acid catalyzed hydrolysis of
ethyl acetate to ethanol and acetic acid will predominate over the rate of acid catalyzed formation of ethyl acetate. A small amount will be formed by
a simple reflux, but will probably be very hard to isolate from the large amount of reaction mixture.
Entropy51 mentions ethyl chloride. This particular compound does not need particularly dry conditions. The product boils well below the reflux
temperature of the reaction mixture and flash boils out where it can be condensed. With heavier alcohols, the conditions need not be anhydrous either.
However, they are fairly concentrated and acidic to minimize the activity of the water.
http://www.orgsyn.org/orgsyn/prep.asp?prep=cv1p0025
[Edited on 1-15-12 by UnintentionalChaos]
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