JefferyH
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Boiling off water formed by reaction of hydroxide with carbonyl?
If my substrate before deprotonation has a higher bp than water, and is dissolved in another high boiling point organic solvent, is it possible for me
to boil off the formed water by its reaction with a hydroxide? Or is the water in some sort of locked equilibrium with the enolate, that prevents it
from being boiled off?
If my organic solvent is not miscible with water and the formed enolate is soluble in the organic phase, then the water would naturally separate out
into a separate phase, allowing it to be boiled off, would it?
Edit:
If phase separation even occurs, I could just decant it off. A better question now is, does phase separation occur in such an instance?
[Edited on 17-5-2014 by JefferyH]
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blogfast25
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Quote: Originally posted by JefferyH  |
If phase separation even occurs, I could just decant it off. A better question now is, does phase separation occur in such an instance?
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That depends simply on the organic solvent, doesn't it? If it isn't miscible with water and your reaction product is soluble in the organic phase,
then yes, separation of phases will occur and simply using a separation funnel will allow to separate organic phase + reaction product from watery
phase.
[Edited on 17-5-2014 by blogfast25]
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BromicAcid
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To avoid cooking your mixture too hard, especially with something like an inorganic hydroxide (you didn't say this but assuming the worst), check out
a Dean-Stark trap. In my experience you usually add some toluene to your mixture, toluene forms a low boiling azeotrope with water. The
water/toluene azeotrope leaves the system, condenses in your condenser and then falls down. The Dean-Stark trap catches this and the water sinks to
the bottom, the toluene overflows the top and goes back to your system to scavenge more water. The bottom of the Dean-Stark trap can be graduated to
let you measure how much water is coming off so you can see when your reaction is complete. Pretty common setup for a reaction that produces
by-product water.
If water is completely immisicible and your reactants, products are resistant to hydrolysis then yes, you could run the reaction and then remove the
aqueous phase from the mixture, sometimes this is easy, sometimes more difficult. When it is more difficult the water droplets cling to the walls or
refuse to coalesce (emulsion) so it's hard to get that last little bit.
Without an azeotrope to drive it, you might be impressed how difficult it can be to remove the water from a solution by heat alone. Water has a very
high specific heat and heat of vaporization afterall, one of the reasons people usually use the azeotrope method.
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