Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: katehovey on April 23, 2007, 02:09:41 PM
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In the Preparation of 3-methyl -1-butyl ethanoate why is the reflux time so long (1.5 hours)? Is it simply because the reaction is so slow?
Also, it is then poured onto ice. Is this to get a more distinguished two layers? and it is poured onto ice rather than just water to avoid revearsing the reaction?
It is then washed with diethyl ether, then iron (II) sulfate solution and finally sodium carbonate solution. Why is this? Is there a reason why 3 different chemicals are used to wash it?
Is the iron (II) sulphate added to remove any peroxides formed by the diethyl ether?
I then added magnesium sulfate to dry my product and it was left for ten minutes. Is the reason it is left for 10 minutes to assure all the water had been absorbed?
Thanks.
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In the Preparation of 3-methyl -1-butyl ethanoate
From what?
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Sorry, from 3-methylbutan-1-ol (isoamyl alcohol) and ethanoic acid, with concentrated sulfuric acid as a catalyst.
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In the Preparation of 3-methyl -1-butyl ethanoate why is the reflux time so long (1.5 hours)? Is it simply because the reaction is so slow?
Exactly. Fischer esterifications are generally slow processes because they are easily reversible, so the reaction will reach equilibrium instead of speeding to completion like some other reactions.
Also, it is then poured onto ice. Is this to get a more distinguished two layers? and it is poured onto ice rather than just water to avoid revearsing the reaction?
Exactly. Esters are succeptible to hydrolysis, so you want it to be in the presence of only cold water so that your esters (which you spent 1.5hrs making) don't hydrolyze back to your starting material.
It is then washed with diethyl ether, then iron (II) sulfate solution and finally sodium carbonate solution. Why is this? Is there a reason why 3 different chemicals are used to wash it?
Is the iron (II) sulphate added to remove any peroxides formed by the diethyl ether?
You extract with diethyl ether to isolate your ester from the aqueous layer (containing water soluble contaminants like the sulfuric acid and acetic acid). You are correct that washing with iron (II) sulfate is to decompose any explosive peroxides. The sodium carbonate wash helps remove any traces of acid left in the organic phase (question for you: how does sodium carbonate do this? why not use another base like NaOH?)
I then added magnesium sulfate to dry my product and it was left for ten minutes. Is the reason it is left for 10 minutes to assure all the water had been absorbed?
Yup. Presumably, the last step will be a distilation. If you have water present when you distill your ester, the water will hydrolyze your ester (especially since you will be heating your ester during the distilation).
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Just as a guess. Does it react with the acid to produce NaOH and CO2(g)? And NaOH isn't used because it would produce extra H2O which wants to be avoided because of the reverse hydrolysis.
That's just a guess - I'm just a first year student, and have not had much input with the experiment I've been doing. This is my final one for the year though!
Kate
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Nope. Think in terms of weak acids and conjugated bases. You use CO32-.