Alcohols
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Why is Na2Cr2O7 added to butan-1-ol, and not the other way around, and why is it possible to distil out the product as it is formed?
Corrie writes ...
In the preparation of butanal from butan-1-ol, the oxidising agent, sodium dichromate, is added slowly to the butan-1-ol so that the alcohol is in excess. If the butan-1-ol was added to the dichromate, the oxidising agent would be in excess and the first product formed, butanal, could be oxidised further to butanoic acid before it escapes from the mixture.
The butanal can be distilled off as it is formed because it has a lower boiling point (76 C) than either the starting butanol (117 C) or any butanoic acid (166 C) that might be formed.
The reason butanal has a much lower boiling point compared to the other two is that it lacks an -OH group, so there is no hydrgogen-bonding possible between butanal molecules.
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updated: 09 March 2007
