Question

1) when mixing 1-pentanol with glacial acetic acid and sulfuric acid to form an ester. Which reagent is the exess? and why is this reagent excess? why not have an equimolar reaction?

2) which 2 signals in the IR spectra can be used to differentiate between the starting alcohol and the ester product? Give specific bonds and waves numbers.

Please explain.

Answer 1

Reaction product is pentyl acetate.

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This reaction is done in excess of n-pentanol as it's cheaper than acetic acid. Usually 4-5 equivalents of excess alcohol would be enough for reaction to drive it to completion according to Le Chatlier principle.

Predicted IR spectral values for alcohol (n-pentanol) and the ester (n-pentyl acetate):

n-pentanol will have a stretching frequency of broad peak for OH group around 3000Cm^-1

^​​Whereas the ester, n-pently acetate will have a stretching frequency for C=O group around 1720 Cm^​-1