Why does methyl ethanoate not give iodoform test while ethyl ethanoate does?

Why does methyl ethanoate not give iodoform test while ethyl ethanoate does?


2 Answers

Har Simrat Singh
42 Points
10 years ago

iodoform test for esters is the test given by its products on hydrolysis

methyl ethanoate gives methanol and ethanoic acid 

etyl ethanoate gives ethanol and ethanoic acid 

fuirther methanol on oxidation gives formaldehyde and ethanol gives ethanal so ethanal and hence ethanol gives positive iodoform test therefore ethyl ethanoate responds whereas methyl ethanotae doesnt

yours katarnak Suresh
43 Points
10 years ago

The chemistry of the triiodomethane (iodoform) reaction

What the triiodomethane (iodoform) reaction shows

A positive result - the pale yellow precipitate of triiodomethane (iodoform) - is given by an aldehyde or ketone containing the grouping:

"R" can be a hydrogen atom or a hydrocarbon group (for example, an alkyl group).

If "R" is hydrogen, then you have the aldehyde ethanal, CH3CHO.

  • Ethanal is the only aldehyde to give the triiodomethane (iodoform) reaction.

  • If "R"is a hydrocarbon group, then you have a ketone. Lots of ketones give this reaction, but those that do all have a methyl group on one side of the carbon-oxygen double bond. These are known as methyl ketones.

Equations for the triiodomethane (iodoform) reaction

We will take the reagents as being iodine and sodium hydroxide solution.

The first stage involves substitution of all three hydrogens in the methyl group by iodine atoms. The presence of hydroxide ions is important for the reaction to happen - they take part in the mechanism for the reaction (not required for UK A level).

In the second stage, the bond between the C I3 and the rest of the molecule is broken to produce triiodomethane (iodoform) and the salt of an acid.

Putting all this together gives the overall equation for the reaction:

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