[Doom91]

Does anyone know why the iodoform reaction does not work for ethyl ketones

[azmanam]

what are the differences between methyl and ethyl ketones?  where do the mechanisms for the two reactions differ?  why do you think one continues, but the other does not?

to be clear, it's not that you can't iodinate an ethyl ketone, its that you won't get the carboxylic acid product... you can't do an 'iodoform test' on an ethyl ketone.

[Doom91]

Dear azmanam,
 Yes , I am asking exactly why the iodoform test does not work for ethylketone but work for methylketone , the base extract the proton in the reaction to form the negatively charged species. Oh it is because the beta hydrogen is not that acidic and the chemical species produced would not be stable for it exist for the period of time that required for it to react with iodine molecule, while the alpha hydrogen would be more acidic and would exist for an amount of time required for it to react with iodine molecule

[Morderkerl]

If you look at the mechanism you will see that the initial step is a nucleophilic attack on the carbonyl carbon by the hydroxide ion. In the next step C-C bond cleavage occurs and the :CX3- departs. This can occur because the :CX3- anion is unusually stable, due to the negative charge that is dispersed by the three electronegative halogen atoms. When you look at ethyl ketone the carbanion that would form does not have the ability to stabilize the negative charge, since the halogens are not directly bonded to the carbon bearing the negative charge. and for this reason iodoform reactions does not work for ethyl ketones.

[Morderkerl]

When you look at ethyl ketone the carbanion that would form does not have the ability to stabilize the negative charge, since the halogens are not directly bonded to the carbon bearing the negative charge. and for this reason iodoform reactions does not work for ethyl ketones.

sorry, two halogens are bonded to the a-carbon.

[alexjaco]

Look at the mechanism, it wouldnt be the iodoform reaction if it was an ethyl chain.  The carbon of the iodoform comes from the methyl of the ketone