<P> 2 . When the α (alpha) position has been exhaustively halogenated, the molecule undergoes a nucleophilic acyl substitution by hydroxide, with CX being the leaving group stabilized by three electron - withdrawing groups . In the third step the CX anion abstracts a proton from either the solvent or the carboxylic acid formed in the previous step, and forms the haloform . At least in some cases (chloral hydrate) the reaction may stop and the intermediate product isolated if conditions are acidic and hypohalite is used . </P> <P> Substrates are broadly limited to methyl ketones and secondary alcohols oxidizable to methyl ketones, such as isopropanol . The only primary alcohol and aldehyde to undergo this reaction are ethanol and acetaldehyde, respectively . 1, 3 - Diketones such as acetylacetone also give the haloform reaction . β - ketoacids such as acetoacetic acid will also give the test upon heating . Acetyl chloride and acetamide don't give this test . The halogen used may be chlorine, bromine, iodine or sodium hypochlorite . Fluoroform (CHF) cannot be prepared by this method as it would require the presence of the highly unstable hypofluorite ion . However ketones with the structure RCOCF do cleave upon treatment with base to produce fluoroform; this is equivalent to the second and third steps in the process shown above . </P> <P> This reaction forms the basis of the iodoform test which was commonly used in history as a chemical test to determine the presence of a methyl ketone, or a secondary alcohol oxidizable to a methyl ketone . When iodine and sodium hydroxide are used as the reagents a positive reaction gives iodoform, which is a solid at room temperature and tends to precipitate out of solution causing a distinctive cloudiness . </P> <P> In organic chemistry, this reaction may be used to convert a terminal methyl ketone into the analogous carboxylic acid . </P>

Propan 2 ol on reaction with iodine and sodium hydroxide gives