How Haloform reaction proceed ?
The general reaction is represented as
The CH3 carbon is lost as CHX3 and the remaining part exists as acid salt, which can be acidified to liberate free acid.
The structural feature essential in the compound to show haloform reaction is that any of the following moieties should be present in the molecule attached to some electron−withdrawing group or electron donating group by +I only.
or any other grouping that can be converted to any of the above moieties.
The mechanism of the reaction can be outlined as:
The reaction has 3 important steps. Step I is the oxidation, caused by mild oxidizing agent (hypo halite ion). The second step is base−promoted halogenation and the third step is cleavage of C–C bond.
Some of the compounds which responds positively to iodoform test are
CH3CH2OH (only primary alcohol)
, , (secondary alcohols)
(only aldehyde) ,, , (ketones)
,, , (after heating with OH–)
The compounds that respond negatively to iodoform test are
, , , ,
The chemical properties of an alcohol, ROH, are determined by its functional group, –OH, the hydroxyl group. Reactions of an alcohol can involve the breaking of either of two bonds: the C-- OH bond, with removal of the –OH group; or the O--H bond, with removal of –H. Either kind of reaction can involve substitution, in which a group replaces the –OH or –H, or elimination, in which a double bond is formed. Differences in the structure of R cause differences in reactivity, and in a few cases even profoundly alter the course of the reaction. We shall see what some of these effects of structure on reactivity are, and how they can be accounted for. Check out Chemistry Formulas and NCERT Solutions for class 11 Chemistry prepared by Physics Wallah.
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