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haloform reaction


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A reaction for producing haloforms from methyl ketones. An example is the production of chloroform from propanone using sodium chlorate(I) (or bleaching powder):CH3COCH3+3NaOCl → CH3COCl3+3NaOH The substituted ketone then reacts to give chloroform (trichloromethane):CH3COCCl3+NaOH → NaOCOCH3+CHCl3 The reaction can also be used for making carboxylic acids, since RCOCH3 gives the product NaOCOR. It is particularly useful for aromatic acids as the starting ketone can be made by a Friedel-Crafts acylation.

CH3COCH3+3NaOCl → CH3COCl3+3NaOH

CH3COCCl3+NaOH → NaOCOCH3+CHCl3

The reaction of methyl ketones with sodium iodate(I) gives iodoform (triiodomethane), which is a yellow solid with a characteristic smell. This reaction is used in the iodoform test to identify methyl ketones. It also gives a positive result with a secondary alcohol of the formula RCH(OH)CH3 (which is first oxidized to a methylketone) or with ethanol (oxidized to ethanal, which also undergoes the reaction).

Subjects: Chemistry.


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