The Haloform reaction given by only methyl ketones because it can form enolate ions by removal of alpha hydrogen and which is stabilised by de localisation of electron with carbonyl carbon therefore the alpha carbon can be bonded with three halogens atoms .
Tuesday, January 28, 2020
Which alcohol does not give iodoform test?
Ethanol and other terminal 2°alcohol like Iso propyl alcohol , butan-2-ol, Petan-2-ol etc gives Iodoform test positive other alcohol does not give Iodoform form reactions .
Why does ethanol cause Haloform (Iodoform) reactions?
Ethanol gives Iodoform test positive because, under the reaction conditions it oxidised to ethanal (acetaldehyde) which is the only aldehyde that undergoes Haloform reaction.
What is a haloform reaction?
The oxidative cleavage
of Methyl ketones as well as acetaldehyde and 2° terminal alcohol into into a
carboxylate anion and a trihalomethane (haloform) by the reaction of one
of halogen in the presence of strong alkali like NaOH or KOH is known as Haloform
reaction.
The respective halogen
can be chlorine, bromine or iodine.The methyl group of a methyl ketone is converted
into an trihalomethane by multiple subsequent steps, that involve
formation of an intermediate enolate anion.
Related Questions:
Chlorination of ethane to ethyl chloride is more practicable than chlorination of n-Pentane to 1-Chloropentanc. Why ?What is the chemical formula of substances which gives a positive iodoform test?
The ketones containing terminal -COCH3 group generally gives positives Iodoform test. For example butan-2-one, Pentan-2-one, Acetone etc.
It is Most common test for terminal methyl ketones but Iodoform also given by terminal 2° alcohols like Ethanol (CH3CH2OH), Propan-2-ol (CH3CH2(OH) CH3 ), Butan-2-ol, Pentan-2-ol etc
Aldehyde does not gives Iodoform test positive except CH3CHO.
Methylene active hydrogen containg ketones also gives positive Iodoform test for example pentane-2,4-dione , Chatechol, and resorcinol etc
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