Triodomethane Test
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description
for cambridge a-level A2 syllabus
Transcript of Triodomethane Test
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TRI-IDOMETHANE ContentTri-iodomethaneLearning Outcome(a) Deduce the presence of a CH3CH(OH) group in an alcohol from its reaction with alkaline aqueous iodine to form tri-iodomethane.(b) Describe the reaction of CH3CO- compounds with alkaline aqueous iodine to give tri-iodomethane.
AlcoholAlcohols with CH3CH(OH) group produce a ____________ precipitate of triodomethane when warmed with aqueous _______________ and aqueous________________________.This reaction is used to test for CH3CH(OH) group in alcohols.Example Ethanol is the only primary alcohol shows a positive tri-iodomethane test.CH3CH2OH(l) + 4I2(aq)+ 6NaOH(aq) Secondary alcohol that has a CH3 group attached to the carbon containing OH shows positive tri-iodomethane test.Example (CH3 )2CHOH or CH3CH(CH3CH2 )OHNote: Methanol, Propanol and Tertiary alcohol do not show positive test. Besides that , Ethanoic acid does not show positive test.Carbonyl compounds with CH3 CO- groups produce a _______________precipitate of tri-iodomethane(CHI3) when warmed with aqueous iodine and aqueous sodium hydroxide.ExampleEthanal shows a positive tri-iodomethane testO
CH3C
+ 3 I2 + NaOH H
Propanone also shows positive tri-iodomethane test CH3O
+ 3 I2 + NaOH CH3C
Note: Ethyl ethanoate however does not give positive test.Equations for the tri-iodomethane (iodoform) reactionWe will take the reagents as being iodine and sodium hydroxide solution.The first stage involves substitution of all three hydrogens in the methyl group by iodine atoms.
In the second stage, the bond between the C I3 and the rest of the molecule is broken to produce triiodomethane (iodoform) and the salt of an acid.
Putting all this together gives the overall equation for the reaction:
