Test For Carbonyls Flashcards
Outline Fehling’s solution test
-bridge blue and when two parts added and warmed with aldehyde a red precipitate of copper (I) oxide produced, ketone does not react
-aldehyde oxidised to carboxylic acid
-Cu2+ ions in solution reduced to Cu+
What is Benedicts solution
Similar to fehlings but more stable and less corrosive
What do tests for aldehydes involve
Mild oxidising agents oxidising the aldehyde to carboxylic acid (RCOO-) which is present as a carboxylate ion in the alkaline conditions
Explain the Tollen’s reagent test
Tollen’s agent is amoniacal silver nitrate high when heated with aldehyde produces a silver mirror
-silver ions reduced to silver atoms and aldehyde oxidised to carboxylic acid
Test for all carbonyl compounds and how to find specific ketone or aldehyde
Treat with 2,4-dinitrophenylhydrazine (2,4-DNPH) which produces an orange precipitate
-this derivative formed has a specific melting point that can be tested and checked in data book after product filtered, recrystallised and dried then melting point cetermined
Explain the iodoform test and what it tests for
Reagent is iodine in potassium hydroxide which when warmed with compound containing CH3CO- group (methyl ketone, methyl group next to carbonyl group) produces yellow precipitate of CHI3 (triiodomethane)
Overall triiodomethane reaction equation
CH3COR + 3I2 + 4NaOH —-> RCOO-Na+ + CHI3 (yellow precip) + NaI + 3H2O
What are the two steps in the triiodomethane reaction
Substitution of three iodine atoms on three hydrogen atoms of methyl group then hydrolysis when carbon carbon bond broken
Use of triiodomethane reaction
Can be used to shorten carbon chain by removing methyl group
Which aldehyde gives positive result for iodoform test
Ethanal
Does 2,4-DNPH give positive result with carboxylic acids
No
Organic products from reaction between iodine and propanone in alkaline
CHI3 and CH3COONa
Two observations with iodoform
Yellow precipitate and antiseptic smell
