8. Characteristic tests for carbonyl compounds (aldehydes and ketones)

Question 1

how to test for carbonyl functional group

Answer 1

add bradys reagent

orange precipitate if aldehyde/ketone present

Question 2

what is bradys reagent

Answer 2

methanol, sulfuric acid and solution of 2,4-dinitrophenylhydrazine (2,4-DNP)

Question 3

how to identify specific aldehyde or ketone

Answer 3

positive Bradys test 
collect precipitate (filtration)
purify (recrystallisation)
dry 
measure mpt and compare to database

Question 4

steps to form tollen’s reagent

Answer 4

NaOH(aq) + AgNO3(aq) -> brown precipitate 
add dilute NH3 (aq) dropwise 
precipitate redissolves 
weak oxidising reagent 
(only reacts with aldehyde)

Question 5

how is the reaction between tollens reagent and an aldehyde a redox reaction

Answer 5

silver ions reduced
Ag+(aq) + e- -> Ag(s) (silver mirror/precipitate observed)
aldehyde oxidised
RCOH + [O] -> RCOOH