Carbonyl compounds Flashcards
What is a carbonyl functional group, and what molecules are these found in?
C=O
Aldehyde, Ketone.
How do you form an aldehyde?
Gently heat (distill) a primary alcohol with acidified potassium dichromate.
How do you from a ketone?
Heat a secondary alcohol under reflux
What are the tests for aldehydes
Fehlings test
Tollens reagent test
How do you carry out a Fehlings test
- Add 2cm3 of Fehlings solution into a test tube
- Add 5 drops of the aldehyde or ketone to test tube
- Put test tube in a hot water bath for 5mins.
What result does a Fehlings test give for an aldehyde and ketone?
Aldehyde - Blue solution will form a brick red precipiatate
Ketone - Nothing happens
Why does Fehlings solution turn brick red when an aldehyde is added?
Cu2+(aq) + e- -> Cu+(s)
Cu2+ is blue
Cu+ is a red solid
Copper 2+ is reduced as it acts an oxidising agent for the aldehyde.
How do you make Tollens reagent?
- Put 2cm3 of 0.1mol/dm3 of silver nitrate solution in a test tube.
- Add a few drops of dilute NaOH, which forms a light brown precipitate.
- Add drops of dilute ammonia until the precipitate dissolves completely.
- Place in hot water bath for 10 mins then add drops of aldehyde or ketone.
Results for aldehyde and ketone?
Aldehyde - A silver mirror forms on the walls of a test tube
Ketone - Nothing happens.
Why does a silver precipitate form when an aldehyde is added to tollens reagent?
Ag(NH3)2+ (aq) +e- -> Ag(s) + 2NH3 (aq)
Diamminesilver is reduced.
In what reaction do carbonyl compounds react with hydrogen cyanide?
Nucleophilic substitution
What acts as the nucleophile in the reaction between HCN and C=O, and how is it formed?
HCN = H+ + CN-
CN- is the nucleophile.
How is the cyanohydrin formed?
- The CN- group attacks the partially positive carbon atom and donates a pair of electrons.
- H+ ( from HCN or water) bonds to the oxygen to form the hydroxyl group)
