Carbonyl Compounds Flashcards
(54 cards)
What are aldehydes and ketone?
Carbonyl compounds that contain the functional group C=O
What is the difference between aldehydes and ketones?
Aldehydes have their C=O at the end of the chain and ketones have their C=O within the chain.
Why are aldehydes easily oxidised and ketones aren’t?
Aldehydes have a hydrogen atom attached to the carbonyl group. the only way to oxidise a ketone would be to break a carbon- carbon bond so not easily oxidised.
What are two ways to distinguish between an aldehyde and a ketone?
- Tollens
- Fehlings
Describe Tollens and the reaction of an aldehyde and a ketone with Tollen’s.
Tollen’s reagent is a colourless solution of silver nitrate dissolved in aqueous ammonia.
ALDEHYDE: If it is heated in a test tube with an aldehyde, a silver mirror forms after a few minutes.
As the aldehyde is oxidised the diaminesilver ions in the Tollen’s reagent are reduced, producing silver and ammonia.
Ag(NH3)2+(aq) +e- = Ag(s) + 2NH3(aq)
KETONE: No reaction.
Why must aldehydes an ketones be heated in a water bath rather than over a flame?
They are flammable.
Describe Fehling’s solution and the reaction of an aldehyde an a ketone with Fehling’s.
BLUE SOLUTION of complexed copper (II) ions in sodium hydroxide.
ALDEHYDE: if heated with an aldehyde the copper(II) ions are reduced to a brick red precipitate of copper(II) oxide.
Cu2+(aq) + e- = Cu+(s)
What compound can be used to reduce aldehydes and ketones to alcohols?
NaBH4, in equations usually just written as [H]
How does nucleophilic addition work? (aldehyde/ketone to alcohol)
1: The C=O bond is polar so the Cδ+ attracts the -vely charged lone pair of electrons on H- ion/
2: The H- ion attacks the slightly +ve carbon atom and donates its lone pair of electrons forming a bond with carbon.
3: As carbon can only have 4 bonds, the addition of the H+ ion causes one of the carbon-oxygen bonds to break. This forces a lone pair of electrons from the C=O bond onto the oxygen.
4: The oxygen donates its lone pair of electrons to a H+ ion (usually from water but sometimes a weak acid)
5: primary (from aldehyde) alcohol produced/ secondary (from ketone) alcohol produced.
What are hydroxynitriles?
Hydroxynitriles are molecules which contain a hydroxyl group (OH) and a nitrile group (CN).
How do you name hydroynitriles?
Nitrile group is the most important so the suffix is -nitrile and the carbon that’s attached to the nitrogen is always carbon-1. Hydroxy- prefix because OH group.
e.g. CH3CH(CH3)CH(OH)CN
2-hydroxy-3-methylbutanenitrile
How do you make hydroxynitriles?
Reacting aldehydes or ketones with hydrogen cyanide (HCN). NUCLEOPHILIC ADDITION.
Describe how you make hydroxynitriles from aldehydes/ketones by nucleophilic addition.
1: Hydrogen cyanide is a weak acid- partially dissociates in water to form H+ ions and CN- ions: HCN H+ +CN-
2: The CN- ion from the HCN attacks the partially positive carbon atom and donates a pair of electrons forming a bond with the carbon.
3: A pair of electrons from the C=O double bond is pushed onto the oxygen.
4: The oxygen bonds to a H+ ion (from either HCN or water) to form the hydroxyl group.
Why is HCN a risk? How is it avoided?
EXTREMELY TOXIC GAS.
So to reduce risk KCN is used.
KCN also toxic but stored more easily.
What are carboxylic acids?
Contain functional group -COOH.
Why do carboxylic acids partially dissociate in water?What into?
Weak acid
RCOOH RCOO- + H+
Equilibrium lies to left because most doesn’t dissociate.
What do carboxylic acids form when they react with carbonates (CO3^2-) or hydrogencarbonates (HCO3-)?
Salt, CO2 and water
e.g.2CH3COOH + Na2CO3 = 2CH3COONa +H2O + CO2
HCOOH + NaHCO3 = HCOONa + H2O +CO2
What do you get when you react a carboxylic acid with an alcohol in the presence of a strong acid catalyst?
Ester (esterification)
What catalyst is usually used in esterification reaction?
conc. H2SO4 or HCl or H3PO4
How do you name an ester?
- Look at the alkyl group that came from the alcohol. first part of name.
- Look at part that came from the carboxylic acid. Swap -oic to -oate.
e.g. ethanoic acid + methanol = CH3COOCH3
methyl ethanoate
What are useful properties of esters?
- SWEET SMELL- perfumes, food flavourings
- POLAR LIQUIDS- Lots of polar organic molecules will dissolve in them.
- LOW BOILING POINTS- evaporate easily from mixtures, good solvents in glues and printing inks.
- PLASTICISERS- Added to plastics during polymerisation to make plastics more flexible. Over time plasticiser molecule escapes and molecule becomes brittle and stiff.
What is hydrolysis?
When a substance is split up by water.
What is added to speed up hydrolysis?
An acid or an alkali
What is acid hydrolysis and how does it work?
Splits ester into an acid and an alcohol.
You have to reflux the ester with a dilute acid, such as HCl or H2SO4. The ester will then split back into its acid and alcohol that it was originally made from.
