Chapter 26 - Carbonyls and Carboxylic Acids Flashcards
What are carbonyl compunds ?
Compounds that contain a carbonyl functional group, C=O.
Nomenclature for aldehydes?
Aldehydes have the suffix -al. As the C=O bond is always at the end of the carbon chain, there is no need for a number. A unbranched chain of 5 carbons, with an C=O bond at the end would be pentanal.
Nomenclature for ketones?
The suffix is -one. For ketones with five or more carbons, you have to say which carbon the function group is on. For an unbranched 5 carbon chain, with the C=O bond on the second carbon, the name would be pentan-2-one.
What do aldehydes oxidise to become?
Carboxylic acids
Why are aldehydes easily oxidised?
There’s a hydrogen attached to the carbonyl group.
What are the conditions to oxidise aldehydes?
You need to reflux them with acidified potassium dichromate.
Why are ketones not easily oxidised?
You would have to break a carbon-carbon bond
What does the reduction of an aldehyde form?
A primary alcohol.
What does the reduction of a ketone form?
A secondary alcohol.
What is the reducing agent used to turn ketones/aldehydes back into alcohols?
NaBH4- sodium tetrahybridoborate (III)
What is the mechanism for the reduction of carbonyl compunds?
Nucleophillic addition
How does Nucleophillic addition reactions work?
1) oxygen has negative dipole and carbon has positive dipole.
2) an arrow from the lone pair on the H- ion to the carbon atom. Then arrow from double bond to oxygen atom.
3) H atom now covalently bonded to carbon atom and oxygen has lone pair of electrons and a minus charge.
4) arrow from lone pair on oxygen to H atom on water molecules. Then from the bond to the oxygen atom in the water molecule. Make sure to draw dipoles on water molecules.
5) this forms an alcohol and a OH- ion.
What does the reaction of carbonyl compounds with hydrogen cyanide produce?
Hydroxynitriles
How does Nucleophillic addition work with hydrogen cyanide?
1) hydrogen cyanide dissociates in water to produce H+ ions and CN- ions.
2) arrow from CN- ion to carbon atom. Arrow from double bond to oxygen atom.
3) CN bonded to carbon and Oxygen Atom now has a lone pair of electrons. Arrow from lone pair to H+ ion
4) this forms a hydroxyl group and a hydroxynitrile is produced.
What is used instead of hydrogen cyanide in labratories?
Sodium cyanide and Sulfuric acid.
What reagent is used to identify is a carbonyl group is present?
Brady’s reagent - 2,4- dinitrophenylhydrazine
What will you see if a carbonyl group is present when Brady’s reagent is added?
A bright orange precipitate forms. This only happens with ketones and aldehydes, not with COOH groups .
How to identify the carbonyl compound from the orange precipitate formed from Brady’s reagent?
1) the precipitate is filtered and then recrystallised to form pure crystals.
2) then measure the melting point and compare to the literature values.
How to distinguish between an aldehyde and a ketone?
Tollen’s reagent
How does tollen’s reagent work + positive result?
Tollen’s reagent is a colourless solution of silver nitrate (AgNO3) dissolved in aqueous ammonia. It is heated in a test tube with an aldehyde. The aldehyde is oxidised to form a carboxylic acid. Then the silver ions in the Tollen’s reagent are reduced to produce a silver mirror.
Ag+ (aq). + e- ->. Ag(s)
What are carboxylic acids?
Compounds with a -COOH functional group
Why are carboxylic acids soluble?
Carboxylic acids are polar molecules, as there is a difference in electronegativity between the carbon and oxygen atoms. This allows carboxylic acids to form hydrogen bonds with water molecules.
What is the dissociation of carboxylic acids?
As carboxylic acids are weak acids they dissociate into a carboxylate ion and H+. The H from the OH in the COOH is removed to form a H+ ion and a negative charge is left on the oxygen.
Reaction of carboxylic acids and metals?
They react with metals to form a salt and hydrogen
Example : ethanoic acid + Mg -> magnesium ethanoate + H2
Reaction of carboxylic acids with carbonates?
Carboxylic acids react with carbonates to form salt, carbon dioxide and water.
Example: ethanoic acid + sodium carbonate -> sodium ethanoate + H20 + CO2
Reaction of carboxylic acid and metal oxide?
This is a neutralisation reaction forming water and a salt.
Example: ethanoic acid + magnesium oxide -> magnesium ethanoate + H2O
What are acyl chlorides?
Acyl chlorides have the functional group COCl.
General formula of acyl chlorides?
CnH2n-1OCl
How to name acyl chlorides?
The names end with a -oyl chloride. So a five carbon chain with a COCl functional group at the end of the chain is called pentanoyl chloride.
How to form acyl chlorides?
By reacting carboxylic acids with SOCl2 (thionyl chloride). This forms the acyl chloride, SO2 and HCl
What is the reaction of acyl chloride with water?
Acyl chlorides react vigorously with cold water, producing a carboxylic acid.
Example: ethanoyl chloride + H2O -> ethanoic acid + HCl
Reaction of acyl chlorides with alcohols?
Acyl chlorides react vigorously with alcohols at room temperature, producing an ester and HCl.
Example: ethanoyl chloride + Methanol -> methyl ethanoate + HCl
Reaction of acyl chlorides with ammonia?
Acyl chlorides react violently with ammonia at room temperature, producing a primary amide.
Example: ethanoyl chloride + NH3 -> ethanamide + HCl
Reaction of acyl chlorides with amines?
Acyl chlorides react violently with amines at room temperature to form a secondary amide + HCl
Example: ethanoyl chloride + methylamine -> N-methylethanamide + HCl
Reaction of acyl chlorides with phenol?
Acyl chlorides react slowly with phenol at room temperature to form an ester +HCl.
Example: ethanoyl chloride + phenol -> phenylethanoate + HCl
What is an ester?
An ester is formed from a carboxylic acid and an alcohol group
How do you name esters?
The first half of the name comes from the alcohol. The second part comes from the carboxylic acid group. So methanoic acid + ethanol would form ethyl methanoate.
Reaction of ethanoic acid and ethanol + conditions?
Produces ethyl ethanoate + water. The reaction is called esterificstion and requires an acid catalyst usually concentrated H2SO4. The reaction is reversible
What is an acid anhydride?
An acid anhydride is produced from two identical carboxylic acid molecules. The OH from one carboxylic acid is removed and the H from another is removed to form water.
How do acid anhydrides produce esters?
They are heated with alcohols to form esters and a Carboxylic acid which can be seperated by distillation.
How does acid hydrolysis of esters work?
This splits the ester into a carboxylic acid and an alcohol. You have to heat the ester under reflux with a dilute acid, such as hydrochloric or Sulfuric.
How does base hydrolysis of esters work?
You reflux the ester with a dilute alkali such as sodium hydroxide. When heated, OH- ions from the base react with the ester and you get a carboxylate ion and an alcohol
