Carbonyl Compounds Flashcards
What is a carbonyl group?
A carbon atom double bonded to an oxygen atom.
What is the test for aldehydes?
Tollen’s reagent (silver mirror, 5 minutes, water bath) or Fehling’s solution (brick red precipitate, water bath).
Give the equation for the reduction of Tollen’s reagent, and state what happens to the aldehyde.
Ag(NH3)2^+ + e- –> Ag +2NH3
This goes from colourless solution to silver precipitate. The aldehyde is oxidised to a carboxylic acid.
Give the equation for the reduction of Fehling’s solution, state what Fehling’s solution is and state what happens to the aldehyde.
Cu^(2+) + e- –> Cu^+
Copper(II) ions dissolved in NaOH.
This goes from a blue solution to a brick red precipitate.
The aldehyde is oxidised to a carboxylic acid.
What is Benedict’s solution?
The same as Fehling’s solution, but the copper(II) ions are dissolved in sodium carbonate instead.
Describe the method, product and risks of reacting carbonyls with hydrogen/potassium cyanide.
The HCN/KCN dissociates and the CN- ions attack the partially positively charged carbon atom of the C=O. The lone pair on the oxygen atom then grabs a H+ ion. This is nucleophilic addition and forms a hydroxynitrile. CN- ions are highly toxic.
What would you use as a reducing agent on an aldehyde or ketone?
H+ with a nickel catalyst/NaBH4 dissolved in water with methanol
Describe the mechanism for the reduction of an aldehyde.
A H- ion with a lone pair of electrons attacks the partially positively charges carbon of the C=O. The lone pair on the oxygen atom then grabs a H+ from water or a weak acid. This forms a primary alcohol.
Describe the mechanism for the reduction of a ketone.
A H- ion with a lone pair of electrons attacks the partially positively charges carbon of the C=O. The lone pair on the oxygen atom then grabs a H+ from water or a weak acid. This forms a secondary alcohol.
State the type of reaction that occurs when reducing an aldehyde or ketone.
Nucleophilic addition.
What is the functional group in a carboxylic acid?
-COOH
Where is the carboxyl group found?
At the end of a molecule.
Are carboxylic acids weak or strong?
Weak.
Describe the reaction of a carboxylic acid with a carbonate (CO3^(2-)).
carboxylic acid + carbonate –> salt + carbon dioxide + water
Name and decribe the reaction of a carboxylic acid with an alcohol.
This is called esterification. With heat, and in the presence of a strong acid catalyst (usually conc. H2SO4), you will produce an ester and water.
What is the functional group in an ester?
-COO-
What do esters smell like?
They smell sweet and usually fruity.
Name some common uses of esters.
Perfume, sweets, food, solvents (glue and printing ink) and plasticisers (make plastics more flexible).
Why do esters make good solvents?
They are polar liquids, so will dissolve in most polar organic compounds. They have low boiling points, so evaporate easily.
Vegetable oils and animal fats are esters of which alcohol?
Propan-1,2,3-triol.
What is a fatty acid?
A long-chain carboxylic acid.
Out of fats and oils, which are earier to melt and why?
Oils, because they contain unasaturated hydrocarbon chains. The double bonds in these chains mean they don’t pack together well, decreasing the effect of the van der Waals forces.
What is hydrolysis?
When a substance is split up by water.
When hydrolysing an ester, what can be used to speed up the process?
An acid or alkali.
Describe acidic hydrolysis of an ester.
An equilibrium reaction of an ester with water to form a carboxylic acid and an alcohol. This reaction is the reverse of esterification and needs an acid catalyst (eg. HCl) and reflux.
Describe basic hydrolysis of an ester.
This is an equilibrium reaction of an ester with OH- ions to form a carboxylate ion and an alcohol. This needs reflux conditions.
Descrobe the hydrolisis of an oil or fat.
An oil or fat reacted with sodium hydroxide will produce glycerol (propan-1,2,3-triol) and a sodium salt.
How do we form a fatty acid from a sodium salt?
Reacting it with HCl.
What is biodiesel?
A mixture of methylesters of long chain carboxylic acids.
How can we make biodiesel?
Reacting vegetable oils with methanol in the presence of a potassium hydroxide catalyst. This forms glycerol and biodiesel.
Why isn’t biodiesel completely carbon neutral?
Because we use energy from fossil fuels to make the fertilizer that grows the crops to make biodiesel, and to plant, harvest and convert the oils.
What is an acyl chloride?
A molecule with the functional group -COCl.
What is an acid anhydride?
It is made from two identical carboxylic acids, that join across one oxygen molecule, ejecting water.
Give the reaction for an acyl chloride with water.
acyl chloride + water –> carboxylic acid + HCl
Give the reaction for an acyl chloride with an alcohol.
acyl chloride + alcohol –> ester + HCl
Give the reaction for an acyl chloride with ammonia.
acyl chloride + ammonia –> amide + HCl
Give the reaction for an acyl chloride with a primary amine.
acyl chloride + primary amine –> N-substituted amide + HCl
Give the reaction of an acid anhydride with water.
acid anhydride + water –> 2 carboxylic acids
Give the reaction for an acid anyhdride with an alcohol.
acid anhydride + alcohol –> ester + carboxylic acid
Give the reaction for an acid anhydride with ammonia.
acid anhydride + ammonia –> amide + carboxylic acid
Give the reaction for an acid anhydride with a primary amine.
acid anhydride + primary amine –> N-substituted amide + carboxylic acid
Name and describe the mechanism of reactions involving acyl chlorides.
This is a nucleophilic addition elimination reaction. A nucleophile attacks the partially positively charged carbon atom of the C=O in the acyl chloride, and electrons from the double bond retreat to the oxygen atom. This leaves the nucleophile positively charged. The oxygen then reforms the double bond, and the C-Cl bond is broken. The chlorine is then a nucleophile, and attacks a hydrogen atom, forming HCl and allowing the positively charged nucleophile to gain electrons.
Explain the industrial advantages of ethanoic anhydride over ethanoyl chloride in the manufacture of the drug aspirin.
It is cheaper, and it is safer - because it’s less corrosive, reacts more slowly with water, and doesn’t produce HCl gas when it reacts.
