3.3.8 Aldeyhydes and ketones Flashcards
What are aldehydes oxidised to?
Carboxylic acids
What are aldehydes reduced to?
Primary alcohols
What are ketones reduced to?
Secondary alcohols
What conditions are used to reduce aldehydes and ketones?
NaBH4 in and aqueous solution
What mechanism is used to reduce aldehydes and ketones?
Nucleophilic addition
What are the properties of the products from the reduction of a ketone?
They may form stereoisomers with a chiral carbon
What are the conditions and products for the nucleophilic addition between carbonyl compounds and KCN?
Conditions: dilute acid
Products: hydroxynitriles
What are the properties of the products formed when aldehydes and unsymmetrical ketones react with KCN?
They form mixtures of enantiomers
Why are racemic mixtures formed in nucleophilic substitution with KCN and carbonyl groups occur?
The carbonyl group is planar. So, the nucleophile can attack from above or below the plane. If the product has a chiral centre, then, a racemic mixture is formed.
Why does NaBH4 reduce aldehydes but not alkenes?
The H- ion from NaBH4 is attracted to the delta + carbon of the aldehyde. But, the double carbon bond in the alkene repels the ions, it can only be attracted by electrophiles.
Why is KCN preferred over HCN for nucleophilic addition of an aldehyde?
It is a stronger acid
HCN is an extremely poisonous gas
What are the hazards of using KCN for nucleophilic substitution?
KCN is an irritant and is also extremely dangerous if it’s ingested or inhaled. It can react with moisture to produce HCN, a highly toxic gas.
How can you reduce the risks of using KCN for nucleophilic substitution?
Gloves
Safety goggles
Lab coat
Fume cupboard
Which base do carboxylic acids always react with?
Although they’re weak acids, they liberate CO2 from carbonates.
What are the reactants, products and conditions for esterification?
Reactants: alcohols, carboxylic acids
Conditions: concentrated acid catalyst (H2SO4)
Products: ester
Why are the common uses of esters?
Plasticisers
Solvents
Perfumes
Food flavourings
Why are esters suitable for food flavourings and perfumes?
They have a sweet smells.
Long-chain esters have fruity scents.
Why are esters suitable solvents? How are they used as solvents?
They’re polar so, polar organic compounds dissolve in it.
They have a low bpt so, they can easily be removed.
Used a solvents in glue and printing inks
Which esters are formed from glycerol and fatty acids?
Vegetable oils
Animal fats
What type of carboxylic acids are animal fats made up of?
They’re made up of saturated chains which fit together neatly. So, they have strong van der waals forces so, they have a high boiling point and are solid at room temperature.
What type of carboxylic acids are vegetable oils made up of?
Unsaturated chains which causes the chains to bend, decreasing Van der waals forces and reducing bpt. So, they’re liquid at room temperature.
What reaction is used to turn an ester into a carboxylic acid and alcohol?
Hydrolysis in acid or alkaline conditions.
What are the reactants, conditions and products for the acid hydrolysis of esters?
Reactants: ester, water
Conditions: reflux, dilute acid like HCl or H2SO4
Products: carboxylic acid, alcohol
What are the reactants, conditions and products for the base hydrolysis of esters?
Reactants: ester, dilute alkali like NaOH
Conditions: reflux
Products: carboxylate ion, alcohol
What substances can be produced by reactions of vegetable oils and animal fats?
Glycerol + soap
Glycerol + biodiesel
What is biodiesel?
A mixture of methyl esters of long chain carboxylic acids.
What are the reactants, conditions and products of the base hydrolysis of vegetable oils and animal fats, saponification?
Reactants: vegetable oil or animal fats, NaOH
Products: sodium salt (soap), glycerol
Conditions: alkaline conditions
What are the reactants, conditions and products of the reaction of vegetable oils or animal fats and methanol?
Reactants: vegetable oil or animal fats, methanol
Products: methyl esters (biodeisel), glycerol
Conditions: catalyst (acid or alkaline)
What nucleophiles are used in nucleophilic addition elimination?
Water
Alcohols
Amines
Ammonia
How are acyl chlorides named?
-oyl
Ethanoyl chloride
How are acid anhydrides named?
Ethanoic andhydride
What are the advantages and disadvantages of the reaction between acyl chlorides and alcohol?
+ Very reactive, good rate of reaction
+ Good atom economy
- Hazardous HCl gas waste product
- Hard to store as it reacts with water in air to form HCl gas which can be explosive.
What are the advantages and disadvantages of the reaction between acid anhydrides and alcohol?
+ Waste product, carboxylic acid, is not harmful
+ Decent rate of reaction
- Bad atom economy
What are the products for the reaction between an acyl chloride and an alcohol?
Ester
HCl
What are the products for the reaction between an acyl chloride and water?
Carboxylic acid
HCl
What are the products for the reaction between an acid anhydride and an alcohol?
Ester
Carboxylic acid
What are the products for the reaction between an acid anhydride and water?
2 carboxylic acids
What are the products for the reaction between an acyl chloride and an amine?
An N-substituted amide
Alkyl ammonium chloride
What are the products for the reaction between an acid anhydride and an amine?
An N-substituted amide
Alkyl ammonium carboxylate salt
What are the products and observations for the reaction between ethanoyl chloride and ammonia?
Products: ethanamide, ammonium chloride
Observations: white smoke and solid due to both of the products
What was aspirin used for?
To treat pain, fever and inflammation
What reacts with 2-hydroxybenzoic acid to make aspirin?
Ethanoic acid
Ethanoyl chloride
Ethanoic anhydride
What are the advantages and disadvantages of using ethanoic acid to make aspirin?
+ low hazards
+ good atom economy
+ harmless by-product
- Slow reaction as it is a reversible reaction.
- Bad yield
What are the advantages and disadvantages of using ethanoyl chloride to make aspirin?
+ Fast reaction
+ Good yield
+ Good atom economy
- Hazardous by-product
- Hard to store reagent
What are the advantages and disadvantages of using ethanoic anhydride to make aspirin?
+ Relatively quick rate with a catalyst
+ Harmless by-product
+ Good yield
+ Relatively harmless reagents
- Low atom economy
What are the steps to aspirin synthesis?
- Heat the reactants together, then add cold water to crystallise the aspirin.
- Vacuum filter out the solid aspirin from the mixture.
- Recrystallise the aspirin (purification)
- Vacuum filter the aspirin again.
- Dry the product in an oven and record the final mass. Dry to a constant mass.
Describe the process of the purification step in aspirin synthesis.
- Warm in the minimum amount of hot solvent, just enough to dissolve the desired product.
- Filter hot to remove the soluble impurities
- Cool in a salt water bath to recrystallise the product
- Filter to remove the solvent (and any dissolved impurities.)
- Dry by rinsing with a volatile solvent and pat dry with filter paper
What are optical isomers?
A type of geometric isomer that occurs in molecules with chiral centres.
What is an asymmetric carbon atom?
A chiral, with 4 different groups attached tetrahedrally around it.
What are enantiomers?
Optical isomers that are non super-imposable mirror images and differ in their effect on plane-polarised light.
What is a racemic mixture?
A mixture of equal amounts of enantiomers. So, rotational effects on light cancel out.
