3.3.8 Aldeyhydes and ketones

Question 1

What are aldehydes oxidised to?

Answer 1

Carboxylic acids

Question 2

What are aldehydes reduced to?

Answer 2

Primary alcohols

Question 3

What are ketones reduced to?

Answer 3

Secondary alcohols

Question 4

What conditions are used to reduce aldehydes and ketones?

Answer 4

NaBH4 in and aqueous solution

Question 5

What mechanism is used to reduce aldehydes and ketones?

Answer 5

Nucleophilic addition

Question 6

What are the properties of the products from the reduction of a ketone?

Answer 6

They may form stereoisomers with a chiral carbon

Question 7

What are the conditions and products for the nucleophilic addition between carbonyl compounds and KCN?

Answer 7

Conditions: dilute acid
Products: hydroxynitriles

Question 8

What are the properties of the products formed when aldehydes and unsymmetrical ketones react with KCN?

Answer 8

They form mixtures of enantiomers

Question 9

Why are racemic mixtures formed in nucleophilic substitution with KCN and carbonyl groups occur?

Answer 9

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.

Question 10

Why does NaBH4 reduce aldehydes but not alkenes?

Answer 10

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.

Question 11

Why is KCN preferred over HCN for nucleophilic addition of an aldehyde?

Answer 11

It is a stronger acid
HCN is an extremely poisonous gas

Question 12

What are the hazards of using KCN for nucleophilic substitution?

Answer 12

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.

Question 13

How can you reduce the risks of using KCN for nucleophilic substitution?

Answer 13

Gloves
Safety goggles
Lab coat
Fume cupboard

Question 14

Which base do carboxylic acids always react with?

Answer 14

Although they’re weak acids, they liberate CO2 from carbonates.

Question 15

What are the reactants, products and conditions for esterification?

Answer 15

Reactants: alcohols, carboxylic acids
Conditions: concentrated acid catalyst (H2SO4)
Products: ester

Question 16

Why are the common uses of esters?

Answer 16

Plasticisers
Solvents
Perfumes
Food flavourings

Question 17

Why are esters suitable for food flavourings and perfumes?

Answer 17

They have a sweet smells.
Long-chain esters have fruity scents.

Question 18

Why are esters suitable solvents? How are they used as solvents?

Answer 18

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

Question 19

Which esters are formed from glycerol and fatty acids?

Answer 19

Vegetable oils
Animal fats

Question 20

What type of carboxylic acids are animal fats made up of?

Answer 20

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.

Question 21

What type of carboxylic acids are vegetable oils made up of?

Answer 21

Unsaturated chains which causes the chains to bend, decreasing Van der waals forces and reducing bpt. So, they’re liquid at room temperature.

Question 22

What reaction is used to turn an ester into a carboxylic acid and alcohol?

Answer 22

Hydrolysis in acid or alkaline conditions.

Question 23

What are the reactants, conditions and products for the acid hydrolysis of esters?

Answer 23

Reactants: ester, water
Conditions: reflux, dilute acid like HCl or H2SO4
Products: carboxylic acid, alcohol

Question 24

What are the reactants, conditions and products for the base hydrolysis of esters?

Answer 24

Reactants: ester, dilute alkali like NaOH
Conditions: reflux
Products: carboxylate ion, alcohol

Question 25

What substances can be produced by reactions of vegetable oils and animal fats?

Answer 25

Glycerol + soap Glycerol + biodiesel

Question 26

What is biodiesel?

Answer 26

A mixture of methyl esters of long chain carboxylic acids.

Question 27

What are the reactants, conditions and products of the base hydrolysis of vegetable oils and animal fats, saponification?

Answer 27

Reactants: vegetable oil or animal fats, NaOH Products: sodium salt (soap), glycerol Conditions: alkaline conditions

Question 28

What are the conditions and products of the reaction of vegetable oils or animal fats and methanol?

Answer 28

Products: methyl esters (biodeisel), glycerol Conditions: catalyst (acid or alkaline)

Question 29

What nucleophiles are used in nucleophilic addition elimination?

Answer 29

Water Alcohols Amines Ammonia

Question 30

How are acyl chlorides named?

Answer 30

-oyl Ethanoyl chloride

Question 31

How are acid anhydrides named?

Answer 31

Ethanoic andhydride

Question 32

What are the advantages and disadvantages of the reaction between acyl chlorides and alcohol?

Answer 32

+ 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.

Question 33

What are the advantages and disadvantages of the reaction between acid anhydrides and alcohol?

Answer 33

+ Waste product, carboxylic acid, is not harmful + Decent rate of reaction - Bad atom economy

Question 34

What are the products for the reaction between an acyl chloride and an alcohol?

Answer 34

Ester HCl

Question 35

What are the products for the reaction between an acyl chloride and water?

Answer 35

Carboxylic acid HCl

Question 36

What are the products for the reaction between an acid anhydride and an alcohol?

Answer 36

Ester Carboxylic acid

Question 37

What are the products for the reaction between an acid anhydride and water?

Answer 37

2 carboxylic acids

Question 38

What are the products for the reaction between an acyl chloride and an amine?

Answer 38

An N-substituted amide Alkyl ammonium chloride

Question 39

What are the products for the reaction between an acid anhydride and an amine?

Answer 39

An N-substituted amide Alkyl ammonium carboxylate salt

Question 40

What are the products and observations for the reaction between ethanoyl chloride and ammonia?

Answer 40

Products: ethanamide, ammonium chloride Observations: white smoke and solid due to both of the products

Question 41

What was aspirin used for?

Answer 41

To treat pain, fever and inflammation

Question 42

What reacts with 2-hydroxybenzoic acid to make aspirin?

Answer 42

Ethanoic acid Ethanoyl chloride Ethanoic anhydride

Question 43

What are the advantages and disadvantages of using ethanoic acid to make aspirin?

Answer 43

+ low hazards + good atom economy + harmless by-product - Slow reaction as it is a reversible reaction. - Bad yield

Question 44

What are the advantages and disadvantages of using ethanoyl chloride to make aspirin?

Answer 44

+ Fast reaction + Good yield + Good atom economy - Hazardous by-product - Hard to store reagent

Question 45

What are the advantages and disadvantages of using ethanoic anhydride to make aspirin?

Answer 45

+ Relatively quick rate with a catalyst + Harmless by-product + Good yield + Relatively harmless reagents - Low atom economy

Question 46

What are the steps to aspirin synthesis?

Answer 46

- 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.

Question 47

Describe the process of the purification step in aspirin synthesis.

Answer 47

- 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

Question 48

What are optical isomers?

Answer 48

A type of geometric isomer that occurs in molecules with chiral centres.

Question 49

What is an asymmetric carbon atom?

Answer 49

A chiral, with 4 different groups attached tetrahedrally around it.

Question 50

What are enantiomers?

Answer 50

Optical isomers that are non super-imposable mirror images and differ in their effect on plane-polarised light.

Question 51

What is a racemic mixture?

Answer 51

A mixture of equal amounts of enantiomers. So, rotational effects on light cancel out.