3.8/3.9 - Aldehydes and Ketones/Carboxylic acids and derivatives

Question 1

What is the definition of a carbonyl

Answer 1

Caronyls are compounds with a C=O bond, they include aldehydes and ketones

Question 2

Why are smaller carbonyls soluble in water

Answer 2

They can form hydrogen bonds with the water

Question 3

What sort of intermolecular forces are present in carbonyls

Answer 3

Pure carbonyls cannot hydrogen bond to themselves but are attracted by permanent dipole forces

Question 4

Why are carbonyls

Answer 4

O is more electronegative that the C, bond becomes polarised

Question 5

What are the reagents/conditions for the reaction for aldehyde and ketones to alcohols

Answer 5

Reagents- NaBH4 in aqueous ethanol
Conditions- Room temperature and pressure
Mechanism- Nucleophillic addition, with a H+ from water or weak acid

You can also use LiAH4

Question 6

What is an alternative way to reduce carbonyls

Answer 6

Cataytic hydrogentation

.Hydrogen and nickel catalyst
. High pressure

Question 7

What are the reagents/conditions for the reaction of carbonyl > hydroxynitrile

Answer 7

Reagent- Sodium cyanide and dilute sulfuric acid
Conditions - Room temperatures and pressure
Mechanism- Nucleophillic addition

Question 8

Why is it better to use KCN/NaCN rather than HCN

Answer 8

HCN is a toxic gas that is difficult to contain, there will be a higher concentration of CN- ions with KCN /NaCN as they fully ionise, HCN is a weak acid and only partially ionises

Question 9

What is the acidity of a carboxylic acid

Answer 9

The carboxylic acids are only weak acids in water, becuase the only slightly dissociate but they are strong enough to displace carbon dioxide from carbonates

Question 10

How soluble are carboxylic acids in water

Answer 10

The smaller carboxylic acids up to C4, all dissolve in water in alol proportions but after this the solubility rapidly reduces, they dissolve because they can hyrdorgen bond to the water molecules

Question 11

Why are carboxylic acids salts stable

Answer 11

The pi charge cloud has delocalised and spread out, the delocalisation makes the ion more stable and therfore more likely to form

Question 12

What does increasing the carbon chain length do for acid strength

Answer 12

Increasing chain length pushes electron density on to the COO- ion making it more negative and less stable, this makes the acid less strong

Question 13

What does adding an electronegative element to the carbon chain do to acidity

Answer 13

Electronegative atoms withdraw the electron density from the COO- ion, making it less negative and more stable, this makes the acid more strong

Question 14

What reactions form a salt inolving carboxylic acids

Answer 14

Acid + Metal > Salt + Hydrogen

Acid + Metal > Salt + Water

Acid + Metal > Salt + Water + CO2

Question 15

Why cannot carboxylic acids be oxidised other than methanoic acid, and give the product of the oxidationh

Answer 15

Carboxulic acids cannot be oxidised by using oxidising agents but methanoic acid is an exception as its structure has effectively an aldehyde group, it would form carbonic acid when reacting

Question 16

Give the reaction for esterification with water

Answer 16

Carboxylic acid + Alcohol > Ester + Water

Containing a strong acid catalyst

Question 17

How would you name a carboxylic acid

Answer 17

The bit ending in -yl comes from the alcohol and the bit ending in -anoate comes from the carboxylic acid

Question 18

Give all the different uses of esters, and why they can be used in this manner

Answer 18

. Esters are sweet smelling and can be used in perfumes and flavourings, for use in these perfumes they need to be non toxic, soluble in solven such as ethanol, volatile and not able to react with water

. Esters can also be used as solvents for polar organic substances, they do not form hydrogen bonds and they are almost insoluble in water

. Esters can be used in plasticisers, pure polymers have limited flexibility , incorporating plasticisers allows the polymer chain to move more easily and become more flexible

Question 19

What are the reagents/conditions for the hydrolysis of esters via acid

Answer 19

Reagents- Dilute HCL
Conditions- Heat under reflux

This reaction is the reverse reaction of ester formation,and a carboxylic acid and alcohol are formed

Question 20

What are the reagents/conditions for the hydrolysis of esters via sodium hydroxide

Answer 20

Reagents- Dilute sodium hydroxide
Conditions- Heat under reflux

This reaction goes fully to completion and using excess sodium hydroxide will ensure that the ester if fully hydrolyses the products will be a carboxylic acid salt and an alcohol , addition of a strong acid will convert the salt to the carboxylic acid form

Question 21

What is the IUPAC name for glycerol

Answer 21

Propane 1-2-3 triol

Question 22

What are fats and oils

Answer 22

They are esters of glycerol and long chain carboxylic fatty acids, these vegtable oils and fats can be hydrolysed to give soap,glycerol and long chain carboxylic fatty acids

Question 23

How does soap work

Answer 23

Long chain carboxylic fatty acids that are produced by the hydrolysis of fats act as soaps, the polar CO2- end is hydrophllic and mixes with the water, and the long non polar hydrocarbon chain is hydrophobic and will mix with the grease, this allows the grease and the water to mix and then be washed away

Question 24

What is biodiesel

Answer 24

Biodiesel is a mixture of methyl esters of long chain carboxylic acids

Question 25

How can vegtable oils be converted to biodiesel

Answer 25

They can be converted by the reaction with methanol in the prescence of a strong alkali catalyst

Question 26

What are the 2 derivatives of carboxylic acids

Answer 26

Acyl chlorides and acid anhydrides

Question 27

Why are the derivatives more reactive than carboxylix acids

Answer 27

The Cl and the OCOCH3 groups are classes as good leaving groups with means they go less effective delocalisation, this makes them more reactive

Question 28

What are the reagents/conditions for the reaction of acyl chloride/acid anyhydride > Carboxylic acid

Answer 28

Reagent : Water
Conditions: Room temperature
Mechanism:Nucleophillic addition

. When you use acyl chloride HCl is given off
.When you use acid anyhydride you make twice the amuntof acid

Question 29

What are the reagents/conditions for the reaction of acyl chloride/acid anyhydride > ester

Answer 29

Reagent: Alcohol
Conditions: Room temperature

With acyl chloride HCl is made, with acid anyhydride carboxylic acid is made

Question 30

Why is it more efficient to make esters using derivatives

Answer 30

Reaction is much quicker and it is not a reversible reaction

Question 31

What are the reagents/conditions for the reaction of acyl chloride/acid anhydride > primary amide

Answer 31

Reagent: Ammonia
Conditions: Room temperature

With acyl chloride NH4Cl is given off which is white smoke, and with acid anhydride RCO2- NH4 + salt is given off

Question 32

What are the reagents/conditions for the reaction of acyl chloride/acid anhydirde > secondary amide

Answer 32

Reagent: Primary amine
Conditions: Room temperature
Mechanism: Nucleophillic addition elimination

Question 33

How do you measure the degree of purity using melting point

Answer 33

.Determine the melting range for the sample
.If the sample is pure melting point will be sharp and the same as the value quoted in the data booklet
.If impurties are present the melting point will be lowered and will melt over a range
. You can use an electronic melting point machine, or byusing a cappilary tube strapped to a themometer that is submeged in heating oil
. You would add a small amount of salt and then heat up slowly near the melting poin t