Topic 17.3 Carboxylic acids

Question 1

Carboxylic acid group

Answer 1

(-oic acid suffix)
O
II
R-C-OH

Question 2

Bonding in carboxylic acids

Answer 2

• Many reactions involve the loss of a H+ ion.
• This produces a carboxylate ion where the charges are evenly distributed across C-O bonds.

Question 3

Physical properties of carboxylic acids

Answer 3

• High boiling point due to presence of hydrogen bonds.
• Boiling point increase with chain length (increased London forces).
• Pure carboxylic acid, hydrogen bonding can occur between two molecules of acid to produce a dimer.
• Shorter chains are soluble as they can form H bonds as they don’t contain a bulky group in the way.
• Weakly acidic.

Question 4

Preparation of carboxylic acid: By oxidation

Answer 4

This uses a primary alcohol or aldehyde along with an oxidising agent, usually acidified potassium dichromate.
CH3CH2CH2OH + 2[O] —> CH3CH2COOH + H2O

Question 5

Preparation of carboxylic acid: By hydrolysis

Answer 5

• Can be formed by hydrolysis of nitriles under reflux with either dilute or aqueous alkali.
• Acidic hydrolysis: CH3CH2CN + H+ + 2H2O –> CH3CH2COOH + NH4^+
• Alkaline hydrolysis: CH3CH2CH2CN + OH- + H2O –> CH3CH2CH2COO- + NH3

Question 6

Reactions with carboxylic acids diagram

Answer 6

Question 7

Reactions with carboxylic acids: Reduction

Answer 7

Carboxylic acids can be reduced to primary alcohols, but not to aldehydes
Reducing agent: lithium tetrahydridoaluminate (lithium aluminium hydride)

Question 8

Acyl Chloride

Answer 8

• Known as acid chlorides.
• General formula: RCOCl.
• The C in RCOCl is attached to 2 electronegative atoms, so it is electron deficient (this means it is susceptible to attack by nucleophiles).

Question 9

Reactions of Acyl chlorides: Water

Answer 9

Question 10

Reactions of Acyl chlorides: Alcohols

Answer 10

Question 11

Reactions of Acyl chlorides: Conc. Ammonia solution

Answer 11

Question 12

Reactions of Acyl chlorides: Amines

Answer 12

Question 13

Esters

Answer 13

-Colourless liquids
-Relatively low melting points/ boiling points
-Insoluble in water
-Present in: perfumes, food flavourings, solvents
-Pleasant smell

Question 14

Esterification

Answer 14

• Esters are formed from the reaction of an alcohol and a carboxylic acid.
• Esters form in the presence of HCl or sulphuric acid (which acts as acids).
• The O-H bond in the alcohol and the C-O bond in the carboxylic acid will break.
• A new bond between the oxygen atom from the alcohol and the carbon atom in the carboxylic acid.

Question 15

Naming an ester

Answer 15

-Alcohol ends in -ly
-Acid ends in -oate
-Alcohol first, then acid

Question 16

Addition polymerisation

Answer 16

Involves an alkene monomer becoming a long chain polymer.
(One product)

Question 17

Condensation polymerisation

Answer 17

The joining of two monomers, with the elimination of a small molecule (eg. H2O)
Polyesters are polymers that have monomers bonded via an ester link

Question 18

Two ways to form polyesters

Answer 18

There are two ways to form a polyester:
1) Two different monomers, a diol and a dicarboxylic acid
(eg. Ethane-1,2-diol)
2) One monomer with -OH and -COOH groups
(eg. Poly(lactic acid))

Question 19

Making polyesters

Answer 19