28.2 Preparation of an Organic Solid & 28.3 Further Synthetic Routes

Question 1

What are the 3 stages of purifying an organic solid?

Answer 1

• Filtration under reduced pressure
• Recrystallisation
• Determining the melting point

Question 2

What does filtration under reduced pressure do?

Answer 2

• It separates the solid from the solvent or the liquid reaction mixture

Question 3

How does filtration under reduced pressure work?

Answer 3

• A Buchner flask is fitted with a Buchner funnel with filter paper
• Pressure is created through a vacuum pump that is connected to the flask through a side arm

Question 4

What does recrystallisation do?

Answer 4

• It removes impurities after filtration

Question 5

How does recrystallisation work?

Answer 5

• You choose a solvent that your solid will dissolve in when it’s hot, and the impurities will dissolve in when it’s cold
• Dissolve the impure solid in the minimum possible volume of hot solvent
• Cool the solution and filter the solid under reduced pressure
• Wash the crystals with cold solvent and dry them

Question 6

What can melting points determine about substances? Give 2 details.

Answer 6

• How pure they are
• Pure samples will have a sharp melting point close to the literature value (impurities lower the melting point, and causes the substance to melt over a range of temperatures)

Question 7

What are 2 methods for determining melting points?

Answer 7

• Using electrically heated melting point apparatus
• Using an oil bath/ Thiele tube

Question 8

What products can benzene react to form?

Answer 8

• Nitrobenzene
• Halobenzene
• Alkylbenzene
• Phenylketone

Question 9

Benzene to nitrobenzene. Reactants, conditions and mechanism if applicable.

Answer 9

• Reactants: concentrated nitric acid and benzene
• Conditions: concentrated sulfuric acid catalyst, 50°C
• Mechanism: electrophilic substitution
• HNO3 (conc) + H2SO4 (conc) -> NO2+ + HSO4- + H2O
• C6H6 + NO2+ -> C6H5NO2 + H+
• H+ + HSO4- -> H2SO4

Question 10

Benzene to bromobenzene. Reactants, conditions and mechanism if applicable.

Answer 10

• Reactants: bromine and benzene
• Conditions: halogen carrier catalyst
• Mechanism: electrophilic substitution
• Br2 + FeBr3 -> FeBr4- + Br+
• C6H6 + Br+ -> C6H5Br + H+
• H+ + FeBr4- -> FeBr3 + HBr

Question 11

Benzene to alkylbenzene. Reactants, conditions and mechanism if applicable.

Answer 11

• Reactants: haloalkane and benzene
• Conditions: halogen carrier catalyst
• Mechanism: electrophilic substitution
• Benzene + haloalkane -> alkyl benzene + hydrogen halide

Question 12

Benzene to phenylketone. Reactants, conditions and mechanism if applicable.

Answer 12

• Reactants: acyl chloride and benzene
• Conditions: iron (III) chloride/ aluminium chloride
• Mechanism: electrophilic substitution
• Benzene + acyl chloride -> phenylketone + hydrogen chloride

Question 13

What can phenol react to form?

Answer 13

• 2,4,6-tribromophenol
• Nitrophenol
• Metal phenoxide

Question 14

Phenol to 2,4,6-tribromophenol. Reactants, conditions and mechanism if applicable. Give 2 extra details.

Answer 14

• Reactants: phenol and bromine water
• Conditions: room temperature, no catalyst
• Mechanism: electrophilic substitution
• C6H5OH + 3Br2 -> 2,4,6-tribromophenol + 3HBr
• Bromine water is decolourised
• A white precipitate (2,4,6-tribromophenol) is formed

Question 15

Phenol to nitrophenol. Reactants, conditions and mechanism if applicable. Give 1 extra detail.

Answer 15

• Reactants: phenol and dilute nitric acid
• Conditions: room temperature, no catalyst
• Mechanism: electrophilic substitution
• Phenol + dilute nitric acid -> 2-nitrophenol/ 4-nitrophenol + water
• A mixture of 2-nitrophenol and 4-nitrophenol is formed

Question 16

Phenol to sodium phenoxide. Reactants, conditions and mechanism if applicable. Give 1 extra detail.

Answer 16

• Reactants: phenol and sodium hydroxide
• Conditions: room temperature, no catalyst
• Products: sodium phenoxide and water
• Neutralisation