Organic synthesis routes

This question is about reactions of haloalkanes.

Haloalkanes can react with potassium cyanide to form new carbon–carbon bonds.

Outline the mechanism for the reaction of 2-bromopropane with cyanide ions.

Show curly arrows, relevant dipoles and products.

Name this type of mechanism.

The table below shows the boiling points of propan-1-ol and 1-bromopropane.

Propan-1-ol can be reacted to form 1-bromopropane.

Suggest suitable reagents for this reaction.

The reaction to form 1-bromopropane from propan-1-ol is carried out in a flask.

After the reaction, the flask contains a mixture of an organic layer (density = 1.35 g cm^–3) and an aqueous layer (1.04 g cm^–3).

Describe how to obtain pure 1-bromopropane from the mixture.

Oil of wintergreen is a liquid used in medicine to relieve muscle pain.

Compound H is a component in oil of wintergreen and can be synthesised from compound G, as shown below. The boiling point and density of compound H are stated.

Compound G
Compound H boiling point = 222 °C density = 1.174 g cm⁻³

A student prepares a sample of compound H by the method below.

Step 1 Reflux 8.97 g of compound G for 30 minutes with an excess of methanol in the presence of a small amount of sulfuric acid as a catalyst.

Step 2 Add an excess of aqueous sodium carbonate, Na₂CO₃(aq). Two layers are obtained.

Step 3 Purify the impure compound H that forms from the resulting mixture.

The student follows this method and obtains 5.32 g of pure compound H.

Why does the student use reflux in Step 1 ?

In Step 2, Na₂CO₃(aq) removes the sulfuric acid catalyst and any unreacted compound G from the mixture.

Write equations for this removal.

Removal of sulfuric acid

Removal of unreacted compound G

Compound G

Another student suggests that adding aqueous sodium hydroxide would be more effective in removing the sulfuric acid catalyst than Na₂CO₃(aq).

Comment on whether the student’s suggestion is an improvement for the preparation of compound H.

Calculate the percentage yield of compound H.

Give your answer to three significant figures.

Describe how to purify the impure compound H from the two layers in Step 2.

The structure of the painkiller paracetamol is shown below.

Which functional groups are present in paracetamol?

A alcohol, amide

B alcohol, arene, ketone, amine

C phenol, amide

D phenol, ketone, amine

Outline the mechanism for this reaction, including the role of H₂SO₄ as a catalyst.

Determine the percentage yield of 1,3-dinitrobenzene.

Give your answer to 3 significant figures.

Describe how to purify the impure crystals in Step 3.

Aspirin tablets are used for pain relief.

The structure of aspirin is shown below.

A student uses the reaction of aspirin with cold NaOH(aq) to determine the mass of aspirin in one tablet.

In this reaction, 1 mol of aspirin reacts with 1 mol of cold NaOH(aq).

The student’s method is outlined below.

Step 1 The student reacts three aspirin tablets with 100 cm³ of 0.500 mol dm^–3 NaOH(aq). The NaOH is in excess. A colourless solution forms.

Step 2 The colourless solution from Step 1 is made up to 250.0 cm³ with distilled water.

Step 3 A 25.00 cm³ sample of the diluted solution from Step 2 is titrated with 0.200 mol dm^–3 HCl(aq) in the burette.

The HC l (aq) reacts with excess NaOH(aq) that remains in Step 1:

The student repeats the titration to obtain concordant (consistent) titres.

Titration results The trial titre has been omitted.

The burette readings have been read to the nearest 0.05 cm³.

Analysis of results From the results, the student can determine the following.

1. The amount, in mol, of excess NaOH(aq) that remains after the reaction of aspirin with NaOH(aq).

2. The amount, in mol, of NaOH(aq) that reacted with the aspirin.

Use the results to determine the mass, in mg, of aspirin in one aspirin tablet.

Aspirin reacts with hot NaOH(aq), under reflux.

Draw a labelled diagram of suitable apparatus for reflux.

In this reaction, 1 mol of aspirin reacts with 3 mol of hot NaOH(aq).

Complete the equation for the reaction of aspirin with an excess of hot NaOH(aq).

Show structures for organic compounds.

The skeletal formula of an organic compound is shown below.

Which functional groups are present?

A amide and alcohol

B amide and carboxylic acid

C amine and carboxylic acid

D amine, ketone and alcohol

This question is about compounds that contain the carboxylic acid functional group.

Carboxylic acids react with alkalis, metals and carbonates to form salts.

Write full equations for the following three reactions. Show structures for organic compounds.

• the reaction of propanoic acid with aqueous potassium hydroxide:

• the reaction of aqueous methanoic acid with magnesium:

• the reaction of the –amino acid, aspartic acid (R=CH₂COOH), with an excess of aqueous sodium carbonate, Na₂CO₃:

This part is about polymers derived from carboxylic acid monomers.

Poly(pent-3-enoic acid) is an addition polymer.

Draw the structure of pent-3-enoic acid and two repeat units of this polymer.

Butanedicarboxylic acid and 1,4-dihydroxy-2-methylbenzene react to form a condensation polymer.

Draw one repeat unit of this condensation polymer.

Three repeat units of a condensation polymer are shown below.

Draw the structure of the monomer required to form this polymer.

A polymer is formed from 400 molecules of 2-aminopropanoic acid.

Draw one repeat unit of this polymer.

What is the relative molecular mass, M_r, of the polymer?

Information about 1-bromobutane and butan-1-ol is shown in the table.

A student prepares a sample of 1-bromobutane by refluxing 9.25 g of butan-1-ol with sodium bromide and sulfuric acid.

After reflux, the reaction mixture is purified.

The student obtains 6.10 cm³ of pure 1-bromobutane.

* Draw a diagram to show how the student would have carried out the reflux and calculate the percentage yield of 1-bromobutane that the student obtains.

Describe how the student could have obtained pure 1-bromobutane from the reaction

mixture obtained after reflux.

Butan-1-ol reacts with sodium bromide and sulfuric acid to form 1-bromobutane by nucleophilic substitution.

The mechanism for this reaction takes place by two steps.

Step 1 The oxygen atom of the alcohol group accepts a proton to form a positively-charged intermediate.

Step 2 Bromide ions react with the intermediate from Step 1 by nucleophilic substitution to form 1-bromobutane.

Show both steps in this mechanism.

This question is about organic acids.

Table 18.1 shows the R groups in four amino acids.

Most amino acids show optical isomerism.

Explain the term optical isomerism.

Draw 3-D diagrams to show the optical isomers of alanine.

How many optical isomers does threonine have?

Ibuprofen, shown below, is used as a painkiller.

What is the molecular formula of ibuprofen?

One ibuprofen tablet contains 400 mg of ibuprofen.

Calculate the number of ibuprofen molecules in one ibuprofen tablet.

Give your answer to 3 significant figures.

Tablets based on ibuprofen and lysine are now available from pharmacies.

These tablets are claimed to act faster than ibuprofen by being absorbed into the body more quickly than ibuprofen alone.

One type of these tablets contains a salt of ibuprofen and the amino acid lysine (R = –(CH₂)₄NH₂) in a 1:1 molar proportion.

Suggest why tablets based on a salt of ibuprofen should act faster in the body than ibuprofen.

This question is about reactions of phenol.

Complete the mechanism below for Stage 1 and Stage 2.

Show curly arrows, the structure of the intermediate and the missing formulae on the dotted lines.

Two molecules of salicylic acid can react together in the presence of an acid catalyst to form compound B.

Compound B has three rings and a molecular formula of C₁₄H₈O₄.

Write the equation for this reaction showing the structures of organic compounds.

A student reacts phenol with nitric acid and sulfuric acid at 100 °C to form impure crystals of an organic compound, C. The student purifies the crystals by recrystallisation.

Describe how the student could recrystallise the impure crystals to obtain a pure sample of C.

The pure sample of C is analysed to give the following results.

Percentage composition by mass: C, 31.44%; H, 1.31%; N, 18.34%; O, 48.91%.

The mass spectrum of C shows a molecular ion peak at m / z = 229.0

The¹³C NMR spectrum of C is shown below.

The table shows directing effects for different groups in the electrophilic substitution of aromatic compounds.

Analyse all the information to suggest the structure for C.

Show all your reasoning.

compound C

Which of these reagent(s) will not react with HOCH₂CH₂CH₂COOH?

A NaCN in ethanol

B C₂H₅OH in the presence of an acid catalyst

C (CH₃CO)₂O

D concentrated H₂SO₄

Cyclopentanol can be reacted to form cyclopentene. Cyclopentene is a liquid with a boiling point of 44 °C and a density of 0.74 g cm⁻³.

A student plans to prepare 4.00 g of cyclopentene by reacting cyclopentanol (boiling point 140 °C) with an acid catalyst.

The expected percentage yield of cyclopentene is 64.0%.

Method The student carries out the preparation using apparatus set up for distillation, as shown below.

1 The reaction mixture is heated gently, and a distillate containing impure cyclopentene is collected.

2 The distillate has an aqueous layer and an organic layer. The student purifies the cyclopentene from the distillate.

* Calculate the mass of cyclopentanol that the student should use and explain how pure

cyclopentene could be obtained from the distillate.

This question is about organic compounds containing nitrogen.

Salt H, (CH₃)₂CHNH₃Cl, is used in the manufacture of garden weedkillers.

The flowchart shows the synthesis of the salt H from propanone.

Complete the flowchart. Show structures for organic compounds.

Aspartame, shown below, is an artificial sweetener commonly used as a sugar substitute.

Aspartame contains several functional groups.

Apart from the benzene ring, name the functional groups in aspartame.

A sample of aspartame is hydrolysed with aqueous acid.

Draw the structures of the three organic products of the complete acid hydrolysis aspartame.

This question is about organic chemistry.

This part is about two practical techniques used in organic preparations.

Complete the missing labels on the diagram and name the technique.

Name of technique:........

Draw a labelled diagram to show apparatus set up for filtration under reduced pressure (vacuum filtration).

This part is about amines.

Amine A is a liquid at room temperature and pressure.

When vaporised, 0.202 g of the amine produces 72.0 cm³ of gas at 1.00 × 10⁵ Pa and 100 °C. The¹³C NMR spectrum of amine A has 3 peaks.

Determine the molecular formula of A and suggest a possible structure for amine A.

Molecular formula of A........

Structure of A

The structure of a compound used to treat influenza is shown below.

Which functional group(s) is/are in a molecule of the compound?

1 Ester

2 Secondary amide

3 Ketone

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

In Step 1, sodium carbonate, Na₂CO₃, makes the reaction mixture alkaline.

Write an ionic equation to show how carbonate ions form an alkaline solution in water.

In Step 2, explain why the mixture must be acidified so that crystals of benzoic acid appear.

Write the overall equation for the preparation of benzoic acid from phenylmethanol.

Use [O] for the oxidising agent.

Calculate the percentage yield of benzoic acid.

Give your answer to 3 significant figures.

In Step 3, describe how the student can recrystallise the impure crystals to obtain pure benzoic acid.

Dettol ® is a disinfectant containing the antiseptic chloroxylenol, shown below.

Chloroxylenol is a weak Brønsted–Lowry acid.

What is the systematic name of chloroxylenol?

Predict the number of peaks in a¹³C NMR spectrum of chloroxylenol.

Name the functional group responsible for the acidity of chloroxylenol and describe a simple test which would confirm the presence of this group.

Functional group........

Test........

A student measures the pH of the contents in a bottle of Dettol ® as 5.14.

The label on the bottle shows the percentage of chloroxylenol in Dettol ® as 4.80% i.e. 100 cm³ of Dettol^® contains 4.80 g of chloroxylenol.

Assume the following:

• Chloroxylenol is the only acidic component in Dettol ®.

• Chloroxylenol is a weak monobasic acid.

• The density of Dettol ® is 1.00 g cm −3.

Write the equation, using molecular formulae, for the acid dissociation of chloroxylenol.

Calculate the acid dissociation constant, K_a, for chloroxylenol.

K_a =........ mol dm⁻³

Dettol^® contains other chemicals including -terpineol, shown below.

-Terpineol is a chiral compound.

Show with an asterisk, (*), the chiral centre(s) in the structure of -terpineol.

-Terpineol meets the requirements for E / Z isomerism. However, only one E / Z isomer of -terpineol exists.

Explain

• why -terpineol meets the requirements for E / Z isomerism

• whether -terpineol is an E- or Z- isomer

• why only one E / Z isomer of -terpineol exists.

-Terpineol contains two functional groups.

For each functional group, choose a reagent that reacts with that group only. Draw the structures for the organic products of the reactions.

Show structures for organic compounds.

Reagent(s)........

Name of functional group that reacts........

Structure of organic product

Reagent(s)........

Name of functional group that reacts........

Structure of organic product

A solid organic compound can be purified by recrystallisation.

Which statement(s) about recrystallisation is/are true?

1 The organic compound is more soluble in hot solvent.

2 The hot solution is cooled before the purified organic compound is collected.

3 The melting point of the purified organic compound is lower than the impure compound.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

This question is about the hydrolysis of haloalkanes.

The rate of hydrolysis of a haloalkane depends on the halogen present.

State and explain how the halogen in the haloalkane affects the rate of hydrolysis.

A student hydrolyses a haloalkane, E, using the following method.

• 0.0100 mol of haloalkane E is refluxed with excess NaOH(aq) to form a reaction mixture containing an organic product F.

• The reaction mixture is neutralised with dilute nitric acid.

• Excess AgNO₃(aq) is added to the reaction mixture. 1.88 g of a precipitate G forms.

Organic product, F, has a molar mass of 74.0 g mol⁻¹ and has a chiral carbon atom.

Draw a labelled diagram to show how the student would carry out the hydrolysis of haloalkane E.

Analyse the information to identify E, F and G.

Show your working.

This question is about two compounds used in medicine.

Cis-platin, PtCl₂(NH₃)₂, is a complex of platinum which is used in cancer treatment.

What is the oxidation number of platinum in cis-platin?

Cis-platin is prepared in a ligand substitution reaction which takes place in multiple steps.

The equation for the final step forming cis-platin is shown below.

cis-platin

In the box, outline the mechanism for the formation of cis-platin from [PtCl₃(NH₃)]^–. Use curly arrows and lone pairs where appropriate.

cis-platin

Paracetamol is a solid organic compound used in tablets as a painkiller.

Name the functional groups present in paracetamol.

Which molecule is a secondary amine?

This question is about the chemistry of aromatic compounds.

Benzoic acid can be nitrated by concentrated nitric acid in the presence of concentrated sulfuric acid as a catalyst, as shown in Equation 17.1.

The organic product of this reaction is 3-nitrobenzoic acid.

Outline the mechanism for this nitration of benzoic acid.

Show how H₂SO₄ behaves as a catalyst.

* A chemist carries out the reaction in Equation 17.1 using 4.97 g of benzoic acid.

The chemist obtains 3-nitrobenzoic acid as an impure solid.

The chemist purifies the solid to obtain 4.85 g of 3-nitrobenzoic acid.

Describe a method to obtain a pure sample of 3-nitrobenzoic acid from the impure solid, determine the percentage yield and check its purity.

A student investigates the relative ease of nitration of phenol, benzene, and benzoic acid.

The student finds that the conditions required for the nitration of each compound are different, as shown in Table 17.1.

State the trend in the relative ease of nitration of phenol, benzene, and benzoic acid.

Apply your knowledge of the bonding in arenes to explain the trend in part (b)(i).

A student synthesises 3-bromophenylamine, shown below, starting from nitrobenzene.

Complete the flowchart showing the structure of the intermediate and the formulae the reagents for each stage.

Another student attempts the same synthesis but carries out reduction before bromination. The student was surprised to find that two structural isomers of 3-bromophenylamine had been formed instead of the desired organic product.

Explain this result and suggest the structures of the two isomers that formed.

Explanation........

Structures