Acylation & nucleophilic addition-elimination

This question is about polymers.

A section of the polymer PVC is shown.

Name the monomer used to make PVC.

Draw the structure of the monomer used to make PVC.

Structure

State why PVC is not biodegradable.

Diisobutyl phthalate (DIBP) is a plasticiser added to PVC to modify its properties.

State how the properties of PVC are modified by the addition of DIBP.

An incomplete equation for the reaction used to make DIBP is shown.

Complete the equation.

Give the name of the mechanism for this reaction.

Deduce the empirical formula of DIBP.

Empirical formula of DIBP

A different plasticiser, DEHA, is added to PVC used for food packaging.

The structure of DEHA is

Identify the organic compound that would react with hexanedioic acid to form DEHA.

DEHA can be absorbed into food from PVC packaging.

In an investigation, 1 kg samples of three different foods are stored in PVC packaging for 30 days.

Table 1 shows the water content, fat content and mass of DEHA in each type of food after 30 days.

Use your knowledge of intermolecular forces to explain these results.

The polymer nylon 6,6 can be made from hexanedioyl dichloride and hexane-1,6-diamine.

Figure 2 shows an incomplete mechanism for the first steps in this reaction.

Draw the missing intermediate in the box in Figure 2.

Complete Figure 2 by adding the curly arrows and any relevant lone pairs of electrons involved in these steps in the mechanism.

The polymer nylon 6 can be made by heating caprolactam with water.

Figure 3 shows the species involved in the first three steps of the mechanism for this reaction.

Complete Figure 3 by adding the curly arrows and any relevant lone pairs of electrons involved in these steps in the mechanism.

Hexanedioic acid is an important compound used in organic synthesis.

Hexanedioic acid can be prepared from cyclohexanol.

The equation for the reaction is

C₆H₁₁OH(l) + 2 HNO₃(aq) HOOC(CH₂)₄COOH(s) + N₂O(g) + 2 H₂O(l)

Method

Step 1 Add 5 cm³ of concentrated nitric acid to a boiling tube.

Step 2 Place the boiling tube in a beaker of water at 85 °C

Step 3 Add 2 cm³ of cyclohexanol dropwise to the boiling tube.

Step 4 Leave the reaction mixture for 10 minutes.

Step 5 Cool the boiling tube in a beaker of cold water for a further 10 minutes.

Step 6 Filter the contents of the boiling tube and collect the impure solid.

Step 7 Recrystallise the impure solid using methanol.

Step 8 Wash the purified crystalline product with some ice-cold distilled water, and dry.

Step 9 Measure the melting point of the hexanedioic acid.

Suggest why the apparatus should be set up in a fume cupboard.

Deduce the role of the concentrated nitric acid in the reaction.

Outline how Steps 7 and 8 should be done to obtain the purified crystalline product.

In Step 8, the distilled water must be ice-cold.

Suggest why using water at room temperature lowers the recorded yield of product.

Figure 4 shows how a student set up the apparatus for measuring the melting point of hexanedioc acid in Step 9 (data book value 152 °C).

The apparatus is supported by clamps but these are not shown.

Identify two mistakes the student made in setting up this apparatus.

State the problem caused by each mistake.

Figure 5 shows an alternative process to make hexanedioic acid.

Scientists disagree about whether this alternative process is more sustainable or less sustainable than the process starting from cyclohexanol.

Use the information given in Figure 5 to provide a justification for each point of view.

This question is about the preparation of an ester.

Ester F can be prepared from propan-2-ol and ethanoic acid.

Give an equation for this reaction.

Name ester F.

Equation

This method is used to prepare a sample of ester F.

Step 1 Mix 10 cm³ of propan-2-ol with 10 cm³ of ethanoic acid. Add 5 drops of concentrated sulfuric acid. Reflux this reaction mixture for 20 minutes.

Step 2 Transfer the cooled reaction mixture to a separating funnel. Add 20 cm³ of aqueous sodium carbonate and shake the mixture.

Step 3 Transfer the organic layer to a beaker and add 5 g of anhydrous magnesium sulfate. Decant off the organic liquid.

Step 4 Collect the ester using simple distillation.

Describe how Step 1 should be done.

In your description you should

• give details of suitable equipment used to add each reagent to the reflux apparatus

• draw a labelled diagram of the apparatus used for refluxing the reaction mixture

• explain any safety precautions needed other than eye protection.

In Step 2 the reaction mixture from Step 1 is shaken with aqueous sodium carbonate.

State the purpose of the sodium carbonate.

Suggest a precaution that should be taken while this mixture is shaken in the separating funnel.

Give a reason for your suggested precaution.

Purpose of sodium carbonate

Suggest how the purity of the ester can be confirmed during the distillation in Step 4.

The structure of 2-hydroxybenzenecarboxylic acid is shown.

Give the equation for the reaction of 2-hydroxybenzenecarboxylic acid with methanol.

In your equation, include the skeletal formula of the organic product.

Aspirin is produced from 2-hydroxybenzenecarboxylic acid by reaction with ethanoic anhydride in the presence of concentrated phosphoric acid.

Method

1. Add 2-hydroxybenzenecarboxylic acid to a conical flask.

2. Add excess ethanoic anhydride.

3. Add a few drops of concentrated phosphoric acid.

4. Heat the flask to 85 °C for 10 minutes.

5. Cool the flask and pour the contents into 150 cm³ of cold water.

6. Filter and wash the impure solid aspirin.

7. Recrystallise the aspirin using a 50:50 mixture of water and ethanol.

8. Check the purity of the aspirin.

Aspirin can also be produced by reacting 2-hydroxybenzenecarboxylic acid with ethanoyl chloride.

State why ethanoic anhydride is preferred to ethanoyl chloride for this preparation.

Give the name of the mechanism for the reaction of 2-hydroxybenzenecarboxylic acid with ethanoic anhydride.

Suggest the role of the concentrated phosphoric acid.

Suggest why reflux is not essential when the flask is heated to 85 °C for 10 minutes.

Complete and label the diagram to show how the impure solid is filtered.

Suggest the identity of two impurities present in the filtered solid aspirin before it is washed in Step 6 of the method.

Describe the recrystallisation process used to purify the aspirin.

Include the method and apparatus used.

State the physical property that is measured to check the purity of the aspirin.

Describe two ways the result would show that the product is impure.

Physical property

This question is about intermediates in reaction mechanisms.

Figure 3 shows an intermediate formed in the first step of a nucleophilic addition–elimination mechanism.

Figure 3

Complete Figure 3 to show the structures of the two reactant species with curly arrows and relevant lone pairs of electrons involved in the formation of the intermediate.

Draw curly arrows and relevant lone pairs of electrons on the intermediate to show how the final products are formed.

Figure 4 shows an intermediate formed in the first step of a reaction mechanism of methylbenzene.

Complete Figure 4 to show the reactant species and any curly arrows involved in the formation of the intermediate.

Draw a curly arrow on the intermediate to show how the product is formed.

Give the name of the reaction mechanism.

Name of mechanism

Figure 5 shows the reactant species involved in the first step of a mechanism.

Figure 5

Complete Figure 5 to show the structure of the intermediate formed with curly arrows involved in its formation.

Give the name of the reaction mechanism.

Name of mechanism

Ethyl ethanoate can be made by reacting ethanol with ethanoic acid in the presence of concentrated sulfuric acid.

1. A mixture of ethanol, ethanoic acid, and concentrated sulfuric acid, with anti-bumping granules, is heated under reflux for 10 minutes.

2. The apparatus is rearranged for distillation.

3. The mixture is heated to collect the liquid that distils between 70 and 85 C

4. The distillate is placed in a separating funnel. Aqueous sodium carbonate is added, and a stopper is placed in the funnel. The mixture is shaken, releasing pressure as necessary.

5. The lower aqueous layer is removed and the upper organic layer is placed in a small conical flask.

6. Anhydrous calcium chloride is added to the sample in the conical flask. The flask is shaken well and left for a few minutes.

7. The liquid from the flask is redistilled and the distillate is collected between

State the role of concentrated sulfuric acid in this reaction.

The reaction mixture is flammable.

Suggest how the reaction mixture should be heated in step 1.

Figure 1 shows how a student set up the apparatus for reflux in step 1. You should assume that the apparatus is clamped correctly.

Identify two mistakes the student made in setting up the apparatus. State the problem caused by each mistake.

State why sodium carbonate is added to the distillate in step 4.

Explain why there is a build-up of pressure in the separating funnel.

Give a reason why two layers form in the separating funnel.

Suggest why ethyl ethanoate forms the upper layer.

State why anhydrous calcium chloride is added in step 6.

A student uses the method to prepare some ethyl ethanoate.

The student adds 10.0 cm³ of ethanol (M_r = 46.0) to 5.25 g of ethanoic acid (M_r = 60.0) and obtains 5.47 g of ethyl ethanoate (M_r = 88.0).

For ethanol, density = 0.790 g cm^–3

Determine the limiting reagent.

Calculate the percentage yield of ethyl ethanoate.

Suggest a reason why the percentage yield is not 100%.

This question is about the preparation of hexan-2-ol. Hexan-2-ol does not mix with water and has a boiling point of 140^oC

Hexan-2-ol can be prepared from hex-1-ene using this method.

a Measure out 11.0 cm³ of hex-1-ene into a boiling tube in an ice bath. b Carefully add 5 cm³ of concentrated phosphoric acid to the hex-1-ene. c After 5 minutes add 10 cm³ of distilled water to the mixture and transfer the boiling tube contents to a separating funnel.

d Shake the mixture and allow it to settle. e Discard the lower (aqueous) layer. f Add a fresh 10 cm³ sample of distilled water and repeat steps d and e. g Transfer the remaining liquid to a beaker. h Add 2 g of anhydrous magnesium sulfate and allow to stand for 5 minutes. i Filter the mixture under reduced pressure. j Distil the filtrate and collect the distillate that boils in the range 130–160^oC

It is important to wear eye protection and a lab coat when completing this experiment.

Suggest, with a reason, one other appropriate safety precaution for this experiment.

Give a reason for adding the distilled water in steps c and f.

Give a reason for adding anhydrous magnesium sulfate in step h.

Complete and label the diagram of the apparatus used to filter the mixture under reduced pressure in step i.

Identify the most likely organic impurity, other than hex-1-ene, in the distillate collected in step j.

Suggest one reason why it could be difficult to remove this impurity.

Calculate the mass, in g, of hexan-2-ol formed from 11.0 cm³ of hex-1-ene if the yield is 31.0%

Give your answer to 1 decimal place.

Density of hex-1-ene = 0.678 g cm⁻³

Which compound is an amide?

This question is about making a diester from cyclohexanol.

State the type of reaction in step 1.

Give the name of the reagent needed for step 1.

State the reagents needed and give equations for step 2 and step 3.

Show the structure of Compound G in your equations.

Step 2 equation

Step 3 equation

Cyclohexane-1,2-diol reacts with ethanedioyl dichloride.

Give the name of the mechanism for this reaction.

Complete the mechanism to show the formation of one ester link in the first step of this reaction.

Mechanism

Suggest why chemists usually aim to design production methods

• with fewer steps

• with a high percentage atom economy.

High percentage atom economy

This question is about ketones.

Solution X reacts with liquid ketones to form a crystalline solid.

This reaction can be used to identify a ketone if the crystalline solid is separated, purified by recrystallisation, and the melting point determined.

Describe how the crystalline solid is separated and purified.

Propanone (CH₃COCH₃) reacts with the weak acid HCN to form a hydroxynitrile.

This hydroxynitrile is usually made by reaction of propanone with KCN followed by dilute acid, instead of with HCN

State the hazard associated with the use of KCN

Suggest a reason, other than safety, why KCN is used instead of HCN.

Why KCN is used

Outline the mechanism for the reaction of propanone with KCN followed by dilute acid.

Which compound forms a white precipitate when added to aqueous silver nitrate?

Which compound reacts with warm dilute aqueous sodium hydroxide?

Prilocaine is used as an anaesthetic in dentistry. Figure 3 shows the structure of prilocaine.

Draw a circle around any chiral centre(s) in Figure 3.

Identify the functional group(s) in the prilocaine molecule.

Tick (✓) the box(es) corresponding to the functional group(s).

Prilocaine is completely hydrolysed in the human body to give a mixture of products.

Draw the structures of the two organic products formed in the complete hydrolysis of prilocaine in acidic conditions.

Figure 4 shows optical isomers F and G.

Isomer F is the active compound in the medicine ibuprofen.

In the manufacture of ibuprofen both isomers F and G are formed. An enzyme is then used to bind to isomer G and catalyse its hydrolysis.

After the products of hydrolysis of G are removed, a pure sample of isomer F is collected.

Explain how a structural feature of this enzyme enables it to catalyse the hydrolysis of isomer G but not the hydrolysis of isomer F.

Describe the instruction that is missing from step 4 of the method.

Justify why this step is necessary.

Suggest a suitable piece of apparatus to measure out the ethanoic anhydride in step 5.

Identify a hazard of using concentrated phosphoric acid in step 6.

Complete the equation for the reaction of salicylic acid with ethanoic anhydride to produce aspirin.

A 6.01 g sample of salicylic acid (M_r = 138.0) is reacted with

The density of ethanoic anhydride is 1.08 g cm^–3

Show by calculation which reagent is in excess.

Calculate the mass, in g, of aspirin (M_r = 180.0) produced.

Suggest two ways in which the melting point of the crude aspirin collected in step 9 would differ from the melting point of pure aspirin.

The crude aspirin can be purified by recrystallisation using hot ethanol (boiling point = 78 °C) as the solvent.

Describe two important precautions when heating the mixture of ethanol and crude aspirin.

The pure aspirin is filtered under reduced pressure. A small amount of cold ethanol is then poured through the Buchner funnel.

Explain the purpose of adding a small amount of cold ethanol.

A sample of the crude aspirin is kept to compare with the purified aspirin.

Describe one difference in appearance you would expect to see between these two solid samples.

Which reaction involves addition-elimination?

A student prepared cyclohexene by heating cyclohexanol with concentrated phosphoric acid. The cyclohexene produced was distilled off from the reaction mixture.

Complete the diagram of the apparatus used to distil the cyclohexene from the reaction mixture at 83 °C.

The distillate was shaken with saturated sodium chloride solution. The cyclohexene was separated from the aqueous solution using a separating funnel.

State why cyclohexene can be separated from the aqueous solution using the separating funnel.

The cyclohexene separated in Question 02.2 was obtained as a cloudy liquid. The student dried this cyclohexene by adding a few lumps of anhydrous calcium chloride and allowing the mixture to stand.

Give one observation that the student made to confirm that the cyclohexene was dry.

In this preparation, the student added an excess of concentrated phosphoric acid to

Calculate the percentage yield of cyclohexene obtained. Give your answer to the appropriate number of significant figures.

Cyclohexene reacts with bromine.

Complete the mechanism for this reaction.

Paracetamol is a medicine commonly used to relieve mild pain. Traditionally, paracetamol has been made industrially in a three-step synthesis from

Name the mechanism of the reaction in Step 1.

Complete the equation for the reaction in Step 2.

In theory, either ethanoyl chloride or ethanoic anhydride could be used in Step 3.

Complete the mechanism for the reaction of 4-aminophenol with ethanoyl chloride. RNH₂ is used to represent 4-aminophenol in this mechanism.

In practice, ethanoic anhydride is used in the industrial synthesis rather than ethanoyl chloride.

Give one reason why ethanoyl chloride is not used in the industrial synthesis.

In Step 3 other aromatic products are formed as well as paracetamol.

Draw the structure of one of these other aromatic products.

Chemists have recently developed a two-step process to produce paracetamol from phenol. In the first step, phenol is oxidised to hydroquinone.

In the second step, hydroquinone reacts with ammonium ethanoate to form paracetamol.

Complete the equation for this second step.

Calculate the mass, in kg, of hydroquinone (M_r = 110.0) needed to produce 250 kg of paracetamol.

This question is about esters including biodiesel.

An ester is formed by the reaction of an acid anhydride with CH₃CH₂OH

Complete the equation. In your answer show clearly the structure of the ester. Give the IUPAC name of the ester.

In a reaction to form biodiesel, one mole of a vegetable oil reacts with an excess of methanol to form two moles of an ester with molecular formula C₁₉H₃₄O₂ and one mole of an ester with molecular formula C₁₉H₃₆O₂

Draw the structure of the vegetable oil showing clearly the ester links.

You should represent the hydrocarbon chains in the form C_xH_y where x and y are the actual numbers of carbon and hydrogen atoms.

The compound C₁₉H₃₄O₂ is the methyl ester of Z,Z-octadeca-9,12-dienoic acid.

Part of the structure of the acid is shown.

Complete the skeletal formula to show the next part of the hydrocarbon chain to carbon atom number 14. In your answer, show the Z stereochemistry around both C=C double bonds.

Give an equation for the complete combustion of the ester C₁₉H₃₄O₂

Combustion of biodiesel produces greenhouse gases such as carbon dioxide that cause global warming. Part of the infrared spectrum of carbon dioxide is shown in Figure 3.

State how the infrared spectrum of carbon dioxide in Figure 3 is not what you might predict from the data provided in Table A in the Data Booklet.

Explain how carbon dioxide causes global warming.

A student is required to dry a liquid sample of pentanoic acid.

Which drying agent is suitable?

Which compound can be purified by forming a hot aqueous solution that recrystallises on cooling?

The elements sodium to sulfur in Period 3 all react with oxygen to form oxides.

Give an equation and two observations made for the reaction that occurs when sodium is heated in oxygen.

Give an equation and one observation made for the reaction that occurs when phosphorus is heated in oxygen.

The melting points of the highest oxides of the elements sodium to sulfur are shown in Table 2.

Explain the increase in melting point from sodium oxide to magnesium oxide.

Explain why the melting point of the oxide of silicon is much higher than that of the highest oxide of phosphorus.

A sample of the highest oxide of phosphorus was prepared in a laboratory.

Describe a method for determining the melting point of the sample. State how the result obtained could be used to evaluate its purity.

Cyclohexene (boiling point = 83 °C) can be prepared by the dehydration of cyclohexanol (boiling point = 161 °C) using concentrated phosphoric acid.

A student prepared cyclohexene by placing 10 cm³ of cyclohexanol (density = 0.96 g cm^–3) into a round-bottomed flask. 3 cm³ of concentrated phosphoric acid were then carefully added to the flask. The student added a few anti-bumping granules and set up the apparatus shown in Figure 3.

• The student heated the mixture and collected the liquid that distilled at temperatures below 100 °C

• The distillate was poured into a separating funnel and washed by shaking with sodium carbonate solution.

• Periodically, the separating funnel was inverted and the tap opened.

• The aqueous layer was discarded and the final organic product was dried using anhydrous calcium chloride.

• After the product was dried, the drying agent was removed by filtration under reduced pressure.

The student collected 5.97 g of cyclohexene in the experiment.

Calculate the percentage yield of cyclohexene.

Describe a test-tube reaction, on the product, to show that the cyclohexanol had been dehydrated. State what you would observe.

Suggest why sodium carbonate solution was used to wash the distillate.

Explain why it is important to open the tap of the separating funnel periodically.

Give a property of anhydrous calcium chloride, other than its ability to absorb water, that makes it suitable as a drying agent in this preparation.

Describe the apparatus used to remove the drying agent by filtration under reduced pressure. Your description of the apparatus can be either a labelled diagram or a description in words.

A sample of cyclohexene has been contaminated with cyclohexanol. The cyclohexene can be separated from the cyclohexanol by column chromatography. Silica gel is used as the stationary phase and hexane as the mobile phase.

Explain why cyclohexene has a shorter retention time than cyclohexanol.

Explain how an infrared spectrum would confirm that the cyclohexene obtained from the chromatography column did not contain any cyclohexanol.

This question is about amino acids and peptide (amide) links.

Draw the structure of the zwitterion formed by phenylalanine.

Draw the structure of serine at high pH.

Draw the structures of both dipeptides formed when phenylalanine reacts with serine.

In each structure show all the atoms and bonds in the amide link.

An amide link is also formed when an acyl chloride reacts with a primary amine.

Name and outline a mechanism for the reaction between CH₃CH₂COCl and

Give the IUPAC name of the organic product.

Name of mechanism

Mechanism

IUPAC name of organic product