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Paracetamol is a medicine commonly used to relieve mild pain - AQA - A-Level Chemistry - Question 8 - 2019 - Paper 2

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Paracetamol is a medicine commonly used to relieve mild pain. Traditionally, paracetamol has been made industrially in a three-step synthesis from phenol. Step 1 S... show full transcript

Worked Solution & Example Answer:Paracetamol is a medicine commonly used to relieve mild pain - AQA - A-Level Chemistry - Question 8 - 2019 - Paper 2

Step 1

Name the mechanism of the reaction in Step 1.

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Answer

The mechanism of the reaction in Step 1 is electrophilic substitution.

Step 2

Complete the equation for the reaction in Step 2.

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Answer

The equation for the reaction in Step 2 is:

C6H4(OH)+HNO2→C6H4(NO2)(OH)+H2OC_6H_4(OH) + HNO_2 \rightarrow C_6H_4(NO_2)(OH) + H_2O

Step 3

Complete the mechanism for the reaction of 4-aminophenol with ethanoyl chloride.

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Answer

The mechanism for the reaction of 4-aminophenol with ethanoyl chloride is as follows:

  1. The lone pair on the nitrogen of 4-aminophenol attacks the carbonyl carbon of ethanoyl chloride, forming a tetrahedral intermediate.
  2. The intermediate collapses, releasing HCl and forming paracetamol.

The overall equation can be illustrated as follows:

C6H4(NH2)(OH)+CH3COCl→C6H4(CONH2)(OH)+HClC_6H_4(NH_2)(OH) + CH_3COCl \rightarrow C_6H_4(CONH_2)(OH) + HCl

Step 4

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

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Answer

One reason why ethanoyl chloride is not used in industrial synthesis is that it is corrosive and can release harmful fumes during the reaction.

Step 5

Draw the structure of one of these other aromatic products.

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Answer

One other aromatic product that can be formed is 4-nitrophenol, represented structurally as:

    OH
     |  
  C6H4-NO2

Step 6

Complete the equation for this second step.

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Answer

The equation for the reaction of hydroquinone with ammonium ethanoate is:

C6H4(OH)+NH4C2H3O2→C6H4(CONH2)+H2OC_6H_4(OH) + NH_4C_2H_3O_2 \rightarrow C_6H_4(CONH_2) + H_2O

Step 7

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

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Answer

To calculate the mass of hydroquinone needed:

  1. Calculate the moles of paracetamol: extMolesofparacetamol=250 kg0.15 kg/mol=1666.67 moles ext{Moles of paracetamol} = \frac{250 \text{ kg}}{0.15 \text{ kg/mol}} = 1666.67 \text{ moles}

  2. You'll need the same amount of hydroquinone (1:1 molar ratio in the reaction). So, moles of hydroquinone = 1666.67 moles.

  3. Calculate the mass of hydroquinone: extMassofhydroquinone=moles×Mr=1666.67 moles×110.0 g/mol=183333.7 g=183.34 kg ext{Mass of hydroquinone} = \text{moles} \times M_r = 1666.67 \text{ moles} \times 110.0 \text{ g/mol} = 183333.7 \text{ g} = 183.34 \text{ kg}

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