Organic synthesis routes

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.

Consider this reaction scheme.

Which step is shown with a correct reagent and a correct condition?

Which type of reaction is not involved in this reaction sequence?

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

A possible synthesis of a compound found in jasmine flower oil is shown.

Which mechanism is not used in this synthesis?

Amines E, F and G are weak bases.

Explain the difference in base strength of the three amines and give the order of increasing base strength.

Amine F can be prepared in a three-step synthesis starting from methylbenzene.

Suggest the structures of the two intermediate compounds.

For each step, give reagents and conditions only. Equations and mechanisms are not required.