Edexcel A-Level Chemistry A2 20 Organic Synthesis Questions

This question concerns six isomers each with the molecular formula $\mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}_{2}$.

Isomer F is a neutral compound that smells of pears.

It can be formed by the reaction between compounds V and W in the presence of concentrated sulfuric acid.

Compound V has an absorption in its infrared spectrum at $1720 \mathrm{~cm}^{-1}$ and a broad absorption around $3050 \mathrm{~cm}^{-1}$.

Compound W can be formed directly from propanal.

Identify, by name or formula, compounds V, W and F.

Justify your answer by using all the available information.

Benzoic acid is a white crystalline solid with the structure shown.

It is found in many plants as it is an important building block for the biosynthesis of a variety of compounds, such as plant hormones and attractants for pollinators.

The role of benzoic acid in the chemical industry is also widespread and approximately 500000 tonnes are produced annually. It is used in the synthesis of many compounds, including medicines, dyes and insect repellents.

Such synthetic dyes are often classified as aryl azo dyes. These dyes have a range of vivid colours and a wide range of uses in many industries, including food and textiles. Their synthesis involves the formation of a diazonium ion. This ion then reacts with a phenol in a coupling reaction, to form the dye. The relative simplicity of the reactions involved and ready availability of starting materials make azo dyes cheap to produce.

Salts of benzoic acid, such as calcium benzoate and sodium benzoate, are used in the food industry as preservatives.

Devise a reaction scheme to produce benzoic acid from benzene, via bromobenzene and then a Grignard reagent.

Include the reagents and essential conditions for each step and give the name or structure of each of the intermediate compounds.

Details of practical procedures and reaction mechanisms are not required.

This question is about benzene and some of its compounds.

Devise a synthesis to convert bromobenzene into benzamide.

Include reagents, conditions and the structures of the intermediate compounds.

A student prepared a sample of aspirin. The equation for the reaction is shown.

The aspirin was recrystallised using an ethanol-water mixture as the solvent.
The student determined its melting temperature using the apparatus shown.

The student's sample melted over a range of 8 degrees starting at $125^{\circ} \mathrm{C}$.
The published melting temperature of pure aspirin is $135^{\circ} \mathrm{C}$.

Which is likely to be the main impurity in the sample of aspirin?

This question is about the nitration of methyl benzoate.

The equation for the reaction is shown.

Procedure

Step 1 Weigh between 1.9 g and 2.1 g of methyl benzoate in a $50 \mathrm{~cm}^{3}$ conical flask.
Step 2 Slowly add $5 \mathrm{~cm}^{3}$ of concentrated sulfuric acid to the methyl benzoate with swirling and place the flask in an ice-water bath to cool.

Step 3 Place $2.0 \mathrm{~cm}^{3}$ of concentrated nitric acid into a test tube.
Cool the nitric acid by immersing the test tube in an ice-water bath before slowly adding $2.0 \mathrm{~cm}^{3}$ of concentrated sulfuric acid.
Allow this nitrating mixture to cool.
Step 4 Using a teat pipette, add the nitrating mixture very slowly to the conical flask, ensuring the temperature does not exceed $7^{\circ} \mathrm{C}$.

Step 5 Allow the flask to stand at room temperature for about 15 minutes and then pour the contents into a beaker containing some crushed ice. Impure methyl 3-nitrobenzoate will form.

Step 6 Recrystallise the methyl 3-nitrobenzoate using methanol as the solvent.
Step 7 Weigh the dry crystals and determine their melting temperature.