Organic molecules are an important source of colour both in the natural world and in a wide range of industrial applications.
Curcumin contributes to the yellow colour of turmeric spice and is used as an additive in cosmetics and foods. It has been suggested that curcumin can act as an antioxidant and anticancer agent, through reactions with free radicals and proteins, and may also inhibit Alzheimer’s disease by complexing to toxic metal ions.
Azo dyes are synthetic compounds that do not occur naturally. They can be used to colour textiles such as cotton. The acid‐base indicator methyl red is an azo dye.
Indigotin is used to dye denim a blue colour and coumarin 440 is used to generate blue light in lasers. Both dyes occur naturally in plants but can be synthesised in the laboratory.
The equation shows the reaction between a free radical T• and curcumin (shown by a simplified structure).
Complete the left‐hand side of the equation by adding curly half‐arrows.
Selenide anions attached to protein side‐chains may undergo nucleophilic addition reactions with curcumin.
Complete the mechanism for one of the steps in such a reaction, adding curly arrows to the simplified structures shown.
Curcumin anions can act as bidentate ligands in metal‐curcumin (M‐curc) complexes. The oxygen atoms of the curc ligand occupy adjacent coordination sites in the complex, as shown.
Complete the table relating to two M‐curc complexes.
|
[Au(curc)2]+ |
[Al(curc)(C2H5OH)2(NO3)2] | |
| Coordination number | 4 | |
| O–M–O bond angle | 90° | |
| Shape | octahedral | |
| Charge on metal ion | +3 |
An incomplete synthesis for methyl red starting from 2‐nitrobenzaldehyde and phenylamine is shown.
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The temperature used in Steps Y and Z should be kept as close to 5 °C as possible. State why the temperature should be neither higher nor lower than 5 °C.
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5 marksIndigotin can be synthesised from 2‐nitrobenzaldehyde and propanone in aqueous sodium hydroxide.
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Give the structure of the organic product of each of the following reactions of coumarin 440.
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Deduce the structures of the two monomers that produce this polymer.
