Explain why diamorphine passes more readily than morphine through the blood-brain barrier.

Suggest a reagent used to prepare diamorphine from morphine.

Suggest one reason why codeine is available without prescription in some countries whilst morphine is administered under strict medical supervision.

Any two of:

diamorphine has ester/ethanoate/acetate «groups» AND morphine has hydroxyl «groups»

diamorphine/ester/ethanoate/acetate groups less polar

diamorphine more soluble in lipids

Accept “alcohol/hydroxy” for “hydroxyl” but not “hydroxide”.

Accept “diamorphine non-polar”.

Accept converse statements.

[2 marks]

ethanoic/acetic anhydride
OR
ethanoyl/acetyl chloride

Accept other possible reagents, such as ethanoic/acetic acid or acetyl bromide.

Accept chemical formulas.

[1 mark]

morphine has a smaller therapeutic window

Accept converse statements.

Accept “codeine has lower activity” OR “codeine has lower risk of overdose” OR “codeine is less potent”.

Do not accept “lower abuse potential for codeine” OR “codeine less addictive” OR “codeine has a lower bioavailability”.

[1 mark]