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Date November 2011 Marks available 1 Reference code 11N.3.hl.TZ0.D5
Level HL Paper 3 Time zone TZ0
Command term State Question number D5 Adapted from N/A

Question

Some drugs can be converted into ionic salts in order to increase their solubility in water.

State the equation for the formation of the ionic salt of aspirin, \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COO(}}{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{4}}}{\text{)COOH}}\).

[1]
a.i.

Chiral auxiliaries are used in drug design. Describe how a chiral auxiliary works.

[2]
b.

Markscheme

\({\text{C}}{{\text{H}}_3}{\text{COO(}}{{\text{C}}_6}{{\text{H}}_4}{\text{)COOH}} + {\text{NaOH}} \to {\text{C}}{{\text{H}}_3}{\text{COO(}}{{\text{C}}_6}{{\text{H}}_4}{\text{)COONa}} + {{\text{H}}_2}{\text{O}}\);

Accept Na2CO3 or NaHCO3.

Accept ions for strong base and salt or net ionic equation.

a.i.

chiral auxiliaries are enantiomers/optically active;

auxiliary creates stereochemical condition necessary to follow a certain pathway / is used to manufacture one enantiomer (so avoids need to separate a racemic mixture);

attaches/connects itself to non-chiral molecule / makes it optically active;

only desired/one enantiomer/molecule formed (and chiral auxiliary removed);

b.

Examiners report

The equations for the formation of the ionic salt of aspirin and the ionic salt of fluoxetine were poorly done with \({{\text{H}}_{\text{2}}}{\text{O}}\), NaCl, HCl and Na used in the first case instead of NaOH and \({{\text{H}}_{\text{2}}}{\text{O}}\) and NaOH used in the second case instead of HCl.

a.i.

Description of how a chiral auxiliary works was not well understood and chiral axillaries function in synthesis was also sometimes confused.

b.

Syllabus sections

Options » D: Medicinal chemistry » D.2 Aspirin and penicillin
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