Date | November 2011 | Marks available | 2 | Reference code | 11N.3.hl.TZ0.D5 |
Level | HL | Paper | 3 | Time zone | TZ0 |
Command term | Describe | 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, \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COO(}}{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{4}}}{\text{)COOH}}\).
Chiral auxiliaries are used in drug design. Describe how a chiral auxiliary works.
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.
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);
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.
Description of how a chiral auxiliary works was not well understood and chiral axillaries function in synthesis was also sometimes confused.