Question

1.

a. Many medications are absorbed into the blood through the cells lining the stomach and small intestine. The rate of absorption (passage through a cell membrane into the blood stream) for a molecule depends on the structure and properties of the molecule. Which substance would be more easily absorbed into the blood stream; a polar, ionic, or nonpolar substance? Choose one and justify your reasoning using chemical and molecular details.

b. Furosemide is a diuretic used to treat fluid retention in patients with congestive heart failure or liver disease, among others. It is a weak acid with a pKa of 3.9. It is absorbed into the blood through the cells lining the stomach (pH 1.5) and small intestine (pH 6.0). Is more furosemide absorbed into the bloodstream from the stomach or the small intestine? Clearly justify your answer using chemical and molecular details.

2. You are given a mixture of benzoic acid and cyclohexanamine. You have access to a separatory funnel, an organic solvent, sodium bicarbonate, concentrated hydrochloric acid, and water. Devise a way to separate these two molecules using a simple organic extraction method.

Answer 1

a. The major constituent of blood is water which is polar in character. Water is polar due to the high electronegativity difference between the oxygen and hydrogen atoms.

It is common knowledge that a polar substance dissolves polar substances via dipole-dipole or ion-dipole and hydrogen bonding interactions. Hence, polar, ionic substances will more readily dissolve in water via the above mentioned forces.

b. The pH of the cells lining the stomach and the small intestine are 1.5 and 6.0 respectively. Hence, the components present in the stomach cells and the cells of the small intestine are acidic in nature.

It is known that the lower the pH of a chemical species, the more acidic is the species. Hence, the chemical component present in the cells lining the stomach is a stronger acid as compared to the component present in the small intestine. Further, it is common knowledge that a strong acid can readily dissolve a weak acid (actually an equilibrium reaction exists). Since the stomach cells contain a stronger acid, hence, Furosemide is absorbed more readily into the blood stream via the stomach cells.