Question

T-pentyl Chloride Lab

1. Define Le Chatilier’s principle, and describe how it applies to the synthesis of t-pentyl chloride in concentrated HCl, or the conversion of t-pentyl chloride to t-pentyl alcohol during the aqueous extraction.

2. When doing boiling point determination with a capillary tube and boiling bell, what is the gas that is appearing in slow bubbles when t-pentyl chloride is heated to 70 °C?

3. When doing boiling point determination with a capillary tube and boiling bell, what is the gas that is appearing in rapid bubbles when t-pentyl chloride is heated to 86 °C?

Answer 1

Le Chatilier’s principle: When a system at equilibrium is subjected to stress (i.e. change in temperature or pressure or concentration), the system moves in a direction to nullify the stress.

Let's consider the synthesis of t-pentyl chloride from t-pentyl alcohol in acidic medium:

Step 1

Acid-base reaction: Protonation of alcoholic oxygen to make better leaving group (i.e. H₂O), which is a fast step.

Step 2

Formation of planar t-pentyl cation (3^o carbocation), which is the slow step.

Step 3

Attack of nucleophilic Cl- on the electrophilic carbocation to form t-pentyl chloride, which is a fast step.

According to Le Chatilier’s principle, the concentration of alcohol and acid species are more, then the reaction moves in a forward direction to decrease the concentration, i.e. formation of t-pentyl chloride.

2. When doing boiling point determination with a capillary tube and boiling bell, the gas that is appearing in slow bubbles when t-pentyl chloride is heated to 70 °C: Vapors of t-pentyl chloride

Reason: The B.P of t-pentyl chloride = 85-86 ^oC, which is about to reach. That's why corresponding slow bubbles start appearing.

3. When doing boiling point determination with a capillary tube and boiling bell, the gas that is appearing in rapid bubbles when t-pentyl chloride is heated to 86 °C: Vapors of t-pentyl chloride.

Reason: The B.P of t-pentyl chloride = 85-86 ^oC, which is already reached. That's why corresponding rapid bubbles appear.