n-Butyllithium Titration

1. Preparation of Titrant

1. To a flame-dried round bottom flask equipped with a stir bar under N₂, add diphenylacetic acid (250 mg, 1.18 mmol) and anhydrous THF (5 mL).

2. Titration of n-BuLi

1. Calculate the approximate amount of n-BuLi solution (in hexanes) needed to consume the diphenylacetic acid. Using a syringe, slowly adda solution of n-BuLi dropwise. The reaction mixture will turn temporarily yellow and back to a colorless solution with each drop.
2. Continue adding the solution of n-BuLi dropwise until the reaction mixture continues to stay a deep yellow color. This will be the end point of the reaction.
3. Repeat the titration 3x to obtain an average volume of the n-BuLi used.

3. Calculation of Molarity

1. The moles of n-BuLi used in the titration are equivalent to the moles of diphenylacetic acid used in the reaction. Since the moles of diphenylacetic acid used is known, the calculation of concentration of n-BuLi is given by the following equation: mmol diphenylacetic acid/mL n-BuLi = molarity of n-BuLi solution.

4. Addition of n-BuLi to Benzaldehyde (Figure 2)

1. To a flame-dried round bottom flask equipped with a stir bar under N₂, add anhydrous THF (30 mL) and benzaldehyde (3 mmol, 1 equiv.). Cool the solution to −78 °C.
2. Add n-BuLi (1.1 equiv.) and let the reaction warm to room temperature.
3. Add saturated NH₄Cl (aq., 10 mL) to quench the reaction and extract the aqueous layer with diethyl ether (2 x 25 mL).
4. Wash the combined organic layers with water (2 x 15 mL) and brine (1 x 20 mL).
5. Dry with Na₂SO₄, filter, and concentrate the combined organic layers under reduced pressure to afford the product.

Figure 2. Addition of n -BuLi to benzaldehyde.