Question

Please help with 4-6

4. The lab textbook says that tertbutylammonium bromide is to "aid in the transfer of the hydrophobic 4-bromoacetophenone to the aqueous phase." How does Bu NBr do this? Include the IMFs between Bu NBr and 4-bromoacetophenone as well as those between Bu NBr and water. 5. The lab textbook says that "potassium carbonate reacts with water to provide the hydroxide ions that are involved in the ligand exchange." Write a balanced chemical equation for this reaction below, with all productions in their dissociated state. 6. Predict the product(s) of the following reaction: B(OH) + 2 Pd(OAC), BuNBI K2CO3, H20

Answer 1

Answer 4: Tetrabutylammonium bromide (TBAB) is a quaternary ammonium salt with a bromide counterion commonly used as a phase transfer catalyst. The role of phse transfer catalyst is to provide an interface between organic and aqueous phase. If some reactants which are only soluble in organic phase cannot reach a reactant which is present in aqueous phase and vice versa. For this problem to solve, we generally use phase transfer catalyst to aid the reaction. In the present case (Suzuki coupling), the reactant 4-bromoacetophenone is not soluble in water and therefore interacts with TBAB with the involvement of hydrophobic interaction as the structure given in figure suggests that TBAB have long hydrophobic chain which helps to carry 4-bromoacetophenone to aqueous layer as TBAB is soluble in water also due to electrostatic interaction with water (hydrogen bonding or ion-dipole interaction between TBAB ion and polar water molecule acting as a dipole).

tetrabutyl ammonium bromide

Answer 5: The balanced chemical equation for the reaction of potassium carbonate with water where all ions are dissociated.

K₂CO₃ + H₂O -----> 2K⁺ + H⁺ + CO₃^2- (HCO₃^-) + OH^-

(As in the solution, it may be possible that K⁺  + OH^- to form KOH and similarly HCO₃^- could also be formed)

Answer 6: This is an example of Suzuki coupling between dibromobenzene and boronic acid. As 2 equivalent of boronic acid is present hence the coupling occurs at both the bromide containing C atom thus forming the final product as given in the figure below.

8:00 AB(OH)2 + 21 Pd(OAc)2 Bu NBr K2CO3, H20