-B(OH)2 + Br aq. Na CO3 1-propanol benzeneboronic acid 4bromoacetophenone 4-acet

Question

-B(OH)2 + Br aq. Na CO3 1-propanol benzeneboronic acid 4bromoacetophenone 4-acetylbiphenyl The work-up procedure was as follows: G) Add 7 mL water and extract the aqueous layer with ethyl acetate (2 x 10 mL). (ii) Combine the organic extracts and wash them with 5% aqueous sodium bicarbonate solution (2 x 10 mL) and saturated sodium chloride solution (brine) (2 x 10 mL). (ii) Transfer the organic layer to a 125 mL Erlenmyer flask and add decolorizing charcoal (0.50 g) and sodium sulfate ( g). Stir for 10 min., then vacuum filter through a 1 cm bed of Celite, using a Buchner funnel. Rinse the Celite with several small portions of ethyl acetate (iv) Evaporate the filtrate down to dryness using a rotory evaporator. (a) (2 pts.) Draw the structure of the catalyst in this reaction. (b) (2 pts.) Why is it necessary to perform this reaction under nitrogen? (e) (2 pts.) The first step in the catalytic cycle for this reaction is an oxidative addition of the catalyst to the 4-bromoacetophenone. Write a balanced equation for this reaction step, and indicate the oxidation state of the palladium in the reactant catalyst and in the product. What is being reduced? (d) (2 pts.) List (or draw structures for) all of the compounds that are expected to be present in the ethyl acetate phase after step ) of the work-up. (e) (2 pts.) List (or draw structures for) all of the compounds that are expected to be extracted from the ethyl acetate phase into the aqueous sodium bicarbonate phase in step(ii of the work-up.

Explanation / Answer

Coupling reaction,

(a) active catalyst here is Pd(0)(PPh3)2

(b) Pd(0) is very reactive and thus to keep it stable under reaction, the reaction is performed in nitrogen atmosphere.

(c) balanced equation for first reaction,

Pd(0)(PPh3)2 + 4-bromoacetophenone ---> CH3COC6H5-Pd(II)-Br

(d) the ethylacetate layer after first extraction would have product biaryl compound, H3BO3, 1-propanol

(e) The compound present in extraction with aqueous NaHCO3 from ethyl acetate layer would be Na2B4O7, NaHCO3 (excess).

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