Question

1) Given that the pKa of acetic acid in water is about 5 and that of ethanol is about 17, what do you estimate the pKa for acetaminophen to be? Explain your answer. Keep in mind that pKa = -log[acid ionization constant], so the lower the pKa, the stronger the acid.

2) If you could choose any of the common alkali metal carbonates (Cs, Li, Na, Li) to use as a base in this reaction, which would you expect to be least effective? Which would be most effective? Explain why.

Please help :)

Answer 1

Solution :-

1) Acetic acid is the carboxylic acid therefore it has pka = 5 which is more acidic as compared to ethanol which is alcohol which has pka = 17

in the acetaminophen we have phenolic OH group and amide linkage at the para position of the ring. The phenolic OH is more acidic than straight chain alcohols.

The mide geoup at the para position will also have the electron withdrawing effect which can stabilize the anion formed on the alcoholic oxygen after loss of proton thre fore it makes the phenolic OH more acidic than alcoholic OH but less acidic than acetic acid

So the pka for the acetaminophen is about 9 to 10

2) The reactivity of the alkali metal increases down the group. The carbonate of the Na or K would more effective and carbonate of the Cs or Li is less effective.

Because Li and Cs are very reactive compared to the Na and K