Phenols generally are not changed on treatment with sodium borohydride followed by acidification to destroy the excess, unreacted hydride. For example, the 1, 2-, 1, 3-, and 1, 4-benzenediols and 1, 2, 3-benzenetriol are unchanged under these conditions. However, 1, 3, 5-benzenetriol (phloroglucinol) gives a high yield of a product A that has these properties:
MS (m/z): 110
IR (cm-1): 3250 (broad), 1613, 1485
1H NMR (δ in DMSO): 6.15 (m, 3H), 6.89 (t, 1H), and 9.12 (s, 2H)
(a) What is the structure of A?
(b) Suggest a mechanism by which the above reaction occurred. (1, 3, 5-Benzenetriol is known to have more tendency to exist in a keto tautomeric form than do simpler phenols.)