Complete the following reactions and explain the formation of the products.
(a) `HCOOH overset (Conc. H_2 SO_4) rarr`
`CH_3 COOH overset (Conc. H_2 SO_4) rarr`
( c)
(d) Glacial acetic acid `(CH_3 COOH) overset (973 K)rarr`
( e) .

Explanation

(a) `HCOOH` decomposes to `CO` and `H_2 O`.

The acylium ion `(I)` is a power ful acid which loses `H^(oplus)` to give `CO`.
(b)`CH_(3) COOH` does not react since the formation of acylium ion `(Me-C-=O^(o+))` does not lose `H^(o+)` but reforms proptonated acetic acid.

( c) `Ph_3 C - COOH` decomposes to `Ph_3 C - OH + CO`.

The intermediate acylium ion `(I)` loses `CO` to give stable triphenyl carbocation, which then reacts with `H_2 O` to give `PH_3 C-OH`.
(d)
( e) If is an example of ipso substitution.

`(OH)` is a ring-activating substituent , an `o- or p-COOH` is displaced as `CO_2` and substituted by electrophile `Be^(oplus)`. Excess of `Br_2` further borminates the phenol to give product `(I)`.