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Directions: The decarboxylation of aromatic acids is most often carried out by heating with Cu-quinoline \[ArCOOH\xrightarrow[{}]{Cu-quinoline}ArH+C{{O}_{2}}\] Cuprous salts of aromatic acids, actually undergoes decarboxylation. However, two other methods can be used with certain substrates.

Method 1: Salt of acid, \[ArCO{{O}^{-}}\]is heated (SE1)

Step I:

Step II:

Method II: Carboxylic acid is heated with a strong acid, often sulphuric acid.

Decarboxylation takes place by the arenium ion mechanism, with\[{{\text{H}}^{+}}\] electrophile. Evidently, the order of electrofugal ability is \[C{{O}_{2}}>{{H}^{+}}>COO{{H}^{+}}\]Rearrangements are also known to take place. For example,, when the phthalate ion is heated with catalytic amount of cadmium, the terephthalate ion is produced. In a similar process, potassium benzoate heated with cadmium salts disproportionates. The rearrangement is named as 'Henkel rearrangement'.

In the 'Henkel reaction' when potassium benzoate is heated with cadmium salts, the products are

A)

B)

C) ?                                 

D)