Reactions involving displacement of diazo group

The diazonium group, -N2(+), carried on an arene diazonium salt is a genuinely VERY GOOD leaving group, precisely because of the positive charge sitting on the nitrogen atom directly bonded to the aromatic ring -- and because it leaves so readily, arene diazonium salts undergo nucleophilic substitution reactions with a wide variety of different nucleophiles, each nucleophile displacing the -N2(+) group (which departs as N2 gas) and taking its place on the ring instead. Table 13.5 sets out five distinct named reactions/product types built this way: the Sandmeyer reaction (using a copper(I) halide/cyanide salt together with the matching hydrohalic acid or KCN, giving good yields of Ar-Cl, Ar-Br or Ar-CN respectively); the Gatterman reaction (using plain copper powder together with HCl or HBr directly, giving Ar-Cl or Ar-Br, a related but reagent-simpler alternative to Sandmeyer); iodoarene formation (simply using KI, no copper catalyst needed at all, to give Ar-I); and two distinct MILD REDUCTION routes to plain Ar-H (removing the amino-derived nitrogen from the ring entirely, with no new substituent installed in its place) -- using hypophosphorous acid (H3PO2) in water, or alternatively using ethanol as both solvent and the actual reducing agent (itself oxidised to acetaldehyde in the process). A further reaction, phenol formation, simply uses water itself as the nucleophile at 283 K, giving Ar-OH. Two further reactions are described in the running text beyond Table 13.5: reaction of the arene diazonium salt with fluoro …