1) friedel crafts acylation (CO + HCl+ AlCl3(cat.) ====> benzaldehyd
2) nitration (HNO3/H2SO4(cat.) ====> 3-nitro-m-benzaldehyd <---> 3-nitro-p-benzaldehyd
3)double wolf-kishner (N2H4 + KOH, t*)===> 3-amino-m/pbenzaldehyd (dynamic stability m- and p- form)
4)sandmeyer rxn I) NaNO2 + HCl II) H3O+ + t*-----> m- p- cresol
p-cresol + NaOH----> C7H7ONa (sodium cresol)
p-cresol + PCl5 -----> C7H6Cl + HCl + POCl3 (1-methyl-4-chlorobenzene