Bromination of Toluene

If you treat toluene with 2 equivalences of bromine, you will get aminly 2,4-dibromotoluene and not 2, 6-dibromotoluene.  However, you can produce 3, 5-dibromotoluene by treating 4-aminotoluene with 2 equivalences of bromine.  Then first treating the product, 4-amino-3,5-dibromotoluene, with HNO2 in H2SO4, and secondly treating the resulting product with hypophosphorus acid, H3PO2.  Fully explain why this series of reaction will produce the 3,5-dibromotoluene and direct bromination of toluene produces the 2,4-dibromotoluene.