自环t行 Reaction Mechanism 院 人一人 allylic shift Copyright 2010 Pearson Prentice Hall,Inc. The mechanism involves an allylic radical stabilized by resonance. Both allylic radicals can react with bromine. Resonance hybrid
Reaction Mechanism The mechanism involves an allylic radical stabilized by resonance. Both allylic radicals can react with bromine
Reaction Mechanism Free radical chain reaction oinitiation,propagation,termination. Br2hy 2Br. H Br. HBr H Br Br
Reaction Mechanism Free radical chain reaction initiation, propagation, termination. H H Br H + HBr Br Br H Br + Br Br2 2Br h
Sec 1 Preparation of RX ■2.Vith HX HX c= C reflux H X HX is coming from Nax conc.H2SO
Sec 1 Preparation of RX 2. With HX C C HX reflux C C H X HX is coming from NaX + conc. H 2SO 4
Sec 1 Preparation of RX ■3.From alcohol ROH PCls>RCI POCl3 HCI (phosphorus oxychloride) ROH PCl3 RCI H2PO3 ROH+P+Br2→RBr+H3PO We rarely start with PClar.PBr3 or PI3r since they are easily hydrolysed by moisture in air.Instead,they are made in situ,using red phosphorus in the alcohol and halogen is put into the reaction flask as the reaction proceeds
Sec 1 Preparation of RX 3. From alcohol We rarely start with PCl 3, PBr 3 or PI 3, since they are easily hydrolysed by moisture in air. Instead, they are made in situ, using red phosphorus in the alcohol and halogen is put into the reaction flask as the reaction proceeds. ROH + PCl 5 RCl + POCl 3 + HCl (phosphorus oxychloride) ROH + PCl 3 RCl + H 3PO 3 ROH + P + Br 2 RBr + H 3PO 3
Sec 1 Preparation of RX 3.From alcohol-cont. ROH+HX→RX+HO (usually HBr,HI BUT RCI cannot be prepared by this method) Pyridine (as solvent) ROH SOCI2 RCI SO2 ,HCI (This product is most easily purified)
Sec 1 Preparation of RX 3. From alcohol – cont. ROH + HX RX + H 2 O (usually HBr, HI BUT RCl cannot be prepared by this method) ROH + SOCl2 RCl + SO 2 + HCl Pyridine (as solvent) (This product is most easily purified)