Benzene and phenol revision aid

Mathsandscience.net Benzene and phenol All bonds same length, hydrogenation of benzene releases less energy then cyclohexene therefore more stable. P orbitals lap forming ∏ bonds each carbon giving one electron. Nitration C6H6 +HNO3 g nitrobenzene + H2O Conc Nitric and conc sulphuric at 50oC Halogenation (Cl and Br) C6H6 +Cl2 g Chlorobenzene + HCl Need carrier FeCl3 or AlCl3 (only 1 Cl on ring!) electrophilic mechanism Benzene ∏ bonds electrons delocalised (low electron density)so no reaction with Br2 so need a carrier. Formation of electrophyles HNO3 +H2SO4g NO2+ +HSO4-+ H2O at the end of the reaction HSO4-+ H+g H2SO4 So H2SO4 is acting as catalyst Br2 +FeBr3 g Br++FeBr4-at the end of the reaction FeBr4-+ H+g FeBr3+ Hbr Phenols dissolved in water is a weak acid losing H+ from OH group therefore neutralised by NaOH to form sodium phenoxide and water reacts with Na to produce sodium phenoxide and H2. Bromination of phenol NOTE!! Benzene has ONE Br attached Phenol has THREE + 3Br2 g + 3HBr O in OH donates Lone pair to ∏ bond increasing electron density so increase in reactivity. Copyright 2010 Tutoring for AS and A2 Mathsandscience.net NO2+ H+ NO2 NO2 + H+ OH O-Na+ OH OH Br Br Br