CHEM 3332 1st Edition Lecture 14Outline of Last Lecture Chapter 17: Reactions of Aromatic CompoundsBenzene resists the electrophilic addition reactions common to alkenes and alkynesElectrophillic Aromatic Substitution: Benzene does react with electrophilesGeneral Mechanism:Step 1:Step 2:I. Halogenation A. Catalyst –B. MechanismStep 1Step 2Step 3II. NitrationA. CatalystB. MechanismStep 1Step 2Step 3Step 4III. SulfonationA. E+ = SO3Pure H2SO4 contains a small amount of SO3-B. Mechanism:Step 1Step 2C. Desulfonation- All steps of sulfonation are reversible-position of EQ can be influenced by reaction conditionsSulfonation:Desulfonation:IV. Friedel – Crafts AlkylationA. CatalystB. E+ is a carbocationC. MechanismStep 1Step 2Step 3D. Other methods of generating the carbocation 1. Alkene + hydohalic acid (HF is best)2. Alcohol + BF3These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.E. Limitations of F-C Alkylation1. Carbocations that can rearrange, will2. F-C reactions will not occur if strong electron withdrawing (deactivating) groups of either of two types are on the ring.a. Any deactivating group stronger than halogen b. Lewis acid-base adduct formed from amino groupsc. Polyalkylation is difficult to control, because alkyl group are activators Outline of CurrentLecture .V. Friedel-Crafts Acylation – solves some problems with F-C alkylationA. Synthesis of a necessary reagent – the acyl chlorideB. Generation of E+C. Advantages of acylation over alkylation1. Polyacylation is not a problem2. No C+ rearrangement, so F-C acylation is best method for synthesizing unbranched alkylbenzenesD. Gatterman-Koch Formlyation: The Proper Synthesis of BenzaldehdeReactions of Substituted BenzenesHow does a substituent on the benzene ring affect the 5 EAS reactions?I. Reactivity (rxn rate): 2 types of substituents causes ring to be more reactive than beforeII. Orientation of the incoming group: 2 types of substituents: ortho/para directorsException: halogens, O/PCurrent
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