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Friedel-Crafts Alkylation

Freidel-Crafts Alkylation. Reaction IssuesBiphenyl is substituted for Benzene, which is a known carcinogenAnhydrous Ferric Chloride (FeCl3) is substituted for Anhydrous Aluminum ChlorideNote: Instructor will assist student with addition of Anhydrous Ferric Chloride in the hood to minimize moistur

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Friedel-Crafts Alkylation

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    1. Friedel-Crafts Alkylation Purpose Preparation of 4,4-di-tert-butylbiphenyl using the Friedel-Crafts alkylation of Biphenyl through Electrophilic substitution of a Lewis Base (t-Butyl Chloride (Haloalkane)) in the presence of Ferric Chloride acting as a Lewis Acid References: Slayden, et. al. pp. Website: http://classweb.gmu.edu/jschorni Solomon’s - pp. 669-671 8/13/2012 1

    2. Freidel-Crafts Alkylation Reaction Issues Biphenyl is substituted for Benzene, which is a known carcinogen Anhydrous Ferric Chloride (FeCl3) is substituted for Anhydrous Aluminum Chloride Note: Instructor will assist student with addition of Anhydrous Ferric Chloride in the hood to minimize moisture contamination Safety Issues Dichloroethane (solvent) is also a known carcinogen – use caution and work in the hood Experimental Issues Determine Limiting Reagent in the reaction Determine which layer in separatory funnel is organic Note: Always check densities of solvents used in experiment Recrystallize from 95% Ethanol 8/13/2012 2

    3. Friedel-Crafts Alkylation Related Subjects Electrophile – Electron deficient (electron seeking) species Lewis Acid – Electron pair acceptor (electron seeking) e.g. - Protons, aluminum, zinc & iron halides Lewis Base – Electron pair donor e.g. - Ammonia, Alcohols, Alkyl Halides Arenium Ion (Pentadienyl Cation) – non-aromatic carbocation (also called sigma ? complex) produced as an intermediate product during the electrophilic attack on the ? electrons in an aromatic ring Aromatic rings undergo electrophilic substitution because the ring ? electrons are regenerated, thus reestablishing stable ring resonance Aromatic Electrophilic Substitution vs. Alkene Electrophilic addition Recrystallization – slow cooling after solution in minimal amount of an appropriate solvent 8/13/2012 3

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