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Organic Chemistry

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10 Apr 2009 15:35:48 IST

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the catalist in friedel craft is strong Lewis acid,,and usually use AlCl3.. can we us FeCl3???is Fe

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the catalist in friedel craft is strong Lewis acid,,and usually use AlCl3..can we us FeCl3???is FeCl3 a Lewis acid??can u give me the proof??please help me

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Rajat Agarwal

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10 Apr 2009 15:51:30 IST

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A lewis acid is a compond which can take lone pair of electrons...

AlCl₃, FeCl₃, BF₃, TiCl₃, ZnCl₂, SnCl₄ are all Lewis Acids as they all have vacant orbital in which they can accomodate electrons

Yes in Freidel Crafts alkylation we can use FeCl₃, but AlCl₃ is a better lewis acid in case of Freidel Crafts alkylation.

pranav agrawal

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10 Apr 2009 15:54:48 IST

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the motive for adding lewis acids is to provide electrophile that will attck the electron rich benzene ~~ add any lewis acid ~~ wht we wnt is a electrophile to attack to attack benzene ~~ hope it helps ~

Madhusudan Chavan

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12 Apr 2009 19:40:33 IST

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Two types of catalysts are used in the friedel-craft's reaction :

i) Metal halides ( Lewis acids): their general order of reactivity is as shown and usually, the more reactive the substrate, the weaker need be the Lewis acid used.

AlCl3 > BF3 > SbCl5 > FeCl3 > SnCl4 > ZnCl2

ii) Proton catalysts : HF, H2SO4, H3PO4.

Aluminium chloride is the most widely used catalyst ( this is the one originally used by Friedel and Crafts). It may be used with any alkylating or acetylating agent. In case of alkenes, it is necessary to have a small amount of halogen acid present. The amount of AlCl3 required depends on the nature of substrate and /or reagent. Thus for non-oxygenated substrates, about 0.2 molecule is required for alkyl halides and alkenes, 0.5-1.0 molecules for alcohols ( ROAlCl2 IS FORMED), 1 molecule of acid chlorides and 2 molecules of acid anhydrides ( RCOClAlCl3 and RCO2AlCl2 are formed). When substrate contains oxygen, then large amounts of catalyst are required.

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