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AROMATIC COMPOUNDS - REACTIVITY

AROMATIC COMPOUNDS - REACTIVITY. TYPICAL REACTION OF AROMATIC COMPOUNDS - SUBSTITUTION ELEKTROPHILIC AROMATIC. Mechanizm of substitution electrophilic aromatic. E. reaktion coordinate. AROMATIC COMPOUNDS - REACTIVITY. Aromatic compounds are forming complexes.

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AROMATIC COMPOUNDS - REACTIVITY

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  1. AROMATIC COMPOUNDS - REACTIVITY TYPICAL REACTION OF AROMATIC COMPOUNDS - SUBSTITUTION ELEKTROPHILIC AROMATIC Mechanizm of substitution electrophilic aromatic E reaktion coordinate

  2. AROMATIC COMPOUNDS - REACTIVITY Aromatic compounds are forming complexes - crystaline compound - X-ray analysis - when heated it decomposes back

  3. AROMATIC COMPOUNDS - REACTIVITY Preparation of electrophilic reagents HALOGENATION is limited to chlorination and bromination For the reaction Lewis acid is necessary similarly aluminium halogenide is active, sometimes addition of powdered metal is used reactive aromates Fluorination as SEAr is not applied, is carried out as Schiemann reaction (by decomposition of aromatic diazonium salts) Iodine is less active and therefore elektrophilic reagent I+ is generated directly in reaction mixture by iodine oxidation oxidation by H3AsO4 , HNO3

  4. AROMATIC COMPOUNDS - REACTIVITY NITRATION - Nitration of activated aromatic systems is possible even by HNO3 - I case of substituted derivatives it is necessary to také to consideration reaction of substituents with strong acid SULFONATION conc. sulfuric acid, oleum, sufur trioxide the reagent is sulfur trioxide Sulfonation is reversible reaction Conditions: conc. acid, oleum diluted acid + steam (overheated)

  5. AROMATIC COMPOUNDS - REACTIVITY FRIEDEL –CRAFTS reaction – alkylation and aryltion (1877 – Friedl (F), Crafts (US) ALKYLATION Differnt Lewis acids: AlCl3, BF3, TiCl4, SnCl4, ZnCl2, but also acids HF, H2SO4 Alkylation agents may be also alcohols and alkenes:

  6. AROMATIC COMPOUNDS - REACTIVITY FRIEDEL –CRAFTS reaction – alkylation and aryltion (1877 – Friedl (F), Crafts (US) ALKYLATION • Conditions and restrictions: • Reactionscannotbeappliedataromaticsystemswithstrongelectronwithdrawinggroups (-NO2, -NH3+, - CN) • Halogen derivatives and vinyl derivatives do not work. • Theformedalkylatedsystemisalways more reactivethanthestartingcompound a severalfoldsubstitutioncanbeobserved • Whenyou are tryingalkylationwith a longerchain – whencarbocationisformed, oftenitsrearrangement to the more stablecationisobserved • ReactionscannotbeappliedataromateswithaminogroupbecauseaminogroupinteractswithLewis acid formingcomplexwith free electron pair ofnitrogen and thiswayisdesactivatingaromaticsystem

  7. AROMATIC COMPOUNDS - REACTIVITY FRIEDEL –CRAFTS reactions ACYLATION - formation of aromatic ketones

  8. AROMATIC COMPOUNDS - REACTIVITY REIMER – TIEMAN reaction dichlorkarben je electrophile o- and p-substituted hydroxybenzaldehydes are formed

  9. AROMATIC COMPOUNDS - REACTIVITY CHLORMETHYLATION - introduction of chlormethyl group

  10. AROMATIC COMPOUNDS - REACTIVITY AZOKOPULATION - formation of azodyes

  11. AROMATIC COMPOUNDS - REACTIVITY REACTIONS AT SUBSTITUTED AROMATICS - influence of substitution STATISTICS: o- 40% m- 40% p- 20%

  12. AROMATIC COMPOUNDS - REACTIVITY

  13. AROMATIC COMPOUNDS - REACTIVITY

  14. AROMATIC COMPOUNDS - REACTIVITY Donating o- and p- directingsubstituents Stronglyactivating Weakactivating desactivating m - directing Forthequantitativevalueof substituent influence consultHammettconstants

  15. AROMATIC COMPOUNDS - REACTIVITY

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