benzene

reactions of benzene

combustion, bromination, nitration, friedel crafts alkylation, friedel crafts acylation

reagents and conditions for bromination

B2, catalyst AlBr3, warm

reagents and conditions for nitration

conc HNO3, catalyst conc H2SO4, warm to 55 degrees

reagents and conditions for friedel crafts alkylation

halogenoalkane, e.g. CH3Cl, catalyst anhydrous AlCl3, heat under reflux

reagents and conditions for friedel crafts acylation

acyl chloride, e.g. CH3COCl, catalyst anhydrous AlCl3, heat under reflux

generating the electrophile for bromination reaction

AlBr3 + Br2 → AlBr4- + Br+ (heterolytic fission of Br-Br bond)

regeneration of catalyst for bromination reaction

AlBr4- + H+ → AlBr3 + HBr

generation of electrophile for nitration reaction

HNO3(base) + H2SO4(acid) → H2NO3+(conj acid) + HSO4-(conj base)

H2NO3+ breaks down to form H2O and NO2+ (electrophile)re

regeneration of catalyst for nitration reaction

HSO4- + H+ → H2SO4

generation of electrophile for friedel crafts alkylation

AlCl3 + CH3Cl → AlCl4- + CH3+

regeneration of catalyst for friedel crafts alkylation

AlCl4- + H+ → AlCl3 + H+

generation of electrophile for friedel crafts acylation

RCOCl + AlCl3 → AlCl4- + RCO+

CH3COCl + AlCl3 → AlCl4- + CH3CO+

regeneration of catalyst for friedel crafts acylation

AlCl4- + H+ → AlCl3 + HCl

what is a phenol

OH group directly attached to benzene ring

phenol reaction with bromine water

C6H5OH + 3Br2 → C6H2Br3OH (cream ppt, 2,4,6-tribromophenol) + 3HBr (room temp)

why is phenol more reactive than benzene?

the oxygen atom in phenol has 2 electron lone pairs, one of the lone pairs is at the correct orientation to overlap with the delocalised Pi system of the benzene ring - this increases electron density in the benzene ring, making it more susceptible to electrophilic attack

what sort of flame would phenol burn compared to ethanol? why?

phenol is smoky, ethanol is clean → the proportion of carbon in phenol is greater than that in ethanol, when phenol combusts its unlikely that all the carbon will oxidise fully, so some CO will be produced as well as soot

what happens to phenol in water

dissociates to form C6H5O- + H+, the phenoxide ion is relatively stable → loss of a proton is possible because the neg charge on the oxygen in phenoxide ion overlaps with delocalised pi system in benzene ring so phenoxide ion is stabilised

how does phenol react with strong bases

phenol reacts with strong bases to form salts, e.g. C6H5OH + NaOH → C6H5O-Na+ (sodium phenoxide) + H2O, phenol is not strong enough acid to react with weak bases, so u can distinguish phenol from carb acids by testing with weak base like Na2CO3

why does benzene not undergo addition reactions even though it is unsaturated

an addition reaction would cause benzene to lose its delocalised pi system, substitution allows benzene to retain the delocalised pi system and therefore its stability