lecture 7 Flashcards
how do we activate bromine
bromine
AlCl3
make the Br+ and the Al-
bromination: benzene + Br2,,, does the bromine need to be activated
yess
nitration: nitric acid and benzene,, does the nitric acid need to be activated
yess
how do we activate nitric acid HNO3
HNO3 and H2SO4
product of nitric acid activation using H2SO4
NO2+
sulfonation: what is needed
activated H2SO4
and benzene
what do we need in order to activate H2SO4
H2SO4
H2SO4
what is the product of H2SO4 activation
HSO3+
hydrogen sulfite
what is needed in a friedel crafts acylation
acyl chloride
what is needed for friedel crafts acylation with acyl chloride
acyl chloride
AlCl3
describe the friedel crafts acylation with acyl chloride
Cl attacks the AlCl3
AlCl4 is removed
R-C=O remains with resonance forms
the benzene attacks the C+
what is friedel crafts acylation about
using carbon as an electrophile
aka we will probably be using a CC+
describe an acyl chloride
like an aldehyde but with Cl instead of H
what is needed in freidel crafts alkylation
alkyl chloride
tertbutanol
describe an alkyl chloride
alkene with a Cl
what is needed in friedel crafts alkylation with an alkyl chloride
alkyl chloride
AlCl3
Cl attacks AlCl3 and AlCl4 is removed leaving a CC+ for benzene to attack
what is needed for a fridel craft alkylation with alcohol
H+ is needed
the OH attacks this and water is removed
a CC+ is left and a benzene can attack this
when an electrophile reacts with benzene,, what is not influenced
there is no influence on what Carbon to attack
the electrophile can bond to any carbon atom
how do electron donating groups attached to a benzene affect electrophilic addition reactions
the electrophile doesnt need to be activated
why doesnt the electrophile need to be activated when reacting with an aromatic with an e- donating group
the lone pairs in the group donate themselves into the ring system which increases its nucleophilicity
the e- donating groups activated the benzene
name some e- donating groups
OH
NH2
CH3
halogens
what else do e- donating groups bonded to a benzene do
they can stabilise CC+ in the reactions
this is a good thing
direct electrophiles closer to / opposite themselves
electron donating groups on benzene are what directing
ortho
para
directing
describe phenol and ONE Br2
no Br2 activation needed
Br is added to the para position on benzene
phenol and diluted nitric acid
no activation needed
nitro group is added (NO2) either:
para 25%
ortho. 36%
the 2 are structural isomers and have different chemical and physical properties meaning thhey can be separated
nitrophenol can be reduced by XXX to give what
can be reduced using H2 and Pd to give amino phenol
phenol with NH2
acetylation of 4 amino phenol gives
paracetamol
what is used to acetylate 4 amino phenol
acetic anhydride
describe aniline
benzene with NH2 attached to it
describe aniline and Br2
no Br2 activation needed
NH2 lone pairs are transported across to attack Br2 from the para position
the Br then takes a H and the e- are transported back to the NH2+ to neutralise it.
this gives 4bromo aniline and HBr
aniline + phenol with excess Br2 products
Br in ortho and para positions
ortho + para directing
what type of directing are ED groups OH, NH2, halogens, CH3 etc
ortho
para directing
their e- densities help stabilise the CC+ formed
difference between electron donating substituents
OH and NH2
lone pairs activate benzene
CH3 doesnt activate benzene
benzene and CH3
toluene
toluene and Br2
needs activation using a lewis acid (Ae-)
Br2 and AlCl3
Br goes
ortho : 60%
meta : 5%
para : 35%
why does toluene and activated Br2 give mostly ortho and para additions
ortho and para = tertiary CC+
meta = secondary CC+
less stable and therefore formed less.
its formation is not energetically favoured
toluene and nitric acid
nitric acid needs activation (H2SO4) gives nitro toluene (NO2)
gives:
ortho: 55%
meta: 5%
para: 40%
phenol and NaOH with CO2 reaction description : aspirin formation
removes most acidic proton (OH)
this activates the phenol at the O is now O-
Co2 can react even tho its a bad electrophile
aromaticity is then regenerated by removing a proton
then OH is acetylated to give aspirin (sodium salicylate)
toluene and H2SO4 then NaCl
toluene sulfonation
- H2SO4 is activated
- goes in ortho + para positions (SO3H)
- NaCl : removes the H in SO3H and forms SO3Cl in the ortho and para positions
electron withdrawing groups on benzene examples
CF3
NO2
C triple N
COOR
CHO
SO3R
trifluoro toluene description
toluene but with F instead of Hs on the CH3
trifluoro toluene and HNO3
needs to be activated (H2SO4)
NO2 is directed to go to the meta position by CF3
why are e- withdrawing groups on benzene meta directing
so the CC+ and its resonance structures are far from the group itself
a CC+ next to an e- withdrawing group will remove even more e- density making it even more unstable
meta substitution
why are ortho and para substitutions not favoured with e- withdrawing groups (NO2, CF3, COOR, CHO, SO3R, CtripleN)
unfavourable as its resonance structures are destabilised when the CC+ is near the EW substituent
ED groups are
ortho
para directing
ortho + para substitutions
due to favourable tertiary CC+ formations during resonance
EW groups are
meta directing
meta substitutions
due to unfavourable interactions when the CC+ is near the EW substituent
