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Azo Compounds (Diazonium Salts) - Coggle Diagram
Azo Compounds
(Diazonium Salts)
Physical
Properties
normally used in aqueous
solution (explosive when dry)
white
crystalline
solids
Reaction with
Water
method
aqueous solution of benzene
diazonium chloride
HEATED
phenol + N2 produced
equation
phenol
- formed:
in solution
black oily liquid
Reactions with
Potassium Iodide Solution
method
benzene diazonium chloride
WARMED
with KI solution
iodobenzene + N2 produced
iodobenzene
dense
oily
liquid
(cannot be formed from bromination)
equation
Coupling Reactions
D: reaction in which 2 benzene rings linked together through azo
(-N=N-)
group
method
'coupling reagents'
(phenol/aromatic amines)
added to diazonium salts
produces
AZO-COMPOUNDS
reaction w/ PHENOL
method
solution of
benzene diazonium chloride
(white ppt)
added to
COLD solution of
phenol
dissolved in sodium hydroxide
4-hydroxyphenyl azobenzene
formed
bright yellow precipitate
equation
diazonium ion = electrophile
readily attacks benzene ring
(electron rich)
phenol conditions
dissolved in alkali
cooled below 5°C
why?
produces more reactive
phenoxide ion
provides more electron density than -OH group
benzene diazonium ion
couples in para position (4th C)
ion = LARGE
less steric hindrance
reaction w/ PHENYLAMINE
4-aminophenylazobenzne
produced
yellow solid
reaction needs
HIGH pH
(
important
)
if low no. of H+
protonate amino group on phenylamine
deactivate benzene ring
∴ no reaction
equation
Formation
amine + nitrous acid
Colours of Azodyes
difference to
diazonium compound:
quite stable
do not lose colour
(colourfast)
uses
dyestuffs industry
indicators
(eg methyl orange)
azo compounds contain
highly delocalised π-system of electrons
in both benzene rings
& 2 N atoms between rings
delocalisation can extend
to groups attached to rings
as well as -N=N-
shade
of colour, depend on:
+
SIZE of DELOCALISED SYSTEM
NATURE of SUBSTITUTES on rings
explained using
electronic energy levels...
1.electrons occupy molecular orbitals
(molecular energy levels)
2.delocalisation of Es
leads to closer proximity of energy levels
3.
greater extent of delocalisation,
closer energy levels
4.Es move up energy levels
absorb energy
absorb certain wavelengths of visible light
leaves complementary colour (observed)
chromophore
- groups which
contribute to delocalisation
example
METHYL ORANGE
azo dye which exists in
2 forms in equilibrium w each other
RED FORM
YELLOW FORM
monobasic
= one acid
group, proton group
acid added
equilibrium shifted to RED form
∴ MO = red in acidic solutions
alkali added
H ions removed
equilibrium shifted to YELLOW from
MO = yellow in basic solutions
equal amounts of red + yellow forms
MO is ORANGE in colour