Aromatic Amines
Synthesis with Aromatic Diazonium Ions
N
NH2
N
NaNO2/HCl
HO N O
(nitrous acid)
Nu
Nu
-N2
diazonium ion
acts like
Some Characteristics of Diazonium Salts
1. Aliphatic diazonium salts are very unstable even at low temperatures and
decompose instantly upon formation
CH3CH2CH2 N N
CH3CH2CH2
+
N N
2. Aromatic diazonium salts are much more stable due to conjugation with an
aromatic ring and decompose only slowly at ice bath temperatures
3. Groups ortho and para to the diazonium salt functionality act to stabilize it
4. Aromatic diazonium salts function as weak electrophiles and will only react with
aromatic rings containing strongly activating groups
O H
O R
N R
R
Azo Dyes
Aromatic diazonium ions can be trapped (before loss of N2) by electron-rich
aromatic compounds (e.g., possessing activating groups)
O2N
NH2
NaNO2/HCl
0 oC
Cl
O2N
an aromatic
diazonium salt
N N
4-Nitrobenzenediazonium
chloride
4-Nitroaniline
NO2
Cl
O2N
N N
OH
+
N
2-Naphthol
Para Red
N
OH
Azo Dyes
Two azo dyes are prepared: para red and one from another naphthol-aromativ
amine combination
Sodium Nitrite Solution: dissolve NaNO2 (1 g) in H2O (10 mL). This provides
enough 10% NaNO2 solution to prepare two azo dyes
Aromatic Amine Solution: disolve aromatic amine (250 mg) in 10% HCl (10 mL)
Naphthol Solution: dissolve naphthol (250 mg) in 10% NaOH (10 mL)
Diazotized Amine Solution: cool the aromatic amine solution to 0 oC and add
sodium nitrite solution (5 mL) dropwise with mixing. Allow the solution to stand 2
min
Azo Dye Solution: insert a cloth strip into diazotized amine solution, allow to
become saturated and add the naphthol solution dropwise
Azo Dyes
This procedure is to be used employing 4-nitroaniline and 2-naphthol to prepare
para red and a second azo dye using a different combination of amine and
naphthol
Aromatic Amines
Naphthols
OH
O2N
NH2
4-Nitroaniline
2-Naphthol
OH
NH2
NO2
2-Nitroaniline
1-Naphthol
Rinse the cloth samples with water to determine color-fastness
Synthesis with Aromatic Diazonium Ions
What starting materials are needed to synthesize the following azo compound?
O
O S
Na
O
N N
methyl orange
O
Na
O S
O
N N
Cl
+
Me
N
Me
Me
N
Me