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Dyes in Food
Food Coloring Natural colors Synthetic dyes Why add food
coloring ? Regulation Structure
Mauve
Perkin’s idea:
Mauveine
2 C10H13N + 3/2 O2 - H2O C20H24N2O2
NH
3/2 O2
- H2O
OH
N
H
O
N
2
NH2 N
N CH3
NH2
H3C
HN
CH3
Azo Dyes
Preparation: Diazonium salt (Ar-N2
+)and activated aromatic compound
Diazotization step
Coupling step
HNO2Ar N NAr NH2
diazonium ion
HCl
Cl
+ 2 H2O
Ar' HAr N N Ar N N Ar'
azo compound
In-class Assignment
Draw a mechanism for the coupling of aniline with a diazonium ion. Pay close attention to regiochemistry (i.e. will the coupling occur ortho, meta, or para?)
Draw the two aromatic compounds that would be used to synthesize Para red.