DYES

Dr. Sheppard, CHEM 4201, Fall 2014

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

Types of Synthetic Dyes

Triphenylmethyl

Azo

NH2

N

N

azobenzene

Triphenylmethyl Dyes

Pararosaniline, malachite green, crystal violet

Azo Dyes

Aniline Yellow

Bismarck Brown

N

N

NH2

N

N N

N

NH2

NH2

NH2

H2N

Azo Dyes

Methyl orange

Orange II

Para red

Amaranth red

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.

Dyeing

Natural dyes vs. synthetic dyes

Fastness Levelness Fabric/fiber

Direct Dyeing

O

N

S

O

O-O

N

-O

O

N

NS

O

-O

O Na+

Na+

Na+

tartrazine malachite green

Direct Dyeing

Congo red

Ingrain Dyeing

Mordant Dyes

tannic acid

Vat Dyes

NH

O

HN

O

[H]

[O]NH

OH

HN

HO

indigo leucoindigo

Disperse Dyes

Fiber-reactive Dyes