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

Types of Synthetic Dyes  Triphenylmethyl  Azo

Triphenylmethyl Dyes  Pararosaniline, malachite green, crystal violet

Azo Dyes  Aniline Yellow  Bismarck Brown

Azo Dyes  Methyl orange  Orange II  Para red  Amaranth red

Azo Dyes  Preparation:  Diazonium salt (Ar-N 2 + )and activated aromatic compound  Diazotization step  Coupling step

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 malachite green

Direct Dyeing Congo red

Ingrain Dyeing

Mordant Dyes tannic acid

Vat Dyes

Disperse Dyes

Fiber-reactive Dyes