This document discusses chemistry and applications of leuco dyes. It begins by defining dyes and their sources, as well as leuco dyes, which are colorless or light-colored compounds that change color with oxidation or temperature changes. The document then covers the three main classes of leuco dyes - triphenylmethane, sulfur, and indigo dyes - and provides examples like malachite green. Finally, it discusses various applications of leuco dyes in products like color-changing cups, hair color, and thermal indicators.

1. CHEMISTRY AND
APPLICATION OF
LEUCO DYES
PRESENTED BY:
ASMA MUQADAS
ROLL # 7632

2. Contents
Dyes
Natural & synthetic Dyes
Leuco Dyes
Application Method
Properties
Two forms of Leuco Dyes
Classes of Leuco Dyes
Applications
Limitations
References

3. Dyes
 The colored, ionizing and aromatic organic
compound to which it is being applied.
 Dyes are applied to numerous substrates
e.g. textile, ,plastic, paper, etc.
 Certain kind of dyes can be toxic,
carcinogenic or mutagenic and can pose as
a hazard to health.
 Dyes are the larges group that can easily
be influence to our liking.

4. Natural and Synthetic Dyes
Natural dyes are get from natural resources
such as plants, invertebrates and minerals.
The first synthetic organic dye, mauveine, by
William Henry Perkin in 1856.
Synthetic dyes replaced the natural dyes.
Cost less, range of new colors.
Imparted better properties to the dyed
materials. Special and high technology
application .

5. Dyes Give Colors
 Due to the presence of Chromophore.
 Chromophores are the groups which imparts
color.

6. Leuco Dyes
Certain leuco Dyes insoluble in water.
The term Leuco, meaning white and was
applied to the reduced form of vat dyes.
 Change color on oxidation or with
fluctuating of temperatures.
The products found in forms of slurry,
powder, solvent-based ink, epoxy, master
batch, etc.

7. Method of Application
These dyes are insoluble in water.
 Reduce with sodium hydrosulphite yield
alkali soluble forms (Leuco-compounds).
 It is in this form they are introduced into the
fabric.
 The reducing operation carried out in
wooden vats.

8. ……………
 After the reduction, dye has been absorbed in
the fiber.
 The original insoluble colored dye is
reformed by oxidation with air or chemical.
 These dyes are used to dye
cotton etc.
 Very fast because of their
insolubility in water.
e.g. Indigo

9. Forms of Leuco dyes
 Colorless.
 Colored when changing temp.
e.g.
Spiro form Oxazine form

10. Classes of Leuco Dyes
1.Triphenyle
methane
2.Sulfur
Dyes
3.Indigo
Dyes

11. 1.Triphenylemethane
Aniline green, malachite green,
or china green
Synthesis

13. Applications of Malachite Green
 Used pharmaceutically in dilute solution as a
local antiseptic.
 Effective against fungi and gram-positive
bacteria.
 In the fish-breeding industry it has been used
to control the fungus Saprolegnia .
 Used as a dye for silk ,wool, jute, leather and
to dye cotton that has been mordanted with
tannin.

14. Sulfur Dyes
 Inexpensive complex reaction mixtures
of selected aromatic compounds with
sodium polysulfide.

15. Synthesis
Sulfur black

16. Applications
 Used for black, blue, brown, khaki and
green colors.
 Applied to cellulosic fibers and blends of
cellulosics with polyester, nylon and
acrylics.
 Excellent results at a relatively low cost.
 With good application methods, sulfur dyes
are extremely wash-fast.
 Not fast to chlorine bleaching.

17. …..…..
 Dark and medium colors are most common
 Light colors can be produced by special
procedures involving:
• Blended reducing agents.
• Blends of surfactants.
• Controlled oxidation.
• Preparation methods like
Mercerizing and bleaching.

18. Indigo Dyes
Indigo dye is an organic compound with a
distinctive blue color.
Natural indigo get from a plant ‘indigofera
tinctorie’.
1st Synthetic indigo replace natural product
in textile trade in 1897.

19. Synthesis
Indigo Dye

21. Application of Indigo Dyes
 Use as a dye for cotton yarn, for the
production of denim cloth for blue jeans.
 Use for dyeing wool and silk.
 ’Qing Dai’’ a Chinese name for Indigo
natural it has a salty taste and cooling
properties.

22. Application of Other Leuco
Dyes  A wide range of organic leuco dyes are
available changing color between -5 °C and
60 °C.
 Application wherever sharpness of the
temperature change is not important.
 Novelties such as bath toys, color changing
spoons, mugs and cups.
 Microwave temperature indicators on food
packaging

23. Color Changing Cups

24. Thermal paper

25. Hair Color

26. Battery status indicators
The Duracell indicator makes use of
leuco dyes applied to a resistive strip
indicating the heating temperature of
the strip that is related to the
battery's current deliver.

27. Color Changing Ducks
The color changing ducks are covered with
a layer of leuco dyes.
Cold
Hot

28. Flat Thermometer

29. Microencapsulation
Process in which tiny particles are surrounded
by a coating to give small capsules of many
useful properties.
 Leuco Dyes require a special system i.e.
combination of chemicals.
 This process is effectively shown in the
photo-microgh.

30. Thermo chromic inks
These are very high temperature uses Leuco
Dyes change color with changes in
temperature.
LD's are reversible.
It takes about a 5ºF (3ºC) temperature
change for the LD to change color.

31. Cold Activated Thermo chromic
Ink
It is used on labels and packaging to create
a color change when cooled. (Clear to
Color at 15ºC / 59ºF).

32. Touch Activated Thermochromic
Ink:
• It will vanish when rubbed or touched to
reveal an image or another color printed
beneath. (ColortoClearat31ºC/88ºF).

33. High Temperature Thermo
chromic Ink
It is designed to change color just below the
pain threshold alerting consumers and users
to a safety hazard - Too Hot! (Color to Clear
at 47ºC / 117ºF).

34. References
 1. Chemistry and Applications of Leuco Dyes by Ramaiah Muthyala
Springer, 30-Jun-1997.
 2. Industrial Dyes, Chemistry, Properties, Application by Klaus Hunger
 3. Kolorjet Chemicals Pvt. Ltd.
 4. LCR Hall crests Thermodynamic Leuco Dyes.
 5. Gilbert N. Lewis, Jacob Bigeleisen J. Am. Chem. Soc., Photochemical
Reactions of Leuco Dyes in Rigid Solvents. Quantum Efficiency of Photo-oxidation.,
1943, 65 (12), pp. 2419–2423
 6. Thermochromism in commercial products" M A White & M LeBlanc
 7. Journal of Chemical Education, Vol 76, No 9, P 1201, Sept 1999.
 8. en.wikipedia.org/wiki/ Leuco _dye.
 9. Marjan Kooroshnia The Swedish School of Textiles, University of Boras,
Boras Sweden.
 MARJAN.KOOROSHNIA@HB.SE