CHEMISTRY AND APPLICATION OF LEUCO DYES

PRESENTED BY:

ASMA MUQADASROLL # 7632

Contents

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

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.

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 .

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

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.

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.

…………… 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

Forms of Leuco dyes

Colorless. Colored when changing temp.

e.g.

Spiro form Oxazine form

Classes of Leuco Dyes

1.Triphenyle

methane2.Sulfur Dyes

3.Indigo

Dyes

1.TriphenylemethaneAniline green, malachite green, or china green Synthesis

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.

Sulfur Dyes

Inexpensive complex reaction mixtures

of selected aromatic compounds with

sodium polysulfide.

SynthesisSulfur black

2

NH2

R1

2S

S

N

R1

R2

H

R2

R1

S

NaOHR2

-H2S

-NH3

S

N S

S

N

R1

R2

H

R3

H

R4 R4

R2

R1

8C4HBr

C4H9OH

S

N S

S

N

R6

R9

R7

R9

R8 R8

R6

R5

8HBr

R5

R7

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.

…..…..

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.

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.

Synthesis

Indigo Dye

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.

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

Color Changing Cups

Thermal paper

Hair Color

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.

Color Changing Ducks

The color changing ducks are covered with a layer of leuco dyes.

Cold

Hot

Flat Thermometer

MicroencapsulationProcess 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.

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.

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).

Touch Activated Thermochromic Ink:

•    It will vanish when rubbed or touched to reveal an image or another color printed beneath. (ColortoClearat31ºC/88ºF).

 

High Temperature Thermo chromic InkIt 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).

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

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