ingrain dye explantaion.pdf

Online edition for students of organic chemistry lab courses at the University of Colorado. Boulder. Dept of Ctiem and Biochem. (2002)

@ Supplement to Experiment 8

Essay: Dyes and Dyeing

The dyeing of cloth is an ancient art. Prior to 1856, all dyes came from plant or ani-mal sources. In that year, William Henry Perkin accidentally discovered the firstsynthetic dye while trying to synthesize quinine from allyltoluidine. Instead of qui-nine he produced a purple solution which proved to be a good dye for fabrics. Thepurple dye came to be known as Perkins Mauve, and Perkin went on to found theBritish coal tar dye industry. (He retired from the business world at age 36 to devotefull time to chemical research.)

The founding of the first dye company isconsidered the birth of the organic chemi-cal industry.

2

Although numerous colored compoundsand, thus, potential dyes have been pro-duced since the 1850s, the successfuldyeing of a cloth sample depends both onthe structure of the fibers in the cloth andthe structure of the dye. Perkins Mauve

The structures of some common fibers are given below. Wool, silk, and cotton arenatural fibers. Wool and silk are polypeptides, or polymers made of amino acidunits. The acidic and basic amino acids present in these polymers provide manypolar groups to which a dye can bind. Cotton, which is pure cellulose, has manyhydroxyl groups (-OH) which can form hydrogen bonds to dyes. Rayon (or acetate)is cellulose in which some of the hydroxyl groups have been acetylated. Thus, rayonhas fewer hydrogen bonding sites and is more difficult to dye than cotton. The syn-thetic fibers (nylon, dacron, and orlon) have fewer polar sites than the natural fibers.Nylon, a polyamide, is made by polymerizing a dicarboxylic acid and a diarnine. Itcan be synthesized so that either -NH3 + or -coo- groups predominate at the ends ofthe chains. Dacron is a polyester made by polymerizing ethylene glycol and tereph-thalic acid. Orlon is a polymer of acrylonitrile.

Orlan

Nylon

8 Essay: Dyes and Dyeing 55

Online edition for students of organic chemistry lab courses at the University of Colorado, Boulder, Oept of Ctiem and Biocnem. (2002)

Wool, Silk fo H ° H ° H 1II I II I II IC-N-CH-C-N-CH-C-N-CH

I I IR R' R" n

where R = amino aci-d resi-due

Cotton

Rayon(Cellulose Acetate)

P-otO~CH2CH2i.In order to dye the various types of fibers, numerous methods have been developed.Dyes have come to be classified according to the dyeing method most commonlyemployed in their use. These classifications are: direct dyes, disazo dyes, ingrain ordeveloped dyes, mordant dyes, vat dyes, fiber reactive, disperse dyes, and opticalbrighteners. Some dyes fall into more than one of the above classifications; dyes are .sometimes also classified according to their structural class, e.g., azo, triphenyl-methane, anthraquinone, etc.

Dacron

Direct DyesA direct dye forms a strong ionic bond with the fabric. The dye either contains or iscapable of forming a positive or negative charge which is electrostatically attractedto a negative or positive charge on the fiber. For example, the direct dye picric acid isa strong acid and interacts with the basic side chains in wool to form a salt linkagebetween itself and the fiber. On the other hand, malachite green bonds to the acidicside chains in the wool fibers. Malachite green is a member of the important triphe-nylmethane structural class of dyes.


Online edition for students of organic chemistry lab courses at the University of Colorado. Boulder. Dept of Cnem and Biocnetn. (2007)

} "It

NH2I

wool or silk fiber

Disazo Dyes

Also called substantive dyes, this type of dye contains two azo linkages. Disazo dyeslink via hydrogen bonding to the hydroxyl (-OH) groups in a fabric. Cotton andsometimes rayon (depending on the amount of acetylation of the hydroxyl groups)can be dyed directly with disazo dyes. Congo red (a benzidine dye) is a disazo dye.

cotton

IOH

IOH

II

I

II

I

-N N-'0 ~ J\_ '/

N~N

Ingrain Dyes

Also called developed dyes, these dyes are actually made inside the fibers of the fab-ric. The fabric is treated with the two components used to synthesize the dye. Theseprecursor molecules are small enough to diffuse into the pores and spaces betweenthe fibers in the fabric. They then react to form the dye, which is trapped inside or"in the grain" of the fibers, because of the large size of the dye molecule. Azo dyes,such as para red ("American flag red"), are used as ingrain dyes for cotton. The fab-


Online edition for students of organic chemistry lab courses at the University of Colorado, Boulder, Dept of Cnem and Biochem. (2002)

ric is soaked first in a solution of the coupling component b-naphthol and then in asolution of diazatized p-nitroaniline.

Para Red: formedin the fiber

OH

{}-N=N-Q-N02oThe azo dyes are the largest and the most important structural group of syntheticdyes. Synthesized by the coupling of diazonium salts with various aromatic aminesand phenols, the resulting products encompass a broad range of colors, includingyellows, oranges, reds, browns, and blues. It is the structure of each particular dyethat determines the color that will be exhibited. In general, the more the conjugated11: system of a molecule, the longer the wavelength of visible light it will absorb, andthe observed color will change accordingly. (White ~ Yellow ~ Orange ~ Red ~Green ~ Blue.)

Diazonium salts are prepared from the corresponding aromatic amine by treating anacidic solution of the amine with aqueous sodium nitrite solution. The diazoniumsalt generated is an electrophilic intermediate, and can effect electrophilic substitu-tion reactions on highly activated aromatic compounds such as amines and phenols.The resulting molecules have the -N=N- (azo) system linking two aromatic rings.Azo dyes are discussed in Carey in section 22.] 9 (pp. 895-897).

NaN02

+

¢N -HSO, _;n-I_-:-ap-h-:-O-J-O_H

N02

p-nitroanilineN02

diazonium ion Para Red

Mordant Dyes

Certain dyes form chelated complexes with heavy metals such as copper, chromium,tin, iron, and aluminum. Cotton, wool, and silk can also coordinate with these met-


Online edition for students of organic chemistry lab courses at the University of Colorado, Boulder, Dept of Ctiem and Bioctiem. (2001)

alsoTo dye a fabric with a mordant dye, the fabric is first treated with a mordant, orthe salt of a heavy metal. The fabric is then treated with the dye, the dye complexeswith the mordant, and is thus linked to the fabric. Different metals (mordants) canlead to different colors with the same dye. Alizarin (an anthraquinone dye) is a typi-cal mordant dye, shown in a chelated complex with cotton using chromium as themordant.

%~ ;/ alizarin

Ij ~ (insoluble complex)o -

OH OH, /, /cr- -OH2H20~1 \

1 \

OH OH

I I, rv rv n, rv I,rv rv rv

cotton

With some mordant dyes, especially the triphenylmethane dyes (e.g., malachitegreen and crystal violet, cationic dyes) tannic acid is used as the mordant. Tannicacid is actually a mixture of tannin structures and is isolated from the bark of differ-ent plants.

Vat Dyes

Vat dyes can be used for all fibers, both natural and synthetic. Most vat dyes are sol-uble (and colorless) in water in their reduced form, but become insoluble and col-ored when oxidized. They are introduced to the fabric in their soluble form and thenoxidized or "developed" to precipitate them both on the inside and outside of thefabric fibers. The vat dye indigo (a quinonoid dye) is used to dye blue jeans. It isvery insoluble in all solvents, and thus is fast. However, since it is not covalentlybound to the fabric, and only adheres to the surface of the fiber, it is subject toremoval by abrasion. This explains why the knees and other parts of blue jeans sub-


Online edition for students of organic chemistry lab courses at the University of Colorado, Boulder, Dept of Ctiem and Biochetn. (2002)

jectto wear will gradually turn white. It also accounts for the appearance of the cur-rently popular "stone-washed" jeans.

leucoindigo(soluble)

indigo(insoluble)

Disperse Dyes

Disperse dyes are similar to vat dyes in that they are applied to the fabric in solubleform and remain on the fabric as a water-insoluble precipitate. These dyes are solu-ble in an organic solvent and insoluble in water. They may be used to dye the fabricslike dacron and rayon that have few groups present to allow any direct dye-fiberinteractions. Many of the dyes used above can be used as a disperse dye: para red isa common disperse dye.

Fiber-Reactive Dyes

This is the newest type of dye.These dyes attach to the fiber byreacting with either an amino or ahydroxyl group in the fiber to form acovalent bond. The main class of

Cyanuric chloridethese dyes are the procion dyes,based on cyanuric chloride. The dyemolecule and the fiber molecule must each contain either an -OH or an -NH2 group,

CI

N~NJL. ~ + DYE

CI N CI

Procion dye


Online edition for students of organic chemistry lab courses at the University of Colorado, Boulder, Dept of Chern and Biochem. (2007)

each of which replaces one of the chlorines in cyanuric chloride. The result is thatthe dye is covalently attached to the fiber through cyanuric chloride.

Dye~ covalent bond ?ye

N N ~)l ~ ( N "NCleN/. CI ~)lN~CI

O-H 0I I

fabric

Optical Brighteners

Many detergents contain a blue-white fluorescent dye that is adsorbed on the clothduring the washing process. These dyes fluoresce, that is, absorb UV light and ree-mit light in the visible blue region of the spectrum. This blue color counteracts thepale yellow color of white goods, which develops because of a buildup of soilembedded in lipid.

Representative Dyes

The following compounds are dyes which represent the types discussed above.OH

02NAN02

YN02

O-NH/

~N02

~N02

Picric Acid(direct)

Martius Yellow(direct)

Methyl Orange(direct)

o

oIndigo(vat)

OHg-~-0-N=N ~ /; N02

:; ~

Para Red(ingrain, disperse)


Online edition for students of organic chemistry lab courses at the University of Colorado, Boulder, Dept of Cnem and Biochem. (2002)

Chlorantin Light Blue 8G(disperse)

o$- HO

I~ ~ ~ 't-N H

'I '\ I// 0 0 OH N)----N)=N

o OH Q-N,

Alizarin - H(mordant)

OH~ N=(N--{ N

N~ _

Na+ .-~t--oBlankophor B

(optical brightener)

\

+6H'''CI

(CH3hN--o-~-o-N(CH3h

Crystal Violet(mordant, triphenylmethane dye)

Q(CH3hN--0-C=O=~(CH3hCI -

Malachite Green(direct and mordant: triphenylmethane dye)


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ingrain dye explantaion.pdf