INTRODUCTION TO INTRODUCTION TO PREPARATION AND STRUCTURE OF SOME COMMON DYESTUFFS

By Granch Berhe

Dyes are colored organic compounds that are used to impart color to various substrates, including

PaperLeatherHair Drugs CosmeticsWaxesGreasesPlastics and Textile materials

Dyes may be classified according to their chemical structure or by the method by which they are applied to the substrate.

The dye manufacturers and dye chemists prefer the former approach of classifying dyes according to chemical type.

The dye users, however, prefer the latter approach to of classification according to application method.

Classification by application or usage is the principal system adopted by the Color Index (C.I.).

Azoic Dyes Acid DyesBasic (Cationic) DyesDirect DyesDisperse DyesReactive DyesMordant DyesSulfur DyesVat Dyes

1.1 Azo DyesAre:- Larger groups N=N NH2, NR2, OH

There may be more than one azo group Mono, Di, Tri, Tetrakis and poly

Prepared by Diazotization of primary aromatic amines= Diazonium salt/diazo and then coupled with phenol or amine

DiazotizationWhen aromatic amine is added on aqueous acid medium by nitrous acid a diazonium salt is formed and the amine is said to be has been diazotized.

Rate determining step-nitration of amine

Ar. = aromatic hydrocarbon radical

Diazo CouplingDiazo Coupling Electrophilic substitution by diazonium salt.Electrophilic substitution by diazonium salt. Comparing with Comparing with ++NONO2 2 and SOand SO33

- - thethe diazonium diazonium cation is a weak electrophile and powerful cation is a weak electrophile and powerful electron donating groups such as -OH, -NH2, -electron donating groups such as -OH, -NH2, -NR2 must be present in the aromatic system of the NR2 must be present in the aromatic system of the coupling component for coupling to take place. coupling component for coupling to take place.

Coupling Components areCoupling Components are Benzene Derivatives like amines at acidic Benzene Derivatives like amines at acidic

mediummedium Hydroxyl derivatives at alkaline mediumHydroxyl derivatives at alkaline medium Salicylic Acid at alkaline mediumSalicylic Acid at alkaline medium Naphthalene Derivatives at alkaline mediumNaphthalene Derivatives at alkaline medium

Examples of Diazotization and coupling on fiber

1.2 Cationic Dyes( Mono Azo)

Usually hydrochlorides of bases having moderate solubility in water

Drawing chiefly on Azo, Anthraquinone and Triarylmethane and are now commercially available.

water-soluble and produce colored cations in solution.mostly amino and substituted amino compounds soluble in acid and made insoluble by the solution being made basic.attached to the fibers by formation of salt linkages (ionic bonds) with anionic groups in the fiber.used to dye paper, polyacrylonitrile, modified nylons, and modified polyesters.

1.3 Reactive dye

Main chromophores employed in this are Azo, Metal Azo, Anthraquinone and Phthalocyanin containing the groups which can react directly with the fiber

react with the cellulose fiber to form a covalent bond. This produces dyed fiber with extremely high wash fastness properties.Cotton, rayon, and some nylons are dyed by this relatively simple dye.

Reactive Azo DyesReactive Azo Dyes

1.4 Vat Dyes

Commercial name Indathrene Cibanone Caledon

Divided into Dyes derived from Indigo: Include natural and synthetic

indigos and its Bromide and Thioindigo Dyes Derived from Anthraquinone

insoluble complex polycyclicreduced with sodium hydrosulfite in a strongly alkaline medium to give soluble leuco forms that have a great affinity for cellulose.After the reduced dye has been absorbed on the fiber, the leuco forms are reoxidized to the insoluble keto forms.

SynthesisHeumann Process

+ heat + KOH and NANH2

Sadamine Process

Alinine + heat + CS2= Thiocarbonilide + heat + Lead carbonate + NaCN, S = Cyano

compound structure

+ Sodium Hydrosulphide =thioisatin + Alkali=Indigo

1.5 Disperse Dyes1.5 Disperse Dyes Mono azo, Diazo, Mono azo, Diazo,

Anthraquinone, Anthraquinone, Methine, Quinoline, Methine, Quinoline, Nitro, Nitro, AroylenebenzimidazoleAroylenebenzimidazole

substantially water-insoluble nonionicapplication to synthetic hydrophobic fibers from aqueous dispersions.primarily used for polyester and acetate fibers.

N.BN.BPresence of halogens, Presence of halogens, NO2, CN or electron- NO2, CN or electron- withdrawing groups in withdrawing groups in the Diazo component the Diazo component causes a shift of λcauses a shift of λmax max

to wards the longer to wards the longer wavelength wavelength bathometric effectbathometric effect..