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CLASSIFICATION OF DRUGS

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CONTENTS INTRODUCTION DEFINITION TYPES CLASSIFICATIONS

INTRODUCTION A dye is a coloured substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber. Both dyes and pigments appear to be colored because they absorb some wavelengths of light more than others. In contrast with a dye, a pigment generally is insoluble, and has no affinity for the substrate. Some dyes can be precipitated with an inert salt to produce a lake pigment, and based on the salt used they could be aluminum lake, calcium lake or barium lake pigments. Dyed flax fibers have been found in the Republic of Georgia dated back in a prehistoric cave to 36,000 BP. Archaeological evidence shows that, particularly in india and Phoenicia, dyeing has been widely carried out for over 5,000 years. The dyes were obtained from animal, vegetable or mineral origin, with none to very little processing. By far the greatest source of dyes has been from the plant kingdom, notably roots, berries, bark, leaves and wood, but only a few have ever been used on a commercial scale.

DEFINITION A dye is a coloured substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber. Dyeing wool cloth, 1482.

TYPES NATURAL DYES SYNTETIC DYES The Hunt of the Unicorn Tapestry, dyed with weld (yellow), madder (red), and woad (blue). NATURAL DYES Dyes which are obtained from nature. Eg: roots,leaves, flowers etc SYNTETIC DYES Dyes which are made by man using natural sources. Synthetic dyes

CLASSIFICATION BASED ON STRUCTURE APPLICATION METHODS

CLASSIFICATION OF DYES BY STRUCTURE NITRO AND NITROSO AZO TRIARYLMETHANE ANTHRAQUINONE INDIGO

(1) NITRO AND NITROSO DYES The NO2 and NO groups are chromophores in this classification of dyes. Examples are,

2) AZO DYES The azo dyes contain one or more azo group, -N=N-, as the primary chromophore. The common auxochromes are NH2,NR2,OH,SO3H,etc. Azo dyes form the largest and most important group of synthetic dyes.They are highly colored and can prepared by diazoting an aromatic amine and subsequent coupling with a suitable aromatic phenol or amine.By varying the substituents present in both the diazonium salt and the coupling compound a series of azo can be produced with almost any color .

AZO DYES PARA RED METHYL ORANGE CONGO RED BISMARCK BROWN

(a)Para Red It was the first azo dye to be prepared. Para red is obtained by the reaction of diazotized p-nitroaniline b-naphthol on fabric itself.

(b)Methyl Orange Methyl Orange is obtained from sulfanilic acid by the following steps:

Methyl Orange color to wool and silk but the color is not fact to sunlight or washing.It is a Valuable indicator for acid-base tirations beacous it gives yellow color in basic solution and red color in acid soiution.The change in color is due to the change in the structure of the ion.

c)Congo Red Congo Red contains two Azo groups.It is Obtained by coupling tetrazotized benzidine(1) with two molecules of naphthionic acid(2).

(d)Bismarck Brown It is obtained by coupling tetrazotized m-diaminobenzene(1) with two molecules of m-diaminobenzene(2). Bismarck brown is a dye used in boot polishes, and for dyeing wool and cotton.

(3)Triarylmethane Dyes In triarylmethane dyes,a central carbon is bonded to three aromatic rings, one of which is in the quinoid from the auxochromes are NH2-NR2 and –OH2 examplees are.

TRIARYLMETHANE DYES MALACHITE PHENOLPHTHALEIN FLUORESCEIN

(a)Malachite Green Malachite Green has a deep green-blue color.Although the color fades in light,Malachite green is used as a direct dyes for wool and silk. It is Obtained by treating benzaldehyde with n, n-dimethylaniline In the presence of concentrated sulfuric acid to give Leuco Base. Oxidation of the leuce base with lead oxide followed by treatment with HCI yields the dye.

(b)Phenolphthalein It is also a triarylmethane dyes but it is better known as an acid-base indicator. Phenolphthalein is prepared by heating phthalic anhydribe and phenol as the presence of anhydrous zinc at 120 C.

(c)Flurescein It is a red powder insoluble in water. It dissoves in dilute alkali and the solution gives beautiful yellow-green fluorescence. The sodium salt of fluorescein in known as Uraine which is use for dyeing wool or silk yellow. Fluorescein is obtained by heating resorcinol and phthalic anhydride with zinc chloride at 190 C.

(4)Anthraquinone Dyes The para quinoid chromophore is present in these anthracenetype dyes. Alizarin is a typical anthraquinone dyes. Alizarin is obtained from phthalic anhydride and benzene by the following steps. Alizarin forms ruby red crystals which dissolve in alkali to given purple solutions. It is used to dye wool and cotton.

(5) Indigo Dyes Indigo is an example of the dyes which contain carbonyl chromophore. Indigo is obtained from anthranilic acid and chloroacetic acid by the following steps. It is a dark-blue crystalline compound,insoluble in water. It is used for dyeing cotton by the Vat Process.

BASED ON METHODS OF APPLICATION DIRECT DYES VAT DYES MORDANT DYES AZOIC DYES DISPERSE DYES

DIRECT DYES These can be applied to a fabric by direct immersion in a water solution of the dye They can de acidic or basic auxochrome which combines with the opposite polar group present in the chemical structure of the fibre. Wool silk are readily dyed with this method Martius yellow a typical dye has the acidic auxochrome OH which interacts with the basic group of wool or silk. FIBRE_______NH2 + HO______DYE = FIBRE________NH3+-------O-_______DYE

CHROMOPHORE AUXOCHROMES The colour of organic compound due to the presence of certain multiple bonded groups calle chromophores. Eg: nitro ,azo ,nitroso,etc chroma = colour phorein= to bear Certain groups while not producing colour themselves when present along with chromophorein an organic subatance intensify the colour such is known as auxochromes Eg: hydroxy,sulphonic ,carboxyl groups etc. chroma = colour auxanein= to bear

VAT DYE They are insoluble in water but on reductiomm with sodium hydrosulphide in a vat form a colourless soluble compound which has a affinity for cotton and other cellulose fibres. The cloth is soaked in a solution osf a redused dye and the n hung in air or treated with oxidants . As a result colourless compound is oxidised back to the insoluble dye which is bound to the fabric

MORDANT DYES This class of dyes have no natural affinity for the fabric and are applied to it with the help of salts.eg salts of aluminium or chromium. A fibre such as cotton is first treated with a mordant and the with the dye solution. The mordant forms an dinsoluble coordination complex with the fibre and the dye,and binds the two The complex compound appears in the form of ‘lakes’ that are fast to light and washing

AZOIC DYES In this method for dyeing,the water insoluble azo dye is produced in the fabric itself. The cloth is first soaked in the solution of a coupling reagent usually a phenol naphthol. Then it is immersed in the solution of an appropriate diazonium salt .the dye that is developed in the fabric binds fast to it via auxochromes. The azoic dyeing is particularly suitable for cotton and othe cellulosic fibres but may also be used for nylon

DISPERSE DYES These dyes are insoluble in water but can be dispersed in a colloidal form. The fabric is immersed in the colloidal dispersion of the dye. The fine particle are absorbed into the ‘ crystal structure’ of the fabric. Disperse dyes are used with modern synthetic fabrics such as nylon.orlon,polyesters and cellulose acetate.

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