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Chemistry in Dyes Natural dyes are extracted from natural sources. They are used for making coloured fabrics. Probably, the earliest known natural dyes were indigo (a blue dye) and alizarin (a red dye). These were obtained from plants. Definition of Dyes A dye is a coloured substance that can be applied in solution or dispersion to a substrate, giving it a coloured appearance. Usually the substrate is a textile fiber , but it can also be paper, leather, hair, fur, plastic material, wax, a cosmetic base or a foodstuff. Now a days synthetic dyes are used for dyeing purpose. Classification of Dyes Dyes are classified either according to their constitution or method of application. 1. Classification of dyes based on Constitution This classification is based on the distinguishing structural units present in the dye. 1. Azo 2. Nitro 3. Phthalein 4. Triphenyl Methane 5. Indigoid 6. Anthraquinone 2. Classification of dyes based on Application Depending upon the process of application the dyes ...

Vat Dyes Vat dyes are insoluble in water and cannot be used directly for dyeing. But on reduction to a leuco form (colour less), they become soluble in an alkali and acquire affinity for cellulose fibres. A solution of the leuco form can be applied for dyeing or printing. On oxidation the original insoluble dye is formed within th structure of the fibre. Indigo and indigosol O are dyes which belong to this class. Mordant Dyes Mordant dyes are primarily used for dyeing of wool in the presence of metal ions. The metal ion binds to the fabric and the dye acting as ligand co-ordinates to the metal ion. The same dye in the presence of different metal ions imparts different colours to the fabrics. The colours imparted by Alizarin in presence of different ions are given below Ions and colours Al3+ = Rose red Ba 2+ = Blue Cr 3- = Brownish red Mg 2+ = Violet Sr 2+ = Red For details about Dyes visit http://entrancechemistry.blogspot.com/2012/08/chemicals-in-every-day-life...

Fibre Reactive Dyes Fibre Reactive Dyes attach themselves to the fibre by an irreversible chemical reaction. The dyeing is fast and the colour is retained for a long time. The bonding is through the substitution of leaving group of dye via the hydroxy or amino group of fibres like cotton, wool or silk Insoluble Azo Dyes Insoluble Azo Dyes are obtained by coupling phenols, naphthols, arlamines, amino naphthols adsorbed on the surface of a fabric with a diazonium salt. Over 60% of the dyes used are Azo dyes . Cellulose, silk, polyester, nylon, polypropylene, polyurethanes, poly acrylonitriles and leather can be dyed by using these dyes. Azo dyes also find use in cosmetics, drugs, biological stains and as indicators in chemical analysis. Use of such dyes for colouring of food stuffs is not permitted . To know classification of dyes visit Chemicals in every day life: Dyes

Direct Dyes Direct dyes are water soluble dyes. As the name suggests, these dyes are directly applied to the fabric from aqueous solution and are practically suitable for fabrics like cotton, rayon, wool, silk and nylon which from hydrogen bonds with water. Martius yellow and congo red are important example of this class of dyes. Disperse Dyes Disperse Dyes in the form of minute particles of a suspension diffuse into the fabric, get fixed and impart colour. Such dyes are used for dyeing synthetic fibres like polyesters, nylon and polyacrylo nitrile . Many anthraquinone disperse dyes are suitable for application to synthetic polyamide fibres. T o know more about Dyes visit Chemicals in every day life: Dyes

Acid Dyes Acid dyes are usually salts of sulphonic acid and can be applied to wool, silk, polyurethane fibres and nylons. The affinity of acid dyes for nylon is higher than that for other types because polycaprolactum fibers fibers contain a higher proportion of free basic amino groups. Acid dyes do not have affinity for cotton. Orange-1 is a versatile acid dye. Basic Dyes Basic dyes contain amino group which in acid form water soluble salts. These dyes get attached to the anionic sites present on the fabrics. Such dyes are used to dye reinforced nylons and polyesters. Aniline yellow and malachite green belong to this class of dyes. To Know more about dyes visit Chemicals in every day life: Dyes

Perfumes Perfumes are the materials which give fragrance. A good perfume should have three essential ingredients. They are 1. Vehicle or Solvent 2. Fixative 3. Odorous substance 1. Vehicle or Solvent The vehicle or Solvent is used to keep the odour producing substances in solution. Ethanol and water mixture is most commonly used in perfumery. 2. Fixative Fixative regulate the evaporation of various odoriferous components of perfumes. Sandal wood oil, Benzoin, glyceryl diacetate and esters of cinnamyl alcohols are used as fixative. 3. Odorous Substance The function of odorous substance is to provide pleasant fragrance to perfume. Odorous substances may be natural or synthetic. Terpenoids like linalool is a natural odoriferous substance. Anisaldehyde (p-methoxy benzaldehyde) is an example for synthetic odoriferous substance. Related posts Chemicals in Food

Many chemical substances such as flavourings, sweeteners, dyes, antioxidants, fortifiers, emulsifiers and antifoaming agents are added to food for their preservation and enhancing their appeal. With the exception of preservatives, fortifying agents, antioxidants and artificial sweeteners. The other classes of chemicals are added either for ease in processing or for cosmetic purposes. In real sense, these substance have no nutritive value. Preservatives Usually food is most appetizing when it comes from the production line in the food processing plant. But, during storage and distribution undesirable changes occur in flavour, colour, texture and appetitic appeal. To delay these changes many chemical substances are added to food. These chemicals are called food preservatives. They prevent spoilage of food due to microbial growth. commonly used preservative is sodium benzoate (C6H5COONa).In order to preserve colourless food materials potassium metabisulphite or sodium metabisulphite is us...