Classify organic dyes according to their chemical composition.
Colouring materials have been used for many thousands of years by man. Leather, cloth, food, pottery and housing have all been modified in this way. The two old ways were to cover with a pigment (painting), or to colour the whole mass (dyeing). Pigments for painting were usually made from ground up coloured rocks and minerals, and the dyes were obtained from animals and plants. Today, many of the traditional dye sources are rarely, if ever, used (onion skins, for instance). However, some of our most common dyes are still derived from natural sources. These are termed natural dyes. The Colour Index uses this as a classification and naming system. Each dye is named according to the pattern:
–Natural + base colour + number
These dyes are thereby specifically identified as dyes of the stated colour, and which may still be derived from animals or plants. Note that this is a classification based on the dye’s source and colour. It contains no chemical information; neither does it imply that dyes with similar names but unique numbers are in any way related. It gives no information about the mechanism by which staining occurs.
Natural dyes are often negatively charged. Positively charged natural dyes do exist, but are not common. In other words, the coloured part of the molecule is usually the anion. Although the molecular charge is
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Write the main product of the following reactions giving reasons for your answer.
How are following compounds prepared using ethereal solution of diazomethane?
Write the mechanism of the reactions.
i) CH3CH2COOCH3
ii) CH3CH2OCH3
How are following conversions carried out?
i) 6-hydroxy-6-Methyl- 2-heptanone from 5-bromo-2-propanone using Grignard
reagent
ii) Cyclopentyl methyl ketone from acetoacetic ester
iii) Barbituric acid from molonic ester
iv) Propanol from ethylene oxide
v) Butane from chloromethane
In Wittig reaction, the methyl, primary and secondary alkyl halide can be used to
prepare Wittig reagent (ylide) but not tertiary alkyl halide.
Reaction of primary amine, in presence of an acid, with carbonyl compound
gives an imine. The rate of reaction increases by an increase in acidity but
beyond a certain limit, the rate decreases with further increase of acidity.
Electron withdrawing substituents at carbonyl carbon increase its
reactivity towards nucleophilic addition reactions.
Complete following reactions:
