Dyes ppt

Dyes topic for B.Sc. final year students of SGB University Amravati
and also for other university students

1. Dyes Dr. Nilesh R. Thakare

2. Intorduction “ Dyes are coloured substances capable of being fixed to fabrics like silk, wool and cotton and other substances such as paper, leather. When fixed, dyes must be fast to light and resistant to the action of water, dilute acids, alkali solution and bleaching.”

3. Two important conditions for a coloured compound to act as a dye are- Presence of Chromophore :- These are the groups which are responsible for producing colour to a dye because they are capable of absorbing light in the near U.V. region. Some important chromophores are ; ─N═O, ─NO 2 , ─N═N, >C═O, ═C═S, ─C≡N, etc. The compounds bearing chromophores are known as chromogens . Presence of auxochromes :- Dye must be attached to fibres by means of stable chemical bonds. Those bonds are formed by some acidic or basic groups. Such groups are known as auxochromes . e.g. ─OH, ─COOH, ─SO 3 H (acidic) ─NH 2 , ─NHR, ─NR 2 (basic)

4. Classification 1. Classification of dyes on the basis of structure Depending upon the type of chromophore present in their structures the dyes are classified into following main types. Nitro and Nitroso dyes. Azo dyes. Triphenyl methane dyes. Phthalein dyes. Indigoid and Thioindigoid dyes. Anthraquinone dyes. Miscellaneous dyes. ( Azine dyes, sulphur dyes, xanthene dyes, phthalo -cyanine dyes )

5. Nitro and Nitroso dyes These are polynitro derivatives of phenols and naphthols in which at least one nitro (-NO 2 ) group or nitroso (-N=O) group is ortho or para to the -OH group. Colours of these dyes are not fast and hence they are industrially less important. Naphhthol yellow-S is one of the dyes used for colouring edible materials.

6. Nitro and Nitroso dyes

7. Azo Dyes These contain one or more azo (─N=N─) groups as chromophores . The auxochromes present in these dyes are ─OH, ─SO 3 H, ─NH 2 , ─NR 2 etc. These dyes possess a wide range of colours ranging from yellow to orange and red. These are prepared in the following stages.

8. Methyl Orange

9. It is an azo dye containing one azo N=N group.It also contains SO3H group (acidic) making it more souble . Preparation :- Step- 1: Diazotisation of sulphanilic Acid

10. Step 2 : Coupling of diazo compound with dimethyl aniline

11. Properties and Uses Water is soluble because it contains acidic -SO 3 H group. It is not sufficiently fast to light and soap. Hence it is used as a dye. It is generally isolated as the sodium salt, which is used as dyeing. It imparts orange colour to wool and silk. It is used as an indicator in acid alkali titration. It is orange in alkaline solution an red in acid solution. The change in the structure of the ion.

12. Triphenyl Methane Dyes. ( Triaryl Methane)

13. Crystal Violet Preparation: It involves two steps - Step 1:- Preparation of Michler’s ketone

14. Step 2 : Condensation of Michler’s ketone with dimethyl aniline

15. Properties and Uses This dye forms large crystals which are violet in colour . Hence the name Crystal violet. It is soluble in water and gives deep blue colour . It dyes wool, silk and tannin mordanted cotton fibre . Uses In the manufacture of inks, stamping pads and type –writer ribbons. As an indicator to find out H + ion concentration of solution. Gentian violet (a combination of crystal violet and methyl violet) is used as an antiseptic for certain skin diseases like burn, ulcers and also used for washing the wounds. Used as biological stain. Used in making pencils.

16. Phthalin Dyes The term phthalein is used to represent the dyes formed from phthalic anhydride and phenols; in presence of dehydrating agents like fused ZnCl 2 or conc.H 2 SO 4 . The characteristic chromophoric group present in these dyes is triphenyl -methane structure.

17. Phenolphthalin :-

18. Indigoid and thioindigoid Dyes The Indigoid dye contains above linkage as a chromophoric group

19. Preparation:- Indigo is used on large scale for dyeing cotton by vat process. The fabric is soaked in solution of indigo and then exposed to air when fabrics gets a dark blue colour which is extremely fast to washing.

20. Thioindigoids :- Thioindigo is similar to indigo but differs only in one respect that in place of two ─NH groups there are two ‘S’ -atoms . Thioindigo is used to dye cotton, wool and polyester.

21. Anthraquinone Dyes:- These include hydroxy or amino derivatives of anthraquinone . The para quinoid chromophore is present in these anthracene -type dyes. Alizarin is the typical anthraquinone dye.

22. Preparation of Alizarin:- Step : 1 Preparation of Anthraquinone

23. Step 2 : Sulphonation of anthraquinone Step 3 : Conversion of 2-Anthrquione sulphonic acid into Alizarin Preparation of Alizarin:-

24. Properties and Uses:- It forms ruby red crystals M.P. 290 C. Sparingly soluble in water, soluble in alcohol and ether. It dissolves in alkalis to give violet or purple coloured salt called alizarate . It sublimes on heating. It is a mordant dye i.e.it forms coloured salts with metallic oxides. It forms a red lake with aluminum and a violet black lake with Iron (Fe 3+ ). Alizarin is used to dye cotton and wool. It is used as purgative in medicine. It is used in manufacture of printing inks.

25. Exercise : What are Dyes Discuss properties and Uses of Crystal Violet Discuss Classification of Dyes What are Indigoids and Thioindigoids Give Preparation, Properties and uses of Alizarin Give Preparation, Properties and uses of Methyl Orange Explain with example Chromophore and Auxochrome