How to Prepare Azo Dye

Written by madeline masters
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How to Prepare Azo Dye
Synthetic dyes have nearly replaced natural dyes for fabric-making uses. ( Images)

Azo dyes are synthetic dyes used to colour fabric and food. They are the most common form of synthetic dyes. In general, azo dyes are made when a coupling component is combined with a diazo component under the proper conditions, such as suitable water temperature. These instructions will guide you in preparing Sudan I, a common red azo dye used for waxes, oils, solvents and polishes.

Skill level:

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Things you need

  • Nitrile gloves
  • Safety goggles
  • Protective clothing
  • 2 boiling tubes
  • 1 test tube
  • Test tube rack
  • Dropping pipettes
  • Distilled water
  • Phenylamine
  • Concentrated hydrochloric acid
  • Crushed ice
  • Plastic container (to hold ice)
  • Scale
  • 2-naphthol
  • 2 mol dm-3 solution of sodium hydroxide
  • Cotton square, 1/2 inch by 1/2 inch
  • Tweezers

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    Prepare the Dye Mixture

  1. 1

    Using the pipette, put eight drops of phenylamine in a boiling tube, then add 30 drops of distilled water and 15 drops of concentrated hydrochloric acid.

    How to Prepare Azo Dye
    Sudan I is an azo dye used to make red fabric. (Hemera Technologies/ Images)
  2. 2

    Shake the boiling tube carefully from side to side to mix its contents, then rest it in an ice bath, making sure none of the ice bath enters the tube.

  3. 3

    Measure 1ml of sodium nitrite solution into a test tube using a clean pipette.

  4. 4

    Cool the second tube in the ice bath for 2 minutes, then pour into the phenylamine and hydrochloric acid solution. Shake to mix well, then rest again in the ice bath.

  5. 5

    Using the scale, weigh out 0.45g of 2-naphthol, and add it to another boiling tube. Add 3ml of sodium hydroxide solution to the naphthol with a clean pipette. Swirl to dissolve the naphthol into the sodium hydroxide solution.

    Dye the Fabric

  1. 1

    Take the piece of cotton and, using the tweezers, dip it into the naphthol solution. Make sure the solution completely soaks the cotton before you remove it.

  2. 2

    Next, dip the cotton into the hydrochloric acid solution. Make sure the cloth is completely immersed in the liquid.

  3. 3

    Leave the cloth in the tube for 1 to 2 minutes. Then, using the tweezers, remove the fabric from the tube.

  4. 4

    Rinse the fabric square under running tap water. The fabric should have taken on a red colour from the azo dye.

Tips and warnings

  • The amount and type of acid and the amount of naphthol used to mix a dye will vary based on which azo dye you intend to produce.
  • Temperature control is essential to preparing dye effectively. Chemicals handled at room temperature when they should be chilled will not produce the desired results.
  • The chemicals used to produce azo dyes, especially hydrochloric acid, can be harmful, so always wear protective clothing, goggles and gloves while handling.

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