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University of San CarlosDepartment of Chemistry

John Darwin O. Namata Mrs. Lora Mae Villegas

BS Chemistry II Chem 23L

Experiment 17

Preparation of Azo DyesAbstract

This experiment synthesizes p-nitrobenzene azoresorcinol and helianthin dyes. P-nitrobenzene Azoresorcinol was synthesized by first preparing the diazonium salt by adding

sodium nitrite in a hychloric acid-p-nitroaniline solution. The prepared diazonium salt was added

to a cold resorcinol-sodium hydroxide mixture with constant stirring. The solution was thenadded with slight excess of hydrochloric acid. The solid was collected through suction filtration

and was washed.

Helianthin was prepared by first preparation of the diazonium salt. The diazonium salt

was prepared by the addition sodium nitrite to a sulfanilic acid-sodium hydroxide solution. Thesolution was then added to a solution of dimethylaniline and hydrochloric acid. The resulting

mixture was then made alkalin by the addition of sodium hydroxide. The solids are then

collected.

Introduction

Azo compounds are chemical compounds with the general formula R-N=N-R', where R

and R' can be either aryl (aromatic) or alkyl (aliphatic) functional groups. The N=N group is

called an azo group, although the parent compound, HNNH, is called diimide. The more stable

azo compounds contain two aryl groups. Azo compounds with alkyl functional groups are

particularly unstable and should be handled with care, to prevent them from exploding.

Aryl azo compounds have vivid colors, especially reds, oranges, and yellows. They are

therefore used as dyes and are classified as azo dyes. Examples include methyl red and Disperse

Orange 1. The ability to manufacture azo dyes was an important step in the development of the

chemical industry.( http://www.newworldencyclopedia.org/entry/Azo_compound, March 2011)

Diazonium compounds or diazonium salts are a group of organic compounds sharing a

common functional group R-N2+

X-where R can be any organic residue such alkyl or aryl and X

is an inorganic or organic anion such as a halogen. Diazonium salts, especially those where R is

an aryl group, are important intermediates in the organic synthesis of azo dyes.

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An azo coupling is an organic reaction between a diazonium compound and a dialkylaniline

(C6H5NR2), phenol or other aromatic compound which produces an azo compound.

Experimental Details

P-nitrobenzene azoresorcinol Dye

A solution of concentrated hydrochloric acid in 25 mL of water was added to finelypowdered p-nitroaniline. The solution was cooled to 2C and was stirred well.

A 0.6g of sodium nitrite in 15 mL water was added slowly to the p-nitroaniline solution.

The resulting solution was poured slowly to a cold solution of 1.0 g resorcinol, 25mL water, and4mL of 8N sodium hyrdroxide. The resulting mixture was chilled and was added with slight

excess of hydrochloric acid.

The solid was collected on a Bchner funnel, using a very light suction. It was then

washed several times with water. The compound was then dried.

Helianthin

Four grams of Sulfanilic acid was dissolved in 10mL of 2N sodium hydroxide solution.The sulfanilic acid-NaOH mixture was then added with a solution of 2 g of sodium nitrite in 20

mL of water. The mixture was cooled in an ice bath and was poured into 10mL of cold 2N

hydrochloric acid.

The resulting mixture was then added with a solution of 2.5 g of dimethylamine in 20 mLof 1N hydrochloric acid. The mixture was made alkaline by the addition of sodium hydroxide.

The solution was left for few hours. After an hour, the solution was filtered through suction.

Results and Discussion

The addition of sodium nitrite to the solution of p-nitroaniline, formed a clear and

colorless liquid. The addition of the sodium nitrite initiates the formation of the diazonium salt

with a temperature approximately 2C.

+ HCl + HNO2 + H2O

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The p-nitroaniline underwent a process of diazotization in the presence of hydrochloric

acid and nitric acid. The process formed the diazonium salt.

The diazonium salt undergoes a coupling reaction with resorcinol in basic medium.

Conclusion

References

http://www.newworldencyclopedia.org/entry/Azo_compound

http://www.newworldencyclopedia.org/entry/Azo_compoundhttp://www.newworldencyclopedia.org/entry/Azo_compoundhttp://www.newworldencyclopedia.org/entry/Azo_compound