Week 9: Synthesis of Azo Dyes

The inspiration for this experiment is from: “A Combinatorial Experiment Suitable for Undergraduate Laboratories” by Benjamin W. Gung and Richard T. Taylor. Journal of Chemical Education, Vol 81, No. 11, November 2004.

2) Changes to published procedure
We doubled the quantities used in the JCE article.
The 2.6% aqueous sodium carbonate solution was prepared ahead of time.
The first part was done in beakers and no test tubes.
In 2008, we used the 3 positional isomers of aminobenzenesulfonic acid with 1-naphthol, 2-napthol, and 1-bromo-2-napthol. The latter nucleophile was a new addition to the scheme. 

3) Positive
+This experiment goes well with the “reactions of benzene derivatives” chapter.
+ Its colorful. The multifabric strip is a unique analysis technique – a little variation from the characterization of a white solid by melting point.
+ I really like these combinatorial schemes where students can comtrast and compare their products.

4) Neutral
±A precipitation is not really necessary in Part I. 
±In Part II, a little additional concentrated HCl helps with the final precipitation.
±If the student does not get a precipitate, they use the colored solution as a dye bath in Part III.
±The 1-bromo-2-naphthol behaved well. Unfortunately it had a pretty strong bromine odor. 

5) Negative  
-It may be rather difficult to determine the actual structure of the products. Has this ever been done? Is it a mixture, or what?
6) Inquiry & Extension ideas.
=Combinatorial schemes are always interesting to contrast and compare products.
=Could be incorporated with alot more information and discussion on the interactions between dyes and fabrics. Why do certain fabrics “hold” certain dyes?
=It is possible to vary the nucleophile (e.g. naphthol derivative). It may be possible to vary the sulfonilic acid too. Alot of possibilities!
=At one time in the past I used a study of chemical dyes as a semester-long project. There is so much chemistry history associated with the dying industry. There is also a whole field of natural dyes that can be explored.
=I ofen pair this up with a “Natural Dyes” lab where we dye the same multifiber strips that we use in the “Azo Dyes” lab.
=I am interested in learning how to use a document scanner to measure (quantitate) the optical properties of the different fibers on the dyed strips.



One Comment

  1. Posted March 27, 2008 at 7:36 am | Permalink

    I was just discussing the analysis of images to detect precipitates of our Ugi reactions with my friend Rajarshi. I’ll ask him to give you info about the software program he had in mind.

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