AZO DYES PREPARATION
INTRODUCTION AND OBJECTIVES
The preparation of azo dyes is a standard reaction in an Organic Chemistry lab. Its adaptation to a parallel synthesis format is straightforward. Since the dyes vary widely in color, the diversity of this parallel synthesis becomes obvious. It includes techniques on diazotization and electrophilic substitiution. The experient belo is made to allow studens to btain pure compounds that can be characterized by NMR and other analytical techniques, but color test is well enough for synthesizing the dyes and purification process is omitted.
Safety considerations. Due diligence should be exercised in this reaction. The scale of the work is such as to minimize chemical wastes, but products should be discarded as organic waste. Diazonium ions should be used immediately. Stored compounds can decompose, sometimes violently. DO synthesis inside the fumehood.
Conc, sulphuric acid aniline N,N-dimethylaniline nitroaniline phenol naphthol pyridine pH paper beaker, test tubes graduated cylinder filter paper
A. Preparation of Diazonium Salt
Since these are immediately reacted, they should be prepared in parallel fashion, i.e. one vessel per prospective reaction. Into each vessel, place 1 gram or NaNO2. At 0 C, add a solution of 50 mg aniline in 2 mL conc H2SO4. Agitate for 5 minutes and isolate the diazonium by filtration. This is your stock solution of diazonium salt containing aniline.
Make also a diazonium salt using nitroaniline using the same process.
Make stock solutions of the following compounds to be coupled with the diazonium compounds above. Use, phenol, naphthol and dimethyl aniline. Dissolve each in 4 mL 10% NaOH. For dimethyl aniline, include 250 mg pyridine. The reactions proceed with stirring and solid precipitates formed rapidly. The