A DielsAlder Synthesis狄尔斯阿尔德合成.docVIP

CHEM 334L Organic Chemistry Laboratory Revision 1.0 Diazo Coupling A Synthesis of Methyl Orange In this experiment the azo dye methyl orange is prepared by a electrophilic substitution with arenediazonium salts (diazo coupling). p-Dimethylamino-Azobenzenesulfonic Acid (Methyl Orange) Methyl orange is a pH indicator and due to its clear color change it is very often used in titrations. Methyl orange changes color at the pH of a mid-strength acid and is usually used in titrations for acids. Unlike a so called universal indicator, methyl orange does not have a full spectrum of color change, but has a sharper end point. Space-filling model of methyl orange /wiki/File:Methyl-orange-3D-vdW.png Powder of methyl orange /wiki/File:Methyl-orange-sample.jpg Left: Methyl orange in an acidic solution Right: Methyl orange in an basic solution /wiki/File:Methyl_orange_02035.JPG Methyl orange is prepared from sulfanilic acid and N,N-dimethylaniline. The first product obtained from the coupling is the bright red acid form of methyl orange, called helianthin. In base, helanthin is converted to the orange sodium salt, called methyl orange. Dyes are used to give colors to substances, especially fabrics. Chromopohores, functional groups that absorb light, give color to these dyes. The most common chromophores are azo, nitro, and carbonyl groups. Auxochromes, functional groups that increase the intensity of the color, are also important parts of dyes. The most common chromophores are hydroxyl, amino, sulfonate, and carboxylate groups. Azo dyes have a nitrogen to nitrogen double bond as their chromophore. These dyes are created by taking a diazonium salt and adding it to a strongly activated aromatic system. In this experiment, you will synthesize methyl orange, an azo dye, by a diazonium coupling reaction with diazotized sulfanilic acid and N,N-dimethylaniline. Preparation of the diazonium salt of sulfanilic acid Although sulfanilic acid is insoluble in acid solutions, it is neverthe