Benzocaine Essay

746 Words3 Pages
Organic Chemistry Preparation of Methyl Orange Purpose In this experiment the azo dye methyl orange is prepared by the diazo coupling reation. Introduction The first step is called “diazotization”. The first product obtained from the coupling is the bright red acid for of methyl organge, called helianthin. In base, helianthin is converted to the orange sodium salt, called methyl organge (1). Reaction Scheme [pic] Although sulfanilic acid is insoluble in acid solutions, it is nevertheless necessary to carry out the diazotization reaction in an acid (HNO2) solution. This problem can be avoided by precipitating sulfanilic acid from a solution in which it is initially soluble. The precipitate is a fine suspension and reacts instantly with nitrous acid. The first step is to dissolve sulfanillic acid in basic solution. When the solution is acidified during diazotization to form nitrous acid, the sulfanilic acid is precipitated out of solution as a finely divided solid, which is immediately diazotized. The finely divided diazonium salt is allowed to react immediately with dimethlaniline in the solution in which it was precipitated. Mechanism Diazotization: [pic] Diazo Coupling: Methyl orange is often used as an acid-base indicator. In solutions that are more basic than pH 4.4, methyl orange exists almost entirely as the yellow negative ion. In solutions that are more acidic than pH 3.2, it is protonated to form a red dipolar ion. Thus, methyl orange can be used as an indicator for titrations that have end point in the pH 3.2- 4.4 region. The indicator is usually prepated as a0.01% solution in water. In higher concentrations in basic solution, of course, methyl orange appears orange. Acid-Base Indicator Properties of Methyl Orange [pic] Procedure Pretreatment before Diazotization 1. Dissolve 1.2 g anhydrous Na2CO3 with 50 ml DI H2O

More about Benzocaine Essay

Open Document