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The experiment described below is a microscale adaptation of a popular synthesis for the undergraduate laboratory which illustrates both bromination of a double bond and diastereoisomerism. The stereospecific (trans) addition of halogens to alkenes is one of the benchmark reactions in organic chemistry and is discussed in all major organic texts. A typical example used in several lab manuals (1) involves the addition of bromine to maleic and fumaric acids (eqs 1, 2). The diastereomeric products formed are remarkable in that their melting points differ by some 90 oC. Their solubilities are also totally different: the racemic isomer is very soluble in cold water, whereas the meso form can be recrystallized from water.
meso-2,3-Dibromosuccinic Acid (2)
Procedure
A stock solution of bromine (7.75 g) and potassium bromide (6.25 g) in 10 mL of water is prepared in a 25-mL volumetric flask and diluted to the mark with water. CAUTION: Bromine is moderately toxic by vapor inhalation and poisonous by ingestion. Its vapor is extremely corrosive. It should be used in a good fume hood and protective gloves should be worn when handling it (3a). Fumaric acid (200 mg) is weighed into a 25-mL Erlenmeyer flask and 2.5 mL of the stock bromine solutionl is added. CAUTION: Fumaric acid is mildly toxic by ingestion and is a skin and eye irritant (3b). The contents of the flask are mixed and the flask is placed in a...