Question

any excess bromine that persists after the reaction will mostly be left in the choos: (filtered solid, filtrate, or reaction vile) and quenched with the choose: (oxidizing agent, reducing agent, strong acid, or strong base) choose: (acetic acid, methanol, sodium bisulfate, sodium bisulfite).

Procedure: Bromination of E-Stilbene SAFETY INFORMATION Carry out this experiment in a fume hood and wear nitrile gloves. Pyridinium tribromide is an oxidizing agent, is corrosive, and can severe skin and eye burns. Glacial acetic severe skin and acid (ie, 100% acetic acid) is flammable, corrosive and can cause eye burns. It is also a lachrymator (i.e. causes irritation to eyes mucous membranes). Use in the fume hood, and transport between fume in a closed container (e.g. capped reaction vial) Methanol is flammable and toxic. B a 3-ml reaction vial svith cap and seprum to the analytical balances. Accurately weigh so your fume Inside the hood, clamp the vial inside the green aluminum heating block atop your thermocouple probe is connected to the back of your stirrer/hotplate, that a test tube containing mang: stilbenc on a picce of folded weighing paper, record the mass, and transfer to your reaction vial Dispense I ml of glacial acctic acid to the vial cap the vial, and carry it care stirrer/hotplate. Fit the vial with a magnetic stir vane and an air condenser. Make sure a ethylene glycol is also inserted into the block, and that the tip of the probe is immersed at least 1" into the ethylene glycol. Start stirring, and set the heat to 40 °C. Incrementally increase the temperature as required (i.e. when the numbers stop flashing) until the stilbene just barely dissolves. Record this temperature and maintain it for the next step. The solution should not become warm enough for the acetic acid (bp 118 C) to evaporate significantly, but the air condenser is used anyways as a precaution against this. Remove the condenser, and add the pyridinium tribromide (~100 mg) that your TA provided to the reaction vial. Replace the condenser and stir the reaction mixture while maintaining gentle heat. You should initially observe an orange-red color from the bromine that is generated. This should then fade as bromine is consumed, with formation of a white solid (your product). When no further formation of product or loss of bromine color is observed (expected reaction time: 1-2 min), remove your apparatus from the heat. Cool the reaction vial in an ice/water bath and collect the solid product by suction filtration using a Hirsch funnel. Wash the reaction vial and crystal cake with a minimal amount of cold methanol, and allow your product to dry in the filter funnel with the vacuum left on. Obtain a mass of your crude product, and obtain a melting point (expected: 236-237 C).

Answer 1

In the above bromination reaction, after the reaction has been performed. The excess bromine in the reaction is quenched with sodium bisulfite which acts as an reducing agent.

The excess Br2 in the reaction vile, filtered solid or filtrate is reduced to Br- and sodium bisulfite in turn gets oxidized to sulfate species. Once this step is done, the residue/filtrate can be disposed off easily without any harmful effect or reaction. This is called quenching or neutralization of active reagent in the reaction.