Question

In the bromination and debromination lab what exactly is happening? Is there any Chemical reactions?

This is what we did in the lab. Added 100 mL of acetic acid into a test tube, and placed it in a warm water bath. We then weighed 400 mg of NaBr, 90 mg of Sodium Bromate (NaBrO3) and 100 mg of stilbene. We then added all those compounds to the test tube containing the acetic acid and once the color of the solution changed into a yellow, mustard color, the test tube was placed in an ice bath to induce crystallization. Once crystals were apparent it was filtered. Once filtered the crystals were separated into two sets of test tubes. In tube 1, distilled water was added to it and it was placed in a sand bath, then into an ice bath to induce crystalization and then filtered. In test tube 2, diethyl ether, zinc dust,acetic acid was added to make a solution containing two layers. The top layer (the organic layer) was transferred into another tube and placed in a warm water bath wich eventually formed crystalls. IR spectrum, melting point, and the masses for each tube crystalls were determined.

I am not sure what is happening in this lab and would like an explanation.

Are there any chemical reactions?

What exactly are the chemicals and what are the reagents?

Why did we have to look at the crystals in the IR spectrum?

Answer 1

In this experiment you were doing bromination of stilbene in presence of NaBr and NaBrO3 and in glacial acetic acid solvent.

In this experiment NaBr and NaBrO3 mixture is the source of bromine. First it will form a cyclic intermediate and finally you will get a di bromo product The colour change that is disappearances of reddish brown colour of bromine indicates that reaction is happening. And finally when reaction is over then you are supposed to get yellow colour solution.

The final product is dibromo stilbene. And that will be easily characterised by mass and IR spectroscopy. Basically crystalline compound is always pure in nature that why you have made crystal if those products. You have to look at crystals in ir spectrum because crystals will give you a clear or spectrum where you will understand all those stretching frequency.

By Melting point determination of those crystals also you could identify your product purity by matching with literature melting point of the same compound.