Bromonation+Lab

=__A Greener Bromonation of Stilbene~__=

__Introduction__:
The purpose of this lab is to bromonate stilbene, resulting in dibromostilbene. This is an example of an SN2 reaction, which means that it occurs via a one-step mechanism, is a substitution reaction involving a nucleophile, and it has a bimolecular rate determining step. hang on! It's NOT a substitution reaction, it's an addition. In the process of the reaction, 2 atoms of bromide bromine will be added across the double bond of a stilbene molecule, in between the two benzene rings. To achieve this reaction, ethanol will be used as a solvent. Ethanol is a polar protic solvent, meaning that is it has a hydrogen atom attached to either an O, N or X, where X represents the halogens. This lab requires the use of a water cooled reflux condenser in order to condense and collect the product, dibromostilbene.

Ethanol will be the solvent.

(E)-Stilbene is one of the reactants.

Br2 is one of the reactants.

Dibromostilbene is the expected product of the reaction.

__Procedure__:
The procedure for this lab can be located at the web address listed below: []

__Data/Analysis:__
Amount of (E)-Stilbene used: 0.500g Amount of Ethanol used: 10.0 mL Amount of aqueous Hydrobromic Acid used: 1.20 mL Amount of 30% H2O2 used: 0.80 mL Amount of concentrated aqueous NaHCO3 used: 150 drops (using pipette)

Mass of Product (Dibromostilbene) : 0.841g Melting Point Range of Product: 221.0*C (sweating)- 229.5* (melted) did your product melt normally, or did it decompose? % yield calculation is good, so are the sig figs. yay!



__Observations (by step):__
Step 3: Not all of the (E)-Stilbene dissolved fully in the solvent.

Step 4: Not all of the precipitate re-dissolved.

Step 5: Mixture changed from a clear substance to a mango yellow (see below).



Step 7: Mix separated; yellow (Br2) on top, and milky white (dibromostilbene) (see below) pH when first tested=1; pH after NaHCO3= 6



Step 8: Product was a white powder after it dried.

__**Conclusion:**__
The bromination of (E)-Stilbene is a process which requires careful steps in order to receive a pure product of dibromostilbene in the end. The mass of product that resulted was well above that of the starting mass of (E)-stilbene and the melting point of the dibromostilbene product was significantly lower than that of the theoretical temperature. I think the term "literature value" is more fitting here, since the temp is not based on theory but on the numbers that we find in the literature. The theoretical melting point of dibromostilbene is 140**°C.** I don't believe this is correct. The mass being so much greater could be from the addition of bromine to the original molecule which is a fairly heavy element, the percent yield, however shows that the recovered product is within a reasonable range from the theoretical yield. Yep, that's true. As for the melting point, the same factors could play a part in the level being lower than that of the theoretical value. This experiment also followed the guidelines of green chemistry by using bromine in the form of a less volatile reactive? hazardous? substance to brominate the stilbene. The experiment also introduced more practice of vacuum filtration and the use of a water-cooled reflux condenser. Your melting point range is 8.5 degrees wide. What does this say about the purity of your product?

**__Error Analysis__**
Possible sources of error include adding bromine to the refluxing mixture too rapidly, I don't understand this statement since you didn't add Br2 to your mixture. as well as possibly not having the product completely dry before end mass was taken and melting point was observed.

This report earned the following scores for: format (1.5/2) style (2/2) data (2.5/3) quality of result (1/1) quality of reported data (1/1) conclusion (1/2) error (0.5/1) post-lab Question (2/2) for a total of 11.5/14. The conceptual misunderstandings that are suggested by a few of the things you say concern me!