Grignard Reactions - Organic Chemistry lab

The Grignard reaction that was performed involved reacting bromobenzene and magnesium to produce phenylmagnesium bromide. Methyl benzoate, an ester, was then added, and the addition of a sulfuric acid served to reprotonate the result, giving triphenylmethanol(from Wikipedia):


It was an interesting experiment and definitely the longest, lasting nearly 7 hours over two lab times. It was done on November 8th and 15th. The most important requirement for this lab was that all the glassware used had to be completely dry, because the Grignard reagent (phenylmagnesium bromide) is such a strong base that it reacts with water. Even the humidity level in the lab can affect the reaction. All glassware was carefully washed and dried the week before, using a heat gun when needed:

The apparatus for the initial reaction was set up like so, and also heated to remove traces of vapor:
Then, drying tubes were packed with cotton and calcium chloride and inserted into the top of the condenser (higher part) and the addition funnel (lower part) to keep the enviroment anhydrous.




Note that the bromobenzene has already been added to the funnel. In the actual experiment, that happens after the drying tubes have been attached. Then, magnesium turnings were added to a flask at the bottom of the apparatus, and bromobenzene was added to cover them. The mixture began to react spontaneously with no additional heat. When the reaction slowed, more bromobenzene was added.




Video showing the vigorous reaction:





After all 9 mL of bromobenzene had been used up, the reaction continued for a little while with the help of a warm water bath.


The methyl benzoate was then added, as was ether, turning the mixture a reddish-punch color. Methyl benzoate, used to train drug-sniffing dogs to detect cocaine, smells like new shoes at Payless. With the help of a hot water bath, the reaction started and a solid formed.

As much solid as possible (someone next to me compared it to pumpkin pie) went into a slurry of sulfuric acid and ice, and a vigorous reaction was seen. The whole caboodle was then transferred to a seperatory funnel to remove the aqueous layer. The yellow layer was kept.




As in other experiments, sodium sulfate was added to the ether to remove water. This material comes as an anhydrous powder, and upon absorbing any water remaining in the ether it takes on the appearance of salt. Afterwards, the mixture was filtered and the ether evaporated.


This experiment leaves lab benches covered in interesting glassware:


A week later, the solid left after the ether had been evaporated was triturated (mixed) with petroleum ether. The solid turned white, and the now yellow ether was removed.

After a bit of warming, isopropyl alcohol was added to dissolve all the solid. After this mixture cooled down, crystals began to form out of solution, looking for all the world like the inside of a snowglobe.

This was then filtered, and voila - 3.224 grams of triphenylmethanol were produced.

Organic Chemistry - Steam Distillation

Last Monday the lab titled 'Steam Distillation' was performed (semi-microscale procedure). Basically, 10g of ground cloves were put into a flask with water and the mixture was boiled to extract the essential oil, eugenol. This process is called steam distillation, and is used because the normal boiling point of eugenol is 254 degrees C. This way, when water boils, the cloves boil, and eugenol drips out.

The whole lab smelled like gingerbread cookies or besamim. The TA said it reminded her of an alcoholic drink from Sweden, probably glogg.

So here is a diagram of the set-up - somewhat modified simple distillation, since a small separatory funnel had to be used to add water to the boiling mixture (so that the concentrations would remain the same and you wouldn't wind up getting eugenol diluted with a lot of water).


Here's the set-up as it was actually done:

Locked and loaded:

Joints greased - check.
Rubber bands tight - check.
Sep funnel loaded - check.
500 mL flask loaded - check.
Condenser water on - check.
Heating Mantle on - check.

Raise Mantle... BOIL!

Ever so slowly, the condensation line crept up the Claisen connecting tube and then the distilling head, and then began to trickle down into the Erlenmeyer flask as a whitish liquid.


When about 105 mL had been collected the heating mantle was lowered. Now came the solvent extraction, which we are by now familiar with. The white liquid was mixed with ether and the layers separated out. This time, ether was on top, visible here as a bit of a layer on the surface.

Draining of the ether layer:

Eugenol was now dissolved in the ether rather than mixed with water. It was dried out with sodium sulfate, after which it looked like this...

...and then 'twas evaporated with rotary evaporator. Afterwards, just a bit of (hopefully) pure eugenol was left.

Cleanup and completion of procedure:


Post-lab: Find a store that carries glogg. :)

Organic Chemistry lab - Extraction

This semester I am taking Organic Chemistry, and concomitantly the lab that goes with it. Last week Solvent Extraction was done. Here are some pictures from the lab:


First, you take a separatory funnel and put it on a ring stand. Then you add a mixture of acetanilide, p-toluic acid, and p-tert-butylphenol to some TBME, and pour it in. Then you add 10 mL of sodium bicarbonate, and after some venting to release CO2, the layers separate, like so.



Add HCl to precipitate p-toluic acid. As this is done, foaming occurs with some pretty cool effects. Once that's complete, vacuum filtration follows, with a vacuum hose, Buchner funnel, and Erlenmeyer flask. The vacuum created in the flask pulls the liquid in a solution through the funnel, leaving crystals behind.



Much later, NaOH extract has HCl added to it to precipitate p-tert-butylphenol. Crystals form, seen here as the white mass in the beaker. I think too much HCl was added; was it supposed to test out to a pH of 1.5?


During separation of acetanilide from ether, ether is evaporated using a rotary evaporator and a round-bottom flask. This leaves a small bead of orange liquid in the beaker, left to dry for a week.


Here's a real world application of solvent extraction, lest you think this is all fun and games. :)

Andrographis

Andrographis paniculata is an herb used in Scandinavia to treat colds and the flu. After reading this page I think I will try to grow it this year, at home and in the greenhouse. As far as I know no one has tried to grow it in Houston. Let's see how things turn out.