Organic compounds and materials play a vital role in our everyday lives,
and many chemists work in the industry are involved in their production.
Today I am going to prepare a pure organic liquid: 2-chloro-2-methylpropane. This process has 3 key steps...
Preparation: where we complete the reaction to produce the desired product.
Separation: the important step of getting the bulk of the product away from any unreacted
starting reactants, by-products and often, importantly, water.
And finally, purification: you can think of this as a next level separation, where we remove any traces of water,
unreacted starting reactants and by-products that still remain, to get our product pure.
Although there are several steps and some specialised techniques to go through
it's important to think about the chemistry that underpins each step.
And also how to work safely in the lab throughout.
The first step is to prepare our desired product by reacting 2-methylpropan-2-ol with concentrated
hydrochloric acid. This should be performed in a fume cupboard and the concentrated hydrochloric
acid should be kept cold. I need to make sure I wear eye protection for this.
I'm going to start by measuring out 20 centimeters-cubed of concentrated hydrochloric acid
and pouring it into a conical flask.
Use mineral wool to plug the neck of the flask (you can also use cotton wool for this).
Now I will gradually add around six centimeters-cubed of the 2-methylpropan-2-ol
to the conical flask, one centimeter-cubed at a time. Replace the plug and give a swirl after each addition.
This will take a couple of minutes. Now I need to leave this, with the plug in,
to allow the reaction to take place. This will take around 20 minutes.
As you can see, two layers have formed. We're now going to use a separating funnel to separate out our product.
Little tip: make sure the tap is closed, before you pour in the mixture.
Now you can clearly see, we have this cloudy layer at the bottom, and this clear layer above.
The cloudy layer is the aqueous layer and it's more dense than the organic layer in this reaction.
To remove the aqueous layer, we can open the tap and allow it to drain.
Another tip: make sure the lid is removed from your separating funnel or the solvent will not run freely.
Now we have completed the initial separation of our organic product.
The next step is to purify the sample.
There may still be unreacted hydrochloric acid in our sample.
To remove this we can react it with an alkali and separate it using a separating funnel.
To do this i'm going to measure out 10 centimeters-cubed of sodium hydrogen carbonate solution,
and add it to our separating funnel. Note, I'm using a funnel every time I add a solution to
our separating funnel. I now need to mix this. So, I'm going to put the stopper back into the flask and invert it.
As I invert the separating funnel I'm going to keep my finger on the stopper.
I'm now going to open the separating funnel, this allows gas to escape.
Note, I'm swirling this and not shaking it, so to prevent pressure from building up. Sometimes you
may see effervescence. This is carbon dioxide being given off from our neutralization reaction.
We know this removal of acid is completed, because the effervescence has stopped. Keeping my finger on
the stopper, I'm now going to close the tap of our separating funnel and invert it again.
Just like I did previously, I'm going to remove the aqueous layer -- again this is the bottom layer in our separating funnel.
Before we open the tap, I need to remove the stopper from the separating funnel.
I'm now ready to open the tap.
Again, I'm going to stop it when all the aqueous layer is removed.
I now need to repeat this step once more.
I can now collect the organic layer in a clean dry conical flask.
We now need to remove the trace amounts of water from our organic liquid.
To do this, I'm going to add anhydrous sodium sulfate. The anhydrous sodium sulfate
is a drying agent and will form a complex with any water that remains in the liquid.
I'm going to add it by the half spatulaful -- and swirl each time.
As you can see, the sodium sulfate has clumped together. This is because there was trace water
in the liquid. Once all the trace water is removed the sodium sulfate will no longer clump together.
It is now ready to be filtered into a pear-shaped flask.
We are now ready to dry our organic liquid.
Now we have removed the excess acid and water from our organic product.
However, there may still be some unreacted reactant or organic by-product that remains.
Therefore, we're going to purify our organic products further using distillation.
Here I have our organic product from our filtration step
and I've added some anti-bumping granules to the flask.
The product we are making in this reaction is 2-chloro-2-methylpropane,
which has a boiling point of 51 degrees celsius.
Therefore, we will collect any liquid from the distillation in the range of 49 degrees celsius to
52 degrees celsius. As such, hot water from a kettle in a water bath is sufficient to heat the reaction.
The product in the correct temperature range is collected in a clean dry test tube.
Note, we must not allow the flask to boil dry.
Now we're ready to start our distillation.
Don't forget, our water inlet is at the bottom of the condenser and our water outlet is at the top of the condenser.
So there we have it, my (hopefully) pure organic liquid sample. I hope you have enjoyed all the
processes involved in making this organic liquid and have success in making your own.
You can use the additional resources with this video to explore the reactions and calculations in more detail
And for some suggestions with what to do with the products you have made.
Thank you for watching and have fun with your experiments!