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A famous experiment which changed organic chemistry: purple benzene. 

Crown ethers are an unusual series of molecules that have the ability to complex small cations, notably alkali metals such as lithium, sodium and potassium. These cyclic molecules, upon complexing a cation, can allow a salt to go into organic solvent that otherwise wouldn’t. This makes reactions that are otherwise impossible accessible.

Charles John Pedersen (October 3, 1904 – October 26, 1989) was a pioneer of this field of chemistry. He was an American organic chemist best known for describing methods of synthesizing crown ethers.  He shared the Nobel Prize in Chemistry in 1987 with Donald J. Cram and Jean-Marie Lehn.

A good example is how 18-crown-6 (shown above) can help potassium permanganate (a beautiful purple oxidizing agent based on manganese (VII)) go into organic solvent. Normally, you can only get permanganate into very polar solvents (as seen on the first pics where the benzene dissolves 0% of the permanganate), but when adding 18-crown-6, it allows the permanganate ion to go into solution as well forming a beautiful purple solution as seen above.

An inspiring article, what is worth to read about crown ethers, by Charles J. Pedersenhttp://pubs.acs.org/doi/abs/10.1021/ja01002a035

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Just for fun: deflagration test of some recently prepared nitrocellulose. 

Interesting fact: Around 1846 Christian Friedrich Schönbein, a German-Swiss chemist, discovered a practical solution to prepare nitrocellulose:

As he was working in the kitchen of his home in Basel, he spilled a bottle of concentrated nitric acid on the kitchen table. He reached for the nearest cloth, a cotton apron, and wiped it up. He hung the apron on the stove door to dry, and, as soon as it was dry, there was a flash as the apron exploded. His preparation method was the first to be widely imitated—one part of fine cotton wool to be immersed in 15 parts of an equal blend of sulfuric and nitric acids. After two minutes, the cotton was removed and washed in cold water to set the esterification level and remove all acid residue. 

Nowdays there are much better and safer methods for the preparation of this compound, the only important thing is, that the acids used for nitration (in my case 100% nitric and phosphoric acid) should be very careful washed out from the acidified cotton. Unwashed nitrocellulose (sometimes called pyrocellulose) may spontaneously ignite and explode at room temperature, as the evaporation of water results in the concentration of unreacted acid.

For more: http://en.wikipedia.org/wiki/Nitrocellulose