PURPLE?!?!

Hmm, here’s a quick little puzzle that I’m in the middle of solving. If anyone knows the answer, feel free to let me know.

Attempting to make the acid chloride of 2-picolinic acid by SOCl2. In dichloromethane, combined ~5g of 2-picolinic acid with a slight excess of SOCl2 (~1.2:1), refluxed for ~20 minutes, removed solvent, set it aside. The initial solid was tan-brown. After a few days, it was dark. Massively dark. And green-blue, as far as the eye can tell. After a week, it’s bone dry and still massively dark. A rough yield of around 6g. So it picked up some mass…

Solubility testing… Very soluble in water, forms a deep purple solution. Soluble in methanol, solution is a bit more blue. Very slightly soluble in chloroform, purple solution. Very slightly soluble in acetonitrile, greenish leaning toward blue solution.

NMR (in D2O)… Four clean aromatic signals, consistent with the 4 protons of an ortho-substituted pyridine ring, nothing else.

20140204nmrpurple01

UV-Vis (in water)… Peak at ~540nm, shoulder at ~650nm. Strong peak at ~260nm.

20140204uvvis01 20140204uvvis02

This has not been exhaustively lit searched yet, but the intensity of the color of the product is intriguing AND a ~20% mass increase makes it a fun little puzzle. We will be exploring more…

Recrystallization

Recrystallization is a process that takes an impure substance and purifies it, removing the unwanted substances from the wanted solid.  This method involves heating the solid to dissolve it in a solvent , cooling it to reform the solid, then vacuuming and drying the newly formed pure crystals.  First, you have to choose a proper solvent, something that the desired solid is insoluble in at room temperature, but soluble in when heated. If the solvent is too strong, the solid won’t fully reform, resulting in a poor yield of final product. If it is too weak, the start material will not fully dissolve and the final product will still contain impurities. You then dissolve the solid in the solvent using heat, when the solid is dissolved, the impurities are also dissolved and escape into the solvent. Then the solution is removed from heat and cooled to room temperature, allowing the crystals to reform, leaving the impurities in the solvent. The recrystallization process can be helped by placing the solution in an ice bath to cool it down to 0o C. Once the crystals have formed you filter out the solvent and impurities and dry the purified solid.  Once you have obtained pure, dry crystals, you can take the mass of them to discover your mass yield, and test the melting point of the solid to determine the purity of the solid. For this experiment we had crystals that contained Lead bromide (PbBr2), Lead iodide (PbI2), and Lead chloride (PbCl2). We chose water as the solvent for all of our solids. We heated all of the solutions on hot plates while they were being stirred. Once all of the solid had dissolved, we cooled the solution at room temperature, continuing to stir them. Crystals as the solutions cooled, crystals began to form, see below for pictures. Since these recrystallizations were done for the purpose of show, we did not filter and dry the solids.

Materials Used Amount Cost
PbBr2 20g $16
PbI2 5g $5
PbCl2 50g $15
Water ~5L FREE
Lead Iodate in solution

Lead Iodide in solution

Lead Chlorate in solution

Lead Chloride in solution

Lead Bromide in solution

Lead Bromide in solution