I just got a really aberrant result during a synthesis of iodoform, a few flakes of resublimed iodine, analytical grade, were dissolved in OTC tincture of iodine, containing 2% I2 and 2% KI, this was added to the correct amount of 20% NaOH solution, lab grade, and a strange thing happened.

The NaOH solution reacted, and instead of iodoform precipitating in yellow crystalline plates, the solution gelled up and turned solid, appearing much like the water-holding gel present in diapers and the like, this, on heating, gradually took on a slight lemon yellow color, indicating the formation of a small amount of iodoform.

I am prety unsure as to why the stuff gelled up, the strong smell of iodoform is not apparrent, but some amount is visibly present, anyone ever get a rxn like this?

Use acetone instaead fo alcohol.

Indeed, the reaction also works with acetone, but... I don't think this is the reason of the gelling.

The iodoform reaction works both with acetone and with ethanol.

I think that the tincture, used in the preparation is not just KI/I2 dissolved in a mix of water and ethanol, but that it is a so-called povidone-iodine-derivate. This contains iodine, complexed to very large molecules, such that the iodine is given off more slowly, when the tincture is applied and such that a wound is covered by some crust, which protects the underlying tissue. This modern tincture of iodine is much less interesting than the plain old stuff, which indeed is I2 dissolved in ethanol or I2 dissolved in a solution of KI in ethanol/water.

So, Limpet Chicken, try to dissolve some flakes of iodine in either acetone or ethanol and add a solution of NaOH. Then you'll certainly get your CHI3. Add some extra water in order to be sure that the CHI3 does not remain dissolved in acetone or ethanol.

I didn't use povidone iodine, I don''t buy the stuff, and i don't use it in my lab, povidone iodine solution is a royal pain in the ass, and my guess, is it is cheifly made to foil the less ingenious of meth cooks in the US.

UK tincture of iodine as bought at any chemist is the decent stuff, I don't much use it, but for this experiment, what better to use, after all, it is already ethanol with dissolved I2, I simply beefed up the I2 content somewhat with a few flakes of good grade crystals.

Well, if it isn't the tincture of iodine which is gelling, then it must be some other impurity. One thing for sure I know is that plain ethanol+I2+KI should not become like a gel, when NaOH is added. I've done the iodoform reaction a few times myself, both with ethanol and with acetone, and it worked like a charm, every time I did the experiment.