Yuck...one of my flasks, after having to do a distillation using an open flame, carefully of course, has been really dirty inside for ages, have had a monster of a troublesome time getting the scrudge out of the fucker, its a small flask, about 200ml, round bottom flask and I need to get this filth out of the thing.
I think its time I think about subjecting it to a chromic acid bath (dichromate in concentrated sulfuric acid, forms an oxidizing chromic acid/dichromic acid mixture, used for cleaning glassware, a lot more in the past than now, as it produces some noxious chromium wastes, and nobody likes hexavalent chromium. I'll of course recycle the waste for the chromium salt content, turn it into chromium trioxide (chromic anhydride) perhaps, or make some chromyl chloride from it, a generally pretty vicious oxidizer that comes as a reddish-brown fuming toxic and corrosive as hell liquid, similar physically to bromine, but with a much greater propensity to set things on fire on contact. Useful though for oxidizing alcohols to aldehydes surprisingly enough, without overoxidation to the carboxylic acid; quite astonishing really, considering one has to be very careful as to what solvents are used, since it sets most of them on fire, although chloroform or dichloromethane work well. Will even oxidize a benzylic methyl group to a benzaldehyde (such as toluene to benzaldehyde). Its made by distillation at a bit over 120 'C of a mixture of concentrated sulfuric acid, salt (as in ordinary salt, sodium chloride, although potassium chloride will work fine) and a dichromate, and collecting (carefully) the water-sensitive, vicious little bastard that starts to distill over in a suitably resistant container, such as glass with a fluoropolymer cap and seal, with the screw threads wrapped in teflon tape.
I've made it before, and its really quite useful stuff, but you really have to be careful with CrO2Cl2, as 'vicious' is the understatement of the year, and that goes a thousandfold when its heated to 120 'C or so, I've seen a spill of it go and burn its way straight through a wooden bench top at that temperature, just chewed it up and turned the bench section it hit to ashes and charcoal whilst giving off a lot of noxious fumes.
