Stopcock materials

Eosin (Tetrabromofluorescein). Place 16 5 g. of powdered fluorescein and 80 ml. of rectified (or methylated) spirit in a 250 ml. flask. Support a small dropping funnel, containing 36 g. (12 ml.) of bromine, above the flask make sure that the stopcock of the funnel is well lubricated before charging the latter with bromine. Add the bromine diopwise during about 20 minutes. When half the bromine has been introduced, and the fluorescein has been converted into dibromofluor-escein, all the solid material disappears temporarily since the dibromo derivative is soluble in alcohol with further addition of bromine the tetrabromofluorescein (sparingly soluble in alcohol) separates out. Allow the reaction mixture to stand for 2 hours, filter ofiF the eosin at the pump, wash it with alcohol, and dry at 100°. The yield of eosin (orange-coloured powder) is 25 g. 

Some of the more obvious sources of contamination of solvents arise from storage in metal drums and plastic containers, and from contact with grease and screw caps. Many solvents contain water. Others have traces of acidic materials such as hydrochloric acid in chloroform. In both cases this leads to corrosion of the drum and contamination of the solvent by traces of metal ions, especially Fe. Grease, for example on stopcocks of separating funnels and other apparatus, e.g. greased ground joints, is also likely to contaminate solvents during extractions and chemical manipulation. 

If the chloropyruvic acid remains essentially as a viscous liquid, it may be introduced via a dropping funnel containing a large-bore stopcock. If the material has set up to a waxy solid, it must be introduced in portions through a powder funnel. 

In evaporating the fractions, do not allow the mobile solvent to boil. A two-way stopcock of 4-mm. bore inserted between the trap and pump will make it convenient to stop the evacuation of the flasks if boiling occurs. If the system is tight, the fractions will continue to evaporate evenly and there will be no danger of loss of material through spattering. 

Extremely shock-sensitive and violently explosive initiation has been caused by prolonged freezing at —196°C, or by sawing a stopcock off a metal trap containing trace amounts [1], It may be stored safely at — 80°C [2], Detonative explosion during trap-to-trap distillation of purified material is noted [3],... 

All stopcocks and joints should be lubricated with materials not particularly reactive with the reagent, such as Apiezon N (James G. 

Materials Gas bag, 3.8 liter capacity (rubber bladder), with stopcock Rubber tubing of appropriate size Aluminium foil squares (10 x 10 cm)... 

Burets with ground-glass stopcocks should not be used, as leaking is caused by polymethylene formed preferentially on the ground surfaces. A buret such as Ultramax F and P, having a stopcock of plastic material, is satisfactory. The buret should be filled immediately before commencement of the reaction to keep the diazomethane solution cool and thus to minimize polymerization. The technique used is very similar to that of a titration, and a number of methylations of prepared batches can be quickly performed with one filling of the buret. 

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