Freezing baths

Anon., Sichere Chemiearbeit, 1992, 44(6), 70 Jahresbericht, 1991, 72 A substantial explosion, followed by a fire causing fatal bums to the experimenter, occurred when working with butyllithium in tetrahydrofuran cooled by a propan-2-ol/solid carbon dioxide freezing bath. It was considered that the explosion might have been fueled by isopropanol vapour in air. This explanation was rejected since the alcohol should have been below its flash point. However, making up such cooling baths, containing flammable solvents, does disperse considerable quantities of vapour and mist before the mix is fully cooled. There is a period of potential hazard, as there may be when the bath warms above the flash point once more. 

Dissolution is endothermic, solution becomes cold (and hence its apphca-tion in freezing bath) elevates the boiling point of water by 1°, 7.5°, 28.5° and 70°C at 10, 40, 80 and 95% (w/w) concentrations, respectively vapor pressure of saturated solution, 11.2 torr at 20°C. 

To the deep-red solution is added 550 g. of sodium hydrosulfite (of at least 80 per cent purity) the mixture is stirred for five minutes and then for five 30-second periods during half an hour (Note 5). The solution slowly loses its red color (a thin layer of aniline collects on the surface), and the temperature rises from 25° to 50°. At the end of half an hour the solution should no longer be red it is then rapidly cooled to 20° in a freezing bath and by the addition of about 500 g. of ice. 

When the latter is half full, stop the process and withdraw the small glass tube from it, taking care not to wet the constriction. Bring the tube, still in the freezing bath, to the blast lamp and seal it at the constriction. This will take some skill, and it is well to try the manipulation on an empty tube or one half nhe... 

Tissue specimens are snap-frozen at -60°C in an isopentane freezing bath (Neslab, Portsmouth, NH) (Resnick et al., 1995). Sections (5 pan thick) are cut on a cryostat,... 

The product temperature when taken out of the freezing bath is approximately -80 °C. 

Diethyl ether, solvent grade Solid C02-methylated spirit freezing bath Procedure... 

Allow the frozen mixture to stand in the freezing bath for another 10 min, then remove the beaker and stand it in tepid water until the frozen plug loosens. 

About 125 g. of phosphorus(V) oxide is quickly spread over the surface of the frozen acid in D, the flask stopper sealed tight, the freezing bath of Dry Ice and alcohol removed from under D and replaced with a water bath at room temperature. The ozonizer is put into operation prior to removal of the freezing bath. As the acid slowly melts, the liquid portion reacts with the large excess of phosphorus (V) oxide. When the initial intense reaction has subsided, the mass is stirred quickly and the reaction allowed to subside again. After the second rush of oxides, the water bath is heated slowly to 40 for several hours until the reaction appears to be substantially complete. 

A number of the simple ethjdene derivatives may be titrated quantitatively with bromine. The test is, of course, applied only when the previous classification reaction has shown that bromine is decolorized wdthout appreciable substitution taking place. The weighed substance (about 1 g.) is dissolved in 25 cc. of carbon tetrachloride, the mixture cooled in a freezing bath, and titrated with a bromine solution of known sh ength (about N/2) until a faint bromine color remains. 

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