Cooling slush baths

In the laboratory, a range of slush baths may be used for speciality work. These are prepared by cooling organic liquids to their melting points by the addition of liquid nitrogen. Common examples are given in Table 8.2. Unless strict handling precautions are instituted, it is advisable to replace the more toxic and flammable solvents by safer alternatives. 

After leaving the reactant zone, the product stream enters a 0.5 in diameter FEP tube cooled by either a salt-ice bath or acetone-carbon dioxide slush bath [16]. The gas mixture was scrubbed in a soda-Hme tower. Hydrogen fluoride was trapped by adding sodium fluoride to the reaction mixture or simply adding water. Then, the product solution was extracted with dichloromethane, washed with aqueous... 

A 1-L, 3-necked, round-bottomed flask was equipped with magnetic stirrer, pressure-equalizing addition funnel with N2 inlet, low temperature thermometer, and a Friedrich condenser with N, outlet. The outlet was attached to two traps in series. The first was cooled in a Dewar of salt/ice water (- 15 C) and the second in a Dewar of dry ice/i-PrOH (— 78 C). 2-Bromo-3,3,3-trifluoropropene (50 g, 0.286 mol) and hexane (250 mL) were added to the flask. 1.6 M BuLi in hexane (190 mL, 0.304 mol, commercial) was added to the addition funnel. The flask was cooled with a hexane slush bath by addition of liquid N2 until the temperature of the solution inside the flask was - 85 °C. Then the BuLi soln was added over a period of 25 min at such a rate that the temperature remained below - 80 C. The slightly cloudy, yellowish solution was allowed to stir for an additional 10 min. Then, the hexane slush was removed, Upon reaching - 30 C, a gelatinous precipitate formed and the temperature rapidly rose to 28 "C. The volatile product was removed from solution by heating the mixture at reflux for 30 min with a slow flow of N2 through the system. The product was obtained from the dry ice trap yield 21 g (97%). 

A solution of tricyclohexylphosphine (4.65 g, 16.58 mmol) dissolved in diethyl ether (120 mL) is added to a freshly prepared solution of Li[GaH4]16 (16.30 mmol) in diethyl ether (100 mL), cooled in a liquid nitrogen-chloroform slush bath. The mixture is stirred for 30 min and warmed to ambient temperature as it stirs overnight. 

As already mentioned, there are two general approaches to cooling the cell, immersion in the coolant and pumping coolant through the cell jacket. The simplest approach [21,27] for immersion is to use standard slush baths or salt-ice mixtures that are available for temperatures down to -160°C [28]. Crude but effective control of temperature can be achieved by cooling the cell in liquid nitrogen followed by slow warm-up in the vapor above the boiling liquid [5]. 

A. /3-Isovalerolactam-N-sulfonyl chloride. A 200-ml. fournecked flask fitted with a mechanical stirrer, a dry ice-jacketed dropping funnel (Note 1), and a thermometer is cooled with a dry ice-methylene chloride slush bath while 67 ml. of sulfur dioxide (Note 2) is condensed into the flask Both the dry ice condenser and the dropping funnel are protected with drying... 

E. Example Separation of BF3 and CH2CI2. Boron trifluoride (bp —110.7°C) is readily separated from methylene chloride (bp 40.7°C) as illustrated in Fig. 5.6. Inspection of the vapor pressure data in Appendix V reveals that BF3 exerts 75 torr at — 126°C, whereas extrapolation of the vapor pressure data for CH2CI2 to this temperature (log P vs. 1/T plot) indicates a vapor pressure of less than 10 3 torr for this component. Therefore, the reaction mixture is slowly passed through a trap cooled to — 126°C (methylcyclohexane slush bath, see below), which retains the methylene chloride, and into another trap at — 196°C (liquid nitrogen), which retains the boron trifluoride. The rate of trans-... 

The sequence of operations (assuming the initial solid is not air sensitive) would be to load the sample tube with a weighed amount of reactive compound and the stirrer, to attach this tube to the tensimeter, and to pump out the air in the tensimeter. The sample tube is cooled to liquid nitrogen temperature and solvent is then condensed into the sample tube from a storage container on the vacuum line. The main valve on the tensimeter is then closed and the sample container allowed to warm so the solid may dissolve, perhaps with the aid of the stirrer. A constant temperature slush bath is next placed around the sample tube as illustrated in Fig. 9.5 and an initial pressure measurement is taken on the manometer. Next, the first alloquot of the reactive gas is transferred from a storage bulb elsewhere on the vacuum system into the calibrated bulb using the techniques outlined in Section 5.3.G (the bubbler manometer shown in Fig. 9.5 is used for the pressure determination required for this process). This gas is con-... 

Generally it is better (and safer) to cool the liquid in thermometer than it is to heat it. First, try to cool the thermometer with a (table) salt-and-ice slush bath. This method should bring the liquid into the contraction chamber or bulb. Once the liquid is in the chamber or bulb, it should rejoin, leaving the air bubble on top. If there is not a clean separation of the air bubble, it may be necessary to softly tap the end of the thermometer. This tapping should be done on a soft surface such as a rubber mat, stopper, or even a pad of paper. Alternatively, you may try swinging the thermometer in an arc (such as a nurse does before placing it in your mouth)." Once joined, the liquid in the thermometer can slowly be reheated. 

An alternative to the slush bath is the coolant, or cooling bath. These baths are handy when you may not have (or wish to use) the required low-melting-tempera-ture liquid for a particular temperature. However, they require more work to maintain their specific temperatures. Liquid nitrogen is recommended for cooling baths because dry ice can be difficult to introduce to the bath in sufficiently small amounts. Like the slush bath, the cooling bath should be mixed in a fume hood. 

Solid Na[Zn2(CH3)2H3] can be isolated in high yield by cooling the solution in a Dry Ice bath for several days, whereupon large, colorless, needle-like crystals form. These may be filtered off at — 78° using the apparatus shown in Fig. 3. After the crystals are washed with several 10-mL portions of cold, dry THF, they are held under vacuum at —22° (carbon tetrachloride slush bath)7 for several hours to remove excess THF. Under these conditions, the crystals lose solvent to form a white powder, which unlike the parent crystals does not melt upon warming to room temperature. Anal. Found Na/Zn/CH3/H, 1.01 1.98 1.98 3.01. In addition, 2.3 mol of THF was retained per mole of Na[Zn2(CH3)2H3] for this sample however, the exact value varies from one preparation to another. No iodide was detected in the product. 

Cool the Schlenk tube under argon down to -78°C (dry ice-isopropanol slush bath), and then admit the tube to a vacuum (c. 0.1 mmHg). Pump for 60 s, then admit argon gas and allow the apparatus to warm up to room temperature. Repeat this freeze-thaw process twice more. Heat the stirred mixture at 160°C under argon for 2 h. An abundant yellow precipitate of the molybdenum tricarbonyl complex develops. 

Take an oven-dried (electric oven, 105°C, 1 h) double-necked round-bottomed flask (500 mL) and add a stirrer bar, the tetratosylamide (2.59 g, 2.85 mmol), dry ethanol (5 mL) and dry tetrahydrofuran (60 mL). Purge the flask with nitrogen gas for 10 min. Equip the flask with a dry ice condenser fitted with a nitrogen inlet, cool the flask to -78°C in a dry ice/isopropanol slush bath and add dry ice and isopropanol to the dry ice condenser maintaining a strong nitrogen flow. Allow ammonia gas, from a cylinder, to condense into the cooled flask, until approximately 200 mL has been added. 

Many reactions are carried out in the temperature range 0 to—100°C and a range of cooling systems are available for achieving these temperatures. Table 1.1 is a list of common slush bath compositions, however, many others are available.9,14,15... 

Stir the solution while cooling to -78°C (dry ice/isopropanol slush bath) under nitrogen. Add by syringe through the septum butyllithium solution in hexanes (2.5 M, 4.0 mL, 10 mmol) and stir at -78°C for 2 h. 

To a double-necked, round-bottomed flask (100 mL), add triphenyl phosphite (3.02 g, 10 mmol), dry dichloromethane (50 mL) and a magnetic stirrer bar. Fit the flask with a gas inlet tube and cool the solution to -78°C (dry ice/isopropanol slush bath). Connect the gas inlet tube to an electrical ozone generator, which is connected to a source of dry oxygen. 

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