Dry-ice/isopropanol bath

Syntheses. Isotactic poly(methyl methacrylate) was synthesized by the method of Tsuruta et al. (9 ). Under a nitrogen atmosphere, a quantity of 6 mL (0.056 mole) of methyl methacrylate (MMA) dried over 4A molecular sieve was dissolved in 24 mL of similarly dried toluene. To the glass vial containing the reaction was added 0.65 mL of 1.6 M n-butyllithium, and the reaction was kept at -78°C in a dry ice/isopropanol bath. The polymerization was halted 24 hr later with the addition of hydrochloric acid and methanol (methanol/water 4.1 by volume). The polymer was dried in vacuo at 50°C, redissolved in methylene chloride, precipitated by being poured into water-containing methanol, and dried in vacuo at 50°C. Tacticlty and composition were verified with % NMR. Yield 47%. 

Under a dinitrogen atmosphere, a 300-mL, two-necked, round-bottomed flask containing a magnetic stir bar and fitted with a pressure-equalizing dropping funnel and an inert gas inlet is charged with a solution of 2-aminopropane (10.6 g, 0.180 mol) in dry diethyl ether (70 mL). The flask and its contents are cooled in a dry ice—isopropanol bath to — 78°C then a solution of l-bromo-3-methyl-2-butanone (10.0 g, 0.0606 mol)1 in diethyl ether (20 mL) is added dropwise from the dropping funnel to the stirred solution of amine over 15 min. 

A solution of n-butyl lithium in hexane (2.1 M, 9.2 ml, 0.019 mole) is added dropwise to a solution of diisopropylamine (0.021 mole) in anhydrous tetrahydrofuran (40 ml) at -40°C (dry ice/isopropanol bath). After standing at this temperature for 10 minutes, the cold solution is added dropwise to a stirred, cooled (-60°C) solution of 5-chloro-3-[(lH-imidazol-l-yl)ethyl]-l,2-... 

Solid Ni(COD)2 (0.76 g, 2.76 mmol) is added to a solution of PNP (2.30 g, 5. 52 mmol) in tetrahydrofuran (60 mL) that has been cooled to —80°C using a dry ice/isopropanol bath. The resulting suspension is allowed to warm to room temperature while stirring over a period of ca. 1 h. Solvent is removed from the light yellow solution under vacuum to produce the product as a white solid. The solid is washed with acetonitrile (10 mL) and dried again under vacuum to give an analytically pure product. Yield 1.2 g (81%). 

A soln. of the startg. dioxolane amide in methylene chloride cooled to -78° in a Dry Ice-isopropanol bath, treated rapidly with BBrg, and agitation continued 2 hrs. at the same temp. -> aldehyde amide (startg. m. f. 927). Y 93%. - Other methods were not successful. - This method has limited applicability. A. I. Meyers et al., J. Org. Chem. 38, 1974 (1973). 

A stirred soln. of triphenylethylene in diloroform cooled in a Dry Ice-isopropanol bath, stirred and treated rapidly during ca. 1 min. with a soln. of bromine in the same solvent until the first appearance of a permanent amber color, then decomposed at once by addition of a satd. soln. of Ag-nitrate in methanol-water, and stirred overnight at room temp. -> phenyl benzhydryl ketone. Y 94-96%. F. e. and procedures s. F. J. Kakis, D. Brase, and A. Oshima, J. Org. Chem. 36, 4117 (1971). 

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 three-necked round-bottomed flask (250 mL) and add the tetratoluenesulfonamide (1.96 g, 2,04 mmol), prepared as described in step 15, under a positive pressure of nitrogen. Equip the flask with a dry ice condenser, a nitrogen inlet and a stopper, and add dry tetrahydrofuran (30 mL) and dry ethanol (2 mL). Cool the suspension in a dry ice/ isopropanol cold bath and add dry ice and isopropanol to the dry ice condenser. Allow ammonia gas (from a cylinder) to condense into the cooled flask until about 75 mL of liquid ammonia has been added. 

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. 

The irradiation light source is a Hanovia 450 W medium-pressure Hg vapour lamp placed in a quartz immersion well. The reaction solution is contained in a 150 ml quartz semicircular flask mounted as closely as possible to the immersion well. No light filter is used. The entire apparatus is immersed in a large Dewar flask charged with dry ice-isopropanol with the bath temperature maintained between —60 and —40°C during irradiation. 

To each tube, add 75 pL of 4.0 M sodium acetate, pH 5.5, and then add 1.0 mL of isopropanol. Mix very well and incubate overnight at -20°C. Alternatively, samples can be incubated in a dry ice/ethanol bath for 1 h (thaw samples for 5 min at room temperature before centrifugation). 

In a 5-1. three-necked flask fitted with a powerful mechanical stirrer (Note 1), a low temperature thermometer, and an addition funnel topped with a drying tube is placed 2.5 1. of dry toluene and 147 g. (2 moles) of f-butylaminc (Note 2). The flask is surrounded by a suitable container to act as an isopropanol-dry ice cooling bath. The stirrer is started and the container is charged with isopropanol and dry ice until the inside temperature is —20° to —30°, and 160g. (1 mole) of bromine is added over a period of 10 min. The solution is then cooled to —70° to —75° by addi-... 

A diagram of a simplified apparatus is shown in Figure 8-9, p. 88, and is used for this experiment. A 500 mL r.b. flask is used as the sample holder. A trap is made out of a 30 cm long test tube, which is cooled by a dry ice-isopropanol mixture held in a Dewar flask. An ordinary vacuum pump is used, and because this is not a high vacuum, the sample in some cases may have to be cooled partially by immersing it a short distance into the ice bath. 

ClsSi—SiCls, 2-chloro-l,3-dimethylimidazolinium chloride, dry dichloromethane, dry methyl terf-butyl ether, dry diethyl ether, cooling bath (dry ice/isopropanol). 

Alternatively, a solution of crude product prepared at room temperature may be cooled to a low temperature. Filter stick filtration is again convenient for this procedure since it facilitates collection of the crystallized product at low temperature. It is common to cool the solvent to -78°C by slow addition of dry ice to an acetone cooling bath, but one convenient variation is to place the room temperature solution Inside a Dewar flask containing some isopropanol in a low temperature freezer (-80°C). The solution will then cool over a period of 6 - 12 hrs to -70°C. 

The samples taken were stored in a freezer at temperatures below —30°C (3) They were freeze dried by freezing them to temperatures below —70°C by immersing them in an isopropanol-dry ice bath and subjecting them to vacuum. The temperature was gradually brought up to room temperature over a period of 48-72 h. 

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