Low-temperature cooling bath

Endate formation with LDA is typically carried out at -78 C, a convenient temperature to maintain in the laboratory because it is the temperature at which dry ice (solid CCy sublimes. A low-temperature cooling bath can be made by adding dry ice to acetone until the acetone cools to -78 C. Immersing a reaction flask in this cooling bath keeps its contents at a constant low temperature. 

According to Rai [16], nitrogen trichloride can also be prepared by reaction of bleaching powder (calcium hypochlorite) solution on a saturated solution of ammonium chloride. The reaction is very vigorous and must be carried out at low temperatures. Ice bath cooling is recommended and the reaction temperature should not exceed 0 °C. The reaction does not require special equipment or extraction of the product and is therefore suitable for small-scale preparation or class demonstration of the explosive properties of nitrogen trichloride [16]. 

In a 5-1, 3-necked flask fitted with a mechanical stirrer (Note 1), a dropping funnel, and a thermometer for reading low temperatures is placed 790 ml. (7 moles) of 48% h drobromic acid. The fl.ask and contents are cooled to 10-20 in an ice-salt bath, and 150 g, (1.59 moles) of 2-aminopyridine (Note 2) is added over a period of about 10 minutes. While the temperature is kept at 0° or lower, 240 ml. (4.7 moles) of bromine is added dropwise (Note 3). A solution of 275 g. (4 moles) of sodium nitrite in 400 ml. of water is added dropwise over a period of 2 hours, the temperature being carefully maintained at 0° or lower (Note 4). After an additional 30 minutes of stirring, a solution of 600 g. (15 moles) of sodium hydroxide in 600 ml. of water is added at such a rate that the temperature does not rise above 20-25° (Note 5). The nearly colorless reaction mixture is extracted with... 

The phenol (Imol) in 5% aqueous NaOH is treated (while cooling) with benzoyl chloride (Imol) and the mixture is stirred in an ice bath until separation of the solid benzoyl derivative is complete. The derivative is filtered off, washed with alkali, then water, and dried (in a vacuum desiccator over NaOH). It is recrystalUsed from ethanol or dilute aqueous ethanol. The benzoylation can also be carried out in dry pyridine at low temperature ca 0°) instead of in NaOH solution, finally pouring the mixture into water and collecting the solid as above. The ester is hydrolysed by refluxing in an alcohol (for example, ethanol, n-butanol) containing two or three equivalents of the alkoxide of the corresponding alcohol (for example sodium ethoxide or sodium n-butoxide) and a few ca 5-10) millilitres of water, for half an hour to three hours. When hydrolysis is complete, an aliquot will remain clear on dilution with four to five times its volume of water. Most of the solvent is distilled off. The residue is diluted with cold water and acidified, and the phenol is steam distilled. The latter is collected from the distillate, dried and either fractionally distilled or recrystalUsed. 

OSM OTIC DIURETICS. Mannitol is administered only via the IV route The nurse inspects the solution carefully before administration because when exposed to low temperatures, mannitol solution may crystallize If crystals are observed, the bottle is warmed in a hot water bath, a dry heat oven, or autoclave to dissolve the crystals. The solution must be cooled to body temperature or lower before administering. The rate of administration and concentration of the drug is individualized. The nurse must monitor the urine output hourly. The rate of administration is adjusted to maintain a urine flow of at least 30 to 50 mL/h. 

When a flask containing orange NO2 gas at room temperature (top) is cooled in a low-temperature bath... 

At a very low temperature the lithium tetramethylpiperidide solution may become too thick for smooth addition. If that occurs, the dry ice-acetone cooling bath is either partially or completely removed for a short period until addition can take place. The checkers warmed this mixture to -20°C to -10°C (whereupon it became a clear solution) prior to addition. 

If desired, the a-diazo /3-keto ester can be purified by a low-temperature crystallization. The diazo ester (10 g.) is cooled to —70° to —75° in a dry ice-acetone bath, and crystallization is initiated by rubbing. (Caution The rubbing should not be continued after crystallization has been initiated.) This material is treated with 5 ml. of anhydrous ether which has been previously cooled, and the mixture is filtered with suction. The residue... 

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