Coohng baths

Coohng is often required during a chemical reaction in order to maintain proper reaction temperatures. Not properly cooling reaction mixtures can lead to conditions including evolution of poisonous gases, decomposition of products, and unwanted side reactions. Coohng baths are cheap and readily available. Dry ice is readily available and is used to make excellent cooling baths. 

A slurry of crushed ice and water can be used to give a coohng bath in the range 0°C to 5 C. Pure crushed ice does not give good contact with the glassware and inefficient cooling results. 

Figure 3. Flow-sheet diagram of the supercritical fluid extraction semi-pilot plant at the University of Burgos. CO2 storage (1), Purge valves (PI, P2, P3), Shutoff valves (SI, S2,..., S8), Check valve (Cl), Coohng bath (2), Temperature controllers (TC), Total mass flow meter (3), Pump (4), Rupture disks (5, 8), Heating bath (6), Extractor (7), Temperature transducers (TT), Pressure transducers (PT), Expansion valve (El), Separator (9).

Y-Phenylbutyric acid. Prepare amalgamated zinc from 120 g. of zinc wool contained in a 1-litre rovmd-bottomed flask (Section 111,50, IS), decant the liquid as completely as possible, and add in the following order 75 ml. of water, 180 ml. of concentrated hydrochloric acid, 100 ml. of pure toluene (1) and 50 g. of p benzoylpropionic acid. Fit the flask with a reflux condenser connected to a gas absorption device (Fig. II, 8, l,c), and boil the reaction mixture vigorously for 30 hours add three or four 50 ml. portions of concentrated hydrochloric acid at approximately six hour intervals during the refluxing period in order to maintain the concentration of the acid. Allow to cool to room temperature and separate the two layers. Dilute the aqueous portion with about 200 ml. of water and extract with three 75 ml. portions of ether. Combine the toluene layer with the ether extracts, wash with water, and dry over anhydrous magnesium or calcium sulphate. Remove the solvents by distillation under diminished pressure on a water bath (compare Fig. II, 37, 1), transfer the residue to a Claisen flask, and distil imder reduced pressure (Fig. II, 19, 1). Collect the y-phenylbutyric acid at 178-181°/19 mm. this solidifies on coohng to a colourless sohd (40 g.) and melts at 47-48°. 

Amino-5-methylthiazole. Suspend 76 g. of thiourea in 200 ml. of water in a 500 ml. three-necked flask equipped as in the preceding pre paration. Stir and add 92 -5 g. (80 ml.) of monochloroacetone (1) over a period of 30 minutes. The thiourea dissolves as the reaction proceeds and the temperature rises. Reflux the yellow solution for 2 hours. To the cold solution immersed in an ice bath add, with stirring, 200 g. of solid sodium hydroxide. Transfer to a separatory funnel, add a little ice water, separate the upper oil layer and extract the aqueous layer with three 100 ml. portions of ether. Dry the combined oil and ether extracts with anhydrous magnesium sulphate, remove the ether by distillation from a steam bath, and distil the residual oil under diminished pressure. Collect the 2-amino-5-methylthiazole at 130-133°/18 mm. it solidifies on coohng in ice to a solid, m.p. 44-45°. The yield is 84 g. 

Mix 42 5 g. of acetone cyanohydrin (Section 111,75) and 75 g. of freshly powdered ammonium carbonate in a small beaker, warm the mixture on a water bath FUME CUPBOARD) and stir with a thermometer. Gentle action commences at 50° and continues during about 3 hours at 70-80°. To complete the reaction, raise the temperature to 90° and maintain it at this point until the mixture is quiescent (ca. 30 minutes). The colourless (or pale yellow) residue solidifies on coohng. Dissolve it in 60 ml. of hot water, digest with a little decolourising carbon, and filter rapidly through a pre-heated Buchner funnel. Evaporate the filtrate on a hot plate until crystals appear on the surface of the liquid, and then cool in ice. Filter off the white crystals with suction, drain well, and then wash twice with 4 ml. portions of ether this crop of crystals of dimethylhydantoin is almost pure and melts at 176°. Concentrate the mother liquor to the crj staUisation point, cool in ice, and collect the... 

Propiophenone. Prepare a solution of diphenyl-cadmium in 110 ml. of dry benzene using 4 9 g. of magnesium, 32 4 g. of bromobenzene and 19 5 g. of anhydrous cadmium chloride. Cool the solution to 10°, and add during 3 minutes a solution of 14 -8 g. of propionyl chloride (b.p. 78-79°) in 30 ml. of dry benzene use external coohng with an ice bath to prevent the temperature from rising above 40°. Stir the mixture for 2 hours at 25-35°. Work up the product as detailed above except that 6 per cent, sodium carbonate solution should replace the saturated sodium bicarbonate solution. The yield of propiophenone, b.p. 100-102°/16 mm., is 17 6 g. 

Add 40 ml. of ethyl alcohol to 21 -5 g. of 70 per cent, ethylenediamine solution (0 -25 mol) dissolve 36 -5 g. of adipic acid (0 -25 mol) in 50 ml. of a 6 1 mixture of ethyl alcohol and water. Mix the two solutions, stir and cool. Filter off the resulting salt and recrystalliae it from 60 ml. of a 6 1 ethyl alcohol - water mixture, and dry the salt in the air. Heat the salt in an atmosphere of oxygen-free nitrogen or of carbon dioxide in an oil bath until it melts (ca. 160°) the product will sohdify after a short time. Reduce the pressure to 15 mm. of mercury or less and raise the temperature of the oil bath until the product remelts (about 290°) and continue the heating for 4r-5 hours. Upon coohng, a nylon type polymer is obtained. 

Dissolve 18.2 g vanadium pentoxide in 300 ml aqueous sodium carbonate solution, (cn. co, = 1 mol/1), with heating after coohng carefully add 460 ml sulfuric acid, (ch so. = 2.5 mol/1), and make up to 11 with water. Remove excess CO2 in the ultrasonic bath [1, 3, 4]. 

In a 250 ml. conical flask mix a solution of 14 g. of sodium hydroxide in 40 ml. of water and 21 g. (20 ml.) of pure benzaldehyde (Section IV,115). Add 15 g. of hydroxylamine hydrochloride in small portions, and shake the mixture continually (mechanical stirring may be employed with advantage). Some heat is developed and the benzaldehyde eventually disappears. Upon cooling, a crystalline mass of the sodium derivative separates out. Add sufficient water to form a clear solution, and pass carbon dioxide into the solution until saturated. A colourless emulsion of the a- or syn-a.ldoxime separates. Extract the oxime with ether, dry the extract over anhydrous magnesium or sodium sulphate, and remove the ether on a water bath. Distil the residue under diminished pressure (Fig. II, 20, 1). Collect the pure sj/n-benzaldoxime (a-benzald-oxime) at 122-124°/12 mm. this gradually solidifies on coohng in ice and melts at 35°. The yield is 12 g. 

Coohng is not as easy as it may appear. In some ice baths the ice will melt rapidly during the chemical reaction. Ice that rapidly melts must be continuously refilled in order to maintain proper reaction temperature. 

Flush eyes with copious amounts of tepid water for at least 15 min. Animals should be bathed with soap and water. Bathing will not only remove the BZ but will also provide external coohng to combat hyperthermia. BZ may be detected in urine, serum, or blood, but there are no rapid tests to diagnose exposure to BZ, so clinical use is minimal. 

Cooling probes are commonly found in constant temperature baths, when a temperature below ambient temperature is required, and probes can be used instead of solid CO2 to produce temperatures down to -100 °C. CooHng probes are expensive pieces of equipment therefore you will find them dedicated to a specific experiment and they are not usually available for basic laboratory operations. 

---