Cooling compounds

Liquid mixtures of the 2 xenon compounds, cooled in liquid nitrogen, tend to flash, then explode after a few seconds. 

Dissolve 160 mg of adipic acid dihydrazide (Aldrich) in 5 ml of 0.1 M sodium phosphate, pH 6.0. Some heating of the tube under a hot-water tap may be required to help solubilize the compound. Cool to room temperature. 

Diethylaminoacetonitrile is made by adding formalin to a solution of sodium bisulfite to form the addition compound, cooling to 35°, and stirring in diethylamine afte 2 hrs. an aqueous solution of sodium cyanide is added with good stirring to mix th two layers. "The upper layer is separated, dried, and dlstHled,... 

B) [CO(NH3)fiONO] CI2. Dissolve 1.5 grams of chloropentam-mine cobaltic chloride in 25 ml of water to which 5 ml of concentrated ammonia has been added, warming gently if necessary. Filter, and add 6M hydrochloric acid carefully until the solution is just neutral to litmus. Add 1.5 grams of sodium nitrite to the cold solution, then 1.5 ml of 6M hydrochloric cid, and leave to stand in the cold for an hour or so. A salmon-pink precipitate slowly forms. This, the desired product, is a good deal less soluble than the isomeric nitro compound. Cool in ice, filter, and wash with ice water and alcohol. 

Cyclopentadithiophenes. 3,4 -Dibromo-2,3 -dithienylmethane treated at -70° with n-butyllithium in abs. ether, the resulting soln. of the dilithio compound cooled and added dropwise under dry Ng during 0.5 hr. to a vigorously stirred ice-cooled suspension of anhydrous CuClg in abs. ether, stirring continued 6hrs. at 0° 7H-cyclopenta[l,2-b 3,4-c ]dithiophene. Y 46%. F. e. s. A. Kraak et al., Tetrahedron 24, 3381 (1968). 

Manganese metal is able to react directly with an organic compound cooled by liquid nitrogen by evaporating the compound under vacuum. For example, reactions with aromatic compounds such as toluene, xylene and mesitylene are shown in eq. (14.8) [19-21]. In these reactions, at first, iodide complexes ne)2Mn I are yielded by a reaction with iodide, and the more stable ( / -Are-ne)2Mn PF6 is isolated by reaction with NH4PF6 as shown in eq. (14.8) [19]. 

Boil the tablet mixture with 200 ml of water for two to three minutes to dissolve the thiouracil compound, cool to 70° before adding the sodium hydroxide and allow to stand for five minutes with occasional shaking. Complete as above beginning with add 10 g of sodium acetate. . . cooling to room temperature before titrating. (If no stearic acid is present in addition to the lactose, the addition of the sodium hydroxide solution may be omitted.)... 

Procedure A. (To be used for alcohols of unknown chemical constitution or under conditions in which the alcohol is accompanied by unstable compounds.) Cool the xylene solution, add 40 ml of pyridine containing 4 ml of water and boil for fifteen minutes. 

Early calculations of a similar kind indicated that the compound AlCl is unlikely to exist but at temperatures above about HOOK aluminium oxide AI2O3 and the trichloride AICI3 react to form the compound AlCl on cooling this disproportionates to give the trichloride and aluminium metal... 

Suppose that a given volume of the solvent when cold can dissolve 15 g. of A and 5 g. of B. If too g. of the crude product are dissolved in this volume of the hot solvent, and the solution allowed to cool, then (ignoring the small mutual effect on the solubility of each compound caused by the presence of the other) it is clear that 82 g. of A will crystallise, whilst the whole of B will remain in solution, since the latter is not saturated with respect to B. 

Decolorisation by Animal Charcoal. It sometimes hap pens (particularly with aromatic and heterocyclic compounds) that a crude product may contain a coloured impurity, which on recrystallisation dissolves in the boiling solvent, but is then partly occluded by crystals as they form and grow in the cooling solution. Sometimes a very tenacious occlusion may thus occur, and repeated and very wasteful recrystallisation may be necessary to eliminate the impurity. Moreover, the amount of the impurity present may be so small that the melting-point and analytical values of the compound are not sensibly affected, yet the appearance of the sample is ruined. Such impurities can usually be readily removed by boiling the substance in solution with a small quantity of finely powdered animal charcoal for a short time, and then filtering the solution while hot. The animal charcoal adsorbs the coloured impurity, and the filtrate is usually almost free from extraneous colour and deposits therefore pure crystals. This decolorisation by animal charcoal occurs most readily in aqueous solution, but can be performed in almost any organic solvent. Care should be taken not to use an excessive quantity... 

Students should carry out the purification by steam distillation of (a) crude nitrobenzene or chlorobenzene, or of (b) crude naphthalene, o-nitrophenol (p. 170) or />-tolunitrile (p. 194) as examples of solid compounds which may also be purified in this way. When the distillation is complete, disconnect the tubing (Fig. 15) between C and D before removing the flame from under D, otherwise the contents of C will be sucked back into D as the latter cools. 

Hydrolysis of Potassium Ethyl Sulphate. Dissolve about i g. of the crystals in about 4 ml. of cold distilled water, and divide the solution into two portions, a) To one portion, add barium chloride solution. If pure potassium ethyl sulphate were used, no precipitate should now form, as barium ethyl sulphate is soluble in water. Actually however, almost all samples of potassium ethyl sulphate contain traces of potassium hydrogen sulphate formed by slight hydrolysis of the ethyl compound during the evaporation of its solution, and barium chloride almost invariably gives a faint precipitate of barium sulphate. b) To the second portion, add 2-3 drops of concentrated hydrochloric acid, and boil the mixture gently for about one minute. Cool, add distilled water if necessary until the solution has its former volume, and then add barium chloride as before. A markedly heavier precipitate of barium sulphate separates. The hydrolysis of the potassium ethyl sulphate is hastened considerably by the presence of the free acid Caustic alkalis have a similar, but not quite so rapid an effect. 

Dissolve 15 ml. (15-4 g.) of aniline in a mixture of 40 ml. of concentrated hydrochloric acid and 40 ml. of water contained in a 250 ml. conical flask. Place a thermometer in the solution, immerse the flask in a mixture of ice and water, and cool until the temperature of the stirred solution reaches 5°. Dissolve I2 5 g. of powdered sodium nitrite in 30 ml. of water, and add this solution in small quantities (about 2-3 ml. at a time) to the cold aniline hydrochloride solution, meanwhile keeping the latter well stirred by means of a thermometer. Heat is evolved by the reaction, and therefore a short interval should be allowed between consecutive additions of the sodium nitrite, partly to allow the temperature to fall again to 5°, and partly to ensure that the nitrous acid formed reacts as completely as possible with the aniline. The temperature must not be allowed to rise above 10°, otherwise appreciable decomposition of the diazonium compound to phenol will occur on the other hand, the temperature... 

Dissolve 8 8 g. (9 0 ml.) of cyclohexanone in 50 ml. of glacial acetic acid, add 8 ml. of phenylhydrazine, and boil the solution under reflux for 5 minutes. Cool the solution, when the tetrahydrocarbazole will crystallise out. Filter at the pump, drain well, and recrystallise either from aqueous ethanol or (better) from aqueous acetic acid. The recrystallisation should be performed rapidly, for the tetrahydrocarbazole undergoes atmO" spheric oxidation in hot solutions after recrystallisation, the compound should be dried in a vacuum desiccator and not in an oven. Repeated recrystallisation should be avoided. The tetrahydrocarbazole, after thorough drying, is obtained as colourless crystals, m.p. 118° yield of recrystallised material, 11 g. 

Bisulphite addition compound. Shake 1 ml. of benzaldehyde with about 0 5 ml. of saturated NaHSOj solution. The mixture becomes warm, and the white addition product separates (rapidly on cooling). 

Place about 1 g. of the nitro-hydrocarbon in a boiling-tube and add 5 ml. of cone. HCl and several pieces of granulated tin. Warm the mixture and shake continuously to break up the oily drops of the nitro-compound. When all the oil has disappeared (about 3 minutes heating) pour off the liquid from any undissolved tin into a 100 ml. conical flask. Cool and add cautiously 30% aqueous NaOH solution until the precipitate formed redissolves to give a dark-coloured solution. Cool the latter thoroughly and shake well with about 15 ml. of ether. Separate the ethereal layer in a separating-funnel, wash with water and evaporate the ether in a basin on a previously heated water-bath in a fume-cupboard atoay from all flames. The residue is either... 

Meanwhile, the organic compound can be prepared for analysis whilst the sealed end C (Fig. 72) of the Carius tube has been cooling dow n. For this purpose, thoroughly clean and dry a small tube, which is about 6 cm. long and 8-10 mm. w ide. Weigh it carefully, supporting it on the balance pan either by means of a small stand of aluminium foil, or by a short section of a perforated rubber stopper (Fig. 73 (A) and (B) respectively) alternatively the tube may be placed in a small beaker on the balance pan, or suspended above the pan by a small hooked wire girdle. 

Benzene. Pure benzene (free in particular from toluene) must be used, otherwise the freezing-point is too low, and crystallisation may not occur with ice-water cooling alone. On the other hand, this benzene should not be specially dried immediately before use, as it then becomes slightly hygroscopic and does not give a steady freezing-point until it has been exposed to the air for 2-3 hours. Many compounds (particularly the carboxylic acids) associate in benzene, and molecular weights determined in this solvent should therefore be otherwise confirmed. 

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