Dehydration with calcium chloride

Calcium chloride reacts with acetone so it is not a suitable dehydrating agent, but potassium carbonate, anhydrous sodium sulphate (Drierite) and 4A molecular sieves can be safely used to dry acetone to 0.1% water or less. 

Both forms sublime very readily, even at room temperature a small sample on exposure to the air will completely volatilise in a short time, particularly on a warm day or if the sample is exposed to a gentle current of air. Hence the above method for rapid drying. A sample confined in an atmospheric desiccator over calcium chloride rapidly disappears as the vapour is adsorbed by the calcium chloride. A sample of the hexahydrate similarly confined over sodium hydroxide undergoes steady dehydration with initial liquefaction, for the m.p. of the hydrated-anhydrous mixture is below room temperature as the dehydration proceeds to completion, complete resolidification occurs. 

Metallic sodium. This metal is employed for the drying of ethers and of saturated and aromatic hydrocarbons. The bulk of the water should first be removed from the liquid or solution by a preliminary drying with anhydrous calcium chloride or magnesium sulphate. Sodium is most effective in the form of fine wire, which is forced directly into the liquid by means of a sodium press (see under Ether, Section II,47,i) a large surface is thus presented to the liquid. It cannot be used for any compound with which it reacts or which is affected by alkalis or is easily subject to reduction (due to the hydrogen evolved during the dehydration), viz., alcohols, acids, esters, organic halides, ketones, aldehydes, and some amines. 

Another difficulty in this reaction lies in the preparation of pure chloroacetaldehyde. The low yield observed is due to simultaneous formation of by-products (polyhalogenation). So vinylchloride was used as a starting material for this synthesis (449). A simpler method is to react chlorine with vinylchloride in aqueous solution and then to dehydrate the semihydrated chloroacetaldehyde by distillation through a column of calcium chloride heated to 70 to 90 C (451). 

The amyl alcohol and sodium nitrite are mixed in a flask (500 C.C.), and whilst the mixture is cooled in ice-water, the cone, sulphuric with constant shaking. Towards the end of the process a more vigorous reaction sets in, when care must be taken to add the sulphuric acid more slowly. When the whole of the acid has been added, the top layer of amyl nitrite is decanted into a separating-funnel. A little water is then added to the residue and, after shaking, a further quantity of amyl nitrite separates and is decanted as before. The whole of the amyl nitrite is then separated from water, dehydrated over calcium chloride and distilled. The liquid boiling at 95—100° is collected separately. Yield, 30—35 grams. 

The potassium benzenesulphonate is carefully dried on the water-bath, powdered, and mixed with the phosphorus pentachloride in a flask. A vigorous reaction sets in. When it hats abated, the flask is heated on the water-bath for one hour, and the mass occasionally stirred with a glass rod. The product is poured into a flask containing 200 c.c. cold water and allowed to stand an hour. The sulphonic chloride, which separates as an oil, is then extracted with ether, dehydrated over calcium chloride, decanted, and the ether removed on the water-bath. Yield, 10 grams of a light brown oil. 

The methyl alcohol is poured into a round flask (250 c.c.) connected with an upright condenser. The sodium, cut into small pieces, is then added, the flask being detached from the condenser for a moment and replaced. When the sodium has dissolved, the phenol and methyl iodide are added. The mixture IS heated on the water-bath until the solution has no longer an alkaline reaction (two to three hours). As much as possible of the methyl alcohol is distilled off on the water-bath and water added to the amber-coloured residue. A colourless oil separates out, which is e.xtracted with ether. The ethereal solution is dehydrated over calcium chloride and distilled, first on the water-bath until the ether has been driven off, and then over the flame. Almost the whole of the residue distils at 150—155. Yield, nearly theoretical. 

Calcium chloride has several industrial applications. The major applications of this compound are in deicing of roads, dust control, imparting stability to roads and buildings, and to improve traction in tractor tires. It is mixed with ice to make freezing mixtures. Hexahydrate mixed with crushed ice can lower the temperature of the cooling bath to below -50°C. It also is used as a desiccant for dehydrating gases and liquids. It is added to cement in various proportions to manufacture different types of concrete. Other uses are in adhesives, to lower gel temperatures, and as a calcium source in liquid feed supplements for dairy cattle. Also, the compound is used to control particle size development and reduce coalescence in plastics. 

Calcium chloride is obtained as a by-product in the manufacture of sodium carbonate (soda ash) by ammonia-soda (Solvay) process. The process involves the reaction of sodium chloride with calcium carbonate and ammonia. Calcium chloride is currently produced in bulk amounts by evaporation of natural underground brines. In the laboratory, calcium chloride can be prepared by treating bmestone with hydrochloric acid followed by evaporation of solution to obtain crystals. The crystals are dehydrated to obtain anhydrous salt. Calcium oxide or hydroxide may be used instead of carbonate. 

The insoluble Mg(OH)2 is filtered off and the seawater containing calcium chloride is returned to the sea. The hydroxide is then neutralized with hydrochloric acid. Evaporation of the solution yields hexahydrate, MgCb 6H2O. The hexahydrate is either fuUy dehydrated to anhydrous MgCE by heating in dryers or partially dehydrated to monohydrate for electrolytic... 

Selenium oxychloride may be prepared by several methods (1) by passing chlorine gas into a suspension of selenium dioxide in carbon tetrachloride, (2) by heating thionyl chloride, SOCE, with selenium dioxide, (3) by dehydration of dichloroselenious acid, H2Se(CE)02, and (4) by fusion of selenium dioxide, selenium, and calcium chloride. 

C. How can you make sure that dehydration has terminated Cool the preparation in a desiccator over calcium chloride and transfer it into a previously weighed dry jar with a good ground-glass stopper. Weigh the jar with the preparation and calculate the yield in per cent. 

Benzonitrile (BN) [5c] The purity of commercially available BN is 99% or more and the major impurities are water, benzoic acid, isonitriles and amines. In getting pure BN, the commercial product is dried with a mild dehydrating agent like calcium chloride, the supernatant is transferred to a distilling vessel containing P205, and then it is distilled at reduced pressure under an inert atmosphere to collect the 10-80% fraction. 

Dissolve nearly all of the partially dehydrated solid in the minimum amount of hot water, filter, cool the filtrate, and place the clear solution in a crystallizing dish in a desiccator over anhydrous calcium chloride. If necessary, seed with a crystal of iodic acid. When but a very little mother liquor remains, reject this and wash the crystals with a few drops of cold water, drying them on paper. 

Mischmetal is produced commercially by electrolysis, The usual starting ingredient is the dehydrated rare earth chloride produced from monazite or bastnasite. The mixed rare earth chloride is fused in an iron, graphite, or ceramic crucible with the aid of electrolyte mixtures made up of potassium, barium, sodium, or calcium chlorides. Carbon anodes are immersed in the molten salt. As direct current flows through the cell, molten mischmetal huilcls up in the bottom of the crucible. This method is also used to prepare lanthanum and cerium metals. 

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