Sulfur fractional crystallization

Yttrium and lanthanum are both obtained from lanthanide minerals and the method of extraction depends on the particular mineral involved. Digestions with hydrochloric acid, sulfuric acid, or caustic soda are all used to extract the mixture of metal salts. Prior to the Second World War the separation of these mixtures was effected by fractional crystallizations, sometimes numbered in their thousands. However, during the period 1940-45 the main interest in separating these elements was in order to purify and characterize them more fully. The realization that they are also major constituents of the products of nuclear fission effected a dramatic sharpening of interest in the USA. As a result, ion-exchange techniques were developed and, together with selective complexation and solvent extraction, these have now completely supplanted the older methods of separation (p. 1228). In cases where the free metals are required, reduction of the trifluorides with metallic calcium can be used. 

In most commercial processes, the compound is either derived from the sea water or from the natural brines, both of which are rich sources of magnesium chloride. In the sea water process, the water is treated with lime or calcined dolomite (dolime), CaO MgO or caustic soda to precipitate magnesium hydroxide. The latter is then neutralized with hydrochloric acid. Excess calcium is separated by treatment with sulfuric acid to yield insoluble calcium sulfate. When produced from underground brine, brine is first filtered to remove insoluble materials. The filtrate is then partially evaporated by solar radiation to enhance the concentration of MgCb. Sodium chloride and other salts in the brine concentrate are removed by fractional crystallization. 

The monazite sand is heated with sulfuric acid at about 120 to 170°C. An exothermic reaction ensues raising the temperature to above 200°C. Samarium and other rare earths are converted to their water-soluble sulfates. The residue is extracted with water and the solution is treated with sodium pyrophosphate to precipitate thorium. After removing thorium, the solution is treated with sodium sulfate to precipitate rare earths as their double sulfates, that is, rare earth sulfates-sodium sulfate. The double sulfates are heated with sodium hydroxide to convert them into rare earth hydroxides. The hydroxides are treated with hydrochloric or nitric acid to solubihze all rare earths except cerium. The insoluble cerium(IV) hydroxide is filtered. Lanthanum and other rare earths are then separated by fractional crystallization after converting them to double salts with ammonium or magnesium nitrate. The samarium—europium fraction is converted to acetates and reduced with sodium amalgam to low valence states. The reduced metals are extracted with dilute acid. As mentioned above, this fractional crystallization process is very tedious, time-consuming, and currently rare earths are separated by relatively easier methods based on ion exchange and solvent extraction. 

Yttrium sulfate is produced as an intermediate in recovering yttrium from monazite or xenotime (see Yttrium, Recovery). Rare earth sulfates are separated on a cation exchange resin bed. Yttrium fraction is purified by fractional crystallization. Alternatively, yttrium sulfate may be prepared by reacting yttrium oxide with sulfuric acid. 

Rubidium acid salts are usually prepared from rubidium carbonate or hydroxide and the appropriate acid in aqueous solution, followed by precipitation of the crystals or evaporation to dryness. Rubidium sulfate is also prepared by the addition of a hot solution of barium hydroxide to a boiling solution of rubidium alum until all the aluminum is precipitated. The pH of the solution is 7.6 when the reaction is complete. Aluminum hydroxide and barium sulfate are removed by filtration, and rubidium sulfate is obtained by concentration and crystallization from the filtrate. Rubidium aluminum sulfate dodecahydrate [7488-54-2] (alum), RbA SO 12H20, is formed by sulfuric acid leaching of lepidolite ore. Rubidium alum is more soluble than cesium alum and less soluble than the other alkali alums. Fractional crystallization of Rb alum removes K, Na, and Li values, but concentrates the cesium value. Rubidium hydroxide, RbOH, is prepared by the reaction of rubidium sulfate and barium hydroxide in solution. The insoluble barium sulfate is removed by filtration. The solution of rubidium hydroxide can be evaporated partially in pure nickel or silver containers. Rubidium hydroxide is usually supplied as a 50% aqueous solution. Rubidium carbonate, Rb2C03, is readily formed by bubbling carbon dioxide through a solution of rubidium hydroxide, followed by evaporation to dryness in a fluorocarbon container. Other rubidium compounds can be formed in the laboratory by means of anion-exchange techniques. Table 4 lists some properties of common rubidium compounds. 

The synthetic route to R(+)-MPTSO is outlined in Reaction 6. The experimental detail followed that of Boucher and Bosnich (39) and is a modification of literature methods (46, 41). Chlorination of the para-toluene sulfinate gives the sulfinyl chloride that was converted to the (—)menthyl sulfinates. This di-astereomer mixture was resolved by fractional crystallization, and the subsequent Grignard reaction, that is known to proceed by direct inversion at the sulfur (42),... 

Beryllium Sulfate. Beryllium sulfate tetrahydrate [7787-56-6], BeS04 4H20, is produced commercially in a highly purified state by fractional crystallization from a beryllium sulfate solution obtained by the reaction of beryllium hydroxide and sulfuric acid. The salt is used primarily for the production of beryllium oxide powder for ceramics. Beryllium sulfate dihydrate [14215-00-0], is obtained by heating the tetrahydrate at 92°C. Anhydrous beryllium sulfate [13510-49-1] results on heating the dihydrate in air to 400°C. Decomposition to BeO starts at about 650°C, the rate is accelerated by heating up to 1450°C. At 750°C the vapor pressure of S03 over BeS04 is 48.7 kPa (365 mm Hg). 

C. Aromatic Hydrocarbons. The methods listed for saturated hydrocarbons may be used with benzene. Thiophene and similar sulfur-containing impurities are removed by sulfuric acid washes. Very-high-purity benzene may be prepared by fractional crystallization from ethanol followed by distillation. 

Benzo[c]thiophene readily forms adducts with maleic anhydride (m.p. 153°-154°,5 6 148°-152°52), dimethyl acetylenedicarboxylate (see above),61 and A-phenylmaleimide (to give 62).52,61 In the last case the exo and endo isomers of the adduct may be separated by fractional crystallization.52 Benzo[c]thiophene reacts with acetyl nitrate by 1,3-addition in preference to substitution.6 It exhibits halochromy with concentrated sulfuric acid, trichloroacetic acid, and stannic chloride.62... 

In large scale operations the aconitic acid is usually recovered from the crude calcium magnesium aconitates by acidification with a mineral acid followed by the crystallization of the aconitic acid from the liquors obtained. Thus Ventre, Henry and Gayle,88 acidified the crude salts with dilute sulfuric acid. The insoluble calcium sulfate was removed by filtration and the aconitic acid was separated from the magnesium sulfate by fractional crystallization. 

Ambler and Roberts,81-89 in subsequent work, found that if the calcium magnesium salts were heated to remove a portion of the water of hydration the magnesium content could be replaced by calcium by treating the dried salts with a hot concentrated calcium chloride solution. Thus the aconitates could be converted into tricalcium aconitate and subsequent treatment of this salt with sulfuric acid enabled the removal of the cations as insoluble calcium sulfate. The crystallization of aconitic acid from such a filtrate was therefore not complicated by the necessity of a fractional crystallization to separate the aconitic acid and the magnesium sulfate formerly obtained. 

In a boiling mixture of nitric (d 1.50) and concentrated sulfuric acids 2-chloroben-zimidazole gives 2-chloro-5,6-dinitrobenzimidazole in a 75-80% yield [67], In analogous conditions, benzimidazole and 2-alkyl substituted benzimidazoles are also transformed into 5,6-dinitro derivatives however, in this case simultaneous formation of 4,6-dinitro isomers, which can be separated by fractional crystallization, has been fixed [48, 68], 5(6)-Nitro-2-heterylbenzimidazoles (thiazolyl-4-, furyl-4-, and pyrrolyl-4-) having antihelminthic activity were obtained by nitration with sulfuric-nitric mixture on cooling [69],... 

Raab M. and Spiro B. (1991) Sulfur isotopic variations during seawater evaporation with fractional crystallization. Chem. Geol. 86, 323-333. 

The ground drug was extracted with ethanol. Distillation of the alcohol afforded a residue which was dissolved in diluted sulfuric acid. After separation of undissolved materials by filtration and extraction of non-basic products with ligroin the solution was made alkaline. First the solution was extracted exhaustively with ether and then with ethyl acetate. An oily residue was obtained from the ether solution and a solid one from the ethyl acetate solution. The ether-soluble oily fraction, dissolved in 2-propanol, yielded mesembrine hydrochloride upon acidification with ethereal hydrochloric acid. Fractional crystallization of the concentrated mother liquors gave, besides some mesembrine hydrochloride, the hydrochloride of mesembrenine. Crystallization of the solid ethyl acetate residue from a mixture of ethyl acetate and 2-propanol afforded channaine. 

Method of purification Fractional crystallization from strong sulfuric acid, or in the form of their alkali salts from either acid or alkaline solutions. 

Derivation (1) By treatment of potassium chloride either with sulfuric acid or with sulfur dioxide, air, and water (Hargreaves process) (2) by fractional crystallization of a natural sulfate ore (3) from salt-lake brines. 

From liquid sulfur small amounts of endo-Sis have been isolated from quenched sulfur melts by extraction and fractional crystallization see above under Preparation of S12, Sig, and S20 from liquid sulfur . 

The maximum amounts of pure sulfur allotropes [71] isolated from 400 g liquid sulfur quenched from 160 °C, extracted at 20 °C by C82 followed by fractional crystallization are as given below [88] ... 

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