United States Patent Office Patented Apr
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3,440,006 United States Patent Office Patented Apr. 22, 1969 2 supernatant liquid by decantation, filtration or centrifug 3,440,006 ing. On heating the magnesius halide-alcohol-cycloaliphatic METHOD OF PREPARNG ANHYDROUS MAG ether complex, it was surprisingly found that the alcohol NESIUM CHILORIDE, BROMIDE, AND ODIDE appears to desolvate more easily than the cycloaliphatic Ulrich W. Weissenberg, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich, a corpora ether. On further desolvation, the cycloaliphatic ether is tion of Delaware volatilized without appreciable reversion of the magnesium No Drawing. Filled Oct. 31, 1966, Ser. No. 590,521 halide. The desolvation of the alcohol depends largely Ent, C. COf 5/26 on the alcohol used. With ethanol, this effect can be no U.S. C. 23-91 6 Claims ticed at a temperature as low as 35 C., particularly under O vacuum. The ether is desolvated at an elevated tempera ture, usually 200-300° C., preferably under vacuum. The alcohols which can be used for dissolving the ABSTRACT OF THE DISCLOSURE magnesium halide are monohydric alkanols which are A method of preparing a substantially MgO-free an iquid at room temperature. They can have from 1 to 3 hydrous magnesium chloride, bromide or iodide which 15 carbon atoms in the alkyl group. The alcohol can be comprises admixing a saturated solution of a hydrated primary or secondary, so long as it does not split out magnesium halide and an absolute alkanoi with a cycloali water at temperatures up to about 150° C. The preferred phatic ether, separating the precipitate formed by such alkanols are methanol and ethanol and mixtures thereof. admixture, and heating the precipitate in the substantial The cycloaliphatic ethers can be tetrahydrofurane, absence of moisture to form the substantially MgO-free 20 dioxane and lower alkyl derivatives thereof. The term magnesium halide salt. “lower alkyl' is intended to mean a group of from 1 to about 4 carbon atoms. These ethers have from 5 to 6 w-raciassisms atoms in the cyclic ring and 1 to 2 oxygen atoms in the This invention relates to a new complex of magnesium ring. The only limitation on the type of alkyl substitution halides, particularly halides of halogens having an atomic 25 and the number of alkyl groups on the ring is that it weight above 35, containing alcohol and cyclic ether should be so great as to increase the boiling point of molecules, and to a method for preparing such magnesium the ether above about 100 C., and that it does not de halides of high purity from the complexes, and more compose with the formation of water or alcohols at its particularly pertains to complexes of such magnesium boiling point. The dioxanes can be 1.3 or 14. halides containing both a low molecular weight mono 30 The magnesium halides which can be reacted and puri hydric alkanol and a cycloaliphatic ether as solvate mole fied include magnesium iodide, magnesium bromide and cules, and to a method of preparing a magnesium halide magnesium chloride. The preferred magnesium halide is of high purity by removing the solvating organic molecules magnesium chloride, because of its abundance, industrial at an elevated temperature. importance and potentially low cost. The magnesium Numerous attempts have been made to produce an halide can be an alcoholate dissolved in alcohol or a hydrous magnesium halides which contain less than 1 solution of the salt in a monohydric alkanol of the type percent Water and only small amounts of oxides, but described. no feasible process attempted heretofore has been very In the preparation of the solution of the magnesium successful. halide and in all subsequent treatments, it is essential to Chlorides, bromides and iodides of magnesium obtained 40 maintain all ingredients as far from water or water vapor by crystallization from water solution are invaribly as is practical. Thus, the alcohol used for preparing the hydrates. On heating these hydrates, there can be a com solution of the magnesium halide and the cycloaliphatic plete or partial reversion, so that considerable amounts of ether should be of at least commercial anhydrous grade. magnesium oxide and/or magnesium oxyhalide are The recovery step for separating the magnesium halide formed. This reversion can be suppressed to a considerable alcohol-cyclic ether complex should be carried out with degree by heating the hydrates in an atmosphere of dry a minimum exposure to moist atmospheres, and the final HCl, which is expensive and requires corrosion resistant desolvating of the cycloaliphatic ether should also be apparatus for proper functioning. effected in a substantially moisture-free atmosphere and The magnesium halide hydrates can be converted to preferably under vacuum at 200-300° C. ammonium carnallite which then can be heated in a 50 The ratio of alcohol to cycloaliphatic ether is not criti two stage pyrolysis to temperatures of 350° C. or higher cal, but it is desirable to have sufficient ether present to to sublime the ammonium halide. This process suffers form complexes of the magnesium halides having at least from the disadvantage that the magnesium halide must one mol of alcohol per mol of magnesium salt. Preferably, first be converted to the carnallite, and from the fact the molar ratio of alcohol to the cyclic ether is from about that the sublimation is a slow reaction. 55 1 to 1 to about 20 to 1. Such complexes are not very Alcoholates of magnesium halides can be obtained di soluble in the alcohol-ether mixture, and thus, will pre rectly from naturally occurring alkali metal carnallites, cipitate from the liquid. particularly potassium carnallite, by leaching the latter The complexes which form contain at least 0.2 mol of mineral with a liquid anhydrous alcohol. On heating the ether per mol of magnesium salt, and for this reason, the magnesium halide-alcohol complex, however, severe de 60 molar ratio of Mg salt to cyclic ether should be at least composition of both the organic compound and the 0.2 to 1 and preferably about 1 to 1 to 2 to 1. magnesium halide occurs, so that the end product con Representative alcohols which can be used for dissolv tains relatively large amounts of carbon and magnesium ing the magnesium halide include methanol, ethanol, oxide. n-propanol and isopropanol. I have found that by adding a cycloaliphatic ether to a 65 Typical cyclic ethers which can be used for the forma liquid monohydric alkanol solution of a magnesium chlor tion of complexes are dioxane, tetrahydrofuran, and their ide, bromide or iodide, a complex containing both the alkyl or phenyl substituted derivatives. The preferred alcohol and ether is formed with the magnesium halide ether is dioxane. at room temperature. The complex is insoluble in the 70 The examples which follow are intended to illustrate, alcohol and in the ether in the proportions of those but not to limit, the invention. Parts are by Weight, unless solvents employed and can be readily removed from the otherwise specifically indicated. 3,440,006 3 4. Example 1 1 to 3 carbon atoms can be used for preparing billigands which can be converted to dioxanates and further desol A Saturated solution of MgCl2 in absolute methanol, wated to pure magnesium halides. obtainable by extracting potassium carnallite with anhy drous methanol, consisting of about 15 g. MgCl2 and Example 3 about 123 g. methanol, was added rapidly with vigorous 5 In a series of runs, various proportions of magnesium stirring at room temperature to 345 g. of absolute 1,4- chloride were dissolved in methanol. The amount of dioxane. A white precipitate settled out immediately. dioxane added to precipitate the billigand of the mag After permitting the solids to settle for several hours, the nesium salt in relation to the amount of methanol present precipitate was filtered with the exclusion of atmospheric was also varied. In Table I below, the percentage of mag moisture and then subjected at a vacuum of 200 mm. Hg O nesium is based on the Mg content of MgCl2. TABLE-METHANOL-DOXANE SOLVATES OF MAGNESUM CHLORIDE: MOLAR COMPONENT RATIOS OF PREPAREID SAMELES Sample Wt. percent Wit. percent Wt. percent Molar ratio Molar ratio l Mg i,4-dioxane methanol dioxane-MeOH Mg-Diox.- MeOH 5. 39 6.5 49 1.00-20.7 1.00-0.33-6.9 6,73 18 46 1.00-7, 05 0-0. 73-5.2 7.56 7.3 50 1.00-18.8 1,00-0.27-5.0 9.02 28 32 1.00-3.14 100-102-3.18 for 5 hours. The residue weighed 37.9 grams. On analysis, When these complexes were subjected to heat treat it was shown to have the composition MgCl, 1 dioxane: 3 ment, the methanol in the complex was preferentially methanol. released and continued heating to 290-300° C. liberated The product is very deliquescent and tends to liberate 25 all of the solvent to produce a magnesium chloride with methanol preferentially when heated under vacuum. At a a relatively low magnesium oxide contaminant. final temperature of 290-300 C, and 50-100 mm. Hg Similar tests were run with ethanol. In this instance, Vacuum, total desolvation occurs. The MgCl2 contains however, the amount of magnesium chloride is recorded only about 1.6 to about 2 percent MgO as impurity. Only as percent by weight of salt. Data obtained with the minute traces of carbon were observed. 30 ethanol containing complexes are listed in Table II. For comparative purposes, under essentially the same In run 1, the analyses were made on a precipitate conditions, MgCl2 methanolate, initially containing -6 which was subjected to a vacuum of 100 microns of mer mols CH3OH as a ligand, yielded a product having about cury at room temperature for ten minutes.