Decomposition dihydrate

Nickel formate dihydrate [15694-70-9] Ni(HCOO)2 is a green monoclinic crystalline compound which melts with decomposition to nickel... 

Anhydrous oxaUc acid normally melts and simultaneously decomposes at 187°C. Sublimation starts at slightly below 100°C and proceeds rapidly at 125°C partial decomposition takes place during sublimation at 157°C. Anhydrous oxaUc acid is hygroscopic and thus absorbs moisture in the air to form the dihydrate. 

Anhydrite also has several common classifications. Anhydrite I designates the natural rock form. Anhydrite 11 identifies a relatively insoluble form of CaSO prepared by high temperature thermal decomposition of the dihydrate. It has an orthorhombic lattice. Anhydrite 111, a relatively soluble form made by lower temperature decomposition of dihydrate, is quite unstable converting to hemihydrate easily upon exposure to water or free moisture, and has the same crystal lattice as the hemihydrate phase. Soluble anhydrite is readily made from gypsum by dehydration at temperatures of 140—200°C. Insoluble anhydrite can be made by beating the dihydrate, hemihydrate, or soluble anhydrite for about 1 h at 900°C. Conversion can also be achieved at lower temperatures however, longer times are necessary. 

Traditionally, sodium dichromate dihydrate is mixed with 66° Bh (specific gravity = 1.84) sulfuric acid in a heavy-walled cast-iron or steel reactor. The mixture is heated externally, and the reactor is provided with a sweep agitator. Water is driven off and the hydrous bisulfate melts at about 160°C. As the temperature is slowly increased, the molten bisulfate provides an excellent heat-transfer medium for melting the chromic acid at 197°C without appreciable decomposition. As soon as the chromic acid melts, the agitator is stopped and the mixture separates into a heavy layer of molten chromic acid and a light layer of molten bisulfate. The chromic acid is tapped and flaked on water cooled roUs to produce the customary commercial form. The bisulfate contains dissolved CrO and soluble and insoluble chromic sulfates. Environmental considerations dictate purification and return of the bisulfate to the treating operation. 

Physical and Chemical Properties - Physical State at 15 XI and I atm. Solid Molecular Weight 170.48 (dihydrate) Boiling Point at I atm Not pertinent Freezing Point not pertinent Critical Temperature not pertinent Critical Pressure Not pertinent Specific Gravity 2.54 at 20 C (solid) Vapor (Gas) Density Not pertinent Ratio of Specific Heats cf Vapor (Gas) Not pertinent Latent Heat of Vaporization Not pertinent Heat of Combustion Not pertinent Heat cf Decomposition Not pertinent. 

The solid is collected on a Buchner funnel and washed with three 30-cc. portions of cold water. The alloxantin is dissolved by boiling the wet solid for fifteen minutes with 250 cc. of water, and the hot solution is filtered to remove the sulfur (Note 2). Alloxantin dihydrate crystallizes from "the filtrate in glistening plates which should be pressed as dry as possible on a Buchner filter, washed with about 30 cc. of ether, and dried in a vacuum desiccator (Note 3). The yield is 8-10 g. (55-69 per cent of the theoretical amount) (Note 4). The product melts with decomposition at 234-238° (Note 5), and is pure enough for most purposes. 

The water of crystallization may be removed by heating the dihydrate at 120-150° under reduced pressure for two hours. The melting points reported in the literature vary considerably. The anhydrous material turns yellow at about 225-230° and decomposes at temperatures ranging from 238-242° to 253-255°, depending on the rate of heating. The instantaneous decomposition temperatures determined on the Maquenne block were 270-275°. 

For temperatures in excess of 320 °C the gas-phase decomposition of anhydrous H0C103 (or of its dihydrate) is a homogeneous, unimolecular reaction close to its first-order limit at pressures in excess of 20 torr440. Levy440 obtained a value... 

In aqueous solution, the dihydrate, CaS04 2H2O (soluble in water) undergoes double decomposition reactions with other soluble salts, precipitating out insoluble salts ... 

The anhydrous form constitutes yellow to brown monoclinic crystals. It is hygroscopic forms dihydrate on exposure to moist air density 3.40 g/cm melts around 630°C with decomposition soluble in water, ethanol and acetone. 

The dihydrate is colorless crystalline substance (the anhydrous salt consists of white monoclinic crystals) density 4.8 g/cm melts at 70°C with partial decomposition soluble in water (hydrolyzes) soluble in cold dilute nitric acid. 

Recently, the in situ thermal decomposition monitoring capability of TOF-SIMS has been reported, in which zinc acetate dihydrate, Zn(CH3COO)2 2H20 (77), decomposed to form ZnO nanoparticles. The only organozinc ions detected at room temperature were [ZnCH3]+ (in the positive-ion mode) and [OZnCHs] (in the negative-ion mode), both of relatively low abundances. 

An aq. soln. of perchloric acid contains about 70 per cent, of HCIO —approximating to the dihydrate—when it has been evaporated on a hot plate until dense white fumes appear. If this acid be distilled at ordinary press., when it boils at 203°, about 10 per cent, is decomposed. Perchloric acid can be heated without decomposition under reduced press, much above the temp, at which it begins to decompose under ordinary atm. press. Perchloric acid boils at 19° under a press, of 11 mm., and between 135° and 145° when the press, is between 50 and 70 mm. Consequently, if a mixture of perchloric and sulphuric acids be fractionally distilled under reduced press., the perchloric acid volatilizes at a lower temp., and its decomposition is largely avoided. A. Vorlander and R. von Schilling12 distilled the acid between 45 and 50 mm. A. Michael and W. T. Conn between 10 and 20 mm. T. W. Richards and H. H. Willard between 150 and 200 mm., and between 15 and 20 mm. 

The last-named mixture suffers no decomposition when boiled at ordinary temp. Although the constant boiling 72-4 per cent, acid approximates to the dihydrate, HC104.2H20 (73 63 per cent. HC104), it is not a compound, since, H. E. Roscoe has shown, its composition and b.p. depend on the press, under which the distillation is performed. In this respect, the phenomena are analogous with those presented by other constant boiling acids. 

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). 

When m-acetamidophenylseleninic acid is oxidised by alkaline permanganate it yields m-acetamidophenylselenonic acid, isolated in the form of the tetrahydrated barium salt, which crystallises in colourless needles, double decomposition giving the sodium salt. The latter separates from water in colourless needles and from alcohol in prismatic needles. Treatment of the barium salt with sulphuric acid releases the free acid as a dihydrate, which melts and decomposes at 229° C, (corr.). The sodium salt separates from water in plates. 

---