Salts hygroscopic

Properties. Anhydrous potassium fluoride [7789-23-3] is a white hygroscopic salt that forms two hydrates, KF -2H20 [13455-21-5] and KF 4H2O [34341 -58-7]. The tetrahydrate exists at temperatures below 17.7°C. The dihydrate is stable at room temperature and starts to lose water above 40°C. Temperatures on the order of 250—300°C are requited to remove the last few percent of water ia a reasonable period of time. Potassium fluoride does not pyrohydroly2e at temperatures as high as 1000°C (1). Chemical and physical properties of KF are summarized ia Table 1. 

Hexyltrimethylammonium bromide [2650-53-5] M 224.3, m 186 . Recrystd from acetone. Extremely hygroscopic salt. [McDowell and Kraus 7 Am Chem Soc 73 2170 1951.]... 

Calcium chloride is a hygroscopic salt which can exist as pure anhydrous CaClj or as a series of hydrate forms ranging from a monohydrate (CaCl2 -HjO) to a hexahydrate (CaCl j - 6 H j O). In the drying process, hydrocarbon passes up through a bed of calcium chloride and the water from the hydrocarbon forms hydrates with the calcium chloride. At the bottom of the bed the hydrate evenmally reaches a hexahydrate which turns into a brine and is drawn off. 

Certain chemicals (sorbents) have the ability to absorb moisture from a gas they may be either solid or liquid. Performance of a chemical dehumidifi cation device depends on the sorbent used. The sorbent must t>e able to attract and remove the sorbate, such as water, from the gas stream, Stirbems absorb water on the surface of the material by adsorption or by chemically combining with water (absorption). If the unit is regenerative, the process is reversible, allowing water to be removed. This is achieved by a sorbent such as silica gel, alumina gel, activated alumina, lithium chloride salt, lithium chloride solution, glycol solution, or molecular sieves. In the case of nonregenerative equipment, hygroscopic salts such as calcium chloride, urea, or sodium chloride are used. 

The pyrolysis of sodium chlorodinuoroacetate is still a widely used, classical method for generating difluorocarbene, especially with enol and allyl acetates [48, 49, 50, 51] (equation 21) A convenient alternative that avoids the hygroscopic salt uses methyl chlorodifluoroacetate with 2 equivalents of a lithium chlonde-hexa-methylphosphoric triamide complex at 75-80 °C in triglyme [52], Yields are excellent with electron-rich olefins but are less satisfactory with moderately nucleophilic alkenes (4-5% yields for 2-bulenes)... 

Nitrites are white, crystalline hygroscopic salts that are very soluble in water. When heated in the absence of air they disproportionate ... 

The presence of moisture on steel above the critical humidity but below the saturation point may be caused by an adsorption mechanism or by the presence of particles of deliquescent salts on the surface. Once rusting has begun, the composition of the rust already formed will influence the relative humidity at which further rusting will occur, because rusts formed in polluted atmospheres contain hygroscopic salts. The method by which moisture reaches the surface is probably less important, however, than the length... 

Electronic humidistats generally depend on the properties of a hygroscopic salt. The signal has to he measured and amplified. 

In several cases application of various additives to the surface of a semiconductor adsorbent, specifically adsorbing or reacting with particles to be detected enables one to improve selectivity. As an example we can mention the use of hygroscopic salts to bind water in humidity sensors, the application of particles of sulfanilic acid to the surface of hhO to detect NO2 [10]. However, the high operational temperature in majority of semiconductor sensors deprives the method of specific surface additives of its general character. 

Sw = grams of water per grams of hygroscopic salt in a saturated solution... 

L = grams of salt per cubic meter of tablet (load of hygroscopic salt)... 

Addition of water to an intimate mixture of zinc powder and the salts causes spontaneous ignition [1], and a mixture of ammonium nitrate and ammonium chloride (9 1) sprinkled with zinc dust ignites vigorously when moistened [2], Premature spontaneous ignition of the mixture was attributed to absorption of moisture by the hygroscopic salt mixture [3],... 

Hygroscopic Salts Salts that have a high affiinity for water. 

Rust samples scraped off from exposed AISI 1019 steel surfaces were ground to fine size in a morter with a pestle. A fraction of the samples was subjected to a salts extraction process using distilled water to determine the concentration of most common ions by chemical analysis and to study changes in adsorption isotherm after elimination of hygroscopic salts. Samples were obtained from AISI 1019 steel coupons, exposed for up to six months at coastal and rural locations. 

Dimethylformamide (99.8%), mthenium chloride hydrate (RUCI3 XH2O, 35 0% Ru), hydrogen chloride (4 M solution in 1,4-dioxane), and triphenyl-phosphine (99%) are purchased from Aldrich and used as received. DMF is conveniently dried with activated 4-A molecular sieves. As RUCI3 XH2O is a hygroscopic salt, it should be handled only briefly under ambient conditions. 

Hexyltrimethylammonium bromide [2650-53-5] M 224.3. Recrystd from acetone. Extremely hygroscopic salt. 

Tetra-n-butylammoaium azide, (f -C4H,)4NN3 . This hygroscopic salt (1) is prepared by reaction of (n-C4H,)4NOH with NaN4 in CH2C12. ... 

To dimethyl sulfate (19 ml, 0.2 mol) in acetone (80 ml) was added dimethyl sulfide (15 ml. 0.2 mol). After a few minutes, the reaction mixture became turbid and warm. It was then cooled with cold water. The salt crystallized slowly, and after 4-5 h it was filtered. The white crystals were washed several times with acetone and dried under vacuum 26-28 g of the very hygroscopic salt were obtained (70-75% yield), m.p. 100-104°C. 

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