Grades hydrogen chloride

Because of the tendency for buildup of particulates, cylinder valves on technical grade hydrogen chloride cylinders are normally wrench operated to facilitate application of torques in excess of that which can be applied manually with a handwheel. Electronic grade hydrogen chloride cylinders are equipped with a tied-diaphragm valve. 

The production of sihcon tetrachloride by these methods was abandoned worldwide in the early 1980s. Industrial tetrachlorosilane derives from two processes associated with trichlorosilane, the direct reaction of hydrogen chloride on sihcon primarily produced as an intermediate for fumed sihca production, and as a by-product in the disproportionation reaction of trichlorosilane to silane utilized in microelectronics. Substantial quantities of tetrachlorosilane are produced as a by-product in the production of zirconium tetrachloride, but this source has decreased in the 1990s owing to reduction in demand for zirconium in nuclear facihties (see Nuclearreactors). The price of tetrachlorosilane varies between l/kg and 25/kg, depending on grade and container. 

Dichloroethane, an important intermediate for vinyl chloride production, is produced by catalytic chlorination of ethylene in either vapor or Hquid phase or by oxychlorination of ethylene. Thermal dehydrochlorination of 1,2-dichloroethane produces vinyl chloride and coproduct hydrogen chloride. Hydrogen chloride is commonly recycled to an oxychlorination unit to produce 1,2-dichloroethane or is processed into sales-grade anhydrous or aqueous hydrogen chloride. 

The hydrohalide is usually prepared by passing hydrogen chloride into a solution of masticated high-grade raw rubber in benzene at 10°C for about six hours. Excess acid is then neutralised and plasticisers and stabilisers are added. The benzene is removed by steam distillation and the product washed and dried. Alternatively the solution is cast on to a polychloroprene rubber belt, leaving a tough film after evaporation of the solvent. 

The triethylamine is used to trap any hydrogen chloride present as the insoluble triethylammonium chloride which is collected in the glass wool filter. A reagent grade of triethylamine (b.p. 88°) was distilled from calcium hydride prior to use. 

Eastman Organic Chemicals or Matheson Coleman and Bell practical grade material was distilled before use. Since hydrogen chloride and sulfur dioxide are evolved, the preparation should be carried out in an efficient hood. 

Violet ultramarine can be prepared by heating a mid-range blue grade with ammonium chloride at ca. 240 °C in the presence of air. Treating the violet with hydrogen chloride gas at 140 °C gives the pink derivative. 

The mixture was allowed to stand for 70 hours and then concentrated to a small volume under reduced pressure. The residue was dissolved in 100 ml of methylene chloride, washed with 75 ml of water, three times with 50 ml of saturated brine solution each time and filtered over neutral alumina (grade 1). The filtrate was evaporated to dryness and the resulting colorless oil taken up in ether, which was then saturated with hydrogen chloride. The pale yellow precipitate was filtered off and recrystallized from methanol/ether yielding 1-[2-(diethylamino)ethyl]-5-(2-fluorophenyl)-7-chloro-2,3-dihydro-1H-1,4-benzodiazepinone-(2) dihydrochloride as pale yellow rods melting at 190° to 220°C with decomposition, (from British Patent 1,040,548). 

S. Bade, U. Hoffmann, K. Schonert, Mechano-chemical reaction of metallurgical grade silicon with gaseous hydrogen chloride in a vibration mill, Int. J. Miner. Process, 1996, 44-AS, 167. 

Stevens et al. (1992) exposed 5 men and 5 women (aged 18-25) to filtered air or to hydrogen chloride at 0.8 ppm (parts per million) or 1.8 ppm for 45 min.The 45-min exposure sessions consisted of a 15-min exercise period on a treadmill walking at 2 miles per hour at an elevation grade of 10%, followed by a 15-minute rest period and then by another 15-min exercise period. Subjects were asked to report any symptoms, such as upper respiratory effects (sore... 

White crystals. When heated to decomposition it evolves highly toxic fumes of phosgene and hydrogen chloride. The technical grade is a tan to dark brown solid containing 85% or more of HHDN. M.p. 104° (pure grade), 49° to 60° (technical grade). Practically insoluble in water soluble 1 in 20 of ethanol, 1 in 1 of acetone, 1 in 0.55 of benzene, and 1 in 0.33 of carbon tetrachloride soluble in ether. 

The purity of silicon in this first step is only ca. 98%, and is referred to as metallurgical grade silicon (MG-Si). In order for the silicon to be used for electronics applications, additional steps are necessary to decrease the number of impurities. Reaction of MG-Si with hydrogen chloride gas at a moderate temperature converts the silicon to trichlorosilane gas (Eq. 3). When SiHCl3 is heated to a temperature of ca. 1,150°C, it decomposes into high-purity silicon and gaseous by-products (Eq.4). This reaction is typically performed in a bell-shaped Siemens-type reactor, where Si is deposited onto heated electrodes. 

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