Hazardous halogenated solvent

Although these reactions operate under solvent-free conditions (with an excess of the arene), many Friedel-Crafts acylations utilize volatile and hazardous halogenated solvents. Here, their replacement by ionic liquids can considerably lower the environmental risks and provide a greener chemistry . Ionic liquids with their unique miscibility properties, high thermal stability and miniscule vapor pressure are valuable alternatives for the wide range of traditional solvents available. 

Solutions of the hydroperoxide in halogenated solvents, and especially dichloro-ethane are much less stable than in toluene (reference 5 above). On a large scale, the azeotropic drying of solutions of the hydroperoxide in dichloroethane may present a thermal hazard. 

With the exception of chlorobenzene and 1,2-dichloroethane, halocarbon solvents are unsuitable diluents, as carbon tetrachloride and chloroform may react violently with alkylalumimum derivatives. The hazards of individually mixing 7 alkyla-luminiums with 7 chlorinated solvents have been assessed comparatively. Most of a series of cyclic coordination complexes between triethylaluminium and a-iminoketones decomposed violently when dissolved in halogenated solvents. 

Potential hazards arising from slow formation of explosive azides from prolonged contact of halogenated solvents with metallic or other azides are outlined. 

Generic wastes produced by manufacturing and industrial processes are included in the list of hazardous wastes from non-specific sources. Spent halogenated solvents, bottom sludge from electroplating operations, wastes from various chemicals manufacturing, and the like are examples of hazardous wastes from non-specific sources. These are designated by prefix F [2-4],... 

National Emission Standards for Hazardous Air Pollutants from the Pulp and Paper Industry National Emission Standards for Halogenated Solvent Cleaning... 

Hazard May explode in contact with heat or flame or with oxygenated and halogenated solvents. Ig-... 

Despite the attention paid to dioxin, these pollutants do not pose as acute a hazard as a large spill of a lethal gas (such as the Bhopal tragedy), or a burning disposal site. Rather, concern about dioxin focuses on long-term effects such as potential cancer formation or bloaccumulatlon In the food chain. Unlike many pollutants, PCDD are very Insoluble In water and are not as likely to leach Into groundwater as, for example, halogenated solvents. 

Absorption in halogenated solvents, such as refrigerant R-12, CF2CI2, has been extensively studied at Brookhaven [S21], Harwell [T3], and Oak Ridge [M6, V4]. The process has several advantages. Fire or explosion hazards are minimal, and gas purification prior to absorption is not required. The process is flexible and does not use extremely low temperatures. Disadvantages are operation at 8 to 10 bar pressure, a fairly complex flow sheet, and the need for an auxiliary system to separate krypton from xenon and CO2. 

Li, C., Shih, T.-L., Jeong, J.U. era/. (1994) The use of tetramethylguanidinium azide in non-halogenated solvents avoids potential explosion hazards. Tetrahedron Letters, 35, 2645-2646. 

Generally speaking, the halogenated hydrocarbons do not present a significant fire hazard (Table 10). Halogenated solvents commonly used in vapor degreasing, including trichloroethylene, perchloroeth-ylene, 1,1,1-trichloroethane, trichlorotri-fluoroethane, and methylene chloride, do not have a flash point by ASTM flashpoint test methods. They have been shown to be essentially nonflammable under prescribed use conditions. 

Photochemical stability also can play an important role in solvent selection. Ethers are for instance easily attacked by UV light, to form in the presence of oxygen explosive peroxides a well-known industrial hazard. Fully halogenated solvents are on the other hand so stable, that, once evaporated, they remain a long time in the atmosphere without being degraded by sunlight. In this way they indirectly, finally affect the stratosphere ozone layer around the earth. 

Solvent use is controlled by both state and federal regulations. The federal Clean Air Act Amendments of 1990 mandate controls on solvent use in the industry. Almost all organic solvents are classified as Volatile Organic Compounds (VOCs) under Title I of the 1990 Amendments and these regulations will require further reductions in future solvent use. Title III of the 1990 Amendments contains a long list of substances considered Hazardous Air Pollutants (HAPs). Many of the halogenated solvents are on the HAP list. The solvents discussed in this chapter and that are on the HAP list include methylene chloride, chloroform, carbon tetrachloride, 1,1,1-trichloroethane, trichloroethylene, 1,2-dichloroethane, 1,2-dibromoethane, bromoform, and chlorobenzene. The Maximum Achievable Control Technology (MACT) stan-... 

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