Dichloromethane toxicity

Dichloromethane toxic, carcinogenic in animals, harmful vapour, skin irritant... 

Distilled water Hexane [FLAMMABLE] Dichloromethane [TOXIC]... 

One of the chief uses of chloromethane is as a starting material from which sili cone polymers are made Dichloromethane is widely used as a paint stripper Trichloromethane was once used as an inhalation anesthetic but its toxicity caused it to be replaced by safer materials many years ago Tetrachloromethane is the starting mate rial for the preparation of several chlorofluorocarbons (CFCs) at one time widely used as refrigerant gases Most of the world s industrialized nations have agreed to phase out all uses of CFCs because these compounds have been implicated m atmospheric processes that degrade the Earth s ozone layer... 

These incombustible substances are halogenous derivatives whose extinction properties are well known and some molecules were used as extinction agents before it was realised they were toxic. Paint stripper containing methanoi and dichloromethane... 

So acrylic acid would bear R25 (LD50 o-n 34 mg/kg) R22 (LD50 o-r 235 340 353 355) or no code (LD50 o-r 2590). Benzene, toluene, 1-propanol, dichloromethane, etc., can be either R22 or have no code by ingestion depending on the values (labour regulations actually chose not to allocate any acute toxicity code to them). 

There is an anomaly in the higher index value for dichloromethane compared with chloroform although dichloromethane is noted for being the less toxicity halogenous solvent. But this figure only reflects the extreme volatility of this substance since its LC50 is lower than the one for chloroform. There is probably a similar problem for acetonitrile, which is underestimated by this approach. 

The main drawback to this reaction is the toxicity of diazomethane and some of its precursors. Diazomethane is also potentially explosive. Trimethylsilyldia-zomethane is an alternative reagent,42 which is safer and frequently used in preparation of methyl esters from carboxylic acids.43 Trimethylsilyldiazomethane also O-methylates alcohols.44 The latter reactions occur in the presence of fluoroboric acid in dichloromethane. 

The most industrially significant polymerizations involving the cationic chain growth mechanism are the various polymerizations and copolymerizations of isobutylene. In fact, about 500 million pounds of butyl rubber, a copolymer of isobutylene with small amounts of isoprene, are produced annually in the United States via cationic polymerization [126]. The necessity of using toxic chlorinated hydrocarbon solvents such as dichloromethane or methyl chloride as well as the need to conduct these polymerizations at very low temperatures constitute two major drawbacks to the current industrial method for polymerizing isobutylene which may be solved through the use of C02 as the continuous phase. 

Methylene chloride This solvent is a slightly polar solvent also known as dichloromethane, CH2C12. Its solubility in water is 1.32 g/100 mL. It is denser than water (density = 1.33 g/mL) thus it would be the bottom layer when used with a water solution in a separatory funnel. It may form an emulsion when shaken in a separatory funnel with water solutions. It is not flammable and is considered to have a low toxicity level. 

Passino-Reader, D.R., Hickey, J.P., and Ogilvie, L.M. Toxicity to Daphnia pulexmA QSAR predictions for polycyclic hydrocarbons representative of Great Lakes contaminants. Bull. Environ. Contam. Toxicol, 59(5) 834-840, 1997. Pathare, S., Bhethanabotla, V.R., and Campbell, S.W. Total vapor-pressure measurements for 2-ethoxyethanol with carbon tetrachloride, chloroform, and dichloromethane at 303.15 K, J. Chem. Eng. Data, 49(3) 510-513, 2004. 

Illing HPA, Shillaker RO Toxicity Review 12. Dichloromethane (Methylene Chloride). Health and Safety Executive, 87pp. London, Her Majesty s Stationery Office, 1985... 

In recent years, much effort has been spent on developing both selective and environmentally friendly oxidation methods using either air or oxygen as the ultimate, oxidant. One of the most selective and efficient catalyst systems reported to date is based on the use of stable nitroxyl radicals as catalysts and transition metal salts as co-catalysts (15). The most commonly used co-catalysts are (NH4)2Ce(N03)6 (16), CuBr2-2,2 -bipiridine complex (17), RuCl2(PPh3)3 (18,19), Mn(N03)2-Co(N03)2 and Mn(N03)2-Cu(N03)2 (20). However, from an economic and environmental point of view, these oxidation methods suffer from one common drawback. They depend on substantial amounts of expensive and/or toxic transition metal complexes and some of them require the use of halogenated solvents like dichloromethane, which makes them unsuitable for industrial scale production. 

Very recently, Hu et al. claimed to have discovered a convenient procedure for the aerobic oxidation of primary and secondary alcohols utilizing a TEMPO based catalyst system free of any transition metal co-catalyst (21). These authors employed a mixture of TEMPO (1 mol%), sodium nitrite (4-8 mol%) and bromine (4 mol%) as an active catalyst system. The oxidation took place at temperatures between 80-100 °C and at air pressure of 4 bars. However, this process was only successful with activated alcohols. With benzyl alcohol, quantitative conversion to benzaldehyde was achieved after a 1-2 hour reaction. With non-activated aliphatic alcohols (such as 1-octanol) or cyclic alcohols (cyclohexanol), the air pressure needed to be raised to 9 bar and a 4-5 hour of reaction was necessary to reach complete conversion. Unfortunately, this new oxidation procedure also depends on the use of dichloromethane as a solvent. In addition, the elemental bromine used as a cocatalyst is rather difficult to handle on a technical scale because of its high vapor pressure, toxicity and severe corrosion problems. Other disadvantages of this system are the rather low substrate concentration in the solvent and the observed formation of bromination by-products. 

Dichloromethane is also formed during water chlorination and is emitted into the air from wastewater in treatment plants (Agency for Toxic Substances and Disease Registry, 1993). 

About 2% of environmental releases of dichloromethane are to water. Industrial releases of dichloromethane to surface water and underground injection (potential ground-water release) reported to the United States Toxic Chemical Release Inventory in 1988 totalled 158 tonnes. Dichloromethane has been identified in industrial and municipal waste-waters from several sources at concentrations ranging from 0.08 pg/L to 3.4 g/L (Agency for Toxic Substances and Disease Registry, 1993 WHO, 1996). 

Dichloromethane has been detected in surface water, groundwater and finished drinking-water throughout the United States. It was detected in 30% of 8917 surface water samples recorded in the STORET database of the United States Environmental Protection Agency, at a median concentration of 0.1 pg/L. In a New Jersey survey, dichloromethane was found in 45% of 605 surface water samples, with a maximum concentration of 743 pg/L. Dichloromethane has also been identified in surface waters in Maryland, in Lakes Erie and Michigan, and at hazardous waste sites (Agency for Toxic Substances and Disease Registry, 1993 WHO, 1996). 

Since volatilization is restricted in groundwater, concentrations of dichloromethane are often higher there than in surface water. Occurrence of dichloromethane in ground-water has been reported in several surveys across the United States, with concentrations ranging from 0 to 3600 pg/L (Agency for Toxic Substances and Disease Registry, 1993). 

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