Methylene chloride, toxicity

CeUulose triacetate is insoluble in acetone, and other solvent systems are used for dry extmsion, such as chlorinated hydrocarbons (eg, methylene chloride), methyl acetate, acetic acid, dimethylformamide, and dimethyl sulfoxide. Methylene chloride containing 5—15% methanol or ethanol is most often employed. Concerns with the oral toxicity of methylene chloride have led to the recent termination of the only triacetate fiber preparation faciHty in the United States, although manufacture stiH exists elsewhere in the world (49). 

Solubility and Solvent Resistance. The majority of polycarbonates are prepared in methylene chloride solution. Chloroform, i7j -l,2-dichloroethylene, yy -tetrachloroethane, and methylene chloride are the preferred solvents for polycarbonates. The polymer is soluble in chlorobenzene or o-dichlorobenzene when warm, but crystallization may occur at lower temperatures. Methylene chloride is most commonly used because of the high solubiUty of the polymer (350 g/L at 25°C), and because this solvent has low flammabiUty and toxicity. Nonhalogenated solvents include tetrahydrofuran, dioxane, pyridine, and cresols. Hydrocarbons (qv) and aUphatic alcohols, esters (see Esters, organic), or ketones (qv) do not dissolve polycarbonates. Acetone (qv) promotes rapid crystallization of the normally amorphous polymer, and causes catastrophic failure of stressed polycarbonate parts. 

AH volatile organic solvents are toxic to some degree. Excessive vapor inhalation of the volatile chloriaated solveats, and the central nervous system depression that results, is the greatest hazard for iadustrial use of these solvents. Proper protective equipment and operating procedures permit safe use of solvents such as methylene chloride, 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene ia both cold and hot metal-cleaning operations. The toxicity of a solvent cannot be predicted from its chlorine content or chemical stmcture. For example, 1,1,1-trichloroethane is one of the least toxic metal-cleaning solvents and has a recommended threshold limit value (TLV) of 350 ppm. However, the 1,1,2-trichloroethane isomer is one of the more toxic chloriaated hydrocarboas, with a TLV of only 10 ppm. 

Studies in which pregnant rats and mice were exposed to 1250 ppm of methylene chloride for seven hours a day on days 6—15 of gestation indicated no significant maternal, embryonal, or fetal toxicity (34). Methylene chloride was shown to be nonteratogenetic to either animal at the concentration studied. 

The use of CFCs such as fluorotrichloromethane became quite widespread, particularly as for many years the material was believed to cause few toxic and environmental problems. However, evidence that such materials were damaging the ozone layer became substantial and the use of such materials is to be discouraged and is illegal in many countries. To some extent CFCs have been substituted by methylene chloride (also illegal in some countries) and other fluoro compounds, but these too may prove to be environmentally unacceptable. For this reason there has been increased dependence on the use of the isocyanate-water reaction to generate sufficient carbon dioxide to give products of the required density. 

Between 4 and 5 Appear to classify as somewhat less toxic than Group 4. Much less toxic than Group 4 but somewhat more toxic than Group 5. Methylene chloride Ethyl chloride Refrigerant 113... 

Toxic Pollutants (gg/L) Toxic organics Methylene chloride Metals and inorganics 2/2 10-630 — 320... 

Human toxicity values have not been established or have not been published. However, based on available information, this material appears to be more toxic than either methylene chloride or methylene chlorobromide. It is carbon monoxide in the body. 

Burton, D.J. and D.J. Fisher. 1990. Acute toxicity of cadmium, copper, zinc, ammonia, 3,3 -dichlorobenzidine, 2,6-dichloro-4-nitroaniline, methylene chloride, and 2,4,6-trichlorophenol to juvenile grass shrimp and killifish. Bull. Environ. Contam. Toxicol. 44 776-783. 

A new US EPA air pollution ruling will drastically restrict the flexible PU foam industry s use of the auxiliary blowing agent methylene chloride. Methylene chloride has been identified as 98% of the flexible PU foam industry s toxic emissions, and foam facilities have until 7 October 2001 to comply with the new standards. Under a rule from the OSHA, PU foam makers must reduce methylene chloride emissions in the workplace to 25ppm by 10 October 1999. 

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. 

When a solution is tested, both analyte and solvent absorption bands will be present in the spectrum, and identification, if that is the purpose of the experiment, is hindered. Some solvents have rather simple IR spectra and are thus considered more desirable as solvents for qualitative analysis. Examples are carbon tetrachloride (CC14, only C-Cl bonds), choloroform (CHC13), and methylene chloride (CH2C12). The infrared spectra of carbon tetrachloride and methylene chloride are shown in Figure 8.21. There is a problem with toxicity with these solvents, however. For quantitative analysis, such absorption band interference is less of a problem because one needs only to have a single absorption band of the analyte isolated from the other bands. This one band can be the source of the data for the standard curve since the peak absorption increases with increasing concentration (see Section 8.11 and Experiment 25). See Workplace Scene 8.2. 

Unfortunately, lycopene is insoluble in water but soluble in highly toxic hydrophobic organic solvents such as benzene, chloroform, methylene chloride, etc. Moreover, lycopene decomposes easily during the extraction process. 

Alexander, H.C., McCarty, W.M., and Bartlett, E.A. Toxicity of perchloroethylene, trichloroethylene, 1,1,1-trichloroethane, and methylene chloride to fathead minnows, Bull. Environ. Contam. Toxicol, 20(3) 344-352, 1978. 

Chlorinated derivatives of methane include methyl chloride, methylene chloride, chloroform, carbon tetrachloride, and several chlorofluorohydrocarbons (CFCs). We discuss carbon tetrachloride (CT) as a representative example of this group. CT was originally prepared in 1839 and was one of the first organic chemicals to be produced on a large scale by the end of the nineteenth century and beginning of the twentieth century. CT is the most toxic of the chloromethanes and the most unstable on thermal oxidation (Holbrook 2000). 

The toxic pollutants present in raw wastewaters from tire and inner tube manufacturing operations are volatile organic pollutants that are used as degreasing agents in tire production. These toxic pollutants (methylene chloride, toluene, trichloroethylene) were found to be reduced to insignihcant levels across sedimentation ponds. 

Limited animal studies bave suggested that methylene chloride is slightly fetotoxic at doses that also produce maternal toxicity in rats and mice exposed at 12 50 ppm on days 6-15 of gestation, delayed ossification of sternabrae and increased incidence of extra sternabrae were noted, respectively. " ... 

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

Agency for Toxic Substances and Disease Registry (AFSDR) Toxicological Profile for Methylene Chloride (Update). 268pp. US Department of Health and Human Services, Public Health Service, 2000... 

However, CO2 does not always work the best for all analytes. It is not very polar, so in cases where the extracted analyte is polar, small amounts of organic modifiers such as methanol, ethanol, or isopropyl alcohol must be added to increase the polarity of the solvent (142). Methanol is the most commonly used modifier because it is the least toxic of the polar solvents that can be used. Other modifiers are water, acetonitrile, tetrahydrofuran, and methylene chloride. The addition of a small percentage of modifier to the solvent can increase the efficiency of the extraction by 100%. Changes in polarity with small additions of... 

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