Chemical Properties
Methylene chloride is a colorless liquid with a mild, sweet odor. It does not occur naturally in the environment. It is made from methane gas or wood alcohol. Industrial uses of methylene chloride are extensive, as a solvent in paint strippers, as a propellant in aerosols, and as a process solvent in the manufacturing of drugs. Methylene chloride is also used as a metal cleaning and fi nishing solvent, and it is approved as an extraction solvent for spices and hops. Exposure to methylene chloride occurs in workplaces by breathing fumes from paint strippers that contain it (check the label), breathing fumes from aerosol cans that use it (check the label), and breathing contaminated air near waste sites.
General Description
A colorless liquid with a sweet, penetrating, ether-like odor. Noncombustible by if exposed to high temperatures may emit toxic chloride fumes. Vapors are narcotic in high concentrations. Used as a solvent and paint remover.
Reactivity Profile
DICHLOROMETHANE(75-09-2) reacts vigorously with active metals such as lithium, sodium and potassium, and with strong bases such as potassium tert-butoxide. DICHLOROMETHANE(75-09-2) is incompatible with strong oxidizers, strong caustics and chemically active metals such as aluminum or magnesium powders. The liquid will attack some forms of plastic, rubber and coatings. This compound reacts with sodium-potassium alloy, (potassium hydrogen + N-methyl-N-nitrosurea), nitrogen tetraoxide and liquid oxygen. DICHLOROMETHANE(75-09-2) also reacts with titanium. On contact with water DICHLOROMETHANE(75-09-2) corrodes iron, some stainless steels, copper and nickel. DICHLOROMETHANE(75-09-2) is incompatible with alkali metals. DICHLOROMETHANE(75-09-2) is incompatible with amines, zinc and alloys of aluminum, magnesium and zinc. This compound is liable to explode when mixed with dinitrogen pentaoxide or nitric acid. Mixtures of this compound in air with methanol vapor are flammable.
Air & Water Reactions
Somewhat water soluble. Subject to slow hydrolysis which is accelerated by light.
Hazard
Toxic. A narcotic. Central nervous systemimpairment and carboxyhemoglobinemia. Possiblecarcinogen.
Health Hazard
Exposures to methylene chloride cause adverse health effects and poisoning to users. Methylene chloride harms the human CNS. The symptoms of poisoning include, but are not limited to, dizziness, nausea, tingling, and numbness in the fi ngers and toes. Laboratory animals exposed to very high levels of methylene chloride suffer unconsciousness and fatal injury/death. Occupational workers who are exposed to direct skin contact with methylene chloride indicate symptoms of intense burning and mild redness of the skin, damage to the eyes and cornea.
Health Hazard
INHALATION: anesthetic effects, nausea and drunkenness. CONTACT WITH SKIN AND EYES: skin irritation, irritation of eyes and nose.
Potential Exposure
Methylene chloride is used mainly as
a low-temperature extractant of substances which are
adversely affected by high temperature. It can be used
as a solvent for oil, fats, waxes, bitumen, cellulose acetate;
and esters. It is also used as a paint remover;
as a degreaser; and in aerosol propellants
Fire Hazard
Special Hazards of Combustion Products: Dissociation products generated in a fire may be irritating or toxic.
First aid
If this chemical gets into the eyes, remove any
contact lenses at once and irrigate immediately for at least
15 minutes, occasionally lifting upper and lower lids. Seek
medical attention immediately. If this chemical contacts the
skin, remove contaminated clothing and wash immediately
with soap and water. Seek medical attention immediately.
If this chemical has been inhaled, remove from exposure,
begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR if
heart action has stopped. Transfer promptly to a medical
facility. When this chemical has been swallowed, get medical attention. Give large quantities of water and induce
vomiting. Do not make an unconscious person vomit
Shipping
UN1593Dichloromethane, Hazard Class: 6.1;
Labels: 6.1-Poisonous materials
Incompatibilities
Incompatible with strong oxidizers,
caustics; chemically active metals, such as aluminum,
magnesium powders; potassium, lithium, and sodium;
concentrated nitric acid causing fire and explosion hazard.
Contact with hot surfaces or flames causes decomposition
producing fumes of hydrogen chloride and phosgene gas.
Attacks some forms of plastics, rubber and coatings.
Attacks metals in the presence of moisture.
Description
A colorless liquid with an ethereal, but penetrating odor. Its miscibility in alcohol and ether and slight solubility in water has made
it an ideal solvent and otherwise extremely versatile chemical. It
has been used industrially (solvent and paint remover), as a drug
(inhalation anesthetic) and as an agricultural chemical (growth
regulator and fertilizer). It is narcotic in high concentrations and
carcinogenic.
Waste Disposal
Consult with environmental
regulatory agencies for guidance on acceptable disposal
practices. Generators of waste containing this contaminant (≥100 kg/mo) must conform to EPA regulations
governing storage, transportation, treatment, and waste
disposal. Incineration, preferably after mixing with
another combustible fuel; care must be exercised to
assure complete combustion to prevent the formation
of phosgene; an acid scrubber is necessary to remove the
halo acids produced.
Physical properties
Clear, colorless liquid with a sweet, penetrating, ethereal odor. Leonardos et al. (1969) determined
an odor threshold concentration of 214.0 ppmv. The average least detectable odor threshold
concentrations of technical grade methylene chloride in water at 60 °C and in air at 40 °C were 5.6
and 24 mg/L, respectively (Alexander et al., 1982).
Definition
ChEBI: Dichloromethane is a member of the class of chloromethanes that is methane in which two of the hydrogens have been replaced by chlorine. A dense, non-flammible colourless liquid at room temperature (b.p. 40℃, d = 1.33) which is immiscible with water, it is widely used as a solvent, a paint stripper, and for the removal of caffeine from coffee and tea. It has a role as a polar aprotic solvent, a carcinogenic agent and a refrigerant. It is a member of chloromethanes and a volatile organic compound.
Production Methods
Dichloromethane was first prepared by Regnault in 1840 by the chlorination of methyl chloride in sunlight. It became an industrial chemical of importance during the Second World War. Two commercial processes are currently used for the production of dichloromethane—hydrochlorination of methanol and direct chlorination of methane (Rossberg et al., 1986; Holbrook, 1993).
The predominant method of manufacturing dichloromethane uses as a first step the reaction of hydrogen chloride and methanol to give methyl chloride. Excess methyl chloride is then mixed with chlorine and reacts to give dichloromethane, with chloroform and carbon tetrachloride as co-products. This reaction is usually carried out in the gas phase thermally but can also be performed catalytically or photolytically. At low temperature and high pressure, the liquid-phase process is capable of giving high selectivity for dichloromethane (Rossberg et al., 1986; Holbrook, 1993).
The older and currently less used production method for dichloromethane involves direct reaction of excess methane with chlorine at high temperatures (400–500°C), or at somewhat lower temperatures either catalytically or photolytically. Methyl chloride, chloroform and carbon tetrachloride are also produced as co-products (Rossberg et al., 1986; Holbrook, 1993).
Global production of dichloromethane increased from 93 000 tonnes in 1960 to an estimated 570 000 tonnes in 1980 (IARC, 1986), and is estimated to range from 764 000 to 814 000 tonnes per year from 2005 to 2010 (OECD/SIDS, 2011). In 2009, dichloromethane was produced by 26 manufacturers worldwide and was available from 133 suppliers (NTP, 2011). Production and imports of dichloromethane in the USA totalled 45 000–227 000 tonnes between 1996 and 2006 (NTP, 2011). In the European Union, the total tonnage band for dichloromethane was reported to be 100 000 to 1 000 000 tonnes per year (ECHA, 2016). The production and import of dichloromethane reported in Japan was 58 000 tonnes in 2011 (METI, 2013).
Production Methods
Methylene chloride can be produced by direct chlorination of methane. The usual procedure involves a modification of the simple methane process. The product from the first chlorination passes through aqueous zinc chloride, contacting methanol at about 100 °C.
Reactions
Methylene chloride reacts violently in the presence of alkali or alkaline earth metals and will hydrolyze to formaldehyde in the presence of an aqueous base. Alkylation reactions occur at both functions, thus di-substitutions result.
Flammability and Explosibility
Noncombustible. Dichloromethane vapor concentrated in a confined or poorly ventilated area can be ignited with a high-energy spark, flame, or high-intensity heat source.
Chemical Reactivity
Reactivity with Water No reaction; Reactivity with Common Materials: No reaction; Stability During Transport: Stable; Neutralizing Agents for Acids and Caustics: Not pertinent; Polymerization: Not pertinent; Inhibitor of Polymerization: Not pertinent.
Carcinogenicity
Dichloromethane is reasonably anticipated to be a human carcinogen based on sufficient evidence of carcinogenicity from studies in experimental animals.
Environmental Fate
Biological. Complete microbial degradation to carbon dioxide was reported under anaerobic
conditions by mixed or pure cultures. Under enzymatic conditions formaldehyde was the only
product reported (Vogel et al., 1987). In a static-culture-flask screening test, methylene chloride (5
and 10 mg/L) was statically incubated in the dark at 25 °C with yeast extract and settled domestic
wastewater inoculum. After 7 d, 100% biodegradation with rapid adaptation was observed (Tabak
et al., 1981).
Under aerobic conditions with sewage seed or activated sludge, complete biodegradation was
observed between 6 h to 1 wk (Rittman and McCarty, 1980).
Soil. Methylene chloride undergoes biodegradation in soil under aerobic and anaerobic
conditions. Under aerobic conditions, the following half-lives were reported: 54.8 d in sand (500
ppb); 1.3, 9.4, and 191.4 d at concentrations of 160, 500, and 5,000 ppb, respectively, in sandy
loam soil; 12.7 d (500 ppb) in sandy clay loam soil; 7.2 d (500 ppb) following a 50-d lag time.
Under anaerobic conditions, the half-life of methylene chloride in clay following a 70-d lag time is
21.5 d (Davis and Madsen, 1991). The estimated volatilization half-life of methylene chloride in
soil is 100 d (Jury et al., 1990).
Photolytic. Reported photooxidation products via OH radicals include carbon dioxide, carbon
monoxide, formyl chloride, and phosgene (Spence et al., 1976). In the presence of water, phosgene
hydrolyzes to HCl and carbon dioxide, whereas formyl chloride hydrolyzes to hydrogen chloride
and carbon monoxide (Morrison and Boyd, 1971).
Chemical/Physical. Under laboratory conditions, methylene chloride hydrolyzed with
subsequent oxidation and reduction to produce methyl chloride, methanol, formic acid, and
formaldehyde (Smith and Dragun, 1984). The experimental half-life for hydrolysis in water at 25
°C is approximately 18 months (Dilling et al., 1975).
storage
Color Code—Blue: Health Hazard/Poison: Storein a secure poison location. Prior to working with thischemical you should be trained on its proper handling andstorage. Before entering confined space where this chemicalmay be present, check to make sure that an explosive concentration does not exist. Methylene chloride must be storedto avoid contact with strong oxidizers (such as perchlorates,peroxides, chlorates, nitrates, or permanganates), strongcaustics, and chemically active metals (such as aluminum,magnesium powder, sodium, potassium, or lithium) becauseviolent reactions occur. Store in tightly closed containers ina cool, well-ventilated area away from heat and moisture. Aregulated, marked area should be established where thischemical is handled, used, or stored in compliance withOSHA Standard 1910.1045.
Purification Methods
Shake it with portions of conc H2SO4 until the acid layer remains colourless, then wash with water, aqueous 5% Na2CO3, NaHCO3 or NaOH, then water again. Pre-dry with CaCl2, and distil it from CaSO4, CaH2 or P2O5. Store it away from bright light in a brown bottle with Linde type 4A molecular sieves, in an atmosphere of dry N2. Other purification steps include washing with aqueous Na2S2O3, passage through a column of silica gel, and removal of carbonyl-containing impurities as described under Chloroform. It has also been purified by treatment with basic alumina, distillation, and stored over molecular sieves under nitrogen [Puchot et al. J Am Chem Soc 108 2353 1986]. Dichloromethane from Japanese sources contained MeOH as stabiliser which is not removed by distillation. It can, however, be removed by standing over activated 3A Molecular Sieves (note that 4A Sieves cause the development of pressure in bottles), passed through activated Al2O3 and distilled [Gao et al. J Am Chem Soc 109 5771 1987]. It has been fractionated through a platinum spinning band column, degassed, and distilled onto degassed molecular sieves Linde 4A (heated under high vacuum at over 450o until the pressure readings reached the low values of 10-6 mm, ~1-2hours ). Stabilise it with 0.02% of 2,6-di-tert-butyl-p-cresol [Mohammad & Kosower J Am Chem Soc 93 2713 1971]. [Beilstein 1 IV 35.] Rapid purification: Reflux over CaH2 (5% w/v) and distil it. Store it over 4A molecular sieves.
Toxicity evaluation
Dichloromethane is usually released to the atmosphere. It can
react withhydroxyl radicals with a half-life of about a fewmonths.
Dichloromethane released to water can be evaporated to atmosphere
with a half-life of 35.6 h at moderate mixing conditions.
Some of dichloromethane in water can be biodegraded
completely within several hours and a few days. Small part of
dichloromethane released to water can be degraded by hydrolysis.
However, hydrolysis is not an important process under
natural condition and may take 18 months or more to degrade
completely. Dichloromethane released to soil will go to the soil
surface and then the atmosphere. Some part of dichloromethane
in soil will leak to the groundwater and water cycle.
DCM’s production and use as solvent, chemical intermediate,
grain fumigant, paint stripper and remover,metal degreaser, and
refrigerant may result in its release to the environment through
various waste streams. Vapor-phase DCM is expected to be
degraded in the atmosphere by reaction with photochemically
produced hydroxyl radicals; the half-life for this reaction in air is
estimated to be approximately 119 days (in the absence of direct
photolysis). If released to soil,DCMis expected to have very high mobility based on an estimated Koc of 24. Volatilization
from moist soil surfaces is expected to be an important fate
process based on an estimated Henry’s law constant of
3.25×10-3 atm-m3 mol-1. DCM may volatilize from dry soil
surfaces based on its vapor pressure. Biodegradation in soil may
occur. DCM, when released into water, is not expected to adsorb
to suspended solids and sediment in water based on the estimated
Koc. Biodegradation is possible in natural waters but will
probably be very slow compared with evaporation.
Regulations
Several jurisdictions have acted to reduce the use and release of various volatile organic compounds, including dichloromethane. The California Air Resources Board was one of the first jurisdictions to regulate dichloromethane; in 1995, it limited the levels of total volatile organic compounds (VOCs) contained in aerosol coating products. Subsequent regulations prevented manufacture, sale, supply, or application of any aerosol coating product containing dichloromethane (Air Resources Board, 2001). California has also prohibited the manufacture, sale, or use of automotive cleaning and degreasing products containing dichloromethane.
In Japan, the environmental quality standards for dichloromethane state that outdoor air levels shall not exceed 0.15 mg/m3 (Ministry of the Environment Government of Japan, 2014).
A guideline value of 3 mg/m3 for 24-hour exposure is recommended by WHO. In addition, the weekly average concentration should not exceed one seventh (0.45 mg/m3) of this 24-hour guideline (WHO, 2000).
In the European Union, the VOC Solvent Emissions Directive (Directive 1999/13/EC) was implemented for new and existing installations on 31 October 2007 (European Commission,1999). The Directive aims to reduce industrial emissions of VOCs from solvent-using activities, such as printing, surface cleaning, vehicle coating, dry cleaning, and manufacture of footwear and pharmaceutical products. Installations conducting such activities are required to comply either with emission limit values or with a reduction scheme. Reduction schemes allow the operator to reduce emissions by alternative means, such as by substituting products with a lower solvent content or changing to solvent-free production processes. The Solvents Directive was implemented in 2010 into the Industrial Emission Directive 2010/75/EU (IED).
