Dichloromethane reacts vigorously with active metals such as lithium, sodium and potassium, and with strong bases such as potassium tert-butoxide. Dichloromethane 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. Dichloromethane reacts with sodium-potassium alloy, (potassium hydrogen + N-methyl-N-nitrosurea), nitrogen tetraoxide and liquid oxygen. Dichloromethane also reacts with titanium. On contact with water Dichloromethane corrodes iron, some stainless steels, copper and nickel. Dichloromethane is incompatible with alkali metals. Dichloromethane is incompatible with amines, zinc and alloys of aluminum, magnesium and zinc. Dichloromethane is liable to explode when mixed with dinitrogen pentaoxide or nitric acid. Mixtures of Dichloromethane in air with methanol vapor are flammable.
Pharmaceutic aid (solvent).
Special Hazards of Combustion Products: Dissociation products generated in a fire may be irritating or toxic.
Dichloromethane enters the human body mainly through inhalation and can cause anesthetic effects such as damages to the respiratory system and the central nervous system. When being used as a paint remover, DCM has been found to be present in high concentrations in indoor environments. The compound can be exposed to the general population through drinking water, air, and food contact, albeit in much smaller levels. Moreover, it is impossible for the compound to accumulate in the atmosphere due to its photolysis rate. Workers who are engaged in the manufacture of DCM, polycarbonate resin and paint remover formulation are at high risk of exposure.
Hazards & Safety Information
toxicity grade:WHO Class II
acute toxicity:acute peroral LD50 in rats 1600 mg/kg; mouse intraperitoneal LD50: 437 mg/kg
Physiological stimulation:skin-rabbit 810 mg/24hours Severe; eyes-rabbit 500 mg/24hours Mild
Explosive hazard characteristics:Explosive when mixed with air or oxygen
Combustible hazard characteristics:It releases phosgene when heated. Its vapor is non-flammable
transportation and storing characteristics:In ventilated dry storeroom at low temperature, kept apart from oxidizing agent and nitric acid
extinguishant: Foam extinguisher, carbon dioxide, sprayed water, yellow sand.
professional standard: TWA 350 mg/m3;STEL 879 mg/m3.
INHALATION: anesthetic effects, nausea and drunkenness. CONTACT WITH SKIN AND EYES: skin irritation, irritation of eyes and nose.
Also known as methylene chloride, dichloromethane (DCM) is a transparent, colorless, volatile halogenated aliphatic hydrocarbon compound with an ether-like mildly sweet smell. It is moderately soluble in water as well as in most organic solvents namely; ether, ethanol, ketones, aldehydes, and phenols (1). Notably, DCM vapors are heavier than air and are normally non-explosive, stable, and non-flammable when exposed in the air; however, temperatures above 100oC must be avoided. Although natural sources do not largely contribute to the global release of DCM, the latter may lead to the formation of the former.
Purification and dehydration method
Dichloromethane is safer than chloroform. So it is often used instead of chloroform as the extractant Heavier than water. Ordinary dichloromethane generally can be used directly as extractant. If purification is needed, it can be washed with 5% sodium carbonate solution, and then washed with water, and then dried with anhydrous calcium chloride, distillated to collect 40~41℃ distillate and stored in a brown bottle.
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.
Air & Water Reactions
Methylene chloride is a colourless liquid with a mild, sweet odour. Somewhat water soluble. Subject to slow hydrolysis which is accelerated by light.
Methylene chloride reacts strongly with active metals such as potassium, sodium, and lithium, and strong bases, for instance, potassium tert-butoxide. However, the compound is incompatible with strong caustics, strong oxidizers, and metals that are chemically active such as magnesium and aluminum powders.
It is noteworthy that methylene chloride can attack some forms of coatings, plastic, and rubber. In addition, dichloromethane reacts with liquid oxygen, sodium-potassium alloy, and nitrogen tetroxide. When the compound comes into contact with water, it corrodes some stainless steels, nickel, copper as well as iron.
When exposed to heat or water, dichloromethane becomes very sensitive as it is subjected to hydrolysis that is hastened by light. Under normal conditions, solutions of DCM such as acetone or ethanol should be stable for 24 hours.
Methylene chloride does not react with alkali metals, zinc, amines, magnesium, as well as alloys of zinc and aluminum. When mixed with nitric acid or dinitrogen pentoxide, the compound can vigorously explode. Methylene chloride is flammable when mixed with methanol vapor in the air.
Since the compound can explode, it is important to avoid certain conditions such as sparks, hot surfaces, open flames, heat, static discharge, and other ignition sources.
Dichloromethane can be separated by dibutyl phthalate (DBP), then detected by GC with TCD, and quantified by comparison with standard dichloromethane.
Reagents: carrier gas, helium (> 99.5%); carrier for white diatomaceous earth 6201 (40-60 mesh) or equivalent; stationary phase, DBP (in ether); standard dichloromethane, chromatographically pure dichloromethane;
Instruments: a gas chromatograph with TCD, a column, a 3 m x 3 to 4 mm (inner diameter) stainless steel column.
Conditions: fixed phase, 20%:DBP/6021 gasification temperature, 100℃, detection temperature 100℃; carrier gas flow rate, 70ml/min, column temperature of 70 ℃; TCD bridge current, 200mA ~; injection volume, <20μL; temperature. retention time (R) of other chlorinated solvents related to dichloromethane: methyl chloride 0.15; monochloroethane 0.34; 1,1-dichloroethylene 0.59; monochloropropylene, 0.85; carbon tetrachloride 1.86; chloroform 2.47.
ADI gives no specific stipulation (the residual amount of dichloromethane in the products should be minimized as long as the production demand is meet；FAO/WHO。1998)。
House Hold Uses
The compound is used in bathtub refurbishing. Dichloromethane is highly used industrially in the production of pharmaceuticals, strippers, and process solvents.
Industrial and Manufacturing Uses
DCM is a solvent that is found in varnish and paint strippers, which are often used to remove varnish or paint coatings from various surfaces. As a solvent in the pharmaceutical industry, DCM is used for the preparation of cephalosporin and ampicillin.
Food and Beverage Manufacturing
It is also used in manufacturing beverage and food manufacturing as an extraction solvent. For instance, DCM can be used to decaffeinate unroasted coffee beans as well as tea leaves. The compound is also used in creating hops extract for beer, beverages and other flavoring for foods, as well as in processing spices.
DCM is normally used in the degreasing of metal parts and surfaces, such as railroad equipment and tracks as well as airplane components. It can also be used in degreasing and lubricating products utilized in automotive products, for instance, removal of the gasket and for preparing metal parts for a new gasket.
Experts in automotive commonly use vapor dichloromethane degreasing process to for the removal of grease and oils from car parts of car transistor, spacecraft assemblies, aircraft components, and diesel motors. Today, specialists are able to safely and quickly clean transportation systems using degreasing techniques that depend on methylene chloride.
Dichloromethane is used in laboratories in the extraction of chemicals from foods or plants for medicines such as antibiotics, steroids, and vitamins. In addition, medical equipment can be efficiently and quickly cleaned using dichloromethane cleaners while avoiding damage to heat-sensitive parts and corrosion problems.
Methylene chloride is used as a solvent in the production of cellulose triacetate (CTA), which is applied in the creation of safety films in photography. When dissolved in DCM, CTA begins to evaporate as the fibre of acetate remains behind.
Methylene chloride is used in the production of printed circuit boards in the electronic industry. DCM is utilized to degrease the foil surface of the substrate before the photoresist layer is added to the board.