ДИХЛОРМЕТАН

Описание

Метилен хлористый (дихлорметан) принадлежит к классу галогеноалканов, наиболее безопасный среди них. Представляет собой бесцветную легколетучая и легкоподвижную жидкость, летучий жидкий хлорированный углеводород. Имеет характерный едкий сладковатый запах, схожий с запахом эфира. Дихлорметан является членом класса хлорметанов, то есть метана, в котором два атома водорода заменены хлором. В 1840 году был впервые синтезирован способом выдерживания смеси хлора с хлористым метилом на свету. Негорючий но при воздействии высоких температур может выделять токсичные пары хлорида.

Описание

Dichloromethane is 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. Inhalation exposure to this substance irritates the nose and throat and affects the central nervous system.

Химические свойства

Dichloromethane 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 dichloromethane are extensive, as a solvent in paint strippers, as a propellant in aerosols, and as a process solvent in the manufacturing of drugs. dichloromethane 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 dichloromethane 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.

Физические свойства

Clear, colorless liquid with a sweet, penetrating, ethereal odor. Leonardos et al. (1969) determined an odor threshold concentration of 214.0 ppm_v. 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).

Использование

Dichloromethane, also called methylene chloride, is widely used as a solvent, as a degreasing and cleaning reagent, in paint removers, and in extractions oforganic compounds from water for analyses.

Методы производства

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).

Реакции

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.

Использование

Широко используется в качестве растворителя и средства для удаления краски.
В пищевой промышленности его используют для приготовления быстрорастворимого кофе, чая, удаления кофеина из кофе.
Используется в аэрозольных составах, в качестве растворителя при производстве фармацевтических препаратов.
Обезжириватель в производстве электроники.
Растворитель для проведения реакций, экстракций, в том числе и в лабораториях.
Применяется для растворения смол, жиров и битума.
Используется в хроматографии.
Растворитель для большинства пластиков, используемых в 3Д печати.

Общее описание

Dichloromethane has been tested as a solvent medium for the dipyridine-chromium(VI) oxide. Solubility was reported to be 12.5g/100ml. Role of quantity of TiO₂ loading on activated carbon support employed in the photodecomposition of dichloromethane has been investigated.

Реакции воздуха и воды

Methylene chloride is a colourless liquid with a mild, sweet odour. Somewhat water soluble. Subject to slow hydrolysis which is accelerated by light.

Профиль реактивности

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.

Опасность

Toxic. A narcotic. Central nervous systemimpairment and carboxyhemoglobinemia. Possiblecarcinogen.

Угроза здоровью

Dichloromethane is classified as only slightly toxic by the oral and inhalation routes. Exposure to high concentrations of dichloromethane vapor (>500 ppm for 8 h) can lead to lightheadedness, fatigue, weakness, and nausea. Contact of the compound with the eyes causes painful irritation and can lead to conjunctivitis and corneal injury if not promptly removed by washing. Dichloromethane is a mild skin irritant, and upon prolonged contact (e.g., under the cover of clothing or shoes) can cause burns after 30 to 60 min exposure. Dichloromethane is not teratogenic at levels up to 4500 ppm or embryotoxic in rats and mice at levels up to 1250 ppm.

Пожароопасность

Special Hazards of Combustion Products: Dissociation products generated in a fire may be irritating or toxic.

Воспламеняемость и взрывоопасность

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.

Химическая реактивность

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.

Профиль безопасности

Confirmed carcinogen with experimental carcinogenic and tumorigenic data. Poison by intravenous route. Moderately toxic by ingestion, subcutaneous, and intraperitoneal routes. Mildly toxic by inhalation. Human systemic effects by ingestion and inhalation: paresthesia, somnolence, altered sleep time, convulsions, euphoria, and change in cardlac rate. An experimental teratogen. Experimental reproductive effects. An eye and severe skin irritant. Human mutation data reported. It is flammable in the range of 12-19% in air but ignition is difficult. It will not form explosive mixtures with air at ordinary temperatures. Mixtures in air with methanol vapor are flammable. It will form explosive mixtures with an atmosphere having a high oxygen content, in liquid O2, N2O4, K, Na, NaK. Explosive in the form of vapor when exposed to heat or flame. Reacts violently with Li, NaK, potassiumtert- butoxide, (KOH + N-methyl-Nnitrosourea). It can be decomposed by contact with hot surfaces and open flame, and then yield toxic fumes that are irritating and give warning of their presence. When heated to decomposition it emits highly toxic fumes of phosgene and Cl-.

Возможный контакт

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

Угроза здоровью

Хотя он и является наименее ядовитым среди галогеналканов, но нужно быть осторожным при обращении, так как он очень летуч и может вызвать острое отравление. Работы следует проводить при работающей вытяжной вентиляции.
В организме дихлорметан метаболизируется до монооксида углерода, что может вызвать отравление им. Длительный покровный контакт с дихлорметаном может вызвать его накопление в жировых тканях и привести к ожогу. Также при длительной работе с ним возможно поражение печени и нейропатия.
В Евросоюзе запрещены краски с дихлорметаном как для личного пользования, так и для профессонального применения.
Для регулярной работы с дихлорметаном не подходят перчатки из латекса или нитриловые.
Контакт дихлорметана с щелочными металлами приводит к взрыву.

Канцерогенность

Dichloromethane is reasonably anticipated to be a human carcinogen based on sufficient evidence of carcinogenicity from studies in experimental animals.

Перевозки

UN1593Dichloromethane, Hazard Class: 6.1; Labels: 6.1-Poisonous materials

Методы очистки

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.

Несовместимости

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.

Утилизация отходов

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.