Article No : a06_233 Chloromethanes MANFRED ROSSBERG, Hoechst Aktiengesellschaft, Frankfurt/Main, Germany WILHELM LENDLE, Hoechst Aktiengesellschaft, Frankfurt/Main, Germany GERHARD PFLEIDERER, Hoechst Aktiengesellschaft, Frankfurt/Main, Germany ADOLF TO¨ GEL, Hoechst Aktiengesellschaft, Frankfurt/Main, Germany THEODORE R. TORKELSON, Dow Chemical, Midland, Michigan, United States 48674 KLAUS K. BEUTEL, Dow Chemical Europe, Horgen, Switzerland 1. Introduction.......................... 15 5.2. Analysis ............................. 33 2. Physical Properties .................... 16 6. Storage, Transport, and Handling ......... 34 3. Chemical Properties ................... 19 7. Behavior of Chloromethanes 4. Production ........................... 20 in the Environment .................... 35 4.1. Theoretical Bases...................... 20 7.1. Presence in the Atmosphere.............. 35 4.2. Production of Monochloromethane ........ 23 7.2. Presence in Water Sources .............. 36 4.3. Production of Dichloromethane and 8. Uses and Economic Aspects .............. 36 Trichloromethane ..................... 25 9. Toxicology ........................... 37 4.4. Production of Tetrachloromethane ........ 29 References ........................... 39 5. Quality Specifications................... 33 5.1. Purity of the Commercial Products and their Stabilization.......................... 33 1. Introduction methyl chloride by the chlorination of methane occurred before World War I, with the intent of Among the halogenated hydrocarbons, the chlo- hydrolyzing it to methanol. A commercial meth- rine derivatives of methane monochloromethane ane chlorination facility was first put into opera- (methyl chloride) [74-87-3], dichloromethane tion by the former Farbwerke Hoechst in 1923. In (methylene chloride) [75-09-2], trichloro- the meantime, however, a high-pressure metha- methane (chloroform) [67-66-3], and tetrachlor- nol synthesis based on carbon monoxide and omethane (carbon tetrachloride) [56-23-5] play hydrogen had been developed, as a result of an important role from both industrial and eco- which the opposite process became practical – nomic standpoints. These products find broad synthesis of methyl chloride from methanol. application not only as important chemical inter- mediates, but also as solvents. Dichloromethane was prepared for the first time in 1840 by V. REGNAULT, who successfully Historical Development. Monochloro- chlorinated methyl chloride. It was for a time methane was produced for the first time in produced by the reduction of trichloromethane 1835 by J. DUMAS and E. PELIGOT by the reaction (chloroform) with zinc and hydrochloric acid in of sodium chloride with methanol in the presence alcohol, but the compound first acquired signifi- of sulfuric acid. M. BERTHELOT isolated it in 1858 cance as a solvent after it was successfully pre- from the chlorination of marsh gas (methane), as pared commercially by chlorination of methane did C. GROVES in 1874 from the reaction of and monochloromethane (Hoechst AG, Dow hydrogen chloride with methanol in the presence Chemical Co., and Stauffer Chemical Co.). of zinc chloride. For a time, monochloromethane Trichloromethane was synthesized indepen- was produced commercially from betaine hydro- dently by two groups in 1831: J. VON LIEBIG chloride obtained in the course of beet sugar successfully carried out the alkaline cleavage of manufacture. The earliest attempts to produce chloral, whereas M. E. SOUBEIRAIN obtained the Ó 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/14356007.a06_233.pub3 16 Chloromethanes Vol. 9 compound by the action of chlorine bleach on Originally, tetrachloromethane played a role both ethanol and acetone. In 1835, J. DUMAS only in the dry cleaning industry and as a fire showed that trichloromethane contained only a extinguishing agent. Its production increased single hydrogen atom and prepared the substance dramatically, however, with the introduction of by the alkaline cleavage of trichloroacetic acid chlorofluoromethane compounds 50 years ago, and other compounds containing a terminal CCl3 these finding wide application as non-toxic group, such as b-trichloroacetoacrylic acid. In refrigerants, as propellants for aerosols, as analogy to the synthetic method of M. E. SOU- foam-blowing agents, and as specialty solvents. BEIRAIN, the use of hypochlorites was extended to include other compounds containing acetyl groups, particularly acetaldehyde. V. REGNAULT 2. Physical Properties prepared trichloromethane by chlorination of monochloromethane. Already by the middle of The most important physical properties of the the last century, chloroform was being produced four chloro derivatives of methane are presented on a commercial basis by using the J. VON LIEBIG in Table 1; Figure 1 illustrates the vapor pressure procedure, a method which retained its impor- curves of the four chlorinated methanes. tance until ca. the 1960s in places where the The following sections summarize additional preferred starting materials methane and mono- important physical properties of the individual chloromethane were in short supply. Today, tri- compounds making up the chloromethane series. chloromethane – along with dichloromethane – is prepared exclusively and on a massive scale by Monochloromethane is a colorless, flam- the chlorination of methane and/or monochlor- mable gas with a faintly sweet odor. Its solubility omethane. Trichloromethane was introduced in- in water follows Henry’s law; the temperature to the field of medicine in 1847 by J. Y. SIMPSON, dependence of the solubility at 0.1 MPa (1 bar) is: who employed it as an inhaled anaesthetic. As a result of its toxicologic properties, however, it t, C 15304560 has since been totally replaced by other com- gofCH3Cl/kg of H2O 9.0 6.52 4.36 2.64 pounds (e.g., Halothane). Tetrachloromethane was first prepared in 1839 by V. REGNAULT by the chlorination of Monochloromethane at 20 C and 0.1 MPa (1 3 trichloromethane. Shortly thereafter, J. DUMAS bar) is soluble to the extent of 4.723 cm in 100 succeeded in synthesizing it by the chlorination cm3 of benzene, 3.756 cm3 in 100 cm3 of tetra- 3 3 of marsh gas. H. KOLBE isolated tetrachloro- chloromethane, 3.679 cm in 100 cm of acetic methane in 1843 when he treated carbon disulfide acid, and 3.740 cm3 in 100 cm3 of ethanol. It with chlorine in the gas phase. The corresponding forms azeotropic mixtures with dimethyl ether, liquid phase reaction in the presence of a catalyst, 2-methylpropane, and dichlorodifluoromethane giving CCl4 and S2Cl2, was developed a short (CFC 12). time later. The key to economical practicality of this approach was the discovery in 1893 by Dichloromethane is a colorless, highly vol- Mu€LLER and DUBOIS of the reaction of S2Cl2 with atile, neutral liquid with a slightly sweet smell, CS2 to give sulfur and tetrachloromethane, there- similar to that of trichloromethane. The solubility by avoiding the production of S2Cl2. of water in dichloromethane is: Tetrachloromethane is produced on an indus- trial scale by one of two general approaches. The t, C À 30 0 þ 25 first is the methane chlorination process, using gofH2O/kg of CH2Cl2 0.16 0.8 1.98 methane or mono-chloromethane as starting ma- terials. The other involves either perchlorination or chlorinolysis. Starting materials in this case The solubility of dichloromethane in water and include C1 to C3 hydrocarbons and their chlori- in aqueous hydrochloric acid is presented in nated derivatives as well as Cl-containing resi- Table 2. dues obtained in other chlorination processes Dichloromethane forms azeotropic mixtures (vinyl chloride, propylene oxide, etc.). with a number of substances (Table 3). Vol. 9 Chloromethanes 17 Table 1. Physical properties of chloromethanes Unit Monochloromethane Dichloromethane Trichloromethane Tetrachloromethane Formula CH3Cl CH2Cl2 CHCl3 CCl4 Mr 50.49 84.94 119.39 153.84 Melting point C À 97.7 À 96.7 À 63.8 À 22.8 Boiling point at 0.1 MPa C À 23.9 40.2 61.3 76.7 Vapor pressure at 20 C kPa 489 47.3 21.27 11.94 Density of liquid at 20 C kg/m3 920 1328.3 1489 1594.7 (0.5 MPa) Density of vapor at bp kg/m3 2.558 3.406 4.372 5.508 0 Enthalpy of formation DH298 kJ/mol À 86.0 À 124.7 À 132.0 À 138.1 Specific heat capacity of kJ kgÀ1 KÀ1 1.595 1.156 0.980 0.867 liquid at 20 C Enthalpy of vaporization at bp kJ/mol 21.65 28.06 29.7 30.0 Critical temperature K 416.3 510.1 535.6 556.4 Critical pressure MPa 6.68 6.17 5.45 4.55 Cubic expansion coeff. of KÀ1 0.0022 0.00137 0.001399 0.00116 liquid (0 – 40 C) Thermal conductivity at 20 CWKÀ1 mÀ1 0.1570 0.159 0.1454 0.1070 Surface tension at 20 C N/m 16.2 Â 10À3 28.76 Â 10À3 27.14 Â 10À3 26.7 Â 10À3 Viscosity of liquid at 20 CPaÁ s 2.7 Â 10À4 4.37 Â 10À4 5.7 Â 10À4 13.5 Â 10À4 (0.5 MPa) 20 Refractive index nD 1.4244 1.4467 1.4604 Ignition temperature C 618 605 – – Limits of ignition in air, lower vol% 8.1 12 – – Limits of ignition in air, upper vol% 17.2 22 – – mg=LðairÞ Partition coefficient air/water mg=LðwaterÞ 0.3 0.12 0.12 0.91 at 20 C Dichloromethane is virtually nonflammable the definitions established in DIN 51 755 and in air, as shown in Figure 2, which illustrates the ASTM 56–70 as well as DIN 51 758 and ASTM D range of flammable mixtures with oxygen – 93–73. Thus, it is not subject to the regulations nitrogen combinations [10, 11]. Dichloromethane governing flammable liquids. As a result of the thereby constitutes the only nonflammable com- existing limits of flammability (CH2Cl2 vapor/ mercial solvent with a low boiling point. The air), it is assigned to explosion category G 1 (VDE substance possesses no flash point according to 0165). The addition of small amounts of dichlor- omethane to flammable liquids (e.g., gasoline, esters, benzene, etc.) raises their flash points; addition of 10 – 30 % dichloromethane can render such mixtures nonflammable. Trichloromethane is a colorless, highly volatile, neutral liquid with a characteristic sweet odor.