Dichloromethane

Structural formula
Wedge line formula to clarify the geometry
General
Surname	Dichloromethane
other names	Methylene chloride Methylene dichloride R-30 DCM
Molecular formula	CH 2 Cl 2
Brief description	colorless liquid with a sweet odor
External identifiers / databases
CAS number 75-09-2 EC number 200-838-9 ECHA InfoCard 100,000,763 PubChem 6344 Wikidata Q421748
properties
Molar mass	84.93 g mol −1
Physical state	liquid
density	1.33 g cm −3 (20 ° C)
Melting point	−97 ° C
boiling point	40 ° C
Vapor pressure	470 h Pa (20 ° C) 701 hPa (30 ° C) 1016 hPa (40 ° C)
solubility	little in water (20 g l −1 at 20 ° C)
Dipole moment	1.62 D
Refractive index	1.4242 (20 ° C)
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary Caution H and P phrases H: 315-319-335-336-351-373 P: 261-281-305 + 351 + 338
MAK	Switzerland: 50 ml m −3 or 180 mg m −3
Global warming potential	11 (based on 100 years)
Thermodynamic properties
ΔH f 0	−124.2 kJ / mol
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Dichloromethane ( DCM , also methylene chloride ) is an organic chemical compound from the group of chlorinated hydrocarbons with the empirical formula CH ₂ Cl ₂ . Compared to the parent compound methane , two hydrogen atoms are substituted by chlorine atoms .

Presentation and extraction

On an industrial scale, dichloromethane is produced in a radical substitution by direct reaction of methane or chloromethane with chlorine at a temperature of 400–500 ° C. At this temperature, a gradual radical substitution up to carbon tetrachloride takes place:

${\displaystyle {\ce {CH4 + Cl2 -> CH3Cl + HCl}}}$

${\displaystyle {\ce {CH3Cl + Cl2 -> CH2Cl2 + HCl}}}$

${\displaystyle {\ce {CH2Cl2 + Cl2 -> CHCl3 + HCl}}}$

${\displaystyle {\ce {CHCl3 + Cl2 -> CCl4 + HCl}}}$

Methane reacts with chlorine with the formation of hydrogen chloride to form chloromethane, further to dichloromethane, trichloromethane and finally carbon tetrachloride .

The result of the process is a mixture of the four chloromethanes, which can be separated by distillation .

Dichloromethane can be dried by refluxing over phosphorus pentoxide (or drying agents containing phosphorus pentoxide) and subsequent distillation . The storage of dried dichloromethane takes place via a molecular sieve 3 Å = 0.3 nm.

properties

Physical Properties

Dichloromethane is a colorless, hardly inflammable liquid with a melting point of −96.7 ° C. The boiling point at normal pressure is 39.8 ° C. The enthalpy of vaporization is 28.82 kJ / mol. According to Antoine, the vapor pressure function results from log ₁₀ (P) = A− (B / (T + C)) (P in bar, T in K) with A = 4.53691, B = 1327.016 and C = −20.474 in the temperature range from 233 to 313 K. It smells sweet, similar to chloroform . The miscibility with water is limited. As the temperature rises, the solubility of dichloromethane in water decreases or the solubility of water in dichloromethane increases.

Solubilities between dichloromethane and water
temperature	° C	0	9.2	17.3	26.8	35.7
Dichloromethane in water	in%	2.03	1.92	1.80	1.72	1.77
Water in dichloromethane	in%	0.082	0.106	0.135	0.186	0.218

Near-infrared absorption spectrum of dichloromethane with complex, overlapping overtones in the mid-infrared range

Safety-related parameters

Dichloromethane can form flammable vapor-air mixtures. The explosion range is between 13% by volume (450 g / m³) as the lower explosion limit (LEL) and 22% by volume (780 g / m³) as the upper explosion limit (UEL). The lower explosion point is −8 ° C. The maximum explosion pressure is 5.9 bar. However, the connection is very difficult to ignite. This can be seen in the very high minimum ignition energy of 9300 mJ. It was therefore not possible to measure a flash point in air. A flash point of −7 ° C is observed in pure oxygen . The ignition temperature is 605 ° C. The substance therefore falls into temperature class T1. The electrical conductivity is rather low at 4.3 · 10 ⁻⁹  S · m ⁻¹ .

use

The highly volatile dichloromethane dissolves many organic substances and is used, for example, as a solvent for resins , greases , plastics and bitumen .

Dichloromethane is used as paint stripper for paints , degreasers , propellant for aerosols, blowing agents in the production of foams , refrigerants in refrigeration units as well as extracting agent for caffeine , hop extracts and flavorings .

It has long replaced the non-toxic but ozone-depleting refrigerant 1,2-dichloro-1-fluoroethane (R-141) in the manufacture of polyurethane foams . Due to the substitution requirement, most rigid polyurethane foams in Europe today are foamed with water or pentane / cyclopentane .

In laboratory synthesis, dichloromethane is one of the most common solvents in reactions and extractions and is often used as a substitute for the more expensive chloroform , which already tends to form phosgene in air and light .

In model making (e.g. architecture) it is often used as an adhesive due to its ability to connect acrylic glass transparently and quickly without sticking the fingers. It is also used for polystyrene in model making.

In industry, dichloromethane is also often used to loosen plastics and thereby bond them. This includes a variety of thermoplastics such as polystyrene , acrylic glass , polycarbonate , polyethylene terephthalate and acrylonitrile butadiene styrene . Polypropylene and polyethylene cannot be glued with dichloromethane because they are not soluble.

Dichloromethane is used in the "direct process" to decaffeinate coffee .

Because of its low boiling point , dichloromethane can be used in heat engines to generate kinetic energy from small temperature differences. One example is the drinking bird .

Dichloromethane-d ₂

Deuterated dichloromethane (dichloromethane-d ₂ )

Fully deuterated dichloromethane (dichloromethane-d ₂ ) - in which both hydrogen atoms have been exchanged for deuterium - is used as a solvent in NMR spectroscopy .

safety instructions

Dichloromethane is less toxic than other simple organochlorine compounds . However, due to its high volatility , it is a dangerous breath poison .

When liquid dichloromethane is absorbed - also through the skin - symptoms of poisoning such as headache, dizziness , nausea , numbness, irritation of the respiratory tract and eyes, loss of appetite, poor concentration and fatigue up to anesthesia-like conditions and asphyxia occur.

Dichloromethane in the body to carbon monoxide implemented and can lead to carbon monoxide poisoning cause.

Inhalation can damage the optic nerve and cause hepatitis . Prolonged skin contact leads to the dissolution of the fatty tissue in the skin and causes itching and chemical burns .

The vapors are heavier than air. When dichloromethane is burned, the gaseous, highly toxic phosgene can be produced. When dissolved in water, it damages small organisms such as daphnia .

Dichloromethane is suspected of having a carcinogenic effect. In test animals, cancer developed in the lungs, liver, pancreas , mammary gland tissue and salivary gland . Dichloromethane also passes into the placenta .

If you have heart problems, you can trigger arrhythmias and heart attacks. Protective clothing including gloves should be worn when handling dichloromethane. Latex or nitrile gloves are not sufficient. Viton or PVA gloves should be used instead. Butyl gloves should only be used as splash protection, as the breakthrough time is 8 minutes. This compound should be stored in a temperature range of 15 to 25 ° C. Dichloromethane must never come into contact with metallic sodium or other alkali metals , as this can lead to explosions.

Legal situation

The use of dichloromethane in paint strippers was banned by resolution 455/2009 / EC of the European Parliament on May 6, 2009 for private individuals and commercial use. Industry remains an exception to this. This step was preceded by Directive 76/769 / EEC, which was adopted by the new decision in Annex XVII of the REACH regulation . The prerequisite for this guideline in Germany was the adoption of TRGS 612 "Substitute materials, replacement processes and restrictions on use for paint strippers containing dichloromethane".

Statements of the decision 455/2009 / EG

The new regulation as EU law, which applies in all European countries, provides for the following restrictions:

• This affects paint strippers which contain dichloromethane in an amount greater than / equal to 0.1 percent by weight.
• Prohibition of first placing on the market for private individuals or businesses after December 6, 2010.
• Prohibition of supply to private individuals or businesses after December 6, 2011.
• Prohibition of commercial use from June 6, 2012.

This does not apply to businesses that are permitted to continue using dichloromethane-based paint strippers with a special permit. For this purpose, the resolution provides that the individual member states may make special regulations.

Furthermore, since December 6, 2012, all dichloromethane-containing paint strippers must be explicitly labeled for purely industrial use.

Reasons for this decision

With the decision by the European Union to ban paint strippers containing dichloromethane, a major step has been taken towards greater occupational safety. The reasons for this are varied:

• There is no effective respiratory protection that can protect against the inhalation of dichloromethane. Effective respiratory protection can only be provided by breathing apparatus that is independent of the ambient air , which is not found at all in the private sector and only in rare cases in trade.
• Due to the low boiling point of this substance, extremely high concentrations of this chemical are released in the workplace. Measurements in poor conditions in the open air showed that the legal limit values ​​were exceeded five times and indoors even ten times.
• Dichloromethane is suspected to be mutagenic and carcinogenic.
• According to the trade association for the construction industry (BG BAU), 30 people have died in Europe since the start of the use of dichloromethane-containing paint strippers. This is mainly due to the fact that dichloromethane is broken down into carbon monoxide in the body. If the ventilation is poor, there is a risk of suffocation.

Criticism of the new legislation

When using dichloromethane-free paint strippers, the workflow must be adapted, as these work more slowly. But they are problematic on 2K paints and partly on synthetic resin paints. With the alternatives, attention must be paid to the type of paint, as these are not universally effective. In addition, some of these contain other unsafe solvents such as N- methyl-2-pyrrolidone .

Use for decaffeination

For reasons of cost, dichloromethane is often used as an extractant for coffee. This is permitted according to the current law in Germany, but according to the Technical Auxiliaries Ordinance (THV) the residues must not exceed 2 mg / kg of coffee. According to the THV, the permissible limit in drinking water and when used in flavorings in food is 0.2 mg / kg.

environmental Protection

Dichloromethane is a CHC and is therefore completely banned for certain applications in many EU member states and severely restricted in Germany (e.g. when used in laundry detergents and cleaning agents). This is regulated, among other things, in the Reach Regulation from 2010. The environmental aspects of dichloromethane and CHCs are regulated in the ordinance on plants requiring approval (4th BImSchV).

Ozone layer

The Montreal Protocol of September 1987 restricted CFCs that deplete the ozone layer . In 2014 it was recognized that the ozone hole over the Antarctic had not increased in more than 10 years. In 2017, Ryan Hossaini et al. in Nature that the recovery of the ozone layer, which was previously expected by 2050 - except for the level of 1980 - could last until 2080. Dichloromethane is short-lived and is therefore less damaging to the ozone layer, but since its (near-ground) concentration doubled between 2004 and 2014, this is assumed to be the cause of the slow recovery of the ozone layer.

Risk assessment

In 2016, dichloromethane was included in the EU's ongoing action plan ( CoRAP ) in accordance with Regulation (EC) No. 1907/2006 (REACH) as part of substance evaluation . The effects of the substance on human health and the environment are re-evaluated and, if necessary, follow-up measures are initiated. The reasons for the uptake of dichloromethane were concerns regarding high (aggregated) tonnage and the suspected dangers of carcinogenic properties, the possible dangers of mutagenic, reproductive and sensitizing properties and as a potential endocrine disruptor . The re-evaluation has been running since 2016 and is carried out by Italy .

literature

• M. Rossberg; W. Lendle; G. Pfleiderer, A. Tögel; TR Torkelson, KK bag: Chloromethanes , in: Ullmanns Enzyklopädie der Technischen Chemie , Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2012; doi : 10.1002 / 14356007.a06_233.pub3 .

Web links

Commons : Dichloromethane  - Collection of pictures, videos and audio files

• Dichloromethane Fact Sheet in the Australian National Pollutant Inventory

Individual evidence

1. ↑ ^{a b c d e f g h i j k l m n o} Entry on dichloromethane in the GESTIS substance database of the IFA , accessed on March 14, 2018(JavaScript required) .
2. ↑ G. Rippen: Handbook of environmental chemicals. Status: 1990; Loose-leaf collection in 3 folders, 3rd edition, ecomed-Verlagsgesellschaft, Landsberg / Lech, 1991, ISBN 978-3-609-73210-7 .
3. ^ CRC Handbook of Chemistry and Physics , 85th Edition, CRC Press, Boca Raton, 2004.
4. ↑ Dichloromethane data sheet from Sigma-Aldrich , accessed on March 24, 2011 ( PDF ).
5. ↑ Entry on dichloromethane in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
6. ↑ Swiss Accident Insurance Fund (Suva): Limit values ​​- current MAK and BAT values (search for 75-09-2 or dichloromethane ), accessed on November 2, 2015.
7. ↑ G. Myhre, D. Shindell et al .: Climate Change 2013: The Physical Science Basis . Working Group I contribution to the IPCC Fifth Assessment Report. Ed .: Intergovernmental Panel on Climate Change . 2013, Chapter 8: Anthropogenic and Natural Radiative Forcing, pp. 24-39; Table 8.SM.16 ( PDF ).
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9. ^ DR Lide (Editor-in Chief): CRC Handbook of Chemistry and Physics . 73rd edition, Boca Raton 1992.
10. ↑ JM Ganeff, JC Jungers: Tensions de Vapeur du Systeme CH ₃ Cl - CH ₂ Cl ₂ . In: Bull. Soc. Chim. Belg. 57 (1948), 82-87, doi: 10.1002 / bscb.19480570109 .
11. ^ ^{A b} R. M. Stephenson: Mutual Solubilities: Water-Ketones, Water-Ethers, and Water-Gasoline-Alcohols. In: J. Chem. Eng. Data . 37 (1992) 80-95, doi: 10.1021 / je00005a024 .
12. ↑ ^{a b} E. Brandes, W. Möller: Safety-related parameters - Volume 1: Flammable liquids and gases. Wirtschaftsverlag NW - Verlag für neue Wissenschaft GmbH, Bremerhaven 2003.
13. ^ E. Brandes, M. Mitu, D. Pawel: The lower explosion point - A good measure for explosion prevention: Experiment and calculation for pure compounds and some mixtures. In: J. Loss Prev. Proc. Ind. 20 (2007), 536-540, doi : 10.1016 / j.jlp.2007.04.028 .
14. ↑ ^{a b} Technical rule for operational safety - TRBS 2153, BG RCI leaflet T033 Avoidance of ignition hazards due to electrostatic charges , as of April 2009, Jedermann-Verlag Heidelberg.
15. ↑ Kong, D .; at the end, D .; Breneck, SJ; Weston, NP: Determination of flash point in air and pure oxygen using an equilibrium closed bomb apparatus in J. Hazard. Mat. 102 (2003) 155-165, doi : 10.1016 / S0304-3894 (03) 00212-7 .
16. ↑ M. Rossberg; W. Lendle; G. Pfleiderer, A. Tögel; TR Torkelson, KK bag: Chloromethanes , in: Ullmanns Enzyklopädie der Technischen Chemie , Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2012; doi : 10.1002 / 14356007.a06_233.pub3
17. ^ Office of Environmental Health Hazard Assessment: Dichloromethane . In: Public Health Goals for Chemicals in Drinking Water . California Environmental Protection Agency . September 2000  ( page no longer available , search in web archives )
18. ^ Rioux JP, Myers RA: Methylene chloride poisoning: a paradigmatic review . In: J Emerg Med . 6, No. 3, 1988, pp. 227-238. doi : 10.1016 / 0736-4679 (88) 90330-7 . PMID 3049777 .
19. ↑ CDC: Fatal Exposure to Methylene Chloride Among Bathtub Refinishers - United States, 2000-2011 . In: MMWR . 61, No. 07, 2012, pp. 119-122.
20. ↑ Fagin J, Bradley J, Williams D: Carbon monoxide poisoning secondary to inhaling methylene chloride . In: Br Med J . 281, No. 6253, 1980, p. 1461. doi : 10.1136 / bmj.281.6253.1461 . PMID 7437838 . PMC 1714874 (free full text).
21. ↑ Kobayashi A, Ando A, Tagami N, Kitagawa M, Kawai E, Akioka M, Arai E, Nakatani T, Nakano S, Matsui Y, Matsumura M: Severe optic neuropathy caused by dichloromethane inhalation . In: J Ocul Pharmacol and Ther . 24, No. 6, 2008, pp. 607-612. doi : 10.1089 / jop.2007.0100 . PMID 19049266 .
22. ↑ Cordes DH, Brown WD, Quinn KM: Chemically induced hepatitis after inhaling organic solvents . In: West J Med . 148, No. 4, 1988, pp. 458-460. PMID 3388849 . PMC 1026148 (free full text).
23. ^ Wells GG, Waldron HA: Methylene chloride burns . In: Br J Ind Med . 41, No. 3, 1984, p. 420. doi : 10.1136 / oem.41.3.420 . PMID 6743591 . PMC 1009322 (free full text).
24. ↑ USDHHS: Toxicological Profile for Methylene Chloride (PDF) Retrieved September 10, 2006.
25. ↑ "NIOSH Pocket Guide to Chemical Hazards # 0414" . National Institute for Occupational Safety and Health (NIOSH).
26. ^ ^{A b} Ronald M. Hall: Dangers of Bathtub Refinishing . National Institute for Occupational Safety and Health. February 4, 2013. Retrieved January 21, 2015.
27. ↑ Bell BP, Franks P, Hildreth N, Melius J: Methylene chloride exposure and birthweight in Monroe County, New York . In: Environ Res . 55, No. 1, 1991, pp. 31-9. doi : 10.1016 / S0013-9351 (05) 80138-0 . PMID 1855488 .
28. ↑ Expertise: Is it possible without dichloromethane? ( Memento of the original from May 14, 2014 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 862 kB), In: APPLICA. 5/2013, accessed on May 14, 2014. 
29. ↑ Stiftung Warentest: Color Removal - It hardly works without poison , accessed on May 14, 2014.
30. ↑ Stefanie Schramm: Decaffeination: Bush without stimulants. In: zeit.de. May 29, 2012, accessed December 8, 2014 . 
31. ↑ coffee on withdrawal on mpg.de, August 12, 2014 accessed December 8, 2014.
32. ↑ Ordinance on the use of extraction solvents and other technical auxiliaries in the production of food (Technical Auxiliaries Ordinance - THV) of November 8, 1991.
33. ↑ Information center for operational environmental protection Baden-Württemberg: Chlorinated hydrocarbons ( Memento of the original dated May 9, 2016 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed December 8, 2014. 
34. ↑ Regulation (EU) No. 260/2014 (PDF) of the Commission of January 24, 2014 amending Regulation (EC) No. 440/2008 on the definition of test methods in accordance with Regulation (EC) No. 1907/2006 of the European Parliament and the Council for the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) for the purpose of adapting to technical progress.
35. ↑ Why the ozone hole is shrinking more slowly orf.at, June 27, 2017, accessed June 28, 2017.
36. ↑ Ryan Hossaini, Martyn P. Chipperfield, Stephen A. Montzka, Amber A. Leeson, Sandip S. Dhomse & John A. Pyle: The increasing threat to stratospheric ozone from dichloromethane nature, June 27, 2017, accessed June 28, 2017. - English.
37. ↑ Community rolling action plan ( CoRAP ) of the European Chemicals Agency (ECHA): Dichloromethane , accessed on March 26, 2019.