Chloromethane

Structural formula
Wedge line formula to clarify the geometry
General
Surname	Chloromethane
other names	Methyl chloride Monochloromethane R-40
Molecular formula	CH 3 Cl
Brief description	colorless, ethereal-smelling gas
External identifiers / databases
CAS number 74-87-3 EC number 200-817-4 ECHA InfoCard 100,000,744 PubChem 6327 Wikidata Q422709
properties
Molar mass	50.49 g mol −1
Physical state	gaseous
density	2.3065 g l −1 (0 ° C, 1013 mbar) 1.003 kg l −1 (at boiling point) 2.151 kg m −3 (15 ° C)
Melting point	−97.4 ° C
boiling point	−23.8 ° C
Vapor pressure	490 k Pa (20 ° C) 660 kPa (30 ° C) 1090 kPa (50 ° C)
solubility	poor in water (5 g l −1 at 20 ° C)
Dipole moment	1.892 D (6.31 * 10 -30  C  *  m )
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 220-280-351-361-373 P: 202-210-260-281-314-377-235 + 410-403
MAK	DFG : 50 ml m −3 or 100 mg m −3 Switzerland: 50 ml m −3 or 105 mg m −3
Global warming potential	15 (based on 100 years)
Thermodynamic properties
ΔH f 0	−81.9 kJ / mol
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Methyl chloride or chloromethane is a colorless , slightly sweet smelling, harmful and easily flammable gas .

Occurrence

Methyl chloride is the most abundant chlorine-containing compound in the atmosphere. In addition to the industrial sources, natural emissions from evergreen trees, but also from other plants such as potatoes, contribute to significant quantities.

Extraction

Chloromethane can be produced by heating chlorine and methane to 400–500 ° C. At this temperature a gradual radical substitution up to carbon tetrachloride takes place. All reaction steps are exothermic.

${\displaystyle \mathrm {CH_{4}+Cl_{2}\longrightarrow CH_{3}Cl+HCl} }$with Δ _R H = −103.5 kJ mol ⁻¹

${\displaystyle \mathrm {CH_{3}Cl+Cl_{2}\longrightarrow CH_{2}Cl_{2}+HCl} }$with Δ _R H = −102.5 kJ mol ⁻¹

${\displaystyle \mathrm {CH_{2}Cl_{2}+Cl_{2}\longrightarrow CHCl_{3}+HCl} }$with Δ _R H = −99.2 kJ mol ⁻¹

${\displaystyle \mathrm {CHCl_{3}+Cl_{2}\longrightarrow CCl_{4}+HCl} }$with Δ _R H = −94.8 kJ mol ⁻¹

Methane reacts with chlorine to form hydrogen chloride first to form chloromethane, and then to dichloromethane , trichloromethane ( chloroform ) and finally carbon tetrachloride .

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

A second technical process is methanol hydrochlorination, i. H. Methanol is reacted with hydrogen chloride to form chloromethane. The reaction takes place catalysed in the gas or liquid phase. The reaction is slightly exothermic.

${\displaystyle \mathrm {CH_{3}OH+HCl\longrightarrow CH_{3}Cl+H_{2}O} }$with Δ _R H = −33 kJ mol ⁻¹

properties

Physical Properties

Chloromethane is a colorless gas. According to Antoine, the vapor pressure function results from log ₁₀ (P) = A− (B / (T + C)) (P in kPa, T in K) with A = 6.9, B = 1449 and C = 48 in the temperature range of 308 to 373 K. The critical temperature is 143 ° C, the critical pressure 66.7 bar and the critical density 0.353 g · cm ⁻³ . The miscibility with water is limited. The solubility of chloromethane in water decreases with increasing temperature.

Solubility of chloromethane in water
temperature	° C	0	10	20th	30th	40	50	60	70	80	90	100
Chloromethane in water	in%	3.42	3.19	3.01	2.88	2.79	2.72	2.68	2.66	2.67	2.69	2.73

Chemical properties

Chloromethane and water form a snow-like solid gas hydrate with the composition CH ₃ Cl · 6H ₂ O, which breaks down to its components at 7.5 ° C and normal pressure . Slow hydrolysis takes place in water at room temperature, which is significantly accelerated in the presence of bases. Mineral acids have no effect on the rate of hydrolysis. Corresponding organometallic compounds are formed with alkali or alkaline earth metals as well as zinc and aluminum .

${\displaystyle \mathrm {CH_{3}Cl+Mg\rightarrow CH_{3}MgCl} }$

${\displaystyle \mathrm {3\,CH_{3}Cl+2\,Al\rightarrow Al(CH_{3})_{3}*AlCl_{3}} }$

The reaction with a sodium-lead amalgam leads to the formation of tetramethyl lead .

${\displaystyle \mathrm {4\,CH_{3}Cl+Pb\rightarrow Pb(CH_{3})_{4}} }$

The reaction with silicon , known as the Müller-Rochow synthesis, produces the methylchlorosilanes. The corresponding methylamines are formed as methylation reagents with ammonia and amines . Similarly, the reaction with compounds containing hydroxyl groups leads to the corresponding methyl ethers, such as, for example, the production of methyl cellulose from cellulose .

Safety-related parameters

The compound forms highly flammable gas-air mixtures. The explosion range is between 7.6% by volume (160 g / m ³ ) as the lower explosion limit (LEL) and 19% by volume (410 g / m ³ ) as the upper explosion limit (UEL). The limit gap width was determined to be 1 mm (50 ° C). This results in an assignment to explosion group IIA. The ignition temperature is 625 ° C. The substance therefore falls into temperature class T1.

use

Chloromethane is used as a methylating agent in organic chemistry, as a polymerization medium for butyl rubber (liquefied at approx. −90 ° C), for the etherification of alcohols and phenols, and in silicone production. Its high evaporation heat also enables it to be used as a refrigerant . It used to be used for anesthesia , but also as a local cold anesthetic .

Toxicity and Risk Assessment

The anesthetic gas triggers central nervous system disorders and damages the liver , kidneys and heart . Methyl chloride is considered a substance with justified suspicion of carcinogenic potential and damage to the fetus.

In 2012, chloromethane 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 chloromethane were concerns about its classification as a CMR substance, high risk characterization ratio (RCR) and as a potential endocrine disruptor . The re-evaluation took place from 2012 and was carried out by Italy . A final report was then published.

literature

• Ohligschläger et al. (2020): Chloromethanes , in: Ullmann's Enzyklopädie der Technischen Chemie , Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim doi : 10.1002 / 14356007.a06_233.pub4 .
• Marshall, KA and Pottenger, LH (2016). Chlorocarbons and Chlorohydrocarbons. In Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley & Sons, Inc (Ed.). doi: 10.1002 / 0471238961.1921182218050504.a01.pub3

Web links

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

• Gordon W. Gribble: Environmental toxins from the gift table of nature . In: Spectrum of Science June 2005, p. 38ff; PDF
• ESO : ALMA and Rosetta expose Freon-40 in space after October 2, 2017

Individual evidence

1. ↑ ^{a b c d e f g h i j k l m} Entry on chloromethane in the GESTIS substance database of the IFA , accessed on July 31, 2020(JavaScript required) .
2. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Permittivity (Dielectric Constant) of Gases, pp. 6-188.
3. ↑ Entry on chloromethanes 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 .
4. ↑ Swiss Accident Insurance Fund (Suva): Limit values ​​- current MAK and BAT values (search for 74-87-3 or chloromethane ), accessed on May 14, 2020.
5. ↑ 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 ).
6. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Standard Thermodynamic Properties of Chemical Substances, pp. 5-20.
7. ↑ Gordon W. Gribble: Environmental poisons from the gift table of nature . In: Spectrum of Science June 2005, p. 38ff; PDF
8. ↑ ^{a b c d} M. Rossberg, W. Lendle, G. Pfleiderer, A. Tögel, TR Torkelson, KK bag: Chlormethanes , in: Ullmanns Enzyklopädie der Technischen Chemie , Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2012; doi : 10.1002 / 14356007.a06_233.pub3 .
9. ↑ ^{a b c} André Ohligschläger, Katharina Menzel, Antoon Ten Kate, Javier Ruiz Martinez, Christoph Frömbgen: Chloromethanes . In: Ullmann's Encyclopedia of Industrial Chemistry . Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany 2019, ISBN 978-3-527-30673-2 , pp. 1–31 , doi : 10.1002 / 14356007.a06_233.pub4 ( wiley.com [accessed July 30, 2020]).
10. ↑ ^{a b c d e f} E. Brandes, W. Möller: Safety-related parameters - Volume 1: Flammable liquids and gases , Wirtschaftsverlag NW - Verlag für neue Wissenschaft GmbH, Bremerhaven 2003.
11. ↑ European Chemicals Agency (ECHA): Substance Evaluation Conclusion and Evaluation Report .
12. ↑ Community rolling action plan ( CoRAP ) of the European Chemicals Agency (ECHA): Chloromethane , accessed on March 26, 2019.