Chloroform, or trichloromethane (often abbreviated as TCM), is an organic compound with the formula CHCl3 and a common solvent. It is a very volatile, colorless, strong-smelling, dense liquid produced on a large scale as a precursor to refrigerants and PTFE.[11] Chloroform is a trihalomethane that serves as a powerful anesthetic, euphoriant, anxiolytic, and sedative when inhaled or ingested. Chloroform was used as an anesthetic between the 19th century and the first half of the 20th century.[12][13] It is miscible with many solvents but it is only very slightly soluble in water (only 8 g/L at 20°C).

Chloroform
Chloroform in its liquid state shown in a test tube
Names
Preferred IUPAC name
Trichloromethane
Other names
  • Chloroform[1]
  • Chloroformium
  • Freon 20
  • Methane trichloride
  • Methyl trichloride
  • Methenyl trichloride
  • Methenyl chloride
  • Refrigerant-20
  • terchloride/perchloride of formyle[2][3] (archaic)
  • Trichloretum Formylicum (Latin)
Identifiers
3D model (JSmol)
Abbreviations R-20, TCM
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.603 Edit this at Wikidata
EC Number
  • 200-663-8
KEGG
RTECS number
  • FS9100000
UNII
UN number 1888
  • InChI=1S/CHCl3/c2-1(3)4/h1H checkY
    Key: HEDRZPFGACZZDS-UHFFFAOYSA-N checkY
  • InChI=1/CHCl3/c2-1(3)4/h1H
    Key: HEDRZPFGACZZDS-UHFFFAOYAG
  • ClC(Cl)Cl
Properties
CHCl3
Molar mass 119.37 g·mol−1
Appearance Highly refractive colorless liquid
Odor Sweet, minty, pleasant
Density 1.564 g/cm3 (−20 °C)
1.489 g/cm3 (25 °C)
1.394 g/cm3 (60 °C)
Melting point −63.5 °C (−82.3 °F; 209.7 K)
Boiling point 61.15 °C (142.07 °F; 334.30 K)
decomposes at 450 °C
10.62 g/L (0 °C)
8.09 g/L (20 °C)
7.32 g/L (60 °C)
Solubility Soluble in benzene
Miscible in diethyl ether, oils, ligroin, alcohol, CCl4, CS2
Solubility in acetone ≥ 100 g/L (19 °C)
Solubility in dimethyl sulfoxide ≥ 100 g/L (19 °C)
Vapor pressure 0.62 kPa (−40 °C)
7.89 kPa (0 °C)
25.9 kPa (25 °C)
313 kPa (100 °C)
2.26 MPa (200 °C)
3.67 L·atm/mol (24 °C)
Acidity (pKa) 15.7 (20 °C)
UV-vismax) 250 nm, 260 nm, 280 nm
−59.30·10−6 cm3/mol
Thermal conductivity 0.13 W/(m·K) (20 °C)
1.4459 (20 °C)
Viscosity 0.563 cP (20 °C)
Structure
Tetrahedral
1.15 D
Thermochemistry
114.25 J/(mol·K)
202.9 J/(mol·K)
−134.3 kJ/mol
−71.1 kJ/mol
473.21 kJ/mol
Pharmacology
N01AB02 (WHO)
Hazards[10]
Occupational safety and health (OHS/OSH):
Main hazards
Decomposes to extremely toxic phosgene and hydrogen chloride in presence of light – IARC group 2BReproductive toxicitySpecific target organ toxicity (STOT)[4][5][6]
GHS labelling:
GHS06: Toxic GHS08: Health hazard GHS05: Corrosive
Danger
H302, H315, H319, H331, H336, H351, H361d, H372
P201, P202, P235, P260, P264, P270, P271, P280, P281, P301+P330+P331, P302+P352, P304+P340, P305+P351+P338, P308+P313, P310, P311, P314, P332+P313, P337+P313, P362, P403+P233, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 0: Will not burn. E.g. waterInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no code
2
0
1
Flash point Nonflammable
Lethal dose or concentration (LD, LC):
704 mg/kg (mouse, dermal)[7]
47,702 mg/m3 (rat, 4 hr)[8]
  • 20,000 ppm (guinea pig, 2 hr)
  • 7,056 ppm (cat, 4 hr)
  • 25,000 ppm (human, 5 min)
[9][clarification needed]
NIOSH (US health exposure limits):
PEL (Permissible)
50 ppm (240 mg/m3)[5]
REL (Recommended)
Ca ST 2 ppm (9.78 mg/m3) [60-minute][5]
IDLH (Immediate danger)
500 ppm[5][clarification needed]
Safety data sheet (SDS) [1]
Related compounds
Related compounds
Supplementary data page
Chloroform (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Structure and name edit

The molecule adopts a tetrahedral molecular geometry with C3v symmetry.[14] The chloroform molecule can be viewed as a methane molecule with three hydrogen atoms replaced with three chlorine atoms, leaving a single hydrogen atom.

The name "chloroform" is a portmanteau of terchloride (tertiary chloride, a trichloride) and formyle, an obsolete name for the methylidene radical (CH) derived from formic acid.

Natural occurrence edit

The total global flux of chloroform through the environment is approximately 660000 tonnes per year,[15] and about 90% of emissions are natural in origin. Many kinds of seaweed produce chloroform, and fungi are believed to produce chloroform in soil.[16] Abiotic processes are also believed to contribute to natural chloroform productions in soils, although the mechanism is still unclear.[17]

As chloroform is a volatile organic compound,[18] it dissipates readily from soil and surface water and undergoes degradation in air to produce phosgene, dichloromethane, formyl chloride, carbon monoxide, carbon dioxide, and hydrogen chloride. Its half-life in air ranges from 55 to 620 days. Biodegradation in water and soil is slow. Chloroform does not significantly bioaccumulate in aquatic organisms.[19]

History edit

Chloroform was synthesized independently by several investigators c. 1831:

In 1834, French chemist Jean-Baptiste Dumas determined chloroform's empirical formula and named it:[28] "Es scheint mir also erweisen, dass die von mir analysirte Substanz, … zur Formel hat: C2H2Cl6." (Thus it seems to me to show that the substance I analyzed … has as [its empirical] formula: C2H2Cl6.). [Note: The coefficients of his empirical formula should be halved.] ... "Diess hat mich veranlasst diese Substanz mit dem Namen 'Chloroform' zu belegen." (This had caused me to impose the name "chloroform" upon this substance [i.e., formyl chloride or chloride of formic acid].)

In 1835, Dumas prepared the substance by alkaline cleavage of trichloroacetic acid.

In 1842, Robert Mortimer Glover in London discovered the anaesthetic qualities of chloroform on laboratory animals.[29]

In 1847, Scottish obstetrician James Y. Simpson was the first to demonstrate the anaesthetic properties of chloroform in humans, provided by local pharmacist William Flockhart of Duncan, Flockhart and company,[30] and helped to popularize the drug for use in medicine.[31]

By the 1850s, chloroform was being produced on a commercial basis. In Britain, about 750,000 doses a week were being produced by 1895,[32] using the Liebig procedure, which retained its importance until the 1960s. Today, chloroform – along with dichloromethane – is prepared exclusively and on a massive scale by the chlorination of methane and chloromethane.[11]

Production edit

Industrially, chloroform is produced by heating a mixture of chlorine and either methyl chloride (CH3Cl) or methane (CH4).[11] At 400–500 °C, free radical halogenation occurs, converting these precursors to progressively more chlorinated compounds:

CH4 + Cl2 → CH3Cl + HCl
CH3Cl + Cl2CH2Cl2 + HCl
CH2Cl2 + Cl2 → CHCl3 + HCl

Chloroform undergoes further chlorination to yield carbon tetrachloride (CCl4):

CHCl3 + Cl2 → CCl4 + HCl

The output of this process is a mixture of the four chloromethanes: chloromethane, methylene chloride (dichloromethane), trichloromethane (chloroform), and tetrachloromethane (carbon tetrachloride). These can then be separated by distillation.[11]

Chloroform may also be produced on a small scale via the haloform reaction between acetone and sodium hypochlorite:

3 NaOCl + (CH3)2CO → CHCl3 + 2 NaOH + CH3COONa

Deuterochloroform edit

Deuterated chloroform is an isotopologue of chloroform with a single deuterium atom. CDCl3 is a common solvent used in NMR spectroscopy. Deuterochloroform is produced by the reaction of hexachloroacetone with heavy water.[33] The haloform process is now obsolete for production of ordinary chloroform. Deuterochloroform can also be prepared by reacting sodium deuteroxide with chloral hydrate.[34][35]

Inadvertent formation of chloroform edit

The haloform reaction can also occur inadvertently in domestic settings. Bleaching with hypochlorite generates halogenated compounds in side reactions; chloroform is the main byproduct.[36] Sodium hypochlorite solution (chlorine bleach) mixed with common household liquids such as acetone, methyl ethyl ketone, ethanol, or isopropyl alcohol can produce some chloroform, in addition to other compounds, such as chloroacetone or dichloroacetone.[citation needed]

Uses edit

In terms of scale, the most important reaction of chloroform is with hydrogen fluoride to give monochlorodifluoromethane (HCFC-22), a precursor in the production of polytetrafluoroethylene (Teflon) and other fluoropolymers:[11]

CHCl3 + 2 HF → CHClF2 + 2 HCl

The reaction is conducted in the presence of a catalytic amount of mixed antimony halides. Chlorodifluoromethane is then converted to tetrafluoroethylene, the main precursor of Teflon.[37]

Solvent edit

The hydrogen attached to carbon in chloroform participates in hydrogen bonding,[38][39] making it a good solvent for many materials.

Worldwide, chloroform is also used in pesticide formulations, as a solvent for lipids, rubber, alkaloids, waxes, gutta-percha, and resins, as a cleansing agent, as a grain fumigant, in fire extinguishers, and in the rubber industry.[19][40] CDCl3 is a common solvent used in NMR spectroscopy.[41]

Refrigerant edit

Chloroform is used as a precursor to make R-22 (chlorodifluoromethane). This is done by reacting it with a solution of hydrofluoric acid (HF) which fluorinates the CHCl3 molecule and releases hydrochloric acid as a byproduct.[42] Before the Montreal Protocol was enforced, most of the chloroform produced in the United States was used in the production of chlorodifluoromethane. However, its production remains high, as it is a key precursor of PTFE.[43]

Although chloroform has properties such as a low boiling point, and a low global warming potential of only 31 (compared to the 1760 of R-22), which are appealing properties for a refrigerant, there is little information to suggest that it has seen widespread use as a refrigerant in any consumer products.[44]

Lewis acid edit

In solvents such as CCl4 and alkanes, chloroform hydrogen bonds to a variety of Lewis bases. HCCl3 is classified as a hard acid, and the ECW model lists its acid parameters as EA = 1.56 and CA = 0.44.

Reagent edit

As a reagent, chloroform serves as a source of the dichlorocarbene intermediate CCl2.[45] It reacts with aqueous sodium hydroxide, usually in the presence of a phase transfer catalyst, to produce dichlorocarbene, CCl2.[46][47] This reagent effects ortho-formylation of activated aromatic rings, such as phenols, producing aryl aldehydes in a reaction known as the Reimer–Tiemann reaction. Alternatively, the carbene can be trapped by an alkene to form a cyclopropane derivative. In the Kharasch addition, chloroform forms the •CHCl2 free radical which adds to alkenes.[citation needed]

Anaesthetic edit

 
Antique bottles of chloroform

The anaesthetic qualities of chloroform were first described in 1842 in a thesis by Robert Mortimer Glover, which won the Gold Medal of the Harveian Society for that year.[48][49] Glover also undertook practical experiments on dogs to prove his theories, refined his theories, and presented them in his doctoral thesis at the University of Edinburgh in the summer of 1847.

The Scottish obstetrician James Young Simpson was one of those required to read the thesis, but later claimed to have never read it and to have come to his own conclusions independently.[citation needed] On 4 November 1847, Simpson argued that he had discovered the anaesthetic qualities of chloroform in humans. He and two colleagues entertained themselves by trying the effects of various substances, and thus revealed the potential for chloroform in medical procedures.[30]

A few days later, during the course of a dental procedure in Edinburgh, Francis Brodie Imlach became the first person to use chloroform on a patient in a clinical context.[50]

In May 1848, Robert Halliday Gunning made a presentation to the Medico-Chirurgical Society of Edinburgh following a series of laboratory experiments on rabbits that confirmed Glover's findings and also refuted Simpson's claims of originality. The laboratory experiments that proved the dangers of chloroform were largely ignored.[51]

The use of chloroform during surgery expanded rapidly in Europe; for instance in the 1850s chloroform was used by the physician John Snow during the births of Queen Victoria's last two children.[52] In the United States, chloroform began to replace ether as an anesthetic at the beginning of the 20th century;[citation needed] it was abandoned in favor of ether on discovery of its toxicity, especially its tendency to cause fatal cardiac arrhythmias analogous to what is now termed "sudden sniffer's death". Some people used chloroform as a recreational drug or to attempt suicide.[53] One possible mechanism of action of chloroform is that it increases the movement of potassium ions through certain types of potassium channels in nerve cells.[54] Chloroform could also be mixed with other anaesthetic agents such as ether to make C.E. mixture, or ether and alcohol to make A.C.E. mixture.[citation needed]

In 1848, Hannah Greener, a 15-year-old girl who was having an infected toenail removed, died after being given the anaesthetic.[55] Her autopsy establishing the cause of death was undertaken by John Fife assisted by Robert Mortimer Glover.[29] A number of physically fit patients died after inhaling it. In 1848, however, John Snow developed an inhaler that regulated the dosage and so successfully reduced the number of deaths.[56]

The opponents and supporters of chloroform disagreed on the question of whether the medical complications were due to respiratory disturbance or whether chloroform had a specific effect on the heart. Between 1864 and 1910, numerous commissions in Britain studied chloroform but failed to come to any clear conclusions. It was only in 1911 that Levy proved in experiments with animals that chloroform can cause ventricular fibrillation.[citation needed] Despite this, between 1865 and 1920, chloroform was used in 80 to 95% of all narcoses performed in the UK and German-speaking countries. In Germany, comprehensive surveys of the fatality rate during anaesthesia were made by Gurlt between 1890 and 1897.[citation needed] At the same time in the UK the medical journal The Lancet carried out a questionnaire survey[57] and compiled a report detailing numerous adverse reactions to anesthetics, including chloroform.[58] In 1934, Killian gathered all the statistics compiled until then and found that the chances of suffering fatal complications under ether were between 1:14,000 and 1:28,000, whereas with chloroform the chances were between 1:3,000 and 1:6,000.[citation needed] The rise of gas anaesthesia using nitrous oxide, improved equipment for administering anesthetics, and the discovery of hexobarbital in 1932 led to the gradual decline of chloroform narcosis.[59]

The latest reported anaesthetic use of chloroform in the Western world dates to 1987, when the last doctor who used it retired, about 140 years after its first use.[60]

Criminal use edit

Chloroform has been used by criminals to knock out, daze, or even murder victims. Joseph Harris was charged in 1894 with using chloroform to rob people.[61] Serial killer H. H. Holmes used chloroform overdoses to kill his female victims. In September 1900, chloroform was implicated in the murder of the U.S. businessman William Marsh Rice. Chloroform was deemed a factor in the alleged murder of a woman in 1991, when she was asphyxiated while asleep.[62] In 2002, 13-year-old Kacie Woody was sedated with chloroform when she was abducted by David Fuller and during the time that he had her, before he shot and killed her.[63] In a 2007 plea bargain, a man confessed to using stun guns and chloroform to sexually assault minors.[64]

The use of chloroform as an incapacitating agent has become widely recognized, bordering on cliché, through the adoption by crime fiction authors of plots involving criminals' use of chloroform-soaked rags to render victims unconscious. However, it is nearly impossible to incapacitate someone using chloroform in this way.[65] It takes at least five minutes of inhalation of chloroform to render a person unconscious. Most criminal cases involving chloroform involve co-administration of another drug, such as alcohol or diazepam, or the victim being complicit in its administration. After a person has lost consciousness owing to chloroform inhalation, a continuous volume must be administered, and the chin must be supported to keep the tongue from obstructing the airway, a difficult procedure, typically requiring the skills of an anesthesiologist. In 1865, as a direct result of the criminal reputation chloroform had gained, the medical journal The Lancet offered a "permanent scientific reputation" to anyone who could demonstrate "instantaneous insensibility", i.e. loss of consciousness, using chloroform.[66]

Safety edit

Exposure edit

Chloroform is formed as a by-product of water chlorination, along with a range of other disinfection by-products, and it is therefore often present in municipal tap water and swimming pools. Reported ranges vary considerably, but are generally below the current health standard for total trihalomethanes (THMs) of 100 μg/L.[67] However, when considered in combination with other trihalomethanes often present in drinking water, the concentration of THMs often exceeds the recommended limit of exposure.[68]

While few studies have assessed the risks posed by chloroform exposure through drinking water in isolation from other THMs, many studies have shown that exposure to the general category of THMs, including chloroform, is associated with an increased risk of cancer of the bladder or lower GI tract.[69]

Historically, chloroform exposure may well have been higher, owing to its common use as an anesthetic, as an ingredient in cough syrups, and as a constituent of tobacco smoke, where DDT had previously been used as a fumigant.[70]

Pharmacology edit

Chloroform is well absorbed, metabolized, and eliminated rapidly by mammals after oral, inhalation, or dermal exposure. Accidental splashing into the eyes has caused irritation.[19] Prolonged dermal exposure can result in the development of sores as a result of defatting. Elimination is primarily through the lungs as chloroform and carbon dioxide; less than 1% is excreted in the urine.[40]

Chloroform is metabolized in the liver by the cytochrome P-450 enzymes, by oxidation to chloromethanol and by reduction to the dichloromethyl free radical. Other metabolites of chloroform include hydrochloric acid and diglutathionyl dithiocarbonate, with carbon dioxide as the predominant end-product of metabolism.[71]

Like most other general anesthetics and sedative-hypnotic drugs, chloroform is a positive allosteric modulator at GABAA receptors.[72] Chloroform causes depression of the central nervous system (CNS), ultimately producing deep coma and respiratory center depression.[71] When ingested, chloroform causes symptoms similar to those seen after inhalation. Serious illness has followed ingestion of 7.5 g (0.26 oz). The mean lethal oral dose in an adult is estimated at 45 g (1.6 oz).[19]

The anesthetic use of chloroform has been discontinued, because it caused deaths from respiratory failure and cardiac arrhythmias. Following chloroform-induced anesthesia, some patients suffered nausea, vomiting, hyperthermia, jaundice, and coma owing to hepatic dysfunction. At autopsy, liver necrosis and degeneration have been observed.[19]

Chloroform has induced liver tumors in mice and kidney tumors in mice and rats.[19] The hepatotoxicity and nephrotoxicity of chloroform is thought to be due largely to phosgene, one of its metabolites.[71]

Conversion to phosgene edit

Chloroform converts slowly in the presence of UV light and air to the extremely poisonous gas, phosgene (COCl2), releasing HCl in the process.[73]

2 CHCl3 + O2 → 2 COCl2 + 2 HCl

To prevent accidents, commercial chloroform is stabilized with ethanol or amylene, but samples that have been recovered or dried no longer contain any stabilizer. Amylene has been found to be ineffective, and the phosgene can affect analytes in samples, lipids, and nucleic acids dissolved in or extracted with chloroform.[74] Phosgene and HCl can be removed from chloroform by washing with saturated aqueous carbonate solutions, such as sodium bicarbonate. This procedure is simple and results in harmless products. Phosgene reacts with water to form carbon dioxide and HCl,[75] and the carbonate salt neutralizes the resulting acid.[76]

Suspected samples can be tested for phosgene using filter paper (treated with 5% diphenylamine, 5% dimethylaminobenzaldehyde in ethanol, and then dried), which turns yellow in phosgene vapour. There are several colorimetric and fluorometric reagents for phosgene, and it can also be quantified using mass spectrometry.[77]

Regulation edit

Chloroform is suspected of causing cancer (i.e. it is possibly carcinogenic, IARC Group 2B) as per the International Agency for Research on Cancer (IARC) Monographs.[78]

It is classified as an extremely hazardous substance in the United States, as defined in Section 302 of the US Emergency Planning and Community Right-to-Know Act (42 U.S.C. 11002), and is subject to strict reporting requirements by facilities that produce, store, or use it in significant quantities.[79]

Bioremediation of chloroform edit

Some anaerobic bacteria use chloroform for respiration, termed organohalide respiration, converting it to dichloromethane.[80][81]

Gallery edit

References edit

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    "Es scheint mir also erweisen, dass die von mir analysirte Substance, … zur Formel hat: C2H2Cl6." (Thus it seems to me to show that the substance [that was] analyzed by me … has as [its empirical] formula: C2H2Cl6.) [Note: The coefficients of his empirical formula must be halved.]
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