Chloroform
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| Names | |||
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| Preferred IUPAC name
Trichloromethane | |||
| Other names | |||
| Identifiers | |||
3D model (JSmol) |
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| Abbreviations | R-20, TCM | ||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider | |||
| ECHA InfoCard | 100.000.603 | ||
| EC Number |
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| KEGG | |||
PubChem CID |
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| RTECS number |
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| UNII | |||
| UN number | 1888 | ||
CompTox Dashboard (EPA) |
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| 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) | ||
Henry's law constant (kH) |
3.67 L·atm/mol (24 °C) | ||
| Acidity (pKa) | 15.7 (20 °C) | ||
| UV-vis (λmax) | 250 nm, 260 nm, 280 nm | ||
| −59.30·10−6 cm3/mol | |||
| Thermal conductivity | 0.13 W/(m·K) (20 °C) | ||
Refractive index (nD) |
1.4459 (20 °C) | ||
| Viscosity | 0.563 cP (20 °C) | ||
| Structure | |||
| Tetrahedral | |||
| 1.15 D | |||
| Thermochemistry | |||
Heat capacity (C) |
114.25 J/(mol·K) | ||
Std molar entropy (S⦵298) |
202.9 J/(mol·K) | ||
Std enthalpy of formation (ΔfH⦵298) |
−134.3 kJ/mol | ||
Gibbs free energy (ΔfG⦵) |
−71.1 kJ/mol | ||
Std enthalpy of combustion (ΔcH⦵298) |
473.21 kJ/mol | ||
| Pharmacology | |||
| N01AB02 (WHO) | |||
| Hazards[3] | |||
| Occupational safety and health (OHS/OSH): | |||
Main hazards |
Decomposes into phosgene and hydrogen chloride in presence of heat – likely carcinogenic – reproductive toxicity – hepatotoxic[4][5] | ||
| GHS labelling: | |||
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| 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) | |||
| Flash point | Nonflammable | ||
| Lethal dose or concentration (LD, LC): | |||
LD50 (median dose) |
704 mg/kg (mouse, dermal)[6] | ||
LC50 (median concentration) |
47,702 mg/m3 (rat, 4 hr)[7] | ||
LCLo (lowest published) |
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| NIOSH (US health exposure limits): | |||
PEL (Permissible) |
50 ppm (240 mg/m3)[4] | ||
REL (Recommended) |
Ca ST 2 ppm (9.78 mg/m3) [60-minute][4] | ||
IDLH (Immediate danger) |
500 ppm[4] | ||
| Safety data sheet (SDS) | |||
| Related compounds | |||
Related compounds |
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| 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).
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Chloroform,[9] or trichloromethane (often abbreviated as TCM), is an organochloride with the formula CHCl3 and a common solvent. It is a volatile, colorless, sweet-smelling, dense liquid produced on a large scale as a precursor to refrigerants and polytetrafluoroethylene (PTFE).[10] Chloroform was once used as an inhalational anesthetic between the 19th century and the first half of the 20th century.[11][12] It is miscible with many solvents but it is only very slightly soluble in water (only 8 g/L at 20°C).
Structure and name
[edit]The molecule adopts a tetrahedral molecular geometry with C3v symmetry.[13] 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 methylylidene radical (CH) derived from formic acid.[14]
Natural occurrence
[edit]Many kinds of seaweed produce chloroform, and fungi are believed to produce chloroform in soil.[15] Abiotic processes are also believed to contribute to natural chloroform productions in soils, although the mechanism is still unclear.[16]
History
[edit]Chloroform was synthesized independently by several investigators c. 1831:
- Moldenhawer, a German pharmacist from Frankfurt an der Oder, appears to have produced chloroform in 1830 by mixing chlorinated lime with ethanol; however, he mistook it for Chloräther (chloric ether, 1,2-dichloroethane).[17][18]
- Samuel Guthrie, a U.S. physician from Sackets Harbor, New York, also appears to have produced chloroform in 1831 by reacting chlorinated lime with ethanol, and noted its anaesthetic properties; however, he also believed that he had prepared chloric ether.[19][20][21]
- Justus von Liebig carried out the alkaline cleavage of chloral. Liebig incorrectly states that the empirical formula of chloroform was C2Cl5 and named it "Chlorkohlenstoff" ("carbon chloride").[22][23]
- Eugène Soubeiran obtained the compound by the action of chlorine bleach on both ethanol and acetone.[24]
In 1834, French chemist Jean-Baptiste Dumas determined chloroform's empirical formula and named it:[25] "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.[26]
In 1847, Scottish obstetrician James Y. Simpson was the first to demonstrate the anaesthetic properties of chloroform (provided by local pharmacist William Flockhart of Duncan, Flockhart and company,[27]) in humans, and helped to popularize the drug for use in medicine.[28]
The application of chloroform remained dangerous, and many deaths occurred through accidental overdose.[29][30] In 1848, English physician John Snow developed an inhaler that regulated the dosage.[29]
By the 1850s, chloroform was being produced on a commercial basis.[30] An apparatus that could apply it safely and controllably was invented by English physician Joseph Thomas Clover in 1862.[31][32]
In Britain, about 750,000 doses a week were being produced by 1895,[30] 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.[10]
Production
[edit]Industrially, chloroform is produced by heating a mixture of chlorine and either methyl chloride (CH3Cl) or methane (CH4).[10] At 400–500 °C, free radical halogenation occurs, converting these precursors to progressively more chlorinated compounds:
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.[10]
Chloroform may also be produced on a small scale via the haloform reaction between acetone and sodium hypochlorite:
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. 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.[36][37]
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:[10]
- 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.[38]
Solvent
[edit]The hydrogen attached to carbon in chloroform participates in hydrogen bonding,[39][40] 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 cleaning agent, as a grain fumigant, in fire extinguishers, and in the rubber industry.[41][42] CDCl3 is a common solvent used in NMR spectroscopy.[43]
Refrigerant
[edit]Chloroform is used as a precursor to make R-22 (chlorodifluoromethane). This is done by reacting it with hydrofluoric acid (HF) which fluorinates the CHCl3 molecule and releases hydrochloric acid as a byproduct.[44] 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.[45]
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.[46]
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.[47] It reacts with aqueous sodium hydroxide, usually in the presence of a phase transfer catalyst, to produce dichlorocarbene, CCl2.[48][49] 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.[50]
Anaesthetic
[edit]
Chloroform is a powerful general anesthetic, euphoriant, anxiolytic, and sedative when inhaled or ingested. 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.[51][52] Glover also undertook practical experiments on dogs to prove and refine his theories, and subsequently presented them in his doctoral thesis at the University of Edinburgh in the summer of 1847, identifying anaesthetizing halogenous compounds as a "new order of poisonous substances".[51]
The Scottish James Young Simpson, an obstetrician, was one of those examiners required to read the thesis, but later claimed to have never read it and to have come to his own conclusions independently.[51] Perkins-McVey, among others, have raised doubts about the credibility of Simpson's claim, noting that Simpson's publications on the subject in 1847 explicitly echo Glover's and, being one of the thesis examiners, Simpson was likely aware of the content of Glover's study, even if he skirted his duties as an examiner.[51] In 1847 and 1848, Glover would pen a series of heated letters accusing Simpson of stealing his discovery, which had already earned Simpson considerable notoriety.[51] Whatever the source of his inspiration, 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.[27]
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.[53]
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.[54]
The use of chloroform during