Chloral

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Chloral
Chloral Chloral
Identifiers
CAS number 75-87-6 YesY
PubChem 6407
ChemSpider 6167 YesY
UNII FLI06WS32H YesY
EC number 200-911-5
KEGG C14866 YesY
Jmol-3D images Image 1
Properties
Molecular formula C2HCl3O
Molar mass 147.388 g/mol
Appearance colorless, mobile, oily liquid
Odor pungent and irritating
Density 1.404 g/cm3
Melting point −57.5 °C (−71.5 °F; 215.7 K)
Boiling point 97.8 °C (208.0 °F; 370.9 K)
Solubility in water forms soluble hydrate
Solubility in ethanol miscible
Solubility in diethyl ether miscible
Solubility in chloroform miscible
Acidity (pKa) 9.66
Refractive index (nD) 1.45572
Hazards
LD50 480 mg/kg (rat, oral)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Chloral, also known as trichloroacetaldehyde, is the organic compound with the formula Cl3CCHO. This aldehyde is a colourless oily liquid that is soluble in a wide range of solvents. It reacts with water to form chloral hydrate, a once widely used sedative and hypnotic substance.

Production[edit]

Chloral is produced commercially by the chlorination of acetaldehyde in hydrochloric acid, producing chloral hydrate. Ethanol can also be used as a feedstock. This reaction is catalyzed by antimony trichloride:

H3CCHO + 3 Cl2 + H2O → Cl3CCH(OH)2 + 3 HCl

The chloral hydrate is distilled from the reaction mixture. The distillate is then dehydrated with concentrated sulfuric acid, after which the heavier acid layer (containing the water) is drawn off:

Cl3CCH(OH)2 → Cl3CCHO + H2O

The resulting product is purified by fractional distillation.[1] Small amounts of chloral hydrate occur in some chlorinated water.

Key reactions[edit]

Chloral tends to form adducts with water (to give chloral hydrate) and alcohols.

Aside from its tendency to hydrate, chloral is notable as a building block in the synthesis of DDT. For this purpose, chloral is treated with chlorobenzene in the presence of a catalytic amount of sulfuric acid:

Cl3CCHO + 2 C6H5Cl → Cl3CCH(C6H4Cl)2 + H2O

This reaction was described by Othmar Zeidler in 1874.[2] The related herbicide methoxychlor is also produced from chloral.

Treating chloral with sodium hydroxide gives chloroform and sodium formate

Cl3CCHO + NaOH → Cl3CH + HCOONa

Chloral is easily reduced to trichlorethanol, which is produced in the body from chloral.[1]

Safety[edit]

Chloral and chloral hydrate have the same properties biologically since the former hydrates rapidly. Chloral hydrate was routinely administered to patients on the gram scale with no lasting effects. Prolonged exposure to the vapors is unhealthy however, with a LC50 for 4-h exposure of 440 mg/m3.[1]

See also[edit]

References[edit]

  1. ^ a b c Reinhard Jira, Erwin Kopp, Blaine C. McKusick, Gerhard Röderer, Axel Bosch and Gerald Fleischmann "Chloroacetaldehydes" in Ullmann's Encyclopedia of Industrial Chemistry, 2007, Wiley-VCH, Weinheim. doi:10.1002/14356007.a06_527.pub2
  2. ^ Othmar Zeidler (1874). "Verbindungen von Chloral mit Brom- und Chlorbenzol". Berichte der deutschen chemischen Gesellschaft 7 (2): 1180–1181. doi:10.1002/cber.18740070278.