Chloral, also known as trichloroacetaldehyde or trichloroethanal, is the

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

with the formula Cl₃CCHO. This

aldehyde In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...

is a colourless liquid that is soluble in a wide range of solvents. It reacts with water to form

chloral hydrate Chloral hydrate is a geminal diol with the formula . It was first used as a sedative and hypnotic in Germany in the 1870s. Over time it was replaced by safer and more effective alternatives but it remained in use in the United States until at ...

, a once widely used

sedative A sedative or tranquilliser is a substance that induces sedation by reducing irritability or Psychomotor agitation, excitement. They are central nervous system (CNS) Depressant, depressants and interact with brain activity, causing its decelera ...

and

hypnotic A hypnotic (from Ancient Greek, Greek ''Hypnos'', sleep), also known as a somnifacient or soporific, and commonly known as sleeping pills, are a class of psychoactive drugs whose primary function is to sleep induction, induce sleep and to trea ...

substance.

Production

Chloral was first prepared, and named, by the German chemist

Justus von Liebig Justus ''Freiherr'' von Liebig (12 May 1803 – 18 April 1873) was a Germans, German scientist who made major contributions to the theory, practice, and pedagogy of chemistry, as well as to agricultural and biology, biological chemistry; he is ...

in 1832. Liebig treated anhydrous ethanol with dry chlorine gas. Chloral is produced commercially by the chlorination of

acetaldehyde Acetaldehyde (IUPAC systematic name ethanal) is an organic compound, organic chemical compound with the chemical formula, formula , sometimes abbreviated as . It is a colorless liquid or gas, boiling near room temperature. It is one of the most ...

in the presence of hydrochloric acid, producing

. Ethanol can also be used as a feedstock. This reaction is catalyzed by

antimony trichloride Antimony trichloride is the chemical compound with the formula SbCl3. It is a soft colorless solid with a pungent odor and was known to alchemists as butter of antimony. Preparation Antimony trichloride is prepared by reaction of chlorine with a ...

: :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 Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

, 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. Small amounts of chloral hydrate occur in some chlorinated water.

Key reactions

Chloral tends to form

adducts In chemistry, an adduct (; alternatively, a contraction of "addition product") is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all components. The resultant is ...

with water (to give

) and alcohols. Aside from its tendency to hydrate, chloral is notable as a building block in the synthesis of

DDT Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochloride. Originally developed as an insecticide, it became infamous for its environmental impacts. ...

. For this purpose, chloral is treated with

chlorobenzene Chlorobenzene (abbreviated PhCl) is an aryl chloride and the simplest of the chlorobenzenes, consisting of a benzene ring substituted with one chlorine atom. Its chemical formula is C6H5Cl. This colorless, flammable liquid is a common solvent a ...

in the presence of a catalytic amount of

: : Cl₃CCHO + 2 C₆H₅Cl → Cl₃CCH(C₆H₄Cl)₂ + H₂O This reaction was described by

Othmar Zeidler Othmar Zeidler (29 August 1850 – 17 June 1911)Though many sources mention 1859 as Zeidler's year of birth, this would make him a mere 14 years old at the time of his dissertation in 1873. The 1859 birth yeawas usedby Joseph S. Fruton, in his '' ...

in 1874. The related herbicide

methoxychlor Methoxychlor is a synthetic organochloride insecticide, now obsolete. Tradenames for methoxychlor include ''Chemform'', ''Maralate'', ''Methoxo'', ''Methoxcide'', ''Metox'', and ''Moxie''. Usage Methoxychlor was used to protect crops, ornamental ...

is also produced from chloral. Treating chloral with

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive base (chemistry), ...

gives

chloroform Chloroform, or trichloromethane (often abbreviated as TCM), is an organochloride with the formula and a common solvent. It is a volatile, colorless, sweet-smelling, dense liquid produced on a large scale as a precursor to refrigerants and po ...

Cl₃CH and

sodium formate Sodium formate, HCOONa, is the sodium salt of formic acid, HCOOH. It usually appears as a white deliquescent powder. Preparation For commercial use, sodium formate is produced by absorbing carbon monoxide under pressure in solid sodium hydroxide ...

HCOONa. : Cl₃CCHO + NaOH → Cl₃CH + HCOONa Chloral is easily reduced to

trichloroethanol 2,2,2-Trichloroethanol is the chemical compound with formula . Its molecule can be described as that of ethanol, with the three hydrogen atoms at position 2 (the methyl group) replaced by chlorine atoms. It is a clear flammable liquid at room tem ...

, which is produced in the body from chloral.

Toxicity

Chloral and

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 toxic with a LC₅₀ for 4-hour exposure of 440 mg/m³.

References

{{Authority control Aldehydes Organochlorides GABAA receptor positive allosteric modulators Trichloromethyl compounds IARC Group 2A carcinogens Substances discovered in the 19th century

Production

Key reactions

Toxicity

See also

References