Chloral, also known as trichloroacetaldehyde or trichloroethanal, is the

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...

with the formula Cl₃CCHO. This

aldehyde In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...

is a colourless oily 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 is a colorless solid. It has limited use as a sedative and hypnotic pharmaceutical drug. It is also a useful laboratory chemical reagent and precursor. It is derived from chloral (trichl ...

, a once widely used

sedative A sedative or tranquilliser is a substance that induces sedation by reducing irritability or excitement. They are CNS depressants and interact with brain activity causing its deceleration. Various kinds of sedatives can be distinguished, but t ...

and

hypnotic Hypnotic (from Greek ''Hypnos'', sleep), or soporific drugs, commonly known as sleeping pills, are a class of (and umbrella term for) psychoactive drugs whose primary function is to induce sleep (or surgical anesthesiaWhen used in anesthesia ...

substance.

Production

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

Justus von Liebig Justus Freiherr von Liebig (12 May 1803 – 20 April 1873) was a German scientist who made major contributions to agricultural and biological chemistry, and is considered one of the principal founders of organic chemistry. As a professor at t ...

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 chemical compound with the formula CH3 CHO, sometimes abbreviated by chemists as MeCHO (Me = methyl). It is a colorless liquid or gas, boiling near room temperature. It is one of the mos ...

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 an ...

: :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 ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...

, 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 An adduct (from the Latin ''adductus'', "drawn toward" 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 co ...

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 is an aromatic organic compound with the chemical formula C6H5Cl. This colorless, flammable liquid is a common solvent and a widely used intermediate in the manufacture of other chemicals. Uses Historical The major use of chlorob ...

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. Usage Methoxychlor was used to protect crops, ornamentals, livestock, and pets against fleas, mosquitoes, cockroaches, and other insects. It was intended to be a replacement ...

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 NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alkali ...

gives

chloroform Chloroform, or trichloromethane, is an organic compound with chemical formula, formula Carbon, CHydrogen, HChlorine, Cl3 and a common organic solvent. It is a colorless, strong-smelling, dense liquid produced on a large scale as a precursor to ...

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.

Safety

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

References

{{Authority control Aldehydes Organochlorides GABAA receptor positive allosteric modulators Trichloromethyl compounds