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In chemistry, the haloform reaction (also referred to as the Lieben haloform reaction) is a chemical reaction in which a haloform (CHX 3, where X is a halogen) is produced by the exhaustive halogenation of an acetyl group (R−C(=O)CH 3, where R can be either a hydrogen atom, an alkyl or an aryl group), in the presence of a base.
Most of the haloforms — specifically, chloroform (CHCl 3), bromoform (CHBr 3), and iodoform (CHI 3) — are easy to prepare through the haloform reaction, although this method does not lend itself to bulk syntheses. (Fluoroform (CHF 3) cannot be prepared in this manner.)
Subsequent halogenation (which usually cannot be stopped by control of stoichiometry) occurs at the position which already has a halogen substituent, until all hydrogens have been replaced by halogen atoms. For methyl alkyl ketones (2-alkanones), the haloform reaction proceeds to give the carboxylic acid selectively. [2]
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. [citation needed]
Bromoform was discovered in 1832 by Löwig who distilled a mixture of bromal and potassium hydroxide, as analogous to preparation of chloroform from chloral. [5]Bromoform can be prepared by the haloform reaction using acetone and sodium hypobromite, by the electrolysis of potassium bromide in ethanol, or by treating chloroform with aluminium bromide.
A methane molecule in 3D space filling model.. Halomethane compounds are derivatives of methane (CH 4) with one or more of the hydrogen atoms replaced with halogen atoms (F, Cl, Br, or I).
The Favorskii rearrangement is principally a rearrangement of cyclopropanones and α-halo ketones that leads to carboxylic acid derivatives. In the case of cyclic α-halo ketones, the Favorskii rearrangement constitutes a ring contraction.
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