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Reaction mechanism for the bromination of acetone while in the presence of acetic acid. Basic (in aqueous NaOH): Reaction mechanism for the bromination of acetone while in the presence of aqueous NaOH. In acidic solution, usually only one alpha hydrogen is replaced by a halogen, as each successive halogenation is slower than the first.
For example, a change of reaction medium from hexane to water increases the rate of tert-Butyl chloride (t-BuCl) heterolysis by 14 orders of magnitude. [5] This is caused by very strong solvation of the transition state. The main factors that affect heterolysis rates are mainly the solvent's polarity and electrophilic as well as its ionizing power.
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.
As with all ketones, acetone enolizes in the presence of acids or bases. The alpha carbon then undergoes electrophilic substitution with bromine. The main difficulty with this method is over-bromination, resulting in di- and tribrominated products. If a base is present, bromoform is obtained instead, by the haloform reaction. [5]
The Hofmann rearrangement (Hofmann degradation) is the organic reaction of a primary amide to a primary amine with one less carbon atom. [1] [2] [3] The reaction involves oxidation of the nitrogen followed by rearrangement of the carbonyl and nitrogen to give an isocyanate intermediate.
Ring expansion and ring contraction reactions expand or contract rings, usually in organic chemistry. The term usually refers to reactions involve making and breaking C-C bonds, [1] Diverse pathways lead to these kinds of reactions. Many of these reactions are primarily of theoretical or pedagoogical interest, but some are very useful.
The Weiss–Cook reaction consists in the synthesis of cis-bicyclo[3.3.0]octane-3,7-dione employing an acetonedicarboxylic acid ester and a diacyl (1,2 ketone). The mechanism operates in the same way as the Knoevenagel condensation: [ 10 ]
The reaction is much slower with ketones than aldehydes. [42] For example, in Nicolaou's epothilones synthesis, asymmetric allylboration (with an allylborane derived from chiral alpha-pinene ) is the first step in a two-carbon homologation to acetogenin : [ 43 ]