Haloform reaction of methyl ketones

Fig. 30. Haloform reaction of methyl ketones with BTMA Bt3...

The reaction of methyl ketones with excess hydroxide and chlorine, bromine or iodine leads to the formation of a carboxylic acid together with CHX3 in a haloform reaction. The use of iodine gives CHI3 (iodoform), which is the basis of a functional group test for methyl ketones. 

Figure 5.5. Mechanism of the haloform reaction with methyl ketones. From Morris and Baum (1978). Reprinted by permission of Lewis Publishers.

The reaction of methyl ketones with a halogen in an alkaline medium is known as the haloform reaction. In this experiment, halogen and base are present because of the equilibrium reaction shown here ... 

The haloform reaction of unsymmetrical perfluoroalkyl and co-hydroper-fluoroalkyl trifluororaethyl ketones gives the alkane corresponding to the longer alkyl chain [54] (equation 53) If the methyl group contains chlorine, the reaction can take different pathways, leading to loss of chlorine (equation 54), because of the variable stability of the chlorine-substituted methyl carbanions in alkali. 

In addition to the applications indicated on p. 858. hypohalous acids are useful halogenating agents for Ixjth aromatic and aliphatic compounds. HOBr and HOI are usually generated in silii. The ease of aromatic halogenation increa.ses in the sequence OCl < OBr < Ol and is facilitated by salts of Pb or Ag. Another well-known reaction of hypohalites is their cleavage of methyl ketones to form carboxylates and haloform ... 

Hi) Oxidation of methyl ketones by haloform reaction Aldehydes and ketones having at least one methyl group linked to the carbonyl carbon atom (methyl ketones) are oxidised by sodium hypohalite to sodium salts of O corresponding carboxylic... 

The haloform reaction of unsymmctrical perfluoroalkyl and m-hydroperfluoroalkyl trifluoro-methyl ketones 6 gives the alkanes 7 corresponding to the longer alkyl chain.174... 

This sequence is called the haloform reaction because it results in the production of chloroform, bromoform, or iodoform, depending upon the halogen used. The haloform reaction is a useful method for identification of methyl ketones, particularly when iodine is used, because iodoform is a highly insoluble, bright-yellow solid. The reaction also is very effective for the synthesis of carboxylic... 

The use of the haloform reaction for the conversion of methyl ketones into carboxylic acids (Sections 5.11.1, p. 667) is also applicable in the aromatic field. The conditions may be readily adapted from those described for the conversion of aliphatic methyl ketones into carboxylic acids (Expt 5.124). 

Iodoform test (Section 23.7B) A test for the presence of methyl ketones, indicated by the formation of the yellow precipitate, CHI3, via the haloform reaction. 

Lieben haloform reaction Conversion of methyl ketones to one-carbon shorter carboxylic acids. 262... 

Lieben iodoform reaction. Cleavage of methyl ketones with halogens (mostly iodine) and base to carboxylic acids and haloform. 

An electrocatalytic Haloform reaction to convert methyl ketones into esters has been described by two groups,33,34 and the Haloform reaction has been extended to nonmethyl ketones, but this is considered to be outside the scope of the present article. Likewise, a Haloform reaction of B-sulfonylmethyl ketones affords a-halosulfones and acetate,36 and various quinones yield iodoform upon treatment with alkaline iodine.37... 

Despite its age, the Haloform reaction remains a unique and powerful transformation of methyl ketones to carboxylic acids. The range of substrates is truly enormous. In addition to the examples shown below, the Haloform reaction has been employed to synthesize these carboxylic acids (from the corresponding methyl ketones) 3-... 

Haloform reaction l .limination of trihalomethane (haloform) from halogenated methyl ketone iti the prcsctice of bti.se. 

The oxidation of methyl ketones by hypochlorite (the haloform reaction) [164]. 

EXPERIMENT 34 Hypochlorite Oxidation of Methyl Ketones by the Haloform Reaction 403... 

Hypochlorite is a well known oxidizing agent in the haloform reaction for the oxidation of methyl ketones to carboxylic acids. It has been shown that the hypochlorite anion can be transferred into organic solutions by PTC (quaternary cations). Some of the applications of this technique are given as follows (Scheme 91). 

Inversion of configuration (Section 7.11C) The opposite relative stereochemistry of a stereogenic center in the starting material and product of a chemical reaction. In a nucleophilic substitution reaction, inversion results when the nucleophile and leaving group are in the opposite position relative to the three other groups on carbon. Iodoform test (Section 23.7B) A test for the presence of methyl ketones, indicated by the formation of the yellow precipitate, CHI3, via the haloform reaction. 

Halogenation followed by hydrolysis of methyl ketones in the haloform reaction... 

Halogenation of methyl ketones in base—The haloform reaction (23.7B)... 

The haloform reaction is sometimes used for the preparation of carboxylic acids from methyl ketones... 

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