Chlorination, Haloform reaction

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. 

Methyl ketones 1, as well as acetaldehyde, are cleaved into a carboxylate anion 2 and a trihalomethane 3 (a haloform) by the Haloform reaction The respective halogen can be chlorine, bromine or iodine. 

In the haloform reaction, methyl ketones (and the only methyl aldehyde, acetaldehyde) are cleaved with halogen and a base. The halogen can be bromine, chlorine, or iodine. What takes place is actually a combination of two reactions. The first is an example of 12-4, in which, under the basic conditions employed, the methyl group is trihalogenated. Then the resulting trihalo ketone is attacked by hydroxide ion ... 

Apparently the only previous case of the isolation of a chlorinated acid from a haloform reaction is that reported by Arnold et al. [8], who acidified the reaction mixture before decomposition of the excess hypochlorite. (Even though we decomposed the excess hypochlorite before acidification, the unchlorinated acid was not obtained.) These authors [8] also obtained an ester as the product of the haloform reaction. It seems likely that conditions for performing the haloform reaction can be found which will make the one-step conversion of a methyl ketone to the ester of the corresponding acid a general reaction. ... 

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. 

PROBABLE FATE photolysis, could be important, only identifiable transformation process if released to air is reaction with hydroxyl radicals with an estimated half-life of 8.4 months oxidation, has a possibility of occurring, photooxidation half-life in air 42.7 days-1.2 yrs hydroiysis too slow to be important, first-order hydrolytic half-life 275 yrs voiatilization likely to be a significant transport process, if released to water or soil, volatilization will be the dominant environmental fate process, volatilization half-life from rivers and streams 43 min-16.6 days with a typical half-life being 46 hrs sorption adsorption onto activated carbon has been demonstrated bioiogicai processes moderate potential for bioaccumulation, biodegradation occurs in some organisms, in aquatic media where volatilization is not possible, anaerobic degradation may be the major removal process other reactions/interactions may be formed from haloform reaction after chlorination of water if sufficient bromide is present... 

The source of bromine-containing haloforms has been established by a number of investigators to be the rapid oxidation of bromide by hypochlorite to hypobromite, BrO", and the participation of this species in the haloform reaction with dissolved organic matter. Hypobromite appears to be a more reactive halogenating agent, but a less reactive oxidant, than HOCl (Bunn et al., 1975 Macalady et al., 1977 Rook et al., 1978). Some of the factors influencing brominated haloform production in natural waters include pH, temperature, bromide and ammonia concentration, and chlorine dose (Minear and Bird, 1980 Amy et al., 1984). 

Intermediates of the types expected to persist under some conditions of the haloform reaction have been isolated in aqueous chlorination experiments. Suffet et al. (1976) identified 1,1,1-trichloroacetone in treated river water samples from the Philadelphia area. This compound is unstable to hydrolysis at pH greater than about 5. 

When water is chlorinated to purify it for public consumption, chloroform is produced from organio impurities in the water via the haloform reaction. (Many of these organic impurities are naturally occurring, such as humic substances.) The presence of chioroform in pubiic water is of concern for water treatment... 

Purpose. The well-known haloform reaction is explored as a synthetic route to the preparation of organic acids. You wiU investigate the use of a basic aqueous solution of hypochlorite ion as a source of molecular chlorine (CI2). 

The same process occurs with chlorine and iodine, and the by-products are chloroform and iodoform, respectively. This reaction is named after the by-product that is formed and is called the haloform reaction. The reaction must be followed by treatment with a proton source to protonate the carboxylate ion and form the carboxylic acid. This process is synthetically useful for converting methyl ketones into carboxyhc acids. 

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