Haloforms reactions with

Trifluoroacetylindoles are useful stable equivalents of acid chlorides, giving amides or acids in haloform reactions with lithium amides or aqueous base respectively. The reactivity of the A -hydrogen compounds is greater than of those with A -alkyl, indicating the intermediacy of a ketene in the reactions of the former. ... 

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

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). 

The following oxidants were reported to give colour reactions with aromatic amines, which may be used for identification purposes under controlled conditions chloric acid , ammonium persulphate-silver nitrate , benzoyl peroxideand sodium hypochlorite . Amines with partial structures 26 and 27, where R, R = H, alkyl, give the haloform reaction with hypochlorites in basic media . 

The mechanism of the haloform reaction begins with a halogenation via the eno late The electron attracting effect of an a halogen increases the acidity of the protons on the carbon to which it is bonded making each subsequent halogenation at that car bon faster than the preceding one... 

Haloform reaction (Section 18 7) The formation of CHX3 (X = Br Cl or I) brought about by cleavage of a methyl ketone on treatment with Br2 CI2 or I2 in aqueous base... 

Efaloform Reaetion. Ethyl alcohol reacts with sodium hypochlorite to give chloroform [67-66-3] (haloform reaction). 

Methyl ketones are cleaved on reaction with excess halogen in the presence of base. The products are a trihalomethane (haloform) and a carboxylate salt. 

Besides its synthetic importance, the haloform reaction is also used to test for the presence of a methylketone function or a methylcarbinol function in a molecule. Such compounds will upon treatment with iodine and an alkali... 

Haloforms react with potassium /-butoxide to form dihalocarbenes, which add smoothly to olefins giving 1,1-dihalocyclopropanes (2). The reaction does not appear... 

Haloform reaction (Section 22.6) The reaction of a methyl ketone with halogen and base to yield a haloform (CHX3) and a carboxylic acid. 

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

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 ... 

It is exactly the same with the haloform reaction. If chloroform is poured onto the acetone/sodium hydroxide mixture, there can be an explosion whereas incorporating hydroxide in the other two substances would not be dangerous. In this case the risk factor is the high hydroxide concentration. 

There is also the haloform reaction (effect of a haloform on a ketone in a basic medium), already described with halogen derivatives on p.272 (the danger is more related to the interaction of the polyhalogen derivative with the base, according to the author). A large number of accidents involved the ketone as much as butanone. The accident below illustrates the danger of this reaction ... 

Acylation of enol ethers. Reaction of 1 with ethyl vinyl ether in ether provides an intermediate that undergoes dehydrochlorination when heated to provide the trichloromethyl ketone 2, which is converted by base (haloform reaction) to the ester 3 in high yield. 

The reaction of 2- and 4-hydroxyadamantane-l-carboxylic esters with dibromo-carbene produces the corresponding 2- and 4-bromo derivatives (10-20%). Slow hydrolysis of the ester groups may also occur under the basic conditions. l-Acetyl-4-hydroxyadamantane yields 4-bromoadamantane-l -carboxylic acid (37%), as a result of a concomitant reaction with dibromocarbene and a haloform-type reaction [8]. 

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