Haloform

This IS called the haloform reaction because the trihalomethane produced is chloroform (CHCI3) bromoform (CHBrj) or iodoform (CHI3) depending on the halogen used... 

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... 

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

The methyl ketone shown in the example can enohze in only one direction and typifies the kind of reactant that can be converted to a carboxylic acid in synthetically accept able yield by the haloform reaction When C 3 of a methyl ketone bears enolizable hydro O... 

The haloform reaction using iodine was once used as an analytical test in which the formation of a yellow precipitate of iodoform was taken as evidence that a substance... 

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

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... 

Carbene Reactions. The best procedure for preparing dihalocarbene adducts of olefins consists in stirring a haloform—methylene chloride solution with an excess of concentrated aqueous caustic soda in the presence of hen 2y1triethy1 amm onium chloride. Even stericahy hindered and electronically deactivated compounds give excellent yields (32). Mixed dihalocarbenes, CXY (X,Y = E, Cl, Br, I), except for CE2, can be prepared. 

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

One of these reactions is the well-known haloform reaction Another leads to some unusual trifluoromethylamines... 

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. 

Haloforms react with Huonnated alkoxides [4] or phenoxides [5] by carbene processes (equations 3 and 4)... 

Intermediate carbenes are also involved in the alkylation by haloforms of carbanions derived from Schiff bases of a-ammo esters [126] or aminomalonates... 

Phase-transfer systems for generating fluorohalocarbenes from the corre spending haloforms are simple and effective with nucleophilic olefins [5J, 54 55, 56, 57, 58, 59] (Table 3 and equations 23 and 24), and the process was extended recently to difluorocarbene [60] Chlorofluorocarbene also can be generated from fluorotrichloromethane and utanium(O) produced in situ (T1CI4 + L1AIH4) Yields of gem-chlorofluorocyclopropanes range from excellent (85% for a. meth ylstyrene) to poor (12% for 1-hexene) [61]... 

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