Activated halogen groups, compounds

This topic has been reviewed [2, pp 94, 100-111, 130-134] All of the standard approaches to the synthesis of a compound like methyl 2-fluorostearate from methyl 2-bromostearate result mall yield of the 2-fluoro ester and the unsaturated esters. Although silver fluoride is not a new reagent, its use moist in wet acetonitrile to convert methyl 2-bromostearate to its fluoro ester is a departure from the traditional set of anhydrous conditions (Procedure 6, p 194) [71] In contrast, silver tetrafluoroborate converts a-chloroketones to their respective fluoroketones under anhydrous conditions. The displacement of less activated halogen groups by silver tetrafluoroborate to form their respective fluorides is novel Although silver tetrafluoroborate could not be used to convert an aliphatic terminal dichloromethyl or trichloromethyl group to its corresponding fluoro derivative, it is an effective fluorine source in other situations [72] (Table 8)... 

The displacement of less activated halogen groups by silver(I) tetrafluoroborate to the corresponding fluorides is not so widespread. Although silver(I) tetrafluoroborate cannot be used to transform an aliphatic terminal dichloromethyl or trichloromethyl group to the corresponding fluoro compound, it has been known to work in many other cases (Table 13).70... 

The initiation step in ATRP involves homolytic cleavage of an activated halogen-containing compound and subsequent addition of this radical to the monomer as shown in Scheme 23. The fragment that is retained at the a-end of the polymer can be composed of functional groups that are tolerant to the ATRP catalyst and propagating chain end. Two main classes of functionalized initiators have been reported, activated alkyl halides and sulfonyl halides. 

Appropriate active ingredients for non-persistent slimicides one finds above all among the compounds with activated halogen groups (III.7 and III.15). Other active ingredients belong to the carbamates (III.9 and III.3.4.10.1) and the heterocyclic N,S compounds (III. 13). It is also proposed to use glutaraldehyde (III.2.3) or 3,5-dimethyl-tetrahydro-2-thiono-thiadiazine (III.3.3.16). 

It is possible to introduce sulfonic acid groups by alternative methods, but these ate Htde used in the dyes industry. However, one worth mentioning is sulfitation, because it provides an example of the introduction of a sulfonic acid group by nucleophilic substitution. The process involves treating an active halogen compound with sodium sulfite. This reaction is used in the purification of m-dinitrohen7ene. 

Triazines. The most commercially important ttia2ine is 2,4,6-ttichloro-j -ttia2ine [108-77-0] (cyanutic chloride, (99)). Cyanutic chloride has not achieved prominence because of its value as part of a chromogen but because of its use for attaching dyestuffs to cellulose, ie, as a reactive group (see Dyes, reactive). This innovation was first introduced by ICl in 1956, and since then other active halogen compounds have been introduced. 

Direct chlorination of 3,6-dichloropyridazine with phosphorus pentachloride affords 3,4,5,6-tetrachloropyridazine. The halogen is usually introduced next to the activating oxo group. Thus, 1,3-disubstituted pyridazin-6(l//)-ones give the corresponding 5-chloro derivatives, frequently accompanied by 4,5-dichloro compounds as by-products on treatment with chlorine, phosphorus pentachloride or phosphoryl chloride-phosphorus pentachloride. 

Although the primary utility of active halogen compounds is to modify sulfhydryl groups in proteins or other molecules, the reaction is not totally specific. Iodoacetyl (and bromoacetyl) derivatives can react with a number of functional groups within proteins the sulfhydryl group of cysteine, both imidazolyl side chain nitrogens of histidine, the thioether of methionine, and... 

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