Activity halogen

Hydrogen fluoride, HP, when used alone is a comparatively ineffective exchange agent and replaces only active halogens (13), eg, acyl fluorides from acyl chlorides and ben2otrifluoride [98-08-8] from hen2otrich1 oride (eq. 12). 

Amines or ammonia replace activated halogens on the ting, but competing pyridyne [7129-66-0] (46) formation is observed for attack at 3- and 4-halo substituents, eg, in 3-bromopyridine [626-55-1] (39). The most acidic hydrogen in 3-halopyridines (except 3-fluoropyridine) has been shown to be the one in the 4-position. Hence, the 3,4-pyridyne is usually postulated to be an intermediate instead of a 2,3-pyridyne. Product distribution (40% (33) and 20% (34)) tends to support the 3,4-pyridyne also. 

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. 

Fiber-Reactive Dyes. These dyes can enter iato chemical reaction with the fiber and form a covalent bond to become an iategral part of the fiber polymer. They therefore have exceptional wetfastness. Thein main use is on ceUulosic fibers where they are appHed neutral and then chemical reaction is initiated by the addition of alkaH. Reaction with the ceUulose can be by either nucleophilic substitution, using, for example, dyes containing activated halogen substituents, or by addition to the double bond in, for example, vinyl sulfone, —S02CH=CH2, groups. 

The latter is an exttemely reactive species. Trifluoroacetate is a good leaving group and facilitates cleavage of the O—Br bond. The acyl hypohalites are also the active halogenating species in solutions of the hypohalous acids in carboxylic acids, where they exist in equilibrium. 

This rate law could correspond to formation of a CI2-AICI3 complex that acts as the active halogenating agent but is also consistent with a rapid equiUbrium involving formation of C1+ ... 

Bromination can also be carried out using solutions of acetyl hypobromite or trifluoroacetyl hypobromite. Acetyl hypobromite is considered to be the active halogen-ating species in solutions of hypobromous acid in acetic acid ... 

Polyethylene glycol (molecular weight, 300-6(W) can aid in the displacement of activated halogen by fluorine. Propionyl chloride is converted to propionyl fluoride with potassium fluoride and polyethylene glycol in acetonitrile [63] Treatment of benzyl chloride with a mixture of potassium fluoride and potassium iodide for 5 h in acetonitrile containing polyethylene glycol 200 gives benzyl fluoride in 62% yield [64],... 

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)... 

Displacement of the activated halogen in 9 led to a series of compounds with marked anxiolytic activity in laboratory animals. It soon became apparent that fate had intervened a second time in the chemistry of this series the compounds were not... 

Active halogen groups were bonded to a glass surface by nonhydrolyzable links using the reactions set out in Scheme (40) ... 

In a very recent study, it has been demonstrated116 that zinc 5,15-bis(3,5-di-tert-butylphenyl)-porphyrin (13) without any activating halogen atoms at the chromophore can be directly linked in a very simple oxidative coupling reaction with silver(I) hexafluorophosphate to a mixture of porphyrin dimers, trimers and tetramers. The separation of the product mixture was achieved by gel-permeation chromatography based on the molecular weights of the oligomers. The dimer when re-exposed to the same reaction conditions yielded 25% of the tetramer.116... 

The alkylation of activated halogen compounds is one of several reactions of trialkylboranes developed by Brown (see also 15-16,15-25,18-31-18-40, etc.). These compounds are extremely versatile and can be used for the preparation of many types of compounds. In this reaction, for example, an alkene (through the BR3 prepared from it) can be coupled to a ketone, a nitrile, a carboxylic ester, or a sulfonyl derivative. Note that this is still another indirect way to alkylate a ketone (see 10-105) or a carboxylic acid (see 10-106), and provides an additional alternative to the malonic ester and acetoacetic ester syntheses (10-104). 

Versamid 900 Organic compounds containing active halogens. 

Halogenations are strongly catalyzed by mercuric acetate or trifluoroacetate. These conditions generate acyl hypohalites, which are the active halogenating agents. The trifluoroacetyl hypohalites are very reactive reagents. Even nitrobenzene, for example, is readily brominated by trifluoroacetyl hypobromite.19... 

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... 

Dissolve SIAB (Thermo Fisher) in DMSO at a concentration of 1.4mg/ml. Prepare fresh and protect from light to avoid breakdown of the active halogen group. 

The active chain carriers are replaced with the much less active halogen radical slowing the rate of energy production and helping flame extinguishment. 

The noble elements were always thought to be inert and not very reactive because their outer shells have full complements of electrons. Under special circumstances some of these inert elements can be forced to combine with a few other elements, particularly the more active halogens. 

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