Activated halogen atoms

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... 

Alkylation of hydroxylamine with primary halides and sulfonates is rarely used nowadays for preparation of A-alkylhydroxylamines due to the competing formation of N,N-dialkylhydroxylamines. A number of older procedures have been reported with low to moderate yields of Al-alkylhydroxylamines. Yet, in many cases the reported low yields can be attributed to workup losses during distillation and crystallization steps rather than to the polyalkylation. Use of excess of hydroxylamine in reactions with primary alkyl halides (e.g. 3) improves the yields of monoalkylation (equation 2). Most of the examples of alkylation of hydroxylamine in good yield involve a substitution of an activated halogen atom at benzylic positions as well as in haloacetamides 4 leading to alkylhydroxylamines such as 5 where dialkylation rates are lower (equation 3). 

An iminoether bond forms the link between large parts of the molecule in yet another of the unusual conazoles. Bromination of 2,4-dichloropropiophenone (59-1) affords the corresponding bromide (59-2). Treatment with imidazole displaces the activated halogen atom to afford the intermediate (59-3). The second major fragment... 

Combinations of metal halides (e. g. FeCl3, A1C13) with compounds containing an active halogen atom (e. g. a-chloro-dimethyl ether, benzyl chloride, 2,3-dichloro THF). 

Reduction of bromides. gem-Dibromocyclopropanes and g m-dibromoalkenes are reduced to the monobromides by (C,H50)2P(0)H and N(CiHdv Under these conditions gem-bromochlorocyclopropancs are reduced to chlorocyclopropanes.- l,l-Dibromo-2-tri-methylsilyloxycyclopropanes or a-bromo-a, 3-enones are reduced in this way to [3,7-cnones. Other examples indicate that only activated halogen atoms are subject to this reduction. 

Trlmethyl(perfluorophenyl)silane undergoes the same characteristic reactions as trimethyl(tri-fluoroinethyl)silane. Thus, perfluorophenyl groups can be introduced at multiple bonds (C = C, C = N, etc.) with active halogen atoms, e.g. formation of 17 and 18. ... 

When the halogen compound employed in the first step has an activated halogen atom (RCH CHCHjX, QHjCHjX, XCH2CO2H) a simpler procedure known as the Horner phosphonate modification of the Wittig reaction is applicable. When benzyl chloride is heated with triethyl phosphite, ethyl chloride is eliminated from the initially formed phosphonium chloride with the production of diethyl benzylphosphonate. This phospho-... 

In the preparation of di(p-aminophenyl) disulfide, sodium sulfide first displaces the activated halogen atom and then reduces the nitro group. The terminal step is... 

Compounds with activated halogen atoms, e.g., 7-chloro-4-nitrobenzo-furoxan (234), undergo displacement reactions with a variety of nucleophiles, including sulfides,300 443,444 amines,300,443,491 phenoxides,300 and others mentioned earlier.6 Sometimes rearrangements of the type discussed in Section V,C,4 occur, leading to products other than those of simple displacement.300,443 When 7-chloro-4-nitrobenzofuroxan is treated with an aryl-sulfinate, both substituents are replaced, and the 4,7-bisarylsulfonyl compound is formed. One of the arylsulfonyl groups is, in its turn, susceptible to replacement by other nucleophiles.444... 

Rogozinskii [84] proposed the use of Verzamide 900 (polyamide resin) for subtracting compounds with an active halogen atom such as haloalkanes, aromatic halo compounds and ethers of a-bromo fatty acids. 

Many compounds with multiple active halogen atoms have been used to initiate bi- or multi-directional growth to form ABA block copolymers and star-like polymers and copolymers [158]. Active halogens can be incorporated at the chain ends of polymers... 

Example 3. Substances disposing of activated halogen atoms [II, 17.]. 

Figure 11 Mode of action of microbicides with activated halogen atoms.

The electrophilically active substances have as toxophoric constituent an electrophilic group which is responsible for the antimicrobial effect, because it enables these active substances to react with specific nucleophilic entities of the microbial cell (Paulus, 1993) Examples of this class are aldehydes [II, 2.], e.g. Glutaraldehyde, compounds with activated halogen atoms [II, 17.], e.g. Bronopol, and microbiocides with an activated S-N-bond [II, 15.], for example Isothiazolinones. Since Isothiazolinones represent a major class of bactericides for industrial preservation, much research has been performed in this area. 

Compounds with activated halogen atoms, e.g. l,2-dibromo-2,4-dicyanobutane (DBDCB) [II, 17.16.] and 2-bromo-2-nitropropane-l,3-diol (Bronopol) [II, 17.14.]... 

Electrophiles react with nucleophilic functional groups in the cells in particular with enzyms and other proteins. Typical electrophiles are formaldehyde, its releasers and molecules with activated halogen atoms, e.g. 

Alcohols - Aldehydes Aldehyde releasing compounds - Phenol derivatives Adds - Add esters - Amides Carbamates -Dibenzamidines Pyridine derivatives Azoles Heterocyclic N, S compounds - Compounds with activated halogen atoms - Surface-active agents OrganometalUc compounds - Various compounds Chddidng agents... 

The hydroxymethylated nitro-hydrocarbons disposing of an activated halogen are described under 17. Compounds with activated halogen atoms . 

The pyridine derivative 2,3,5,6-tetrachloro-4-(methylsulphonyl)pyridine appropriately is listed under 17. Compounds with Activated Halogen Atoms . 

Microbicides of this kind are electrophilic active substances having at their disposal an activated halogen atom in the a-position and/or in the vinyl position to an electronegative group E (Figure 20). The antimicrobial activity of these substances arises from the fact that nucleophilic entities (H-Nu) of the microbial cell react with the carbon atom boasting an electron hole. It is apparent that a variety of modifications of both the electronegative... 

The following microbieides with activated halogen atoms have already been described within other substance classes ... 

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