Vinyl-activated halogen

These electrophilic substances can react with nucleophilic compounds, for example, of the microbial cell, by way of an elimination reaction in the case of micro-bicides with an activated halogen in the a-position to an electronegative group, whereas microbicides with vinyl-activated halogen combine with nucleophiles by way of an addition-elimination reaction (Fig. 3). 

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. 

Activated acyl donors such as vinyl esters, halogenated methyl or ethyl ester, oxime esters or carboxylic acid anhydrides are often preferred for acylation of alcohols. With vinyl esters, acylation is in general fast and quantitative, as the equilibrium is driven by the release of vinyl alcohol, which will spontaneously tautomerize to volatile acetaldehyde. Amine nucleophiles will typically react spontaneously with these acyl donors, which hence cannot be used for resolution of amines. Vinyl acetate and ethyl acetate are common reagents (and often also solvents) for enzymatic kinetic resolution of alcohols and amines, respectively [9],... 

Substances with an activated halogen group in the apposition or/and in the vinyl position to an electronegative group E (IIL13)... 

In comparision to 2-methyl-4-isothiazolin-3-one (15.1.), the antimicrobial activity of which bases merely on the availability of an activated N-S bond susceptible to nucleophilic attack, the 5-chloro-2-methyl-4-isothiazolin-3-one disposes additionally of a vinyl activated chloro atom and therefore can be characterized as a molecule with two toxophoric structural elements (Paulus, 1988). As a result CMI should exhibit stronger antimicrobial efficacy than the halogen-free MI. This is confirmed by examinations of Diehl and Chapman (1999) see Table 109. Applications for CMI are described under 15.3. 

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 versatility of vinyl chloroacetate has been associated with the fact that the chlorine is greatly activated by the presence of an adjacent carbonyl group. This has led to the development of other activated halogen-containing monomers such as (XI), (XII) and (XIII) (allyl chloroacetate) ... 

Cosmetic manufacturers may use essentially any raw material as a cosmetic ingredient insofar as it is not considered as only a drug active ingredient, and market the product without approval. The law regulates only colour additives specifically approved for cosmetics and a few prohibited and restricted ingredients (e.g. bithionol, mercury compounds, vinyl chloride, halogenated salicylanilides). Cosmetics should not be contaminated with nitrosamines, 1,4-dioxane and pesticide residues, whose potential presence is regularly checked by the FDA (see Section 2.1). 

The activated nickel powder is easily prepared by stirring a 1 2.3 mixture of NiL and lithium metal under argon with a catalytic amount of naphthalene (1(7 mole % based on nickel halide) at room temperature for 12 h in DME. The resulting black slurry slowly settles after stirring is stopped and the solvent can be removed via cannula if desired. Washing with fresh DME will remove the naphthalene as well as most of the lithium salts. For most of the nickel chemistry described below, these substances did not affect the reactions and hence they were not removed. The activated nickel slurries were found to undergo oxidative addition with a wide variety of aryl, vinyl, and many alkyl carbon halogen bonds. 

Like all controlled radical polymerization processes, ATRP relies on a rapid equilibration between a very small concentration of active radical sites and a much larger concentration of dormant species, in order to reduce the potential for bimolecular termination (Scheme 3). The radicals are generated via a reversible process catalyzed by a transition metal complex with a suitable redox manifold. An organic initiator (many initiators have been used but halides are the most common), homolytically transfers its halogen atom to the metal center, thereby raising its oxidation state. The radical species thus formed may then undergo addition to one or more vinyl monomer units before the halide is transferred back from the metal. The reader is directed to several comprehensive reviews of this field for more detailed information. 

The presence of halogen atoms appears to exert little, if any, effect on catalyst activity, but it can influence the course of the metathesis reaction. Vinylic halides are unreactive, as exemplified by the ring-opening polymerization of l-chloro-l,5-cyclooctadiene, which afforded a perfectly alternating copolymer of butadiene and chloroprene (7/2) via polymerization exclusively through the unsubstituted double bond. 

In a slightly less convenient procedure, but one which has general versatility, carbonylation of aryl (or vinyl) palladium compounds produces aryl, heteroaryl, and vinyl carboxylic acids. As with the other procedures, immediate upon its formation, the carboxylate anion migrates to the aqueous phase. Consequently, haloaromatic acids can be obtained from dihaloarenes, without further reaction of the second halogen atom, e.g. 1,4-dibromobenzene has been carbonylated (90% conversion) to yield 4-bromobenzoic acid with a selectivity for the monocarbonylation product of 95%. Additionally, the process is economically attractive, as the organic phase containing the catalyst can be cycled with virtually no loss of activity and ca. 4000 moles of acid can be produced for each mole of the palladium complex used [4],... 

Vinylic halides are virtually unreactive and a high selectivity is to be found in the preferential cleavage of aliphatic carbon-halogen bonds of haloalkanoic amides and esters, and of nitro- and cyanoaryl derivatives. Activated haloarenes, e.g. 1-chloro-2,4-dinitrobenzene, however, give a complex mixture of products [7]. 

A very active elemental rhodium is obtained by reduction of rhodium chloride with sodium borohydride [27]. Supported rhodium catalysts, usually 5% on carbon or alumina, are especially suited for hydrogenation of aromatic systems [iTj. A mixture of rhodium oxide and platinum oxide was also used for this purpose and proved better than platinum oxide alone [i5, 39]. Unsaturated halides containing vinylic halogens are reduced at the double bond without hydrogenolysis of the halogen [40]. 

As usual, the reactivity order with respect to halogen in C=C-X is I > Br > Q. The organic halide in the couplings with alkynylzinc halides is usnaily an iodide, though also activated vinylic bromides (e.g. BrCH=CHCOOC2H5) have been found to react smoothly. We... 

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