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Halogenation stepwise

Halogens add stepwise, giving almost exclusively dihaloaHyl alcohols (24,25). [Pg.104]

Addition of halogens proceeds stepwise, sometimes accompanied by oxidation. Iodine forms 2,3-diiodo-2-butene-l,4-diol (53). Depending on conditions, bromine gives 2,3-dibromo-2-butene-l,4-diol, 2,2,3,3-tetrabromobutane-l,4-diol, mucobromic acid, or... [Pg.105]

Historically, the discovery of one effective herbicide has led quickly to the preparation and screening of a family of imitative chemicals (3). Herbicide developers have traditionally used combinations of experience, art-based approaches, and intuitive appHcations of classical stmcture—activity relationships to imitate, increase, or make more selective the activity of the parent compound. This trial-and-error process depends on the costs and availabiUties of appropriate starting materials, ease of synthesis of usually inactive intermediates, and alterations of parent compound chemical properties by stepwise addition of substituents that have been effective in the development of other pesticides, eg, halogens or substituted amino groups. The reason a particular imitative compound works is seldom understood, and other pesticidal appHcations are not readily predictable. Novices in this traditional, quite random, process requite several years of training and experience in order to function productively. [Pg.39]

The reaction proceeds in a stepwise fashion and products with only one or two halogens can be produced by suitably limiting the reagent. Using alcohols, alkoxy groups are introduced. Either one or all three halogens can be replaced. [Pg.369]

Tin tetrachloride has been used to prepare the stericaHy hindered triisopropylchlorosilane [13154-24-0] (119). Organobromosdanes are obtained under similar conditions through reaction with cupric and mercuric bromide. These reactions are most suitable for stepwise displacement of hydrogen to form mixed hydridochlorosilanes or in systems sensitive to halogen (120). Hydrides have also been displaced using organic bromides. Heating triethylsilane and... [Pg.27]

In general, Grignard reagents are useful in the synthesis of mixed hydridochlorosilanes because these reagents can effect stepwise substitution of the halogen, eg,... [Pg.30]

Numerous carbonyl halides, of which the best known are octahedral compounds of the type [M(C0)4X2] are obtained by the action of halogen on Fe(CO)5, or CO on MX3 (M = Ru, Os). Stepwise substitution of the remaining CO groups is possible by X or other ligands such as N, P and As donors. [Pg.1108]

Nucleophilic substitution has been used for the preparation of many thiophenes. For instance, 2-phenylthio-3,4-dinitro-5-piperidino-thiophene (155) has been prepared " through stepwise reaction of (150) with different nucleophiles. Nitrothienols and derivatives of them have been obtained from halogenated nitrothiophenes. " Allyl ethers have been prepared by the reaction of 5-chJoro-4-nitro-2-acetylthiophene, 3-nitro-2-chlorothiophene, and 2-nitro-3-bromothio-... [Pg.71]

Mono-substitution occurs most readily in the stepwise replacement of the halogen substituents of 2,4,6-trichloro-s-triazine with aqueous methanol and sodium bicarbonate (30°, 30 min), the monomethoxy derivative (324) is obtained on heating (65°, 30 min), the disubstitu-ted derivative is formed and on brief heating (65°) with the more basic sodium carbonate or methanolic sodium hydroxide (25°, 3 hr) complete methoxylation (320) occurs. Ethanolic ethoxide (25°, 1 hr) or sodium carbonate (35°) is sufficient to give complete ethoxy-dechlorination. The corresponding phenoxy derivatives are obtained on treatment with one (0°), two (15°, 1 hr), or three equivalents (25-70°, 3 hr) of various sodium phenoxides in aqueous acetone. The stepwise reaction with phenols, alcohols, or thiols proceeds in better yield in organic solvents (acetone or chloroform) with collidine or 2,6-lutidine as acid acceptors than in aqueous sodium bicarbonate. ... [Pg.302]

The more halogens on a single carbon, the greater the ease of hydrogenol ysis, a fact that makes stepwise dehydrohalogenation an easy process, since each loss increases the resistance to further loss (4,13,21,24,29,71). Reduction of the dichloro compound 17 over palladium black gave 18 in 98% yield (8). [Pg.152]

The usual oxidizing agents transfer oxygen (or halogens and related species with subsequent hydrolysis) stepwise to the sulfur of thioethers Rates of step A compared with those of step B are faster with electrophilic oxidation agents (peroxy acids) inversely, rates of step B compared with those of step A are faster with nucleophilic oxidation agents (peroxy anions)339-341. [Pg.206]

The alkyl groups of PbR4 (R = Me, Et) can be replaced stepwise by halogen atoms, and these may be further substituted by other groups, as illustrated in reaction 8 for the first of three similar CF3 group introductions144. [Pg.446]

The Ni(II) complexes 6 and 7 have been found by Stiles [60] to be soluble catalysts for reductive dehalogenation when combined with NaBH4 or hydrazine at 25-45 °C in protic solvents. Reactivity toward the reducing system increased with the halogen content of the substrate. Aryl bromides were converted much faster than chlorides, polychlorobenzenes, however, reacted readily with stepwise loss of chlorine. [Pg.522]

The dynamics of carbon-halogen bond reductive cleavage in alkyl halides was studied by MP3 ab initio calculations, using pseudopotentials for the halogens and semidiffuse functions for the heavy atoms [104], The effect of solvent was treated by means of the ellipsoidal cavity dielectric continuum model. Both a concerted (i.e., a one-step) and a stepwise mechanism (in which an anion radical is formed at first) were... [Pg.340]

Dibromo-l,4-xylene or its 2,5-dichloro derivative is obtained by bromination or, correspondingly, chlorination of 1,4-xylene. It is oxidized to form 2,5-dibro-moterephthalic acid or its dichloro derivative 59. Subsequent reaction with aryl-amine, for instance in the presence of copper acetate, affords 2,5-diarylamino-terephthalic acid 60. It is also possible to replace the halogen atoms stepwise by arylamino moieties [11]. Cyclization to form linear trans-quinacridones, as in the above-mentioned method, is achieved by using acidic condensation agents ... [Pg.456]

Pigment Yellow 138,56300, has the chemical structure 138 with X = C1 [4], The synthesis of halogenated compounds (138), for instance P.Y.138, can also be achieved by stepwise heating of tetrachloro phthalic anhydride and 8-amino-chinaldine in molten benzoic acid from 125 to 140 and then to 160°C [5],... [Pg.538]

A chlorine-bromine exchange in fluorodichloromethanesulfenyl chloride by means of hydrogen bromide provides a route to additional sulfenyl bromides (109). After the initial halogen exchange at the sulfur, further addition of hydrogen bromide causes stepwise substitution at the methyl group ... [Pg.156]

Dimensionality reduction in solids (Lee Holm, 1990) has received some attention. Three-dimensional metal cluster solids of the kind [MgQ8]X3 (M = Re, Mo Q = chalcogen X = halogen) can be rendered into two-, one- and zero-dimensional phases sequentially by the incorporation of AX type halides (e.g. A = Tl). The stepwise... [Pg.369]

These are readily prepared by adding amines to trihaloarsines in cooled ether solutions. The reaction proceeds stepwise, halogens being successively replaced by alkylamino groups (equations 3-5). Some examples of dialkylaminoarsines are given in Table 1. [Pg.240]

A number of preparatively useful reductions with removal of halogen was discussed in Part I. Often a stepwise removal of the halogens takes place in a polyhalogenated compound. 4-Methyl-2,6-dichloropyrimidine (288) thus gives three peaks in DMF, the third peak being the reduction of the nucleus. Preparative reduction at the potential of the first peak affords 4-methyl-2-chloropyrimidine436 [Eq. (148)]. [Pg.340]


See other pages where Halogenation stepwise is mentioned: [Pg.398]    [Pg.398]    [Pg.209]    [Pg.456]    [Pg.494]    [Pg.26]    [Pg.291]    [Pg.292]    [Pg.79]    [Pg.325]    [Pg.273]    [Pg.19]    [Pg.138]    [Pg.258]    [Pg.340]    [Pg.341]    [Pg.57]    [Pg.3]    [Pg.120]    [Pg.38]    [Pg.254]    [Pg.149]    [Pg.294]    [Pg.91]    [Pg.353]    [Pg.488]    [Pg.696]    [Pg.50]    [Pg.304]    [Pg.339]    [Pg.26]   
See also in sourсe #XX -- [ Pg.14 , Pg.31 , Pg.588 ]




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