Chloronium

In eontrast, dialkylhalonium salts sueh as dimethylbromonium and dimethyliodonium fluoroantimonate, whieh we prepared from excess alkyl halides with antimony pentafluoride or fluoroantimonie acid and isolated as stable salts (the less-stable chloronium salts were obtained only in solution), are very effective alkylating agents for heteroatom eompounds (Nu = R2O, R2S, R3N, R3P, ete.) and for C-alkylation (arenes, alkenes). 

Chloronium lon (Section 6 16) A halonium ion in which the halogen is chlonne (see halonium ion)... 

Chlorohydrination. The mechanism for the formation of propylene chlorohydrin is generally beheved to be through the chloronium ion intermediate (109,112). 

The chloronium ion intermediate can react with water to produce the desired propylene chlorohydrin, with chloride ion to produce 1,2-dichloropropane, or with propylene chlorohydrin to produce isomers of dichloro-dipropyl ether. 

Chloronium ions, tetramethylene-reactions, 1, 566 Chloronium salts cyclic... 

Both proton loss and rearrangement reflect the greater positive charge at carbon in a chloronium ion than in a bromonium ion because of the weaker bridging by chlorine. 

HC1, HBr, and HI add to alkenes by a two-step electrophilic addition mechanism. Initial reaction of the nucleophilic double bond with H+ gives a carbo-cation intermediate, which then reacts with halide ion. Bromine and chlorine add to alkenes via three-membered-ring bromonium ion or chloronium ion intermediates to give addition products having anti stereochemistry. If water is present during the halogen addition reaction, a halohydrin is formed. 

MeBr is a strong poison only with Et2 All coinitiator. Since Et2 All forms the least nucleophilic counterion, Et2AHXe, it is expected to produce a relatively free carbenium ion, facilitating bromonium ion formation by interaction with MeBr solvent. With more nucleophilic counteranions, like Me3 AlXe or Et2 AlXf (X = Cl, Br), bromonium ion formation is more difficult and poisoning is modest. Evidently, the less stable bromonium ions form only with weakly nucleophilic counterions. MeCl is the weakest poison or may be inert, since chloronium ions are highly unstable. 

It is not unlikely that the actual reagent is HOCl attack on the 9,11-olefin by Cl+ would occur from the less hindered side to give the 9a,lla-chloronium intermediate. Attack of OH to give diaxial ring opening would lead to the observed halohydrin. 

See Fluoroniiun perchlorate, also Chloronium perchlorate Iodides... 

Twenty years later, by studying the chlorination of cis- and trans-di-t-butylethylenes, Fahey (1966) showed that halogen bridging is a general rule. It is expected that, owing to steric repulsions between the two branched groups, the cis-alkene would prefer to react via an open / -chlorocarbocation [14] where free rotation can occur rather than via a chloronium ion [15]. 

Chloro-2,3-di(2-thienyl)cyclopropenium perchlorate, 3388 Chloronium perchlorate, 4065... 

The stereochemical behavior observed in the addition of BrCl has been compared with that related to the Br2 and CI2 additions to the same diene and discussed in terms of steric hindrance of the nucleophile approach (chloride ion with respect to bromide or tribromide ion) and different bridging in the bromonium or chloronium intermediates77. 

As an alternative to radical chlorination, use has been made of carbon tetrachloride and hexachloroethane in the presence of a quaternary ammonium salt, as source of the chloronium ion for reaction with activated alkylbenzenes [38], Benzyl chlorides need the additional activation of a nitro group for their conversion into the corresponding nitrobenzotrichlorides, whereas benzal chlorides do not need the extra activation for a similar conversion. The same synthetic protocol, using hexachloroethane, has been used for the conversion of allylic sulphones into the 1,1-dichloro derivatives [39],... 

Solvolysis of butadiene monoxide (10.102) in saline solution is a rather unexpected reaction that further documents this compound s reactivity [168]. In aqueous NaCl solution at physiological pH and temperature, butadiene monoxide disappeared rapidly to form 1,2-dichloro-3,4-epoxybutane (10.111, Fig. 10.25). There was a linear dependence of the rate of reaction on the Cl concentration (in the range investigated (34-135 mM)). The reaction pathway was described as slow solvolytic formation of the bu-tenylchloronium ion, followed by Cl attack to yield Cl2 and butadiene. Cl2 is then rapidly trapped by a second molecule of butadiene monoxide to form a different chloronium ion that also reacts with Cl to yield the final, stable dichloro product (10.111). The formation of 1,2-dichloro-3,4-epoxy-butane under physiological conditions is believed to be toxicologically significant. 

Anodic regioselective acetamidosulfeny-lation of alkenes is similarly achieved by oxidation of diphenyldisulfide in acetonitrile [81]. Cyclic enamines, which are intermediates in the oxidation of cyclic N-methoxycarbonyl amines, react in aqueous acetonitrile that contains chloride ions to a-hydroxy- 8-chloro compounds via intermediate chloronium ions [82]. Enolethers undergo a regioselective azidomethoxyla-tion to yield acetals of a-azido carbonyl compounds upon electrolysis in methanol containing sodium azide [83]. The reaction proceeds possibly via addition of an anodicaUy generated azide radical. 

Yates, B.F. Bouma, W.J. Radom, L. Detection of the Prototype Phosphonium (CH2PH3), Sulfonium (CH2SH2), and Chloronium (CH2CIH) Ylides by Neutralization-Reionization Mass Spectrometry a Theoretical Prediction. J. Am. Chem. Soc. 1984,106, 5805-5808. 

The X-ray structure of the bridged chloronium cation (88) is reported it is described as being unsymmetrical and non-classical. " It shows distinctive electrophilic... 

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