Iodination scavengers

Not every excess acidity mechanistic analysis has been an outstanding success. For instance, several enolization studies have used this technique. The enolization of acetophenone was one of the reactions originally studied by Zucker and Hammett 146 their sulfuric acid rate constant data, obtained by iodine scavenging (the reaction is zero-order in halogen), was used in an excess acidity analysis,242 together with additional results obtained for some substituted acetophenones (using bromine scavenging).243... 

At 3130 A. the first process is the most important and the ratio of (102) to (101) is believed to be 0.046 from iodine scavenger experiments. 

Diem et al. investigated the photolysis of adamantyl iodide as a po ible source of carbocationic initiation for the polymerisation of isobutene. Althou no polymer was obtained with this simple tystem (or with f-butyl iodide as photolyte), addition of iodine scavengers such as zinc, zinc fodide or both together gave some polymerisation, indicating that the carbocations produced in the photolysis of alkyl iodides possess a modest initiating power if generated in the presence of isobutene. 

Estimates of excited state generation by final product analysis. We have already mentioned the product analysis studies on the yield of the solvent excited states and the products of their decomposition [89]. Using iodine scavenging, the radiolytic yields of H2, olefins and radicals were determined... 

It has been suggested that the initial formation of iodine on addition of iodide to a diazonium salt solution is caused by oxidation of the iodide by excess nitrite from the preceding diazotization. Packer and Taylor (1985) demonstrated that, if urea was added as a nitrite scavenger (see Sec. 2.1) to a diazotization solution, that solution produced iodine much more rapidly than a portion of the same diazonium salt solution not containing urea, but eventually the latter reaction too appeared to follow the same course. This confirms the role of excess nitrite, and suggests that the iodo-de-diazoniation steps only occur in the presence of iodine or triiodide (I -). The same authors also found that iodo-de-diazoniation is much slower under nitrogen. All these observations are consistent with radical-chain processes, but not with a heterolytic iodo-de-diazoniation. 

A simplified experimental system results when free radical scavengers such as nitric oxide, iodine, or oxygen are added to the samples before... 

The results were found not to be very sensitive to the presence of scavengers, such as atmospheric oxygen, iodine and FeClj, although the effect was sufficient to indicate clearly the involvement of radical reactions... 

Mn2(CO)io was studied - by means of dissolving the irradiated target in dilute solutions of iodine in petroleum ether, so as to scavenge... 

The mechanisms of these reactions are presumably analogous to those of the Pr6vost and Woodward-Prevost reactions. In the first step of the reaction of iodine and thallium(I) acetate with cyclohexene in both parts A and B of this procedure, trans-2-iodocyclohexyl acetate is formed. The second equivalent of thal-lium(I) acetate scavenges iodide ion during formation of the 1,3-... 

These products are thought to result from attack of an intermediate p-nitro-phenyl radical on the solvent. Evidence for this intermediate was obtained by scavenging the radical with diphenylpicrylhydrazyl, halogens, and nitric oxide.(62) However, the presence of the p-nitrophenetole in the products formed in the presence of iodine, which effectively eliminates most other radical products, suggests that another mechanism involving a phenyl carbonium ion may be also operative ... 

In the paper published in 1900, he reported that hexaphenylethane (2) existed in an equilibrium mixture with 1. In 1968, the structure of the dimer of 1 was corrected to be l-diphenylmethylene-4-triphenylmethyl-2,5-cyclohexadiene 3, not 2 [38]. Since Gomberg s discovery, a number of stable radicals have been synthesized and characterized, e.g., triarylmethyls, phenoxyls, diphenylpicryl-hydrazyl and its analogs, and nitroxides [39-43]. The radical 1 is stable, if oxygen, iodine, and other materials which react easily with it are absent. Such stable radicals scarcely initiate vinyl polymerization, but they easily combine with reactive (short-lived) propagating radicals to form non-paramagnetic compounds. Thus, these stable radicals have been used as radical scavengers or polymerization inhibitors in radical polymerization. 

The reaction of trialkylboranes with 1,4-benzoquinones to give in quantitative yield 2-alkylhydroquinones was the first reaction of this type occurring without the assistance of a metal mediator [81,82], An ionic mechanism was originally proposed but rapidly refuted since the reaction is inhibited by radical scavengers such as galvinoxyl and iodine [83]. This procedure is in many cases superior to the more widely use organometallic additions. For instance, when primary and secondary alkyl radicals have been used and afford the addition products in high yield (Scheme 33) [84],... 

Following a similar strategy, an ingenious mixed resin bed quench and purification strategy was devised for the Dess-Martin periodinane mediated conversion of alcohols to carbonyls. This hypervalent iodine oxidant was viewed as containing an inherent masked carboxylic acid functionality that was revealed at the end of the reaction (Species (11) Scheme 2.30). Therefore purification was easily achieved by treatment of the reaction mixture with a mixed-resin bed containing both a thiosulfate resin and a polymeric base. The thiosulfate polymer was used to reduce excess hypervalent iodine lodine(V) and (III) oxidation states species to 2-iodoben-zoic acid (11), which was in turn scavenged by the polymeric base [51]. 

Isomerically pure chlorofullerene C oClg has been reported to be the predominant product of the reaction of with an excess of iodine monochloride in benzene or toluene at room temperature (Scheme 9.11) [79], The product is very soluble in benzene, carbon disulfide and tetrachloromethane. Deep orange crystals can be obtained by recrystallization from pentane. The synthesis of CjoClg using toluene as a solvent proceeds more slowly than with benzene, indicating that radicals are involved and are scavenged by the toluene [79],... 

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