Iodine transfer

Polymerization of S and certain fluoro-monomers in the presence of alkyl iodides provided the first example of the reversible homolytic substitution process (Scheme 9.35). This process is also known as iodine transfer polymerization (Section 9.5.4).381 Other examples of reversible homolytic substitution are polymerizations conducted in the presence of certain alkyl tellurides or stibines (Sections 9.5.5 and 9.5.6 respectively). 

The history of iodine transfer polymerization may be traced back to telomerization experiments carried out in the 1940fs.26"3" Iodine-transfer... 

Inductive effect 149, see also Field effect Iodine transfer, as probe for aryl radicals 205... 

Iodine-transfer cyclization. Irradiation of unsaturated a-iodo carbonyl compounds in the presence of a hexaalkylditin (5-10%) can result in isomerization to cyclic y-iodo carbonyls.1 The reaction is very slow in the absence of an initiator. Thus under these conditions 1 isomerizes to a mixture of 2 and 3 in which 2 predominates. The reaction is particularly useful for formation of fused bicyclic systems (4 - 5). 

Leblanc C, Colin C, Cosse A, Delage L, La Barre SL, Morin P, Fievet B, Voiseux C, Ambroise Y, Verhaeghe E, Amouroux D, Donard O, Tessier E, Potin P (2006) Iodine transfers in the coastal marine environment the key role of brown algae and of their vanadium-dependent haloperoxi-dases. Biochimie 88 1773-1785... 

If the water containing the iodine is placed in the same container as pure hexane and the container shaken, extraction will be demonstrated because when the iodine transfers to the hexane layer, this layer will turn pink. 

Eq. 19c). The mechanism of this transformation involves either a final iodine transfer step or an electron transfer process that give back the trifluoromethyl radical. 

This mechanism can be illustrated by the reaction of ferrous ions with hydrogen peroxide (42), the reduction of organic peroxides by cuprous ions (63), as well as by the reduction of perchlorate ions by Ti(III) (35), V(II) (58), Eu(II) (71), The oxidation of chromous ions by bromate and nitrate ions may also be classified in this category. In the latter cases, an oxygen transfer from the ligand to the metal ion has been demonstrated (8), As analogous cases one may cite the oxidation of Cr(H20)6+2 by azide ions (15) (where it has been demonstrated that the Cr—N bond is partially retained after oxidation), and the oxidation of Cr(H20)6+2 by 0-iodo-benzoic acid (6, 8), where an iodine transfer was shown to take place. 

Concerning iodinated transfer agents almost all perfluoroalkyl iodides and, a, co-diiodoperfluoroalkanes were successfully utilised in thermal telomerisation ofVDF. 

The cleavage of C-I bond can be achieved from various methods [373-375]. However, according to well chosen monomers, two main ways have been developed in order to control telomerisation from alkyl iodides iodine transfer polymerisation (ITP) and degenerative transfer. ITP can be easily applied to fluorinated monomers whereas degenerative transfer concerns the controlled polymerisation of methyl methacrylate, butyl acrylate [376] or styrene [377] and will not be discussed in this chapter. 

Several investigations have shown that iodine transfer polymerisation can occur by emulsion or radical initiation. When emulsion initiation is chosen, a per-fluoroalkyl iodide is involved and limits the molecular weights [378,379]. This is not described here but several articles and patents from Tatemoto are sug-... 

There are essentially two methods used for the production of commercial FTPEs. The first is referred to as iodine transfer polymerization, which is similar to the living anionic polymerization used to make block copolymers such as styrene-butadiene-styrene (e.g., Kraton ). The difference is that this living polymerization is based on a free radical mechanism. The products consist of soft segments based on copolymers of vinylidene fluoride (VDF) with hexafluoropropylene (HFP) and... 

Since the Barton reaction and the Hofmann-Lofifler-Freytag reaction generate very reactive oxygen-centered and nitrogen-centered radicals respectively, the next 1,5- and 1,6-hydrogen atom abstraction reaction readily happens. However, 1,5-H shift does not proceed effectively by carbon-centered radicals, because there is not so much energy difference between the C-H bond before and after 1,5-H shift. So the reactions are quite limited. Eq. 6.21 shows iodine transfer from reactive 1-iodoheptyl phenyl sulfone (40) to a mixture of 5-iodoheptyl phenyl sulfone (41a) and 6-iodoheptyl phenyl sulfone (41b) initiated by benzoyl peroxide, through 1,5-H shift by an sp3 carbon-centered radical [56-58]. 

Halohydrins are /J-halogenated alcohols. They can be obtained in H20-containing solvents from alkenes and reagents, which transfer Hal ions. N-Broniosuccinnuide (transfers Br Figures 3.43 and 3.44 as well as 3.47), chloramine-T (transfers Cl Figure 3.46), and elemental iodine (transfers I Figure 3.47) have this ability. Bromonium and chloronium ions react with H20 via an SN2 mechanism. This furnishes the protonated bromo- or chlorohydrins, which are subsequently deprotonated. 

Fiirstner reported the first McMurry-type reactions working with 5-10 mol% of titanium trichloride and stoichiometric amounts of zinc powder in the presence of chlorotrimethylsilane. The amount of TiCl3 could be reduced to 2 mol% when (ClMe2SiCH2)2 was used as a reagent [125, 131]. At the same time, Burton and coworkers reported atom transfer radical additions of perfluoroalkyl iodides 39 to alkenes 40 catalyzed by 20 mol% of a low-valent titanium compound generated from TiCLt and zinc powder affording 41 in 10-85% yield (Fig. 13). A tandem radical addition/5-exo cyclization/iodine transfer reaction with diallyl ether proceeded in 66% yield [132]. 

Fig. 53 Copper powder-catalyzed iodine transfer radical additions...

Iodine Transfer about 20 g of sample, accurately weighed, into a 600-mL beaker, and dissolve in about 300 mL of water. Add a few drops of methyl orange TS, neutralize the solution with 85% phosphoric acid, and then add 1 mL excess of the acid. Add 25 mL of bromine TS and a few glass beads, boil until the solution is clear, then boil for an additional 5 min. Add about 50 mg of salicylic acid crystals, 1 mL of phosphoric acid, and 10 mL of a 1 20 potassium iodide solution, and titrate to a pale yellow color with 0.01 N sodium thiosulfate. Add 1 mL of starch TS, and continue the titration to the disappearance of the blue color. Each milliliter of 0.01 N sodium thiosulfate is equivalent to 0.2767 mg of potassium iodide (KI). 

---