Primary radicals manipulation

Manipulation of the Primary Radicals. In the radiolysis of aqueous solutions, the initially formed radicals can be manipulated via appropriate chemical additives to produce solutions that largely contain a single radical species. Solutions containing primarily the HO radical, the hydrated electron, or the hydrogen atom can be produced to study the reactions of individual radicals. As discussed in later sections, solutions of these selected radicals can then be converted to a variety of radical reactants with careful selection of reaction conditions. 

Addition of TEMPO to the reaction resulted in concomitant trapping of the cyclised primary radical, which was used to introduce a handle for further synthetic manipulations. 

The primary effect of radiation on aqueous solution is the decomposition of the water, followed by reactions of the transients from water with the solutes present. Direct effect of radiation on the solute is practically negligible up to concentrations of about 1 M, and because we are usually dealing with reasonably dilute solutions the discussion will be restricted to these indirect effects. It is, therefore, important to know what radicals are produced in irradiated water, how they react with the organic solutes, and how they can be manipulated for the production of certain organic radicals. These subjects have been studied very thoroughly and are sufficiently well understood to enable us to use the radiolysis of aqueous solutions for studies of diverse chemical problems. 

The free-radical addition of TFE to pentafluoroethyl iodide yields a mixture of perfluoroalkyl iodides with even-numbered fluorinated carbon chains. This is the process used to commercially manufacture the initial raw material for the fluorotelomer -based family of fluorinated substances (Fig. 3) [2, 17]. Telomeri-zation may also be used to make terminal iso- or methyl branched and/or odd number fluorinated carbon perfluoroalkyl iodides as well [2]. The process of TFE telomerization can be manipulated by controlling the process variables, reactant ratios, catalysts, etc. to obtain the desired mixture of perfluoroalkyl iodides, which can be further purified by distillation. While perfluoroalkyl iodides can be directly hydrolyzed to perfluoroalkyl carboxylate salts [29, 30], the addition of ethylene gives a more versatile synthesis intermediate, fluorotelomer iodides. These primary alkyl iodides can be transformed to alcohols, sulfonyl chlorides, olefins, thiols, (meth)acrylates, and from these into many types of fluorinated surfactants [3] (Fig. 3). The fluorotelomer-based fluorinated surfactants range includes noiuonics, anionics, cationics, amphoterics, and polymeric amphophiles. 

The first method will be less helpful, because we do not yet know how to manipulate a carboxylic acid group (COOH). That topic will be covered extensively in Chapter 21. In the meantime, we will have to use radical bromination to introduce functionality. The resulting benzylic halide can then be manipulated. But can a Br be converted into an aldehyde The bromine atom must be replaced with an oxygen, which requires a substitution reaction. Since the substrate is primary and benzylic, it is reasonable to choose an 5 2 process. 

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