Reactions via Free Radicals

Stable bubbles are relatively large, are produced at intensities less than 3 W/cm, and oscillate for several acoustic cycles, almost in unison with the acoustic wave, before collapsing, or never collapse at all. Such cavitation can also lead to chemical reaction via free radical formation. 

Acrylics. Historically, acrylics offer several useful characteristics as structural adhesives. Most well known is their relatively high speed of reaction via free-radical polymerization. The details of their reaction provide a useful division... 

Conventional free-radical initiators such as di-t-butyl peroxide can serve as the effective initiators for the inclusion polymerization of diene monomers in DCA and apoCA canals [lO]. During the course of the polymerization we succeeded in observing ESR spectra of living-like propagating radicals of allylic type in the canals. This result confirms the existence of the polymerization reaction via free-radical mechanism. 

Balwin JE, Adlington RM, Singh R. Carbocychc ring expansion reactions via free radical pathways. Part III. Tetrahedron 1992 48(16) 3385-3412. 

The second mechanism is the one followed when addition occurs opposite to Markovmkov s rule Unlike electrophilic addition via a carbocation intermediate this alternative mechanism is a chain reaction involving free radical intermediates It is pre sented m Figure 6 7... 

Cation (Section 1 2) Positively charged ion Cellobiose (Section 25 14) A disacchande in which two glu cose units are joined by a 3(1 4) linkage Cellobiose is oh tamed by the hydrolysis of cellulose Cellulose (Section 25 15) A polysaccharide in which thou sands of glucose units are joined by 3(1 4) linkages Center of symmetry (Section 7 3) A point in the center of a structure located so that a line drawn from it to any element of the structure when extended an equal distance in the op posite direction encounters an identical element Benzene for example has a center of symmetry Cham reaction (Section 4 17) Reaction mechanism m which a sequence of individual steps repeats itself many times usu ally because a reactive intermediate consumed m one step is regenerated m a subsequent step The halogenation of alkanes is a chain reaction proceeding via free radical intermediates... 

Results of studies of the electrocyclic ring opening of 3 fluoro-, 3,3-difluoro-, and 3-tnfluoromethylcyclobutene are consistent with the theoretical predictions of the effect of fluonne on this reaction [142] Surpnsingly, fluonnated analogues of hexa tnene-cyclohexadiene systems undergo complex rearrangements mainly via free radical mechanisms and not by electrocyclic nng operung as expected [143] (equation 35)... 

Chain reaction (Section 4.17) Reaction mechanism in which a sequence of individual steps repeats itself many times, usually because a reactive intermediate consumed in one step is regenerated in a subsequent step. The halogenation of alkanes is a chain reaction proceeding via free-radical intermediates. 

Recently, an interesting reaction of -dinitrobenzene v/ith trialkylborane has been reported, in which the iritro group is replaced by an alkyl group in good yield fEq 913 " The reacdon is not a simple ionic reacdon, but proceeds via free radical intermediates... 

The oxides are gaseous and do not undergo reactions in the atmosphere that produce aerosol particles. Carbon monoxide is a relatively inert material with its main sinks in the atmosphere via reactions with free radicals, e.g.,... 

The time-dependent nature of migration and chemical reaction of free radicals [30] in irradiated polymers can play an important role in altering the polymer structure and properties, e.g., cross-link formation via reactive sites or chain scission, or postirradiation oxidative influences (irradiation in presence of air or oxygen). 

Scheme 36 Preparation of vinylphosphonates via free radical Arbuzov reaction...

In nonaqueous solutions, two other types of reactions have been observed with polycyclic arenes condensation via free-radical reactions and oxidative ring fission. 

PMMA can exist in two simple stereoregular forms, isotactic and syndiotactic, but commercially available samples—prepared via free-radical initiators—tend to have tacticities lying in the range 60-70% syndiotactic triad content, the exact content depending upon the reaction temperature.426 Several terminating side reactions have been identified, the most important of which is intramolecular cyclization leading to methoxide formation, as shown in Scheme 5.427... 

As a result, the decay of antioxidant proceeds via two ways, namely, by the reaction with free radicals and by the oxidation by hydroperoxide on the surface of Cu with the summary rate... 

As previously mentioned, Davis (8) has shown that in model dehydrocyclization reactions with a dual function catalyst and an n-octane feedstock, isomerization of the hydrocarbon to 2-and 3-methylheptane is faster than the dehydrocyclization reaction. Although competitive isomerization of an alkane feedstock is commonly observed in model studies using monofunctional (Pt) catalysts, some of the alkanes produced can be rationalized as products of the hydrogenolysis of substituted cyclopentanes, which in turn can be formed on platinum surfaces via free radical-like mechanisms. However, the 2- and 3-methylheptane isomers (out of a total of 18 possible C8Hi8 isomers) observed with dual function catalysts are those expected from the rearrangement of n-octane via carbocation intermediates. Such acid-catalyzed isomerizations are widely acknowledged to occur via a protonated cyclopropane structure (25, 28), in this case one derived from the 2-octyl cation, which can then be the precursor... 

In the simultaneous interpenetrating networks (SIN), the two reactions are run simultaneously. This reaction will be emphasized in the present paper. One reaction, for example, can be a polyesterification or a polyurethane stepwise reaction, while the other is an addition reaction using styrene to make polystyrene via free radical chemistry. 

The mechanism of this reaction involves free radical oxidation of butane to butane hydroperoxide, which decomposes to acetaldehyde via P scissions. It is similar to the oxidation of cyclohexane to cyclohexanol and cyclohexanone, which will be discussed in Chapter 11, Section 4. 

Intramolecular cyclization of diphenylamines to carbazoles is one of the most versatile and practical methods. This has been achieved photochemically, thermally in the presence of elemental iodine at 350°C, or with platinum at 450-540°C, via free radicals with benzoyl peroxide in chloroform, or by using activated metals such as Raney nickel or palladium on charcoal. Most of these methods suffer from low to moderate yields, and, in some cases, harsh reaction conditions (8,480). 

Didehydroferulic Acid 23 Formation. It should be noted that no direct evidence has ever been obtained in vivo to prove that didehydroferulic acid 23 is formed via free radical coupling reactions. This mechanism is assumed, since in vitro incubation of ferulic acid 1 and wheat pentosan, with... 

The above reactions proceed via free radical coupling. An alternative system for photochemically driven hydrocarbon functionalization evidently proceeds via the carbanion, which is obtained from reduction of the initially formed free radical3. The carbanion reacts with acetonitrile to give, after in situ hydrolysis, the methyl ketone, e.g., formation of (tricyclo[3.3.1.13-7]dec-1-yl)ethanone6. 

---