Thermal or photolytic

Chemical Properties. Acychc di-Z f/-alkyl peroxides efftciendy generate alkoxy free radicals by thermal or photolytic homolysis. 

Heterocycles which provide the NOC or CNO component synthon Isoxazoles can be prepared by the thermal or photolytic cleavage of a number of heterocycles, such as 1,3,5-dioxazolidone, furazans, furoxans and 1,3,2,4-dioxathiazole 2-oxides, in the presence of a reactive alkene or alkyne. 

The thermal or photolytic fragmentation of furazans to nitriles and nitrile Af-oxides has been reported (73JOC1054, 75JOC2880). The irradiation of dimethylfurazan (419) in the presence of cyclopentene, and benzofurazan (420) in the presence of dimethyl acety-lenedicarboxylate, gave isoxazoline (421) and isoxazole (422), respectively, in good yields. The thermolysis of acenaphtho[l,2-c]furazan (423) in the presence of phenylacetylene gave isoxazole (424) in 55% yield. 

The radical X is formed by homolysis of the X—R bond either thermally or photolytically. In the reactions of alcohols with lead tetraacetate evidence suggests that the X—R bond (X = 0, R = Pb(OAc)3) has ionic character. In this case the oxy radical is formed by a one electron transfer (thermally or photochemically induced) from oxygen to lead. 

The interaction of lead tetraacetate with an alcohol leads to an intermediate lead alkoxide [e.g., (1)] which decomposes either thermally or photolytically. 

The addition of halogenated aliphatics to carbon-carbon double bonds is the most useful type of carbon-carbon bond forming synthetic method for highly halogenated substrates Numerous synthetic procedures have been developed for these types of reactions, particularly for the addition of perfluoroalkyl iodides to alkenes using thermal or photolytic initiators of free radical reactions such as organic peroxides and azo compounds [/]... 

The coordination chemistry of NO is often compared to that of CO but, whereas carbonyls are frequently prepared by reactions involving CO at high pressures and temperatures, this route is less viable for nitrosyls because of the thermodynamic instability of NO and its propensity to disproportionate or decompose under such conditions (p. 446). Nitrosyl complexes can sometimes be made by transformations involving pre-existing NO complexes, e.g. by ligand replacement, oxidative addition, reductive elimination or condensation reactions (reductive, thermal or photolytic). Typical examples are ... 

The nitrene can be generated by a variety of methods, the most popular being the thermal or photolytic decomposition of azidoformates. Other methods, particularly the base-catalyzed a-elimination of arylsulfonate ion from 7V-[(arylsulfonyl)oxy]urethanes, are useful as they avoid the use of the potentially explosive azido esters. 

In contrast to the acyl- and sulfonylnitrenes described in this section, arylnitrenes produced thermally or photolytically from aryl azides, including those bearing strongly electron-withdrawing substituents (e.g., CN, N02, CF3), fail to promote ring expansion of arenes to 1H-azepines, although intermolecular substitution of electron-rich substrates, e.g. mesitylene and A.TV-dimethylaniline, have been noted.167... 

Metal carbonyl compounds are other suitable precursors for the synthesis of NPs by thermal decomposition. The main advantage is the formation of CO that is expelled from the IL phase due to its poor solubility. However, high temperatures are commonly used to decompose such precursors. Metal NPs of Cr(0), Mo(0), and W(0) were prepared by thermal or photolytic decomposition of their respective monometallic carbonyl compounds [M(CO)6] dispersed in ILs [52]. Similarly, the precursors [Fe2(CO)9], [Ru3(CO)i2], and [Os3(CO)12] were employed in order to obtain stable metal NPs (1.5-2.5 nm) in BMI.BF4 [53]. The same procedure was extended to the preparation of lr(0), Rh(0), and Co(0) NPs in ILs [54]. 

Continued heating resulted in darkening of the resin, formation of a 1770 cm"l absorption for 6 in the IR, development of a broad absorption covering 1700-1300 cm"- -, and decrease of the absorptions due to CH2CpCo(C0)2- Evidently, 7 was not formed under these conditions. No other absorptions were noted in either the thermal or photolytic decar bony lation. It can thus be concluded that the 1% DVB matrix with 6% substitution does not maintain site-site isolation. 

INITIAL LOSS OF CO MAYBE THERMALLY OR PHOTOLYT CALLY PROMOTED... 

Method (i), the thermal or photolytic ejection of CO, is known to be unfavorable (see above). Method (ii), the removal of CO as C02 by oxidation with Me3NO, is an easily carried-out procedure and has led to the synthesis of many hitherto inaccessible compounds. By this route the ethylene cluster Os3(CO)nC2H4 has been synthesized. 

The oxidative cyclization of Ar,Ar-diarylamines to carbazoles has been achieved by thermal or photolytic induction [7, 75]. However, the yields for this transformation are mostly moderate. Better results are obtained by the palladium(II)-mediated oxidative cyclization of Ar,Ar-diarylamines (Scheme 27). Oxidative cyclization by heating of the Ar,Ar-diarylamines 76 in the presence of a stoichiometric amount of palladium(II) acetate in acetic acid under reflux provides the corresponding 3-substituted carbazoles 77 in 70-80% yield [118]. The cou-... 

Low-valent, 18-electron carbene complexes (Fischer-type) are electronically and coordinatively saturated and must usually be activated to become efficient metathesis catalysts. This activation can be effected by thermal or photolytic [781,782] removal of one ligand, e.g. carbon monoxide, or by treatment with a Lewis acid (Table 3.15) [783]. 

An important route to the carbazoles is the thermal or photolytic decomposition of orf/zo-azidobiphenyls. Of the two procedures, thermolysis proceeds in higher yields. One advantage of photolysis is that it proceeds at room temperature and would therefore be compatible with thermally labile functional groups. 

The primary process following a photoexcitation of nltrosamldes XIV Is the dissociation of the N-N bond to form a radical pair XV and the ensuing chemical events are the reactions of amldyl and nitric oxide radicals In the paired state or Individually In the bulk of solutions. Naturally, secondary reactions, thermal or photolytic, have to be taken Into consideration under Irradiation conditions (21). First of all, the relatively straightforward chemistry of selective excitation In the n-ir transition band (>400 nm) will be discussed, followed by the chemistry of Irradiation with a Pyrex filter (>280 nm). As nitric oxide Is known to be rather unreactlve (23), primary chemical processes In the Irradiation with >400 nm light under... 

Although there are exceptions, which will be mentioned in the appropriate sections of this chapter, A-nitrosation is usually carried out on nitrogen compounds in which the nitrogen bears only one hydrogen. The A-nitroso derivatives frequently are thermally or photolytically unstable or both. Many of them have a corrosive action on the skin or on the mucous membranes, and some are said to be carcinogenic. Consequently all A-nitroso compounds must be handled with extreme caution. 

Vibrational Wavenumbers (cm ) and Intensities for Surface Methyl Groups on Metal Single Crystals Generated by Thermal or Photolytic... 

Chemical Properties. Acyclic di-ferf-alkyl peroxides efficiently generate alkoxy free radicals by thermal or photolytic homolysis. Primary and secondary dialkyl peroxides undergo thermal decompositions more rapidly than expected owing to radical-induced decompositions. Such radical-induced peroxide decompositions result in inefficient generation of free radicals. 

IV, C), have been observed. Others, such as thermal or photolytic bond breaking with subsequent reactions, reductive bond breaking, or insertion reactions, have yet to be developed. 

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