Photochemical preparative methods

There are a wide variety of other synthetic methods for the preparation of oxetanes however, most of these are not very general. They frequently require starting materials which are difficult to prepare, and rarely give high yields (never as high as the better photochemical preparations). It is clear then that in comparison with the alternative methods of oxetane synthesis, the photocycloaddition reaction is more generally useful and convenient. This synthetic utility justifies a brief description of experimental conditions. 

In a series of transition metal oxide semiconductor powders, photochemical activity in the decarboxylation of oxalic acid was controlled by surface properties and the presence of recombination centers, which in turn depended on the preparation method Similar effects have also been noted in the photodecarboxylation of pyruvic acid and formic acid... 

Photochemical activation (15) and thermal activation (11,16, 17) of iron carbonyl complexes In various zeolites have been reported. Part of our study Is to use Mossbauer spectroscopy to Investigate the behavior of Fe(C0)5 on several zeolites when activated photochemically and thermally. Another part of our study Is to Investigate the novel preparation method of Scherzer and Fort (18) that Introduces iron Into (in their study) zeolite NH Y as an anionic complex. Finally, we will report the preparation of ferrocene sublimed onto zeolite ZSM-5. The photochemical and thermal activation of these systems will be reported as well as preliminary results of the photochemical isomerization of olefins by Fe(C0)5 zeolites and the thermal activation of Fischer-Tropsch catalytic systems. It also should be noted here that our Mossbauer studies involve an in-situ pretreatment cell which can be heated to 500°C under various gaseous atmospheres. 

Other preparative methods include the photochemical reaction between xenon and excess of fluorine in the presence of Nip2 as catalyst, thermal decomposition of XePe in the presence of NaP (this method is also convenient for the preparation of pure fluorine) and the pyrolysis of some XeP+ salts suchasXeP+PtPe orXeP+Pd2p9 at 423 K (equations 3 and 4). 

The photochemical cycloaddition method provides good yields of spirothietanes, as illustrated in the preparation of 50. The (—)3-menthyl ester of methacrylic acid gives thietane 51 in 17% optical purity via the diradical mechanism Si Ti), but in only 6% optical purity via the S2 state. ... 

The photocyclization reaction of 2-allylanilines, depending on the degree of alkylation at the N atom, has long been a subject of interest. When iV,iV-dialkylanilines 60a-62a were irradiated in methanol, the corresponding 2-cyclopropylanilines 60b-62b were formed in 73, 60 and 47% yield, respectively (equation 17)163. This reaction proceeds in the triplet state via a clean aromatic di-jr -methane rearrangement. However, no reaction occurs when 2-allyl-l-(Ai,Ai-dimethylamino)naphthalene is irradiated in methanol. Thus, this photochemical cyclopropanization of allylated anilines appears to have only a limited scope as preparative method, because it is successful only for a few substrates. 

Recently, a solution-based method for photochemical preparation of polyfullerences has been discovered [81,82]. In the photopolymerization, carefully deoxygenated fullerene cluster solutions are used. As discussed in the previous section, Cjo and C70 form microscopic aggregates or clusters in room-... 

The synthetic methods which have been used include modern versions of established methods of metal colloid preparation such as the mild chemical reduction of solutions of transition metal salts and complexes and newer methods such as radiolysis and photochemical reduction, metal atom extrusion from labile organometallics. And the use of metal vapor synthesis techniques. Some of these reactions have been in use for many years, and some are the results of research stimulated by the current resurgence in metal colloid chemistry. The list of preparative methods is being extended daily, and, as examples of these methods are described below, the reader will quickly be made aware that almost any organometallic reaction or physical process which results in the deposition of a metal is in fact a resource for the metal colloid chemist. The acquisition of new methods requires only the opportunism of the synthetic chemist in turning a previously negative result into a synthetic possibility. 

Hasegawa Y, Afzaal M, O Brien P, Wada Y, and Yanagida S, (2005) A novel method for synthesizing EuS nanocrystals from a single-source precursor under white LED irradiation. Chem Common 242-243 Zhao W-B, Zhu J-J, and Chen H-Y, (2003) Photochemical preparation of rectangular PbSe and CdSe nanoparticles. J Cryst Growth 252 587... 

The only photochemical preparation of indolines in 1980 has been reported by Schultz and Sha. They have extended some earlier work of their own on the preparation of dihydro-benzofurans, -thiophenes, and -selenoles by heteroatom-directed photoarylation. The latest work has emphasized that this photoarylation technique should be the method of choice for preparing indolines that were previously only accessible with great difficulty [e.g. (284) - (285)]. 

Cycloaddition Reactions.—These form the largest class of useful organic photochemical synthetic methods. The formation of cyclobutanes, with or without further rearrangement, dominates the subject, but larger rings have also been prepared. 

A different approach towards the incorporation of metal oxide clusters into zeo-litic pores via chemical vapor deposition has been studied extensively by Ozin et al. [236 - 240]. They developed a method denoted as intrazeolite metal carbonyl phototopotaxy . Metal carbonyls are used as precursors to obtain the occluded guest component because of their volatility, fitting molecular dimensions, ease of purification, ready availability, and facile and quantitative conversion to the respective metal oxide materials with minimal contamination by carbon [236, 240]. The metal carbonyl precursors are transformed into the metal oxides by photochemical oxidation. The term phototopotaxy is meant to indicate the similarity of this preparation method to epitactical growth of semiconducting oxide layers on planar surfaces commonly used to form low-dimensional quantum nanostructures for applications in electronic and optical devices [238]. 

Xenon dichloride [13780-38-6], XeCl, and xenon(II) chloroduoride [73378-52-6], XeClE, have been prepared by photochemical and electric discharge methods and have been examined at low temperatures by matrix-isolation techniques (39,40). The dichloride has a linear stmcture like that of XeE2. Evidence for the existence of XeCl2, XeBr2, and xenon tetrachloride [14989-42-5], XeCl, has been obtained from Mn ssbauer studies (41,42). Owing to thermal chemical instabiUties, no dihaUde other than the binary duorides has been prepared in macroscopic amounts. 

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