Isolation selective oxidation

Titanium Silicates. A number of titanium siUcate minerals are known (160) examples are Hsted in Table 19. In most cases, it is convenient to classify these on the basis of the connectivity of the SiO building blocks, eg, isolated tetrahedra, chains, and rings, that are typical of siUcates in general. In some cases, the SiO units may be replaced, even if only to a limited extent by TiO. For example, up to 6% of the SiO in the garnet schorlomite can be replaced by TiO. In general, replacement of SiO by TiO bull ding blocks increases the refractive indices of these minerals. Ti has also replaced Si in the framework of various zeofltes. In addition, the catalytic activity of both titanium-substituted ZSM-5 (TS-1) and ZSM-11 (TS-2) has received attention (161), eg, the selective oxidation of phenol, with hydrogen peroxide, to hydroquinone and catechol over TS-1 has been operated at the 10,000 t/yr scale in Italy (162). 

Secondary alcohols are oxidized at room temperature to ketones in high yields by HOCl generated in situ from aqueous NaOCl and acetic acid (109,110). Selective oxidation in the presence of a primary alcohol is possible. In methanol, aldehydes are oxidized to methyl esters (110). Under the proper conditions, alcohols can be esterified with HOCl forming isolable alkyl hypochlorites. 

Zndo Selectivity Example The inlra-molecular Diels-Alder reaction was used to make (19) needed for a synthesis of the natural product torreyol. The intermediate (IS) could not be isolated as oxidation of alcohol (17) gave (19) directly. The intramolecular Diels-Alder must be very efficient. 

The method outUned above was initially investigated for the introduction of isolated Ti(IV) sites onto a sihca substrate for use in selective oxidation catalysis. Since the development of a silica-supported Ti(lV) epoxida-tion catalyst by Shell in the 1970s, titania-sihca materials have attracted considerable attention [135,136]. Many other titania-sihca materials have been studied in this context including, but not hmited to, TSl and TS2 (titanium-substituted molecular sieves), Ti-/i (titanium-substituted zeolite). 

The resulting microgel-stabilized metal nanoclusters are easily isolated, stored and further manipulated. Their remarkable catal5dic activity in technologically relevant reactions, such as C-C couplings [13a- ] and selective oxidations with molecular oxygen [13e] has been demonstrated. Extension of the applications of these nanoparticles to other areas of catalysis and materials science is currently underway. 

One of the exciting results to come out of heterogeneous catalysis research since the early 1980s is the discovery and development of catalysts that employ hydrogen peroxide to selectively oxidize organic compounds at low temperatures in the liquid phase. These catalysts are based on titanium, and the important discovery was a way to isolate titanium in framework locations of the inner cavities of zeolites (molecular sieves). Thus, mild oxidations may be run in water or water-soluble solvents. Practicing organic chemists now have a way to catalytically oxidize benzene to phenols alkanes to alcohols and ketones primary alcohols to aldehydes, acids, esters, and acetals secondary alcohols to ketones primary amines to oximes secondary amines to hydroxyl-amines and tertiary amines to amine oxides. 

In principle, all of the methods for selective oxidations of di- and polyenes28 can be employed for analytical derivatization. However, the complexity of products obtained rules out some of these. Despite this, epoxidation of selected double bonds is used for comparison of spectra (see previous discussion on MS). Epoxidation of isolated non-conjugated... 

D-Glucaric acid, directly produced by nitric oxidation of glucose or starch, is usually isolated as its 1,4-lactone. The technical barrier to its large-scale production mainly includes development of an efficient and selective oxidation technology to eliminate the need for nitric acid as the oxidant. Because it represents a tetrahydroxy-adipic acid, D-glucaric acid is of similar utility as adipic acid for the generation of polyesters and polyamides (see later in this chapter). 

The reaction network for isobutane selective oxidation catalyzed by POMs consists of parallel reactions for the formation of methacrolein, methacrylic acid, carbon monoxide, and carbon dioxide. Consecutive reactions occur on methacrolein, which is transformed to acetic acid, methacrylic acid, and carbon oxides. ° Methacrylic acid undergoes consecutive reactions of combustion to carbon oxides and acetic acid, but only under conditions of high isobutane conversion. Isobutene is believed to be an intermediate of isobutane transformation to methacrylic acid, but it can be isolated as a reaction product only for very low alkane conversion. ... 

Following the discovery of TS-1 [125], a titanium-substituted MFl, the use of zeolitic materials for oxidation increased significantly. The presence of the Ti atom in the framework of a zeolite structure provides a site-isolated Ti center, a situation not possible with other Ti-containing materials while also allowing shape-selective oxidations. The combination of the two effects gives highly active and selective oxidation reactions [126]. 

The trivalent phosphorus atom in triphenylphosphine is quantitatively oxidized by in-situ-generated or isolated DMD, to afford triphenylphosphine oxide under a variety of conditions Recently, the selective oxidation of the phosphite functionality in nucleosides was reported to produce the corresponding nucleotides in nearly quantitative yields". One example of such an oxidation is shown in equation 16, to illustrate that this phosphorus oxidation may offer an expedient way of preparing unusual nucleotides. 

The Role of Site Isolation and Phase Cooperation in Selective Oxidation Catalysis, R. K. Grasselli and J. M. Thomas, eds., Kloster Irsee, 2000 Top. Catal. 15, 83-289 (2001). 

From a mechanistic viewpoint it is worth noting that the TS-1 catalyst contains the same chemical elements in roughly the same proportions as the Shell amorphous TiIV/Si02 catalyst referred to earlier. However, the former displays a much broader range of activities than the latter. A possible explanation may be that the TS-1 catalyst contains more (or more active) isolated titanyl centres than the amorphous Ti1v/Si02. Based on the quite remarkable results obtained with TS-1 we expect many more examples of redox zeolites, i.e. zeolites, alpos, etc. modified by isomorphous substitution with redox metal ions in the crystal lattice, as selective oxidation catalysts.66... 

Ref. 5b IBX performs the selective oxidation of a primary alcohol, leading to a hydroxyaldehyde that is isolated as a lactol that, interestingly, does not suffer a further oxidation to a lactone. ... 

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