The Use of Alumina

The transformation of ditertiary 1,2-diols was found to be non-selective-a mixture of dienes and ketones is formed and diene selectivity often exceeds that for rearrangement products [14-16]. Increasing surface acidity and increasing temperature have been shown to shift the selectivity toward diene formation [17]. 

High carbonyl selectivity has also been reported in the transformation of other diols, e. g. disecondary, secondary-tertiary and ditertiary furyl- [22], and ethynyl-substituted [23] compounds, stereoisomeric 2,3-butanediols, and hydrobenzoins 

2-butanone, formed by hydrogen migration. Interestingly, selectivity in the transformation of mexo-hydrobenzoin depends on the temperature. Steric interactions 

A specific catalyst, an aluminum-containing polymethylsiloxane prepared from aluminum hydroxide and chloromethylsilanes, catalyzes the rearrangement of pinacol in the vapor phase (523 K, pulse technique) [25]. High activity but rapidly decreasing selectivity are characteristic of this catalyst. 

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AI2O3, H2O, hexanes, 81-98% yield. These conditions are selective for the primary derivative. TBDPS and TMS ethers are also cleaved. The use of alumina in a microwave oven is also effective (68-93% yield). ... 

Another method of calculating the % changeover is by the use of alumina balance. 

In a further attempt to improve properties, Brauer, McLaughlin Huget (1968) examined the use of alumina as a reinforcing filler. Alumina is considerably more rigid than fused quartz. They achieved a considerable increase in strength. The preferred composition was the powder defined in Table 9.4, which had a compressive strength of 91 MPa. This zinc oxide based powder was the one most commonly used in subsequent studies by Brauer and coworkers. We shall refer to it as the EBA powder for it is the one used in commercial formulations and in a number of experimental studies. 

Varma and coworkers have explored the use of hypervalent iodine compounds on solid support for the first time and developed a facile oxidative procedure that rapidly converts alcohols to the corresponding carbonyl compounds using alumina-sup-ported IBD under solvent-free conditions and MW irradiation in almost quantitative yields [108]. The use of alumina as a support improved the yields markedly as compared to neat IBD (Scheme 6.33). 1,2-Benzenedimethanol, under these conditions, undergoes cyclization to afford l(3H)-isobenzofuranone. 

With the introduction of synthetic dyes, attempts were made to prepare pigments from them by methods based on those that had been used with the natural dyes. Many soluble azo dyes can be rendered insoluble by precipitating them as the salts of heavy metals in the presence of so-called alumina hydrate. This method will be treated in detail later and here only the making of pigments from acid dyes and basic dyes will be mentioned. The use of alumina hydrate as a basic substrate for making pigments from dyes is now, however, of diminishing commercial importance. 

Another method (EPA 3611) that focuses on the to separation of groups or fractions with similar mobility in soils is based on the use of alumina and silica gel (EPA 3630) that are used to fractionate the hydrocarbon into ahphatic and aromatic fractions. A gas chromatograph equipped with a boiling-point column (nonpolar capillary column) is used to analyze whole soil samples as weU as the aliphatic and aromatic fractions to resolve and quantify the fate-and-transport fractions. The method is versatile and performance based and therefore can be modified to accommodate data quality objectives. 

As long as the /1-alumina sensor remains homogeneous as far as Na+ is concerned (which is achieved by the high fraction of Na20), we see from Eqn. (15.6) that the electron potential varies inversely with the oxygen activity. We have already mentioned that /1-alumina is able to incorporate a number of different cations into the conducting plane. This non-specificity hampers the use of / -alumina as a universal sensor material under ordinary conditions. If more than one mobile component is... 

Both reaction processes are base catalysed, and the use of alumina (Brockmann activity I) at room temperature is a particularly mild method leading to good yields of products.203... 

The use of alumina packing to better distribute the steam bubbles was also investigated, and the kinetic results show that there was enhanced contact of steam and CaBr2. Therefore, various design options for steam distribution should be investigated further. 

Alternative approaches have been proposed over the years. In none of these cases is there sufficient experimental evidence for truly heterogeneous catalysis. Frechet et al. (55) used a polyvinylpyridinium (PVP) material for supporting chlorochromate [Cr(IV)02Cl ] or dichromate [CrCVI Oy-]. Cr3+ can be immobilized by simple ion exchange on polymers such as Nation or on a Y zeolite (59, 60). However, it is doubtful whether these methods ensure complete Cr anchoring when the material is brought into contact with oxidants. Clark et al. (61) advocated the use of alumina-anchored dichromate. Particularly when a neutral alumina is used, surface-anchored species are formed ... 

A number of catalytic reactions studied by Russian authors are necessarily left out of this review. These include nitration and sulfona-tion (138). As an example the use of alumina in the synthesis of heterocyclic compounds may be mentioned. Ethylene oxide with ammonia gave pyridine with hydrogen sulfide about 20 % thiophene was formed at 300-450° (211). At 200°C. ethylene oxide and hydrogen sulfide gave thioxane and dithiane (212,429). Yur ev developed conditions under which the hetero atom of furan, thiophene, and pyrrole could be interchanged (425,426,427,428). 

The earlie industrial developments of vapor phase alkylation processes involved the use of alumina base catalyst systems. They include the Koppers technique industrialized in the Second World War, which operates around 310°C and between 6 and 6. 10 Pa absolute, but does not allow the transalkylation of polyethylbenzenes. 

C. Laurent, H. Billiet, and L. De Galan, On the use of alumina in HPLC with aqueous mobile phases at extreme pH, Chromatographia 17 (1983), 253-258. 

In the years since the last review of sulfonic esters of carbohydrates, there have been many developments in physical methods for isolation of organic compounds and for their structural elucidation. Column chromatography on a variety of adsorbents has found wide application in the separation and isolation of esters of carbohydrates. Caution should be exercised in the use of alumina as the adsorbent for primary sulfonates on neutral or basic alumina of activity I, selective hydrolysis of the primary sulfonate group occurred with methyl 3,4 - di - O - methyl - 2,6 - di - O - (methylsulfonyl) - a - D - glucopyranoside, methyl 2,3-di-0-methyl-4,6-di-0-(methylsulfonyl)-/3-D-glucopyrano-side, and methyl 4-0-methyl-2,3,6-tri-0-(methylsulfonyl)-a-D-manno-pyranoside in benzene or ethanol-free chloroform. Analogous results... 

Alumina membranes made by anodic oxidation were tested for separating hydrogen and carbon monoxide at a temperature up to 9T C [Itaya, 19S4], The ideal separation factor only achieved 3.5. See Table 7.4. Wu et al. [1993] also examined the use of alumina membranes for this application at an even higher temperature of 300 C and obtain a maximum separation factor of only 2.2. The alumina membranes used in the above studies all have pore diameters larger than 4 nm. Their separation factors for the H2/CO gas pair are no higher than the Knudsen diffusion values of 3.7 most likely as a result of the limitation imposed by the relatively large pores involved. 

Despite the limitations of unmodified silica as a stationary phase for normal phase chromatography, it remains the most common adsorbent in this field, although there has been a recent renewal of interest in the use of alumina. 

Ahmad, J. The use of alumina as stationary phase for thin layer chromatography of inorganic and organometallic compounds. JPC, J. Planar Chromatogr. Mod. TLC 1996, 9, 236-239. 

Varma et al. have reported for the first time the use of supported iodobenzene diacetate (IBD) as an oxidant the use of alumina as a support improved the yields markedly as compared to neat IBD (Scheme 8). The solid IBD-alumina system has also been used for the rapid, high yielding, and selective oxidation of alkyl, aryl, and cyclic sulfides to the corresponding sulfoxides upon MW irradiation ... 

Hydrohalogenation. Hydrohalogenation has also become more convenient with the use of alumina (or silica). As a typical example, 1-octene reacts with HBr only very slowly in solution and very quickly onto alumina without competitive radical addition [Eq. (8)] [15]. 

The use of alumina and silica to promote Diels-Alder reactions was first reported by Hudlicky [24]. The reactions of 1-acetoxy-l,3-butadiene with tetrafluoro-p-benzoquinone or / -benzoquinone were considerably accelerated when they occurred inside the pores of the adsorbents. Several other silica- or alumina-catalyzed Diels-Alder reactions, dealing either with investigation of standard model reactions [25] or of reactions of more synthetic utility, were subsequently described. For example, neutral alumina catalyzed the intramolecular reaction of a tetraene to the verrucarol skeleton [26] (Scheme 3). The catalytic action was observed in an attempt to isolate the tetraene by column chromatography. A variety of Diels-Alder reactions were accelerated by silica or the more basic Florisil (Mg0.Si02) in the absence of solvent [27-30]. Table 3 gives some examples of these reactions, which are thought to be catalyzed via multicentered donor-acceptor interactions of the substrates with the active sites of the surface of the adsorbents. 

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