Deactivated basic alumina

The natural product (R)-sulcatol is a male-produced aggregation pheromone of the ambrosia beetle. This insect can devastate entire forests when its population is out of control.Various studies revealed that different species respond to the compound in different enantiomeric excess. The asymmetric synthesis of (R)-sulcatol was accomplished in the laboratory of S.G. Davies using a stereospecific [2,3]-Meisenheimer rearrangement as the key step. The treatment of the allylic amine substrate with mCPBA followed by the filtration of the reaction mixture through deactivated basic alumina afforded the desired hydroxylamine as a single diastereomer. 

Acid siUca neutral silica deactivated basic alumina, elution with hex and hexane DCM... 

Coburn and Comba [115] used activated Florisil (30 g column) and eluted PCDEs with 6% ethyl ether in hexane (200 ml) after they had collected PCBs with hexane (200 ml). Birkholz et al. [120] used a 0.8% deactivated Florisil column (12 g) as an additional cleanup after multisilica column chromatography. PCDEs and PCBs were eluted with 100 ml of hexane from Florisil. PCDEs were then separated from PCBs using a basic alumina column. Newsome and Shields [126] used Florisil (12 g column) deactivated with 2% water and eluted PCDEs with hexane (85 ml) for further cleanup by HPLC using acetonitrile as an eluent. Stafford [121] has also used deactivated Florisil. 

In general, basic compounds are retained more strongly on mildly acidic surfaces, such as silica or acidic alumina. Acidic compounds are retained on basic surfaces, such as basic alumina. Because both silica and alumina are hydroscopic, they adsorb water to their surface. This water greatly reduces the retention of organic solutes because it deactivates the hydrogen-bonding sites. Thus, it is important to keep the SPE sorbents dry and free from water. They may be stored in a dessicator prior to use. Very polar compounds, such as carbohydrates or amino compounds, are tightly bound to nonbonded normal-phase sorbents, such as silica and alumina. However, the use of cyanopropyl or aminopropyl phases often permit the recovery of these compounds when silica does not work. 

Catalytic activity and selectivity of pure and modified aluminas are presented at Figure 2. It can be seen that the activity and selectivity of the aluminas used depend on the cation introduced. 5at.% of basic elements decreases the alumina activity as follows 2.7 times for Mg, 7 times for Li, 40 times for Ca, 340 times for K. B-modified alumina, being more acid than y-Al203, demonstrates higher starting activity with respect to pure alumina, but it deactivates to a greater extent and has about 10% less activity imder steady-state conditions. Pure MgO is almost inactive under the conditions used ( see Table 1 ). 

Catalysts for coal liquefaction require specific properties. Catalysts of higher hydrogenation activity, supported on nonpolar supports, such as tita-nia, carbon, and Ca-modified alumina, are reasonable for the second stage of upgrading, because crude coal liquids contain heavy polar and/or basic polyaromatics, which tend to adsorb strongly on the catalyst surface, leading to coke formation and catalyst deactivation. High dispersion of the catalytic species on the support is very essential in this instance. The catalyst/support interactions need to be better understood. It has been reported that such interactions lead to chemical activation of the substrate 127). This is discussed in more detail in Section XIII. 

In conclusion, decrease in cyclohexanone oxime yield and caprolactam selectivity with time on stream is a major factor in the use of boria on alumina catalyst in the rearrangement reaction. Coke deposition and basic by-product adsorption have been suggested as a means of deactivation. In addition the conversion of water soluble boron, which is selective to lactam formation, to an amorphous water insoluble boron species is another factor that can account for the catalyst deactivation. 

Acid catalysts such as zeolites can be readily poisoned by basic organic compounds. One of the earlier studies of the deactivation of silica-alumina cracking catalysts by organic nitrogen compounds such as quinoline, quinaldine, pyrrole, piperidine, decylamine and aniline was done by Mills et al (6). The results of their partial poisoning studies showed an exponential dependence of the catalyst activity for cumene cracking reaction or... 

Activity-versus-time curves shown in Fig. 25 for alumina-supported Ni and Ni bimetallic catalysts show two significant facts (1) the exponential decay for each of the curves is characteristic of nonuniform pore-mouth poisoning, and (2) the rate at which activity declines varies considerably with metal loading, surface area, and composition. Because of large differences in metal surface area (i.e., sulfur capacity), catalysts cannot be compared directly unless these differences are taken into account. There are basically two ways to do this (1) for monometallic catalysts normalize time in terms of sulfur coverage or the number of H2S molecules passed over the catalysts per active metal site (161,194), and (2) for mono- or bimetallic catalysts compare values of the deactivation rate constant calculated from a poisoning model (113, 195). 

Different conditions (including additives and solvent) for the reaction have been reported,often focusing on the palladium catalyst itself," or the ligand." Catalysts have been developed for deactivated aryl chlorides," and nickel catalysts have been used." Modifications to the basic procedure include tethering the aryl triflate or the boronic acid to a polymer, allowing a polymer-supported Suzuki reaction. Polymer-bound palladium complexes have also been used." " The reaction has been done neat on alumina," and on alumina with microwave irradiation." Suzuki coupling has also been done in ionic liquids," in supercritical... 

Extent of deactivation is a basic criterion determining the efficiency of industrial catalysts. In the case of alumina catalysts widely used in the Claus process the main reason for their deactivation is sulfation (refs. 1,2) The poisoning by sulfates leads to a reduction in life of Claus catalysts, which usually does not exceed ilixee years ... 

Aluminas. Again the active exchange sites are the surface hydroxyl groups, which now have a more basic character and will also exchange or react with anions. These surface hydroxyl groups can again be removed by thermal dehydroxylation or be deactivated by anionic replacement by anions of both minerals and organic acids. The dehydroxylated surface is more readily rehydrated and is fairly readily hydrolysed by mineral acids. 

Although the catalysts showed high initial activity, rapid deactivation was also observed. For example, when using a Pt/t -alumina catalyst at 250 C, essentially complete TCA conversion was observed initially however, after 15 h TCA conversion had declined to < 25 percent. To understand the deactivation process, surface acidity and basicity, coke content, chlorine content, and platinum content were measured for both the fresh and the used catalysts. These measurements showed that up to 40 wt% coke formed on the supported platinum catalyst and that the acidity changed significantly during the reaction at 350°C. 

Alumina forms more and heavier coke than MgO but the latter deactivates faster. This is explained by the fact that on MgO primary aldol condensation reactions and formation of coke precursors species take place on the same basic sites. In contrast, alumina forms predominantly aromatic coke involving Bronsted OH groups that are inactive for aldol condensation reactions. The initial deactivation rate of acetone oligomerization on MgyAlOx oxides is essentially related to the surface basic properties. This is because the activity decline is significantly higher when coke poisons very active basic Mg-0 pairs than when eliminates moderately active acidic Al-O pairs. 

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