Selection inefficiency

Process Technology Evolution. Maleic anhydride was first commercially produced in the early 1930s by the vapor-phase oxidation of benzene [71-43-2]. The use of benzene as a feedstock for the production of maleic anhydride was dominant in the world market well into the 1980s. Several processes have been used for the production of maleic anhydride from benzene with the most common one from Scientific Design. Small amounts of maleic acid are produced as a by-product in production of phthaHc anhydride [85-44-9]. This can be converted to either maleic anhydride or fumaric acid. Benzene, although easily oxidized to maleic anhydride with high selectivity, is an inherently inefficient feedstock since two excess carbon atoms are present in the raw material. Various compounds have been evaluated as raw material substitutes for benzene in production of maleic anhydride. Fixed- and fluid-bed processes for production of maleic anhydride from the butenes present in mixed streams have been practiced commercially. None of these... 

This concept is now applied to the liquefaction of methane initially at atmospheric pressure and 105°F, 105°F being selected because it is a common industrial heat rejection temperature. The theoretical quantity of work (expressed in Btu of work equal to 778 ft-lb, of work) required to cool 1 lb of methane down to its liquefaction point and then to absorb the 219.7 Btu of latent heat of liquefaction at -258°F, is shown in Figure 3-2. It amounts to 510.8 Btu of work per pound of methane and is not to be confused with Btu of heat, although the quantities in this case are not very different. This amount of work per pound of methane is equivalent to 352 hp/MMcfd. An actual process with its expected inefficiencies would require twice this much work. 

Free-radical arylation of heterocyclic compounds is a relatively inefficient process in which yields of particular products greater than 50% are rare. This is the inevitable result of the high reactivity and low selectivity of aryl radicals not only is it usual for the heterocyclic compound to be attacked at each of its available positions, but, as shown in preceding sections, other by-products are numerous. Nevertheless, the method often presents the only short route to a given compound and it has been widely applied. Preparative uses are grouped in this section under the heading of the heterocyclic system concerned. 

An extensive survey has been carried out by McKervey and coworkers [7], who prepared the carbo-alkoxymethyl ethers of p-tert-h x y calix[4]arene, p-/< r/-butyl calix[6]arene, p-tert-bu y calix[8]arene, ca-lix[4]arene, calix[6Jarene, and calix[8]arene, and measured their abilities to extract cations from the aqueous phase into the nonaqueous phase. They concluded the following general aspects for the phase-transfer experiments (1) the calix[4]arene compounds show the greatest selectivity for Na (2) phase-transfer of Li is inefficient with all of the compounds (3) the calix[6]arene compounds show less affinity for Na than for K, with plateau selectivity for Rb" and Cs (4) the calix[8]ar-ene compounds are the least efficient of the cyclic oligomers, showing low levels of transport and low discrimination for all five cations (5) the calix[6]arene... 

A matter of considerable importance in the selection of an application method is its efficiency. Spray techniques are usually inefficient, since many droplets drift past the target and are lost. Even electrostatic spraying can waste as much as 35% of the paint. There is some loss of paint in most methods, but roller coating, curtain coating and electrodeposition are very efficient. Electrodeposition is also a very useful technique where corrosion resistance is important, since it applies a uniform coating over nearly all surfaces of even the most complex-shaped article. 

Protein phosphorylation-dephosphorylation is a highly versatile and selective process. Not all proteins are subject to phosphorylation, and of the many hydroxyl groups on a protein s surface, only one or a small subset are targeted. While the most common enzyme function affected is the protein s catalytic efficiency, phosphorylation can also alter the affinity for substrates, location within the cell, or responsiveness to regulation by allosteric ligands. Phosphorylation can increase an enzyme s catalytic efficiency, converting it to its active form in one protein, while phosphorylation of another converts it into an intrinsically inefficient, or inactive, form (Table 9—1). 

In 2008, Grisi et al. reported three ruthenium complexes 65-67 bearing chiral, symmetrical monodentate NHC ligands with two iV-(S)-phenylethyl side chains [74] (Fig. 3.26). Three different types of backbones were incorporated into the AT-heterocyclic moiety of the ligands. When achiral triene 57 was treated with catalysts 65-67 under identical reaction conditions, a dramatic difference was observed. As expected, the absence of backbone chirality in complex 65 makes it completely inefficient for inducing enantioselectivity in the formation of 58. Similarly, the mismatched chiral backbone framework of complex 66 was not able to promote asymmetric RCM of 57. In contrast, appreciable albeit low selectivity (33% ee) was observed when the backbone possessed anti stereochemistry. 

With the site-selective hole injection and the hole trapping device established, the efficiency of the hole transport between the hole donor and acceptor, especially with respect to the distance and sequence dependence, were examined. Our experiments showed that hole transport between two guanines was extremely inefficient when the intervening sequence consisted of more than 5 A-T base pairs [1]. Hole injection into the DNA n-stack using photoexcited dCNBPU was accompanied by the formation of dCNBPU anion radical. Therefore, hole transport would always compete with the back electron transfer (BET). To minimize the effect of BET, we opted for hole transport between G triplets, that are still lower in oxidation potential than G doublet. With this experimental system, we researched the effect of the bridging sequence between two G triplets on the efficiency of hole transport [2]. 

Enantioselective photocyclization of 74 occurred efficiently in the inclusion complex with 2a. In particular, the selectivity is very high in the case of 74a. However, control is inefficient in the 1 2 complex 85 composed of 2a and 74c. The host guest ratio probably depends on the packing of the components in the crystal. The packing is... 

A primary limitation of sonochemistry remains its energy inefficiency. This may be dramatically improved, however, if a more efficient means of coupling the sound field with preformed cavities can be found. The question of selectivity in and control of sonochemical reactions, as with any thermal process, remains a legitimate concern. There are, however, clearly defined means of controlling the conditions generated during cavitational collapse, which permit the variation of product distributions in a rational fashion. 

The methyl y-oxoalkanoates shown are not available by alternative methods with similar efficiency and flexibility. Although the reaction of enamines with alkyl ot-bromoacetates proceeds well in some cases, yields are only moderate in many examples.8 A further drawback is that the methods for enamine generation lack the high degree of selectivity and mildness that is characteristic of the preparation of silyl enol ethers. Related alkylations of lithium enolates often afford low yields or polyalkylated products, and are in general very inefficient when aldehydes are utilized as the starting materials.9... 

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