Nonselective reductions

As can be seen in Scheme 3.249, a-azido oximes (465) can be involved with advantage in the selective reduction of the azido group in the presence of the oximino fragment and also in the selective or nonselective reduction of the oximino fragment (525). 

Aldol condensation between ketone 307 and aldehyde 298 afforded the E,E)-dienone 308 in 41% yield. Nonselective reduction of the C-9 ketone and base hydrolysis then produced a 77% yield of the seco acids 309. Lactonization utilizing the Corey thiopyridyl ester method and selective oxidation of the C-9 allylic hydroxyl group afforded the protected aglycone 310 in 59% yield. 

AcOH was used in order to maintain the concentration of H constant. Although the presence of H" also catalyzed the competing nonselective reduction, under the optimized reaction conditions, the use of one equivalent of AcOH provided a good compromise between reactivity and selectivity. 

Stereoinversion of (S)-nicotine (a) and deracemization of rac-cripsine A (b) on a preparative scale employing the MAO-N D5 variant with a nonselective reduction agent (NH BH ). 

In an economic comparison of these three common abatement systems, a 1991 EPA study (58) indicates extended absorption to be the most cost-effective method for NO removal, with selective reduction only matching its performance for small-capacity plants of about 200—250 t/d. Nonselective abatement systems were indicated to be the least cost-effective method of abatement. The results of any comparison depend on the cost of capital versus variable operating costs. A low capital cost for SCR is offset by the ammonia required to remove the NO. Higher tail gas NO... 

Cold methanol has proven to be an effective solvent for acid gas removal. Cold methanol is nonselective in terms of hydrogen sulfide and carbon dioxide. The carbon dioxide is released from solution easily by reduction in pressure. Steam heating is required to release the hydrogen sulfide. A cold methanol process is Hcensed by Lurgi as Rectisol and by the Institute Francaise du Petrole (IFP) as IFPEXOL. 

When NO destmction efficiencies approaching 90% are required, some form of post-combustion technology appHed downstream of the combustion 2one is needed to reduce the NO formed during the combustion process. Three post-combustion NO control technologies are utilized selective catalytic reduction (SCR) nonselective catalytic reduction (NSCR) and selective noncatalytic reduction (SNCR). 

Nonselective catalytic reduction systems are often referred to as three-way conversions. These systems reduce NO, unbumed hydrocarbon, and CO simultaneously. In the presence of the catalyst, the NO are reduced by the CO resulting in N2 and CO2 (37). A mixture of platinum and rhodium has been generally used to promote this reaction (37). It has also been reported that a catalyst using palladium has been used in this appHcation (1). The catalyst operation temperature limits are 350 to 800°C, and 425 to 650°C are the most desirable. Temperatures above 800°C result in catalyst sintering (37). Automotive exhaust control systems are generally NSCR systems, often shortened to NCR. 

Nitric Acid Plant - Nitrogen oxide levels should be controlled to a maximum of 1.6 kg/t of 100% nitric acid. Extended absorption and technologies such as nonselective catalytic reduction (NSCR) and selective catalytic reduction (SCR) are used to eontrol nitrogen oxides in tail gases. 

Platinum may be more useful than palladium in reduction of nitro compounds containing functions easily reduced by palladium. Hydrogenation of I over 5% Pd-on-C was nonselective with hydrogenolysis of the benzyl ethers competing with nitro hydrog ation, but over PtO in ethanol 2 was obtained in 96% yield (4). 

Pyrroles are hydrogenated with more difficulty than are carbocyclic aromatics. In compounds containing both rings, hydrogenation will proceed nonselectively or with preference for the carbocyclic ring (/9), unless reduction of the carbocyclic ring is impeded by substituents. Acidic solvents are frequently used but are not necessary. 

Both amine oxides related to pyridines and aliphatic amine oxides (/25) are easily reduced, the former the more so. Pyridine N-oxide has been reduced over palladium, platinum, rhodium, and ruthenium. The most active was rhodium, but it was nonselective, reducing the ring as well. Palladium is usually the preferred catalyst for this type of reduction and is used by most workers 16,23,84 158) platinum is also effective 100,166,169). Katritzky and Monrol - ) examined carefully the selectivity of reduction over palladium of a... 

Reduction of the catalyst/hydrocarbon time in the riser, coupled with the elimination of post-riser cracking, reduces the saturation of the already produced olefins and allows the refiner to increase the reaction severity. The actions enhance the olefin yields and still operate within the wet gas compressor constraints. Elimination of post-riser residence time (direct connection of the reactor cyclones to the riser) or reducing the temperature in the dilute phase virtually eliminates undesired thermal and nonselective cracking. This reduces dry gas and diolefin yields. 

Riser termination. Good riser termination devices, such as closed cyclones, minimize the vapor and catalyst holdup time in the reactor vessel. This reduces unnecessary thermal cracking and nonselective catalytic re-cracking of the reactor product. The benefits are a reduction in dry gas and a subsequent improvement in conversion, gasoline octane, and flexibility for processing marginal feeds. 

Tetrazolium salts can be reduced nonselectively by many endogenous reductants such as thiol-containing proteins, as well as exogenous ones such as ascorbic acid.521 -523 This can lead to serious interferences and several measures have been described to reduce or eliminate their effect.524,525,650... 

When piperidone 60 is condensed with phenyl-acetonitrile, using sodium methoxide, 84 results. Catalytic reduction unexpectedly is nonselective, not only reducing the olefinic linkage, but also removing... 

Compared to photoluminescence processes, no external light source is required, which offers some advantages such as the absence of scattering or background photoluminescence signals, the absence of problems related to instability of the external source, reduction of interferences due to a nonselective excitation process, and simple instrumentation. 

Nonrepairable components, in reliability modeling, 26 989 Nonruminant feeds, 10 836-847 additives to, 10 846 ingredients of, 10 837-838 swine and poultry nutrient requirements, 10 838-845 Nonselective catalytic reduction (NSCR), 10 101-102 17 184 19 626 Nonselective herbicides, 13 313 Nonselective poisoning, 5 258 Nonself-aligned (NSA) HBT fabrication, 22 167... 

Selected ion monitoring mode, mass spectrometer, 6 431 Selection, in chemical product design, 5 759, 772-776 Selective carburizing, 76 205 Selective catalytic reduction (SCR), 77 719-720, 79 626 See also Nonselective catalytic reduction SCR entries... 

The reduction of conjugated dienes by dissolving metals is not extensively reported. This method appears to be nonselective, giving rise to a mixture of the expected olefins and polyolefins as by-products". 

The asymmetric formation of industrially useful diaryl methanols can be realized through either the addition of aryl nucleophiles to aromatic aldehydes or the reduction of diaryl ketones. The latter route is frequently the more desirable, as the starting materials are often inexpensive and readily available and nonselective background reactions are not as common. For good enantioselectivity, chemical catalysts of diaryl ketone reductions require large steric or electronic differentiation between the two aryl components of the substrate and, as a result, have substantially limited applicability. In contrast, recent work has shown commercially available ketoreductase enzymes to have excellent results with a much broader range of substrates in reactions that are very easy to operate (Figure 9.6). ... 

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