Hydrogenation suppressed side reaction

The liquid components are mixed at -78 °C. To suppress side reactions the sulfane component is applied in a large excess (>10 1). The unreacted starting sulfane and hydrogen chloride are distilled off after the reaction has... 

The strategy for the asymmetric reductive acylation of ketones was extended to ketoximes (Scheme 9). The asymmetric reactions of ketoximes were performed with CALB and Pd/C in the presence of hydrogen, diisopropylethylamine, and ethyl acetate in toluene at 60° C for 5 days (Table 20) In comparison to the direct DKR of amines, the yields of chiral amides increased significantly. Diisopropylethylamine was responsible for the increase in yields. However, the major factor would be the slow generation of amines, which maintains the amine concentration low enough to suppress side reactions including the reductive aminafion. Disappointingly, this process is limited to benzylic amines. Additionally, low turnover frequencies also need to be overcome. 

The other commercialized pentane isomerization process is that of the Standard Oil Co. (Indiana) (20). This process differs from the Indiana-Texas butane process in that the aluminum chloride is introduced as a slurry directly to the reactor and that about 0.5% by volume of benzene is added continuously in the feed to suppress side reactions. Temperature, catalyst composition, space velocity, and hydrogen chloride concentration are generally similar to those in the corresponding butane process, but the reactor pressure is about 100 pounds lower. The Pan American Refining Co. operated the Indiana pentane isomerization process commercially during the last nine months of the war and produced about 400 barrels of isopentane per calendar day. 

Reaction of (trimethylsilyl)vinyl selenide 122 with methyl vinyl ketone catalyzed by SnCLt gives the [2 + 2] adduct 123 in 66% yield (equation 51)176. Replacement of the MegSi group with a hydrogen atom or a methyl group produces a complex mixture. Thus, the MesSi group can suppress side reactions by its steric effect. 

Despite its wide application in glycoside synthesis, the Koenigs-Knorr reaction suffers from several disadvantages (i) the glycosyl halides are unstable, (ii) excess toxic heavy metals are needed to activate the donor, and (iii) a desiccant (to absorb any liberated water) and an acid acceptor (to absorb the liberated hydrogen halide and can be a promoter itself) are often needed to increase the yield and suppress side reactions. 

Another example of the synthesis of a compound with pharmaceutical relevance is the chemical transformation of rac-warfarin into enantiomerically pure (R)- or (5)-warfarin. In the first step, rac-warfarin is oxidized to the corresponding ot,p-unsaturated ketone. The latter can be easily hydrogenated to the desired enantiomer by application of the appropriate DuPHOS-catalyst (eq 11). Prior transformation of dehydrowarfarin into the sodium salt or its methyl ether improved the yield and suppressed side reactions. Simultaneously, the enantioselectivity of the hydrogenation product was enhanced. The (5,5)-ethyl-DuPHOS-complex leads to R-configured warfarin. 

In the first step of the process the anthraquinone is hydrogenated to the hydroquinone with palladium as the preferred catalyst on carriers, such as gauze, or in suspension. The reaction is carried out at about 40°C and at pressures up to ca. 5 bar with cooling and only to ca. 50% hydrogenation to suppress side reactions (see below). 

Aluminoxanes suppressed side reactions involving hydrogen transfer. They also formed cyclic structures with starch, giving copolymers that were coated with crystalline polyethylene. A catalyst composed of dicyclopentadienylzirconium dichloride and trimethylaluminium permitted polymerization of ethylene on starch in a toluene suspension at 60 °C for 2h.2806 Graft copolymerization of methyl methacrylate onto starch was also performed with an acetylacetone-copper(II) complex in trichloroacetic acid.2807 The grafting yield and efficiency were proportional to the initiator concentration up to 7.0 x 10-3 mole/L. 

The quantitative conversion of combined oxygen into carbon monoxide on charcoal is used extensively in the trace determination of oxygen in organic compounds [118, 119]. When this method is implemented in practice, it becomes important to maintain the right reaction conditions (type of charcoal, temperature, etc.). For the quantitative conversion of oxygen into carbon monoxide it is recommended that anthracene black is used [120], and to suppress side-reactions between the anthracene black and the walls of the quartz tube it is advisable to use platinized anthracene black at 900°C [121]. The method was developed taking due account of the conditions of the quantitative conversion of carbon monoxide on a nickel catalyst in a flow of hydrogen, which were discussed elsewhere [22,114,115]. 

Reaction time has to be as short as possible in order to suppress side reactions. Especially the conversion of alcohols to carboxylic acids with one more C-atom, which will be discussed subsequently, or formation of ethers and free acids may be undesirable reactions [504]. The carbonylation rate of olefins with carbon monoxide/ROH in the presence of Co carbonyls can be accelerated remarkably by addition of small portions of hydrogen to carbon monoxide, which favors the formation of hydrocarbonyl. The same effect can be achieved by addition of pyridine. 

Nitrated fluoro compounds are synthesized by electrophilic (NOz+), radical (NO2 ), or nucleophilic (NO2-) methods Indirect nitration routes can suppress the side reactions associated with severe reaction conditions and some nitration reagents Novel fluoronitro compounds, unobtainable by direct nitration, can also be pre pared For example, the nitration of (2-fluoro-2,2-dinitroethoxy)acetaldoxime followed by oxidation of the nitroso intermediate with hydrogen peroxide yields 2-fluoro-2,2-dinitioethyl 2,2-dinitroethyl ether [f] (equation 1)... 

The usual procedure is to simply heat a mixture of the starting materials. A common side-reaction is the polyalkylation it can be suppressed by employing an excess of amine. In addition carbonyl substrates with a-hydrogens may undergo competitive aldol reactions the corresponding reaction products may then undergo a subsequent Leuckart-Wallach reaction. 

Monofunctional and Polyfunctional Electrodes At monofunctional electrodes, one sole electrode reaction occurs under the conditions specified when current flows. At polyfunctional electrodes, two or more reactions occur simultaneously an example is the zinc electrode in acidic zinc sulfate solution. When the current is cathodic, metallic zinc is deposited at the electrode [reaction (1.21)] and at the same time, hydrogen is evolved [reaction (1.27)]. The relative strengths of the partial currents corresponding to these two reactions depend on the conditions (e.g., the temperature, pH, solution purity). Conditions may change so that a monofunctional electrode becomes polyfunctional, and vice versa. In the case of polyfunctional electrodes secondary (or side) reactions are distinguished from the principal (for the given purpose) reaction (e.g., zinc deposition). In the electrolytic production of substances and in other practical applications, one usually tries to suppress all side reactions so that the principal (desired) reaction will occur with the highest possible efficiency. 

Desulfurization of organic compounds over Ra-Ni is a well-known procedure.364-369 Ra-Ni exists in different forms (W1 to W8), differing in the preparation procedure and sometimes symbolized as Ni(H). Ra-Ni is sometimes called a catalyst however, it is used usually in large excess and the reaction is stoichiometric. Ra-Ni can desulfurize every C—S bond containing compound but it can also hydrogenate a lot of other functional groups. Unwanted side reactions are sometimes suppressed by using deactivated Ra-Ni. 

Employing a molar excess of the alkyne over the active hydrogen of only 12 percent the selectivity (determined by proton NMR after work-up) may be expressed as the ratio of Si-C=CH- to Si-CH2-CH2-CO-, which is about 100 1 [16]. The same reaction, carried out with silicone polymers with 10 or more pendant silicon-bonded hydrogen atoms, proceeds similarly cleanly without noticeable crosslinking by acrylic hydrosilylation. A slight excess of triple bond over Si-H groups is mandatory to suppress this side reaction as well as hydrosilylation of the olefinic group of the 2-silylalkene isomer product (see Table 2.). 

In the course of our investigations to develop new chiral catalysts and catalytic asymmetric reactions in water, we focused on several elements whose salts are stable and behave as Lewis acids in water. In addition to the findings of the stability and activity of Lewis adds in water related to hydration constants and exchange rate constants for substitution of inner-sphere water ligands of elements (cations) (see above), it was expected that undesired achiral side reactions would be suppressed in aqueous media and that desired enanti-oselective reactions would be accelerated in the presence of water. Moreover, besides metal chelations, other factors such as hydrogen bonds, specific solvation, and hydrophobic interactions are anticipated to increase enantioselectivities in such media. 

A fundamental topic in hydroformylation research is the control of regio-selectivity and the suppression of side-reactions like the hydrogenation reac-... 

ROP of p-lactones is highly prone to numerous side reactions, such as transester-fication, chain-transfer or multiple hydrogen transfer reactions (proton or hydride). Specifically, the latter often causes unwanted functionalities such as crotonate and results in loss over molecular weight control. Above all, backbiting decreases chain length, yielding macrocyclic structures. All these undesired influences are dependent on the reaction conditions such as applied initiator or catalyst, temperature, solvent, or concentration. The easiest way to suppress these side reactions is the coordination of the reactive group to a Lewis acid in conjunction with mild conditions [71]. p-BL can be polymerized cationically and enzymatically but, due to the mentioned facts, the coordinative insertion mechanism is the most favorable. Whereas cationic and enzymatic mechanisms share common mechanistic characteristics, the latter method offers not only the possibility to influence... 

In the case of pentanes, disproportionation to isobutane and hexane is pronounced. This undesirable side reaction can be suppressed by the addition of small amounts of cyclic hydrocarbons or by operation under hydrogen pressure (6). 

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