In situ transformation

The hydride phase may be present in a catalyst as a result of the method of its preparation (e.g. hydrogen pretreatment), or it may be formed during the course of a given reaction, when a metal catalyst is absorbing hydrogen (substrate—e.g. in H atom recombination product—e.g. in HCOOH decomposition). The spontaneous in situ transformation of a metal catalyst (at least in its superficial layer) into a hydride phase is to be expected particularly when the thermodynamic conditions are favorable. 

Activating agents, such as trifluoroacetic anhydride 1,1 -carbonyldiimidazolc carbodiimides sulfonyl, tosyl, and picryl chlorides and a range of phosphorus derivatives can promote direct solution reactions between dicarboxylic acids and diols or diphenols in mild conditions. The activating agents are consumed during the reaction and, therefore, do not act as catalysts. These so-called direct polycondensation or activation polycondensation reactions proceed via the in situ transformation of one of the reactants, generally the carboxylic acid, into a more... 

Monoalkylation of Af-tosylallylamine 10 with dibromoalkane 101 proceeded in 60-90% yield (Eq. 10 see also Scheme 3 and Eq. 2) [17]. The bromoalkyl-amines 102 were converted to nitro compounds 103. In situ transformation of 103 into nitrile oxides led to spontaneous cycloaddition with formation of isox-azolines fused to 5-, 6-, and 7-membered ring heterocycles 104 a-c. Under very high dilution conditions, 103 d was converted to 104 d, an isoxazoline fused to an 8-membered azocine, in low (10%) yield. 

Reusser DE, JD Istok, HR Beller, JA Field (2002) In situ transformation of deuterated toluene and xylene to benzylsuccinic acid analogues in BTEX-contaminated aquifers. Environ Sci Technol 36 4127-4134. 

In this section, generation means formation, usually succeeded by in situ transformation of an unstable nitrile oxide, while preparation relates to stable nitrile oxides, which can be isolated and stored for a long time. A review including data on formation of nitrile oxides was published recently (25). 

Dehydration of primary nitroalkanes results in unstable nitrile oxides and, therefore, is limited by in situ transformation of the latter, for the preparation of various stable products, mainly those of 1,3-dipolar cycloaddition (Scheme 1.4). 

Semprini, L., 1997, In Situ Transformation of Halogenated Aliphatic Compounds under Anaerobic Conditions In Subsurface Remediation (edited by C. H. Ward, J. A. Cherry, and M. R. Scalf), Ann Arbor Press, Chelsea, MI, pp. 429-450. 

For substrates (often low molecular weight allylic alcohols) that are difficult to obtain, due to problems of decomposition and/or water solubility, an in situ transformation was reported by Sharpless and coworkers in 1987 , making possible the effective synthesis... 

Rmix, R(z) mol m s-1 In-situ transformation of chemical (hydrolysis, photolysis, biotransformation etc.)... 

Molecular-level design of catalytic ensemble structures on surfaces in a controllable manner, based on new chemical concepts and strategies regarding composition or structure, provides a promising opportunity for the development of novel and efficient catalysts active for selective oxidation. Novel strategies and concepts for the creation of active ensemble structures on flat and porous surfaces may emerge from self-assembly and in situ transformation of precursors immobilized on the surfaces, with the aid of in situ characterization by sophisticated physical techniques [1-6]. 

Siloxycyclopropane 132 — which is a masked vinyl ketone — has served as test substrate for many in situ transformations. It cleanly reacts with several of O-, N-, and S-nucleophiles under mild acidic or basic conditions leading to polyfunctionalized y-oxoesters 137 (Eq. 55) 83), which for instance can be further converted to y-butyrol-actones, as exemplified by the one-pot-synthesis of 138 76). 

Diatom frustules enhance P. pouchetii colony formation in vitro (Nejstgaard et al. 2006), a process that may therefore accelerate the in situ transformation of solitary motile cells into new colonies. This is the critical step in the formation of colony-based Phaeocystis blooms, and thus is essential in... 

When widespread stagnation suppresses convective transport out of the basin, the accumulation of pollutants may proceed. The buildup of atmospheric constituents will be governed by (a) primary emissions (b) in situ transformations (production or loss terms) (c) intrabasin circulation (d) ventilation and (e) removal by... 

FigUre 3-12 The MaiUard Reaction. Shown are the preliminary rearrangements of functional groups (common to the proteins and sugars in DOM) that could serve as the foundation for additional cross-reactions that may occur during in situ transformations of DOM or during analytical hydrolysis protocols. This could provide a mechanism for the formation of hydrolysis resistant amides that prevent bulk and monomer level characterization of DON. 

The left part of the target molecule has now been made After deprotection of the PMB-protected alcohol with DDQ (72), the primary alcohol is oxidized to the aldehyde with the IBX reagent. Then, a Wittig reaction with PhsP CHCHs formed in situ transforms the carbonyl compound into a Z-configured alkene. At this stage, separation of the C-5-isomers is possible to obtain diastereopure 30. 

Dimethylether (DME) can be synthesized effectively fi om H2/CO2 feed by one-pot synthesis using hybrid catalyst. Hybrid catalyst is composed of mixture of methanol synthesis catalyst and soHd acid catalyst. DME is an important and valuable chemical used as solvent, propellant and raw material to hquid fuels. As shown in Fig.l, methcuiol fixjm H2/CO2 has a severe limitation of thermod3mamic equihbrium compared with that fi om H2/CO. To overcome such a limitation, in situ transformation of methanol to DME is reasonable way to improve total methanol yield (CH3OH + DME). Table 2 shows reaction behavior to DME synthesis over hybrid... 

In situ transformation of ice Ic. It is planned to follow in detail the evolution of the stacking probabilities during the slow transformation of ice Ic to ice Ih. It gives a key to the exact process of rearranging the layers and thus to the kinetics observed, which is different for samples of different origin. 

A method involving the in situ transformation of carboxylic acids into acylfluorides that are reduced by NaBH4 in MeOH has been recently proposed [KN4],... 

Imidazolines can exist as the 2-, 3-, or 4-isomers ((5)- 7)), and whereas (5) can exist as a pair of tautomers, any proton shift in (6) will give (7) by rearrangement. Hydrolysis of A(-unsubstituted 3-imidazolines (6) to a-aminoketones presumably occurs via (7). Nickel boride , prepared in situ, transforms 3-imidazolines into 2-imidazolines by double-bond migration <86H(24)287l>. 

In situ transformations in organic samples can be observed in real time in the DAC by using a microscope equipped with a CCD video monitoring system and luminescence spectrometer. A high-pressure mercury lamp is used to excite fluorescence in the sample. The emitted light from the sample is split with one part used for visual observation and the other part for analysis made possible by use of a grating spectrometer and a photomultiplier detector [22]. 

Amines. In situ transformation of the Grignard reaction products of carbonyl compounds into amines is accomplished by the addition of lithium hexamethyldisilazide and LiC104. 

ADA/DEN] Adair, J. H., Denkewicz, R. P., Arriagada, F. J., Osseo-Asare, K., Precipitation and in situ transformation in the hydrothermal synthesis of crystalline zirconium dioxide, Ceram. Trans., 1, (1987), 135-145. Cited on page 409. 

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