In-Situ Modifications

Fig. 12. Scenario for the in-situ modification of subsoils or aquifers for pollution control. The organoclay formed by injecting a solution of long-chain quaternary ammonium cations (e.g. HDTMA) acts as a sorptive zone where organic contaminants dissolved in a plume from buried waste can be immobilised and degraded. After Xu et al. (1997).

Brixie JM, Boyd SA (1994) Treatment of contaminated soils with organoclays to reduce leachable pentachlorophenol. J Environ Qual 23 1283-1290 Brown MJ, Burris DR (1996) Enhanced organic contaminant sorption on soil treated with cationic surfactants. Ground Water 34 734-744 Burris DR, Antworth CP (1992) In situ modification of an aquifer material by a cationic surfactant to enhance retardation of organic contaminants. J Contam Hydrol 10 325-337... 

For the Pt/cinchona catalysts only preliminary adsorption studies have been reported [30]. From the fact that in situ modification is possible and that under preparative conditions a constant optical yield is observed we conclude that in this case there is a dynamic equilibrium between cinchona molecules in solution and adsorbed modifier. This is supported by an interesting experiment by Margitfalvi [63] When cinchonine is added to the reaction solution of ethyl pyruvate and a catalyst pre-modified with cinchonidine, the enantiomeric excess changes within a few minutes from (R)- to (S)-methyl lactate, suggesting that the cinchonidine has been replaced on the platinum surface by the excess cinchonine. 

Oxoalkoxocomplexes are oligomers of varying molecular complexity. The extent and conditions of distillation allow to control the nature of the species in solution, thus influencing the film-formation process [1368], This process of in situ modification ofmetal alkoxide solution by carboxylate ligand may have certain advantages with respect to the chemical uniformity as compared to the techniques based on simple mixing of a titanium alkoxide with alkaline-earth carboxylates. 

Fig. 18. Voltammetric curves showing the activation of glassy carbon (-) for hydrogen evolution in 0.5 M H2S04 by in situ modification with arP2W12Mo062K6 (------). After ref. 344, by...

Compared to nanocellulose from wood, BC has the major advantage of modifiability during biosynthesis by simple addition of water-soluble compounds to the culture medium (in situ modification). 

For revamps of ammonia synthesis converters, Ammonia Casale offers 1) an in-situ modification of bottle-shaped converters of the Kellogg type, and 2) a three-bed intercooled configuration. The intercooled design is similar in some ways to the Uhde design discussed below213. 

Sml2 is a valuable precursor to other Sm(II) and Sm(III) species. As discussed in Chapter 2, in situ modification of the reagent using additives and cosolvents is the most convenient and the most common method for generating new Sm(II) species. The synthesis and characterisation of new Sm(II) reagents, prior to their deployment in reactions, may, however, prove a key tool in the bid to develop new selective reactions and to unravel the mechanistic complexities that surround the organic chemistry of Sml2. 

Furthermore, Pd-catalyzed aminations can be sequentially coupled with alkene insertion and amination. Wolfe and Lira [102] have established a transformation involving two different sequential metal-catalyzed reactions that lead to AT-aryl-2-benzylindolines 125 in moderate to excellent yields upon formation of two C - N bonds and one C - C bond in a one-pot process (Scheme 45). Interestingly, the selective installation of two different aryl groups in this sequence can be accomplished by in situ modification of the Pd catalyst system Pd-126 upon addition of the chelating ligand dpephos prior to addition of the second aryl bromide (Scheme 46). The selectively substituted indoline derivatives 127 were isolated in good to excellent yields. 

Second, replacement at the interface of an ionocovalent oxide by a metallic one. A typical example of this is provided by the Ti/MgO system. Liquid Ti can react to dissolve several at.% O and form metal-like oxides such as TiO or even solid solutions of Ti with high oxygen contents. The perfect wetting observed for this system (Figure 6.2) can be explained by the double in-situ modification of the interface the adsorption of oxygen at the liquid-side and the formation of a metallic phase at the solid-side. 

In the case of proteins that are not soluble under the conditions used for acetylation of side chain amino groups, SDS-PAGE is employed, followed by transfer to a cationic PVDF membrane, in situ modification of the lysines, and proteolysis. The resulting peptides are recovered from the membrane and the... 

Imanidis G, Helbing-Strausak S, Imboden R, and Leuengberger H. Vehicle-dependent in situ modification of membrane-controlled drug release. J. Control. Rel. 1998 51 23-34. 

X.L. Pan et al., Mesoporous spinel MgA1204 prepared by in situ modification of boehmite sol particle surface I Synthesis and characterization of the unsupported membranes. Colloids Surf. A-Physicochem. Eng. Asp. 179(2-3), 163-169 (2001). 

An in situ modification procedine was adopted the deoxygenated solution, containing the solvent (ethyl acetate, FF Chemicals, 99.8%), the modifier (cin-chonidine, Aldrich, 96%) and the substrate were injected into the reactor, where the activated catalyst was under hydrogen. The reaction commenced immediately. The modifier-to-catalyst mass ratio was 1 150 to 120 150. The initial concentra-... 

For many applications, e.g. in the area of sensing, catalysis or separations, modifications of the inorganic backbone are required to provide a certain specific surface chemistry or active sites on the inner pore surface. Different routes, such as simple inclusion of molecules, or the covalent attachment of functional entities, are applied. Because of the specific synthesis strategy, the structure-directing agent can also be used for functionalization of the mesostructured material. Only in situ modifications are discussed postsynthesis modifications of the final porous material are, in principle, possible, but are beyond the scope of this article. 

Another chelated system was obtained after an in situ modification of ligand 102 via 100 and 101 by introduction of a trimethylsilyl group at the cyclopentadienyl ring to give 254, which was not isolated but treated with FeCh to produce a 30% yield of multiply chelated complex 255 (Scheme 47). If the reaction was performed with FeCl2(CO)4 under irradiation instead of FeCF, the yield increased to 40%."... 

Instead of the conventionally used modification by pre-immersion of the catalyst in a solution of modifier, Osawa et al. used an in situ modification during the enantioselective hydrogenation of MAA. Fine nickel powder modified with (2R,3R)-tartaric acid was used and sodium salt was added to the reaction media. By this method the optical yield was increased up to an ee of 79%. Improvement of this method consists in modification in situ of finely reduced Ni-powder by addition of (2R,3R)-tartaric acid and NaBr to the reaction media. In this case, an ee of 89% was obtained in the hydrogenation of MAA. The addition of small amounts of NaBr to the reaction media increased both the ee and the reaction rate, while, in contrast, the rate decreased with the addition of NaBr to the modification solution in... 

Osawa, T., Ozawa, A., Harada, T., and Takayasu, 0. (2000) Enantio-differentiating hydrogenation of methyl acetoacetate over fine nickel powder with in situ modification, J. Mol. Catal. A Chem. 154, 271-275. 

Burris, D. R. Antworth, C. P. (1992) In situ modification of an aquifer material by a cationic surfactant to enhance retardation of organic contaminants. Journal of Contaminant Hydrology 10, 325-337. 

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