In-Situ Formation

Carbonate reservoir rock is usually found at the place of formation ( in situ ). Carbonate rocks are susceptible to alteration by the processes of diagenesis. 

The direct proof of hydride formation in situ in a reaction vessel is in principle possible. One can follow changes of resistance (of a film, a wire, etc.) or of magnetic susceptibility of a catalyst. Hydride identification by means of the X-ray diffraction method requires a catalyst sample to be taken out from a reaction vessel, and eventually frozen in order to avoid a rapid decomposition of the hydride under ambient conditions (67). 

The relatively easy formation of Ph from Phi (cf Sect. 14.7.2) allows EGB formation in situ and gives trichloromethy-lation of aldehydes in 48 to 61% yield at room temperature [91]. A similar procedure was used for reaction of CF3CCI2H and CCI3CCI2H with aldehydes [91]. 

The aldehyde can be replaced by an imine and the reaction is then called the aza-Baylis-Hillman reaction [87, 88]. (3-Amino-a-methylene structures obtained in this way could further be converted to a range of biologically important molecules, such as p-amino acids [89]. First reaction of this kind was published in 1984 [90]. Tosylimines and ethylacrylate reacted in the presence of DABCO as catalyst to give p-aminoesters. First three-component aza-Baylis-Hillman reaction was published in 1989 by Bertenshaw and Kahn [91], with imine formation in situ from an aldehyde and an amine. In the presence of triphenylphosphine as catalyst, the reaction with methylacrylate led to the formation of the p-amino-ot-methylene esters and ketones in good yields (Scheme 38). 

In regions where tar sand deposits are covered by dense rock or other formations, in-situ recovery may be more practical. Steam injection and underground combustion processes may be used for oil recovery. 

In their catalytic cycle, the authors proposed the formation in situ of a zero-valent nickel species by the reduction of Ni(acac)2 with the organozinc reagent. Since the pioneering studies of Aresta et al., which detailed the isolation of the first nickel-C02 complex, such zero-valent species have been known easily to activate C02 [54]. Transfer of the so-formed Ni(II)-carboxylate occurred following a transmetallation... 

Metal-complex dyes are of minor importance. They can be used as such or can be formed on the hair, although the metal salt treatment entails problems. Brilliant fashion colors (pink, green, etc.) are mosdy obtained with anionic dyes, which are often food colorants. Other methods for dye formation in situ [44] or with reactive dyes have not been accepted because of toxicological concerns. 

The literature contains numerous speculations as to the mechanism. Some involve a condensed phase mechanism, as, for example, in the case of cellulose in which it is suggested the formation in situ of antimony chloride which may react with cellulose to alter the course of thermal decomposition and/or form a heavy vapor tending to extinguish the flame. 28 Some involve a physical gas-phase mechanism such as formation in the flame of nonvolatile, antimony-containing solid or... 

The formation in situ of contact dermatitis producing chemicals is not limited to ethoxylated alcohol degradation. Photocontact allergic dermatitis can be caused by the application of photosensitive chemicals to the skin followed by irradiation with ultraviolet light. Examples of such reactions are discussed in Section 16.4. 

The main differences are concerned with the role of iodide cocatalyst, not yet well understood, and the DPU formation mechanism. It is suggested that the iodide promotes the formation in situ of molecular iodine (reaction 7) which then reacts with the intermediate carbamoyl complex coming from reaction (8) to afford iodoformamide (reaction 9). The in situ reaction of the last one with aniline gives DPU (reaction 10). 

Precipitate flotation (formation in situ—the flotation of insoluble precipitates)... 

Monitor carbon formation in situ with an adiabatic reactor and laser scattering... 

In heterophase polymeric materials such as rubber modified polystyrene or acrylonitrile-butadiene-styrene (ABS) resins, outstanding mechanical properties can be obtained only by regulating the dispersed rubber particle size and by achieving adhesion between the rubber and the resin phase. This can usually be achieved by adding block or graft copolymers, or by their formation in situ, as in industry. 

Of the various compatibilization strategies that have been devised, an increasingly common method is either to add a block, graft, or crosslinked copolymer of the two (or more) separate polymers in the blend, or to form such copolymers through covalent or ionic bond formation in situ during the Reactive Compatibilization step. The first of these processes was described in Chapter 4 of this Handbook, Interphase and Compatibilization by Addition of a Compatibilizer, while the second method is the topic of this Chapter. 

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