Reactions in situ

Other Phases in Portland and Special Cements. In cements free lime, CaO, and periclase, MgO, hydrate to the hydroxides. The in situ reactions of larger particles of these phases can be rather slow and may not occur until the cement has hardened. These reactions then can cause deleterious expansions and even dismption of the concrete and the quantities of free CaO and MgO have to be limited. The soundness of the cement can be tested by the autoclave expansion test of Portiand cement ASTM C151 (24). 

Such in situ reactions are based on the work of Miller and Kirchner [9] and offer the following possibilities [10] ... 

The 2,7-naphthyridine system 53 (Scheme 8.4.18) was combined with 2,4-dinitrochlorobenzene and 2-amino glycerol for in situ reaction of the resulting Zincke salt. The resulting naphthyridinium 54 was trapped by Bradsher cycloaddition with (Z)-vinyl ether 55, providing tetracycle 56 (X-ray) upon internal addition of one of the diastereotopic hydroxymethyl groups to the resulting iminium. This approach was also extended to the use of chiral 2,7-naphthyridinium salts, prepared via the analogous Zincke process. ... 

Tables 7-7-7-11 give a sense of the range of organic molecules present in the atmosphere. Both natural sources and human activity contribute to the variety of organic molecules (Graedel, 1978). The sinks often involve in-situ reactions.

Therefore, such sequential in situ reactions are always carried out either in order to prepare a substance for a color reaction that is to follow or to increase the amount of information that is obtained by exploiting a combination of different independent reactions. This provides information that could not be obtained using one single reagent. 

Secondly it is possible to carry out functional chromatography within the framework of a two-dimensional development [6-8]. The first separation is followed by an in situ reaction of the sample substance on the layer the chromatogram is then developed perpendicular to the direction of the first chromatogram (SRS technique). The decision concerning the type of alcohol, is then made on the basis of the positions of the chromatogram zones esters migrate appreciable further than their parent alcohols and acids. 

The desired results can be obtained by multiple chromatography or multiple in situ reaction at the same chromatogram zone. 

For uncompatibdized blends, the viscosity decreases with increasing number of layers in a multilayer constant stress rheometer. In the present case, the viscosity rather increases due to in situ reaction between nylon and maleated EPDM as illustrated in Figure 11.21. 

The most convenient and successful synthetic preparation of octa-chlorodibenzo-p-dioxin has been described by Kulka (13). The procedure involves chlorination of pentachlorophenol in refluxing trichlorobenzene to give octachlorodibenzo-p-dioxin in 80% yield. Kulka has explained the reaction as coupling between two pentachlorophenoxy radicals. Large amounts (5—15%) of heptachlorodibenzo-p-dioxin were observed in the unpurified product. Since the pentachlorophenol used in this study contained 0.07% tetrachlorophenol, we feel that tetrachloro-phenol may be produced in situ (Reaction 4). Such a scheme would be analogous to the formation of 2,4-dichlorophenol and 3-chlorophenol produced from 2,4,4 -trichloro-2 -hydroxydiphenyl ether (Reaction 2). The solubility of octachlorodibenzo-p-dioxin was determined in various solvents data are presented in Table II. 

In Section 5.1.3 the conversion of aldehydes 491 and 494 into N-silylated Schiff bases and their in-situ reaction with allylmagnesium bromide into unsaturated secondary amines 493 and 495 is described. Likewise, reactions of the N-silylated Schiff bases such as 489 with the lithium enolate of methyl isobutyrate 498 to give yS-lactams such as 499 are also discussed in Section 5.1.3. 

Good yields of chlorides have also been obtained for reaction of isolated diazonium tetrafluoroborates with FeCl2-FeCl3 mixtures.100 It is also possible to convert anilines to aryl halides by generating the diazonium ion in situ. Reaction of anilines with alkyl nitrites and Cu(II) halides in acetonitrile gives good yields of aryl chlorides and bromides.101... 

Epoxidation by Dioxirane Derivatives. Another useful epoxidizing agent is dimethyldioxirane (DMDO),86 which is generated by in situ reaction of acetone and peroxymonosulfate in buffered aqueous solution. Distillation gives about aO.lM solution of DMDO in acetone.87... 

In Situ Reaction Imaging in Fixed-bed Reactors Using MRI... 

In Situ Reaction Imagingin Fixed-bed Reactors Using MR 595... 

Alkenes can also be epoxidized directly with a variety of organic peroxy acids or related reagents such as peroxy carboximidic acid, RC(NH)OOH, which is readily available through an in situ reaction of... 

Macrocyclic lactams making use of the double reaction of bisimidazolides — in this case, prepared from the corresponding dicarboxylic acids by in-situ reaction with C6H5POIm2 - were obtained in acceptable yield considering the unfavorable ring sizes of the products 1-1295... 

Another option is the in situ reaction of the obtained enones in a 1,3-dipolar cycloaddition using nitrones or azomethineylides formed from the corresponding imines with DBU in the reaction mixture [153],... 

Examples of the operation of both types of effect have been documented. Nevertheless, while these effects are useful concepts, as mentioned previously, very often the role of the metal ion in a given in situ reaction may be quite complex and, for instance, involve aspects of both effects. As well, the metal may play less obvious roles in such processes. For example, it may mask or activate individual functional groups or influence the reaction in other ways not directly related to the more readily defined steric influences inherent in both template effects. 

In view of the above, it is not surprising that a detailed understanding of the part played by the metal ion in many (perhaps the majority ) of published template reactions still remains to be elucidated. Nevertheless, in the following discussion an attempt has been made to illustrate a representative cross section of such in situ reactions even though, for many examples, little comment can be made concerning mechanistic details of the respective condensations. 

A disadvantage of borane and borate systems is that the alkylmetallocene cations are more instable and more sensitive to impurities and water. To overcome this higher sensitivity, a dialkyl species can be build by an in situ reaction with tri-isobutylaluminum (TIBA). TIBA acts as alkylation reagent and as a scavenger and stabilizes the dialkyl species in solution it is used as stock solution for the polymerization experiments (Fig. 12). 

In situ reaction of the resultant phosphine, converted to its conjugate base, with several types of electrophiles has been investigated for organophosphorus syntheses. While early reports of the use of white phosphorus in basic solution with haloalkanes did not in themselves provide procedures for the efficient preparation of organophosphorus compounds, they pointed the way for the development of more useful techniques. 

The synthesis of optically active nitrones (95) was carried out by an aldol reaction of aldehydes (93), catalyzed by L- proline, with carbonyl activated compounds (94) and by an in situ reaction with N -alkylhydroxylamines (Scheme 2.36, Table 2.5) (261). 

Preparation of 2-trimethylsilyloxy-i 3-crotyltitanocene and in situ reactions with aldehydes... 

Typical procedure for the preparation of allyltitanium derivatives from allyl halides via oxidative addition, and in situ reaction with aldehydes [57,59]... 

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