Multicomponent processes

Beside the Ugi-MCRs, several other novel multicomponent processes using isocyanides as central substrates are known. Kaime and coworkers have described a MCR between nitro compounds, isocyanides and an acylating agent such as acetic acid anhydride [54]. The a-oximinoamides of type 9-75 obtained are probably formed via the intermediates 9-72 to 9-74 (Scheme 9.14). 

A classical non-isocyanide-based multicomponent process is the Biginelli dihydropyrimidine synthesis from 3-keto esters, aldehydes and urea or thiourea [63], The transformation was first reported in 1893 [64], but during the early part of the... 

Vaclavek and Loucka (1976) extended the approach to multicomponent processes with the assumption that, for any stream, either all or none of the mass fractions are... 

It should be noted that carbonyl compounds, more often aldehydes, are usual second reagent in both the groups. Other building-blocks in these multicomponent processes, leading to the formation of five-, six-, and seven-membered heterocycles, can be numerous acids and their derivatives, p-dicarbonyl compounds or other CH-acids, isocyanides, etc. At this, three-component reactions of ABC and ABB types [32] are the most typical for aminoazole, although some four-component ABCC processes were also published. 

Here we discuss several examples of the multicomponent processes involving aminoazoles, aldehydes, and other organic components such as mercaptoacids, haloacetic acids and their ester, a,p-unsaturated imines, etc., which were not incorporated into the previous two sections of the review. 

In addition to the applications in extractive distillation referred to above, there are other industrial examples where electrolytes in mixed solvents occur. In many industrial situations nonvolatile electrolytes are either added to effect the separation of multicomponent process streams (e.g., the complexing agents added to enhance distribution coefficients in solvent extraction) or are present as a result of the process itself. Ex-... 

Radical chemistry has witnessed remarkable progress since the mid 1980s [1], In addition to common radical C2 synthons such as alkenes and alkynes [2], several radical Cl synthons are also available, including carbon monoxide, isonitriles, and sulfonyl oxime ethers [3, 4]. As featured in Scheme 6.1, a variety of combinations of radical Cl and C2 synthons are now possible, which makes radical methodologies more attractive and permits the design and implementation of a wide range of multicomponent processes. 

A metal-induced one-electron reduction is frequently used to generate radical species. Termination of the radical reactions is due to a one-electron reduction process to give anions and therefore constitutes a non-chain process. As featured in Scheme 6.32, in many cases the multicomponent processes described here are a combination of radical and anionic bond-forming reactions. 

Multicomponent reactions (MCRs) are one-pot processes combining three or more substrates simultaneously [1], MCR processes are of great interest, not only because of their atom economy but also for their application in diversity-oriented synthesis and in preparing libraries for the screening of functional molecules. Catalytic asymmetric multicomponent processes are particularly valuable but demanding and only a few examples have been realized so far. Here we provide an overview of this exciting and rapidly growing area. 

More recently, Porta and co-workers [6] applied similar considerations of the polar effects to a new one-pot multicomponent process for the addition of nucleophilic radicals to aldimines, generated in situ in the presence of Ti(IV). In analogy with the Minisci reaction, Ti(IV), which acts as a Lewis acid, coordinates the nitrogen of the imine, strongly increasing the electron-deficient character of the carbon in the a-posilion and thus the reactivity of the imine toward nucleophilic radicals. This reaction, as well as the Minisci one, represents a useful route for the synthesis of a variety of poly-functionalized derivatives of chemical and biochemical relevance. 

Abstract Sequentially palladium-catalyzed reactions consist of combinations of identical, related, or significantly different palladium-catalyzed processes that occur in a sequential or consecutive fashion in the same reaction vessel without addition of further amounts of catalyst to the reaction media. This novel type of cascade reaction can be elaborated into both domino and multicomponent processes and represents a significant contribution to the highly topical field of diversity-oriented synthesis. 

In the next two chapters, more complex flowsheets are considered. But many of the fundamental ideas developed in this chapter and in Chap. 2 are directly applicable to these complex, multiunit, multirecycle, multicomponent processes. 

Nucleation in the atmosphere is essentially multicomponent process. However, a commonly used classical approach incapable of the quantitative treatment of multicomponent systems due to (a) excessive sensitivity to poorly defined activity coefficients, density and surface tension of multicomponent solutions (b) strong dependence of nucleation rates on thermochemistry of initial growth steps where... 

When it comes to demonstrating structure-property relationships for a food product data characterizing the structure (e.g., object dimensions, circularity, etc.), should be treated with the same rigor as the experimentally measured physical parameters. This means that the intrinsic heterogeneity of biological tissue and multicomponent processed foods as well as intersample variability has to be resolved first. This is one reason why nodestructive, real-time microscopy observations are preferred because at least sample variability is eliminated (although the observed sample may not be representative of the whole product )... 

Besides combinatorial and parallel synthetic strategies [2, 3] in the past two decades the productive concepts of multicomponent processes, domino reactions and sequential transformations have considerably stimulated the synthetic scientific community [4-15]. In particular, combination of diversity and creation of functionality has merged into the field of diversity oriented syntheses [16-20] that have found broad application in the discovery and development of pharmaceutical lead structures, and quite recently and steadily increasing also in the conception of functional 7i-electron systems, such as chromophores, fluorophores, and electro-phores [21, 22]. 

In the study of the adsorption phenomenon by means of adsorption isotlierms it must also be realized that the initial concentration of the adsorbate, the carbon dosage, and particle size all influence the results obtained [3 ]. Some of the observed effects are to be attributed to the complex nature of humic substances so that their adsorption is a multicomponent process. 

Today two models are available for description of combined (diffusion and permeation) transport of multicomponent gas mixtures the Mean Transport-Pore Model (MTPM)[21,22] and the Dusty Gas Model (DGM)[23,24]. Both models enable in future to connect multicomponent process simultaneously with process as catalytic reaction, gas-solid reaction or adsorption to porous medium. These models are based on the modified Stefan-Maxwell description of multicomponent diffusion in pores and on Darcy (DGM) or Weber (MTPM) equation for permeation. For mass transport due to composition differences (i.e. pure diffusion) both models are represented by an identical set of differential equation with two parameters (transport parameters) which characterise the pore structure. Because both models drastically simplify the real pore structure the transport parameters have to be determined experimentally. 

Cation exchange in groundwater is a multicomponent process in which all the solute cations participate. It can be calculated easily with geochemical models such as PHREEQC-2 (Parkhurst and Appelo, 1999) which have databases with representative values of the exchange constants. An example PHREEQC-2 input file for calculating exchangeable iron is given in Table 1. 

Results from two studies involving high volume recovery of multicomponent process effluents are presented here as illustrations of recent applications of hyperfiltration membranes in a tubular configuration supported by porous stainless steel. The first is a laboratory separation of dyes frcm a saline dye manufactiaring process effluent and the second a pilot renovation of wash water from a dye range for reuse. 

A better insight into composition of phases along the separation process is provided by multicomponent process simulation as it can be carried out with commercial process simulating programs, such as ASPEN-h. As usual, the process is separated into theoretical stages. Normally, ASPEN+ provides thermodynamic models and calculates thermodynamic properties such as the distribution coefficients and separation factors. As the accuracy of these results is not sufficient for a design analysis in many cases, distribution coefficients (and if necessary solubilities) can be provided by a user-defined module which uses empirical correlations for these values. 

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