Multicomponent reactions definition

According to our definition a multicomponent reaction (MCR) comprises reactions with more than two starting materials participating in the reaction and, at the same time, the atoms of these educts contribute the majority of the novel skeleton of the product (Scheme 3.1) [1], For example, adenine may be formed by the addition of five molecules of isocyanic acid, a reaction of possible high prebiotic relevance [2]. 

A third, though far less studied possibility, is the one-step synthesis of macrocycles by a multicomponent reaction (MCR). MCR is a process in which three or more reactants are combined in a single reaction vessel to produce a product that incorporates substantial portions of all the components [29]. They have, by definition, sustainable chemistry and are inherently (a) chemo- and regioselective, a prerequisite for a successful MCR since at least three reactive functional groups are involved and they have to react in an ordered and selective fashion (b) atom-economic [30] since most of them involve addition rather than substitution reactions. 

As initially stated, the definition of multicomponent reaction could be extended also to those reactions that implicate the addition of further reagents only after a suitable time from the very beginning of the procedure. Among others, few Chinese groups reported two notable examples of one-pot Michael addition/Pictet-Spengler cyclization sequence. In particular, in 2011, Zhao et al. developed a high enantioselective organocatalytic synthesis of several... 

The lacking special description of the Gibbs phase rule in MEIS that should be met automatically in case of its validity is very important for solution of many problems on the analysis of multiphase, multicomponent systems. Indeed, without information (at least complete enough) on the process mechanism (for coal combustion, for example, it may consist of thousands of stages), it is impossible to specify the number of independent reactions and the number of phases. Prior to calculations it is difficult to evaluate, concentrations of what substances will turn out to be negligibly low, i.e., the dimensionality of the studied system. Besides, note that the MEIS application leads to departure from the Gibbs classical definition of the notion of a system component and its interpretation not as an individual substance, but only as part of this substance that is contained in any one phase. For example, if water in the reactive mixture is in gas and liquid phases, its corresponding phase contents represent different parameters of the considered system. Such an expansion of the space of variables in the problem solved facilitates its reduction to the CP problems. 

There is a large body of literature that deals with the proper definition of the diffusivity used in the intraparticle diffusion-reaction model, especially in multicomponent mixtures found in many practical reaction systems. The reader should consult references, e.g.. Bird, Stewart, and Lightfoot, Transport Phenomena, 2d ed., John Wiley Sons, New York, 2002 Taylor and Krishna, Multicomponent Mass Transfer, Wiley, 1993 and Cussler, Diffusion Mass Transfer in Fluid Systems, Cambridge University Press, 1997. 

This model represents the most frequently used description of chemical reaction equilibrium and should be familiar to most chemical engineering students. However, for multicomponent mixtures in which multiple reactions may take place, this type of non-linear problems may be cumbersome to solve numerically. One important obstacle is that the non-linear equilibrium constant definitions may give rise to multiple solutions, hence we have to identify which of them are the physical solutions. The stoichiometric formulation might thus be inconvenient for mixtures containing just a few species for which only a few reactions are taking place. 

The thermodynamics of irreversible processes begins with three basic microscopic transport equations for overall mass (i.e., the equation of continuity), species mass, and linear momentum, and develops a microscopic equation of change for specific entropy. The most important aspects of this development are the terms that represent the rate of generation of entropy and the linear transport laws that result from the fact that entropy generation conforms to a positive-definite quadratic form. The multicomponent mixture contains N components that participate in R independent chemical reactions. Without invoking any approximations, the three basic transport equations are summarized below. 

In Schemes 1.8.5.1 and 1.85.2 we have eluded to the fact that multicomjxrnent cascade reactions usually lead to a higher number of compounds based on a higher number of core structures as compared to multicomponent one-pot reactions. Reactive building blocks which allow the construction of several different core structures depending on the sequence of mixing bear definitely a novel potential in combinatorial organic synthesis as shown in Scheme 1.95.1. 

Here is by definition the diffusion coefficient and has the dimensions of cm sec if J is expressed in the conventional units given above, and is the concentration, in molecules/cm. Strictly speaking, this equation is correct only for a two-component system it is applicable in multicomponent systems only if the interaction between flows can be neglected [29]. If the flow of substance A is affected by an external potential (for example, electrostatic interactions greatly influence ionic reactions), Eq. (2-83) can be modified to give... 

In contrast, a much better efficiency could be accomplished using domino reactions, which have been defined by us as processes of two or more bond forming reactions under identical reaction conditions, in which the latter transformations take place at the functionahties obtained in the former bond forming reactions [4]. In the processes one, two, three, or more substrates can be involved. Thus, multicomponent transformations are domino reactions per definition. In the meantime, several excellent reviews have also been pubhshed by other authors on this topic [5]. 

Chemical Description. The constituents of the system include atoms, ions, molecules as well as molecular and nonmolecular solids. The homogeneous catalytic reaction of interest occurs in the multicomponent liquid phase Pl- By definition, all the molecular and ionic species S involved directly in the catalysis are soluble in this liquid phase. In particular, one or more organic reagents must be present in Pl- The liquid phase must contain numerous soluble transition-metal... 

The concept of multicomponent processes associated with organocascade reactions allows the installation of new functionalities, which easily give access to quite complex structures. Recently, Jprgensen and coworkers rqxjrted a remaikable application of such definition toward the high stereocontrolled synthesis of optically active pyrroloisoquinolines 115 (dr up to >95, up to 99% ee) (Schane 2.33) [63]. 

The phase behaviour of the binary mixtures between the potential solvents and the system components (reactants and reaction products) should be studied first later the study should be extended to the multicomponent reactive mixtures for definition of feasible operating regions. 

---