Types of multiple reactions

Multiple reactions are of two basic kinds. Taking the case of one reactant only, these are  

When a second reactant B is involved, the situation is basically unchanged in the case of parallel reactions  

The reactions are thus in parallel with respect to both A and B. For reactions in series, however, if the second reactant B participates in the reaction with the product P as well as with A, i.e. if  

As we shall see, however, the series character of these reactions is the more important, because B cannot react to give Q until a significant amount of P has been formed. 

More complex reaction schemes can be regarded as combinations of these basic types of individual reaction steps. 

---

Let us apply this rule to find the proper temperature of operations for various types of multiple reactions. 

We are going to consider two basic types of multiple reactions... 

The contents of the present contribution may be outlined as follows. Section 6.2.2 introduces the basic principles of coupled heat and mass transfer and chemical reaction. Section 6.2.3 covers the classical mathematical treatment of the problem by example of simple reactions and some of the analytical solutions which can be derived for different experimental situations. Section 6.2.4 is devoted to the point that heat and mass transfer may alter the characteristic dependence of the overall reaction rate on the operating conditions. Section 6.2.S contains a collection of useful diagnostic criteria available to estimate the influence of transport effects on the apparent kinetics of single reactions. Section 6.2.6 deals with the effects of heat and mass transfer on the selectivity of basic types of multiple reactions. Finally, Section 6.2.7 focuses on a practical example, namely the control of selectivity by utilizing mass transfer effects in zeolite catalyzed reactions. 

Hie selectivity of a catalyst plays a role as soon as multiple reactions occur (Figure 2.6). We distinguish the following main types of multiple reactions ... 

In this chapter we discuss reactor selection and general mole balances for multiple reactions. There are three basic types of multiple reactions series, parallel, and independent. In parallel reactions (also called competing reactions) the reactant is consumed by two different reaction pathways to form different products ... 

There are four basic types of multiple reactions series, parallel, complex, and independent. These types of multiple reactions can occur by themselves, in pairs, or all together. V en there is a combination of parallel and series reactions. they are often referred to as complex reactions. 

Closure. After completing this chapter the reader should be able to describe the different types of multiple reactions (series, parallel, complex. and independent) and to select a reaction system that maximizes the selectivity. The reader should be able to write down and use the algorithm for solving CRE problems with multiple reactions. The reader should also be able to point out the major differences in the CRE algorithm for the multiple reactions from that for the single reactions, and then discuss why care must be taken when writing the rate law and stoichiometric Steps to account for the rate laws for each reaction, the relative rates, and the net rates of reaction. 

A chain polymerisation reaction is a special type of multiple reaction in which polymeric compounds of differenf chain lengths are produced by a sequence of simultaneous reactions. Reaction is initiated by a monomer molecule M reacting with another monomer molecule to produce a polymer chain P2 having two monomers... 

The solution of various types of multiple-reaction problems is illustrated below. 

Cyclocondensation reactions with perfluoroalkyl-subsbtuted CO and CN multiple bond systems can be divided into several subgroups, according to the charge pattern of both reactants On the basis of this simple concept, hetero-l,3-dienes should undergo two types of condensation reactions, classified by the number of skeleton atoms of the diene being incorporated into the ring system (equation 10). 

Perfluoroalkyl groups adjacent to multiple bond systems lower the frontier molecular orbitals (FMOs) Therefore, cycloaddition reactions preferentially occur with electron-rich multiple-bond systems The preference of bis(trifluoromethyl)-substituted hetero-l,3-dienes for polar reacuons makes them excellent model compounds for developing new types of diene reactions deviating from the well documented Diels-Alder scheme (pathway 1) A systematic study of the reactions of diene (1 =2-3=4)-dienophile (5=6) combinations reveals new synthetic possibilities that have not yet been fully exploited as tools for preparative organic cherrustry (equation 25)... 

There is another type of multiple thermal Diels Alder reaction in which the initial monoadduct is involved, either directly or after one transformation, in a second cycloaddition that affords the final polycyclic compounds. These methodologies have been used especially in the synthesis of polycyclic cage compounds. Paquette was the first to report the conversion of 9,10-dihydroful-valene into polyfused cyclopentanoid systems [124],... 

In Part 2 of this book, we shall be directly concerned with organic reactions and their mechanisms. The reactions have been classified into 10 chapters, based primarily on reaction type substitutions, additions to multiple bonds, eliminations, rearrangements, and oxidation-reduction reactions. Five chapters are devoted to substitutions these are classified on the basis of mechanism as well as substrate. Chapters 10 and 13 include nucleophilic substitutions at aliphatic and aromatic substrates, respectively, Chapters 12 and 11 deal with electrophilic substitutions at aliphatic and aromatic substrates, respectively. All free-radical substitutions are discussed in Chapter 14. Additions to multiple bonds are classified not according to mechanism, but according to the type of multiple bond. Additions to carbon-carbon multiple bonds are dealt with in Chapter 15 additions to other multiple bonds in Chapter 16. One chapter is devoted to each of the three remaining reaction types Chapter 17, eliminations Chapter 18, rearrangements Chapter 19, oxidation-reduction reactions. This last chapter covers only those oxidation-reduction reactions that could not be conveniently treated in any of the other categories (except for oxidative eliminations). 

Huge literature on biological functions of flavonoids and their antioxidant and free radical scavenging activities successfully competes with work on antioxidant effects of vitamins E and C. Flavonoids have been reported to exert multiple biological effects and exhibit antiinflammatory, antiallergic, antiviral, and anticancer activities [85 89], However, considering flavonoids as the inhibitors of free radical-mediated processes, two types of their reactions should be discussed flavonoids as free radical scavengers (antioxidants) and flavonoids as metal chelators. 

A general type of chemical reaction between two compounds, A and B, such that there is a net reduction in bond multiplicity (e.g., addition of a compound across a carbon-carbon double bond such that the product has lost this 77-bond). An example is the hydration of a double bond, such as that observed in the conversion of fumarate to malate by fumarase. Addition reactions can also occur with strained ring structures that, in some respects, resemble double bonds (e.g., cyclopropyl derivatives or certain epoxides). A special case of a hydro-alkenyl addition is the conversion of 2,3-oxidosqualene to dammara-dienol or in the conversion of squalene to lanosterol. Reactions in which new moieties are linked to adjacent atoms (as is the case in the hydration of fumarate) are often referred to as 1,2-addition reactions. If the atoms that contain newly linked moieties are not adjacent (as is often the case with conjugated reactants), then the reaction is often referred to as a l,n-addition reaction in which n is the numbered atom distant from 1 (e.g., 1,4-addition reaction). In general, addition reactions can take place via electrophilic addition, nucleophilic addition, free-radical addition, or via simultaneous or pericycUc addition. 

All of the preceding work was for simple, or one step, reactions. The more interesting case of multiple reactions has been studied by de Maria et al. (D15) and by Tichacek (T7). de Maria et al. considered the catalytic oxidation of naphthalene. They found that the consideration of the dispersion effects enabled them to obtain a better design. Tichacek considered the selectivity for several different types of reactions. Naturally, the results were rather complicated, and the statement of general conclusions is rather diflBcult. For small values of the reactor dispersion group, Dl/uL < 0.05, it was found that the fractional decrease in the maximum amount of intermediate formed is closely approximated by the value of Dl/uL itself. For other ranges of the parameters, we refer to the original work (T7). 

The propagation reactions proceed at multiple radical sites until the monomer is exhausted, or until one of two common types of termination reactions occur either combination or disproportionation. 

Late transition metals have a marked affinity towards coordinating carbon monoxide and carbon-carbon multiple bonds. If there is another suitable ligand on the metal centre, this coordination might be followed by the insertion of a carbonyl group or the carbon-carbon moiety into the metal-ligand bond. Both types of attachment reactions are commonly exploited in catalytic processes and their characteristics will be discussed separately. 

Recently, the transition-metal-catalyzed addition of active methylene C-H bonds to electron-deficient olefins having a carbonyl, a nitrile, or a sulfonyl group has been extensively studied by several research groups. In particular, the asymmetric version of this type of catalytic reaction provides a new route to the enantioselective construction of quaternary carbon centers [88]. Another topic of recent interest is the catalytic addition of active methylene C-H bonds to acetylenes, allenes, conjugate ene-ynes, and nitrile C-N triple bonds. In this section, the ruthenium-catalyzed addition of C-H bonds in active methylene compounds to carbonyl groups and C-C multiple bonds is described. 

There is one important exception Certain types of chain reactions and reactions involving dissociation produce exponents of one half or integer multiples of one half in power-law or one-plus rate equations (see Sections 5.6, 9.2, and 10.3.1). Such exponents should be accepted if found not to vary with conversion and if there is good reason to believe that a mechanism of this kind may be operative. 

---