Sequential reaction

In sequential reactions the active site binds all the substrates before processing them into products. The binding can be ordered  

This equation can be rearranged into a form more suitable for plotting by holding the concentration of one substrate (S2, for instance) constant and writing first 

KmiKmi2/[S2]o + Kmi2[Si]o/[S2]o + Km21 + [SJo and then forming the reciprocal of both sides  

It follows that a plot of 1/v against l/[S ]o for constant (S2I0 is linear with Km21 + KmiKmi2/[S2]o 

For sequential reactions we have one or more of the products of the first reaction serving as a reactant in the second reaction, and so on. Most dibasic acids dissociate in two steps  

Writing Eq. 12.14 twice, inserting the calculated dissociation constants, we find that 

We use the scheme outlined in Section 12.6.1, letting Cj be the mols of H produced by the first ionization reaction and 42 that by the second. Then we can write out Table 13.A, which shows that for H+ and for HSO both reactions must be considered simultaneously to compute the equilibrium. This formulation in terms of e and 2 reduces the number of unknowns from four to two  

This set of equations is easily solved numerically, finding Cl = 0.9906 mol/kg of solvent, C2 = 0.00988 mol/kg of solvent. The corresponding equilibrium concentrations are shown in Table 13.B. The reader may substitute these values in Eqs. 13.1 and 13.J and verify that these equations are 

We see that at this concentration the first ionization is practically complete, but that the second is only about 1 % complete. Most of the sulfuric acid placed in this solution is in the form of HSO4 (bisulfate) ion. In this example we computed the ionization constants from Table A.8 (see Problem 13.1). Most handbooks list the ionization constants directly, saving us this minor effort (see Problem 13.3 (b)). 

Often more than one reaction is required to convert starting materials into the desired products. This is true for many reactions that we carry out in the laboratory and for many industrial processes. These are called sequential reactions. The amount of desired product from each reaction is taken as the starting material for the next reaction. 

At high temperatures, carbon reacts with water to produce a mixture of carbon monoxide, CO, and hydrogen, H2. 

Carbon monoxide is separated from H2 and then used to separate nickel from cobalt by forming a gaseous compound, nickel tetracarbonyl, Ni(CO)4. 

What mass of Ni(CO)4 could be obtained from the CO produced by the reaction of 75.0 g of carbon Assume 100% yield. 

We interpret both chemical equations in the usual way, and solve the problem in two steps. They tell us that one mole of C produces one mole of CO and that four moles of CO is required to produce one mole of Ni(CO)4. 

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The hquid-phase chlorination of benzene is an ideal example of a set of sequential reactions with varying rates from the single-chlorinated molecule to the completely chlorinated molecule containing six chlorines. Classical papers have modeled the chlorination of benzene through the dichlorobenzenes (14,15). A reactor system may be simulated with the relative rate equations and flow equation. The batch reactor gives the minimum ratio of... 

Chain reactions such as those described above, in which atomic species or radicals play a rate-determining part in a series of sequential reactions, are nearly always present in processes for the preparation of thin films by die decomposition of gaseous molecules. This may be achieved by thermal dissociation, by radiation decomposition (photochemical decomposition), or by electron bombardment, either by beams of elecuons or in plasmas. The molecules involved cover a wide range from simple diatomic molecules which dissociate to atoms, to organometallic species with complex dissociation patterns. The... 

Figure 4.6 The bifunctional enzyme PRA-isomerase (PRAI) IGP-synthase (IGPS) catalyzes two sequential reactions in the biosynthesis of tryptophan. In the first reaction (top half), which is catalyzed by the C-terminal PRAI domain of the enzyme, the substrate N-(5 -phosphoribosyl) anthranilate (PRA) is converted to l-(o-carboxyphenylamino)-l-deoxyribulose 5-phosphate (CdRP) by a rearrangement reaction. The succeeding step (bottom half), a ring closure reaction from CdRP to indole-3-glycerol phosphate (IGP), is catalyzed by the N-terminal IGPS domain.

In this type of sequential reaction, all possible binary enzyme substrate complexes (AE, EB, QE, EP) are formed rapidly and reversibly when the enzyme is added to a reaction mixture containing A, B, P, and Q ... 

J -methylpyrrolidone by conversion to the imine ( 7) by sequential reaction with triethyloxonium tetraf1uoroborate and then anhydrous ammonia. When this is reacted with 2,6-dimethyl-phenyl i socyanate, the centrally acting muscle relaxant xilobam (8) is formed. ... 

Another acylated ampicillin derivative with expanded antimicrobial spectrum is piperacil1 in (19). Its synthesis begins with 1-ethyl-2,3-diketopiperazine (j7, which itself is made from ]i-ethylethylenediamine and diethyl oxalate), which is activated by sequential reaction with trimethylchlorosilane and then trichloromethyl chioroformate to give This last... 

Recently, elegant synthesis of ruin -MRS carbapenum has been reported. Sequential reaction of nitromethane via conjugate addition-elimination to a,fi-unsanirated esters followed by Pd-catalyzed subsdnidon of the residdng allyl nitro compound with the naphthosultam affords the allyladon product which is an and fEq. 7.20. ... 

The pyrrolotriazines 32 were prepared from 3,4-dihydro-5-ethoxy-2//-pyrrole 31 by sequential reaction with hydrazine hydrate and a-oxoesters (85GEP3340026). They are useful as selective herbicides (Scheme 10). 

In addition to these cases, which are relatively simple because only two sequential reactions are involved, there are others involving many, many reactions. The methods given here apply as well, although in practical terms the rate constants can be refined for only one or two steps. The others must be fixed at their independently known values. 

The first situation, for parallel pathways, is illustrated by Eq. (6-9), the reaction between H2O2 and I". The limiting order with respect to [H+] increases from zero to one as [H+] increases. The second situation, for sequential reactions, is illustrated by Eq. (6-14). The order with respect to [Fe2+] falls from two to one with increasing [Fe2+], and that with respect to [Fe3 r ] from zero to negative one with increasing [Fe3+]. 

What confuses this issue somewhat is that an entirely different scheme, with no substrate titration, can also give rise to a downward bend. It is a case of sequential reactions. Perhaps its existence will come as no great surprise, in that the second part of Rule 8 in Section 6.2 implied as much. Consider the following two steps ... 

Saddle point. 170 Salt effects. 206-214 Scavenging (see Reactions, trapping) Second-order kinetics. 18-22, 24 in one component, 18-19 in two components (mixed), 19-22 Selectivity. 112 Sensitivity analysis. 118 Sensitivity factor, 239-240 Sequential reactions (see Consecutive reactions)... 

Furthermore, the reaction of several hindered phenols, such as 2,6-di-t-butyl-4-methylphenol, 3,5-di-t-butyl-4-hydroxybenzyl alcohol, and 2,6-di-t-butylphenol, with BTMA Br3 were carried out in dichloromethane in the presence of water, t-butyl alcohol, or aq. sodium hydroxide at room temperature. Sequential reaction processes were provided by the obtained products. As an example, we show the reaction of 2,6-di-t-butyl-4-methylphenol with BTMA Br3 in Fig. 26 (ref. 34). 

The reformation, or formation, of molecules appears to be a stepwise process—that is, it occurs by sequential reactions which may by interrupted at certain stages ... 

Finely symmetrical divinyl tellurides 135, especially useful in transmetallation reactions, have been prepared in situ by sequential reaction of an excess of the ylide 134 with TeCl4 and aldehydes (Scheme 36) [134]. These compounds whatever their geometry lead in presence of -BuLi to the formation of -a,/l-unsat-urated aldehydes. 

In addition to sequential reactions, reactions can occur in parallel and compete with one another. For example, a single reactant A might form two different products, B and C ... 

In sequential reactions, both substrates must combine with the enzyme to form a ternary complex before catalysis can proceed (Figure 8-11, top). Sequential reactions are sometimes referred to as single displacement... 

For a number of reasons, there are some important limitations to the extension of this principle. Biodegradation—as opposed to biotransformation—of complex molecules necessarily involves a number of sequential reactions each of whose rates may be determined by complex regulatory mechanisms. For novel compounds containing structural entities that have not been previously investigated, the level of prediction is necessarily limited by lack of the relevant data. Too Olympian a view of the problem of rates should not, however, be adopted. An overly critical attitude should not be allowed to pervade the discussions—provided that the limitations of the procedures that are used are clearly appreciated and set forth. In view of the great practical importance of quantitative estimates of persistence to microbial attack, any procedure—even if it provides merely orders of magnitude—should not be neglected. 

Chemical deactivation. In chemical deactivation the active surface area changes by strong chemisorption of impurities in the feed, by blocking of active sites by heavy products formed in parallel or sequential reactions, etc. The most important chemical causes of deactivation are poisoning by impurities in the feed and deposition of carbonaceous material, usually referred to as coke . 

The first part of the mechanism is a sequential reaction yielding formic acid, and from that point the typical dual path mechanism for formic acid occurs. In fact, it has been proposed that the mechanisms of formic acid and methanol oxidation consist of the same dominating elemental steps [Okamoto et al., 2005]. However, experiments have revealed that the mechanism is much more comphcated than that. 

The reaction sequence of formaldehyde formation and subsequent COad formation can proceed either as sequential reactions of adsorbed species, or it can involve formation and desorption of formaldehyde into the electrol5d e and subsequent re-adsorption and further decomposition of formaldehyde to COad. Considering the significant transport and catalyst loading effects discussed above, it is clear that desorption and subsequent re-adsorption plus dehydrogenation of formaldehyde will play an important role also for COad formation, although a direct reaction of adsorbed RIad species can not be ruled out. 

CASCSEQ - Cascade of Three Reactors with Sequential Reactions... 

SEMISEQ - Sequential Reactions in a Semi-Continuous Reactor... 

Figure 5.101. Complex sequential reactions in a semi-continuous reactor.

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