Additive deactivation

The Favorsky reaction should be considered a general method for producing pyrazolyl-Q -acetylenic alcohols because even the less reactive 4-ethynyl-l,3,5-trimethylpyrazole, additionally deactivated by three donor methyl groups, reacts with acetone (Scheme 61). 

Additionally, deactivation rate constants (kd) for the more active catalysts such as Cu X/Me4CYCLAM have been estimated from the initial degree of polymerization without reactivation, end functionality, and molecular weight distributions [138,141,142], With recent advances in determination of the equilibrium constant for atom transfer (KATRP=kJkd), deactivation rate constants (k =k KX[M,) can now be easily obtained from readily accessible activation rate constants (k) [115],... 

The same criteria were used for start-of-cycle and deactivation lumping. Start-of-cycle lumping was based on thermodynamics and molecular-reaction similarity. The deactivation kinetic lumps contain the start-of-cycle lumps as a subset. The additional deactivation lumps were required to properly describe the effect of carbon number on aging rate. 

This investigation shows that the GSR dynamics of Pe + can be used as a probe to monitor the time evolution of the ion pair formed upon electron transfer quenching. Indeed, at short interionic distance, an additional deactivation pathway of the excited cation, probably a back electron transfer to the excited reactant, is operative. Further experiments will be carried out to confirm this hypothesis. First, a three-color pump/pump-probe measurement will allow to probe the Pe (Si) population in order to see if the deactivation pathway 2+3 is really operative. Second, higher quencher concentrations have to be used in order to ensure faster formation of ET product and to make the interpretation of the data easier. 

Halogenation of pyridines is easier than nitration or sulfonation because it can be carried out in non-acidic media and the pyridine-halogen adducts are appreciably dissociated. Dihalogenation can occur since one halogen atom causes little additional deactivation of the ring. The mercuration of pyridines (Section 3.2.1.4.9) probably involves coordination of the pyridine nitrogen to the mercury atom, and such coordination causes less ring deactivation than protonation. 

It will be assumed that Q does not absorb the excitation light and does not react with the ground-state M. The decay rate of M in the absence of Q will be denoted m- Such a chemical scheme is independent of any effective mechanism for the interaction between M and Q (Birks, 1970). It only states that, in the presence of Q, an additional deactivation pathway is present, through the creation of Z, which may be non-luminescent. By use of classical kinetic laws, one derives ... 

Excess nucleophile is often needed in polymerization of more nucleophilic monomers. For example, esters, ethers, and amines afe used in large excess over aluminum halides and alkylaluminum halides to control polymerization of vinyl ethers [269]. The original Lewis acid is no longer available and covalent species are activated by the Lewis acid/nucleophile complex. Carbenium ions are additionally deactivated by excess nucleophile. 

In the polymerizations of more reactive monomers such as vinyl ethers, an excess of nucleophile is often used (Section V. A. 2) [64,102,131 ]. This indicates that the complex between Lewis acid and the nucleophile has a sufficient reactivity to ionize covalent species. Excess nucleophile acts as an additional deactivator to convert carbocations to onium ions. In that case, the concentration of naked Lewis acid may be too low to efficiently assist the ionization and the reaction can be described by the highlighted left part of Scheme 16. 

In addition, deactivating nitro and halogen substituents have been introduced by anodic oxidation (see Chapter 24.)... 

By adding a known concentration of quencher to the solution, we can increase the rate of step (iv). Because there is now an additional deactivation pathway for the excited state complex, the steady-state expression and the quantum efficiency expression become ... 

In the previous section, delayed fluorescence has been disregarded although it constitutes an additional deactivation channel for triplets in P1VN (1,56), P2VN (6,57,73), PVCA (4,5,7,13,59,65), P2NMA (74,75) but not in PACN ( ). 

Mn=55,500, Mw/Mn< 1.3) leading to a brush synthesized entirely by a controlled process (Scheme 46B). From either macroinitiator, the ATRP of St and nBA was conducted, leading to the desired densely grafted structures. The grafting reactions were found to be very sensitive to reaction conditions additional deactivator, high concentrations of monomer, and reduced temperatures were all necessary to produce the desired materials. 

There may also be additional deactivation channels for protonated species, for example carbenium ions can attach via C-O bonds to the zeolite framework and form alkoxides, as shown in Fig. 22.1 for isobutene. 

The significantly positive AV values clearly underline the dissociative nature of the reductive elimination process in both solvents. The reactive state is a thermally equilibrated MLCT excited state that can undergo nonradiative deactivation (kn) and simultaneous Pt—N3 bond cleavage (k,) to produce a caged radical species, which subsequently decomposes to Pt(CN)4 and N2 in both solvents, or interacts with ethanol to produce HN3 and ethanol radicals via the abstraction of hydrogen (fc3). The additional deactivation route in ethanol can account for the higher AV value. It follows that bond cleavage plays an important role in both deactivation routes k1 and k2. 

Furthermore, the observed reactivity trends illustrated the interplay of anomeric effect with two other electronic factors described earlier in this book. In particular, the loss of activation associated with the poor lone pair/C-H overlap in the bicyclic system is an example Bredt s rule (restriction on jt-overlap at the bridgehead position) whereas the additional deactivation of is a consequence of Bent s rule. Because the... 

As shown in Scheme 6.3, the process is terminated by the combination of (a) chlorine atoms with each other, regenerating molecular chlorine (CI2) (b) chlorine atoms (Cb) with methyl radicals (CHs ), forming chloromethane (H3CCI) and (c) methyl radicals (CHa ) with each other, forming ethane (CH3CH3). Additionally, deactivation of any of the radical species by a wall reaction serves to end the reaction. 

Although detailed product analysis immediately after irradiation gives a clear picture of the effectiveness of an additive in suppressing direct polymer oxidation, the level of unstable products such as hydroperoxide groups appears to be less important than the extent of additive deactivation. Unhindered or partially hindered phenols are more extensively consumed than conventional, fully... 

Thus, basing on the totality of experimental data on PCA stabilization one may conclude that the most probable stabilization mechanisms are additive deactivation, inhibition of radical oxidation processes and deactivation of electron-excited states. 

A common pigment used in many plastics application is titanium dioxide, TiOa. The pigment is a very effective light scattering inorganic oxide for the coloration and protection of plastic articles. TiOa is also an insoluble material within a polymer matrix that has the ability to adsorb other materials within the matrix. Additionally, a Ti02 particle can catalyze the formation of chromophores from additive deactivation. This paper describes the adsorption behavior of several TiOi materials compares the rate of chromophore formation in a polyethylene matrix compounded. 

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