Reactivity Sources

The principal accidental sources of positive reactivity are 1) core flooding, 2) cold water insertion during equilibrium reactor operation and 3) excessive control rod withdrawal rates. There are two types of failures or errors which must be considered in any discussion on withdrawal of control rods. The two failiires or errors are 1) increased rod withdrawal speeds due to Inadvertent admission of air or gas into the hydraulic systems, and 2) steeper ramps resulting from maximum strength rods being involved in the rod withdrawal. 

From a reactor efficiency standpoint, any power transient should not stress the fuel elements to the point where a rupture rash would occur. Procedural rod withdrawal rates will be less than these maximumly possible and will undoubtedly be governed by fuel rupture considerations. 

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Aromatic acyl halides and sulfonyl halides undergo oxidative addition, followed by facile elimination of CO and SO2 to form arylpalladium complexes. Benzenediazonium salts are the most reactive source of arylpalladium complexes. 

The diazonium salts 145 are another source of arylpalladium com-plexes[114]. They are the most reactive source of arylpalladium species and the reaction can be carried out at room temperature. In addition, they can be used for alkene insertion in the absence of a phosphine ligand using Pd2(dba)3 as a catalyst. This reaction consists of the indirect substitution reaction of an aromatic nitro group with an alkene. The use of diazonium salts is more convenient and synthetically useful than the use of aryl halides, because many aryl halides are prepared from diazonium salts. Diazotization of the aniline derivative 146 in aqueous solution and subsequent insertion of acrylate catalyzed by Pd(OAc)2 by the addition of MeOH are carried out as a one-pot reaction, affording the cinnamate 147 in good yield[115]. The A-nitroso-jV-arylacetamide 148 is prepared from acetanilides and used as another precursor of arylpalladium intermediate. It is more reactive than aryl iodides and bromides and reacts with alkenes at 40 °C without addition of a phosphine ligandfl 16]. 

Wilkinson s catalyst brings about the hydrosilylation of a range of terminal alkenes (1-octene, trimethylvinylsilane) by 2-dimethylsilylpyridine with good regioselectivity for the anti-Markovnikoff product. Both 3-dimethylsilylpyridine and dimethylphenylsilane are less reactive sources of Si-H. In contrast, these two substrates are far more reactive than 2-dimethylsilylpyridine for the hydrosilylation of alkynes by [Pt(CH2 = CHSiMe2)20]/PR3 (R = Ph, Bu ). This difference was explained to be due to the operation of the two different pathways for Si-H addition—the standard Chalk-Harrod pathway with platinum and the modified Chalk-Harrod pathway with rhodium.108... 

Mesitoic acid, for example, will give the amine at 0°, while benzoic acid requires a temperature of 35° for the reaction to go at a convenient rate. Presumably the higher concentration of acylium ion in the former case reacts more rapidly than a lower concentration or a less reactive source of acyl groups in the latter case.286... 

R. Rouhani, W. Lasdon, L. Lebow, and A. D. Warren. A generalized benders decomposition approach to reactive source planning in power systems. Math. Progr. Study, 25 62, 1985. 

Fluorodestannylation. Bu4NF is the most reactive source of F, but is difficult to obtain anhydrous. For fluorodestannylation, Harpp and Gingras1 prefer CsF with a catalytic amount of 18-crown-6. This reagent combines with diorganotin oxides, sulfides, or selenides to liberate the corresponding anion, which can be alkylated to give ethers, sulfides, or selenides. 

When applied to zeolites the term "isomorphous substitution" refers to the replacement of silicon or aluminum atoms by elements with ionic radii and coordination requirements which are compatible with the T (tetrahedral) sites of the zeolite structure. One method of preparing isomorphously substituted zeolites is to include a reactive source of the replacement... 

Fig. 4.5 John Emmett Ellis (born in 1943), a native of California, received his Ph.D. in 1971 from MIT under the direction of Alan Davison who opened his eyes to the challenge and wonder of inorganic syntheses (J. E. E.). In 1971, John joined the faculty at the University of Minnesota, where he is Professor of Chemistry since 1984. His recent honors include a Humboldt Senior Scientist Award, spent in Wolfgang Beck s group in Miinchen, and the F. Albert Cotton Award in Synthetic Inorganic Chemistry for his studies on the synthesis and characterization of compounds containing d-block elements in their lowest known formal oxidation states. John s research also includes investigations on the reactions of polyarene radical anions with high-valent transition metal precursors as a route to new classes of homoleptic polyarene metal species, in particular anionic ones. Those species can function as highly reactive sources of naked metal anions which previously had only been detected in the gas phase (photo by courtesy of J. E. E.)...

Classify sources and sinks, and then find the most reactive source and sink. 

Classify into generic sources sinks Find most reactive source sink Recall how the generic groups react Identify probable reaction archetype... 

A reactive source of cyclopropane derivatives capable of furnishing cyclopropanone acetals is 1-chloro-l-methoxycyclopropane (33), which reacts with methanol in the presence of silver salts to give cyclopropanone dimethyl acetal (34) without rupture of the three-membered ring. It was subsequently shown that methanolysis, which occurs via an S l mechanism, does not require silver salts and occurs in quantitative yield with or without added base. ... 

Dihydrogen reacts with many metals when heated to give metal hydrides, MH , although these are not necessarily stoichiometric (e.g. TiH] 7, see Section 5.7). By the action of an electric discharge, H2 is partially dissociated into atoms, particularly at low pressures. This provides a reactive source of the element, and facilitates combination with... 

Substrates R inRCHa-CH-CO OH 1 NHa Reactivity Source of enzyme Reference... 

Ozone provides a very reactive source of oxygen because it breaks down to an oxygen molecule and a single reactive oxygen. 

Diazonium salts are the most reactive source of arylpalladium species and the reaction can be carried out at room temperature using Pd2(dba)3 as a catalyst in the absence of both phosphine ligand and base [44]. The reaction of diazonium salts means indirect substitution reaction of an amino group of anilines or aromatic nitro group with an alkene. The use of diazonium salts is synthetically more convenient than the use of aryl halides, because many aryl halides, particularly iodides, are prepared from diazonium salts. 

In most syntheses, a gel is initially prepared that contains framework-building inorganic species, typically aluminates, silicates, phosphates or metal-oxyani-ons, available in a reactive form. There are also syntheses that result in crystallisation from clear solution, and others that proceed under essentially dry gel conditions (without added water). The sources of the reagents can determine the products that form in general more reactive sources are favoured. In addition, for zeolites and related solids, structure directing species must be present in the gel that can stabilise the open framework structures relative to denser phases of the same composition. Hydrated metal cations and/or organic cations perform this function in zeolite preparations. 

Aluminosilicate gels are prepared by the mixing of reactive sources of alumina and silica. These include fumed silica, silica sols and alkoxides of silica, and aluminium, aluminates, aluminium salts and alkoxides of aluminium. Other synthetic routes have been explored that use structured aluminosilicate precursors, such as zeolites themselves, to supply aluminate and silicate species to... 

In order to measure these low rate constants (with [O2] limited to below 10 cm" because of quenching of the OH fluorescence) slow decays in the absence of O2 are required, /.e., a clean set-up, pure inert gas, a low level of radicals to avoid radical-radical reactions (here S/N > 100 at 10 cm ) and a non-reactive source of OH (here flash photolysis of H2O). In the absence of reactants the decay rate of OH is as low as 3 to 4 s" with a stability of 0.2 s" ... 

The latter, together with some phosgene and dissolved chlorine, can subsequently be condensed to a liquid (b.p. 58°C) by means of a freezing mixture. Its ultimate disposal is potentially hazardous and expensive unless an outlet can be found for it as a reactive source of silicon compoimds. 

Using Bi(0Tf)3 in catalytic amounts, the efficient conversion of epoxides to thi-iranes with ammonium thiocyanate or thiourea has been reported. It is noteworthy that the reaction works with thiourea, the compound being a less reactive source of sulfur (Equation 43) [86c]. 

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