Liquid metals chain reaction

In fast (neutron) reactors, the fission chain reaction is sustained by fast neutrons, unlike in thermal reactors. Thus, fast reactors require fuel that is relatively rich in fissile material highly enriched uranium (> 20%) or plutonium. As fast neutrons are desired, there is also the need to eliminate neutron moderators hence, certain liquid metals, such as sodium, are used for cooling instead of water. Fast reactors more deliberately use the 238U as well as the fissile 235U isotope used in most reactors. If designed to produce more plutonium than they consume, they are called fast-breeder reactors if they are net consumers of plutonium, they are called burners . 

C. In liquid ammonia the reaction with epoxybutane would be slower than in the case of oxiiane. However, the most important effect of the replacement of the NH3 by DMSO is, that the specific solvatarion of the metal ion by DMSO facilitates attack of the acetylide on the ring. The presence of this solvent does not give rise to difficulties during the aqueous woik-up of alcohols with a longer carbon chain (compare exp. 23). 

Solid extinguishers such as sand or clay are also used to cover the oil or grease under a fire. They also suppress fire by blanketing. They are suitable for metal fires. Sodium and potassium bicarbonate are also used as solid extinguishers for liquid fuel. They act as chain reaction inhibitors. At high temperatures, they decompose to give carbon dioxide that itself is an extinguisher that suppresses fire. 

Anions can be used to promote a chain reaction similarly to cations, except that they act as nucleophiles in their reaction with the organic monomer. The anions are frequently formed in a reaction with alkali metals such as Na, K, or Li. As an example, potassium in liquid ammonia forms KNH2, which generates NH2" anions. These anions further react with the organic monomers in a reaction as shown below ... 

Two further analytical methods are based on the formation of metal complexes. Reaction of dopamine with KzCrjOy gives a Cr complex which can be assayed by atomic absorption spectroscopy, carbon rod absorption spectroscopy or, if Kf CrjO has been used, by liquid scintillation spectroscopy. Since the complex still gives a reaction with fluorescamine, the side-chain is thought not to be involved in the formation of the complex. Methamphetamine hydrochloride can be precipitated as a Bi complex. Determination of the amount of Bi remaining in solution by atomic absorption spectroscopy provides an indirect method of assay for the amphetamine. ... 

For the purification of liquid metal from oxygen, the voltage (/ > Pq has to be applied from the external DC source with the negative polarity on the liquid-metal electrode. The transfer of oxygen ions to the gaseous electrode can result in the following chain reactions ... 

Chemically inhibits combustion chain reaction Ordinary commodities Flammable and combustible liquids Electrical fires Metals Materials that react with heptafluoropropane Sealed compartments required for total flooding systems May generate corrosive byproducts when exposed to fire Concentrations required for extinguishment are not immediately lethal Readily dispersed Electrically non-conductive Self-pressurizing agent Environmentally benisn... 

Urea and potassium bicarbonate Potassium chloride Potassium bicarbonate Sodium bicarbonate Chemically inhibits combustion chain reaction Blocks radiation Cooling Flammable and combustible liquids Electrical fires Ordinary commodities Metals... 

Not all free-radical mechanisms are chain reactions, and those that are not do not require initiators. Reductions with metals such as Li, Na, or Sml2 (often in liquid NH3) and light-promoted rearrangements of carbonyl compounds proceed by nonchain free-radical mechanisms. Compounds containing weak cr bonds (typically either heteroatom-heteroatom bonds or very strained bonds) can undergo intramolecular rearrangements by nonchain free-radical mechanisms upon heating. 

When air or oxygen is bubbled through or otherwise contacted with liquid cumene at temperatures in the range of 100-130 C, oxidation occurs with resultant formation of cumene hydroperoxide, which is comparatively stable under these conditions. The Usual oxidation catalysts, such as salts of the transition metals, cannot be used for the reaction ance they tend to cause decomposition of the cumene hydroperoxide. Purity of the charge material is important since small amounts of certain impurities such as sulfur compounds, phenols, aniline, unsaturated hydrocarbons, and the like act as inhibitors to break the chain reaction and thereby slow down the reaction. The maximum reaction rate is attained after a portion of hydroperoxide is formed in fresh cumene charge. ... 

They laid their plans, often during hikes into the uninhabited wild surroundings of the mesa. They had to rely heavily on theoretical anticipations of the effects they wanted to study that was their basic constraint. Any experimental device that demonstrated a fast-neutron chain reaction to completion would use up at least one critical mass there could be no controlled, laboratory-scale bomb tests, no squash-court demonstrations. They decided they had to analyze the explosion theoretically and work out ways to calculate the stages of its development. They needed to understand how neutrons would diffuse through the core and the tamper. They needed a theory of the explosion s hydrodynamics—the complex dynamic motions of its fluids, which the core and tamper would almost instantly become as their metals heated from solid to liquid to gas. 

Although some spontaneous or thermal SrnI reactions are known, in most of the cases initiation is necessary to trigger the process [4]. The most general method to initiate the chain reaction is the photoinduced ET from the nucleophile to the substrate (for a detailed discussion, see Chapter 14) (1). Other known methods of promoting SrnI reactions are the use of (i) alkali metals in liquid ammonia (ii) ferrous salts or (iii) electrochemistry. 

Early on, it was demonstrated that aromatic nitro compounds may form radical anions in alkaline solutions [4], with the possibilities of photochemical reactions [5]. There followed the development of the radical chain mechanism [6]. An interesting early danonstration of reaction by this mechanism was in the reaction of ort/io-halogenoanisoles with potassium amide in liquid ammonia [7]. Reaction by the benzyne mechanism gives predominantly the uiera-substituted product due to the electronic influence of the methoxy group. Howeva, with an access of potassium metal, which promotes electron transfer, the pathway predominates yielding ort/io-anisidine, as shown in Scheme 6.4. The mechanism now forms an important synthetic pathway, and this and other homolytic processes are covered in Chapters 9 and 10. 

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