Contents 16 General Reactions

One of the important differences between calciothermic and aluminothermic reduction of oxides concerns the interaction between the reduced metal and the reductant. Calcium does not form stable solid solutions or alloys with the reduced metals calcium contamination in the metal is, therefore, relatively small. Aluminum, on the other hand, readily forms solid solutions with the reduced metals, and the product generally contains appreciable quantities of residual aluminum. This is not a serious problem because in many cases either a certain aluminum content is desired in the reduced metal or the residual aluminum can be effectively removed in post-reduction purification operations. The extent of the contamination of a reduced metal with the reductant can be related to factors such as the reaction temperature, the standard free energy change associated with the reaction, and the slag composition. Let the following generalized reaction be considered ... 

Addition of about 100 mg of hexachlorocyclotriphosphazine (also containing some phenoxylated products) to 0.5 ml of DMSO in an NMR tube led to an exothermic reaction which ejected the tube contents. General precautions are suggested. 

Solvent and water content. When reactions are performed in organic solvents [la], the solvent of choice is often a hydrophobic solvent with logP > 1.5. However, despite a massive amount of work on this matter, no general rules can be formulated. Usually one has to scan a number of solvents to find the one that gives the best E for the individual case. The water activity of the reaction system can influence E quite substantially, but no general rules can be formulated, and usually one has to find the optimal conditions for the individual substrate. It is important to note, however, that if the water content is high in, e.g., an acylation reaction system, water can compete with the desired nucleophile and give an acid that can disturb the efficiency of the resolution. 

One embodiment of this general reaction led to a product which was commercially produced for several years by Stauffer as Fyrol 76 (9), a copolycondensation product of dimethyl methyl-phosphonate with bis(2-chloroethyl) vinylphosphonate. The features of Fyrol 76 were high phosphorus content (20%), water solubility, and ability to be polymerized by means of a radical initiator to a crosslinked polymer. A related polycondensation product was developed from tris(2-chloroethyl) phosphate and dimethyl methylphosphonate. By control of the reagents and procedure used for neutralization, these oligomeric products were produced with primary alcohol functional groups (7). 

MoP/Al catalysts after TPS measurements is independent of the phosphorus content, generally having a value of 2. Thermodynamic limitations (70) prevent the reaction of M0S2 with AIPO4 to form MoP species (where V = 1, 2) at temperatures lower than 1000°C. 

IPDI-based prepolymer. This is an aliphatic prepolymer formed by the reaction of IPDI with polyether polyol (3000 molecular weight PPO-based triol) (PPG = polypropylene oxide). The NCO group content of such systems is about 3.4%, and the viscosity about 15 000 CP at 20°C. Solid content is typically 98%-100%. The general reaction is given in Figure 2.22. This prepolymer may typically be used in two-part elastomer systems. 

The general reaction pathways of NOjt in a plasma reactor arc summarized in Fig 8. The dominant removal pathway of NOjc in the gas-phase homogeneous reactions is oxidation than reduction for both electrical corona discharge and elec iron-beam, especially when the oxygen content is higher than around 3-4% [78. 88-90]. Oxidation of NO occurs mostly by ozone (R4) and peroxy radicals (R5, R6) in the presence of hydrocarbons. Some of NOj arc converted to NO by back reactions by UV (R2) and O radical. 

In the first fuel cells, platinum was used in relatively large quantities. This led to the mistaken belief that most of the cost of a fuel cell came from the platinum content. Generally this is no longer the case. Platinum particles are deposited very finely onto carbon powders, so that the platinum is very carefully dispersed with a maximal surface area. With catalysts produced in this way, the raw material platinum cost is just US 10 for a 1-kW cell stack. Before the catalyst layer is applied to the electrolyte, a coating of soluble electrolyte is brushed onto it. This ensures that there is good contact between the platinum and the electrolyte to achieve the important three-phase interaction between gas, catalyst, and electrolyte necessary for the reaction to proceed. 

Additionally, many experimental studies have shown that, for various protein systems, the storage stability improves as the residual humidity decreases and that the optimal final water content is generally around 1% or less. Water contents above the monolayer content increase the mobility of the water that becomes more available for protein degradation reactions with the other solutes of the concentrated phase. Moreover, water is a plasticizer of the amorphous phase that decreases the Tg value, which leads to more difficult storage conditions. Finally, it should be noted that the moisture content is generally not uniform within the vial, the top and the wall zones of the cake being the driest zones and these non-uniformities in the spatial distribution of the water content generally increase with the size of the vial. 

---