Noncatalytic methods

Noncatalytic Reactions Chemical kinetic methods are not as common for the quantitative analysis of analytes in noncatalytic reactions. Because they lack the enhancement of reaction rate obtained when using a catalyst, noncatalytic methods generally are not used for the determination of analytes at low concentrations. Noncatalytic methods for analyzing inorganic analytes are usually based on a com-plexation reaction. One example was outlined in Example 13.4, in which the concentration of aluminum in serum was determined by the initial rate of formation of its complex with 2-hydroxy-1-naphthaldehyde p-methoxybenzoyl-hydrazone. ° The greatest number of noncatalytic methods, however, are for the quantitative analysis of organic analytes. For example, the insecticide methyl parathion has been determined by measuring its rate of hydrolysis in alkaline solutions. 

In general, hydroboration—protonolysis is a stereoselective noncatalytic method of cis-hydrogenation providing access to alkanes, alkenes, dienes, and enynes from olefinic and acetylenic precursors (108,212). Procedures for the protonolysis of alkenylboranes containing acid-sensitive functional groups under neutral or basic conditions have been developed (213,214). 

Two noncatalytic methods have been used to remove amino or hydrazino groups. Diazotization and reduction of the diazonium salt by hypophos-phorous acid removes amino groups from aminotriazolopyridines 173,65 174,66 and 175,65 whereas silver oxide treatment removes hydrazino groups from compounds 176216 and 177.206... 

The hydrides of the heavier congeners of the Group 14 to 16 elements have weak E-H bonds and they can be decomposed under mild conditions to yield the pure element or a low-oxidation-state hydride (in many cases of ill-defined chemical composition and structure). This tendency, which also applies to the E-C bonds, underlies the usefulness of hydrides in many gas and vapor phase deposition methods.3 There is still, however, a need for catalysts, particularly to control the specificity of dehydrocoupling for example, the ability to make rings of a particular size or isomeric composition, or the ability to avoid cyclic products altogether. In addition, it is desirable to control homo- vs hetero-dehydrocoupling selectivity, something difficult to do by noncatalytic methods. 

This chapter is devoted to the discussion of the reduction of carbon-carbon double and triple bonds by noncatalytic methods, These methods include reductions by diimide, by dissolving metals in the presence or absence of proton donors, by low-valent metal ions, by metal hydride-metal halide combinations and by so-called ionic hydrogenation procedures. Of these widely diverse methods of reduction of carbon-carbon double and triple bonds, the reduction by diimide appears to be the most versatile. The reduction of carbon-carbon double and triple bonds by diimide occurs with complete stereoselectivity and stereo-specificity, and can be effected in the presence of a variety of other, very chemically reactive functional... 

Hydroborations of alkynes directed toward the synthesis of alkenylboranes furnishes versatile intermediates for a wide array of chemical transformations. For example, protonolysis of alkenylboranes provides a noncatalytic method for the semireduction of alkynes. 

Postformation nitrogen oxide emission control measures include selective catalytic and noncatalytic reduction with ammonia, which between them are used by some 900 power station installations worldwide [51]. The catalytic removal methods are 70-90% efficient at NOx removal, but are more expensive to operate than the noncatalytic methods which are 30-80% efficient. Ammonia or methane noncatalytic reduction of NOx to elemental nitrogen is also an effective method which is cost-effective for high concentration sources such as nitric acid plants (Chap. 11). NOx capture in packed beds is less expensive, but this method is not particularly effective [23]. It is also not a very practical method either for utilities or for transportation sources. Two-stage scrubbing has also been proposed as an effective end-of-pipe NOx control measure. The first stage uses water alone and the second uses aqueous urea. 

Kinetic methods have been classified according to a number of criteria. One classification distinguishes between catalytic and noncatalytic methods (see Table 1). The former are further divided according to the type of reaction involved, while the latter are categorized according to whether they are used to determine a single species or several components in mixtures (differential reaction-rate methods)... 

Kinetic catalytic methods for determination of species can be classified in a manner similar to that of the kinetic noncatalytic methods described elsewhere in this encyclopedia (Table 1). Methods commonly used to measure induction periods are commented on in dealing with Landolt reactions below. 

In conclusion, the asymmetric alkylation of chiral enolates and enamines can be completed with high stereoselectivity affording final products with high optical purity [17], The chiral economy of this and other noncatalytic methods that use chiral auxiliary agents in a stoichiometric quantity depends on their availability and effective recycling in the process. 

Several noncatalytic methods for the synthesis of PA are known, including electrochemically forming a PA film on a platinum cathode [52]. This special electrochemical cell uses a platinum cathode, nickel anode, and NiBt2 dissolved in acetonitrile as the electrolyte solution. A 4-40-V potential is then applied across the electrodes to commence the polymerization. The PA film forms on the cathode as a thin black layer and becomes thicker with time. 

TEOS) in methanol or ethanol with base catalysts, as discussed recently by Halas [27]. Other common methods of preparing symmetric silica nanowires include the condensation of silicon sources in the gas phase on nanoparticle catalysts [21, 27, 28]. The size of the siUca beads can be controlled by changing the silicates, base catalyst, and the amount of water in the system [1]. For example, the metal catalysts in the case of a nanowire can be used to control the diameter of long, straight siUca nanowires with a circular cross-section. Moreover, both catalytic and noncatalytic methods can be used to synthesize these symmetric nanosilica. 

With the current emphasis on enantioselective synthesis, it is not surprising that numerous, highly successful asymmetric versions of aldol reaction have been developed. Noncatalytic methods involve the use of stoichiometric amounts of a chiral auxiliary in diastereoselective aldol reactions. Small-molecule-catalyzed aldol reactions typically would involve the use of a chiral Lewis acid for aldehyde activation or a chiral Lewis base for donor... 

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