Media equations

A more elegant, but expensive, approach22 has been the use of soluble iridium and rhodium catalysts which contain coordinated dimethyl sulphoxide (e.g. IrHCl2(Me2SO)3) which promote the oxidation of sulphoxides in aqueous media, equation (8). The ease of oxidation depends on the substituents and this decreases in the order Me > Ph > PhCH2. This reaction is especially useful since sulphides are not oxidized under the reaction conditions due to the formation of strong complexes with the catalyst. 

The reaction for the oxidation of sulphoxides by peracids in an alkaline medium is probably best described as shown in equation (16). Here the addition step is usually much slower than the latter step due to the low O—O bond energy which allows easy bond fission. For the reaction in acidic media, equation (17) is probably a good representation. 

As discussed earlier the whole process is a redox reaction. Selenium is reduced using sodium borohydride to give selenide ions. In the above reaction, the metal ion reacts with the polymer (PVP or PVA) solution to form the polymer-metal ion solution. Addition of the selenide ion solution to the polymer-metal ion solutions resulted in instantaneous change in the colour of the solutions from colourless to orange (PVA) and orange red (PVP). This indicates the formation of CdSe nanoparticles. The addition of the selenide solution to the polymer - metal ion solution resulted in gradual release of selenide ion (Se -) upon hydrolytic decomposition in alkaline media (equation 4). The released selenide ions then react with metal ion to form seed particles (nucleation). 

Note that K = 1 and Dm becomes D in aqueous media. Equation (79) suggests that under steady-state conditions the thickness of the film is a function of time. The tangent equation of the concentration curve at z = 0 is... 

For non-scattering media, following the classical Beer-Lambert law, L is equal to the distance between source and detector, denoted as d. For scattering media Equation (1) can be rewritten as... 

Following reports of efficient Cu(I)-catalyzed alkyne/azide cycloaddition on solid phase and in solution by Meldal [42] and Sharpless [43], respectively, the formerly obscure Huisgen reaction soared to prominence as a versatile tool for covalent chemical ligation. The so-called click reaction can be catalyzed by a number of copper sources in a variety of media (Equation 9.14). 

The synthesis of 2-chloro-5,7-dihydro-6//-pyrrolo[2,3-rflpyri idine-6-one, 122, was accomplished by heating the alkenyl pyrimidine, 121, in acidic media (Equation 44) <2001TL999>. 

L. A. Peletier, The Porous Media Equation in Application of Nonlinear Analysis in the Physical Sciences, H. Amann, N. Baxley, and K. Kirchgassner, eds., Pitman, Boston, 1981, pp. 229-241. 

Arnett has observed that heats of reaction for carbocation formation in highly acidic media (Equation 5.12) correlate well with solvolysis rates.47 This... 

An alternative mechanism, proceeding through a double protonation reaction sequence followed by silyl fragmentation, could be envisaged in the highly acidic media (equation 64). The first step at — 130°C leads lo Cp protonation of the alkyne 380 with formation of the vinyl cation 381 (= 372). At the higher temperature (—100 °C)... 

The C=N bonds of imines, oximes and hydrazones can be hydrogenated to form the corresponding amines even under ambient conditions on Pt, Pd, Rh and Raney Ni catalysts in acidic, neutral or basic media (equation 42). The imines, furthermore, are intermediates in the hydrogenation of nitro compounds, nitriles and oximes, and likewise play a key role as intermediates in the reductive amination of carbonyl compounds. 

In many cases, activation of the zinc dust is necessary to reach complete conversion or to accelerate the reaction. This activation can be achieved by treatment of zinc dust with an acid chloride267 but can be achieved also with liquid ammonia268 or by sonoelectrochemical methods.259,269,269a Activation can be achieved by adding metallic salts such as AICI3, CeCb, PbBr2, or Cul to the reaction mixture.2536,257,270 Sonication proved also to enhance the reactivity of Barbier-type reaction in aqueous media (Equation (157)).2S3 255 2S6 270 270a 271... 

Alkynyl(methoxy)borates prepared in situ from an alkynyllithium or sodium and 9-methoxy-9-BBN coupled with 1-alkenyl and aryl halides (Equation (210)).899-902 Addition of triisopropylborate to lithium acetylide yielded an air stable and isolable ate complex that couples with aryl and alkenyl halides (Equation (211)).903 904 Air and moisture stable alkynyltrifluoroborates were probably the most convenient reagents that allow handling in air and coupling reactions in basic aqueous media (Equation (212)).46... 

Hiyama and co-workers have reported that the Mizoroki-Heck-type reaction of aryl- and alkenylsilanols is efficiently promoted by a Pd(OAc)2/Cu(OAc)2/LiOAc system (Equation (9)).50 50a in contrast, a dicationic Pd(ll) complex prepared in situ from Pd(dba)2, a diphosphine (dppe or dppben), and Cu(BF4)2 catalyzes 1,4-addition of aryltrialkoxysilanes to a-enones and a-enals in aqueous media (Equation (10)).51 The Pd-catalyzed 1,4-addition of the arylsilanes can be achieved also by using excess amounts of TBAF 3H20, SbCl3, and acetic acid.52... 

Elemental antimony is known to mediate the Barbier-type allylation of aldehydes by allylic halides.35 The active intermediates are believed to be allylic antimony(m) species, which are generated from the antimony(O) and the halides. In fact, allylic dichlorostibanes, produced by metathesis of SbCl3 with the corresponding allylic stannanes, react with benzaldehyde to give homoallyl alcohols, where the C-C bond is constructed with -selectivity (Equation (l)).36 Fluoride salts such as KF, NaF, RbF, and CsF accelerate the Sb-mediated Barbier-type allylation with allyl bromide in aqueous media (Equation (2)).37 In the absence of the fluoride ion, no allylation occurs. Although aromatic and aliphatic aldehydes are allylated in good yields by a combined use of Sb-KF, acetophenone, cyclohexanone, and methyl pyruvate remain untouched. 

Sequential nucleophilic and electrophilic alkylations of 1,3-dicarbonyl compounds with a trimethylenemethane zwitterion equivalent lead to [3 + 2]-annulation. The nucleophilic carbonyl alkylation step has been carried out via an indium-mediated allylation in water (Equation (30)).200 Indium-mediated allylation of a-chlorocarbonyl compounds with allyl bromides in aqueous media gives the corresponding homoallylic chlorohydrins, which can be transformed to allyloxiranes (Equation (31)).201 Allylation of the G3 position of the cephem nucleus has been accomplished by indium-mediated allylation reaction in aqueous media (Equation (32)).202... 

A review is presented of the electrical properties of polymers filled with different types of conducting particles. Following a theoretical description of a general effective media equation, experimental conductivity-volume fraction data for thermoplastic filled with vanadium oxide particles as well as thermosetting polymer composites, were fitted to the equation. The calculated property-related parameters in the equation are discussed. Data are given for PVC, HDPE, LLDPE, LDPE, and epoxy resin. 12 refs. 

Improved understanding of the mechanism of palladium-induced dehydrogenations has led to the development of significantly better catalysts and reaction conditions. In particular, mixtures of PdCl2(PhCN)2 and silver triflate in the presence of -methylmorpholine have allowed the efficient dehydrogenation of aldehydes under ambient conditions and in nonacidic media (equation 18). Ketones undergo a similar reaction, affording enones in 60-78% yield, but require prior formation of the tin enol-ate with tin(II) triflate.Under these conditions, however, 2 equiv. of palladium(II) chloride were used to effect conversion, which severely limits the usefulness of the method. 

A series of molybdenum alkylidene complexes react with aldehydes, and in some cases ketones, to give the product of methylenation (equation 33). Some of the examples appear to involve an alkylidene, while others may follow an addition-elimination route typical of the Peterson alkenations. Probably the most interesting aspect of this work is the observation that some of the methylenation reactions can be carried out in aqueous or ethanolic media (equation 33). ... 

For flow through homogeneous and isotropic media, Equation 1.30 reduces to the diffusion equation... 

Multigram quantities of A-methoxycarbonyl-3-phenyloxaziridine (53a) and A-Boc-3-phenyl-oxaziridine (53b) are produced by carefully controling the oxidation of the corresponding imines with buffered Oxone in biphasic media (Equation (49)) <91CC435,93JOC4791). The principle product is amide (190) if the oxidation is carried out at room temperature or with MCPBA. 

Phenols can also be formed by aromatic hydroxylation with the hydroxy radical generated from a-azo hydroperoxides in anhydrous organic media (equation 36) . Photo- and thermal decomposition of a-azo hydroperoxides give hydroxy radicals, which can react with an aromatic ring generating a phenolic compound. 

As pointed out in the previous section, phosphate derivatives related to H3VO4 are of interest when it comes to the phosphate-vanadate antagonism. Similarly, vanadate esters are analogues of phosphate esters (Section 5.2.1). Esters of orthovanadic acid have been known since IQIS.I They are obtained by, e. g., condensation of vanadates and alcohols (ROH) in aqueous media [Equation (2.11)], alcoholysis of VOCI3 [Equation (2.12)] or the reaction of vanadium pentoxide and alcohols in the presence of water scavengers [Equation (2.13)]. The triesters are sensitive to moisture. The primary product of hydrolysis is the hexavanadic acid derivative V50i3(0R)4, giving rise to a yellow colouration as the colourless triesters come into contact with moist air. 

In aqueous solution, it is converted to only a small extent to sulfurous acid aqueous solutions of H2SO3 contain significant amounts of dissolved SO2 (see equations 6.18-6.20). Sulfur dioxide is a weak reducing agent in acidic solution, and a slightly stronger one in basic media (equations 15.86 and 15.87). 

Hydrogen peroxide is formed from (a) the dimerization of hydroxyl radicals (equation 63), (b) the proton-induced decomposition of superoxide ions (equation 64), (c) the reductive electrolysis of O2 in acidic media (equation 65), and (d) the base-induced reduction of O2 by 1,2-disubstituted hydrazines (equation 66). ... 

Another important property of thiepine is the equilibrium between thiepine (1) and its valence isomer, benzene episulflde (9). Benzene episuliides are found to be so unstable that they can not be detected hence theoretical treatment should provide helpful information. MNDO molecule force field calculations of the zero point energy, potential energy, and thermodynamic parameters for the valence tautomerization of benzene episulflde (9) and thiepine (1) show that (9) is more stable than (1) both in the gas phase and in polar media (Equation (1)). The equilibrium is shifted towards (1) in polar media. The vapor phase inversion barrier for (1) is 3-5 kJ mol , and is reduced to zero by polar solvents <83MI 903-01 >. 

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