Rare quaternary

The classical structures of pyrrole, furan and thiophene (31) suggest that these compounds might show chemical reactions similar to those of amines, ethers and thioethers (32) respectively. On this basis, the initial attack of the electrophile would be expected to take place at the heteroatom and lead to products such as quaternary ammonium and oxonium salts, sulfoxides and sulfones. Products of this type from the heteroaromatic compounds under consideration are relatively rare. 

We were one of the first groups to report a ternary selenophosphate of a rare-earth metal [11-13]. Since that time, we have uncovered a host of rare-earth metal chalcophosphates [1, 13, 14] that complement the transition-metal compounds found by the Kanatzidis group [15-31]. Despite the host of publications in the area of metal chalcophosphate chemistry, there have only been our systematic studies of the quaternary phase space of the rare-earth metal chalcophosphates [1, 13, 14]. 

In each of the composition diagrams in Fig. 14.2, the numbers represent a series of reactions run at a defined composition and temperature. These are isometric sulfur slices through three-dimensional K/P/RE/S quaternary phase diagrams. As just one example of what we have studied. Table 14.1 identifies the compositions at each point and the resulting phase(s). We have rigorously studied how phase formation is dependent upon the compositions of reactions for the rare-earth elements Y, Eu, and La and we have also discovered key structural relationships between the rare-earth elements, indicating a significant dependence on rare-earth and alkali-metal size for sulfides and selenides. 

Quaternary Rare-earth Metal Chalcoarsenites and Antimonites... 

Quaternary Rare-earth Metal Chalcotrielates and Tetrelates... 

We have developed a systematic study of quaternary chalco-gallates, indates (trielates) and chalco-silicates, and germinates (tetrelates) of the rare-earth metals. We have demonstrated that a series of new compounds could be formed in these families of materials [1, 3, 9, 10, 14, 81, 82]. There have been reports in the literature of a few examples of these types of materials, but there is sufficient evidence to support the fact that this area is wide open for exploring the likelihood for new rare-earth metal-based materials [83-90]. Our studies have focused on the gallium, indium, germanium and sihcon sulfides, selenides, and teUurides. 

Assoud A, Soherinia N, Kleinke H (2007) Thermoelectric properties of the new teUurides SrSc2Tc4and BaSc2Te4 in comparison to BaY2Tc4. IntermetaUics 15 371-376 Wu P, Ibers JA (1995) Quaternary chalcogenides containing a rare earth and an alkali- or alkaMne-earth metal. J Alloy Compd 229 206-215... 

As shown in Fig. 1.117, Se-type and Te-type epithermal Au-Ag vein-type deposits are located in the Cretaceous-Quaternary volcanic terrane of Japan (e.g., northeast and southwest Hokkaido, middle Honshu, south Kyushu). Some Te-type deposits are located in regions similar to the Se-type deposits. Sometimes, Te mineralization is associated with the Se-type deposits, though Te minerals usually do not coexist with Se minerals. However, rarely, Te minerals coexist with Se minerals in the Te-type deposits (e.g., Teine, Suzaki, Kawazu, Iriki) on a polished section scale. For example, coexistence of native Te and Se-bearing tetrahedrite is found at Teine. Generally, Te mineralization occurs at... 

Lubkowski J, Bujacz G, Boque L, Domaille PJ, Handel TM, Wlodawer A. The structure of MCP-1 in two crystal forms provides a rare example of variable quaternary interactions. Nat Struct Biol 1997 4 64-9. 

N-Aziridinylimines are valuable substrates for domino radical cydizations since they are able to serve simultaneously as radical acceptors and donors. They allow a versatile and general construction of quaternary carbon centers from carbonyl compounds [33]. By employing this methodology, an elegant and stereoselective synthesis of ( )-modhephene (3-70), one of the rare naturally occurring [3.3.3]propellanes,... 

As a final comment on terminology, we note that elemental semiconductors are formed from a single element, e.g., Si or Ge, whereas compound semiconductors are formed from two binary), three ternary), four quaternary), or, rarely, more elements. Semiconductor alloys refer to solid solutions where either one anion or one cation can substitute for another, or possibly two or more such substitutions can occur for a binary semiconductor AB a simple alloy with C would be represented as Ai CjcB. Semiconductors are often classified by the group numbers in the periodic table. Thus, for example, I-VII semiconductors include Cul and AgBr, II-VI semiconductors include ZnS, CdTe, and HgTe, III-V semiconductors include GaAs, GaN, InP, and InSb, and IVx-VIv semiconductors include PbSe and Sn02. Fundamental physical properties are compiled in a recent handbook [22]. 

Molten aluminium and gallium fluxes have shown themselves to be excellent routes to complex ternary and quaternary intermetallic phases such as R-T-Al and R-T-Al-Si, R-T-Al-Ge (when Al is used as solvent) or R-T-Ga, R-T-Si, R-T-Ga-Si, R-Ga-Ge (when Ga is used as solvent), where R = rare earth metal, T = transition metal. 

Quaternary ammonium salts are generally stable under neutral or acidic conditions up to 150°C, but decomposition can occur with the quaternary ammonium ion acting as an alkylating agent in its reaction with anions (Scheme 1.1). Soft nucleophiles, such as RS, are more reactive with tetra-n-butylammonium bromide and benzyltriethylammonium chloride, although the latter salt also C-benzylates phenyl-acetonitrile under basic conditions [46], These side reactions are considerably slower than the main catalysed reactions with, for example, a haloalkane and the amount of unwanted impurity in the final alkylated product is never greater than the amount of catalyst used (i.e. generally > 2%). Harder anions, e.g. R2N and RO, rarely react with the ammonium salts. 

The cleavage of resin-bound peptides, produced in the Merrifield synthesis, is aided by the addition of quaternary ammonium salts to the basic medium [17, 18]. In many cases, cleavage is 100% effective and rarely less than 70%. 

The kinetic preference for cis- over imns-olefin elimination from acyclic compounds is rare. Cope and co-workers 91) reported a slight preference for cis- over irans-2-butene and 2-pentene in the thermal decomposition of the quaternary ammonium hydroxides, and Andr u and co-workers 92,93) found a preponderance of cis- over trons-2-butene in the elimination of hydrogen chloride from 2-chlorobutane over solid catalysts. Neureiter and Bordwell 94) found the formation of cis-2-butene rather than alkene from a-chlorosulfone on treatment with alkali ... 

A hydrogen attached to a pyridine or pyridine 1-oxide nucleus cannot be replaced directly by cyanide however, addition of cyanide to various quaternary salts constitutes an important class of reactions of synthetic importance. Before surveying these reactions in detail, the four main classes are outlined. In 1905, Reissert reported the first example, the reaction of quinoline with benzoyl chloride in aqueous potassium cyanide (Scheme 111) (05CB1603). This yielded a crystalline product, C17H12N2O, a Reissert compound (176) which afforded benzaldehyde and quinaldinic acid on acid hydrolysis (Scheme 111). Kaufmann (09CB3776) treated a 1 -methylquinolinium salt with aqueous potassium cyanide and observed 1,4-rather than 1,2-addition (Scheme 112), the Reissert-Kaufmann reaction. Reissert compounds are well known in the quinoline and isoquinoline series, but only rarely have even small yields been found in the pyridine series. On the other hand, cyanide ions add 1,4 with ease to pyridinium salts that have an electron withdrawing substituent at C-3. 

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