Bismuth occurrence

Tin exists in two ahotropic forms white tin (P) and gray tin (a). White tin, the form which is most familiar, crystallizes in the body-centered tetragonal system. Gray tin has a diamond cubic stmcture and may be formed when very high purity tin is exposed to temperatures well below zero. The ahotropic transformation is retarded if the tin contains smah amounts of bismuth, antimony, or lead. The spontaneous appearance of gray tin is a rare occurrence because the initiation of transformation requires, in some cases, years of exposure at —40° C. Inoculation with a-tin particles accelerates the transformation. 

Occurrence. Nearly all the silver ores are compounds of silver with sulphur and the neighbours in the Periodic Table arsenic, antimony and bismuth (argentite Ag2S, the most common silver compound, pyrargyrite Ag3SbS3, proustite Ag3AsS3). Other silver minerals include the halides. Silver is found sometimes as the free metal. Secondary silver (from catalysts, scraps, photographic films, etc.) is an important source. 

Occurrence. Bismuth occurs in minerals such as bismite (Bi203), bismuthinite (Bi2S3), bismutite (Bi0)2(C03). 

A variety of methods have been developed for the preparation of substituted benzimidazoles. Of these, one of the most traditional methods involves the condensation of an o-phenylenediamine with carboxylic acid or its derivatives. Subsequently, several improved protocols have been developed for the synthesis of benzimidazoles via the condensation of o-phenylenediamines with aldehydes in the presence of acid catalysts under various reaction conditions. However, many of these methods suffer from certain drawbacks, including longer reaction times, unsatisfactory yields, harsh reaction conditions, expensive reagents, tedious work-up procedures, co-occurrence of several side reactions, and poor selectivity. Bismuth triflate provides a handy alternative to the conventional methods. It catalyzes the reaction of mono- and disubstituted aryl 1,2-diamines with aromatic aldehydes bearing either electron-rich or electron-deficient substituents on the aromatic ring in the presence of Bi(OTf)3 (10 mol%) in water, resulting in the formation of benzimidazole [119] (Fig. 29). Furthermore, the reaction also works well with heteroaromatic aldehydes. 

Descriptions of the nature and origin of the metals follow the conventional Arabian philosophy of the generation of the metals from sulphur and mercury in various degrees of purity and various degrees of combination and their relation to the seven planets. It is worthy of note, however, that bismuth (Wismiith) is mentioned in relation to its occurrence with silver veins, probably the first mention... 

The general character of Neumann s chemistry is practical rather than theoretical. It describes plainly and in considerable detail the occurrences, properties and preparations of a large number of mineral, animal, and vegetable products, and the value which it must have possessed at that time as a condensed encyclopedia of chemical facts is manifest. Neumann apparently accepts the phlogiston hypothesis without reservation. In the discussion of metals, which he divides into perfect metals—gold and silver imperfect metals—lead, copper, iron and tin and semimetals (not malleable)—mercury, bismuth, zinc, antimony, arsenic, he has this to say under the head of imperfect metals 7... 

Mechanism. The mechanism outlined for the propene oxidation over metal oxides is, in general, fully applicable to bismuth molybdate. The occurrence of a symmetrical allyl intermediate and the participation of lattice oxygen is well established (Hucknall [160], Voge and Adams [343]). 

The occurrence of an almost constant, albeit rather low, activity level, which is reached after a number of pulses, signifies that a certain quasiequilibrium concentration of active sites is maintained by transport of bulk oxygen anions to the surface. Such a mobility of oxygen is particularly observed for bismuth molybdates and some related catalysts (see below). Typical examples of catalysts which completely loose their activity at a low degree of reduction are the antimonates this is primarily caused by the absence of anion mobility. 

Bismuth, as a metal, has been known since the Middle Ages. It is found in ores as native metal, as the sulfide, as oxide, as carbonate, and as a minor constituent in lead, copper and tin ores. The occurrence of bismuth in the crust of the earth has been estimated to be of the same order as silver tungsten. The recovery of bismuth from various ores and by various processes is discussed by Kirk Othmer(Ref 6)... 

The occurrence of a similar reaction has recently been indicated by studies carried out in this laboratory (7). If p-hydroxybenzyl alcohol (XXXVI) was oxidized with sodium bismuthate, the spirocyclic epoxy-cyclohexadienone (XXXVII) was obtained. The epoxide ring of this compound was hydrolyzed almost instantaneously by 2N aqueous hydrochloric acid and in a few hours by 10% aqueous acetic acid. However, the expected glycol (XXXVIII) could not be isolated since it decomposed immediately into equimolar amounts of hydroquinone and formaldehyde. (Attempts are now being made to prepare compounds analogous to XXXVIII but containing, in addition to the HOCH2 group, a carbon sub-... 

The combination of these experimental findings indicate that active bismuth molybdate catalysts undergo phase transformations when exposed to reducing conditions similar to the conditions of catalysis. The phase transformations are highly dependent upon both temperature and the severity of the reducing atmosphere. However, the occurrence of solid state reactions in the catalysts suggests that the bulk structure of the catalysts plays an important role in catalytic reaction. 

The interaction of molybdenum and bismuth ethoxides is also accompanied by ether elimination and the crystallization of a crystalline cubic phase of approximate composition Bi203 3Mo03. The mixed solutions of bismuth and tungsten ethoxides and those of molybdenum and bismuth 2-methoxyethox-ides turned out to be more stable. The occurrence of the interaction between the components was revealed by their tremendously increased solubility in the presence of each other (see Fig. 8.1 h). 

Another principal distinction relates to the time of the occurrence of the NiBi and NiBi3 intermetallic layers. In view of the very large difference in melting points of nickel (1451°C) and bismuth (271°C), at temperatures below 271°C the mobility of the bismuth atoms in the NiBi3 crystal lattice may reasonably be expected to be much greater than that of the nickel... 

The Bi—Mo-S system was investigated by Stemprok31) with respect to mineral occurrences of the tin-tungsten-molybdenum ore type 67). In some metallogenic provinces mineral assemblages such as bismuth + bismuthinite (Bi2S3) + molybdenite (MoS2) are frequently found, because bismuth has a much lower affinity to sulfur as compared with molybdenum. 

Bismuth, its properties, occurrence in nature, and use in alloys. Compounds of bismuth bismuth trichloride, bismuth nitrate, bismuthyl chloride, bismuthyl nitrate. 

Bismuth, considered a potential tracer of volcanic activity, has been extensively studied thanks to the exceptional sensitivity of LEAFS. So far, little attention has been paid to this metal whose atmospheric cycle is likely to be still undisturbed by man. This element can be of extraordinary importance, since it can represent untransformed tracers of specific natural sources and of atmospheric transport pathways. Although data on the occurrence of Bi in the environment are still very scarce, it is indeed likely that this metal is an excellent tracer of volcanic emission into atmosphere, since concomitant emissions from other natural sources are of little importance (84-86). Investigations of the occurrence of this metal in polar archives could produce very valuable time series of volcanic activity in both hemispheres and relevant data on the transport patterns of volcanic aerosols in the atmosphere (87). 

Bismuth iodosubgallate was followed by the introduction of iodochlorhydroxyquin (Vioform ). Unfortunately this latter compound has been linked with the occurrence of subacute myelo-optic neuropathy (SMON syndrome) in Japan. The decisive progress came with the iodine-free chlorquinaldol (Sterosan ). 

A possible alternative would be the formation of a covalent carbon-bismuth intermediate. Such an intermediate (97) may be involved in the ortho and para-phenylation of the sterically hindered 2,6-di-terr-butylphenol derivatives. 2 (Scheme 6.13) However, its occurrence has still not received any conclusive experimental support. 

Occurrence, — Selenium must be considered a rare element, although it is found widely distributed in nature. The distinctive selenium minerals are rare, and they are usually selenides, of such metals as lead, mercury, copper, bismuth, and silver. The element is also found in the free state associated with sulfur and as a selenite. The most common occurrence of selenium is in ores in which the element has partially displaced sulfur. Generally the selenium is present in very small proportions, but on account of the fact that enormous quantities of sulfide ores are used, this represents a considerable amount of selenium. It occurs also in small amounts in meteoric iron, in volcanic lavas, and in certain deposits of coal. Traces of selenium have been detected in rain and snow. Even though present in mineral ores in mere traces, it is readily concentrated either in the flue dusts or in the anode mud of the electrolytic refineries. Considerable quantities are known to exist in Hawaii, Japan,... 

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