Chromium discovery

In 1761 the mineral that disturbed the tin production was subjected to chemical examination. J. G. Lehmann, known from the history of the chromium discovery, investigated a wolframite from Zinnwald (Cinovec in today s Czech Repubhc). When he melted the mineral sample in sodium nitrate, leached it in water and added hydrochloric acid he observed a white precipitate that gradually became yellow. He had in fact seen tungstic acid, but did not reahze that there was a new element in it. 

Around 1800, the attack of chromite [53293-42-8] ore by lime and alkaU carbonate oxidation was developed as an economic process for the production of chromate compounds, which were primarily used for the manufacture of pigments (qv). Other commercially developed uses were the development of mordant dyeing using chromates in 1820, chrome tanning in 1828 (2), and chromium plating in 1926 (3) (see Dyes and dye intermediates Electroplating Leather). In 1824, the first chromyl compounds were synthesized followed by the discovery of chromous compounds 20 years later. Organochromium compounds were produced in 1919, and chromium carbonyl was made in 1927 (1,2). 

Finally, in 1797, the Frenchman L. N. Vauquelin discovered the oxide of a new element in a Siberian mineral, now known as crocoite (PbCr04), and in the following year isolated the metal itself by charcoal reduction. This was subsequently named chromium (Greek xpco ia, chroma, colour) because of the variety of colours found in its compounds. Since their discoveries the metals and their compounds have become vitally important in many industries and, as one of the biologically active transition elements, molybdenum has been the subject of a great deal of attention in recent years, especially in the field of nitrogen fixation (p. 1035). 

Abstract Since its discovery the chromium-mediated benzannulation reaction has been developed into a unique and useful tool in organic synthesis. In this review, topical aspects of this reaction concerning its mechanism and the chemo-, regio- and stereoselectivity are summerised and discussed in detail. Special attention is paid to the asymmetric benzannulation reaction and, finally, the importance of this reaction as a key step in the total synthesis of natural products is outlined. 

Photodriven reactions of Fischer carbenes with alcohols produces esters, the expected product from nucleophilic addition to ketenes. Hydroxycarbene complexes, generated in situ by protonation of the corresponding ate complex, produced a-hydroxyesters in modest yield (Table 15) [103]. Ketals,presumably formed by thermal decomposition of the carbenes, were major by-products. The discovery that amides were readily converted to aminocarbene complexes [104] resulted in an efficient approach to a-amino acids by photodriven reaction of these aminocarbenes with alcohols (Table 16) [105,106]. a-Alkylation of the (methyl)(dibenzylamino)carbene complex followed by photolysis produced a range of racemic alanine derivatives (Eq. 26). With chiral oxazolidine carbene complexes optically active amino acid derivatives were available (Eq. 27). Since both enantiomers of the optically active chromium aminocarbene are equally available, both the natural S and unnatural R amino acid derivatives are equally... 

The observation of induced reactions involving chromate almost coincided with the discovery of the phenomenon of chemical induction itself. According to the the role of chromate ions in these reactions, two groups can be distinguished (i) Chromium(VI) plays the role of actor, whose reaction with various inductors listed in Table 1 results in the oxidation of several acceptor ions or molecules. 

The Phillips catalyst has attracted a great deal of academic and industrial research over the last 50 years. Despite continuous efforts, however, the structure of active sites on the Phillips-type polymerization systems remains controversial and the same questions have been asked since their discovery. In the 1950s, Hogan and Banks [2] claimed that the Phillips catalyst is one of the most studied and yet controversial systems . In 1985 McDaniel, in a review entitled Chromium catalysts for ethylene polymerization [4], stated we seem to be debating the same questions posed over 30 years ago, being no nearer to a common view . Nowadays, it is interesting to underline that, despite the efforts of two decades of continuous research, no unifying picture has yet been achieved. 

Initial reports of cross-metathesis reactions using well-defined catalysts were limited to simple isolated examples the metathesis of ethyl or methyl oleate with dec-5-ene catalysed by tungsten alkylidenes [13,14] and the cross-metathesis of unsaturated ethers catalysed by a chromium carbene complex [15]. With the discovery of the well-defined molybdenum and ruthenium alkylidene catalysts 3 and 4,by Schrock [16] and Grubbs [17],respectively, the development of alkene metathesis as a tool for organic synthesis began in earnest. 

Earlier, in 1801 in Mexico, Andres Manuel del Rio, a chemist and mineralogist, discovered an unusual substance he called erythronium, but he was told it was similar to chromium. Only later was it found to be vanadium. Some early references credit Del Rio with vanadiums discovery, but the most recent references list Sefstrom as the discoverer. 

In the articles from which excerpts 4D and 4E were taken, reported results represent only a small fraction of the data actually collected. The authors found ways to condense their data as they wrote their papers. In excerpt 4D, the authors condensed their data by reporting only representative results (i.e., results from three soils instead of all seven). In excerpts 4D and 4E, the authors initially reported multiple variables (i.e., three chromium compounds and hve cities) but ended with a narrower focus (i.e., one chromium compound and one city). In each case, the readers benehted from the researchers hindsight. Learning to tell your story of scientific discovery in retrospect, by reorganizing your data and highlighting only the most illustrative pieces, is an essential skill in effective writing. 

D uring the last two decades of the eighteenth century, investigations were made which foreshadowed the discovery of chromium, molybdenum, tungsten, uranium, tellurium, chlorine, titanium, and beryllium but some of these elements were not actually isolated until much later. For the sake of simplicity, only the closely related elements, tungsten, molybdenum, uranium, and chromium, will be considered in this chapter. 

Chromium has taken its place among the world s useful metals, and stainless steel, chromium-plated hardware and automobile trimmings, and artistic chromium jewelry now bear witness to the importance of Vau-quelin s discovery. 

It was there that he discovered a new metal which, because of the red color that its salts acquire when heated, he named erythronium (44). Upon further study, however, he decided that he was mistaken, and that the brown lead ore from Zimapan was a basic lead chromate containing 80.72 per cent of lead oxide and 14.80 per cent of chromic acid (12). His paper therefore bore the modest title, Discovery of chromium in the brown lead of Zimapan (21). In 1805 Collet-Descotils confirmed del Rio s analysis (22), and for twenty-five years no more was heard of the new element, erythronium. 

Since the properties of erythronium closely resembled those which Fourcroy had ascribed to the recently discovered metal chromium, del Rio lost confidence in the importance of his discovery and concluded that his supposed new element was, after all, nothing but chromium (11). In a note to his translation of Kars ten s Mineralogical Tables he wrote (7, 9,12) .. . but, knowing that chromium also gives by evaporation red or yellow salts, I believe that the brown lead is a yellow oxide of chromium, combined with excess lead also in the form of the yellow oxide. ... 

Another circumstance which helped to shake del Rio s confidence in his own work was the analysis of this mineral which H.-V. Collet-Descotils, a friend of Vauquelin, published in 1805 (13). When Collet-Descotils concluded that the supposed new metal was merely chromium, del Rio warmly defended his own prior claim to the discovery of chromium in the brown lead ore (14). 

When Vauquelin analyzed a Peruvian emerald (25) after his discovery of chromium and glucina, the results differed greatly from his previous ones and from those of Klaproth. He found ... 

Despite the vast interest shown by coordination chemists in polypyrazolylborate ligands (17) since their discovery in 1966 few complexes of chromium(III) with these ligands have been mentioned in the literature. The complex [ B(pz)4 2Cr]PF6 (147) may be prepared by either of the routes outlined in Scheme 89.657... 

Knapp discovered in 1858 that chromium chloride converted raw skins into leather, but he failed to realize the commercial significance of his discovery. Others developed his ideas. A two-bath process due to Schultz (1894) and an adaptation of Knapp s original one-bath process by Dennis (1893), meant that by the early twentieth century chromium tannage was commercially important. At present it accounts for the vast majority of leather production. 

Examination of the Egyptian material led to a further discovery. The general Nile pattern, produced by Nile muds and the ceramics made from it, is on first glance very close to that of the Palestinian red field clay. When the plots of three clays and six sherds were matched by the scandium—iron points, cobalt, chromium, and europium also matched exactly. Thus in the Nile samples, concentrations of the five elements are highly mutually correlated. This observation then allowed detection of subtle differences between Palestinian and Egyptian materials. The... 

They are isomorphous also with the calcium compounds Ca3(V04)2. CaCl2 and Ca3(P04)2.CaCl2.5 The discovery of isomorphism among these double salts led Roscoe to transfer vanadium from the chromium family, in which it had been previously placed, to Group V. (see p. 2 1). 

I, 5-diphenylcarbazide and chromium(III). P. Cazeneuve (1900), and F. Feigl and F. L. Lederer (1925) later used the procedure for certain separations.5 However, the most pregnant discovery was made by Helmuth Fischer (1925) when he pioneered the analytical applications of dithizone, PhNHNHCSN==NPh. Here both the reagent and its metal complexes are intensely coloured, soluble in organic solvents but insoluble in water. Only a small number of metals react and the procedures can readily be made highly selective.7 8... 

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