Natural Occurrences

Biochemical pesticides thus include many synthetic analogs of naturally occurring substances that can be used to manage pests with little or no impact on human health or the environment. 

Naturally occurring silicon carbide was first discovered by Moissan [8] in a meteorite from the Diablo Canyon in Arizona, and subsequently several small deposits have been found [9-11], Extraterrestrial occurrences of silicon carbide are even 

Zirconium is the eleventh most abundant element in the earth s crust, which contains 0.028 percent of this element. It is more abundant than copper, lead, nickel, or zinc. Zirconium minerals always contain from 0.5 to 2 percent of chemically similar hafnium, which seldom occurs naturally by itself. 

The principal natural sources of zirconium and hafnium are the minerals zircon (Zr,Hf)Si04, and baddleyite (Zr,Hf)02. 

production in these years was around 150,000 short tons. Thus, Australia and the United States are the principal zirconium-producing nations. Most of their production was from dredging of black sands on beaches and in stream beds, where zircon has been concentrated hydraulically along with other relatively dense minerals such as rutile (TiOj), ilmenite (FeTiOs), and monazite (Chap. 6). 

Principal U.S. producers of zircon concentrates in these years were E. I. du Pont de Nemours and Company and Titanium Enterprises, Inc., with operations primarily in northern Florida and southern Georgia. 

In the 1960s, hafnium-free zirconium had been produced by several U.S. companies 

Thirty-five canthin-6-one alkaloids have been isolated from 36 species 

Radium is an extremely rare element in the Earth s crust, with an abundance of 90 ng/kg (i.e., ppt wt.). However, it is always present in uranium minerals and ores and could be extracted, if desired, from the extensive wastes of uranium processing. Today, the carnotite sands of Colorado in the USA furnish some radium, but richer ore deposits are found in the Republic of Zaire. Other large uranium deposits are located in Canada (e.g., Ontario), in the USA (e.g., New Mexico, Utah), Australia, and elsewhere. 

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Carbon 12, the most abundant naturally occurring isotope, has zero spin and thus cannot be studied by NMR. On the other hand, its isotope carbon 13 has an extra neutron and can be its low natural occurrence (1.1%) nevertheless makes the task somewhat difficult. Only pulsed NMR can be utilized. 

Soxhlet Extraction. Occasionally a crude product (often of natural occurrence) is obtained, from which a particular component may be isolated by repeated extraction with a hot soK-ent. For this purpose, Soxhlet s Extraction Apparatus (Fig. 19) is usually employed. 

Some elements contain a fixed number of neutrons, as with fluorine (P = 9, N = 10) and phosphorus (P = 15, N = 16). For their natural occurrences, atoms of any one such element all have the same mass (F= 19 P = 31). 

R. Ditz and co-workers, eds., Gmelin Handbook of Inorganic Chemistg, Thorium, Suppl Hoi A1a, Natural Occurrence, Minerals (Excluding Silicates), Springer-Vedag, Berlin, 1990. 

Owing to the ubiquitous natural occurrence of vitamin K and its production by intestinal bacteria, vitamin K deficiencies are rare. However, they can be caused by certain antibiotics (qv) coupled with a reduced dietary intake. Newborn infants who do not possess the necessary intestinal bacterial population are at danger for vitamin K deficiency. As a result, vitamin K injections are routinely given to the newborn. 

Citric acid occurs widely in the plant and animal kingdoms (12). It is found most abundantiy in the fmits of the citms species, but is also present as the free acid or as a salt in the fmit, seeds, or juices of a wide variety of flowers and plants. The citrate ion occurs in all animal tissues and fluids (12). The total ckculating citric acid in the semm of humans is approximately 1 mg/kg body weight. Normal daily excretion in human urine is 0.2—1.0 g. This natural occurrence of citric acid is described in Table 7. 

R. H. Bunnell and B. Borensteki, Food Technol 21, 13A—16A (1967). A brief review of the history, natural occurrence, properties, market forms, and stabkity of canthaxanthin. 

These results seemed to establish with certainty that the active component of tube curare is derived from Chondrodendron tomentosum, but the matter again became doubtful when King reported that in the stems of a carefully authenticated specimen of the plant, collected at Tarapoto in Peru, he had found 1-curine and Z-tubocurarine chloride. This is the first recorded natural occurrence of the latter and seems to indicate either that the alkaloidal components of the plant are not constant in character, or that the botanical description of Chondrodendron tomentosum covers two species containing the dextro- and Icevo- quaternary alkaloids respectively. 

In addition to its natural occurrence as the free element, carbon is widely distributed in the... 

Some of the important properties of the elements are given in Table 18.1. The imprecision of the atomic weights of Kr and Xe reflects the natural occurrence of several isotopes of these elements. For He, however, and to a lesser extent Ar, a single isotope predominates ( He, 99.999 863% " Ar, 99.600%) and much greater precision is possible. The natural preponderance of " Ar is indeed responsible for the well-known inversion of atomic weight order of Ar and K in the periodic table, and the position of Ar in front of K was only finally accepted when it was shown that the atomic weight of He placed it in front of Li. The second isotope of helium, He, has only been available in significant amounts since... 

Relatively few heteroaromatic N-oxides occur in nature. The chemistry of compounds that contain the oxidized peptide bond (the so-called hydroxamic acids) and their role in iron metabolism have been reviewed (67SC1443). Another review deals with the natural occurrence of N-oxides (68MI1). 

Natural Occurrence of ( — )-proto-Quercitol. Although the dextrorotatory form (12) of proto-quercitol was discovered in acorns more than a century ago by Braconnot (5), who at first thought that it was lactose, the levorotatory form (13) remained unknown until 1961. In that year, Plouvier isolated it from leaves of the tree Eucalyptus populnea the yield was 0.55% (36). The optical rotation of the new compound was equal and opposite to that of the dextro enantiomer, and it was identical to the latter in its crystal form, melting point, solubilities, molecular formula and infrared spectrum. 

In 1947, L-rhamnose was first recognized by Stacey as a constituent of Pneumococcus Type II specific polysaccharide. This finding was confirmed, in 1952, by Kabat et al. and in 1955 again by Stacey when 2,4- and 2,5-di-O-methyl-L-rhamnose were synthesized and the former was shown to be identical with a di-O-methylrhamnose, obtained by hydrolysis of the methylated polysaccharide. This result indicated a pyranose ring structure for the rhamnose units in the polysaccharide. Announcement of the identification of D-arabinofuranose as a constituent of a polysaccharide from M. tuberculosis aroused considerable interest. The L-enantiomer had been found extensively in polysaccharides, but reports of the natural occurrence of D-arabinose had been comparatively rare. To have available reference compounds for comparison with degradation products of polysaccharides, syntheses of derivatives (particularly methyl ethers) of both d- and L-arabinose were reported in 1947. 

The natural occurrence of the group-IIA elements ranges from common to rare e.g., Ca is 5th in the order of atomic abundance of the elements in the earth s crust. Mg is 7th, Ba and Sr are 21st and 22nd, respectively, and Be is 32nd . Radium is of extremely limited availability. It does occur naturally, although it has neither stable nor long-lived radioaetive isotopes it is found in association with U, since ll/2... 

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