Substances occurring in nature

The synthesis of substances occurring in Nature, perhaps in greater measure than activities in any other area of organic chemistry, provides a measure of the condition and power of the science. R. B. Woodward17... 

The safety evaluation of flavoring substances provides a unique challenge to regulators due to their large number and their generally low level of use. In addition, many flavoring substances occur in natural products (i.e., extracts, oleoresins, and essential oils) and have a long history of safe use. 

Vitamin B12 (cobalamine) is one of the most complex low-molecular-weight substances occurring in nature. The core of the molecule consists of a tetrapyrrol system (corrin), with cobalt as the central atom (see p. 108). The vitamin is exclusively synthesized by microorganisms. It is abundant in liver, meat, eggs, and milk, but not in plant products. As the intestinal flora synthesize vitamin B12, strict vegetarians usually also have an adequate supply of the vitamin. 

A mineral is an inorganic substance occurring in nature and having a detiniie chemical composition or a characteristic range of chemical composition, and distinctive physical properties or molecular structure. 

Asbestos constitutes several types of hydrated silicate mineral fibers. The types of asbestos, their chemical compositions, and CAS Numbers are presented in Table 3.8.1. These substances occur in nature in rocks, silicate minerals, fibrous stones, and underground mines. This class of substances exhibits unique properties of noncombustibility, high resistance to acids, and high tensile strength for which they were widely used in many products, including floor and roofing tiles, cement, textiles, ropes, wallboards, and papers. Because of the health hazards associated with excessive exposure to asbestos, the use of these substances is currently banned. 

Humic substances occurring in natural waters in the form of stable negatively charged sols exhibit shielding aetion with respect to colloidal solutions of Si02, Fe(OH)j and Al(OH)3 (Kul skiy, 1960). Colloids shielded by humus do not coagulate and, remaining in the state of sols, can be transported by the waters of rivers, seas, and oceans (Kuznetsov, 1964) for considerable distances, and the Schultz-Hardy rule becomes inapplieable to shielded colloids. 

Annex V Substances including substances occurring in nature, if not chemically modified, e.g.. Natural gas, crude oil. 

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