tailieunhanh - TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY - CHAPTER 17

Organosulfur hợp chất 17,1 GIỚI THIỆU lưu huỳnh là trực tiếp dưới đây oxy trong bảng tuần hoàn. Các nguyên tử lưu huỳnh có sáu electron hóa trị, như thể hiện trong hình , và cấu hình electron của nó là {Ne} 3s23p4. Bởi vì vỏ hóa trị tương tự như cấu hình electron, oxy và lưu huỳnh hoạt động phần nào cũng như hóa học. Tuy nhiên, không giống như oxy, nguyên tử lưu huỳnh có ba quỹ đạo 3d cơ bản, và hóa trị vỏ của nó có thể được mở rộng đến hơn tám electron. Điều này làm. | Chapter 17 Organosulfur Compounds introduction Sulfur is directly below oxygen in the periodic table. The sulfur atom has six valence electrons as shown in Figure and its electron configuration is Ne 3ỉ23p4. Because of their very similar valence shell electron configurations oxygen and sulfur behave somewhat alike chemically. However unlike oxygen the sulfur atom has three underlying 3d orbitals and its valence shell can be expanded to more than eight electrons. This makes sulfur s chemical behavior more diverse than that of oxygen. For example sulfur has several common oxidation states including -2 4 and 6 whereas most chemically combined oxygen is in the -2 oxidation state. Classes of Organosulfur Compounds The hydride of sulfur is H2S Figure a highly toxic gas discussed in Section . Substitution of alkyl or aryl hydrocarbon groups such as phenyl and methyl Figure for H on hydrogen sulfide leads to a number of different organosulfur compounds. These include thiols R-SH and thioethers R-S-R . Because of the availability of 3d orbitals sulfur that is bonded to hydrocarbon moieties can also be bonded to oxygen adding to the variety of organosulfur compounds that can exist. Despite the high toxicity of H2S not all organosulfur compounds are particularly toxic. Many of the compounds have strong offensive odors that warn of their presence which reduces their hazard. Reactions of Organic Sulfur Organic sulfur undergoes a number of toxicological chemical reactions. These include the following Oxidation of sulfur Reduction of sulfur Removal of sulfur from a molecule Addition of sulfur-containing groups Examples of these kinds of reactions some of which are very important in xenobiotic metabolism are given below. Oxidation of sulfur is called S-oxidation. Thiols can be oxidized to form disulfides 2R-SH O R-S S-R H2O Copyright 2003 by CRC Press LLC . S Lewis symbol of sulfur atom H S H Lewis structure of hydrogen sulfide S C S .