Ureas 9,1 Lớp cái nhìn tổng quan và bối cảnh mô tả chung Các hợp chất urê thay thế (các hợp chất trong đó các nhóm chức năng khác nhau thay thế cho một hoặc nhiều hydrogens trong phân tử urê) được sử dụng rộng rãi như các đại lý herbicidal, và đến một mức độ ít hơn như thuốc trừ sâu (1,2). Cấu trúc chung của phân tử urê thay thế được thể hiện trong hình . Nhận dạng, cấu trúc và hoạt động của hợp chất được xác định bởi thế và bố trí của họ trên phân tử (1,2) | chapter nine Ureas Class overview and general description Background Substituted urea compounds compounds in which different functional groups are substituted for one or more of the hydrogens in the urea molecule are widely used as herbicidal agents and to a lesser degree as insecticides 1 2 . The general structure of the substituted urea molecule is shown in Figure . The compound s identity structure and activity are defined by the substituents and their arrangement on the molecule 1 2 . The substituted urea herbicides include the phenylurea herbicides Figure and the sulfonylurea herbicides Figure which are the two major groups of substituted urea herbicides 2 . The benzoylphenylureas Figure are the major class of ureas used for insect control 1 . Examples of these three types of substituted urea compounds are listed in Table . Ureas usage Phenyl- and sulfonylureas The phenylurea compounds include some of the most commercially important herbicides fenuron and diuron 2 . There are at least 20 different compounds within this subgroup. They are principally used for the control of annual and perennial grasses and are applied pre-emergence . before target plants have emerged 2 4 . The sulfonylurea compound group is a relatively new class of herbicides first introduced in 1982 and has fewer members than the phenylurea class 2 . Sulfonyl ureas are also used for control of broadleaf weed species in addition to annual and perennial grasses 2 4 . They may be applied pre- or post-emergence 4 . The sulfonyl urea herbicides are nearly 100 times more toxic to target plants than the older compounds 2 . In addition they are applied at relatively low application rates and have a low toxicity to humans and other animals. Thus this class of compound is expected to see continuing research and development activity in the coming years 3 . Benzoylphenylureas Benzoylphenylurea compounds are very useful in controlling a wide variety of insect pests both within
