亚硫酸钠对碱性硫脲稳定作用的构效关系

Structure-property relationship between the stability of alkaline thiourea and the structure of thiourea and sulfite ion

依据分子力学理论 ,采用HYPERCHEM6 .0化学计算软件 ,结合红外光谱的分析结果 ,研究了硫脲和亚硫酸钠的结构与碱性硫脲稳定性之间的“构效关系” .结果表明 :水溶液中硫脲易产生同分异构体而存在碳氮双键 ;在酸性介质中 ,硫脲分子易与氢形成硫氢键 ,降低了硫原子的最高占据分子轨道 (HOMO)能量 ,使其较为稳定 ;而在碱性介质中 ,硫脲分子不易形成硫氢键 ,硫原子的HOMO能量明显高于酸性介质中相应值 ,硫脲极不稳定 ;亚硫酸根的加入 ,通过氢键与碱性硫脲分子粘接 ,形成稳定的环状结构 ,在不改变硫脲分子性质的前提下 ,降低了硫脲分子中硫原子的HOMO能量 ,增加了硫脲的稳定性 .由此推断 ,碱性硫脲的高效稳定剂能降低硫原子的HOMO的能量 ,但要满足 2个条件 :在碱性介质中易与硫脲分子形成硫氢键 ;与硫脲分子形成稳定的环状结构 .

Based on molecular mechanics (MM), a structure-property relationship between the stability of alkaline thiourea and the structure of thiourea and sodium sulfite is studied by a combination of software calculation of HYPERCHEM6.0 with the experiment of infrared spectrum. The results show that a double-bond between carbon and nitrogen exists in aqueous thiourea because of isomer. Hydrogen-sulfur bond formed easily decreases the energy of HOMO of thiourea molecular, resulting in the stability of thiourea in acidic medium. It is difficult to form hydrogen-sulfur bond in alkaline thiourea, and the energy of HOMO of thiourea molecular in alkaline medium is obviously higher than that in acidic medium, which causes unstability of alkaline thiourea. Sodium sulfite molecular, however, forms a stable orbicular structure with thiourea molecular through interlink of couple isolated electrons, reducing HOMO value of thiourea, and improving the stability of alkaline thiourea. It is concluded from molecular force field that an efficient stability agent for alkaline thiourea must meet the needs of two conditions, i.e., forming hydrogen-sulfur bond easily and a stable orbicular structure with thiourea molecular in alkaline medium.