The thermal chemistry of β-halohydrins on Cu(100) surface

• Main Authors: Chia-Yuan Chen, 陳嘉淵
• Other Authors: Jong-Liang Lin
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/egx26a

碩士 === 國立成功大學 === 化學系碩博士班 === 90 === Abstract Temperature-programmed reaction/desorption (TPR/D) and reflection-absorption infrared spectroscopy have been employed to investigate the adsorption and reactions of β-halohydrins (XCH2CH2OH, X=F,Cl,Br,I) on a Cu(100) surface under ultrahigh vacuum condition. With a OH group, ethanol adsorbs reversibly on Cu(100). In the case of halogenated ethane, ethyl iodide and ethyl bromide decompose via carbon-halogen bond scission to generate halogen atoms and ethyl groups on the surface. Ethyl groups undergo β-hydride elimination to form ethylene. Unlike alkyl iodide and bromide, C-Cl bond dissociation of alkyl chloride dose not occur until the chain length reaches seven carbons. Here we study the thermal chemistry of β-halohydrins with the two functional groups of OH and X. In TPR/D experiments 2-iodoethanol decomposes to produce water, ethylene, ethanol, acetaldehyde, butane, and 1,4-dioxane. But we can not find molecular desorption at submonolayer coverage. For the 2-bromoethanol, the main desorbing products are water, ethylene, acetaldehyde, 1,4-dioxane, and bromoethane. We can not find the monolayer molecular desorption either. In the 2-chloroethanol case, the product distribution is different from those of 2-iodoethanol and 2-bromoethanol. TPR/D shows the thermal products of ethylene, chloroethene, some water, and monolayer molecular desorption. For the 2-fluoroethanol, the products of water, ethylene and 1,4-dioxane is relatively low. In RAIRS experiments, it is found that 2-iodoethanol reacts at relatively low temperature to form hydroxyethyl specie. At 200K, it forms the surface oxametallacycle (–OCH2CH2–) intermediate. In 2-bromoethanol case, we can not find hydroxyethyl intermediate on the surface, but obverse the oxametallacycle intermediate at 200K. In 2-chloroethanol and 2-fluoroethanol case, we do not find any stable intermediate. At low coverages, they adsorbs on the surface in gauche form.