Acidity Characterization of Liquid Acids Using 31P NMR Chemical Shift and the Amount of Change by Trimethylphosphine Oxide

• Main Authors: Jeng-You Chen, 陳振友
• Other Authors: Hsi-Wei Jia
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/30653907952800837625

碩士 === 中原大學 === 化學研究所 === 104 === Solvent acidity is one of the most important chemical properties of a molecule. Almost all chemical reactions will be affected by the solvent effect. Therefore, it is essential to use the spectroscopy technology to obtain the accurate and reproducible acidic character of a solvent. Based on Liu et. al. works in acidic aqueous solutions, we extended the acidity studies to solvent dimethylsulfoxide (DMSO) to obtain 31P chemical shifts of the trimethylphosphine oxide (TMPO) molecule in order to compare the pKa values of acid molecules derived in pH meter with solvents of water and DMSO respectively. In this study, the TMPO molecule was used as the acidic probe to act with the proton dissociated from the acidic molecule in DMSO. According to the ion atmosphere concept and the Coulomb attraction force, the electron cloud density will shift from the partially negative-charged oxygen site of TMPO to the dissolved proton of the acidic molecule. Therefore, the 31P chemical shift value of TMPO will move to the downfield position. The stronger the acidic strength, the more downfield will be the chemical shift. The experimental results demonstrated that 31P chemical shifts of TMPO molecules in acidic DMSO solutions can detect wider acid strength range from superacids to weak acids than traditional pH meter does. Comparing with results obtained in acidic aqueous solutions, acidic molecules dissolved in DMSO have better 31P chemical shift differentiation especially for weak acids or strong acids at low concentrations than in their aqueous solutions.