Studies Of The Solvent Effect On Some Organic Reactions

Solvent effect plays important roles in many organic reactions. Selecting suitablesolvent can enhancing reaction rate and improve yield, so the study of solvent effecthas been received considerable attention from chemists. The study of solvent effectmoves into the new step with the development of experiment method as well ascomputation science. In the present work, the effect of solvent polarity on organicreactions has been studied by experiments and calculations.1,Standard organic solvent effect on two kind of reactions has been studied:â‘ The Selectivity of Anomers in the Hilbert-Johnson Reaction has been studied bymeans of density functional theory (DFT) method. A new possible reaction pathway isproposed. The Calculations further indicate that the proposed pathway is morepreferable than the other two typical ones. In addition, quantum mechanicalcalculations were employed to study the solvent effect on the stability of theintermediates and the ratio of the diastereomers, which could be used to predict theratio of two anomers expected from the proposed pathway. Furthermore, theexperimentally determined products' ratio was compared to theoretical predictionsand the experimental results are in good accordance with the predicted outcomes.â‘¡The mechanism of N-(4-hydroxycyclohexyl)-acetamide cis-trans epimerization hasbeen studied by means of DFT method. A possible reaction pathway is proposedwhich is indicated preferable further by the calculations. In addition, quantummechanical calculations were employed to study the solvent effect on the proposed mechanism which could be used to predict the ratio of two anomers expected from theproposed pathway.2,Ionic liquids' effect on organic reactions by experiments and calculation has beenstudied. Ionic liquids (ILs) have been emerging as potential "greener" altematives tovolatile organic solvents and being used as environmentally benign media for manyimportant organic reactions. In this dissertation, ILs were used in the Knoevenagelcondensation,the chloromethylation of aromatic hydrocarbons,the synthesis of4,4'-methylenebis(N,N-dimethylaniline) and the nitro alkenes' preparation, andreagents' reactivity which is different from that in standard organic solvents are theremarkable features observed in ILs. In addition, the experimental results weredemonstrated by calculations with the Gaussian 98 suite of program and thecalculation results are in good accordance with the experimental outcomes.â‘ TheL-proline-catalyzed Knoevenagel condensation reaction has been successfully carriedout in imidazolium-based ILs with increased yield. Study on the recycling of thecatalyst has revealed that L-proline in an IL can be reused at least four times withcomparable yields. These results created a 'green' class of Knoevenagel condensationwherein both solvent and catalyst are readily recycled and reaction time is minimized.These reactions can be performed on a multi-gram scale under operationally simpleand safe conditions. Moreover, the reactivity of reagents which is different from thatin traditional organic solvents was supposed and proved by calculations with theGaussian 98 suite of program.â‘¡The imidazolium-based IL has been proved to bean effective promoter for the chloromethylation of aromatic hydrocarbons. The present method has many obvious advantages compared to previous methods, such asenvironmentally more benign, the ease of product isolation, the simplicity ofmethodology, the high yield, the generality, the convenience of preparing IL[emim]BF₄ using much cheaper starting material, and the potential for recycling ofionic liquid. We have shown that IL [emim]BF₄ can replace other catalysts, and is asimple system—a good example of green chemistry.â‘¢The synthesis of4,4'-Methylenebis(N, N-dimethylaniline) by using N, N-dimethylaniline andtetrachloromethane is a significant reaction, its mechanism was calculated in diversesolvents. According to the results, IL was selected as a catalytic green solvent in thisreaction, the reaction was found to give 4, 4'-Methylenebis(N, N-dimethylaniline) inconsiderable yield.