Studies On The Silver-Catalyzed Decarboxylative Halogenation Of Aliphatic Carboxylic Acids And Fluorodecarboxylation Of Pily(Methacrylic) Acids

Radical decarboxylative functionalization of aliphatic carboxylic acids has been widely studied. However, these methods suffer from the use of toxic reagents,tedious procedure or limited scope of application, or low efficiencies. Herein, we have developed silver-catatylzed decarboxylative bromination and decarboxylative chlorination of aliphatic carboxylic acids. Furthermore, we have developed silver-catalyzed decarboxylative fluorination of aliphatic carboxylic acids, and applied the method to the fluorodecarboxylation of poly(methacrylic acid).The dissertation is mainly composed of the following three parts:1. With the catalysis of Ag(Phen)2OTf, and NBS as the bromination agent, we found that the phenylacetic acid underwent decarboxylative bromination smoothly in refluxing1,2-dichloroethane. However, this method is applicable only to arylacetic acids without substituted at the benzylic position. Later, with the catalysis of Ag(Phen)2OTf, we found that the reactions of various alkyl carboxylic acids including acrylacetic acids with t-butyl hypochlorite in CH3CN afforded the corresponding chlorodecarboxylation products in high yieids under mild conditions, this is the first example of silver-catalyzed chlorodecarboxyltion of aliphtic acids. This decarboxylative chlorination is not only efficient and general, but also chemoselective, and functional group compatible. The reactivity of carboxylic acids decreases in the order of benzyl≈tertiary> secondary> primary＞＞aromatic. Through mechanistic study, it is concluded that the mechanism of this catalytic chlorodecarboxylation is a single electron transfer followed by chlorine atom transfer.2. Based on Feng Yin’s system of AgNO3\K2S2O8\SelectfluorR that catalyzed the decarboxylative fluorination of aliphatic carboxylic acids, we found that the better result can be reached without K2S2O8. With the catalysis of AgNO3, the reaction of various aliphatic carboxylic acids with SelectfluorR in a mixed solvent of acetone and water afforded the corresponding fluorodecarboxylation products in satisfactory yields under mild conditions. Further investigation revealed that pure water could be used as the solvent for carboxylic acids with better solubility in water. The use of pure water as solvent not only inhibits the interaction between SelectfluorR and the products bearing sensitive groups towords SelectfluorR, but also avoids the side reaction, i.e., the decarboxylative hydrogenation. This fluorination method is not only efficient and general, but also chemoselective, with an excellent functional group tolerance, thus making it highly practical in the synthesis of fluorinated molecules. The reactivity of carboxylic acids decreases in the order of tertiary> secondary> primary＞＞aromatic. Mechanism studies indicated that the fluorodecarboxylation proceeds via Ag(Ⅲ)-mediated single electron transfer followed by fluorine atom transfer.3. The fluorodecarboxylation was applied to poly(methacrylic acid). We found that the extent of fluorodecarboxylation of poly(methacrylic acid) can be controlled by the amount of SelectfluorR. The resulting polymer is equivalent to the copolymer of methacrylic acid and2-fluorpropene. In order to facilitate the procedure of purification, the decarboxylative fluorination of poly(acrylic acid) was followed by methyl esterification, yielding the fluorinated polymer equivalent to the copolymer of methylacrylate and vinyl fluoride. This part of reseach is still in progress.