Study On The Micellar-catalyzed Chloromethylation And Oxidation Of Benzylic Halides In Aqueous Media

In organic synthesis, chloromethylation of aromatic compounds and oxidation of benzylic halides to aromatic aldehydes or aromatic ketones are extremely important reactions. Therefore, the development of a simple, economic, and eco-friendly method is of great significance in both in practice and in theory.The main objective of this dissertation is to perform the chloromethylation reaction of aromatic compounds and the oxidation reaction of benzylic halides in aqueous media with a view to develop new environment-feiendly methods, and the specific research contents include the following aspects.A small amount of electrolyte was added into the micellar catalysis system in which chloromethylation reaction of 2-bromoethylbenzene (BEB) was carried out, and the effect of electrolyte on the catalytic reaction was investigated. The decrease in critical micelle concentration (CMC) and the increase in solubilization of BEB in the micelles formed by surfactant and electrolyte were observed. The chloromethylation reaction of BEB exhibited higher conversion and higher selectivity in mono-chloromethylation in the surfactant micelles containing electrolyte than in the single surfactant micelle. The catalysis effects of anionic, cataioic and non-ionic surfactants were compared; the mechanism of chloromethylation reaction and the synergistic mechanism between electrolyte and three types of surfactants were discussed.For the purpose of industrutial production, the chloromethylation reaction of aromatic compounds was performed successfully by micellar catalysis in oil/water biphasic system at high reactant loadings that exceeded the maximum solubilization capacity of micellar solutions. The effects of the structures of cationic surfactants on the reaction were compared. The mechanism of chloromethylation reaction and the mechanism of micellar catalysis were further investigated. The results show that the micellar catalysis is an effective way to realize the chloromethylation. The chloromethylation reaction consists of electrophilic substitution reaction and nucleophilic substitution reaction, the nucleophilic substitution is the rate-controlling step and the hydroxymethyl cation (⁺CH20H) is the really effective electrophile. Cationic surfactants, especially those containing longer hydrophobic carbon chain, are more effective. Selectivity for mono-chloromethylation was remarkably improved and regioselectivity was found to be dependent on the nature of the surfactant. Under the optimal reaction conditions, chloromethylation of isopropylbenzene could obtain 97.5% selectivity in mono-chloromethylation and 8.28 para/ortho selectivity ratio at 89.8% conversion.A new procedure of phase transfer catalyzed oxidation of benzylic halides to aldehydes or ketones with potassium nitrate (KNO₃) in aqueous potassium hydroxide (KOH) solution has been developed. The oxidation mechism and the effects of different factors on the oxidation reaction were examined. The results show that the phase transfer catalysis is an effective way to realize the oxidation of benzylic halides to aldehydes or ketones with KNO₃ in high yield. The oxidation reaction consists of nucleophilic substitution reaction and a-elimination reaction which is the rate-determining step. Phase transfer catalyst having longer hydrophobic carbon chain, is more effective catalyst.A new method by which benzylic halides are directly oxidized to aldehydes and ketones with molecularr oxygen (O₂) in the presence of catalytic amounts of TEMPO (2,2,6,6-tetramethylpiperidyl-l-oxy) and potassium nitrite (KNO₂) has been developed. The oxidation mechism and the effects of different factors on the oxidation reaction were investigated. The experimental results show that, only in aqueous media, TEMPO/KNO₂ can catalyze the oxidation of benzylic halides to aldehydes or ketones with O₂ in high yield. The oxidation reaction was composed of hydrolysis reaction of benzylic halides and oxidation reaction of the resulting benzylic alcohols. The hydrolysis of benzylic halides is the rate-determining step.