Carboxylation of the nitroxide radical of 2,2,6,6-tetramethyl-4-piperidone-1-oxyl with carbon dioxide and potassium phenoxide,and the physical properties of the products.
作者:HISAKAZU MORI、MASAAKI OHARA、TAKAO KWAN
DOI:10.1248/cpb.28.3178
日期:——
A stable nitroxide radical containing active methylenes, 2, 2, 6, 6-tetramethyl-4-piperidone-1-oxyl (I), was found to be carboxylated by potassium phenoxide and carbon dioxide in an aprotic solvent (N, N-dimethylformamide), producing new nitroxide compounds. The mono- or dicarboxylate was formed selectively, depending on the molar ratio of the substrate to potassium phenoxide. The ultraviolet and visible spectra of the monomethyl- (II) and dimethylester (III) of the carboxylates as well as those of I and 2, 2, 6, 6-tetramethylpiperidine-1-oxyl (IV) were investigated in various solvents. The results indicated that II exists mainly as the keto form in a polar solvent, and as the enol form in a nonpolar solvent, while the enol form of III is predominant in all the solvents tested. The nitrogen hyperfine coupling constants, AN, of I-IV in the electron spin resonance spectra were determined, and the results are discussed in terms of the keto-enol equilibrium. Furthermore, the distribution coefficients of these nitroxide radicals between hexane and water were measured to assess the potential suitability of these newly formed nitroxide radicals for use as spin labels or probes.
发现含有活性亚甲基的稳定氮氧自由基2,2,6,6-四甲基-4-哌啶酮-1-氧基(I)能在无质子溶剂(N,N-二甲基甲酰胺)中被苯酚钾和二氧化碳羰基化,生成新的氮氧自由基化合物。一元羰基化或二元羰基化产物的生成取决于原料与苯酚钾的摩尔比。研究了单甲酯(II)和二甲酯(III)的羰基化产物以及I和2,2,6,6-四甲基哌啶-1-氧自由基(IV)在不同溶剂中的紫外和可见光谱。结果表明,II在极性溶剂中以酮式为主,在非极性溶剂中则以烯醇式为主,而III则无论在何种溶剂中均以烯醇式为主。测定并讨论了I-IV在电子自旋共振谱中的氮超精细耦合常数A_N,以及酮式-烯醇式平衡。此外,通过测定这些氮氧自由基在正己烷和水之间的分配系数,评价了这些新形成的氮氧自由基用作自旋标记或探针的潜在适用性。