Os (VIII) Catalyzed Oxidative Cleavage of Pyrrolidine Ring in L-Proline by Sodium Periodate (NaIO4) in Alkaline Medium
31 Aug 2017-International journal of scientific research in science, engineering and technology-Vol. 3, Iss: 5, pp 362-371
TL;DR: In this paper, a kinetic and mechanistic investigation of catalyzed oxidation of proline by sodium periodate (NaIO4) in alkaline medium in temperature range 30 0 C to 45 0 C was conducted.
Abstract: The present paper deals with the kinetic and mechanistic investigation of Os(VIII) catalyzed oxidation of proline by sodium periodate (NaIO4) in alkaline medium in temperature range 30 0 C to 45 0 C. The experimental result shows a first order kinetics with respect to Os[VIII] and [Periodate] while positive effect with respect to substrate i.e., Proline was observed. The reaction showed negative effect for [OH ]. Negligible effect of [HgOAc)2] and ionic strength of the medium was observed. The reaction is carried out in presence of mercuric acetate as a scavenger. The reaction between sodium periodate and proline in alkaline medium shows 2:1 stoichiometry. The values of rate constants observed at different temperatures (30 to 45 0 C) were utilized to calculate the activation parameters. A mechanism involving the complex formation between catalyst, substrate and oxidant has been proposed. L-glutamic acid has been identified as main oxidation product of the reaction chromatographically and spectroscopically. Based on kinetic data, reaction stiochiometry and product analysis of the reaction a feasible mechanism has been proposed. The rate law has been derived from obtained kinetic data.
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TL;DR: The finding that the amino acid proline is an effective asymmetric catalyst for the direct aldol reaction between unmodified acetone and a variety of aldehydes is reported.
Abstract: Most enzymatic transformations have a synthetic counterpart. Often though, the mechanisms by which natural and synthetic catalysts operate differ markedly. The catalytic asymmetric aldol reaction as a fundamental C-C bond forming reaction in chemistry and biology is an interesting case in this respect. Chemically, this reaction is dominated by approaches that utilize preformed enolate equivalents in combination with a chiral catalyst.1 Typically, a metal is involved in the reaction mechanism.1d Most enzymes, however, use a fundamentally different strategy and catalyze the direct aldolization of two unmodified carbonyl compounds. Class I aldolases utilize an enamine based mechanism,2 while Class II aldolases mediate this process by using a zinc cofactor.3 The development of aldolase antibodies that use an enamine mechanism and accept hydrophobic organic substrates has demonstrated the potential inherent in amine-catalyzed asymmetric aldol reactions.4 Recently, the first small-molecule asymmetric class II aldolase mimics have been described in the form of zinc, lanthanum, and barium complexes.5,6 However, amine-based asymmetric class I aldolase mimics have not been described in the literature.7 Here we report our finding that the amino acid proline is an effective asymmetric catalyst for the direct aldol reaction between unmodified acetone and a variety of aldehydes. Recently we developed broad scope aldolase antibodies that show very high enantioselectivities, have enzymatic rate accelerations, and use the enamine mechanism of class I aldolases.4 During the course of these studies, we found that one of our aldolase catalytic antibodies (Aldolase Antibody 38C2, Aldrich) is an efficient catalyst for enantiogroup-differentiating aldol cyclodehydrations of 2,6-heptanediones to give cyclohexenones, including the Wieland-Miescher ketone.8,9 These intramolecular reactions are also catalyzed by proline (Hajos-Eder-Sauer-Wiechert reaction)10 and it has been postulated that they proceed via an enamine mechanism.11 However, the proline-catalyzed direct intermolecular asymmetric aldol reaction has not been described. Further, there are no asymmetric small-molecule aldol catalysts that use an enamine mechanism.7 Based on our own results and Shibasaki’s work on lanthanum-based small-molecule aldol catalysts,4,6 we realized the great potential of catalysts for the direct asymmetric aldol reaction. We initially studied the reaction of acetone with 4-nitrobenzaldehyde. Reacting proline (30 mol %) in DMSO/acetone (4:1) with 4-nitrobenzaldehyde at room temperature for 4 h furnished aldol product (R)-1 in 68% yield and 76% ee (eq 1). This result
2,283 citations
TL;DR: Spot Tests in Organic AnalysisBy Prof. Fritz Feigl.
Abstract: Spot Tests in Organic Analysis By Prof. Fritz Feigl. Sixth, enlarged and revised English edition. Translated by Prof. Ralph E. Oesper. Pp. xx + 675. (Amsterdam: Elsevier Publishing Company; London: D. Van Nostrand Company, Ltd., 1960.) 65s.
493 citations
TL;DR: In this paper, the effect of the oxidation state, size, geometry and extent of protonation of the HxPyOzm oxoanions on the precursor-complex formation constant, electron-transfer rate constant, and thermal and pressure activation parameters has been investigated.
Abstract: Outer-sphere redox reactions between [CoIII(NH3)5(HxPyOz)](m– 3)–(HxPyOzm–= H2PO2–, H2PO3–, HPO32–, HP2O73–, P2O74–, γ-H2P3O103–, -HP3O104–, -P3O105–, β-H3P3O102–, -H2P3O103–, -HP3O104– or -P3O105–) and [Fe(CN)6]4– have been studied as a function of pH, HxPyOzm– oxoanion, temperature and pressure. The effect of the oxidation state, size, geometry and extent of protonation of the HxPyOzm– oxoanions on the precursor-complex formation constant, electron-transfer rate constant, and thermal and pressure activation parameters has been investigated. The values obtained indicate that all the precursor-complex formation equilibrium constants, KOS, are the same except for the non-linear β-H3P3O102–, -H2P3O103–, -HP3O104– and -P3O105– oxoanions, where the values are consistently larger, indicating that hydrogen bonding plays a very important role. The electron-transfer rate constant for a series of [Co(NH3)5(HxPyOz)](m– 3)–, with linear oxoanions, increases on decreasing the negative charge on the complex {k308= 0.73 × 10–3 and (8.5–11)× 10–3 s–1 for the γ-[Co(NH3)5(P3O10)]2– and γ-[Co(NH3)5(H2P3O10)], respectively}. For the non-linear β-P3O105– oxoanions a threshold is observed when the external oxo groups are protonated {k308= 20 × 10–3 for β-[Co(NH3)5(H3P3O10)]+ species and 0.84 × 10–3 s–1 for β-[Co(NH3)5(H2P3O10)], -[Co(NH3)5(HP3O10)]– or -[Co(NH3)5(P3O10)]2–}. The ΔH‡ values are within the range expected, while those of ΔS‡ and ΔV‡ vary considerably with the extent of protonation of the phosphorus oxoanionic ligands, being 13 J K–1 mol–1 and + 36 cm3 mol–1 and 69 J K–1 mol–1 and + 13 cm3 mol–1, respectively for the [Co(NH3)5(HP2O7)]–[Co(NH3)5(P2O7)]– couple. The ΔV‡ values depend strongly on the oxo group distribution of the oxophosphorus ligand {+ 13 and + 32 cm3 mol–1 for β- and γ-[Co(NH3)5(P3O10)]2–, respectively}. Hydrogen bonding and solvent reorganization play a key role in the interpretation of the activation parameters.
102 citations
94 citations
"Os (VIII) Catalyzed Oxidative Cleav..." refers result in this paper
...This conclusion was supported by earlier reports [23-25]....
[...]
TL;DR: In the presence of catalysts such as animal charcoal and Cu++aq ions, there is a reduction in the amount of intermediate formed, and radioactive tracer experiments indicate the formation of appreciable quantities of dithionate ion as mentioned in this paper.
Abstract: The ferricyanide–sulphite reaction has been shown to proceed via the intermediates [Fe(CN)5(CNSO3)]5– and [Fe(CN)5(CNSO3)]4–, followed by hydrolysis of the latter to ferrocyanide and sulphate. In the presence of catalysts such as animal charcoal and Cu++aq ions, there is a reduction in the amount of intermediate formed, and radioactive tracer experiments indicate the formation of appreciable quantities of dithionate ion.
27 citations
"Os (VIII) Catalyzed Oxidative Cleav..." refers result in this paper
...This conclusion was supported by earlier reports [23-25]....
[...]