Alkali metal ion catalysis and inhibition in nucleophilic displacement reactions at phosphorus centers: ethyl and methyl paraoxon and ethyl and methyl parathion

We report on the ethanolysis of the P=O and P=S compounds ethyl and methyl paraoxon (1a and 1b) and ethyl and methyl parathion (2a and 2b). Plots of spectrophotometrically measured rate constants, kobsd versus [MOEt], the alkali ethoxide concentration, show distinct upward and downward curvatures, pointing to the importance of ion-pairing phenomena and a differential reactivity of free ions and ion pairs. Three types of reactivity and selectivity patterns have been discerned: (1) For the P=O compounds 1a and 1b, LiOEt > NaOEt > KOEt > EtO-; (2) for the P=S compound 2a, KOEt > EtO- > NaOEt > LiOEt; (3) for P=S, 2b, 18C6-crown-complexed KOEt > KOEt = EtO(-) > NaOEt > LiOEt. These selectivity patterns are characteristic of both catalysis and inhibition by alkali-metal cations depending on the nature of the electrophilic center, P=O vs P=S, and the metal cation. Ground-state (GS) vs transition-state (TS) stabilization energies shed light on the catalytic and inhibitory tendencies. The unprecedented catalytic behavior of crowned-K(+) for the reaction of 2b is noteworthy. Modeling reveals an extreme steric interaction for the reaction of 2a with crowned-K(+), which is responsible for the absence of catalysis in this system. Overall, P=O exhibits greater reactivity than P=S, increasing from 50- to 60-fold with free EtO(-) and up to 2000-fold with LiOEt, reflecting an intrinsic P=O vs P=S reactivity difference (thio effect). The origin of reactivity and selectivity differences in these systems is discussed on the basis of competing electrostatic effects and solvational requirements as function of anionic electric field strength and cation size (Eisenman's theory).     

Optically active trivalent phosphorus compounds—I: Diastereoisomeric o-menthyl ethylphenylphosphinites: synthesis,chirality at phosphorus and stereochemistry of nucleophilic displacement reaction

The reaction between racemic ethylphenylchlorophosphine and menthol has been found to give a mixture of diastereoisomeric O-menthyl ethylphenylphosphinites (4) in unequal ratio. The diastereoisomeric content depends mainly on the tertiary amine used for the condensation. The chirality at phosphorus in the diastereoisomeric esters (4a and 4b) has been assigned by means of chemical correlation (conversion into optically active methylethylphenylphosphine oxide) and proton NMR spectra. It has been demonstrated that nucleophilic substitution at phosphorus in 4 occurs with inversion of configuration.     

Isokinetic relationships for nucleophilic substitution reactions at the saturated carbon atom. Reactions in aqueous solutions

An isokinetic relationship (IKR) with the parametersT _iso=6145 K and logk _iso=10.622 is valid for nucleophilic substitution reactions at the saturated carbon atom with the participation of anionic nucleophiles in aqueous solutions. The IKR describes the rate constants of the reactions with different anionic nucleophiles, leaving groups, and substituents at the electrophilic reaction center. Similar reactions with neutral nucleophiles, which follow another mechanism, are described by a separate IKR withT _iso=−1232 K and logk _iso=16.226. The reactions of haloforms with hydroxide ion, which proceed by a specific mechanism involving the haloform ionization equilibrium followed by α-elimination of the halide ion, are described by yet another IKR withT _iso=−1463 K and logk _iso=21.057. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 809–814, May, 2000.     

离子色谱法测定海产品中磷酸盐、焦磷酸盐、偏磷酸盐和总磷

建立了离子色谱法测定海产品中磷酸盐、焦磷酸盐、偏磷酸盐和总磷的分析方法。样品经100 mmol/L NaOH溶液浸提,固相萃取柱去除有机物、阳离子、中和OH~后用于海产品中磷酸盐、焦磷酸盐和偏磷酸盐的测定;样品经干灰化法消化,固相萃取柱净化后用于总磷测定。考察了提取溶液的pH、有机物和共存离子对测定结果的影响。该方法的线性范围为0.3～60 mg/L,检出限为2.1～2.3 mg/kg,相对标准偏差为1.6%～2.6%。海鱼和虾仁样品中目标物的加标回收率为81.8%～100.0%。该方法选择性好,灵敏度高,用于实际样品测定结果令人满意。     

A linear three‐center four electron bonding identity nucleophilic substitution at carbon,boron, and phosphorus. A theoretical study in combination with van't Hoff modeling

We studied various identity nucleophilic substitution reactions based on an S_N2 reaction profile. With calculations and experimental geometries concerning the nature of the various complexes indicated as stable, intermediate, and transition state we were able to show the additional value of van't Hoff 's tetrahedron by changing its geometry via a trigonal pyramid into a trigonal bipyramid. The ratio of the apical and the corresponding tetrahedral bond distance is then 1.333. This value has been used in general as a calibration point for the understanding of the (in)stabilities of the complex formation on the S_N2 reaction coordinate. The relevance of this approach has been also proved for enzymatic reactions focused on carbon and phosphorus substrates. Furthermore, it could be established that identity proton‐in‐line displacements are fully comparable with the relocation of carbon in a nucleophilic substitution reaction as Cl^? + CH₃Cl. The significance of this information will afford new insight in the dynamics of a linear three‐center four‐electron complex. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Metallocomplex catalysis in reactions of inhibition of oxidation processes: Statement of the problem,and current status

This article is a review of research on metallocomplex catalysis of radical reactions — chain breaking and hydroperoxide decomposition — that lead to inhibition of the oxidation of organic compounds by molecular oxygen. Information on the mechanisms and applied aspects of metallocomplex catalysis of these reactions is summarized and correlated.As in Russian original — Translator.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 1, pp. 3–18, January–February, 1993.     

Homolytic displacement at carbon centres: XII. Regiospecific formation of N-allyl and N-cyclopropylcarbinyl sulphonamides and of allyl and cyclopropyl halides in the reaction of N-halogeno compounds with organocobaloximes

Several but-3-enyl and allylcobaloximes react regiospecifically with N-chloro-N-methyl sulphonamides to give N-cyclopopylcarbinyl- or rearranged N-allyl-N-methyl sulphonamides, by a process which is believed to take place by the attack of an N-centred radical at the terminal unsaturated carbon of the organic ligand, with displacement of cobaloxime(II). In contrast, N-bromoacetamide and several other N-halogenoimides react regiospecifically to give the cyclopropylcarbinyl halide or the rearranged allyl halide by a process in which a halogen-containing free radical species attacks the terminal unsaturated carbon of the organocobaloxime.     

Alkali-metal-ion catalysis and inhibition in the nucleophilic displacement reaction of y-substituted phenyl diphenylphosphinates and diphenylphosphinothioates with alkali-metal ethoxides: effect of changing the electrophilic center from P=O to P=S

A kinetic study of the nucleophilic substitution reaction of Y‐substituted phenyl diphenylphosphinothioates 2 a – g with alkali‐metal ethoxides (MOEt; M=Li, Na, K) in anhydrous ethanol at (25.0±0.1) °C is reported. Plots of pseudo‐first‐order rate constants (k_obsd) versus [MOEt], the alkali ethoxide concentration, show distinct upward (KOEt) and downward (LiOEt) curvatures, respectively, pointing to the importance of ion‐pairing phenomena and a differential reactivity of dissociated EtO^? and ion‐paired MOEt. Based on ion‐pairing treatment of the kinetic data, the k_obsd values were dissected into k and k_MOEt, the second‐order rate constants for the reaction with the dissociated EtO^? and ion‐paired MOEt, respectively. The reactivity of MOEt toward 2 b (Y=4‐NO₂) increases in the order LiOEt?NaOEt>KOEt>EtO^?. The current study based on Yukawa–Tsuno analysis has revealed that the reactions of 2 a – g (P?S) and Y‐substituted phenyl diphenylphosphinates 1 a – g (P?O) with MOEt proceed through the same concerted mechanism, which indicates that the contrasting selectivity patterns are not due to a difference in reaction mechanism. The P?O compounds 1 a – g are approximately 80‐fold more reactive than the P?S compounds 2 a – g toward the dissociated EtO^? (regardless of the electronic nature of substituent Y) but are up to 3.1×10³‐fold more reactive toward ion‐paired LiOEt. The origin of the contrasting selectivity patterns is further discussed on the basis of competing electrostatic effects and solvational requirements as a function of anionic electric field strength and cation size (Eisenman’s theory).     

Adsorption and catalysis at the solid/sulfur dioxide interface in the atmosphere. An examination of statistical data

From the official analytical data for sulfur dioxide and smoke in air pollution for one winter and one summer month covering residential and industrial areas in Great Britain, regression lines are computed. These reveal a large deficiency which is of very high significance of sulfur dioxide relative to smoke in winter compared with summer; the data show clearly that the deficiency is not due to the increase in domestic smoke in winter. Several reasons for the deficiency are examined semiquantitatively, and it is suggested that adsorption of sulfur dioxide occurs on solid particles followed by its catalytic oxidation by oxygen to sulfur trioxide. The amount of sulfur dioxide to be accounted for is far too high to be explained by simple adsorption on smoke particles. The catalysis may be due to traces of metals.The data also reveal that whatever may be the mechanism by which the sulfur dioxide is removed, it becomes less effective as the amount of smoke present increases, in all situations. It is suggested that a cause of this change might be the progressive covering of the very active surface of natural inorganic dust, possibly including meteoric dust, in the atmosphere by the less catalytically active smoke particles as their concentration rises.     

Equilibria in complexes ofN-heterocyclic molecules,part IX. Circular dichroism study of nucleophilic attack at tris-(5-nitro1,10-phenanthroline)ruthenium(II)

Summary The reactions between Ho^–, CN^–, MeO^– and EtO^– and -(-)-tris-(5-vitro-1,10-phenantliroline)ruthenium(II) ion in solution were followed by c.d. measurements. The results support the earlier findings that these reactions proceed through the formation of pseudo-bases with the ligand.Part VIII: R. D. Gillard, L. A. P. Kane-Maguire and P. A. Williams,J. Chem. Soc. Dalton Trans. in press.     

S(N)1-like reactions of bicyclic alpha-amino ethers with sulfur,nitrogen, and carbon nucleophiles. Synthesis of 1-azabicyclo[3.2.2]nonanes functionalized at carbon C2 and C6 with complete stereocontrol

[reaction: see text] In the presence of nucleophiles, Lewis acid mediated cleavage of alpha-amino ethers derived from quincorine and quincoridine affords a variety of C2-substituted and C6-vinylated 1-azabicyclo[3.2.2]nonanes. These are enantiopure and are formed in S(N)1-like reactions with complete stereocontrol. There is no leakage into 2-Nu en route to product 1-Nu or vice versa. Me(3)SiCN provides new Strecker-type alpha-amino nitriles. In the presence of TTMPP-BF(3).OEt(2), the ketene acetal Me(2)C=C(OMe)OSiMe(3) delivers enantiopure bicyclic beta-amino acid esters.     

Isokinetic relationships for nucleophilic substitution at the saturated carbon atom. Reactions with anions in the gas phase and various solvents

Isokinetic relationship (IKR) with the parameters T _iso = 6103 K and logk _iso = 10.402 is applicable to the rate constants for 165 reactions of nucleophilic substitution at the saturated carbon atom involving anionic nucleophiles in proton-donor and polar aprotic solvents and their mixtures. For analogous reactions in the gas phase proceeding via a specific mechanism, IKR is obtained with the parameters T _iso = 1505 K and logk _iso = 9.972, which is applicable to the reactions occurring under various pressures of an inert gas.     

The N3+ reactivity in ionized gases containing sulfur, nitrogen, and carbon oxides.

The N(3)(+) reactivity with SO(2), N(2)O, CO(2), and CO is studied by mass spectrometric techniques under a wide range of pressures from 10(-7) to 10(-4) Torr. The kinetics, reaction mechanism, and role of vibrationally excited ions are investigated by experimental and theoretical methods. Key distinguishing features of the N(3) (+) reactivity are evidenced by comparison to N(+) and N(2)(+) ions, which mainly undergo charge-exchange reactions. The N(+) transfer to SO(2) prompts formation of NO(+) ions and neutral oxides NO and SO. The N(+) transfer to N(2)O also leads to NO(+) ions by a process not allowed by spin conservation rules. In both cases no reaction intermediate is detected, whereas CO(2) and CO are captured to form the very stable NCO(2) (+) and NCO(+) ions. NCO(2)(+) ions are characterized for the first time as strongly bound triplet ions of NOCO and ONCO connectivity. DFT and CCSD(T) computations have been carried out to investigate the structural and energetic features of the NCO(2) (+) species and their formation process.     

Hydroxide-promoted redox reactions in water of α-Phenyl-4-nitro-benzenemethanol, α-(p-Nitrophenyl)-4-pyridinemethanol,and α-(p-Nitrophenyl)-4-Pyridinemethanol N-Oxide steric inhibition of resonance

α-Phenyl-4-nitrobenzenemethanol ( 3 ) reacted with 1 M sodium hydroxide to yield 4, 4′-dibenzoyl-azoybenzene ( 5 ) (51%), 4-hydroxy-4′-benzoylazobenzene ( 6 ) and benzoic acid (12% each), and smaller amounts of 4-aminobenzophenone and 4-nitrobenzophenone. Both α-phenyl-2-nitrobenzenemethanol ( 9 ) and 3, 5-dimethyl-4-nitrobenzenemethanol ( 10a ) did not react with 1 M sodium hydroxide, presumably due to steric hindrance. α-(p-Nitrophenyl)-4-pyridinemethanol ( 14 ) and its N-oxide 11 with 1 M sodium hydroxide yielded 4,4′-diaroylazoxybenzenes 15a and 12a , respectively, 4,4′-diaroylazobenzenes 15b and 12b , respectively, as well as 4-hydroxy-4′-aroylazobenzenes 16 and 13 , respectively. The relative reaction rates were 11 > 14 > 3 . Studies with 11 showed that the nitro group is involved in the redox reaction in preference to the N-oxide group.     

Turnover numbers, turnover frequencies, and overpotential in molecular catalysis of electrochemical reactions. Cyclic voltammetry and preparative-scale electrolysis

The search for efficient catalysts to face modern energy challenges requires evaluation and comparison through reliable methods. Catalytic current efficiencies may be the combination of many factors besides the intrinsic chemical properties of the catalyst. Defining turnover number and turnover frequency (TOF) as reflecting these intrinsic chemical properties, it is shown that catalysts are not characterized by their TOF and their overpotential (η) as separate parameters but rather that the parameters are linked together by a definite relationship. The log TOF-η relationship can often be linearized, giving rise to a Tafel law, which allows the characterization of the catalyst by the value of the TOF at zero overpotential (TOF(0)). Foot-of-the-wave analysis of the cyclic voltammetric catalytic responses allows the determination of the TOF, log TOF-η relationship, and TOF(0), regardless of the side-phenomena that interfere at high current densities, preventing the expected catalytic current plateau from being reached. Strategies for optimized preparative-scale electrolyses may then be devised on these bases. The validity of this methodology is established on theoretical grounds and checked experimentally with examples taken from the catalytic reduction of CO(2) by iron(0) porphyrins.     

Nonmetals in the argon-inductively coupled plasma-optical emission spectrometry: I. Phosphorus, sulfur and carbon

The behavior of phosphorus, sulfur and carbon in the argon-ICP-OES was systematically investigated for a wide range of nebulizer gas flows and observation heights. Five lines of phosphorus, four lines of sulfur and three lines of carbon, which have analytical usable detection limits, were taken into consideration. The further parameter set was inspired by the needs of every-day-analysis in the laboratory, especially the low integration time that is necessary for analysis of large amounts of samples. For each element line a signal-to-noise plot was obtained with a method described earlier. The optimum conditions for the combined analysis were determined from signal-to-noise plots of those element lines with the lowest detection limits. The lowest detection limits for phosphorus (0.13 mg/L) and carbon (0.01 mg/L) are useful for solving many analytical problems. However, even the best detection limit for sulfur (2.97 mg/L) is only of limited use without further preconcentration. A major problem was the background of carbon, most probably from carbon dioxide, which increased the available detection limit to about 0.04 mg/L. Surprisingly, the best detection limits were obtained at very low observation heights, which were only a couple of millimeters above the load coil. Fortunately, all elements showed a similar behavior and so the detection limits at compromise conditions were only slightly higher compared with the single-element detection limits.