First Order In Substrate Research Articles

Catalytic role of the enol ether intermediate in the intramolecular Stetter reaction: a computational perspective.

The intramolecular Stetter reaction catalyzed by a carbene is investigated by density functional theory (DFT) calculations and kinetic simulations. Catalyst 1 first reacts with aldehyde 2 to give the primary adduct (PA). The PA undergoes the intramolecular oxa-Michael reaction to irreversibly generate enol ether intermediate 9. The conversion of the enol ether to the Breslow intermediate (BI) requires the assistance of a base such as the PA. The next step involves formation of a carbon-carbon bond through the Michael addition, and expulsion of the catalyst generates the Stetter product 7. Calculations show that the catalytic cycle is composed of two irreversible processes: the first one involves the exergonic formation of the enol ether intermediate, while the second one is the conversion of the enol ether to the final product. Kinetic simulations using initial concentrations of [1]0 = 0.005 M and [2]0 = 0.025 M demonstrate that under a steady-state condition, 35% of the catalyst rests on the state of the enol ether (0.0018 M). The catalyst resting state therefore consists of the unbound form (the free catalyst) and its bound form (the enol ether species). According to variable time normalization analysis, the reaction exhibits a second-order dependence (first order in catalyst and first order in substrate), which agrees with experiments. The oxa-Michael reaction to form the enol ether is identified to be turnover limiting in the intramolecular Stetter reaction, which rationalizes the observed electronic effect of the Michael acceptor on the reactivity, as well as the measured isotope effect with respect to the aldehydic proton/deuteron. The base that participates in the BI formation has a significant effect on the build-up of the resting state 9 and the active catalyst concentration. In addition, the thermodynamic stability of the enol ether is found to depend on the tether length between the aromatic aldehyde and the Michael acceptor, as well as the chemical nature of the carbene catalyst. The favorability for the oxa-Michael reaction is therefore suggested to govern the reactivity of the intramolecular Stetter transformation.

Mechanistic Studies of Alkene Isomerization Catalyzed by CCC-Pincer Complexes of Iridium

Iridium complexes containing CCC-pincer m-phenylene-bridged N-heterocyclic carbene ligands were examined as catalysts for alkene isomerization. Complexes containing either mesityl or adamantyl side groups were found to catalyze the isomerization of a number of alkenes to the internal isomers, including 1-octene, vinylcyclohexane, and allylbenzene. Mechanistic studies indicate a surprising dichotomy, apparently caused by ligand steric effects. For the mesityl-substituted catalyst, several lines of evidence provide strong support for isomerization via an iridium allyl hydride intermediate: (1) H–D crossover experiments indicate that 1,3-hydrogen migration is exclusively intramolecular, (2) the catalyst resting state, a π-allyl hydride species, was isolated and serves as a kinetically competent catalyst, (3) NMR experiments indicate that the π-allyl hydride resting state undergoes reversible C–H reductive elimination that is rapid relative to catalytic turnover, and (4) kinetic studies indicate that the isomerization reaction is first order in substrate and catalyst, consistent with turnover-limiting ligand substitution. H–D crossover experiments for alkene isomerization catalyzed by the adamantyl-substituted complex show selectivity for a 1,3-deuterium shift, as well as the intermolecular transfer of hydrogen. These results are consistent with an insertion/elimination mechanism proceeding selectively through a secondary metal–alkyl or with a π-allyl-type mechanism with an unknown pathway for intermolecular hydrogen crossover.

Testing alternative kinetic models for utilization of crystalline cellulose (Avicel) by batch cultures of Clostridium thermocellum

Descriptive kinetics of batch cellulose (Avicel) and cellobiose fermentation by Clostridium thermocellum were examined with residual substrate and biosynthate concentrations inferred based on elemental analysis. Biosynthate was formed in constant proportion to substrate consumption until substrate was exhausted for cellobiose fermentation, and until near the point of substrate exhaustion for cellulose fermentation. Cell yields (g pellet biosynthate carbon/g substrate carbon) of 0.214 and 0.200 were obtained for cellulose and cellobiose, respectively. For cellulose fermentation a sigmoidal curve fit was applied to substrate and biosynthate concentrations over time, which was then differentiated to calculate instantaneous rates of growth and substrate consumption. Three models were tested to describe the kinetics of Avicel utilization by C. thermocellum: (A) first order in cells, (B) first order in substrate, and (C) first order in cells and substrate, and second order overall. Models (A) and (B) have been proposed in the literature to describe cultures of cellulolytic microorganisms, whereas model (C) has not. Of the three models tested, model (c) provided by far the best fit to batch culture data. A second order rate constant equal to 0.735 L g C(-1) h(-1) was found for utilization of Avicel by C. thermocellum. Adding an endogenous metabolism term improved the descriptive quality of the model as substrate exhaustion was approached. Such rate constants may in the future find utility for describing and comparing cellulose fermentation involving other microbes and other substrates.

Anisole hydrolysis in high temperature water

We investigated the hydrolysis of anisole to phenol in high-temperature water with and without water-tolerant Lewis acid catalysis. With no catalyst present, anisole hydrolyzes to phenol in 97% yield after 24 hours at 365 °C, our experimentally determined optimal temperature and time. Experiments with varied water density and analysis of comparable literature data suggest that anisole hydrolysis is almost third order in water, when the S(N)2 mechanism dominates. Of the water-tolerant Lewis acid catalysts studied, In(OTf)(3) offered the best phenol yield. Anisole hydrolysis was first order in catalyst and first order in substrate. Introducing In(OTf)(3) catalysis lowered the activation energy for anisole hydrolysis to 31 ± 1 kcal mol(-1). Anisole hydrolysis in high-temperature water with In(OTf)(3) catalysis is competitive with other techniques in the literature based on rate and yield. In the presence of 5 mol% In(OTf)(3) catalyst, anisole hydrolyzes to phenol in 97% yield after 90 minutes at 300 °C.

Evidence for the Existence of Terminal Scandium Imidos: Mechanistic Studies Involving Imido–Scandium Bond Formation and C–H Activation Reactions

The anilide-methyl complex (PNP)Sc(NH[DIPP])(CH(3)) (1) [PNP(-) = bis(2-diisopropylphosphino-4-tolyl)amide, DIPP = 2,6-diisopropylphenyl] eliminates methane (k(avg) = 5.13 × 10(-4) M(-1) s(-1) at 50 °C) in the presence of pyridine to generate the transient scandium imido (PNP)Sc═N[DIPP](NC(5)H(5)) (A-py), which rapidly activates the C-H bond of pyridine in 1,2-addition fashion to form the stable pyridyl complex (PNP)Sc(NH[DIPP])(η(2)-NC(5)H(4)) (2). Mechanistic studies suggest the C-H activation process to be second order overall: first order in scandium and first order in substrate (pyridine). Pyridine binding precedes elimination of methane, and α-hydrogen abstraction is overall-rate-determining [the kinetic isotope effect (KIE) for 1-d(1) conversion to 2 was 5.37(6) at 35 °C and 4.9(14) at 50 °C] with activation parameters ΔH(‡) = 17.9(9) kcal/mol and ΔS(‡) = -18(3) cal/(mol K), consistent with an associative-type mechanism. No KIE or exchange with the anilide proton was observed when 1-d(3) was treated with pyridine or thermolyzed at 35 or 50 °C. The post-rate-determining step, C-H bond activation of pyridine, revealed a primary KIE of 1.1(2) at 35 °C for the intermolecular C-H activation reaction in pyridine versus pyridine-d(5). Complex 2 equilibrated back to the imide A-py slowly, as the isotopomer (PNP)Sc(ND[DIPP])(η(2)-NC(5)H(4)) (2-d(1)) converted to (PNP)Sc(NH[DIPP])(η(2)-NC(5)H(3)D) over 9 days at 60 °C. Molecular orbital analysis of A-py suggested that this species possesses a fairly linear scandium imido motif (169.7°) with a very short Sc-N distance of 1.84 Å. Substituted pyridines can also be activated, with the rates of C-H activation depending on both the steric and electronic properties of the substrate.

ChemInform Abstract: Reactions of Carbonyl Compounds in Basic Solutions. Part 14. The Alkaline Hydrolysis of Substituted N-Methylformanilides, N- Methylacetanilides, 1-Phenylazetidin-2-ones, 1-Phenyl-2-pyrrolidones, and 1-Phenyl-2-piperidones.

The rate coefficients for the alkaline hydrolysis of a series of substituted 1-phenylazetidin-2-ones, -2-pyrrolidones, and -2-piperidones, and N-methylacetanilides and N-methylformanilides in aqueous dimethyl sulphoxide and in aqueous dioxane or water have been measured at several temperatures. The reactions were first order in substrate and, for the lactams and acetanilides, first order in base and, for the formanilides, both first and second order in base. Hammett reaction constants and activation parameters have been evaluated for each system. The relative reactivity, salt, solvent and solvent isotope effects have been examined. The following mechanisms for the reactions are suggested. For the β-lactams, the pathway appears to be the rate-determining attack by hydroxide and, for the γ- and δ-lactams and acetanilides, rate-determining fission of the carbon–nitrogen link, which follows equilibrium addition of the base. The formanilides appear to form a tetrahedral intermediate with hydroxide which can collapse to product via rate-determining water- or base-catalysis.

Hydrogenation of fast pyrolyis oil and model compounds in a two-phase aqueous organic system using homogeneous ruthenium catalysts

The use of homogeneous ruthenium catalysts to hydrogenate the water-soluble fraction of pyrolysis oil is reported. Pyrolysis oil, which is obtained by fast pyrolysis of lignocellulosic biomass at 450–600 °C, contains significant amounts of aldehydes and ketones (e.g. 1-hydroxy-2-propanone ( 1) and 1-hydroxy-2-ethanal ( 2)), that are known to have a negative effect on the product properties (a.o. storage stability) of pyrolysis oil. The hydrogenation experiments were performed at mild conditions (40 bar, 90 °C) using a biphasic system (water/toluene) and RuCl 2(PPh 3) 3 as the toluene soluble catalyst. Significant reductions in the amounts of ( 1) and ( 2) were observed, demonstrating the potential of homogeneous Ru-catalysts to upgrade pyrolysis oils. Model studies showed that ( 1) and ( 2) are selectively hydrogenated to 1,2-propanediol and 1,2-ethanediol, respectively. The influence of the temperature (50–90 °C), pressure (20–40 bar) and initial substrate concentration on the reaction rates were investigated. For ( 2), the reaction was shown to be first order in substrate and zero order in hydrogen. An overall kinetic model for the hydrogenation of ( 2) was developed including the rate of active catalyst formation and the kinetic parameters were determined.

Remarkably Efficient Hydrolysis of Methylparathion Catalyzed by [2-(2-Pyridyl)phenyl-C,N]palladium(II) Complexes

The reaction of the palladium(II) acetate derivative [Pd(NwedgeC)(OAc)]2 (NwedgeC = (NC5H4-2-C6H4(C2,N) or (2-(2-pyridyl)-phenyl-C,N)) with methylparathion and water in THF leads to the formation of [Pd(NwedgeC)(mu-SP(=O)(OCH3)2)]2 (1), which reacts with PPh3 in THF to afford mononuclear complex [Pd(NwedgeC)(SP(=O)(OCH3)2)(PPh3)] (2). Compounds 1 and 2 have been characterized by 1H, 13C, and 31P NMR spectroscopy; elemental analysis; and single-crystal X-ray diffraction. When dissolved in water, 1 serves as a precatalyst for the hydrolysis of methylparathion. Kinetic and spectroscopic studies suggest that compound 1 dissociates in aqueous solution to afford cationic diaqua complex [Pd(NwedgeC)(OH2)2]+ (A). At basic pH, A is converted into its deprotonated form [Pd(NwedgeC)(OH2)(OH)] (B), which dimerizes to afford a dinuclear complex, presumably [Pd(NwedgeC)(mu-OH)]2 (C). At pH 7, the reaction is first order in substrate and first order in palladium catalyst A, with k2 = 146 +/- 9 M(-1) s(-1) at 303 K. At more-basic pH, the reaction rate increases and shows an apparent half-order dependence in palladium catalyst. These observations suggest that the active form of the catalyst at basic pH is B, whose concentration is controlled by an equilibrium with inactive C. Analysis of the data obtained at pH 9 yields a dimer formation constant K(f) = [C]/[B]2 = (6.6 +/- 5.6) x 10(6) M(-1) and a second-order rate constant k2 of (8.6 +/- 3.6) x 10(3) M(-1) s(-1) at 298 K. The pH dependence of the reaction rate as well as a spectroscopic titration indicates that the pKa of A is in the 9.5-9.7 range. Determination of the activation parameters at both pH 7 and 9 suggests that catalysis occurs via an associative mechanism whose rate-determining step involves the substitution of a water ligand of A by a molecule of methylparathion at neutral pH and nucleophilic attack of the phosphorus center of methylparathion by a hydroxide ligand of B at basic pH.

Aqueous Reductive Dechlorination of Chlorinated Ethylenes with Tetrakis(4-carboxyphenyl)porphyrin Cobalt

The catalytic dechlorination of chlorinated ethylenes by 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin cobalt ((TCPP)Co), a cobalt complex structurally similar to vitamin B12, was studied. It was found to have superior aqueous-phase dechlorination activity on chlorinated ethylenes (CEs) relative to vitamin B12. Bimolecular rate constants for the degradation of CEs by (TCPP)Co of 250, 24, 0.24, and 1.5 M(-1) s(-1) were found for perchloroethylene (PCE), trichloroethylene (TCE), cis-dichloroethylene (cDCE), and trans-dichloroethylene (tDCE), respectively. Through kinetic analysis, the rate laws for PCE and TCE were determined to be first order in substrate and catalyst, and PCE degradation was shown to be sensitive to the concentration of the titanium citrate bulk reductant and pH. The importance of the Co(I) oxidation state on dehalogenation was studied with UV-vis absorbance spectroscopy, a variety of reducing agents, and cyclic voltammetry. Evidence of chlorovinyl complexes as potential catalytic cycle intermediates was obtained through the preparation of (TPP)Co(trans-C2H2Cl) and the observation of (TPP)Co(C2HCl2) and (TCPP)Co(C2HCl2) by mass spectrometry. The X-ray crystal structure of (TPP)Co(trans-C2H2Cl) is reported.

Scope, mechanism and diene inhibition of isomerization of allylic alcohols to saturated ketones catalyzed by ruthenium(II)-cyclopentadienyl complexes

The isomerization of 3-buten-2-ol to butanone catalyzed by Ru(II)Cp-complexes (Cp = η 5-cyclopentadienyl) with phosphine and amine ligands is described. The reaction catalyzed by [RuCp(MeCN) 3](PF 6) and two equivalents of triphenylphospine is first order in substrate with a k ini of 0.43 h −1 and an initial TOF of 13,000 h −1. The catalyst precursor complex [RuClCp(dppb)] (dppb = bis(diphenylphosphino)butane) has been characterized by X-ray diffraction. This compound features a seven-membered ring incorporating the ruthenium centre and the dppb ligand. Combination of two equivalents of primary, secondary or tertiary amines and [RuCp(MeCN) 3](PF 6) results in active catalyst precursors. Within each group, increasing the bulk of the ligand gives lower isomerization rates. The combined effects of optimal p K a, nucleophilicity and steric bulk make RuCp-complexes with secondary amines the most active precursors. With di- n-butylamine, 745 turnovers can be reached after 1 h. 31P NMR spectra indicate that the resting state in the catalytic cycle is a complex in which 3-buten-2-ol is η 2-coordinated through the alkene moiety. This implies that coordination of the oxygen moiety and concomitant β-hydrogen abstraction is the rate-limiting step. A counterintuitive result is that allylic alcohols bind stronger to RuCp complexes with phosphine ligands than dienes. Inhibition of the catalyst appears to be a result of interaction of the diene with a ruthenium–allyl alcohol complex, which is sufficiently strong to prevent coordination of the oxygen moiety of the allylic alcohol. This hinders orientation of the allylic alcohol substrate in a suitable way to undergo β-hydrogen abstraction, thereby blocking isomerization catalysis.

Chemoselective Electrophilic Oxidation of Heteroatoms by Hydroperoxy Sultams.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Chemoselective electrophilic oxidation of heteroatoms by hydroperoxy sultams.

The synthesis of novel hydroperoxy sultams 1b-d and their potential as renewable chemoselective electrophilic oxidants for a wide range of nitrogen, sulfur, and phosphorus heteroatoms in nonaqueous media is described. Reactions of 1b,c with secondary amines 10f,g yielded the hydroxysultams 2b,c and nitrone 11f or radical 11g depending on the substrate and stoichiometry, while tertiary amines 10a-d gave amine oxides 11a-d. Compounds 1c,d oxidized various thioethers 12a-g to sulfoxides 13a-g smoothly that were isolated by chromatography in nearly quantitative yields. 1c was regenerated from 2c by treatment of the latter with acidified H2O2. Kinetic studies of the reaction of 1c with 1,4-thioxane 12f suggest that the reaction follows the second-order kinetics, first order in substrate and first order in oxidant with the second-order rate constant several orders of magnitude larger than that of the corresponding reaction with hydrogen peroxide and tert-butyl hydroperoxide without the need for any acid or heavy metal catalysts. The phosphines 14a,b were also oxidized by 1c to the respective phosphine oxides 15a,b readily in quantitative yields. The reactions may be conducted at ambient temperature or lower and appear to proceed via a nonradical mechanism. Reactions are sensitive to steric as well as electronic factors.

Kinetics, Substrate Selectivity, and Activation Parameters for the Reaction of Methylbenzenes with Hydroxymethyl Cations in Sulfuric Acid Solutions

The kinetics of the hydroxymethylation of benzene and methylbenzenes in a formaldehyde–sulfuric acid (52.5 wt.%) system in the temperature range 14-90 °C has been studied. With [ArH] ≪ [CH2O] the reaction is first order in substrate and less than first order in formaldehyde. The substrate selectivity, entropy and enthalpy of activation in the series of arenes studied correlate with the basicity of ArH. A reaction mechanism is proposed which includes the rapid equilibrium formation of a charge transfer complex between ArH and CH2OH+ and a slow stage in which it is converted to a σ-complex.

Selective Oxidation of Thioether Mustard (HD) Analogs bytert-Butylhydroperoxide Catalyzed by H5PV2Mo10O40Supported on Porous Carbon Materials

The polyoxometalate H5PV2Mo10O40(1) supported on porous carbons forms selective and recoverable heterogeneous catalysts for the rapid room temperature oxidation of thioether mustard (HD) analogs. Both selectivities (95 to 99% for sulfoxide) and rates (∼20%) vary with the carbon support at parity of all other parameters. A 99% selectivity for the sulfoxide product, even at 75% conversion of the thioether substrate, is seen for the most selective system, 10 wt% 1 on Rohm and Haas Ambersorb (1/Ambersorb). Washing for 125 h in the solvent for catalysis, toluene, results in no significant loss in catalytic activity and a recovery and reusability study at high turnover also indicates that the catalysts are very stable. The polyoxometalate/carbon catalysts can be reactivated between uses by heating to ∼80°C. The oxidation of tetrahydrothiophene (THT) to THTO bytert-butylhydroperoxide (TBHP) catalyzed by 1/Ambersorb is first order in substrate and oxidant and proportional to the concentration of active sites on the 1/Ambersorb. The activation parameters for the process are ΔH‡=11.4±0.05 kcal/mol and ΔS‡=−38.8±0.22 cal/K mol.

Direct and indirect oxidations by peroxynitrite, neither involving the hydroxyl radical

A new mechanism (Mechanism III) that combines features of mechanisms suggested earlier (Goldstein and Czapski, Inorg. Chem. 34:4041–4048; 1995; Pryor, Jin, and Squadrito Proc. Natl. Acad. Sci. USA 91:11173–11177; 1994) is proposed for oxidations by peroxynitrite. In Mechanism III, oxidations by peroxynitrite can take place either directly by ground-state peroxynitrous acid, ONOOH, or indirectly by ONOOH∗, where ONOOH∗ is an activated form of peroxynitrous acid. In the direct oxidation pathway the reaction is first order in peroxynitrite and first order in substrate, and the oxidation yield approaches 100%. In the indirect oxidation pathway the reaction is first order in peroxynitrite and zero order in substrate. In the presence of sufficient concentrations of a substrate that reacts by the indirect oxidation pathway, about 50–60% of the ONOOH directly isomerizes to nitric acid, and about 40–50% of the ONOOH is converted into ONOOH*. Thus, the oxidation yields by the indirect pathway will not exceed 40–50%, and there will always be a residual yield of nitrate even in the presence of very high concentrations of the substrate. Competitive inhibition studies with various free radical scavengers showed that in some cases these scavengers have no effect on oxidation yields. In others, only partial inhibition was observed, far less than that predicted from to the known rate constants for the reactions of these scavengers with the hydroxyl radical. There are some cases where the extent of inhibition correlates well with the known rate constants of the reactions of these scavengers with hydroxyl radical; nevertheless, even in these cases, the involvement of hydroxyl radicals in indirect oxidations by peroxynitrite is ruled out on the basis of kinetics and oxidation yields. Thus, direct oxidations by peroxynitrite are explained in terms of ONOOH, and indirect oxidations in terms of ONOOH∗, and substrates can react by one or both of these pathways.

The Encapsulation of Squid Diisopropylphosphorofluoridate-Hydrolyzing Enzyme within Mouse Erythrocytes

The Encapsulation of Squid Diisopropylphosphorofluoridate-hydrolyzing Enzyme within Mouse Erythrocytes. McGuinn, W. D., Cannon, E. P., Chui, C. T., Pei, L., Petrikovics, I., and Way, J. L. (1993). Fundam. Appl. Toxicol. 21, 38-43.This study describes the entrapment of squid-type diisopropylphosphorofluoridate-hydrolyzing enzyme (DFPase) within mouse red blood cells. These erythrocytes thereby gain the ability to rapidly hydrolyze alkylphosphate cholinesterase (ChE) inhibitors such as diisopropyl fluorophosphate (DFP). DFPase rapidly hydrolyzes DFP to diisopropyl phosphate. Resealed erythrocytes provide a stable carrier system that can preserve the activity of encapsulated enzymes against otherwise rapid in vivo degradation; thus, ChE inhibitors can be degraded to relatively nontoxic metabolites by these erythrocyte carriers. Squid DFPase was purified from the hepatopancreas of Atlantic squid and DFPase activity was determined by measuring changes in fluoride ion concentration using a fluoride ion selective electrode. Mouse erythrocytes in suspension with excess squid DFPase were dialyzed against hypotonic buffer to allow the encapsulation of the enzyme to occur. Cells were then resealed by returning the suspension to isosmotic with saline. Rate of DFP hydrolysis observed with these cells was much greater that the rate of nonenzymatic hydrolysis and was directly proportional to the amount of the erythrocyte suspension added to the assay solution. The rate of hydrolysis was first order in substrate. Erythrocyte controls showed no endogenous DFPase activity. These results suggest that enzyme entrapment may be developed as a method to prevent and antagonize organophosphate poisoning.

Reactions in strongly basic media. Part 10. Base-catalysed isomerisation of Z- to E-substituted chalcones

The rate coefficients for the methoxide-catalysed isomerisation of substituted (Z)-chalcones have been measured in methanolic dimethyl sulphoxide (DMSO) at 30.0 °C, as well as for (Z)-chalcone at several temperatures. The reactions are first order in substrate and base. Further, log k1 for the reaction of (Z)-chalcone and (Z)-4-nitrochalcone correlate with an acidity function, HR–, having slopes equal to 0.53 and 0.45, respectively. The effect of substitution has been assessed using the Hammett equation, with ρ equal to 1.99 for the β-phenyl group and 1.93 for the benzoyl group. For the (Z)-chalcone, the enthalpy and entropy of activation are 14.2 kcal mol–1 and –14 cal mol–1 K–1, respectively, and the kinetic solvent isotope effect, k2MeOD/k2MeOH, is ca. 2.0. The rate coefficients for the amine-catalysed isomerisation of (Z)-chalcone and (Z)-4-nitrochalcone in DMSO have been measured at 30.0 °C. The amino bases are a series of secondary aliphatic amines and the Bronsted coefficients, β, are given as 0.39 and 0.38, respectively. The isomerisation is considered to proceed by rate-determining attack of the base at the β-carbon of the (Z)-chalcone to form a carbanion. The ‘cis’-conformer of the carbanion then rotates to form the ‘trans’-conformer, which eliminates the base to give the (E)-chalcone.

Mechanism of asymmetric epoxidation. 1. Kinetics

The rate of titanium-tartrate-catalyzed asymmetric epoxidation of allylic alcohols is shown to be first order in substrate and oxidant, and inverse second order in inhibitor alcohol, under pseudo-first-order conditions in catalyst. The rate is slowed by substitution of electron-withdrawing substituents on the olefin and varies slightly with solvent, CH 2 Cl 2 being the solvent of choice. Assymetric induction suffers when the size of the alkyl hydroperoxide is reduced. Kinetic resolution of secondary allylic alcohols is shown to be sensitive to the size of the tartrate ester group and insensitive to the steric nature of inhibitor alcohol. Most importantly, the species containing equimolar amounts to Ti and tartrate is shown to be the most active catalyst in the reaction mixture, mediating reaction at much faster rates than titanium tetraalkoxide alone

Structure–activity relations. Part 6. The alkaline hydrolysis of 3-methyl-5-methylidene- and 3,5-dimethylthiazolidine-2,4-diones. The addition of thiols to 3-methyl-5-methylidenethiazolidine-2,4-dione

The rate-coefficients for the alkaline hydrolysis of 3-methyl-5-methylidene- and 3,5-dimethyl-thiazolidine-2,4-diones in water at 25.0 °C have been measured. The reaction of the 5-methylidene substrate is first order in both substrate and hydroxide ion. The reaction of the 5-methyl substrate is two-phase. The first and more rapid reaction of this substrate is 1.4 times faster than the only observed reaction of the former substrate. The second reaction is the hydrolysis of an intermediate, which is first order in substrate and has two components, one first and the other second order in hydroxide ion. The rate coefficients for the addition of a series of thiols to the 5-methylidene substrate in water at pH 7.40 have been measured. A Brønsted coefficient of ca. 0.37 has been found. The detailed reaction pathway and relation to Marcus and related theories are discussed.

Reactions of carbonyl compounds in basic solutions. Part 14. The alkaline hydrolysis of substituted N-methylformanilides, N-methylacetanilides, 1-phenylazetidin-2-ones, 1-phenyl-2-pyrrolidones, and 1-phenyl-2-piperidones

The rate coefficients for the alkaline hydrolysis of a series of substituted 1-phenylazetidin-2-ones, -2-pyrrolidones, and -2-piperidones, and N-methylacetanilides and N-methylformanilides in aqueous dimethyl sulphoxide and in aqueous dioxane or water have been measured at several temperatures. The reactions were first order in substrate and, for the lactams and acetanilides, first order in base and, for the formanilides, both first and second order in base. Hammett reaction constants and activation parameters have been evaluated for each system. The relative reactivity, salt, solvent and solvent isotope effects have been examined. The following mechanisms for the reactions are suggested. For the β-lactams, the pathway appears to be the rate-determining attack by hydroxide and, for the γ- and δ-lactams and acetanilides, rate-determining fission of the carbon–nitrogen link, which follows equilibrium addition of the base. The formanilides appear to form a tetrahedral intermediate with hydroxide which can collapse to product via rate-determining water- or base-catalysis.