| 1. |
- Foreman, Mark, 1973, et al.
(författare)
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PREPARATION AND X-RAY STRUCTURE OF A NEW ORGANO-P-O-S HETEROCYCLE
- 1995
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Ingår i: Chemical Communications. ; :21, s. 2217-2218
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Tidskriftsartikel (refereegranskat)abstract
- Reaction of 1,3-epithio-1 lambda(5),3 lambda(5)-naphtho[1,8-cd][1,2,6]thiadiphohosphinine-1,3-dithione 5 with 3,5-di-tert-butylcatechol gives 3,5-di-tert-butyl-1,8-epithio-1 lambda(5),8 lambda(5)-naphtho[1,8 -cd][1,7,2,6]benzodioxadiphosphonine-1,8-dithione 7 which, from X-ray studies, contains fused C3P2S and C2O2P2S rings.
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| 2. |
- Foreman, Mark, 1973, et al.
(författare)
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The preparation of a solubilized form of Lawessons reagent and its thionation reactions
- 1999
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Ingår i: Heteroatom Chemistry. - 1098-1071 .- 1042-7163. ; 10:7, s. 651-657
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Tidskriftsartikel (refereegranskat)abstract
- 2-tert-Butylanisole and P4S10 react together to give 2,4-bis (3-tbutyl-4-methoxyphenyl) 1,3, 2, 4-dithiadiphosphetane 2, 4-disulfide (LR*) which was characterized by X-ray crystallography. Comparative thionation reactions of LR* and a range of P-S compounds were investigated. If was found that LR* in many cases, gives better yields of thionated complexes than Lawessons Reagent when the reactions are performed at room temperature. (C) 1999 John Wiley & Sons, Inc.
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| 3. |
- Kraka, Elfi, et al.
(författare)
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Trimesitylsilylium cation verification of a free silylium cation in solution by NMR chemical shift calculations
- 1997
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Ingår i: Chemical Physics Letters. - 0009-2614. ; 279, s. 9-16
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Tidskriftsartikel (refereegranskat)abstract
- NMR chemical shift calculations at the SOS-DFPT/PW91/[7s6p2d/5s4p1d/3s]//B3LYP/6-31G(d) level of theory were used to describe the trimesitylsilylium cation 1, recently synthesized in benzene solution and investigated by NMR spectroscopy. The conformation of cation 1 is characterized by mesityl rings rotated by 47° in a propeller-like form. Contrary to other silylium cations investigated, cation 1 forms a weak Van der Waals complex 3 with benzene rather than a Wheland σ-complex. The calculated 29 Si NMR chemical shifts for 1 and 3 are 226 and 227 ppm, compared to the experimental value of 225.5 ppm. The agreement between calculated and measured NMR chemical shifts provides evidence that cation 1 presents the first free silylium cation synthesized. © 1997 Elsevier Science B.V.
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| 4. |
- Shi, Tiesheng, et al.
(författare)
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Equilibrium and High-Pressure Kinetic Study of Formation and Proton-Assisted Aquation of Monodentate Acetate, Propionate, and Glycolate Complexes of Palladium(II) in Aqueous Solution
- 1996
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 1996:35, s. 735-740
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Tidskriftsartikel (refereegranskat)abstract
- SynopsisReversible formation and proton-assisted aquation of 1:1 monodentate carboxylate complexes of palladium(II) takes place via a transition state stabilized by hydrogen bonding in an activation process strongly dominated by bond making. Volume profiles have been established through high-pressure kinetic measurements.AbstractKinetics and equilibria for reversible formation of 1:1 monodentate complexes between Pd(H2O)42+ and acetic, propionic, and glycolic acid (RCOOH) according to the equation Pd(H2O)42+ + RCOOH ⇌ Pd(H2O)3OOCR+ + H3O+ (k1, k-1) have been studied as a function of temperature and pressure in an aqueous medium with 0.60 ≤ [H+] ≤ 1.00 M, [RCOOH]/[H+] ≤ 1.0, and ionic strength 1.00 M. Stability constants β1 for the formation of acetate, propionate, and glycolate complexes are (2.19 ± 0.09) × 104, (2.10 ± 0.24) × 104, and (6.4 ± 0.1) × 103 M-1, repectively, at 25 °C and for a 1.00 M perchlorate medium. The rate expression, kobsd = k1[RCOOH] + k-1[H+], indicates that reaction between palladium and carboxylate anions is negligible under the experimental conditions used. Values for k1/M-1 s-1, k-1/M-1 s-1, ΔH1⧧/kJ mol-1, ΔH-1⧧/kJ mol-1, ΔS1⧧/J K-1 mol-1, ΔS-1⧧/J K-1 mol-1, ΔV1⧧/cm3 mol-1, and ΔV-1⧧/cm3 mol-1 at 25.0 °C are 19.3 ± 0.6, 32.8 ± 0.2, 52.5 ± 0.4, 57.5 ± 0.4, −44 ± 1, −23 ± 1, −8.1 ± 0.3, and −1.7 ± 0.2 for acetic acid; 12.0 ± 1.1, 26.4 ± 0.3, 55.3 ± 0.6, 56.8 ± 0.3, −32 ± 2, −34 ± 1, −8.9 ± 0.8, and −1.7 ± 0.2 for propionic acid; and 21.1 ± 0.3, 13.7 ± 0.1, 53.6 ± 0.4, 59.2 ± 0.6, −40 ± 1, −25 ± 2, −3.4 ± 0.2, and −2.3 ± 0.2 for glycolic acid. There is no relation between formation rate constants and pKa for these carboxylic acids. The nucleophilic properties of the carboxylic acids toward palladium(II) are similar to those of water molecules. A trigonal bipyramidal transition state stabilized by hydrogen bonding between the entering carboxylic acid and the leaving aqua ligand or (equivalent) between the entering oxonium ion and the leaving carboxylate ligand is suggested. Negative entropies, volumes of activation, and volume profiles support a strong contribution from bond making in the activation process.
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| 5. |
- Shi, Tiesheng, et al.
(författare)
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Linear Free Energy Relationships for Complex Formation Reactions between Carboxylic Acids and Palladium(II). Equilibrium and High-Pressure Kinetics Study
- 1997
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 36:4, s. 528-536
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Tidskriftsartikel (refereegranskat)abstract
- SynopsisLinear free energy relationships based on equilibrium and kinetics measurements, including variable-temperature and high-pressure data, for complex formation reactions and aquations of square-planar palladium(II) complexes are derived and discussed. In particular, data for an extensive series of carboxylic acids of widely different basicities and steric properties, acting as nucleophiles toward Pd(II) have been determined.AbstractAbstract ImageKinetics for complex formation between Pd(H2O)42+ and formic, butyric, dl-lactic, 2-methyllactic, methoxyacetic, malonic, succinic, oxydiacetic, l-malic, and citric acids has been studied in an aqueous acidic medium by use of variable-temperature and -pressure stopped-flow spectrophotometry. Kinetics traces for reactions between the metal ion and formic, butyric, lactic, 2-methyllactic, methoxyacetic, oxydiacetic, and citric acids can be described by single exponentials, which are assigned to the formation of monodentate complexes: Pd(H2O)42+ + RCOOH ⇌ Pd(H2O)3OOCR+ + H3O+ (k1, k-1). Equilibrium constants K1 for lactic, 2-methyllactic, methoxyacetic, oxydiacetic, and citric acid reactions calculated from spectrophotometric equilibrium measurements and from kinetics (K1 = k1/k-1) are in good agreement. There is a linear correlation between the stability constants β1 of the carboxylato complexes and the first dissociation constants Ka1 of the carboxylic acids as expressed by log β1 = (0.48 ± 0.03)pKa1 + (2.1 ± 0.1). The formation rate constants k1 are insensitive to the basicity and steric properties of the carboxylic acids at 25 °C, due to an excellent isokinetic relationship between ΔH1⧧ and ΔS1⧧ with an isokinetic temperature of 292 K, suggesting also that all of the carboxylic acids react via the same mechanism. Rate constants k-1 are correlated with pKa1 of the entering carboxylic acids according to log k-1 = (0.47 ± 0.06)pKa1 − (0.7 ± 0.2), indicating that the weaker the carboxylic acid, the larger k-1. These facts together with the observation that a weak carboxylic acid is prone to form a strong complex as shown by the correlation between log β1 and pKa1 are interpreted in terms of a proton-assisted reaction mechanism which is further supported by the ionic strength dependence of the rate constant k-1, consistent with a direct attack of an oxonium ion on Pd(H2O)3OOCR+ for the reverse reaction. High-pressure stopped-flow measurements at 25 °C give activation volumes ΔV1⧧ = −4.9 ± 0.2 cm3 mol-1, ΔV-1⧧ = −2.7 ± 0.5 cm3 mol-1 for malonic acid, and ΔV1⧧ = −3.5 ± 0.2 cm3 mol-1, ΔV-1⧧ = −1.9 ± 0.4 cm3 mol-1 for citric acid, respectively. Existing data so far for Pd(H2O)42+ complex formation reactions obey a linear correlation between ΔV1⧧ and partial molar reaction volumes ΔV1° according to ΔV1⧧ = (0.92 ± 0.04)ΔV1° − (2.2 ± 0.2) cm3 mol-1, the slope of 0.92 indicating that bond-making between palladium and the entering ligands largely dominates the formation of the transition state. There are no linear correlations between ΔV1⧧ and partial molar volumes VL of the entering ligands, as has been claimed in previous literature for related reactions, or between ΔV1⧧ and ΔS1⧧.
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| 6. |
- Shi, Tiesheng, et al.
(författare)
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Structure-Reactivity Correlations for Complex Formation Reactions between Square-Planar Metal Centers and Thioethers
- 1996
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 35:20, s. 5941-5947
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Tidskriftsartikel (refereegranskat)abstract
- SynopsisReactivity trends of thioethers toward square-planar complexes can be generally interpreted by use of an equation of the form: log k = γ + α∑σ* + βθ, where k denotes second-order rate constants, ∑σ* the sum of Taft constants for the thioether substituents, and θ the thioether cone angles. γ represents an intrinsic parameter for each substrate complex, while α is an electronic and β a steric parameter. Large variations in both electronic and steric properties of the entering ligands indicate that there is no duality behavior in the reactions of thioethers with square-planar metal centers.AbstractAbstract ImageKinetics for complex formation between Pd(H2O)42+ and thioethers of largely varying electronic and steric properties, viz. MeSCH2COOH, (n-Pr)2S, EtSCH2CH2OH, S(CH2CH2CH2OH)2, S(CH2CH2OH)2, EtSCH2COOH, S(CH2COOH)2, S(CH2CH2COOH)2, (i-Pr)2S, (s-Bu)2S, (t-Bu)2S, and protonated thiomorpholine, S(C2H4)2NH2+, has been studied by use of stopped-flow spectrophotometry in an acidic aqueous medium. Second-order rate constants k1298 are 1.61 × 104, 8.0 × 104, 3.79 × 104, 3.69 × 104, 2.21 × 104, 1.84 × 104, 1.91 × 103, 1.34 × 104, 1.52 × 104, 7.75 × 103, 900, and 5.2 × 103 M-1 s-1, respectively. The reactivity toward Pd(H2O)42+ of all thioethers studied so far can be described as a function of their σ-donor properties as expressed by the sum of the Taft constants, ∑σ*, and their steric requirements as defined by cone angles, θ, by use of the equation: log k1 = (9.9 ± 0.3) − (0.67 ± 0.05)∑σ* − (0.059 ± 0.003)θ. Similarly, second-order rate constants k298 reported previously for reactions between thioethers and Pd(dien)H2O2+ and Pt(dien)Br+ are described by log k298 = (10.5 ± 0.6) − 0.67∑σ* − (0.081 ± 0.006)θ and log k298 = (4.6 ± 0.6) − 0.72∑σ* − (0.080 ± 0.006)θ, respectively. Hence, the reactivity trends of thioethers toward square-planar complexes can be given a general interpretation in terms of intrinsic, electronic, and steric parameters, by use of log k = γ + α∑σ* + βθ. Large variations in both electronic and steric properties of the entering ligands indicate that there is no “duality behavior” in the reactions of thioethers with square-planar metal centers, as claimed in previous literature. No steric threshold is observed for these sterically unhindered systems. There is a rough compensation effect between ΔH1⧧ and ΔS1⧧, i.e. a smaller ΔH1⧧ is usually accompanied by a larger negative ΔS1⧧, indicating that all thioethers react via the same mechanism. It appears that the much lower reactivity observed for the highly branched (t-Bu)2S is primarily caused by a high activation enthalpy. Volumes of activation have been determined for a series of thioethers with a constant cone angle, viz. EtSCH2COOH, S(CH2COOH)2, and S(CH2CH2COOH)2 through high-pressure stopped-flow measurements. Values of ΔV1⧧ are −7.9 ± 0.5, −8.1 ± 0.4, and −7.6 ± 0.3 cm3 mol-1, respectively. These values together with that for Et2S (−8.7 ± 0.1 cm3 mol-1) determined previously shows that variation of electronic properties, steric factors being kept constant, change the reactivity markedly, but have no observable influence on the activation volumes. Stability constants β1 for five palladium thioether complexes derived as the ratio between rate constants for forward and reverse reactions vary between (1.2 ± 0.3) × 104 and (3.2 ± 0.7) × 104 M-1.
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| 7. |
- Witzgall, Peter, et al.
(författare)
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Sex pheromones and attractants in the Eucosmini and Grapholitini (Lepidoptera, Tortricidae)
- 1996
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Ingår i: Chemoecology. - : Springer. - 0937-7409 .- 1423-0445. ; 7:1, s. 13-23
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Tidskriftsartikel (refereegranskat)abstract
- The geometric isomers (E, E)-, (E, Z)-, (Z, E)-, and (Z, Z)-8, 10-dodecadien-1-yl acetate were identified as sex pheromone components or sex attractants in the tribes Eucosmini and Grapholitini of the tortricid subfamily Olethreutinae. Species belonging to the more ancestral Tortricinae were not attracted. Each one isomer was behaviourally active in males of Cydia and Grapholita (Grapholitini), either as main pheromone compound, attraction synergist or attraction inhibitor. Their reciprocal attractive/antagonistic activity in a number of species enables specific communication with these four compounds. Pammene, as well as other Grapholita and Cydia responded to the monoenic 8- or 10-dodecen-1-yl acetates. Of the tribes Olethreutini and Eucosmini, Hedya, Epiblema, Eucosma, and Notocelia trimaculana were also attracted to 8, 10-dodecadien-1-yl acetates, but several other Notocelia to 10, 12-tetradecadien-1-yl acetates. The female sex pheromones of C. fagiglandana, C. pyrivora, C. splendana, Epiblema foenella and Notocelia roborana were identified. (E, E)- and (E, Z)- 8, 10-dodecadien-1-yl acetate are produced via a common E9 desaturation pathway in C. splendana. Calling C. nigricana and C. fagiglandana females are attracted to wingfanning males.
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| 8. |
- Berglund, P., et al.
(författare)
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Alcohols as enantioselective inhibitors in a lipase catalysed esterification of a chiral acyl donor
- 1995
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Ingår i: Biotechnology Letters. - 0141-5492. ; 17:1, s. 55-60
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Tidskriftsartikel (refereegranskat)abstract
- Increased reaction rates and increased enantioselectivities were observed with decreased concentrations of n-alkanols when resolving 2-methyldecanoic acid by esterification catalysed by immobilised lipase from Candida rugosa at controlled water activities in cyclohexane. The enantioselectivity was found to be independent of the water activity in the reaction medium at the n-heptanol concentrations investigated. However, when n-decanol was used as the acyl acceptor, not only the alcohol concentration but also the water activity in the reaction medium, influenced the enantioselectivity. The results obtained showed that the low enantioselectivity seen at a high alcohol concentration could be explained by the alcohol influencing the apparent V(max)(S) and V(max)(R) differently.
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| 9. |
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| 10. |
- Holmberg, Erland, et al.
(författare)
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Reaction conditions for the resolution of 2-methylalkanoic acids in esterification and hydrolysis with lipase from Candida cylindracea
- 1991
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Ingår i: Applied Microbiology and Biotechnology. - 0175-7598. ; 35:5, s. 572-578
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Tidskriftsartikel (refereegranskat)abstract
- We have demonstrated resolution of 2-methylalkanoic acids using lipase from Candida cylindracea as a catalyst. The resolution of 2-methyldecanoic acid was more successful than that of 2-methylbutyric acid both by esterification and hydrolysis. This indicates that the resolution of the acid is dependent on the chain length of the acid moiety. The chain length of the alcohol moiety of the ester affected the resolution of the long-chain acid only. Using esterification, (R)-2-methyldecanoic acid was produced in an enantiomeric excess (e.e.) of 95% (E = 40). If the enantiomeric ratio is low (E = 3.6), as in the resolution of 2-methylbutyric acid, esterification combined with a high equilibrium conversion could be used to yield the remaining acid in a high e.e. In the hydrolytic reactions, the e.e. and the equilibrium conversion were dependent on the pH and the presence of CaCl2. When octyl 2-methyldecanoate was hydrolysed at pH 8.0 in the presence of CaCl2, the (S)-acid was formed with an e.e. of 80% (E = 9), but when the hydrolysis was carried out at pH 7.5 without CaCl2, a very low e.e. and a low equilibrium conversion were observed. The latter conditions allowed the esterification of 2-methyldecanoic acid with 1-octanol even in aqueous medium.
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| 11. |
- Högberg, Hans-Erik, et al.
(författare)
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Biocatalysis as a useful tool in pheromone synthesis. Enantiomerically pure building blocks from baker's yeast reductions and enzyme catalysed resoluti
- 1994
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 22:3, s. 591-606
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Tidskriftsartikel (refereegranskat)abstract
- Biocatalytical methods are presented which provide useful building blocks for pheromone synthesis. Examples of the utility of this approach are the preparation of building blocks for the synthesis of stereochemically pure isomers of pine sawfly pheromones and some other pheromones. Enantiom- erically pure ( 98% ee) 2-methyl-1-alkanols 2 were obtained via baker's yeast reduction of suitable α,β-unsaturated aldehydes, and by using lipases from Pseudomonas to effect resolution by transesterification of suitable racemic precursors to 2-methyl-1-alkanols 2 which gave high enantiomeric ratios E > 100. The resolution by esterification mediated by lipase from Candida rugosa of racemic 2-methylalkanoic acids also gave high enantiomeric ratios E> 100 after having improved the reaction conditions by regulating water activity, by choice of the appropriate complimentary substrate alcohol and by adjusting the initial equivalents of the latter present at the start. Also discussed is the separation of diastereomers of diprionol 1, which is naturally occurring in the pine sawfly Neodiprion sertifer, where it is the direct precursor of its pheromone.
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| 12. |
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| 13. |
- Erlandsson, Lars, et al.
(författare)
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Purification process for trimethylolethane
- 1996
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Patent (övrigt vetenskapligt/konstnärligt)abstract
- A process for combined recovery and purifn. of trimethylolethane from aq. reactions mixts. obtained by reacting formaldehyde with propionic aldehyde in the presence of a metal hydroxide comprises a no. of steps including evapg. the reaction mixt. allowing only trimethylolethane to at least partially crystallize as crude trimethylolethane, evapg. remaining water, heating obtained reaction mixt. and/or obtained crude trimethylolethane, and sublimating trimethylolethane for recovery as purified product
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| 14. |
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| 15. |
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| 16. |
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| 17. |
- Allenmark, Stig, et al.
(författare)
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Inversion barriers in sulfoxide functions studied by enantioselective liquid chromatography and chiroptical methods
- 1997
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Ingår i: Chirality. - : John Wiley & Sons. - 0899-0042 .- 1520-636X. ; 9:5-6, s. 638-642
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Tidskriftsartikel (refereegranskat)abstract
- A series of 2-substituted 1,3,2-benzodithiazole 1-oxides has been synthesized and the compounds resolved into enantiomers by semipreparative enantioselective liquid chromatography. The low enantiomerization barriers have been determined by chiroptical techniques and were found to be relatively independent of the 2-substituent used. The kinetic results are consistent with a pyramidal inversion mechanism and a reduced barrier due to electronic effects, favouring the transition state over the pyramidal ground state. This mechanistic rationale was further supported by data obtained from molecular modelling using AM1 geometry optimization. The absolute configurations have been determined via a comparison of their CD-spectra with those of analogs with previously determined configuration.
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| 18. |
- Allenmark, Stig, et al.
(författare)
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Optically active 1,3,2-benzodithiazole S-oxides : A study of rates of racemization and absolute stereochemistry
- 1996
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Ingår i: Enantiomer (Basel. Print). - : Taylor & Francis. - 1024-2430 .- 1607-8446. ; 1:1, s. 13-22
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Tidskriftsartikel (refereegranskat)abstract
- The optical isomers of the 1-oxide, 1,3-dioxide and 1,1,3-trioxide, respectively, of 2-benzyl-1,3,2-benzodithiazole have been isolated by chiral liquid chromatography. The rate of racemization was found to be much higher for the monooxide as compared to the dioxide or trioxide. A first-order rate constant of 8.65 × 10-5 s-1 was calculated for the racemization of the 1-oxide in acetonitrile at 21°C. This corresponds to rate constants for the forward and reverse reactions in the enantiomerization process of 4.32 × 10-5 s-1 and a Gibbs' free activation energy of only 96.5 kJ mol-1 separating the enantiomers. The absolute configuration at the tricoordinated sulfur atom in the series of oxides was determined via an X-ray crystallographic structure determination of one of the diastereomeric 2-((S)-α-phenyl-ethyl)-1,3,2-benzodithiazole 1,3-dioxides.
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| 19. |
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| 20. |
- Almqvist, Fredrik, et al.
(författare)
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An Improved Procedure for the Synthesis of Bicyclo[2.2.2]octane- 2,6-dione
- 1993
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Ingår i: Synthetic Communications. - : Informa UK Limited. - 0039-7911 .- 1532-2432. ; 23:11, s. 1499-1505
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Tidskriftsartikel (refereegranskat)abstract
- Conjugate addition of Meldrum's acid to 2-cyclohexenone followed by direct cyclization in PPA/acetic acid constitutes a shorter, more reproducible and higher yielding route to bicyclo[2.2.2]octane-2,6-dione than previous methods. The crude dione could be used as substrate for the baker's yeast reduction to (IR, 4S, 6S)-bicyclo[2.2.2]octane-6-ol-2-one.
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| 21. |
- Almqvist, Fredrik, et al.
(författare)
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Neighboring Group Participation in a Regio- and Stereoselective Chlorination of a Bicyclo[2.2.2]octanone
- 1996
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 1520-6904 .- 0022-3263. ; 61:20, s. 6947-6951
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Tidskriftsartikel (refereegranskat)abstract
- The zinc chloride-mediated acetylation of the optically active silyl enol ether 2a gave the beta-diketone 3a (48%) together with the regio- and stereoselectively chlorinated compound 4 (27%). The yield of 4 increased to 70% by starting from the O-acetyl derivative 2c. The chlorination most likely occurs via neighboring group participation by the endo acetoxy group.
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| 22. |
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| 23. |
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| 24. |
- Almqvist, Fredrik, et al.
(författare)
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Synthesis of Optically Active endo, endo Bicyclo[2.2.2]octane-2,5- diol, Bicyclo[2.2.2]octan-2,5-dione and Related Compounds
- 1996
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 1520-6904 .- 0022-3263. ; 61:11, s. 3794-3798
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Tidskriftsartikel (refereegranskat)abstract
- Optically active C-2-symmetric (1S,2S,4S,5S)-bicyclo[2.2.2]octane-2,5-diol ((+)-12; 98% ee) and several selectivity protected optically active intermediates useful for synthetic transformations were synthesized via a 1,2-carbonyl transposition route starting from the easily available optically active (1R,4S,6S)-6-hydroxybicyclo[2.2.2]octan-2-one ((-)-2). The synthetic route also allowed the preparation of optically active (1S,4S)-bicyclo[2.2.2]octane-2,5-dione ((+)-14; 98% ee).
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| 25. |
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