bluuebunny/crossref_metadata_2025_split huggingface dataset:
An NMR study of the thermal decomposition of dimethoxycarbenium bromides
Authors: Dusseau Ch. H. V. , Steinberg H. , de Boer Th. J. 
Published: September 2010

AbstractBromination of the methyl ortho esters 1a‐i in liq. SO2 at −80°C gives rapidly the dimethoxycarbenium bromides 2a‐i together with methyl hypobromite. The aliphatic bromides 2a‐g display two distinct methoxyl NMR absorptions, suggesting a “cis‐trans” configuration. The aromatic bromides 2h‐i show only one methoxyl absorption, which can be explained by assuming the symmetrical “cis‐trans” conformation of the aryldimethoxycarbenium ion.The bromides 1a‐i are stable up to −50°C and are converted into the corresponding methyl ester 5 and methyl bromide 6 at higher temperatures. During the thermal decomposition of 2a‐i line broadening of the methoxyl absorptions are observed, either due to rotation of the methoxyl groups around the C‐O bonds in the dimethoxycarbenium ion D and/or by a rapid equilibrium between ionic and covalent forms D and E.
Chemistry of small‐ring compounds. Part 42. The rearrangement of methyleneaziridinium ions to cyclopropaniminium ions
Authors: Jongejan E. , Steinberg H. , de Boer Th. J. 
Published: September 2010

AbstractA kinetic study in FSO3H/SbF5 reveals that the 1‐methyl‐2‐methyleneaziridinium ion 4 rearranges in a first order reaction to the ring‐opened enammonium ion 6. At temperatures below 80° this process takes place via isomerisation of the methyleneaziridinium ion to an intermediary cyclopropaniminium ion 5. At higher temperatures the direct conversion 4 → 6 ‐ which is negligible in the lower temperature region ‐ must also be taken into account (cf. Scheme 4).1,1‐Dimethyl‐2‐methyleneaziridinium fluorosulfate undergoes a similar heterocyclic ‐ homocyclic ring rearrangement in FSO3H, but higher temperatures (115°) are required.The rearranged product, N,N‐dimethylcyclopropaniminium fluorosulfate is much more stable than the mono‐N‐methyl derivative i.e. it can be heated up to 150° without decomposition. By analogy the methyleneaziridinium → cyclopropaniminium isomerisation is thought to take place via a ring‐opened biradical cationic species rather than via a diamagnetic 2‐(mono‐ or dialkylamino)allyl cation.
Identification of chiral 1,2‐diacylglycerols in fresh milk fat
Authors: Lok C. M. 
Published: September 2010

AbstractTrityl chloride, which is known to attack primary hydroxyl groups selectively, was used for the isolation of 1,2‐diacylglycerols from a mixture of diacylglycerols, hydroxyacylglycerols and sterols obtained from fresh milk. 1,2‐diacyl‐3‐tritylglycerols could be isolated, which were transformed into 1,2‐diacetyl‐3‐tritylglycerol. The stereochemical relation of this compound with respect to model compounds synthesized from serine showed that the predominating enantiomers of the 1,2‐diacylglycerols present in fresh milk have the sn‐1,2‐configuration. This provides additional evidence that these compounds are biosynthetic intermediates rather than lipolysis products.
The thermolysis of tetramethyl‐1,2‐dioxetane in degassed 1,4‐cyclohexadiene. Hydrogen abstraction by excited acetone
Authors: Bartlett Paul D. , Baumstark Alfons L. , Landis Michael E. 
Published: September 2010

AbstractThe thermolysis of tetramethyl‐1,2‐dioxetane (1) in degassed 1,4‐cyclohexadiene affords products attributable to hydrogen abstraction from solvent by excited acetone: benzene + 2‐propanol (.14–.15 moles each per mole 1), 1,4‐dihydrocumyl alcohol (2‐[2,5‐cyclohexadien‐1‐yl]‐2‐propanol) (.05 moles per mole 1), and a small amount of tetrahydrobiphenyls. These products are formed in the same proportions during the irradiation of acetone in degassed 1,4‐cyclohexadiene. The rate and kinetic order of the decomposition of 1 is the same as in air‐saturated solvents, where no acetone reduction products are observed. Comparison of the product yields with the known rate of quenching of acetone triplets by cyclohexadiene leads to the conclusion that at least one‐third of the quenching is of the nonreactive type, accompanying capture of allylic hydrogen from the hydrocarbon. The mechanism of the reaction is discussed, and a comparison is drawn between different radicals and anions in their modes of coupling with the cyclohexadienyl radical.
Formation of a biologically active complex from two complementary fragments of horse heart cytochrome‐c
Authors: Westerhuis L. W. , Tesser G. I. , Nivard R. J. F. 
Published: September 2010

AbstractThis report describes the formation of a non‐covalent complex between two tryptic peptides of horse heart cytochrome‐c. All amino functions of cytochrome‐c were completely protected with the methylsulfonylethyloxycarbonyl (Msc) group. Trypsin split the protected product specifically at Arg38. After separation the fragments were deprotected by a very short treatment with a base.The complex resulting from the deprotected peptides, exhibited a completely developed 695 nm band, and an enhanced oxidase but diminished reductase activity in comparison with native horse heart cytochrome‐c.
Chemical effects of steric strains. Part XXIII. Steric effects as a factor in the stability of addition compounds of amines with 9‐borabicyclo[3.3.1]nonane
Authors: Brown Herbert C. , Wang Kung K. 
Published: September 2010

AbstractAn infrared technique was developed to establish the equilibrium involved in the reaction of 9‐borabicyclo[3.3.1]nonane with representative amines under standard conditions (25.0°C, cyclohexane or THF solution): (9‐BBN)2 + 2 Amine ⇌ 2 9‐BBN: Amine. Coordination is complete with primary amines, even as hindered as tert‐butylamine. It is complete with diethylamine, but incomplete with diisopropylamine. It is incomplete even with the simple triethylamine. However, the cyclic structure corresponding to triethylamine, namely, quinuclidine, forms a stable adduct. Pyridine is fully coordinated, but the extent of coordination decreases with increasing steric requirements of the 2‐alkyl substituent, becoming essentially zero with 2‐tert‐butylpyridine and 2,6‐dimethylpyridine. Thus the results with the unusual Lewis acid, 9‐borabicyclo[3.3.1]nonane parallel closely the earlier results for the stability of addition compounds produced by the reaction of such amines with trimethyl‐borane, boron trifluoride, and borane.
Some aspects of counter current dialysis through hollow fiber membranes
Authors: Hermans J. J. 
Published: September 2010

AbstractA dilute solution flows through a bundle of parallel fibers, the wall of which is permeable to the solute. On the outside of the fibers, possibly in another solvent, the solution flows in the opposite direction. The mass balance equations are first solved for the limiting case of very large diffusivity, and the concentrations on either side of the membrane are found to be simple exponential functions of the axial coordinate. The role of diffusion can be accounted for in closed form if polarisation is not excessive, so that the velocity of the liquid may be replaced by its cross‐sectional average. In this case the exponential behavior remains the same except that the coefficient in the exponent becomes a function of the Sherwood number.
Hydrolysis of monomeric substrates by porcine pancreatic (pro)phospholipase A2. The use of a spectrophotometric assay
Authors: Volwerk J.J. , Dedieu A.G.R. , Verheij H.M. , Dijkman R. , de Haas G.H. 
Published: September 2010

AbstractIn the course of searching for specific chromogenic substrates which might be useful for the assay of phospholipase A2 at monomeric substrate concentrations, we tested short‐chain lecithin analogues in which the oxygen ester bonds were replaced by thio ester. Spectrophotometric measurement of the hydrolysis of the thio ester in the presence of 5,5′‐dithiobis(2‐nitrobenzoic acid) or di‐4‐pyridyl disulfide provides a continuous and sensitive assay.Using this assay it was found that the zymogen expressed considerably higher enzymatic activities than phospholipase A2 which reinforces the conclusions of Pieterson et al. [Biochemistry 13, 1455 (1974)] that the zymogen, like the phospholipase, has a fully functional active site and that the fundamental difference between phospholipase A2 and the zymogen only becomes evident if the substrate is present in an organized lipid water interface.The use of the spectrophotometric assay allowed a determination of the pH‐rate profile of both phospholipase A2 and its precursor. Phospholipase A2 shows an optimum at pH 8.5 whereas the maximal activity of the precursor remains constant between pH 6 and 9. Initial velocity patterns as a function of Ca2+ and substrate are consistent with a random addition of substrate and cofactor to the enzyme.
Structural effects in the intermolecular exciplex formation of 2‐methylnaphthalene and tertiary amines
Authors: Meeus F. , van der Auweraer M. , Dederen J.C. , de Schryver F.C. 
Published: September 2010

AbstractThe quenching rate constant of 2‐methylnaphthalene (2 MN) with triethylamine (TEA) and N‐methylpiperidine (NMP) in a polar protic solvent is found to be less than diffusion controlled. In a non polar solvent the exciplex stabilisation and entropy of formation indicate a tighter bound complex for the 2 MN‐TEA system than for 2 MN‐NMP. Both observations are interpreted as arising from geometric restrictions in the approach of the amine to the excited 2‐methylnaphthalene.
Hydrogen bonding of 5α‐cholestanol in carbon tetrachloride
Authors: Kunst M. , van Duijn D. , Bordewijk P. 
Published: September 2010

AbstractSelf‐association and complex formation with tetrahydrofuran has been studied for 5α‐cholestan‐3α‐ol and 5α‐cholestan‐3β‐ol in carbon tetrachloride, with the help of infrared measurements in the fundamental hydroxyl stretching range. For the self‐association the monomer/dimer/tetramer model was found to be appropriate, with dimerization constants that are equal to those for cholesterol, while for 5α‐cholestan‐3α‐ol the tetramerization constants are also equal to those for cholesterol, and for 5α‐cholestan‐3α‐ol they are somewhat higher.With tetrahydrofuran 1/1 complexes were found, with equilibrium constants equal to the dimerization constants.
Kinetics of the gas‐phase ammoxidation of toluene to benzonitrile on a Bi‐Mo‐O catalyst
Authors: den Ridder J. J. J. , van Ingen H. W. T. J. , van den Berg P. J. 
Published: September 2010

AbstractFor the selective gas‐phase ammoxidation of toluene on a Bi‐Mo‐O catalyst a kinetic model has been developed in which the combustion of ammonia and benzonitrile has been taken into account. The effect of steam has been investigated. Temperature in the 640‐750 K region has hardly any effect on the selectivity to nitrile, which is maximal at 83%. Values are given for the rate parameters of main and side reactions.
Photochemistry of aromatic nitro compounds, XIII. Photoreduction of sterically hindered nitrobenzenes in aliphatic amines
Authors: Döpp Dietrich , Müller Dietmar 
Published: September 2010

AbstractPhotolysis of sterically hindered nitrobenzenes (1a‐d) in tertiary aliphatic amines as solvents results in efficient photoreduction to hydroxylamine derivatives and/or the corresponding anilines. Quantum yields for conversion of starting material Φconv in triethylamine have been determinded for 1a, c, d to be 0.47, 0.25 and 0.39, respectively, whereas with diethylamine, Φconv ≈︁ 0.09. Support for an electron transfer mechanism of photoreduction in the cases reported here comes from the fact that 1a‐d do not undergo hydrogen transfer photoreduction and from the small isotope effect (kH/kD ≈︁ 1.1) when 1,1‐dideuterio‐triethylamine is used as solvent. A rationale for the formation of several nitrones as products of photolysis of 1a‐c in various tertiary amines is given.
Ionization and mutarotation of hexoses in aqueous alkaline solution as studied by 13C NMR spectroscopy
Authors: de Wit G. , Kieboom A. P. G. , van Bekkum H. 
Published: September 2010

AbstractA 13C NMR spectroscopic study of glucose, mannose and fructose in aqueous alkaline solution has been carried out. Some of the 13C resonances are found to shift substantially with increasing pH. The 13C NMR titration curves allow of the determination of both the pKa values of the hexoses and the differences in acid strength of the α/β‐anomeric forms.The shifts observed cannot be explained by a simple ionization; the ionized species is considered either as a rapid equilibrium between cyclic and pseudo‐cyclic ionized species or as a non‐classical anion. It is concluded that base catalysis in the mutarotation reaction originates from a weakening of the ring C‐O bond in the generated sugar anion.
A formalism for the classification and design of organic reactions. II. The classes of (+ −)n + and (− +)n − reactions
Authors: Arens J. F. 
Published: September 2010

AbstractThe coding system proposed in the previous paper is extended to reactions involving an odd number of atoms, one of which is coordinatively unsaturated. This atom can extend its bonding with two units. Chelotropic reactions fit into this class characterized by operators (+ ‐)n +. Reactions in the reversed direction (operator (‐ +)n‐) are equally important. The coding system allows the design of new reactions.
Phase transitions in solids, studied by adiabatic calorimetry. I. Design and test of an automatic adiabatic calorimeter
Authors: Schaake R. C. F. , Offringa J. C. A. , van der Berg G. J. K. , van Miltenburg J. C. 
Published: September 2010

AbstractThe construction of an automatic adiabatic calorimeter is described. A block diagram is given of the data‐logging system used. n‐Heptane is used to check the performance of the apparatus.
Preparation, structure and properties of halogeno(tetraalkylthiuram monosulfide)copper(I)
Authors: van De Leemput P. J. H. A. M. , Willemse J. , Cras J. A. , Groen L. 
Published: September 2010

AbstractThe preparation and properties of the compounds CuXR4tms (X = Cl, Br, I: R = Me and R2 = Pm; X = SCN: R = Me) are reported. The compound CuI(Pm2tms) from which the crystal structure has been solved crystallizes in the triclinic space group Pl [a = 11.822(3), b = 10.572(3), c = 7.833(3) Å, α = 95.62(3), β = 111.73(3), γ = 68.20(2)°] and contains two formula units per unit cell. The structure was refined to a conventional R value of 0.056 for 3829 independent non‐zero reflections. It consists of dimeric molecules in which copper is approximately tetrahedrally coordinated. The two copper atoms are bridged by one of the sulfur atoms of each thiuram monosulfide.
Synthesis of racemic and chiral codeine and morphineviathe dihydrothebainones. (Chemistry of opium alkaloids, Part XI)
Authors: Lie T. S. , Maat L. , Beyerman H. C. 
Published: September 2010

AbstractRacemic and chiral 1‐(3,5‐dibenzyloxy‐4‐methoxybenzyl)‐1,2,3,4‐tetrahydro‐6‐methoxyisoquinoline (1, Scheme) were N‐methylated, which gave2a. A Birch reduction converted2a,via2b, into the 1,4‐diene3. Acid‐catalysed cyclization of3gave the morphinan4. Selective removal of the hydroxyl group in position 2,viathe 1‐phenyl‐5‐tetrazolyl ether (5), by hydrogenolysis, yielded (‐)‐dihydrothebainone (6). The conversion of6into (‐)‐codeine and (‐)‐morphine is known. In this way our preceding synthesis is shortened by two steps.
Pyrazolato and related anions. Part VI. Vibrational and electronic spectra of salts of 1,2,4‐triazole and 3‐bromo‐1,2,4‐triazole
Authors: van Houten R. , Vos J. G. , Groeneveld W. L. 
Published: September 2010

AbstractSalts of 1,2,4‐triazole and 3‐bromo‐1,2,4‐triazole with Cd, Zn, Co, Ni, Cu and Ag are reported. The compounds have been identified and characterized by chemical analyses, vibrational and electronic absorption spectra. Different coordination possibilities are discussed in view of the observed vibrational spectra. For the salts of 1,2,4‐triazole, 1,2‐bidentate or tridentate coordinations are observed. In the salts of 3‐bromo‐1,2,4‐triazole, bidentate and tridentate coordinations are assumed.
Ab initio calculations on thermodynamic and kinetic aspects of the isomerization process of some acyclic unsaturated C5H6 hydrocarbons
Authors: van Den Berg A. B. A. , den Boer D. H. W. 
Published: September 2010

AbstractAb initio calculations of the thermodynamic stability order of six acyclic unsaturated hydrocarbons are presented. The results are in reasonable agreement with the experimentally observed order in the equilibrium mixture of isomers resulting from the base‐catalyzed isomerizations. The charge distribution and molecular electrostatic potential of two postulated intermediate carbanions involved in these isomerizations are also calculated in order to explain their initial product ratios which have been observed to differ from the thermodynamical order. These properties fail to reproduce the observed kinetic behaviour. Inclusion of polarization does not improve essentially these results. An estimate of the activation entropy on the basis of the shape of the potentials permits of an interpretation in agreement with the observed reactivity.
Cyclic Organolead Compounds II. Synthesis and characterization of several plumbole derivatives
Authors: van Beelen D. C. , Wolters J. , van der Gen A. 
Published: September 2010

AbstractThe synthesis of several plumbole derivatives is reported. Monocyclic compounds may be prepared by the reaction of organoaihthio compounds with diorganolead dibromides. Spirocyclic compounds may be formed from the reaction of dilithio compounds with lead(II) chloride. The compounds are characterized by 1H NMR and IR spectroscopy.
The synthesis of bis(4‐methyl‐3‐pentenyl)thiophenes
Authors: Janssen Cornelus G. M. , Macco Anton A. , Buck Henk M. , Godefroi Erik F. 
Published: September 2010

AbstractAll possible isomers of title compounds 5a‐8a have been prepared. All the routes presented have involved Wittig olefination of dicarbaldehydes 5c‐8c. Synthetic aspects as regards the relevant intermediates are discussed.
A synthetic approach to 17β‐steroidal ethers derived from hydroxymalonic ester
Authors: Loozen H. J. J. , de Winter M. S. 
Published: September 2010

AbstractEthers (1 and 2) derived from dimethyl hydroxymalonate and 3‐methoxy‐1,3,5(10)estratrien‐17β‐ol or 17β‐hydroxy‐4‐androsten‐3‐one have been prepared. The cyclic ethylene acetal of 3‐methoxy‐1,3,5(10)‐estratrien‐17‐one (5) and of 3β‐benzyloxy‐5‐androsten‐17‐one (11) were converted stereoselectively into the corresponding 17β‐(2‐hydroxy‐ethyl) ethers 6 and 12 respectively by LiAlH4/AlCl3. Upon oxidation, esterification and treatment with lithium diisopropylamide/methyl chloroformate the 17‐bis(methoxycarbonyl)methyl esters 1 and 15 were obtained. Catalytic hydrogenolysis of 15, followed by oxidation gave 2.
Functionalized enamines XXVIII. A facile synthesis of 6‐methyl‐19‐norsteroids
Authors: Bieräugel H. , Pandit U. K. 
Published: September 2010

AbstractDienamines derived from 8a‐methyl‐1,6‐dioxo‐1,2,3,4,6,7,8,8a‐octahydronaphthalene (2) and ( + )(7aS)‐7a‐methyl‐2,3,5,6,7,8‐hexahydro‐1,5(1H)‐indandione (12) react with 3‐bromo‐2‐(3‐methoxyphenyl)propene (3) to give the corresponding 5‐ and 4‐substituted alkylation products 8 and 14a, respectively. 8 can be directly cyclized to 6‐methyl‐D‐homoequilenin derivative 9 by heating with acid. While 14a can be similarly converted into the corresponding equilenin methyl ether (15a), better yields in the cyclization step are achieved by initial reduction of the 5‐ring ketone function and acetylation of the resulting alcohol. The latter sequence of reactions with 14a, derived from 12, gives optically active 17β‐acetoxy‐6‐methylestra‐1,3,5,7,9,14‐haxaen‐3‐ol methyl ether (15b), which can serve as an central intermediate for optically active steroids.
The Schmidt reaction. Reaction rates of a number of substituted benzoic acids at 20°C
Authors: de Koning Adrianus Jan 
Published: September 2010

AbstractThe rate of the Schmidt reaction at 20°C has been determined for a variety of substituted benzoic acids. It is shown that electronic effects of substituents affect the reaction rate, electron donation increases the rate and electron withdrawal decreases it. Ortho substituents accelerate the reaction, and the reaction is a good example of steric assistance. The buttressing effect of a tert‐butyl group on an adjacent halogen atom is demonstrated in the high reaction rate of 2‐halogeno‐3,5‐di‐tert‐butylbenzoic acids. An attempt has been made to separate the effect of an ortho substituent into steric, inductive and mesomeric contributions. A discussion on the mechanism of the reaction is included.
A simple synthesis of the new heterocyclic compounds 1,4‐oxathiin and 3,5‐dimethyl‐1,4‐oxathiin
Authors: Schoufs Mart , Meijer John , Brandsma Lambert 
Published: September 2010

AbstractSulfur dichloride adds to vinylic ethers to give 2,6‐dichloro‐1,4‐oxathianes. Dehydro‐halogenation of these products leads to the hitherto unknown heterocyclic compounds 1,4‐oxathiin 6 and 3,5‐dimethyl‐1,4‐oxathiin 7 in good overall yields.
Chemistry of 2H‐thiopyran and derivatives IV. Deprotonation and methylation of 2H‐thieno[2,3‐b]thiopyran and some derivatives
Authors: Gräfing R. , Brandsma L. 
Published: September 2010

AbstractMetallation of 2H‐thieno[2,3‐b]thiopyran 1 by strong bases under relatively apolar conditions proceeds exclusively in the 2‐position of the thiophene ring. In polar media a 2‐proton of the thiopyran ring is removed to give the anion 1b. By addition of hexamethylphosphoric triamide (HMPT) to the lithiated compound 1a conversion into 1b takes place. The anions 1a and 1b react with methyl iodide to give the compounds 2 and 3, respectively. Compound 2 can be further methylated by reaction with BuLi in tetrahydrofuran (THF)/HMPT mixtures or sodamide in liquid NH3, followed by addition of methyl iodide. The resulting compound 4 can be converted into the compounds 5, 6 or 7, depending on the base‐solvent system: Compound 5 is produced by interaction between 4 and KNH2 in liquid NH3 at − 33°, followed by methylation at − 60°. If the reaction with KNH2 is carried out at − 60°, however, methylation gives 6, this result is also obtained from 4, BuLi in THF/HMPT and CH3I. Omission of HMPT during the metallation gives rise to vinylic proton abstraction, and subsequent addition of CH3I leads to 7.
Carbophilic reactions of an arylthio‐substituted sulfine with α‐oxo‐carbanions
Authors: van der Leij M. , Zwanenburg B. 
Published: September 2010

AbstractThe reaction of p‐tolyl(phenylthio)sulfine 1 [TolC(SPh)SO, Tol=p‐MeC6H4] with α‐oxo‐carbanions is described. With 2‐lithiocyclohexanone, sulfine 1 furnishes alkene disulfide 2. Similarly, the carbanion of 3,4‐dihydro‐1‐naphthalenone (α‐tetralone) gives disulfide 5. This introduction of a C(Tol)SSPh group into the α‐position of the ketone is explained by assuming an initial carbophilic displacement of the SPh substituent in 1 by the carbanion. Deprotonation of the so‐obtained β‐oxosulfine 3 gives a vinylsulfenate which in a subsequent reaction with thiophenol produces disulfides 2 and 5, respectively. The suggested intermediate vinylsulfenates could be trapped by a reaction with electrophilic reagents. With methyl iodide or benzyl bromide γ‐oxo‐α,β‐unsaturated sulfoxides 6–9 were obtained [introduction of a C(Tol)S(O)R group (R  Me, CH2Ph) in the position α to the carbonyl function of the ketone]. With ethyl bromoacetate or phenacyl bromide the vinylsulfenate obtained from 1 and α‐tetralone does not lead to unsaturated sulfoxides, but to 4,5‐dihydro‐naphtho[1,2‐c]thiophene S‐oxides 15 and 16 instead. These thiophene S‐oxides are thought to arise from an intramolecular condensation of the primary products, i.e. γ‐oxo‐α,β‐unsaturated sulfoxides 21.
Conformational dependence in the photochemistry of (E,E)‐germacra‐1(10),4,7(11)‐triene
Authors: Reijnders Peter J. M. , van Putten Rob G. , de Haan Jan W. , Koning Henk N. , Buck Henk M. 
Published: September 2010

AbstractIrradiation of (E,E)‐germacra‐1(10),4,7(11)‐triene 1 gives intramolecular reactions of the endocyclic double bonds. Products can be correlated with the crossed and parallel conformation of the title compound and the parallel conformation of its (Z,Z)‐isomer 2.