bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ester interchange using molecular sieves
Authors: Roelofsen D. P. , de Graaf J. W. M. , Hagendoorn J. A. , Verschoor H. M. , van Bekkum H. 
Published: September 2010

AbstractEster interchange reactions using type A molecular sieves which selectively adsorb the displaced alcohol, have been shown to proceed practically to completion. Examples are given which cover a number of starting esters, displacing alcohols, experimental procedures, solvents, and cationic forms of the molecular sieves. Several new t‐butyl esters were obtained and characterized.Equilibrium constants were measured and rate studies made for several representative reactions.The interaction of sodium and potassium isopropoxide catalysts and sieves has also been investigated. Both cation exchange with the sieves and adsorption of alkoxide after the addition of methyl alcohol have been observed. Interesting differences have been found between 3A, 4A, and 5A sieves.The interfering dehydration of t‐butyl alcohol has been studied with different molecular sieves of type A. The influence of traces of water and triethylamine on the dehydration has been investigated.
Preparation of 5,6‐Dimethylazulene and 5,6‐Dimethyl‐2‐Indanylacetic acid
Authors: Ward J. P. , Frost D. J. 
Published: September 2010

Abstract5,6‐Dimethylazulene was prepared from 5,6‐dimethylindan by the diazoacetic ester method. Methyl 5,6‐dimethyl‐2‐indanylacetate was also obtained, and its structure determined from its 220 MHz NMR spectrum.
Formation of open anions from Dihydro‐Oxepin
Authors: Kloosterziel H. , van Drunen J. A. A. 
Published: September 2010

AbstractReaction of 2,3‐dihydro‐oxepin 1 with potassium amide in liquid ammonia yields, as revealed by NMR spectroscopy, the trans‐2,cis‐3,trans‐4,cis‐5 7‐oxaheptatrienyl anion 3, which is of fair configurational stability. The barriers for rotation in the oxaheptatrienyl anion are discussed.
Hindered rotation in diphenylmethane derivatives. Part III. A comparison of NMR kinetic studies with the results of racemization measurements
Authors: Akkerman O. S. 
Published: September 2010

AbstractThe NMR spectra of alkyl‐substituted diphenylmethane derivatives have been measured. In each compound investigated all chemically equivalent protons or group of protons were magnetically non‐equivalent due to hindered rotation. The activation parameters for the rotation of the phenyl groups in 2,4,2′,4′‐tetra‐tert. butyl‐6,6′‐dimethyldiphenylacetic acid were determined from variable temperature NMR experiments and were found to be in good agreement with the activation parameters for the racemization. Due to decomposition no kinetic measurements could be made on the benzhydrols and the benzhydryl methyl ethers.
Hydrogen bonding properties of α‐Diazosulfones and α‐Diazoketones
Authors: Engberts J. B. F. N. , Zuidema G. 
Published: September 2010

AbstractIR and NMR spectral evidence indicates that α‐diazosulfones, RSO2CHN2 (I), and α‐diazoketones, RCOCHN2 (II), donate and accept protons in hydrogen bonding. The proton donor properties involve the methine proton as the donor site. The proton acceptor site is the sulfonyl group for α‐diazosulfones and the carbonyl moiety for α‐diazoketones. Using phenol as a donor molecule, OH stretching frequency shifts, Δν, have been measured for the α‐diazosulfones Ia‐Ig and the α‐diazoketones IIa‐IIf. Substituent effects on Δν values are modest for Ia‐Ig but more pronounced for IIa‐IIf. Compared with α‐diazoketones, α‐diazosulfones are stronger proton donors but weaker proton acceptors in hydrogen bonding.
Studies on polypeptides. Part X: Synthesis of 1‐13[10‐Homoarginine, 13‐Leucine] bovine pancreatic ribonuclease by combined solid‐phase and classical methods
Authors: Visser S. , Kerling K. E. T. , Havinga E. 
Published: September 2010

AbstractMerrifield's solid‐phase method was applied to the synthesis of all‐L‐glutamyl‐homoarginylglutaminylhistidylleucine. Azide coupling in solution with all‐L‐Nα, Nϵ‐di‐t‐butoxycarbonyllysyl‐γ‐t‐butylglutamylthreonylalanylalanylalanyl‐Nϵ‐benzyloxycarbonyllysylphenylalanine hydrazide, also prepared on a solid supportS. Visser, J. Roeloffs, K. E. T. Kerling and E. Havinga, ibid. 87, 559 (1968).
, resulted in the N‐terminal tridecapeptide sequence of bovine pancreatic ribonuclease in which homoarginine and leucine replace arginine‐10 and methionine‐13, respectively.
Photoreactions of aromatic compounds. Part XX: The photosubstitution of nitronaphthalenes in alkaline media
Authors: van Henegouwen G. M. J. Beijersbergen , Havinga E. 
Published: September 2010

AbstractThe photoreactions of some methoxynitro‐, dimethoxynitro‐ and dinitronaph‐thalenes in alkaline medium are described. From the reactions observed (substitution of OCH3 or NO2 by OH) it appears that in the excited state of the naphthalene derivatives a nitro group in the one ring exerts a definite activating influence also on positions in the other ring. In these reactions specific “meta‐activation” was established.
Investigations on sterols. Part XXXVI: Synthesis of steroidal: Spirolactones with a Reformatsky reaction
Authors: de Bruin O. A. , Botterman J. , Westerhof P. 
Published: September 2010

Abstract17‐Oxo steroids in a Reformatsky reaction with the ethyl ester of γ‐bromo‐β‐ethoxycrotonic acid gave rise to isomeric pairs of 17‐spirolactones. The spirolactone moiety of these compounds has been modified and related to that of known spirolactones.
Pyrazoles and imidazoles as ligands. Part IV. Ligand‐field spectra of tetragonal coordination compounds containing the ligand 3(5)‐methylpyrazole
Authors: Reedijk J. 
Published: September 2010

AbstractLigand‐field spectra of compounds with the formula M(anion)2(MPZ)4 in which MPZ is 3(5)‐methylpyrazole are discussed. The metal ions under investigation are Mn, Fe, Co, Ni and Cu(II), and the anions are NO3−, Cl−, Br−, I−, ClO4− and BF4−.The spectrochemical parameters Dqxy, B, Ds and Dt are calculated from the spectral data for a number of isomorphous compounds. The alterations of these parameters are discussed as a function of the metal ions and the anions. Compared with other tetragonal compounds the distortion from octahedral symmetry in the present compounds is quite large. The origin of this strong tetragonal distortion seems to be the hydrogen‐bond formation between the coordinated ligands and the coordinated anions, weakening the metal‐anion bond in the z‐direction.The tetragonal species M(anion)2(MPZ)4 also have been investigated in solutions of acetone, nitromethane and methylene chloride. For some compounds this tetragonal species also exists in solution, but for some other compounds ligand exchange and/or dissociation occurs, as concluded from spectral absorptions in combination with conductivity measurements.
The variation of the activity coefficients of cations with the hydrogen ion concentration in aqueous perchloric acid‐sodium perchlorate and perchloric acid‐lithium perchlorate mixtures of constant ionic strength
Authors: Gelsema W. J. , de Ligny C. L. , Remijnse A. G. 
Published: September 2010

AbstractThe variation of the activity coefficient of some cations and of the ratio of the activity coefficients of the ions of some redox systems with the hydrogen ion concentration has been measured at several (constant) values of ionic strength in perchloric acid‐sodium perchlorate and perchloric acid‐lithium perchlorate mixtures at 25°.These variations differ considerably among different cations or redox systems. They are about the same in perchloric acid‐sodium perchlorate and perchloric acid‐lithium perchlorate mixtures of low ionic strengths but they are much larger in perchloric acid‐sodium perchlorate than in perchloric acid‐lithium perchlorate mixtures at ionic strengths > 3 mole · 1−1.
Temperature dependence of the Raman spectrum of NOSbCl6
Authors: Stufkens D. J. , Gerding H. 
Published: September 2010

AbstractAttention is paid to the tentative preparation of NOSbCl4, the only product being NOSbCl6.The temperature dependence in the Raman spectrum of NOSbCl6 is explained in terms of the coupling between NO+ and SbCl6−.
Réactions D'amines Germaniées avec les Aldéhydes et les Cétones
Authors: Riviere‐Baudet M. , Satgé J. 
Published: September 2010

AbstractThe insertion of aldehydes and ketones onto the germanium‐nitrogen bond of trialkylgermylamines leads to α‐aminoalkoxygermanes which are generally not very stable.Their decomposition leads to trialkylgermanium oxides and enamines or imines corresponding to the aminogermanes and carbonyl derivatives.The formation of enamine or imine takes place through gem‐diamines which are usually unstable. The derivatives obtained by insertion of the halogenated aldehydes and ketones such as chloral and hexachloroacetone decompose through β‐elimination, with formation of trialkyl(trichloromethyl)germane R3GeCCl3, trialkylchlorogermane and dichlorocarbene.
Trans‐substitution and equilibration of phenols: Part II. Trans‐t‐butylation of phenols in the presence of para‐toluenesulfonic acid as the catalyst
Authors: Willemse F.R.J. , Wolters J. , Kooyman E.C. 
Published: September 2010

AbstractPhenols containing a free ortho position can be alkylated by ortho‐t‐butyl‐phenols in the presence of catalytic amounts of p‐toluenesulfonic acid at temperatures between ∼ 60 and 100°.Using, e.g., 2,6‐di‐t‐butyl‐p‐cresol as an alkylating agent, trans‐t‐butylations were carried out with a number of para‐ and ortho‐substituted phenols.The above mentioned reactions lead to equilibria of the type: 2,6‐di‐t‐butyl‐p‐ZC6H2OH + p‐ZC6H4OH ⇄ 2 (2‐t‐butyl‐p‐ZC6H3OH)The equilibrium constant (K = 43 at 80°C) is independent of the substituent present in the phenolic nucleus.For Z = p‐CH3 the energy of activation of the forward reaction amounts to 18.5 kcal/mole. Ortho‐para isomerization occurs, when the 3, 4 and 5 positions are free. Several differences between the catalytic effects of p‐toluenesulfonic acid and aluminium phenoxide are discussed.
Theoretical calculation of retention indices of apolar solutes on apolar stationary phases and a discussion of their temperature coefficients and of the corresponding standard partial molar entropies, enthalpies and free enthalpies of vaporization from solution
Authors: Hammers W. E. , de Ligny C. L. 
Published: September 2010

AbstractA method is proposed for calculating retention indices of apolar solutes on apolar stationary phases from the vapour pressures of the solutes and the molar volumes of the solutes and the solvent. Retention indices calculated by this method, as well as values calculated otherwise, are compared with experimental data.The temperature dependence of the retention indices is discussed from a thermodynamic standpoint.The corresponding standard partial molar entropies, enthalpies and free enthalpies of vaporization from solution appear to depend on molecular size and shape. The latter phenomenon is contributed to more or less shielded solute‐solvent interactions and to less or more restricted molecular translation and rotation.
IR and NMR studies of symmetrically and unsymmetrically bonded N,N‐dialkyldithiocarbamates
Authors: Brinkhoff H.C. , Grotens A.M. 
Published: September 2010

AbstractIn order to find characteristic differences between symmetrically and unsymmetrically bonded N,N‐dialkyldithiocarbamates, their IR and 1H NMR spectra have been examined. The IR data firmly underline a previously reported infrared criterion which makes it possible to distinguish the two types of bonding. In the spectra of the unsymmetrical N,N‐diethyldithiocarbamates a band at 1000 cm−1 is assigned to the CS stretching mode.Although the rotation around the S2C‐NR2, bond in several dithiocarbamato complexes will be strongly hindered at low temperatures, no splitting of the NMR signals of the N‐alkyl groups could be observed. This may be attributed to an extremely small difference in magnetic environment of the N‐alkyl moieties in the rotamers.
Palladium‐catalysed reactions of unsaturated compounds in non‐aqueous solvents: The oligomerization of butadiene using π‐allylpalladium acetate as catalyst
Authors: Medema D. , van Helden R. 
Published: September 2010

AbstractWith π‐allylpalladium acetate as catalyst, butadiene is converted in benzene solution into the linear trimer n‐dodecatetraene. Upon addition of triphenyl‐phosphine the linear dimer becomes the main product. In the trimerization the actual catalyst is a C12 H18Pd2OAc2 complex, formed from π‐allylpalladium acetate via (C7H11PdOAc)2 by displacement of the C7 fragments by three butadiene molecules. The displacement takes place via hydrogen transfer, which also explains the catalytic activity of the C12H18Pd2OAc2 complex. When methanol is used as solvent, butadiene is converted into octadienyl, dodecatrienyl or hexadecatetraenyl methyl esters, depending on reaction conditions. In this reaction a complex is formed in which butadiene is coordinated to zerovalent palladium. The consequences of the isolation of the various intermediate complexes in relation to the reaction mechanism are discussed.
The chemistry of small ring compounds 13: Transmethylations between methyl cyclopropanecarboxylate and various nucleophiles in alkaline media
Authors: van Der Maeden F.P.B. , Steinberg H. , de Boer Th. J. 
Published: September 2010

AbstractThe Claisen‐Tischenko reaction of cyclopropanecarbaldehyde with sodium methoxide gives rise to the unusual yield of 10% of its dimethyl acetal via methylation of the hemiacetal anion by methyl cyclopropanecarboxylate, one of the normal Claisen‐Tischenko products.Similar transmethylations between methyl cyclopropanecarboxylate and a variety of nucleophiles [CH3O⊖, cyclo‐C3H5CH2O⊖, n‐C4H9S⊖ and N(CH3)3] can be effected. With methyl sulfide ion instead of methoxide ion, cyclopropanecarbaldehyde reacts with ring opening and formation of unsaturated aldehydes 9 and 10.
Addition of chlorine to the cyanogen bond IV: Synthesis of diisocyano tetrachloride
Authors: Trompen W. P. , Geevers J. , Hackmann J. Th. 
Published: September 2010

AbstractA comparative study of some isocyanide dichlorides R‐NCCl2 and their isomeric N‐chloro‐formimidoyl chlorides R‐C(Cl) NCl is described. For this purpose we tried to synthesize N‐cyano‐isocyanide dichloride (III) and diisocyano tetrachloride (tetrachloroformalazine) (IX). Chlorination of S,S′‐dimethyl cyanodithiocarbonimidate (II) did not yield III but the dimeric 2,4‐dichloro‐6‐dichloromethylimino‐s‐triazine (IV) (tetramer of cyanogen chloride). IX was prepared by exhaustive chlorination of tetramethylthioformalazine (VI).
The raman and infrared spectra of solid TeCl4 AND SeCl4
Authors: Ponsioen R. , Stufkens D. J. 
Published: September 2010

AbstractThe Raman and infrared spectra of solid TeCl4 and SeCl4 are presented. On the basis of an ionic formulation (MCl3+ and Cl− ions) an assignment of the stretching frequencies of the MCl3+‐ion (with nearly C3v symmetry) is given. The results of a recently published X‐ray analysis of solid TeCl4 made this assignment more detailed. Only suggestions could be made as to the assignment of the bending frequencies of the cations.
Induced vapour phase chlorination of arenes at about 200°C
Authors: Dorrepaal W. , Louw R. 
Published: September 2010

AbstractThe vapour phase (thermal) reaction of arenes (benzene, chlorobenzene, benzonitrile) with molecular chlorine ‐ setting in at roughly 250° ‐ can be made to occur even below 200° by adding small proportions of CCl3‐SO2‐CCl3 (“S”). Products (chlorinated arenes) and relative rates are highly comparable under both sets of conditions. Depending on inter alia, the concentration of S in the feed, from a few to well over 2000 moles of product per mole of S are formed.Both modes of reaction are interpreted as radical chain processes, chlorine atoms ‐ and their arene adducts ‐ being intermediates. In the initiated reactions. S is thought to form CCl3 radicals, which lead to chlorine atoms by reaction with Cl2.
The low temperature reaction of diazomethane with 1,3,5‐trinitrobenzene: Nucleophilic aromatic addition VIII
Authors: van Velzen J.C. , Kruk C. , de Boer Th. J. 
Published: September 2010

AbstractThere is a strong temperature effect on the reaction of 1,3,5‐trinitrobenzene with diazomethane. At 0° three methylene groups are introduced and the product is the trinitro derivative I (found earlier).Below −80°, again three methylene groups are introduced, but the main product is a dinitro compound II, isomeric with I but with strikingly different properties.The methylene groups in II are incorporated in a seven‐membered ring, a cyclopropane ring and an isoxazoline ring, the latter arising by an unusual participation of one of the nitro groups.The structural proof of II rests on spectroscopic evidence and specific chemical reactions.
A gas‐chromatographic investigation of the thermodynamics of solutions of some normal and branched alkanes, cyclohexane, benzene and tetrachloromethane in polyisobutylene
Authors: Hammers W.E. , de Ligny C.L. 
Published: September 2010

AbstractFrom net retention volumes, measured over a wide range of temperatures, solute molar volumes and solute fugacities, standard partial molar free enthalpies, entropies and enthalpies of mixing at infinite dilution in polyisobutylene solution were calculated over a range of temperatures.Gas‐chromatography is an unique method in the sense that it gives thermodynamic data at polymer mole fractions near unity whereas conventional methods usually are not capable of giving accurate data for very concentrated polymer solutions.The residual standard partial molar free enthalpies and entropies and the standard partial molar enthalpies of mixing of the normal and branched alkanes were analysed by the (simplified) Prigogine solution theory. Those of the n‐alkanes, cyclohexane, benzene and tetrachloromethane were discussed in terms of the solution theory of Flory, Orwoll and Vrij.
Alkyl 1,1‐dialkoxy‐alkane‐ and ‐arene‐carboxylates. Part IV 1‐alkoxyalkyl carboxylates
Authors: Scheeren J. W. , Nivard R. J. F. 
Published: September 2010

AbstractAldehydes can be converted into 1‐alkoxyalkyl carboxylates under mild conditions by reaction with dialkoxymethyl carboxylates in the presence of carboxylic acids. A mechanism has been proposed to explain the appearance of orthoformate during the reaction, and the accelerating effect of this compound on the formation of 1‐alkoxyalkyl carboxylates.Thermostable 1‐alkoxyalkyl carboxylates can be prepared also from acetals and carboxylic acids though in low yields.Higher homologues were obtained from the 1‐alkoxyalkyl acetates by exchange of the acid group in a distillation procedure. In a similar way formates were obtained from butyrates and the formic acid/triethylammonium formate azeotrope.
The difference of the standard chemical potentials of KCl in water and in mixtures of water with ethanol, dioxane and acetone
Authors: Bax D. , Alfenaar M. , de Ligny C. L. 
Published: September 2010

AbstractThe difference of standard chemical potentials of KCl in water and in mixtures of water with ethanol, dioxane and acetone has been determined by means of emf measurements on the cell:magnified imageAn improved cell design was used for these measurements.
Synthesis of optically active eremophilane sesquiterpenoids from sabinene
Authors: van Der Gen A. , van Der Linde L. M. , Witteveen J. G. , Boelens H. 
Published: September 2010

AbstractAn efficient route to optically pure sesquiterpenoids of the nootkatane type is described. Stereoselective Michael‐type addition of (‐)‐3‐methylsabinaketone (9) to trans‐3‐penten‐2‐one is used to create the asymmetric centers at C(4) and C(5) in the tricyclic ketone 12. Practical procedures for the conversion of 12 into (‐)‐α‐vetivone (17) and (‐)‐nootkatone (18) are presented.
The dielectric properties of some simple triglycerides
Authors: Ras A.M. , Bordewijk P. 
Published: September 2010

AbstractValues of ϵ′ and ϵ″ were determined for glycerol triacetate, tripropionate, and tributyrate in the frequency ranges 120 Hz to 100 kHz and 100 MHz to 9 GHz. The temperature‐dependence of the static dielectric constant indicates that the conformation of the molecules changes with the temperature. This conclusion is corroborated by the fact that for the triacetate and the tripropionate the distribution of relaxation times becomes broader with increasing temperature.
Synthesis of acetals using molecular sieves
Authors: Roelofsen D.P. , Wils E.R.J. , van Bekkum H. 
Published: September 2010

AbstractAcetals can be prepared in high yield from the corresponding aldehydes or ketones and alcohols using molecular sieves to shift the equilibria by adsorption of the water formed. Examples include acetals of acetone, cyclohexanone, iso‐butyraldehyde, and benzaldehyde.Two batch techniques have been applied using the molecular sieve suspended in the reaction mixture at 0° or room temperature.The first method involves the use of dual‐function proton‐exchanged molecular sieves type Zeolon 500, AW 500, or mordenite. The outer surface of the sieve catalyzes the acetal formation whereas the inner surface selectively adsorbs the water formed.According to the second procedure molecular sieve and catalyst p‐toluene‐sulfonic acid are added to the reaction mixture. In this case proton exchange between catalyst and sieve occurs which appeared to be fast with the molecular sieves types KA and NaA, much less pronounced with the types CaA, Zeolon 500, and AW 500. All these sieves however can be used because of the high rate of acetal formation. With KA and CaA essentially quantitative conversions are obtained within a few minutes.
Deazapurine derivatives. VII: Synthesis of substituted imidazo‐ and triazolo‐pyridines
Authors: de Roos K. B. , Salemink C. A. 
Published: September 2010

AbstractThe syntheses of several 7‐substituted imidazo[4,5‐b]pyridines (6‐substituted 1‐deazapurines) and of 7‐substitutedvic‐triazolo[4,5‐b]pyridines (6‐substituted 1‐deaza‐8‐azapurines) are described. A few 6‐substituted 3‐deazapurines and 3‐deaza‐8‐azapurines were also synthesized.Finally the results of an investigation on the effect of the deazapurines upon the growth ofS. faecalisare described.
Nuclear magnetic resonance contact shifts and delocalization mechanisms in Ni(II)‐dioxo complexes
Authors: Pijpers F. W. , Smeets H. E. , Beentjes L. B. 
Published: September 2010

AbstractThe temperature dependence of the proton NMR‐spectra of bis(1,3‐diphenyl‐1,3‐propanedionato)Ni(II) and of bis(1,3‐di‐p‐tolyl‐1,3‐propanedionato)Ni(II) has been determined.We have interpreted the results using a model with two unpaired electrons per molecule. We conclude that the contact shifts of the various proton resonance signals result from delocalized unpaired electrons in the σ as well as the π system of the ligands.
Decyanation of cyanomethyl derivatives of aza‐aromatic compounds
Authors: van der Plas H. C. , Jongejan H. 
Published: September 2010

Abstract2‐ and 4‐Cyanomethylpyridine, 1‐methyl‐ and 1‐benzyl‐2‐cyanomethylimidazole and 3‐cyanomethyl‐1,2,4‐triazole lose the cyano group on reaction with aqueous hydrazine at about 200°, yielding α‐ and γ‐picoline, 1,2‐dimethyl‐ and 1‐benzyl‐2‐methylimidazole and 3‐methyl‐1,2,4‐triazole, respectively. A mechanism is discussed.
Constantes ρ de Hammett dans les Reactions de Formation D'Oximes et de Combinaisons Bisulfitiques
Authors: Geneste P. , Lamaty G. , Roque J. P. 
Published: September 2010

AbstractThe Hammett reaction constant ρ has been measured for the addition reactions of NH2OH and SO−−3 ion to carbonyl compounds; the slopes of the best straigt lines of the log k, σ correlation fonctions are respectively: 0.32 and 1.12. These values are used to. draw conclusions concerning the structure of the transition state and its position along the reaction coordinate; they are consistent with a ‘reactant like’ transition state.