Showing papers in "Recueil des Travaux Chimiques des Pays-Bas in 2010"

Preparation, metallation and alkylation of allenyl ethers

Abstract: Propargyl ethers HCCCH2OR [R = alkyl or-CH(CH8)(OC2H5)] have been isomerized with good yields into the corresponding allenyl ethers CH2CCHOR by warming with potassium tert.-butoxide at 70°. These allenyl ethers can be metallated with butyllithium in ether or alkali amides in liquid ammonia. In ether, subsequent alkylation with alkyl halides R′Hal affords α-substituted allenyl ethers CH2CC(R′)OR. Alkylation in liquid ammonia produces a mixture of this same compound and the γ-substituted product R′CHCCHOR. In both cases reasonable yields are obtained. Sodamide and potassium amide quickly convert allenyl ethers CH2CCHOR into metallated propargyl ethers MCC-CH2OR (M = Na or K). If alkylation is not performed almost simultaneously with the metallation with sodamide or potassium amide, the only alkylation product obtained is R′CCCH2OR.

The theory of measurement of osmotic pressure

Abstract: Application of Onsager's symmetry relations to the process of diffusion of a solution through a membrane shows that measured osmotic pressures deviate from those calculated thermodynamically in proportion to the permeability of the membrane to the solute molecules. Therefore little is learned from one dynamic osmotic measurement but by simultaneous measurements of osmotic pressure and permeation at different membranes the entire molecular weight distribution of the solute can be computed.

Some comments on the Benesi-Hildebrand equation

Abstract: A modification is given of the Benesi-Hildebrand equation to determine the equilibrium constant for complex formation from spectrophotometric measurements. Difficulties arising from the use of either concentrations or mole fractions are discussed.

The enzymic conversion of all‐cis 8,11,14‐eicosatrienoic acid into prostaglandin E1

Abstract: In the biosynthesis of prostaglandin E1 (PGE1) with an enzyme fraction of sheep vesicular glands glutathione and a moderate amount of antioxidant are required to obtain maximum yield; two oxygen molecules are consumed per mole PGE1 formed. By altering the incubation conditions, besides PGE1 various other products can be obtained. A scheme for the mechanism of the conversion is proposed in which the formation of PGE1 as well as that of the byproducts is assumed to occur on the enzyme in concerted reactions via peroxy-radicals and a cyclic peroxide.

Tetraaza‐macrocyclic cobalt(II) and nickel(II) complexes as electron‐transfer agents in the photo(electro)chemical and electrochemical reduction of carbon dioxide

Abstract: The potential of a number of tetraaza‐macrocyclic complexes of cobalt and nickel to mediate the photoreduction of carbon dioxide has been studied. Carbon monoxide and hydrogen are the main products, which result from illumination of an aqueous solution containing Ru(2, 2′‐bipyridine)2+ 3 as sensitizer, ascorbic acid as sacrificial eletron donor and a tetraaza‐macrocyclic complex as relay. Their ratio strongly depends upon the relay compound used. The complexes can be used as electrocatalysts for CO2 reduction at a mercury electrode since they lower the overpotential for CO2 reduction showing turnover numbers/hour of approximately 3. A minimum potential is required to induce reaction of electrocatalysts and CO2 (and H2O). Finally, the redox properties of the macrocyclic metal complexes at p‐GaP and p‐GaAs photocathodes in acetonitrile are compared with those observed at Pt.

Gas hydrates of nitrogen and oxygen

Abstract: p-t relations of different three phase equilibria in the systems nitrogen-water and oxygen-water are given from -6 to 18° for pressures up to 1000 atm. From the data, the heats of formation of nitrogen- and oxygen-hydrate and the composition of these hydrates were calculated.

A semi-empirical energy-level diagram for octahedral cobalt(II) complexes

Abstract: Methods of calculation for the parameters Dq and B from the ligand-field spectra of octahedral cobalt(II) compounds are discussed. A method of calculation is introduced, which considers the lowering of the 4T1g (F) state by spin-orbit splitting. This calculation is applied to the spectra of 43 octahedrally coordinated cobalt(II) compounds. With the aid of the spectral data an energy-level diagram is constructed, into which the absorption bands are fitted. Comparison of calculated Dq and B values with corresponding values for isomorphous nickel(II) compounds shows that - in general - the crystalfield parameter Dq is highest for cobalt, although the differences with nickel are less than 4 % in most cases. The calculated B values corresponds with those of Ni, with differences less than 1 % for many ligands.

A method for the determination of amyloid in plant seeds

Abstract: 1) A colorimetric method has been elaborated for the determination of amyloids in plant seeds, based on the blue colour of the iodine complex in concentrated sodium sulphate solution. 2) Details of the method are given and its possibilities and limitations are outlined. 3) Three procedures for removing interfering starch are recommended.

Eine Methode der Dehydrierung von Sekundären Alkoholen zu Ketonen. I. Zur Herstellung von Sterinketonen und Sexualhormonen

Abstract: Eine Methode zur Bereitung von kompliziert gebauten Ketonen der Sterinreihe aus den entsprechenden Alkoholen wird beschrieben. Sie besteht darin, dass Sterinalkohole durch Ketone, z.B. Aceton, in Gegenwart von tert. Aluminium-Alkoholaten zu den entsprechenden Ketonen dehydriert werden. Die dabei erhaltenen Ausbeuten sind ausgezeichnet, ausserdem konnen auf diese Weise Ketone bereitet werden, die auf anderem Wege bisher nicht zuganglich waren (Ergosta-trienon).

A simple preparation of phthaloyl amino acids via a mild phthaloylation

Abstract: Phthaloyl amino acids can be synthesized from N-carboethoxy phthalimide and amino acid salts under very mild conditions in water. The preparation of 11 of these phthaloyl derivatives is described, some of which are new. Up to the present the method has only failed with tryptophane. Retention of the optical configuration during the reaction is shown.

Pyrazoles and imidazoles as ligands: Part I. Some simple metal(II) perchlorates and tetrafluoroborates solvated by neutral pyrazole and imidazole

Abstract: A number of new solvates containing pyrazole (Pz) and imidazole (Iz) as ligands, of the general formula M(ligand)n(anion)2 is reported. In these compounds M = Mg, Mn, Fe, Co, Ni, Cu, Zn and Cd, the anions are ClO4− and BF44−, and n is usually 6; n = 4 in the case of the Cu compounds and for Zn in combination with Iz. The compounds are characterized and identified by chemical analysis and physical measurements. With the aid of ligand-field spectra in combination with X-ray powder patterns, octahedrally coordinated metal ions are found in compounds of stoichiometry M(ligand)6(anion)2. Both Pz and Iz are placed in the spectro-chemical and nephelauxetic series. The spectrochemical series appears to be (with increasing Dq): CH3CN NH3 > Iz > Pz > en. The magnetic moments for the transition-metal compounds fall within the range usually observed for octahedrally coordinated ions. Both paramagnetic resonance measurements and the deviation of the magnetic moments from the spin-only value, indicate a considerable amount of covalency in the metal-ligand bond. Infrared spectroscopy evidently shows pure ionic ClO4− and BF4− for all solvates, except those of Cu(II) where the anions are coordinated to the metal ion. Except for the N-H modes, no large shifts occur in the ligand infrared absorptions with respect to the free ligand. Compared with the gaseous ligands, the N-H stretch in the solvates is decreased, whereas the bending modes are increased in frequency. This is attributed to - weak - hydrogen bonding with the anions in the lattice of these solvates. Metal-ligand stretching frequencies for both ligands occur in the 165-330 cm−1 range, and follow the Irving-Williams sequence of metal ions.

The dimensions of charged long chain molecules in solutions containing electrolytes

Abstract: If a long chain molecule in a solution carries electric charges, the statistical coil is inflated, and the average square of the distance between the ends of the chain is larger than in the uncharged state. For a number of properties the determining factor is the value of ∑k (r2k)av, where rk is the distance between the k'th link in the molecule and the centre of gravity. This quantity is proportional to the square of the effective radius and is related to the square of the distance between the ends by a simple formula (section 2), provided the radius of the coil is small compared with the length of the extended chain. In section 3 the electrical free energy of the molecule is derived as a function of effective radius on the assumption that no electrolytes are present. This free energy determines in its turn the average dimensions of the coil. In section 4 a similar theory is developed for charged polymer molecules in the presence of electrolytes. The change of the effective radius with the charge on the polymer and the concentration of the electrolytes is calculated. In the limit of high electrolyte content the equilibrium between the interior and the exterior of the polymer coil may be considered as a Donnan equilibrium.

Specificity in the enzymic conversion of polyunsaturated fatty acids into prostaglandins

Abstract: The enzyme specificity in the biosynthesis of prostaglandins has been investigated by incubation of a particulate fraction of sheep vesicular glands with ω6 tri- and tetraenoic C18 - C22 fatty acids and isomers of ω6 eicosatrienoic acid (20: 3 ω6). The chemical synthesis of the various substrate fatty acids is described. The tetraenoic fatty acids were converted into a series of prostaglandin E2 homologues and the trienoic fatty acids into a series of prostaglandin E1 homologues. The only isomer of 20: 3 ω6 which showed a fairly high conversion into an isoprostaglandin E1 was the ω7 compound. Maximum conversions were obtained from ω6 C20 acids. The smooth muscle stimulating activity of prostaglandin E1 and E2 appears to be very specific. All other prostaglandins had much lower activities.

Synthesis of some new pyrazole-containing chelating agents

Abstract: Procedures are described involving the condensation of l-(hydroxymethyl)pyrazole (1a) and l-(hydroxymethyl)-3,5-dimethylpyrazole (1b) with the following amines (products given in parentheses): ethylamine (2a and 2b), aniline (3a and 3b), N,N′-dimethyl- l,2-ethanediamine (4a and 4b), 1,2-ethanediamine (6a and 6b), diethylenetriamine (7a and 7b), triethylenetetramine (8a and 8b) and ammonia (9a and 9b). All amine hydrogens are completely substituted by pyrazol-1-ylmethyl groups (compounds 2a-9a) or (3,5-dimethylpyrazol-1-yl)methyl groups (compounds 2b-9b with yields being better than 90%.

Molecular complexes and their spectra. VI. Some problems and new developments

Abstract: Although the charge-transfer theory probably affords a correct general account of major aspects of the structure and spectra of molecular complexes, its application to the detailed structures of particular types of complex presents a variety of problems whose definitive solution will require much new experimental and theoretical research, but should then yield many interesting conclusions. The effects of London dispersion forces and classical electrostatic forces as well as charge-transfer forces must always be taken into account. Orientation isomerism, acceptation cross-sections of acceptor molecules, paraffin-halogen interactions and their contact charge-transfer spectra, intensity problems, the blue shift of the iodine visible band in the spectra of iodine complexes, and complexes with two charge-transfer spectra, are discussed below.

Electronic spectra of mono‐ and di‐negative aromatic ions

Abstract: The electronic spectra in the 32-4 kK region of the mononegative ions of naphthalene, anthracene, tetracene, phenanthrene, diphenyl, terphenyl, quaterphenyl, pyrene, perylene, triphenylene and coronene are given. The spectra of the dinegative ions of anthracene, tetracene, terphenyl, quaterphenyl and perylene have also been investigated.

The oxidative coupling of aromatic compounds with palladium salts

Abstract: Reaction of benzene, palladium chloride and sodium acetate in acetic acid solvent produces biphenyl in a high yield. In the absence of sodium acetate no reaction occurs. The reaction is first-order with respect to benzene and PdCl2. With monosubstituted benzenes in general a mixture of isomeric biphenyls (X-C6H4-C6H4-X,X = alkyl, aryl, OR, Cl, COOR) is obtained. The substitution pattern corresponds with that observed in electrophilic aromatic substitution. The substituents exert a weak polar effect: electron-donating groups increase the rate, while the opposite holds for electron-attracting groups. With disubstituted benzenes steric effects play an important role. From o-xylene 3,4,3′,4′- and 2,3,3′,4′-tetramethylbiphenyl have been obtained as the only products in a molar ratio of 2.7 : 1. The results are most satisfactorily described by a mechanism involving complex formation between the aromatic compound and PdCl2 as the rate-determining step. The complex formed is assumed to yield a π-cyclohexadienyl-PdCl complex by a fast reaction with acetate anions. The complex formed, being unstable, decomposes to yield biphenyl and palladium metal.

Investigations on nematicides: I. Isolation and structure of a nematicidal principe occurring in Tagetes roots

Abstract: Some highly nematicidal polythienyls have been isolated from the roots of Tagetes plants. One of the compounds was shown to be α-terthienyl (I).

Chiral catalysts for enantioselective carbenoid cyclopropanation reactions

Abstract: Chiral copper(I) and rhodium(II) catalysts designed to achieve enantioselection in cyclopropanation reactions have recently been reported. These catalysts react with diazo compounds to form intermediate metal carbenes that subsequently react with alkenes, in both intermolecular and intramolecular transformations, to form cyclopropane derivatives. They are constructed with chiral ligands whose function is to orient carbene substituents and control olefin approach to the carbenoid center. Enantioselectivities that are greater than 95% have been achieved. In this review, the major advances in chiral catalyst design and development are described, and a uniform mechanistic interpretation is advanced to explain the results accumulated in reported investigations. Focus is placed on chiral salicylaldimine and semicorrin/bis-oxazoline copper catalysts and on the newest class of chiral catalysts for enantioselective carbenoid reactions, rhodium(II) carboxamides. Although early in their development, sufficient advances have been made to justify placement of this catalytic methodology among the most promising for enantioselective cyclopropanation reactions.

Supramolecular encapsulation of C60 in a water-soluble calixarene - a core-shell charge-transfer complex

Abstract: A calix[8]arene derivative has been found to form a water soluble complex with fullerene-C60, but not with C70, which allows extraction of C60 from e.g. toluene into the aqueous phase. Charge transfer character of the complex is evident from strong charge transfer absorption around 440 nm measured in water. Molecular modeling calculations indicate a core-shell structure for the complex.