Jacques Metzger

A kinetic study of the catalytic decomposition of cyclohexenyl hydroperoxide by RhCl(PPh3)3

Abstract The study of the catalytic decomposition of cyclohexenyl hydroperoxide shows that the reaction occurs by a free-radical process which can be described by a monoelectronic Haber-Weiss mechanism involving rhodium(I), rhodium(II) and rhodium(III) species. The validity of the proposed mechanism was tested by simulating it on a digital computer and comparing the observed and calculated rate constants. Good agreement between kinetic results obtained from the decomposition study and a previously performed autoxidation study was also verified.

Gear effect—10: Conformational aspects of the positive or negative buttressing effects of methyl groups: polymethylpyridines

Abstract The effect of the shape of a methyl group on reactivity, which cannot be accounted for by considering a methyl group as a spherical substituent with the appropriate van der Waals radius, was considered in kinetics of alkylalion of substituted pyridines and barriers to rotation and ground state conformations of an isopropyl group attached to a planar framework. The perturbation of a methyl group by an o-methyl group is accounted for by a unique conformational explanation which involves the polyhedral shape of the methyl group.

GC-MS-SPECMA bank analysis of JUniperus communis needles and berries

Abstract Using a combination of gas chromatography-mass spectrometry (electron impact) as well as the headspace technique, more than 70 compounds were found in the juniper needle oil obtained from plants growing in southeastern France (Provence). A comparison between the headspace of fresh and bottled black berries shows a significant loss of the monoterpenoid fraction with time. In the green berries (unripe) this loss is more marked. A sesquiterpenoid fraction of the Juniperus communis needle oil was also investigated by means of the GC (FID) and GC-MS (EI, PCI). Among more than 100 isolated constituents, 64 were sesquiterpenoids. The presence of several oxygen-containing derivatives based on the calamene and calacorene isomers was established but their structures were not fully determined. The various compounds were identified on the basis of our SPECMA data bank (mass spectra and Kovats indices) and our own files.

An unusual route to the isopolymolybdates; Octamolybdate β-[Mo8O26]4− and hexamolybdate [Mo6O19]2−. Reaction of dioxomolybdenum complexes with triphenylphosphonium ylides. Crystal structures of the salts [PPh3CH2COOEt]+2[NH2Et]+2 [Mo8O26]4−, [PPh3CH2COOEt]+2 [Mo6O19]2−, and [PPh3CH2Ph]+2 [Mo6O19]2−

Abstract Isopolymolybdate anions with various counterions have been obtained from the reaction of dioxomolybdenum(VI) compounds and the triphenylphosphonium ylides RCHue5fbPPh 3 (R = Ph, COOEt, H) in dichloromethane. The polyoxoanions are of two types, β-[Mo 8 O 26 ] 4− and [Mo 6 O 19 ] 2− , depending on the starting molybdates. X-ray structure determinations have been performed on the salts [PPh 3 CH 2 COOEt] + 2 [NH 2 Et] + 2 [Mo 8 O 26 ] 4− , [PPh 3 CH 2 COOEt] + 2 [Mo 6 O 19 ] 2− , and [PPh 3 CH 2 Ph] + 2 [Mo 6 O 19 ] 2− .

Kinetics and thermal degradation of the fructose-methionine Amadori intermediates. GC-MS/SPECMA data bank identification of volatile aroma compounds

Abstract Fructose-methionine Amadori intermediates, prepared from d -glucose and l -methionine, were purified by semi-preparative HPLC. Structural elucidation was achieved by 13 C-NMR and mass spectrometry in the FAB + and FAB − modes. Constant rates of formation of glucosylamine and the Amadori intermediate, and their thermal degradation into reductones and methionine as well as into diglucosylamine, were observed. Thermal degradation of the Amadori intermediate gives not only the well-known degradation products of the sugar moiety and methional (from the Strecker degradation of methionine), but also several heterocyclic compounds (pyridines, pyrazines, pyrroles, and furans). Some of them contain a methylthiopropyl group in their side chain. These new compounds were identified by the fragmentation rules and the Kovats index additive properties. Out of the 80 compounds isolated, ∼ 70 were identified.

Olefin epoxidation followed by epoxide transformation into 1,2-dibromoalkane by a peroxonickel-dibromomolybdenum bimetallic-system

Abstract The interaction of bis(t-butylisocyano)peroxonickel(II) and bis(triphenylphosphine oxide)dibromodioxomolybdenum(VI) in the presence of cyclohexene yields 1,2-dibromocyclohexane as the main product. This result is explained by the prior epoxidation of cyclohexene, followed by its conversion into the 1,2-dibromoalkane. The epoxidation step implies peroxidation of the dioxomolybdenum by the peroxonickel species. It is shown that this occurs by a dioxygen-ligand transfer accompanied by the back transfer of two bromine atom and two triphenylphosphine oxide molecules.

Transformation of an epoxide into a 1,2-dibromoalkane by a dioxodibromomolybdenum(VI) complex

Abstract Dioxodibromomolybdenum(VI) when complexed with acetonitrile reacts with cyclohexane oxide in a 2 1 ratio to give 1,2-dibromocyclohexane. This novel bromination reaction probably proceeds by an initial ring opening to give the β-bromoalkoxide, which then reacts with a second molecule of molybdenum-dibromide to give the 1,2-dibromoalkane.

Ultraviolet Spectrometry Study of Diazoles and Diazines-1, 3: Pyrimidinethione-2 and Alkyl (Allyl, Benzyl) Thio-2 Pyrimidines

Abstract We describe the ultraviolet spectra of mercapto-2 pyrimidine and alkyl (allyl, benzyl) thio-2 pyrimidines, substitution effect and solvent effect are discussed. Comparaison with saturated homologues is given.

Dioxygen ligand transfer in heterobimetallic systems

Abstract A new type of heterobimetallic dioxygen complex is described. On the basis of spectroscopic and analytical data this complex was assigned the following formulation: When M = (PPh3)2N, the corresponding complex dissolved in organic solvents, is stable under an inert atmosphere. Under an atmosphere of oxygen, on the other hand, a new peroxo complex of molybdenum is obtained: This new dioxygen complex is the first example of a peroxo complex obtained directly from oxygen and molybdenum. Experiments carried out with 18O2 clearly show that the entering molecule of oxygen is directly fixed on the molybdenum atom, whereas the original dioxygen ligand remains on the cobalt atom. These results, as well as other experimental observations, are discussed.

The photochemical behaviour of bis aryl-1,3 triazenes

Abstract The photolysis of bis aryl-1,3 triazenes carried out in non-aromatic solvents gives products whose structures are consistent with a cage recombination process of homolytically formed radicals and the subsequent abstraction of hydrogen from the solvent molecules by these arylamino radicals. In aromatic solvents, a free-radical chain process leads to the formation of products resulting from the homolytic substitution on the solvent.