Vaporisation et dissociation thermique des sulfures de phosphore P4S3, P4S7 et P4S10 a l'etat gazeux

Résumé Nous avons montré par spectrométrie Raman à chaud et mesure des tensions de vapeur que P₄S₃ se vaporise de façon congruente tandis que P₄S₇ et P₄S₁₀ se dissocient dès le début de leur vaporisation. P₄S₇ donne réversiblement P₄S₃ et soufre. P₄S₁₀ se dissocie irréversiblement en P₄S₇ et soufre. A l'état de vapeur non saturante, P₄S₃ se dissocie au-dessus de 600° avec formation de phosphore, de soufre et d'autres espèces non identifiées.Nous avons mesuré expérimentalement la capacité calorifique de P₄S₃ liquide, calculé celle de P₄S₃ gazeux et son entropie standard. Nous avons aussi estimé l'enthalpie standard de vaporisation de P₄S₃ à l'aide des mesures des tensions de vapeur saturante. Nous en avons déduit l'entropie standard de P₄S₃ liquide et son point d'ébullition.

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It is shown by Raman spectroscopy at high temperature and by vapor tensimetric measurements that the vaporisation of P₄S₃ is congruent, whereas P₄S₇ and P₄S₁₀ dissociate at the beginning of vaporisation. P₄S₇ gives P₄S₃ and sulfur reversibly. The dissociation of P₄S₁₀ into P₄S₇ and sulfur is irreversible. Above 600°, in non-saturated vapour the dissociation of P₄S₃ gives phosphorus, sulfur and some unidentified gaseous species. The heat capacity of liquid P₄S₃ has been measured. That of gaseous P₄S₃ and its standard entropy have been calculated. The vaporisation standard enthalpy of P₄S₃ has been estimated from the experimental results on the saturated vapour pressures. The standard entropy of liquid P₄S₃ and its boiling point have been derived from these data.

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Zusammenfassung Mittels Raman-Spektrometrie bei erhöhter Temperatur und durch Messung der Dampfdrucke wurde festgestellt, daß sich P₄S₃ verflüchtigt, während P₄S₇ und P₄S₁₀ mit Beginn der Verflüchtigung dissoziieren. P₄S₇ ergibt reversibel P₄S₃ und Schwefel. Im Zustand ungesättigten Dampfes dissoziiert P₄S₃ oberhalb von 600° unter Bildung von Phosphor, Schwefel und anderer nicht identifizierter Substanzen.Die Wärmekapazität von flüssigem P₄S₃ wurde gemessen, während die vom gasförmigem P₄S₃ sowie seine Standard-Entropie berechnet wurden. Die Standard-Enthalpie der Verflüchtigung des P₄S₃ wurde durch Messungen der Sättigungs-Dampfdrucke ermittelt. Daraus wurden die Standard-Entropie des flüssigen P₄S₃ sowie sein Siedepunkt berechnet.

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- - , P₄S₃ , P₄S₇ P₄S₁₀ . P₄S₇ P₄S₃ , P₄S₁₀ P₄S₇ . 600° P₄S₃ , . P₄S₃, P₄S₃ . P₄S₃. P₄S₃ .

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Nous remercions Monsieur Letoffe du laboratoire du Professeur J. Bousquet, INSA de Lyon, 20 Avenue Albert Einstein 401, 69621 Villeurbanne, qui a r6alis6 pour nous les déterminations expérimentales des capacités calorifiques de P₄S₈ liquide.     

New stereoselective syntheses of cis- and trans-2-methyl-4-arylpiperidines

A stereoselective approach has been developed for the synthesis of cis- and trans-2-methyl-4-arylpiperidines from a common intermediate. The Ni-catalyzed hydrogenolysis of N-Boc-2-methyl-4-aryl-4-piperidinols, obtained by addition of organometallic reagents on N-Boc-2-methyl-4-piperidone, afforded the trans derivatives with up to 95% selectivity whereas the corresponding cis isomers were obtained in the presence of palladium catalysts.     

Chiral ditopic receptors. Application to palladium-catalyzed allylic alkylation

Chiral pyridinooxazoline, quinolinooxazoline, bis(oxazolino)pyridine (pybox), and bisoxazoline (box) derivatives containing crown ether residues were prepared. Some of the ligands were assessed in substrate binding studies and in palladium catalyzed allylic alkylations.     

Ring-opening metathesis polymerization (ROMP) of isomerically pure functional monomers and acyclic diene metathesis depolymerization (retro-ADMET) of functionalized polyalkenamers

ROMP and retro-acyclic diene metathesis (ADMET) were used for the synthesis of new functional polymers and functional oligomers, respectively. Purely exo and enantiomerically pure norbornene and 7-oxanorbornene derivatives were prepared using stereospecific synthesis, effective fractionation and high yield condensation reactions. Successful ROMPs of those monomers were performed using either the new carbenic Schrock’s or Grubb’s catalysts or in some cases a classical bicomponent catalyst. New functional polymers such as optically active poly(norbornene-2-carboxylic acid), reactive poly(norbornene-2-azlactone), and side-chain liquid crystal polyoxanorbornenes were fully characterized. On the other hand, successful depolymerizations of 1,4-polyisoprene and of epoxidized 1,4-polybutadiene via cross-metathesis with 4-octene were performed using a stabilized bicomponent catalyst and the Grubb’s catalyst, respectively. Conditions for the controlled synthesis of epoxidized oligobutadienes and of epoxydienic monomers via retro-ADMET were clearly defined.     

Methodology of using expert systems for structure elucidation of organic molecules by their spectra

Major axioms underlying structure elucidation of molecules by their characteristic spectral data are considered. The amount of information obtained by solving the problem on structure elucidation of molecules serves as a basis to evaluate the quality of solution. Conditions for computer-aided solution of problems using expert systems (ES) are analyzed. Reasons for incorrect or zero solutions and for inconsistencies leading to negative results are examined. The role of additional information as a necessary condition for correct solution is discussed. On the basis of this analysis, a general strategy for structure elucidation of molecules by their spectra using ES is suggested. The principal idea is to use the iteration method, gradually increasing the rigidity of constraints. Strategies named ARCHEOLOGIST and SCULPTOR are discussed. Examples are given. Russian Scientific Research Institute of Organic Synthesis. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 3, pp. 548–558, May–June, 1995. Translated by L. Smolina     

A facility for the production of iodine-123 by spallation of caesium

A facility for the continuous production of iodine-123 by spallation of elemental caesium by 482 MeV protons has been in operation at a TRIUMF beam dump for about 2 years. Radioxenon from the target is efficiently trapped on alumina which is subsequently used to remove the¹²¹Te decay product. The yield is 100 mCi/h from a 20 gm/cm² target at 10 μA. Impurities are¹²⁵I<2% and¹²¹Te<0.2% at 27 hours after end of production. The¹²³I consists mainly of iodide along with significant iodate impurity. The product is used extensively in Canadian clinics for thyroid analyses and for labelling radiopharmaceuticals.     

Droplet evaporation study applied to DNA chip manufacturing

DNA chips are potentially powerful technologies for genotyping and gene expression profiling that rely on comparative analyses of up to thousands of "spots of analysis" on a glass support. The spot quality throughout the support influences spot-to-spot variations within an array and the repeatability of data across experiments. For glass slide DNA microarrays, droplets of DNA solution are deposited on functionalized glass slides and left to react through complete evaporation of the droplet. On hydrophobic flat surfaces, different modes of droplet evaporation can be attained. Under atmospheric pressure, water droplets tend to evaporate under two main regimes. Initially, the droplet flattens with a constant contact area, and then the droplet shrinks at a constant contact angle. As a result, the diameter and morphology of thousands of spots on microarrays are not uniform. This leads to poor and unreliable data processing results. In this work, we report the evaporation of an aqueous solution under a constant contact area mode. Evaporation under reduced pressure and the effect of reagent additives to the solution have been investigated. Video microscopy and digital image analysis techniques were applied to monitor the evaporation of the droplets. A mixture of surfactants was developed to maintain a constant area regime during evaporation and to form homogeneous spots. The control of some physicochemical properties (wetting, evaporation rate) of the droplet allows the formation of well-controlled spots compatible with DNA grafting. The influence of surfactant molecules on the mechanisms of evaporation is also discussed.     

Stereoselective synthesis of a new perhydroindole derivative of chiral iminodiacid,a potent inhibitor of angiotensin converting enzyme

The stereoselective synthesis of N-[(s) 1 - carbethoxybutyl)] (s) alanine and of (2S, 3aS, 7aS) 2-t.butoxycarbonyl perhydroindole are described. Their coupling produces the title compound     

Crystal and molecular structure of hexacarbomethoxycyclopropane

A. N. Nesmeyanov Institute of Heteroorganic Compounds, Academy of Sciences of the USSR. N. D. Zelinskii Institute of Organic Chemistry, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 3, pp. 171–173, May–June, 1989.