Dosage de l'hydrogene,de l'azote et de l'oxygene dans le monocarbure d'uranium

A method is described for the determination of hydrogen, oxygen and nitrogen in uranium monocarbide. Hydrogen and oxygen are determined by the classical or modified “Platinum flux” method at 2000° with a coefficient of variation of 10%. Nitrogen is determined at 2000° by the modification of the “Platinum flux” technique. The results obtained are in agreement with those found by Kjeldahl analysis. The coefficient of variation is about 10%. A procedure for the simultaneous determination of the 3 gases is given.     

Greffage radiochimique de l'acrylonitrile sur le poly(methacrylate de methyle)

The radiation-induced polymerization of acrylonitrile with dissolved PMMA exhibits kinetics similar to those found with the pure monomer. The addition of PMMA to the monomer at first leads to an increase in polymerization rate; a maximum in rate is observed for 60 per cent acrylonitrile in the mixture. The unreacted PMMA was quantitatively extracted by toluene from the reaction mixture. In contrast, polyacrylonitrile could not be separated from the graft copolymer by fractional precipitation, presumably due to association of the graft copolymer with the precipitated homopolymer. The free radical yield of PMMA “G_R effective” derived from these results was found to be 8 to 10 in mixtures containing small amounts of monomer. It rapidly decreased as the monomer concentration increased.The solubilities of the graft copolymers were characterized by the precipitation γ determined for several precipitants in DMF solutions. A maximum in solubility was found for copolymers containing 25 to 35 per cent acrylonitrile in DMF-alcohol mixtures. The glass transition temperatures (T_g) of the graft copolymers were measured using a penetrometer. T_g increased with the MMA content in the copolymer. A small minimum of T_g appeared to exist for copolymers containing 90 per cent acrylonitrile.     

Analyse viscosimetrique des telomeres de l'acrylate d'ethyle et du chlorure de vinyle avec le tetrachlorure de carbone et le trichloroacetate de methyle

Telomers of ethylacrylate and vinylchloride with carbon tetrachloride or methyltrichloroacetate have been prepared by redox catalysis. They have the expected viscometric behaviour which depends upon the nature of the telogen. Thus viscometry can be used for determination of average molecular weight for such compounds.     

Copolymerization de l'acenaphtylene avec le n-vinylcarbazole

The copolymerization of acenaphthylene (ANA) with N-vinylcarbazole (NVC) was investigated at 60° in the melt with 1% AIBN and in benzene solution at 20° with gamma ray initiation. In the melt at 60°, the polymerization rate gradually decreases with the amount of NVC in the mixture. The following reactivity ratios were determined: r_NVC = 0.12; r_ANA = 7.0. The copolymers have a fairly narrow distribution of compositions but contain small amounts of poly NVC. Gamma ray initiation at 20° gives rise to the free radical copolymer together with significant amounts of poly NVC which results from a cationic mechanism. In addition, acenaphthylene cyclodimerizes in the process.     

Prevision des equilibres de redistribution sur le phosphore a l'aide d'un schema de decomposition des energies de liaison

The application of a bond-energy decomposition scheme to redistribution free energies permits the establishment of linear relationships between these free energies. The position of numerous equilibria can in this way be predicted from a limited number of experimental measurements. Applications are given to the exchange of F, Cl, Br, NCS, OPh, NEt₂ and Me on phosphorus, phosphoryl and phosphonyl centres.     

Polymerisation cationique de l'indene amorcee par le tetrachlorure de titane-I Influence des impuretes du solvant,le chlorure de methylene,et effets cocatalytiques de l'eau et de l'acide chlorhydrique

The polymerization of the system indene-titanium tetrachloride-methylene chloride gave irreproducible kinetics which have been attributed to variable concentrations of impurities in the solvent. Incomplete yields sometimes observed at ?70° are also caused by impurities, but introduction of water and hydrochloric acid then gives complete yields. A new method of solvent purification has been used giving reproducible yields and rates. In such cases, monomer consumption at ?70° follows the rate law log [M]_o/[M] = kt.     

Heterocyclisation intramoleculaire d'alcools possedant un squelette cedranique. Oxydation par le tetraacetate de plomb et par l'oxyde de mercure et le brome

Oxidation with lead tetra-acetate of neoisocedranol yields the corresponding ether in good yield. Under the same conditions, cedrol remains unchanged; however, when cedrol is reacted with mercuric oxide and bromine, the corresponding ether is obtained as major product. The structure of the substrates is linked with the mechanism of the two reactions and with the nature of the intermediates in the heterocyclisation reaction. The difference in behaviour between the two substrates towards the two oxidising agents is rationalized.     

Enthalpie de dissolution a 298 K des fluorures de potassium et de cesium dans l'acide fluorhydrique et le fluorure d'hydrogene

A calorimetric cell designed for studies of reaction in anhydrous hydrogen fluoride has been constructed. Enthalpies of solution of KF and CsF in aqueous solution of HF (from 0 to 100 % HF) have been measured.     

Etude des reactions de substitution homolytique sur le noyau pyridinique; influence de l'acidite du milieu

Homolytic substitution by the l-n-undecyl radical at positions 2 and 4 of the pyridine nucleus results from thermal decomposition of dodecanoyl peroxide in acetic acid. Rate dependence on pH shows that pyridine protonation increases the rate of addition of the alkyl radical to the pyridine ring but decreases the rate of the reaction of the intermediate radical with the peroxide. Results are interpreted in terms of orbital interaction theory.     

Enthalpies de complexation de quelques phosphoramides avec le chlorure d'antimoine(V). Influence de la structure sur le nombre donneur selon Gutmann

Complexation enthalpies for various compounds with SbCl₅ have been calorimetrically determined in dilute dichloro-1,2 ethane solution at 25°C. In the case of 22 organo-phosphorylated compounds OPX_x,Y_3-x, (X, Y = NMe₂, Net₂, NHEt,

, OEt; x = 0, 1, 2, 3), our calorimetric results allow a characterization of Lewis basicity variations (as Gutmann's donor number DN) against the nature of substituents at the phosphorus atom. Within this scale, many compounds are more basic than HMPA OP(Nme₂)₃ whose DN is, according to our results, greater than currently admitted; if no systematic effects are noted, the influence of conformation may, however, explain the DN variations in each series (for X and Y given, x varying from 0 to 3). Moreover, thanks to conductometric measurements, an instantaneous reaction of triethylamine with the solvent is evidenced.     

Obtention de selenopysultones lors de l'oxydation de thio-1 chromenes par le dioxyde de selenium

Selenium dioxide oxidation of 1-thiochromene leads to 3-formyl (5,6)benzo-1,2 thiaseleninne-1,1-dioxide, which is a representative of a hitherto unknown class of heterocyclic compounds. Pyrolysis of this compound leads to 2-formyl benzo(b)selenophen, by loss of sulphur dioxide. The reaction can be applied to other 1 thiochromenes but no similar behaviour has been observed for their selenium isologues.     

Obtention de cyano-cetones ou le groupe CN est en position equaoriale lors de l'hydrocyanation non-angulaire d'octalones

Contrary to current statement, non-angular hydrocynation of cyclic α, β-ethylenic ketones does not yield only exial cyano group in the final cyano-ketones.     

Reaction de la bromo-3 pyridine avec le diisopropylamidure de lithium. Mecanismes de metallation et de migration d'halogene. Regioselectivite de l'addition polaire sur la pyridyne-3,4

3-bromo pyridine behaviour towards lithium diisopropyl amide (LDA) in THF is studied. A careful study of the experimental conditions point to a metallation reaction in position 4 and a “halogen dance” mechanism with isomerisation into a 4-bromo pyridine. Conversion into diisopropylamino compounds occurs simultaneously with a 3 oriented elimination-addition (EA) reaction from transient isomeric lithio-derivatives and a competing addition-elimination (AE) mechanism from the in situ formed 4-bromo pyridine.     

Sur une cause d'erreur dans le dosage par voie humide de l'azote dans les aciers speciaux

The estimation of nitrogen in normal or special steels by the Kjeldahl method can give results that are too high if the acid used to dissolve the steel (even “pro analysi” acid) contains impurities such as nitrates, and if the metal itself contains even negligible amounts of molybdenum (e g a few ten-thousandths). In this case the blank test can nevertheless give a very weak or negative result.In order to ascertain from this point of view the quality of the acid used, it is necessary to compare the nitrogen contents obtained on a sample with a very low nitrogen content, e g electrolytic iron, in the absence or in the presence, respectively, of a minute addition (about 0.1%) of molybdenum. The difference between these determinations should be negligible. If it is not, then the acid tested should be rejected, or distilled before use.     

Influence de la solvatation par le tert-butanol sur la structure et la reactivite de l'enolate de potassium de l'acetylacetate d'ethyle en presence de couronne ou de cryptand. etude par spectrometrie infra-rouge et cinetique

The structure and the nucleophilic reactivity of crowned (18-crown-6) or cryptated {cryptand (2.2.2)} potassium ethyl acetoacetate enolate have been compared in tert-butanol and in DME (or THF). In the protic solvent tert-butanol, the crowned and the cryptated potassium enolate species both exist as loose ion pairs in which the enolate anion, strongly hydrogen-bonded to the solvent, is in a “transoid” (non chelating) conformation. Both species show similar reactivities towards alkylating agents but completely different reactivities are observed in aprotic weakly dissociating media (THF, DME). In contrast to what is observed in tert-butanol, the cryptated species and the crowned species have very different nucleophilic reactivities in THF or DME; in those solvents only the cryptated species retains a loose ion pair structure; the crowned species is a contact ion pair in which the enolate anion chelates the potassium cation. The solvation of this crowned chelate species by tert-butanol has been demonstrated in binary mixtures of solvents (C₆D₆-t-BuOH, THF-t-BuOH). The oxygen basicity of the enolate anion is very different in the crowned chelated ion pair compared with the cryptand separated ion pair.