Hydrogenation without a transition-metal catalyst: on the mechanism of the base-catalyzed hydrogenation of ketones

The hydrogenation of unsaturated organic substrates such as olefins and ketones is usually effected by homogeneous or heterogeneous transition-metal catalysts. On the other hand, a single case of a transition-metal-free and purely base-catalyzed hydrogenation of ketones was reported by Walling and Bollyky some 40 years ago. Unfortunately, the harsh reaction conditions (ca. 200 degrees C, >100 bar H(2), potassium tert-butoxide as base) limit the substrate spectrum of this reaction to robust, nonenolizable ketones such as benzophenone. We herein present a mechanistic study of this process as a basis for future rational improvement. The base-catalyzed hydrogenation of ketones was found to be irreversible, and it shows first-order kinetics with respect to the substrate ketone, hydrogen, and catalytic base. The rate of the reaction depends on the type of alkali ion present (Cs > Rb - K > Na > Li). Using D(2) instead of H(2) revealed a rapid base-catalyzed isotope exchange/equilibration between the gas phase and the solvent as a concomitant reaction. The degree of deuteration of the product alcohols did not indicate a significant kinetic isotope effect. It is proposed that both ketone reduction and isotope exchange proceed via similar six-membered cyclic transition states involving the H(2)(D(2))-molecule, the alkoxide base, and the ketone (solvent alcohol in the case of isotope exchange). Mechanistic analogies are pointed out which apparently exist between the base-catalyzed hydrogenation of ketones studied here and the Ru-catalyzed asymmetric ketone hydrogenation developed by Noyori. In both cases, heterolysis of the hydrogen molecule appears to be assisted by a Br?nsted-base (i.e., alkoxide), the latter being bound to the substrate ketone or the catalyst ligand, respectively, by a bridging Lewis-acidic alkali ion.     

Determination of low dose concentration profiles in solids by means of (n,p) and (n, α) reactions

The isotopes³He,⁶Li,⁷Be and¹⁰B exhibit extremely large cross sections, between 1 and 48 kilobarn, for (n, p) or (n, α) reactions with thermal neutrons. Together with now available extracted thermal neutron fluxes of 10⁽ n·cm⁻²·sec⁻¹ or more, these reactions present a highly sensitive method of detecting the mentioned light elements in any heavy matrix material. Through the experimentally determined energy losses of the emitted protons or α-particles, also well resolved depth profiles can be obtained, as demonstrated here for some relevant examples from semiconductor and fusion technology.     

Hydroxybromierung und Methoxybromierung von (Z)-Cycloocten

In addition totrans-2-bromocyclooctanol andtrans-1,2-dibromocyclooctane,cis-4-bromocyclooctanol,cis-1,4-dibromocyclooctane,trans-1,4-dibromocyclooctane, and (Z)-5-bromocyclooctene are obtained, when (Z)-cyclooctene is treated with N-bromosuccinimide in the presence of water. Similarly the methoxybromination of (Z)-cyclooctene gives transanular products.     

Template synthesis in the nickel(II)–thiocarbohydrazide–propanone triple system

The complexing process proceeding in the Ni^II–thiocarbohydrazide (H₂N–H–NC(=S)–NH–NH₂)–propanone triple system in EtOH solution and nickel(II)hexacyanoferrate(II) gelatin-immobilized matrix has been studied. It has been found that in the first case, template synthesis leading, as a minimum, to formation of three coordination compounds of Ni^II with (N,N,S,S)-donor tetradentate ligands having NiL¹, NiL² and NiL³compositions where L¹ is 4,6,6-trimethyl-2,3,7,8-tetraazanonen-3-di(thiohydrazide)-1,9, L² is 4,6,6,12-tetrametyl-1,9-dithio-2,3,7,8,10,11-hexaazatridekadien-3,11-hydrazide-1 and L³ is 2,8,10,10,16-pentamethyl-5,13-dithio-3,4,6,7,11,12,14,15-octaazaheptadekatrien-2,7,15 is observed, whereas in the gelatin-immobilized matrix, a complexing process in the system considered does not occur.     

Some investigations on the photostabilization of polypropylene

The effect of substituted hydroxybenzophenone, benzotriazole and organic metal complexes on the photooxidation of PP films has been studied. It has been established that NiDBTC added in 1.0 wt. % is the most effective photostabilizer.While in the case of other stabilizers there is a slight increase in the Co content even during the induction period, with the application of NiDBTC practically no oxidation can be observed before the stabilizer completely disappears. This means that NiDBTC inhibits the photooxidation of the polymer even in low concentration.

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, - . , Ni, 1,0 . %. . , Ni , . , Ni .

     

Reaction of some sympathomimetic amines with sodium 1,2-naphthoquinone-4-sulphonate

Summary The condensation products of 4 sympathomimetic amines with 1,2-naphthoquinone-4-sulphonic acid have been prepared and examined. A spectrophotometric procedure based on the chloroform-soluble orange-red condensation product is described. The same products were investigated fluorimetrically after reduction with sodium borohydride. The results obtained are satisfactory.

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Zusammenfassung Die Kondensationsprodukte vier sympathicomimetischer Amine mit 1,2-Naphthochinon-4-sulfonsäure wurden dargestellt und untersucht. Ein spektralphotometrisches Verfahren auf der Grundlage des chloroformlöslichen, orangeroten Kondensationsproduktes wurde beschrieben. Die gleichen Produkte wurden auch fluoreszenzanalytisch nach ihrer Reduktion mit Natriumborhydrid untersucht. Die Ergebnisse sind befriedigend.

     

1-Alkoxy-2-azaallenyl-komplexe von chrom und wolfram

The successive reaction of (CO)₆M with Na[NCR₂¹] and [Et₃O]BF₄ yields (CO)₅M[C(NCR₂¹)OEt] (II: M = Cr; III: M = W; CR₂¹ = C(C₆H₄Br-p)₂ (a), CPh₂ (b), C(C₆H₄OMe-p)₂ (c), C(C₆H₄)₂O (d), CBu₂^tt (e)). Hexacarbonyltungsten, (CO)₆W, reacts with Na[NCPh₂] and MeOSO₂F to give (CO)₅W[C(NCPh₂) OMe] (IV). X-Ray analysis of IIe shows that: (1) the CNC fragment is almost linear (171.7°); (2) the two NC bond lengths are equal within experimental error; and (3) the O,C,Cr,N plane is perpendicular to the C(Me₃),C,N,C(Me₃) plane (90.0°). Therefore compounds II–IV are best described as 1-alkoxy-2-azaallenyl complexes.     

Zur struktur von CaPdF4, CdPdF4, HgPdF4 und HpPdF2

Single crystals of CaPdF₄ (purple) and CdPdF₄ (dark blue) have been obtained by heating CaF₂ (CdF₂) with PdF₂ at 820°C (900°C) for ca. 20–30 d in sealed Pd (Pt) tubes. CaPdF₄ crystallizes tetragonal (KBrF₄-Type) with a = 5.52₁, c = 10.57₀ Å (space group I4/mcm ? D^18_4h, No. 140) Z = 4, 283 unique reflexions, R = 0.083; R_w = 0.079, CdPdF₄ cubic (CaF₂-variant) with a = 5.40₃ Å (space group Pa3 ? T^6_h, No. 205) Z = 4, 165 unique reflexions, R = 0.047, R_w = 0.032. The high pressure modification of PdF₂, obtained by heating PdF₂ in closed Pt-tubes under a pressure of ≈ 60 kbar and ‘HgPdF₄’, both black, a = 5.32₇ Å and a = 5.43 Å are isotypic. CaPdF₄ is diamagnetic, CdPdF₄ and HPPdF₂ are antiferromegnetic.     

Synthese neuer N-Vinylpyrrole

Syntheses of New N-Vinylpyrroles The reactions of pyrrolyl potassium ( 1 ) with (ethoxymethylene)malonic acid derivatives 2a–e yielded the carbanions 3a–e , which could be hydrolyzed to 4a–e , but with the exception of 4b they were not isolated, because a transformation to the N-vinylpyrroles 5a , c–e by elimination of ethanol took place; 1 reacted with 2b at 80°C to give 4b and 6 . Hydrolysis of 4b with KOH yielded 4g , which eliminated 1 mol of ethanol to form 5f , decarboxylation of which led to N-vinylpyrrole 7 . By cyclization of 5e under various conditions the pyrrolizines 8a , b are obtained, the hydrolysis of which did not give ketone 9 but only amino alcohol 10 . Some other cyclizations of 11a–c and 13 yielded the 3H-pyrrolizine derivatives 12a–c and 14 , respectively.     

Wave mechanics - the first fifty years : edited by W.C. Price,S.S. Chissick and T. Ravensdale,Butterworths, London, 1973, pp. 435, price £12.00

The free NH₃ molecule and the [Zn(NH₃)₄]²⁺ ion were studied by the kinematic coupling approach. The pure effects of this coupling were found to be small, and some modifications had to be introduced in order to get a reasonable force field. The force constants deduced for the skeletal vibrations are comparable with those of a quasi-exact force field. Calculated frequencies for [⁶⁸Zn(NH₃)₄]²⁺ and [⁶⁴Zn(ND₃)₄]²⁺ are reported in addition to those of [⁶⁴Zn(NH₃)₄]²⁺. Mean amplitudes of vibration for [⁶⁴Zn(NH₃)₄]²⁺ are given.