Direct hydrogenation of nitroaromatics and one-pot amidation with carboxylic acids over platinum nanowires

A novel ultrathin platinum nanowire with uniform length and a diameter of 1.5 nm was synthesized by acidic etching of FePt nanowire in methanol. This nanowire was characterized by high‐resolution transmission electron microscopy (HRTEM). X‐ray diffraction (XRD) data indicated that the main plane is (111). The ability of this nanowire to catalyze the heterogeneous hydrogenation of nitroaromatics to give the corresponding amines has been investigated. The catalyst showed satisfactory activity in various solvents under mild conditions and showed excellent stability. The catalytic performance was also evaluated in the one‐pot reduction of nitroaromatics and amidation with carboxylic acids under a hydrogen atmosphere at 100 °C. These methods for the hydrogenation of nitroaromatics and the direct amidation of nitroaromatics with carboxylic acids are simple, economical, and environmentally benign, and have practical advantages for the synthesis of amines and amides without the production of toxic byproducts.     

Adsorption and hydrogenation of unsaturated aldehydes over rhodium black

Hydrogenation selectivity of conjugated ethylenic bonds of unsaturated aldehydes over rhodium black is shown to be determined by intramolecular interactions in surface complexes due to the electronic structure of the initial unsaturated aldehydes.

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Mass spectral studies of alkylbenzenesulphonic acids through their S-benzylisothiouronium salts

The mass spectra of alkylbenzenesulphonic acids in the form of their S-benzylisothiouronium salts have been studied. These S-benzylisothiouronium salts dissociated into two parent reactant ions: (i) alkylbenzenesulphonic acid and (ii) S-benzylisothiourea. The characteristic fragmentation patterns of alkylbenzenesulphonic acids (0-5 substituted alkyls) were studied and compared with those of the parent hydrocarbons. The intensity of the molecular ion peak decreased with the increase in the molecular weight of the sulphonic acids. Desulphonation as well as loss of the alkyl group was observed in all the spectra. Migration of the alkyl group from S to O, followed by degradation, was also observed in all the spectra studied.     

Partial hydrogenation of benzene over platinum supported catalysts

Partial hydrogenation of benzene to cyclohexene has been studied on Pt/Nylon 66, Pt/MgO and Pt/TiO₂. An effect of the support on the selectivity to cyclohexene was observed, Pt/Nylon showing the highest selectivity, followed by Pt/MgO and Pt/TiO₂. An interaction of platinum with the more basic supports (Nylon, MgO) and a pretreatment under oxidizing conditions, results in a higher selectivity to cyclohexene.

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Pt/ 66, Pt/MgO PtTiO₂. , Pt/, Pt/MgO Pt/T,O₂. (, MgO) .

     

High-selectivity hydrogenation of cinnamaldehyde over platinum supported on aluminosilicates

This work studies liquid-phase hydrogenation of cinnamaldehyde to cinnamylalcohol over Pt/K-10 and ion-exchanged Pt/Na-Y. The experiments show the highest selectivity of 78% for Pt/K-10 and 92% for the Pt/Na-Y. By careful analysis, characterisation and changing reaction conditions it was attempted to cover key parameters possibly responsible for the high selectivity. The parameters are described and discussed in detail.     

Preparation, spectral and thermal studies of pyrazinecarboxylic acids and their hydrazinium salts

Some new hydrazinium 2-pyrazinecarboxylate and 2,3-pyrazinedi-carboxylate salts of the formulae N₂H₅pc, N₂H₅pc.H₂O (Hpc = 2-pyrazinecarboxylic acid), N₂H₅Hpdc, (N₂H₅)₂pdc.H₂O and N₂H₅(Hpdc).H₂pdc (H₂pdc = 2,3-pyrazinedi-carboxylic acid) have been prepared by neutralization of aqueous hydrazine hydrate with the respective acids in appropriate molar ratios. The free acids and their hydrazinium salts have been characterized by analytical, IR spectroscopic and thermal studies. IR spectra of all the salts show N-N stretching frequencies of the N₂H₅ ⁺ ion in the region 975–960 cm^-1. The thermoanalytical behaviour of the free acids and their salts has been investigated by simultaneous TG and DTA. While pyrazinecarboxylic acid shows single-step endothermic (229°C) complete decomposition, pyrazindi-carboxylic acid shows exothermic decarboxylation followed by identical endothermic decomposition as that of the former. Similarly, salts of the monocarboxylic acid show endothermic effects during pyrolysis, whereas salts of the dicarboxylic acid show endothermic followed by exothermic decomposition. The acids and their salts both undergo complete decomposition to gaseous products.     

Effect of cyclodextrins on the rhodium-catalysed hydrogenation of unsaturated carboxylic acids in water

Addition of cyclodextrin to the well-known RhCl₃/TPPTS (trisulfonated triphenylphosphine) hydrogenation catalytic system leads to high selectivities in the hydrogenation of unsaturated carboxylic acids in water. The presence of both cyclodextrin and sulfonate ions is required to obtain high selectivities.     

The effect of the substrate structure on the stereoselectivity in an asymmetric hydrogenation of unsaturated carboxylic acids over cinchonidine-modified palladium catalyst

An enantiomeric ratio of 10:1 (82% ee) was achieved for the first time in the hydrogenation of α,β-unsaturated acids with heterogeneous catalysts by designing the substrate structure to enhance the interaction with the catalyst, and to increase the intrinsic stereoselectivity.     

Proton conductivity in phenolsulfonic acids and their salts

The geometric parameters and energies of crystal hydrates of aromatic sulfonic acids and their salts, as well as the pathways of proton transport in them, were calculated by the DFT (B3LYP) method with the 6-31G** basis set. For aromatic sulfonic acids, the proton relay mechanism was shown to be energetically more favorable than rotation of the HSO group or direct proton transfer. Calculations show that an increase in the number of water molecules located near the HSO₃ group from one to four decreases the barrier from 6 to 0.3 kcal/mol. Hence, a moderate increase in humidity should enhance the conductivity, which is fully consistent with experimental data. Calculations predict that the salts where all protons are substituted by metal atoms are unlikely to show good conductivity. Conversely, mixed salts, for example, H₃C₆(OH)(NaSO₃)(HSO₃) and H₃C₆(OH)(RbSO₃)(HSO₃), are expected to be thermally stable and resistant to deliquescence with an increase in the humidity of a medium and to have good conductivity.     

Thermal studies on the sodium salts of aminosalicylic acids

The effect on the stability of the isomers of aminosalicylic acid of formation of their sodium salts has been studied by use of differential scanning calorimetry and thermogravimetry, coupled with evolved gas analysis by Fourier transform infrared spectroscopy. X-ray powder diffraction and infrared spectroscopy provided complementary information. The DSC curves for the sodium salts of all of the isomers showed complex dehydration/decomposition endotherms. From the initial mass losses of the TG curves, the amounts of water per mole of salt were estimated as 0.5, 2.4 and 1.4 moles for the sodium salts of 3-aminosalicylic acid, 4-aminosalicylic acid and 5-aminosalicylic acid, respectively. TG-FTIR results for the sodium salt of 3-aminosalicylic acid showed the evolution of carbon dioxide in three stages: below 150°C, between 200 and 300°C and continuous formation up to 500°C. This behaviour differs from that of 3-aminosalicylic acid itself, which forms CO₂ between 225 and 290°C. For the sodium salt of 4-aminosalicylic acid, the formation of carbon dioxide starts from 250°C and is still being formed at about 650°C. 4-aminosalicylic acid decarboxylates above 150°C. 5-aminosalicylic acid and its sodium salt showed no evolution of carbon dioxide below 600°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stereochemistry of the hydrogenation of o-xylene over a silica-supported polysilazane–platinum complex

Silica-supported polysilazane (SiO₂-Si-N), and its platinum complex (SiO₂-Si-N-Pt) were prepared. It was found that SiO₂-Si-N–Pt can catalyze hydrogenation of o-xylene under mild conditions (40–50°C, 1 atm). The products of the reaction were cis-and trans-1,2-dimethylcyclohexane. The formation of trans-1,2-dimethylcyclohexane may be adequately explained according to the ‘roll-over’ model. The stereoselectivity was influenced by temperature and catalyst concentration, the proportion of the cis isomer decreasing with an increase in each of the two factors. The effects of other reaction parameters, such as the N/Pt mole ratio in the complex, solvents and reaction time, etc. on the hydrogenation of o-xylene were also studied. The SiO₂-Si-N–Pt catalyst is very stable in reaction and turnover numbers amount to 200 in 80 hr.     

On the thermal analysis of aliphatic carboxylic acids and their salts

The thermal behaviour of oxalic, malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic and sebacic acid, and of their mono- and disodium salts and calcium salts has been studied by derivatography. Some of the acids were distilled off without decomposition, while the others were decomposed in accordance with the rule of Blanc.Up to 600°, the decomposition of the monosodium salts consists of two principal steps. The first process is the liberation or the decomposition of the acid formed from the salt, the second step the decomposition of the normal salt into sodium carbonate and organic molecules. This decomposition mechanism was verified also by tracer technique on compounds labelled with the¹⁴C isotope. With most of the compounds unable to form ketones, the decomposition of the normal salt yields a great variety of organic compounds. In the case of adipates and pimelates the formation of cyclanones predominates.

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Zusammenfassung Es wurde das thermische Verhalten von Oxalsäure, Malonsäure, Bernsteinsäure, Glutarsäure, Adipinsäure, Suberinsäure, Azelainsäure und Sebacinsäure, sowie ihrer Mono- und Dinatrium- und Calciumsalze derivatographisch untersucht. Einige dieser Säuren destillierten ohne Zersetzung, die übrigen zerlegten sich entsprechend dem Blancs'schen Gesetz.Die Zersetzung der Mononatriumsalze verlief bis 600° in zwei Stufen. In der ersten wurde die salzbildende Säure freigesetzt oder zersetzt, in der zweiten zersetzte sich das normale Salz in Natriumkarbonat und in organische Moleküle. Der Zersetzungsmechanismus wurde mit durch¹⁴C markierten Verbindungen kontrolliert. Bei der Zersetzung der normalen Salze und der Verbindungen, die unfähig sind Ketone zu bilden, entstehen mannigfaltige organische Verbindungen. Im Falle von Adipaten und Pimelinaten überwiegen Cyclanone.

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Résumé On a étudié par dérivatographie le comportement thermique des acides oxalique, malonique, succinique, glutarique, adipique, pimélique, subérique, azélaique et sébacique, et de leurs sels mono et disodiques et de calcium. Certains de ces acides distillent sans décomposition, alors que d'autres se décomposent suivant la loi de Blanc.La décomposition du sel monosodique se déroule en deux étapes jusqu'à 600°. Dans la première, l'acide formant le sel se dégage ou se désompose; dans la deuxième, le sel normal de sodium se décompose en donnant du carbonate de sodium et des molécules organiques. Le mécanisme de la décomposition a été vérifié à l'aide de combinaisons marquées par le¹⁴C.La décomposition des sels normaux et des combinaisons impropres à donner des cétones fournit une grand variété de composés organiques. Dans le cas des adipates et des pimélates, la formation de cyclanones prédomine.

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, , , , , - . , . 600° . , , — « » . , C¹⁴ . . .

     

Selective hydrogenation of crotonaldehyde over raney cobalt catalysts modified with heteropolyacid salts

RCo-based catalysts were modified with Keggin type heteropolyacid salts, including alkali, alkaline earth and transition metal salts. The selective hydrogenation of crotonaldehyde was investigated over these catalysts. The selectivities to crotyl alcohol can be improved on all modified catalysts. Among them, the catalyst modified with copper salts of 12-molybdophosphates shows the best performance in improving the selectivity. This revised version was published online in June 2006 with corrections to the Cover Date.     

TPD studies of ethylene adsorption over platinum black

TPD studies of ethylene adsorption over Pt-blacks of various dispersity with and without hydrogen at 298 K indicate that the metal dispersity and the presence of hydrogen on the surface influence the direction of hydrocarbon transformation on platinum.

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298 Pt- . .

     

Synthesis and structure of O-alkyl alkylphosphonoselenoic acids and their salts

Conclusions We have prepared O-alkyl alkylphosphonoselenoic acids by reaction of O-alkyl alkylphosphonites with selenium in the presence of amines or alkali metals followed by acidification. We have shown by¹H and³¹P NMR and IR spectroscopy that these acids and their salts exist in solution in the selenophosphoryl form.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya., No. 2, pp. 437–440, February, 1978.