bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Reduction of N-Alkoxypyridinium Ions
Authors: Sumiyoshi Takashi , Katayama Meiseki , Schnabel Wolfram 
Published: July 2006

Abstract
The reduction of 1-ethoxy-2-methylpyridinium (EMP+) ions in aqueous solution at room temperature by eaq−and · CO2− was investigated in a pulse radiolysis study (irradiation with 10 ns pulses of 45 MeV electrons). For comparison, experiments with 1-methylpyridinium (MP+) and unsubstituted pyridinium (PH+) ions were carried out. With MP+ and PH+ the spectra of pyridinyl radicals were observed at the end of the pulse. In the case of EMP+ the spectrum of the pyridinyl radical was not detectable. However, a new absorption band at 340 nm was formed with a significant delay after the reduction. Therefore, it was concluded that pyridinyl radicals formed by reduction of EMP+ decompose very quickly into picoline and ethoxyl radicals. The latter add to EMP+ with a rate constant k=6×107 dm3 mol−1 s−1. The transient absorption band at 340 nm is ascribed to the adduct.
Hydrogen Formation from Water Adsorbed on Zeolite during Gamma-Irradiation
Authors: Aoki Masayoshi , Nakazato Chiyoko , Masuda Takahiro 
Published: July 2006

Abstract
The γ-radiolysis of water adsorbed on synthetic zeolite, MS 13X (Molecular Sieve 13X), has been investigated by the product analysis method using gas chromatography. One of the main products is molecular hydrogen, the G value of which increases with increasing amount of water adsorbed on MS 13X and reaches a first plateau (0.42) at ca. 4 mmol of water per g of MS 13X. At ca. 6 mmol g−1 of water, it resumes the increase and finally approaches a second plateau (1.2) at ca. 9 mmol g−1. The formation of hydrogen is depressed by an electron scavenger, while ammonia, a scavenger of positive hole, enhances the hydrogen formation. The result indicates that hydrogen is produced through a reaction of water with electrons generated in MS 13X. The rate constant for the reaction of electrons with water adsorbed on MS 13X is estimated to be (2.6±0.3)×108 dm3 mol−1 s−1, on the assumption that rate constants for reactions of electrons with some electron scavengers determined in liquid cyclohexane can be applied to this system.
New Synthesis, Properties, and the Formation of the Hexamer of Nickel(II) Ethanethiolate, [Ni(SEt)2]6
Authors: Yamamura Takeshi 
Published: July 2006

Abstract
[Ni3(SEt)8]2− reacted with water in acetone to give the known hexameric ring compound, [Ni(SEt)2]6, where SEt means CH3CH2S−. The [Ni(SEt)2]6 was oxidized electrochemically in a quasi-reversible manner at +0.60 V (vs. SCE) in CH2Cl2. 1H and 13C NMR revealed that this compound has two types of –SEt (low- and high- field types; the chemical shift discrepancy is ca. 0.4 ppm for 1H NMR), probably corresponding to the axial–equatorial configurations of the thiolate. The formation of the cyclic hexamer in CH3CN and CHCl3 in the presence of protic reagents was studied.
Simultaneous Measurement of Electrical Conductivity and the Amount of Adsorbed Oxygen in Porous ZnO
Authors: Fujitsu Satoru , Toyoda Hiroshi , Koumoto Kunihito , Yanagida Hiroaki , Chikazawa Masatoshi , Kanazawa Takafumi 
Published: July 2006

Abstract
Changes in electrical conductivity and the amount of adsorbed oxygen in porous ZnO were measured simultaneously in the temperature range of 200–600 °C. The saturated amount of adsorbed oxygen increased initially, went through a maximum at 500 °C, and then decreased with increasing temperature. The conductivity decreased exponentially with increase in the amount of adsorbed oxygen, which indicates that the energy barrier formed due to the chemisorbed oxygen controls the total conductivity. In a high temperature region, not only the chemisorbed oxygen, but also the oxygen diffused into the grain boundaries played important roles in changing the electrical conductivity. The diffused oxygen was examined by means of a depth profile of tracer 18O measured by SIMS. The formation of the energy barrier at the grain boundary was confirmed by current-voltage characteristic measurements.
The Cyanation of Aromatic Halides Catalyzed by Nickel(0) Complexes Generated In Situ. I. General Scope and Limitations
Authors: Sakakibara Yasumasa , Okuda Fumio , Shimobayashi Akira , Kirino Kunihiko , Sakai Mutsuji , Uchino Norito , Takagi Kentaro 
Published: July 2006

Abstract
The cyanation of chlorobenzene catalyzed by Ni(PPh3)n, which was generated in situ from NiBr2(PPh3)2–Zn–PPh3(Ni : Zn : P=1 : 3 : 2 molar ratio), was at first examined with various MCN (M=K, Na)–solvent systems by three procedures in order to clarify the conditions under which the reaction occurs. The effects of the systems and the procedures on the reaction were remarkable. It was observed that the cyanide ion has an inhibitory action on both the reduction of Ni(II) and the oxidative addition of the halide to Ni(0). However, when such MCN–dipolar aprotic solvent systems as KCN–HMPA, KCN or NaCN–MeCN, which give low cyanide concentrations, were used, the reaction readily took place at 50–60 °C without reducing Ni(II) prior to the addition of MCN and adding MCN slowly. Various Y-substituted chlorobenzenes, except for those with Y=o-Cl, o-CN, and m-NO2, were cyanated to give the corresponding nitriles in fair to good yields. NiBr2–PPh3 can be used in place of NiBr2(PPh3)2 if MCN is added after reduction. In addition, less reactive halides, such as o-dichlorobenzene and o-chlorobenzonitrile, were fairly smoothly cyanated by the use of NiBr2–1,1′-bis(diphenylphosphino)ferrocene.
A Search for New Synthetic Routes toward Siccanin
Authors: Kato Michiharu , Matsumura Yukio , Heima Kiyoshi , Yoshikoshi Akira 
Published: July 2006

Abstract
11-Acetoxy-12bα-methoxymethyl-4,4,6aα,9-tetramethyl-1,2,3,4,4aα,5,6,6a, 12aβ,12b-decahydro-12H-benzo[a]xanthene (34), which has been expected as a promising key intermediate for the synthesis of siccanin (1), was synthesized via acid-catalyzed cyclization of 1α-(2-hydroxy-6-methoxy-4-methylbenzyl)-8aα-methoxymethyl-2,5,5-trimethyl-1,4,4aα,5,6,7,8,8aα-octahydronaphthalene (13) and isomeric exo olefin 21. The phenol acetate 34, however, was so resistant to oxidation that no corresponding 12-oxo derivative, which was expected to provide 11-acetoxy-12bα-acetoxymethyl-12-oxo-4,4,6aα,9-tetramethyl-1,2,3,4,4aα,5,6,6a,12aα,12b-decahydro-12H-benzo[a]xanthene (4) on epimerization at its C(12a) position as well as hydrofuran ring formation at the C(12) position with its angular methoxymethyl substituent, was obtained.
Asymmetric Diels–Alder Reactions of Some Chiral Dienophiles Derived from Cinchona Alkaloids
Authors: Suzuki Hideo , Mochizuki Koichi , Hattori Tatsuya , Takahashi Noriyuki , Tajima Osamu , Takiguchi Toshio 
Published: July 2006

Abstract
Acrylates, crotonate, and fumarates derived from cinchona alkaloids were easily prepared. The highly re-facial selective additions of the dienophiles derived from cinchonidine or quinine to some dienes were achieved in the presence of SnCl4. Similarly, si-facial selective additions were also achieved by the use of cinchonine instead of cinchonidine or quinine as a chiral auxiliary alcohol with equal ease. The inverse diastereofacial selectivity was observed by the use of TiCl4 instead of SnCl4 as a Lewis acid in the case of the reaction of the acrylates cited above with cyclopentadiene. It was suggested by the infrared spectra of the dienophile–SnCl4 complexes and by some circumstantial evidence that in the complexes, SnCl4 coordinates with the oxygen atom of the C–O bond (not C=O bond) and probably also with the nitrogen atom of the quinuclidine framework to form a rigid five-membered ring structure.
Polymerization of Diene-Containing Lipids as Liposomes by Radical Initiators. 6: Polymerization of 1,3-Bis(2,4-octadecadienoyl)-rac-glycero-2-phosphorylcholine
Authors: Takeoka Shinji , Hasegawa Etsuo , Ohno Hiroyuki , Tsuchida Eishun 
Published: July 2006

Abstract
1,3-Bis(2,4-octadecadienoyl)-rac-glycero-2-phosphorylcholine (1,3-DPC), polymerizable lipid which contains diene groups in both 1- and 3-acyl chains, was polymerized as liposomes in an aqueous medium. Polymerization was initiated by water-insoluble azobis(isobutyronitrile) (AIBN) or water-soluble azobis(2-amidinopropane) dihydrochloride (AAPD). AIBN was mixed with the monomeric lipids and the mixture was dispersed in an aqueous medium by sonication to facilitate transfer of AIBN into monomeric lipid liposomes. On the other hand, AAPD was simply added to the liposome suspension. The 1,3-DPC liposomes were easily polymerized by the addition of either water-soluble AAPD or water-insoluble AIBN to give polymerization conversion of over 80% in both cases. No selective polymerization of diene groups in the different acyl chains was found in 1,3-DPC liposomes whereas the selective polymerization was clearly seen in 1,2-bis(2,4-octadecadienoyl)-sn-glycero-3-phosphorylcholine (DODPC). Polymerized 1,3-DPC liposomes were not soluble in organic solvent suggesting the formation of crosslinked bilayer structure. The obtained results suggested that the diene groups in both 1- and 3-acyl chains were almost equivalent and located in the interface between an aqueous phase and hydrophobic region. Polymerized liposomes thus prepared were stable against heating, detergent attack and even methanol washing. Copolymerization of mixed liposomes composed of 1,3-DPC and DODPC (5:1) revealed that the AIBN or AAPD initiated polymerization conversion of DODPC reached about 68%. 1,3-DPC is considered to be radical propagation transfer between diene groups in 1- and 2-acyl chains of DODPC during polymerization.
The 2- or 6-(α-Hydroxyalkyl- and α-Oxoalkyl)-5,8-dimethoxy-1,4-naphthoquinones from the Oxidative Demethylation of 2-(α-Hydroxyalkyl- and α-Oxoalkyl)-1,4,5,8-tetramethoxynaphthalenes with Cerium(IV) Ammonium Nitrate, and the Further Demethylations to Naphthazarins
Authors: Tanoue Yasuhiro , Terada Akira 
Published: July 2006

Abstract
Oxidative demethylation of 2-(α-hydroxyalkyl- and α-oxoalkyl)-1,4,5,8-tetramethoxynaphthalene with (NH4)2Ce(NO3)6 gave two isomeric dimethoxynaphthoquinones: 2-substituted and 6-substituted 5,8-dimethoxy-1,4-naphthoquinones. Further demethylations of the former isomers to the corresponding dihydroxynaphthoquinones required an AgO–40%HNO3 reagent, while the latter isomers needed AlCl3 as the demethylation reagent. Some comments regarding the mechanism of these oxidative demethylations with (NH4)2Ce(NO3)6 are given.
An Observation on Carboxylation of 4H-Cyclopenta[def]phenanthrene
Authors: Minabe Masahiro , Isozumi Keisuke , Kawai Ken-ichi , Yoshida Masaaki 
Published: July 2006

Abstract
Photocarboxylation of 4H-cyclopenta[def]phenanthrene by carbon dioxide in the presence of N,N-dimethylaniline in dimethyl sulfoxide afforded 8,9-dihydro-4H-cyclopenta[def]phenanthrene-8- and 2-carboxylic acid, and 4H-cyclopenta[def]phenanthrene-8-carboxylic acid. These acids were derived into methyl-4H-cyclopenta[def]phenanthrenes.
Conformational Analysis of Methacrylates by IR and 1H NMR Spectroscopies
Authors: Yashima Eiji , Okamoto Yoshio , Hatada Koichi , Kageyama Hiroyuki , Kasai Nobutami 
Published: July 2006

Abstract
The molecular structures of α-methylbenzyl methacrylate, 1,2-diphenylethyl methacrylate, α-t-butylbenzyl methacrylate, 1,2,2,2-tetraphenylethyl methacrylate, diphenylmethyl methacrylate, and 1,1-diphenylethyl methacrylate in solution were investigated by means of IR spectroscopy and 1H NMR spectroscopy using a lanthanoid-induced chemical shift (LIS) reagent [Eu(fod)3] by reference to X-ray analysis data. The preferred conformation between the C=C double bond and the C=O group was estimated to be s-cis in solution. The conformation of ester groups of α-substituted benzyl methacrylates in toluene depended upon the α-substituent and the temperature. On the basis of structural data, the mechanism of the highly enantiomer-selective polymerization of racemic methacrylates with a (−)-sparteine-Grignard reagent complex is discussed.
Flavin Activation by Intramolecular Acid Catalysis at N(1) Position
Authors: Shinkai Seiji , Kawanabe Sayuri , Kawase Akito , Yamaguchi Toshiro , Manabe Osamu , Harada Shigeharu , Nakamura Hideki , Kasai Nobutami 
Published: July 2006

Abstract
In order to assess the effect of intramolecular acid catalysis on the specific flavin reactivities, 3-methyl-10-(2-hydroxyphenyl)isoalloxazine (1(2OH)) and 3-methyl-10-(2-hydroxy-1-naphthyl)isoalloxazine (2(2OH)) were synthesized and the redox properties were compared with those of reference flavins such as 3-methyl-10-(2-methoxyphenyl)isoalloxazine (1(2OMe)) and 3-methyl-10-(2-methoxy-1-naphthyl)isoalloxazine (2(2OMe)). The pKa values for 1(2OH) and 2(2OH) were determined to be 7.7 and 7.0, respectively, which were lower than that of 3-methyl-10-(4-hydroxyphenyl)isoalloxazine (1(4OH): pKa 8.6). It is thus unlikely that 2′-OH and N(1) form a hydrogen bond at the initial state of the reaction (i.e., at the oxidized state). The X-ray crystallographic studies indicated that the phenyl ring makes an angle of 79.7° with the isoalloxazine ring and the 2′-OH group forms a hydrogen bond with methanol included in the crystal lattice. In acetonitrile at 30 °C 1-benzyl-1,4-dihydronicotinamide was not oxidized by 1(2OMe), 1(4OH), and 2(2OMe). On the other hand, the oxidation took place with 1(2OH) and 2(2OH) which have an acidic OH group at the 2′-position of the 10-aryl substituent. The presence of the intramolecular acid catalysis suggests that 2′-OH and N(1) can interact at least at the transition state or at the final state of the reaction (i.e., at the reduced state). In general, the oxidized flavin adopts a “planar” structure which is sterically tense while the reduced flavin adopts a “bent” structure which is sterically relaxed. As the structure of the transition state is more or less similar to the reduced form, the hydrogen-bonding interaction could increase on going from the tense initial state to the relaxed transition state. This is a novel example for acid catalysis in flavin-mediated reactions.
The Reaction of Lupane and Friedo-Oleanane Type Triterpenes with m-Chloroperbenzoic Acid
Authors: Tori Motoo , Matsuda Reiko , Sono Masakazu , Kohama Yoshihiro , Asakawa Yoshinori 
Published: July 2006

Abstract
Lupane-3β,28-diol, lupan-3β-ol, and friedelan-3β-ol were treated with m-chloroperbenzoic acid (mCPBA) in refluxing chloroform to afford corresponding lactones in one step, while lupane-3β,28-diyl diacetate, lupan-3β-yl acetate, and friedelan-3β-yl acetate to give hydroxylated or keto derivatives. Similar reaction of dendropanoxide with mCPBA yielded 6β-, 7β-, 21α-, and 22β-hydroxylated compounds.
The Refractive Index of Molten CaCl2–NaCl Mixtures
Authors: Igarashi Kazuo , Mochinaga Junichi 
Published: July 2006

Abstract
The refractive indices of molten CaCl2–NaCl mixtures were measured goniometrically with visible light at nine wavelengths and represented as a function of both the temperature and the wavelength using a modified Cauchy relation. Information on electronic polarization is also reported.
A New Synthetic Route to Aliphatic and Alicyclic Nitriles via Homolytic Desulfurization of α-(Dithiocarbamoylthio) Nitriles
Authors: Yanagawa Makoto , Moriya Osamu , Watanabe Yoshihiko , Ueno Yoshio , Endo Takeshi 
Published: July 2006

Abstract
Chloroacetonitrile was transformed into aliphatic and alicyclic nitriles through (dimethyldithiocarbamoylthio)acetonitrile. The key steps in the synthetic route consisted of mono- and dialkylation via sulfur-stabilized carbanion and homolytic desulfurization using tributyltin hydride.
Radical Reactions of Alkenylstannanes with S-Benzoyl Se-Phenyl Selenosulfide
Authors: Toru Takeshi , Yamada Yoshio , Maekawa Eturô , Ueno Yoshio 
Published: July 2006

Abstract
Free radical reactions of allyltributylstannane or 2-butenyltributylstannane with S-benzoyl Se-phenyl selenosulfide (1) gave S-allyl benzenecarbothioate or a mixture of S-2-butenyl and S-1-methyl-2-propenyl benzenecarbothioates, respectively. The reaction of tributylvinylstannane with 1 gave an addition product, whereas the reaction of tributylstyrylstannane gave an addition–elimination product.
The Electronic Spectra of 6,6′-Diamino-2,2′-bipyridine
Authors: Yamada Masaki , Araki Koji , Shiraishi Shinsaku 
Published: July 2006

Abstract
The lowest-energy π–π* band of 6,6′-diamino-2,2′-bipyridine (dabp) appeared at near-UV region, and was found to suffer a characteristic solvent effect. The results were discussed in terms of its electronic structure calculated by ab initio method using a STO-3G basis set.
Band Structure of DEBP(TCNQ)4
Authors: Willis Martin R , Mori Takehiko , Inokuchi Hiroo 
Published: July 2006

Abstract
Band structure calculations are reported for the intermediate conducting complex salt, DEBP(TCNQ)4 (DEBP: N,N′-diethyl-4,4′-bipyridinium, TCNQ: tetracyanoquinodimethane). They show that the array of TCNQs forms a two-dimensional band structure with conduction and valence band widths 0.1 and 0.03 eV respectively. Conduction in the third direction is likely to be by hopping or tunnelling. The results are consistent with the experimental observations of electrical conductivity, magnetic susceptibility and thermoelectric power.
The Crystal and Molecular Structure of Diaquadihydroxotetrakis(m-nitrobenzenesulfonato)discandium(III) in a Linear Polymeric Form, [Sc2(OH)2(O2NC6H4SO3)4(H2O)2]n
Authors: Tateyama Yoshikuni , Ohki Yoshiyuki , Suzuki Yasuo , Ouchi Akira 
Published: July 2006

Abstract
The crystal and molecular structures of the title complex has been determined by the single-crystal X-ray diffraction method. It is monoclinic, with the space group Pn, Z=2 (including 4 metal atoms), a=28.90(2), b=10.251(4), c=5.981(1) Å, and β=94.68(3)°. Both of the metal atoms, Sc(1) and Sc(2), have the hexa-coordinated octahedral geometry, being coordinated to four sulfonato oxygen atoms as well as to two water oxygen (Sc(1)) or to two hydroxide oxygen atoms (Sc(2)). Any pair of the neighboring metal atoms along the b-axis are bridged by two sulfonato ions, forming an infinite chain structure; however, the Sc(2)–O bond lengths (2.307(10)–2.556(19) Å; average, Sc(2)–O (sulfonate), 2.422; Sc(2)–O(OH−), 2.394 Å) are much longer than the Sc(1)–O lengths (2.031(7)–2.150(8) Å; average, Sc(1)–O(sulfonate), 2.055; Sc(1)–O(H2O), 2.122 Å).
Hydroxyalkylation and Lactone Formation from Dialkyl Malonate by Means of a EuIII/EuII Photoredox System
Authors: Ishida Akito , Yamashita Shinya , Takamuku Setsuo 
Published: July 2006

Abstract
A EuIII/EuII photoredox system in alcohol induced an effective hydroxyalkylation at an α-position of a dialkyl malonate. The alcohol adduct was then converted to the lactone. A step-by-step hydroxyalkylation mechanism was suggested in which the Eu ion is used as a photocatalyst and also as a condensation catalyst for the reaction of dialkyl malonates and aldehydes.
Conjugate Reduction of α,β-Unsaturated Ketones with Amphiphilic Reaction System
Authors: Nonoshita Katsumasa , Maruoka Keiji , Yamamoto Hisashi 
Published: July 2006

Abstract
The conjugate reduction of α,β-unsaturated ketones has been effected with amphiphilic reaction system consisting of methylaluminum bis(2,6-di-t-butyl-4-alkylphenoxide) and certain complex aluminum hydride reagent.
Crystal Structure of [Chloro[tris[(1-ethyl-1H-benzimidazol-2-yl)-methyl]amine]zinc(II)] Tetraphenylborate Acetone
Authors: Matsumoto Naohide , Akui Toshifumi , Ohyoshi Akira , Okawa Hisashi 
Published: July 2006

Abstract
The crystal structure of the title complex has been determined by the single-crystal X-ray diffraction method. The zinc complex has approximately a trigonal bipyramidal coordination geometry, which is different from the copper(II) complex with the same tripod ligand.
Regioselective Alkylation in the Course of Aldol Condensation under Phase-Transfer Catalytic Conditions
Authors: Gu Xue-Ping , Ikeda Isao , Okahara Mitsuo 
Published: July 2006

Abstract
Regio- and stereoselective alkylation in the course of aldol condensation under liquid-solid phasetransfer catalytic conditions, affording conjugated dienyl ether (5) or α-substituted β,γ-olefinic aldehyde (7) depending on the starting halides, both in good yields, was disclosed. The reaction mechanism is also discussed.
Carbon-13 NMR of N-Substituted 2,4,6-Trimethylpyridinium Salts
Authors: Salman Salman R , Hassan A H , Khayat M A R 
Published: July 2006

Abstract
Carbon-13 chemical shifts of twelve N-substituted, 2,4,6-trimethylpyridinium (TMP) salts were determined. The data have been used to estimate the relative ring current (RRC) of the N-substituents on the pyridinium ring.
Synthesis of New Naturally Occurring 4-Phenyl-2H-1-benzopyran-2-ones
Authors: Parmar Virinder S , Jain Rajni , Singh Suddham 
Published: July 2006

Abstract
5,7-Dimethoxy-4-(4-hydroxyphenyl)-2H-1-benzopyran-2-one and 5,7-dimethoxy-4-(4-methoxyphenyl)-2H-1-benzopyran-2-one, two new neoflavonoids occurring in Courtarea hexandra have been synthesized via Pechmann condensation. Attempts made to synthesize another 4-arylcoumarin, 5-hydroxy-7-methoxy-4-(2,5-dihydroxyphenyl)-2H-1-benzopyran-2-one, constituent of the same plant, led to the formation of the hitherto unknown 2-ethoxy-6-hydroxy-4H-1-benzopyran-4-one.
Liquid-Phase Dehydrogenation of Methanol with Homogeneous Ruthenium Complex Catalysts
Authors: Itagaki Hiroaki , Shinoda Sumio , Saito Yasukazu 
Published: July 2006

Abstract
Catalytic dehydrogenation of methanol proceeded with homogeneous ruthenium(II) complexes, yielding formaldehyde and dihydrogen as primary products under refluxing conditions of the solution. The effects of additives on the initial reaction rate were examined for lithium chloride, lithium acetate, acetic acid and ethyldiphenylphosphine. A catalyst complex, [Ru(OAc)Cl(PEtPh2)3], was deactivated gradually by the displacement of the bidentate OAc ligand with H and CO ligands during the reaction. These cis-disposed sites would be used for splitting the C–H bonds. A catalytic reaction cycle is proposed, in which such processes are included as solvolysis of the catalyst complex, β-H elimination from the OCH3 ligand and attack of acetic acid on the hydride intermediate to generate dihydrogen.
Characterization of Active Sites in Sulfided Molybdenum/ Alumina Hydrodesulfurization Catalysts
Authors: Maezawa Akinori , Kitamura Masaru , Okamoto Yasuaki , Imanaka Toshinobu 
Published: July 2006

Abstract
The site configuration of Al2O3-supported molybdenum sulfides catalytically active for hydrodesulfurization (HDS) of thiophene has been investigated as a function of pretreatment conditions (H2S/H2=0–0.2) by using X-ray photoelectron, laser Raman and IR spectroscopies and temperature-programmed desorption of adsorbed NO. It has been found that when MoO3/Al2O3 catalysts are presulfided with H2S/H2, MoS2-like species are formed, whereas when prereduced and subsequently sulfided during the HDS reaction, molybdenum oxide sulfides or highly dispersed amorphous molybdenum sulfides are initially produced. The turnover frequency of the HDS reaction calculated on the basis of the NO adsorption was shown to increase with decreasing dispersion degree of sulfided molyb denum. It is proposed that two kinds of NO adsorption sites are present; triply and doubly coordinatively unsaturated (cus) molybdenum sites. It is considered that both sites are catalytically active, possibly, the triply cus species being more active. It is concluded that the HDS activity of sulfided MoO3/Al2O3 catalysts is determined by the structure, dispersion and coordinative unsaturation of sulfided molybdenum.