bluuebunny/crossref_metadata_2025_split huggingface dataset:
The 310-Helical Conformation of Aib-Containing Oligopeptide, Boc–(l-Leu–Aib2)2–OBzl
Authors: Okuyama Kenji , Nakanishi Shousuke , Saga Yuji , Umeyama Hiroshi , Narita Mitsuaki 
Published: July 2006

Abstract
The molecular and crystal structure of the Aib (α-aminoisobutyric acid)-containing oligopeptide, Boc–(l-Leu–Aib2)2–OBzl, are determined by X-ray diffraction analysis. The hexapeptide crystallizes in the space group P21, with a=19.912(2), b=16.098(1), c=14.710(2) Å, β=96.81(1)°, and Z=4. The unit cell contains two independent molecules (molecules A and B) in the asymmetric unit. The dihedral angles (φ and ψ) of the peptide back bone show that molecule A folds into a right-handed helix and molecule B folds into a left-handed helix. Both the molecules adopt a 310-helical conformation stabilized by four 4→1 intramolecular hydrogen bonds. The right- and left-handed helical molecules are arranged alternately, in head-to-tail fashion to make columns along the [101] direction. These columns are packed closely in the pseudo-hexagonal arrangement.
Synthesis and Properties of Extended Tridecafulvenes. The Substituent Effect on the Paratropicity of This Fulvene System as a Measure of Polarizability
Authors: Ojima J\={u}ro , Kitamura Keiko , Sugimori Haruyoshi , Higuchi Hiroyuki , Iyoda Masahiko 
Published: July 2006

Abstract
The vinylogues of 14,14-dicyano-5,10-dimethyl-6,8-bisdehydrotridecafulvene have been synthesized and the effect of increasing exocyclic double bonds upon the paratropicity of the thirteen-membered ring is discussed by comparing the polarizability of 2,2-dicyanovinyl, 4,4-dicyano-1,3-butadienyl, and 6,6-dicyano-1,3,5-hexatrienyl groups.
Optical Resolution by Replacing Crystallization of Dl-Threonine
Authors: Shiraiwa Tadashi , Yamauchi Masahiro , Yamamoto Yumi , Kurokawa Hidemoto 
Published: July 2006

Abstract
Optical resolution by replacing crystallization of Dl-threonine (Dl-Thr) was achieved in the presence of an equimolar amount of l-proline as an optically active cosolute. This optical resolution gave d-Thr with 91% optical purity in 78% degree of resolution, and optically pure l-Thr was obtained from the mother liquor.
Foam Ratio as a Measure for Mechanical Foam-Breaking in Gas Bubbling Systems
Authors: Yasukawa Masami , Yamagiwa Kazuaki , Ohkawa Akira 
Published: July 2006

Abstract
The volume fraction of liquid in foam, designated as the foam ratio, was measured for a gas-bubbling system using various foaming liquids. The foam ratio can be used as a substantial measure of the dynamic foaming capacity for gas-bubbling systems. The applicability of the foam ratio for evaluating the performance of mechanical foam-breaking was investigated. Furthermore, the effect of the operating conditions on the foam ratio was related to the extent of mechanical foam-breaking.
The Catalytic Isomerization of Butenes over a Samarium Oxide
Authors: Nakashima Yasushi , Sakata Yoshihisa , Imamura Hayao , Tsuchiya Susumu 
Published: July 2006

Abstract
The ratio, cis-2-/trans-2-butene, formed from 1-butene isomerization, was 22.2. The reaction profile of butenes isomerization obtained from the relative rate constants was of the cis-convex type. The basic sites on the oxide surface have been revealed by the benzoic acid titration method.
Electrical Conductivity and Thallium Spin-Lattice Relaxation Time Measurements of Tl4HgBr6 and Tl4HgI6
Authors: Nagase Hirokazu , Furukawa Yoshihiro , Nakamura Daiyu 
Published: July 2006

Abstract
The ionic transport properties of Tl4HgBr6 and Tl4HgI6 were investigated with 205Tl spin-lattice relaxation time (T1) and electrical conductivity (σ) measurements. The temperature dependence of 205Tl T1 shows that Tl+ ion diffusion is activated at high temperatures in both crystals. The activation energies of diffusion were estimated to be 47 and 55 kJ mol−1 for Tl4HgBr6 and Tl4HgI6, respectively, from the temperature dependence of σ.
The Selective Protection of Uridine with a p-Methoxybenzyl Chloride: A Synthesis of 2′-O-Methyluridine
Authors: Akiyama Takahiko , Nishimoto Hiroyuki , Ozaki Shoichiro 
Published: July 2006

Abstract
2′-O-Methyluridine was prepared through 5 steps from uridine by use of p-methoxybenzyl group (PMB) as an N3-protecting group of uridine. A chemoselective protection method has been developed by use of DBU as a base and deprotection was effected by AlCl3–anisole system.
Spectrophotometric Studies on Complexation Reaction of Some Water-Soluble 5-Nitro-2-Pyridylhydrazones with Bickel(II) and Determination of Trace Nickel with α-(2-Benzimidazolyl)-α-(5-nitro-2-pyridyl)hydrazono-3-toluenesulfonic Acid
Authors: Ishii Hajime , Odashima Tsugikatsu , Kawamonzen Yoshiaki 
Published: July 2006

Abstract
The complexation reaction of four water-soluble hydrazones, α-(5-nitro-2-pyridyl)hydrazono-α-(2-quinolyl)-3-toluenesulfonic acid (NPHQTS), α-(5-nitro-2-pyridyl)hydrazono-α-(2-thiazolyl)-3-toluenesulfonic acid (NPHTTS), α-(2-benzothiazolyl)-α-(5-nitro-2-pyridyl)hydrazono-3-toluenesulfonic acid (BTNPHTS) and α-(2-benzimidazolyl)-α-(5-nitro-2-pyridyl)hydrazono-3-toluenesulfonic acid (BINPHTS), with nickel(II) has been studied spectrophotometrically. These hydrazones react with nickel(II) to form a stable 1:2 (metal: ligand) complexes with high molar absorptivities. A sensitive and selective spectrophotometric method for the determination of nickel with BINPHTS has been developed. The nickel–BINPHTS complex is formed quantitatively in the pH range 6.5–8.9 and its absorption spectrum shows a maximum at 498 nm. Beer’s law is obeyed over the range 0.02–0.8 μg cm−3 of nickel and the apparent molar absorptivity of the complex is 8.67×104 dm3mol−1cm−1 at 498 nm. The proposed method was applied to the determination of nickel in manganese nodule samples, satisfactory results being obtained. Furthermore, the overall formation constants of nickel complexes of the four hydrazones were also determined spectrophotometrically.
The Synthesis of Isocyanurates on the Trimerization of Isocyanates under High Pressure
Authors: Taguchi Yoichi , Shibuya Isao , Yasumoto Masahiko , Tsuchiya Tohru , Yonemoto Katsumi 
Published: July 2006

Abstract
The trimerization of phenyl isocyanate in the presence of triethylamine was accelerated under high pressure to give triphenyl isocyanurate almost quantitatively. The reaction in benzene was remarkably accelerated by compression. The effects of pressure, temperature, catalysts, and solvents were examined on the trimerization of phenyl isocyanate. Aryl and normal alkyl isocyanates trimerized under high pressure to give the corresponding isocyanurates in good yields, whereas isocyanates having bulky alkyl groups such as t-butyl and cyclohexyl did not trimerize even under 800 MPa.
Investigation of the States of Water in Water-Swollen Hydrogels by Liquid Chromatography and Differential Scanning Calorimetry
Authors: Shibukawa Masami , Ohta Naoichi , Onda Nobuhiko 
Published: July 2006

Abstract
A new liquid chromatographic method was proposed for the estimation of the amount of water which exhibits selectivity to solutes in water-swollen hydrogels based on the model regarding the retention of ions on the column packed with the hydrogels. The estimated amount of the water in polyacrylamide, dextran, and poly(vinyl alcohol) gels corresponds to the sum of the amount of freezable bound water and that of nonfreezing water determined by means of differential scanning calorimetry. This means that the freezable bound water takes an important role in the separation process using water-swollen hydrogels contrary to the conventional view of the freezable water.
A Convenient Synthesis of (2R)-1-Amino-1-Deoxy-1-Phosphinylglycerols
Authors: Hanaya Tadashi , Miyoshi Akihiko , Noguchi Ayashi , Kawamoto Heizan , Armour Margaret-Ann , Hogg Alan M , Yamamoto Hiroshi 
Published: July 2006

Abstract
2,3-O-Isopropylidene-d-glyceraldehyde reacts with dimethylphosphine oxide in the presence of triethylamine to give separable (1S,2R)-and (1R,2R)-1-dimethylphosphinylgrycerol (65 :35), from which the (1R) and (1S) title compounds are respectively derived via 1-O-mesyl and 1-azido derivatives. The corresponding 1-dimethoxyphosphinylglycerols are similarly prepared. Structural and conformational assignments of these products are made on the basis of the 1H NMR data and [α]D values.
A New and Convenient Preparation of Conjugated Dienals
Authors: Yahata Nobuhiro , Fujita Makoto , Ogura Katsuyuki 
Published: July 2006

Abstract
For preparation of 5-monosubstituted or 5,5-disubstituted 2,4-dienals, 1-(methylthio)-5-(p-tolylsulfonyl)-1,3-pentadiene (4) is revealed to be an important precursor. When 5-(methylthio)-5-(p-tolylsulfonyl)-1,3-pentadiene, that is easily obtainable from (methylthio)methyl p-tolyl sulfone, was treated with silica gel, 1,5-rearrangement of p-tolylsulfonyl group occurred to give 4. The conditions for mono- or dialkylation of 4 followed by hydrolysis leading to the dienals are described.
Comparison of the Electrochemical Properties of Electric Double-Layer Capacitors with an Aqueous Electrolyte and with a Nonaqueous Electrolyte
Authors: Tanahashi Ichiro , Yoshida Akihiko , Nishino Atsushi 
Published: July 2006

Abstract
The electrochemical properties of phenolic resin-based activated carbon fiber cloth (ACFC) in an aqueous electrolyte and in a nonaqueous organic electrolyte have been investigated. The differential electric double-layer capacitance of ACFC with the specific surface area of 1630 m2 g−1 in the aqueous electrolyte was 1.50-times larger than that of the ACFC in the organic electrolyte. In accordance with the result, the capacitance of capacitors consisted of the ACFC and the aqueous electrolyte was 1.47-times larger than that of capacitors comprising ACFC and the organic electrolyte. The IR drop of capacitors with the aqueous electrolyte was smaller by one order of magnitude than that of capacitors with the organic electrolyte.
Photoexcitation of Potassium Octacyano-Tungstate (IV)-1,10-Phenanthroline System: Kinetics and Mechanism of the Reaction
Authors: Ali S I , Kaur Harpal 
Published: July 2006

Abstract
The kinetics of the reactions of photochemically generated [W(CN)7OH]4− in basic and [HW(CN)7(H2O)]2− in acidic medium with 1,10-phenanthroline have been studied in buffer solutions of pH 4.2–10.6, ionic strength 7.5×10−2 mol kg−1 at 20°C. Quantum yield for formation of photoproduct was calculated and it was found to depend on pH, ligand and, [W(CN)8]4− concentrations. The pseudo-first-order rate constant and quantum yield values in acidic medium are higher than in basic medium and the mechanisms of the photochemical substitution reactions are different in two mediums.
Electrolytically Generated Manganese(III) Sulfate for the Oxidation of l-Histidine in Aqueous Sulfuric Acid: a Kinetic Study
Authors: Pinto Ivan , Sherigara B S , Udupa H V K 
Published: July 2006

Abstract
Conditions have been established for the electrogeneration of Mn(III) from Mn(II) in sulfuric acid medium. Mn(III) formed was identified and characterized by UV spectra. Kinetics of Mn(III) oxidation of l-histidine in aqueous sulfuric acid medium has been studied spectrophotometrically. Oxidation followed second order kinetics in [Mn(III)], first order in [histidine] and increase in [H+] decreased the rate. The reduced product of the oxidant, Mn(II), retarded the rate of reaction. Evidence for the transient existence of the free radical reaction intermediate is given. Effects of ionic strength, solvent composition, HSO4− and certain complexing agents like P2O74−, Cl−, F−, have also been studied. Added complexing agents decreased the redox potential of the Mn(III)/Mn(II) couple, thereby reducing the oxidation rate. Dependence of reaction rate on temperature is examined and activation parameters computed from Arrhenius and Eyring plots. A mechanism consistent with kinetic results has been proposed in which a combined role of Mn(III)aq and MnOH2+aq was envisaged.
Acidic Property and Catalytic Activity of TiO2–SiO2–Al2O3
Authors: Sabu K R , Rao K V C , Nair C G R 
Published: July 2006

Abstract
The acidity evaluations using butylamine titration have been carried out to correlate the surface acidic properties of TiO2–SiO2–Al2O3 catalysts with their alkylating activity. The acid amount of TiO2–SiO2–Al2O3 of silica to alumina molar ratio 16.4 and titania content 10.4% (by weight) is nearly double that of SiO2–Al2O3 of the same silica to alumina molar ratio. The acid strength of TiO2–SiO2–Al2O3 coprecipitated from a solution of pH 2 and the acid amount of the same ternary oxide coprecipitated from solutions of higher pH(&gt;6) are low.
Kinetics and Mechanism of Acid Hydrolysis of Bis(dicarboxylato)carbonatochromate(III) Complexes
Authors: Sai C S T , Anipindi N R , Subbiah V , Pandit M W 
Published: July 2006

Abstract
A study has been made of the acid-catalysed aquation reactions of three complex ions of the general formula [Cr(XX)2(CO3)]3−, where XX=oxalate, malonate, or methylmalonate, by stopped-flow spectrophotometry in the acid range 0.1–2.0 M (M=mol dm−3) and 20–35°C at an ionic strength of 2 M. Only the ring-opening reaction of the carbonate is observed, k=2.12, 3.28, and 4.02 M−1 s−1 at 25°C respectively for oxalato, malonato, and methylmalonato complexes as the subsequent decarboxylation is too fast to measure. The observed trend was explained in terms of the basicity of the coordinated inert ligands.
Application of Surface-Active Substances in Polarographic Determination of Hg(II), V(V), Fe(III), As(III), Sb(III), and Ti(IV) in the Presence of U(VI)
Authors: Ismail M I 
Published: July 2006

Abstract
The reduction of hexavalent uranium in 1 M H2SO4 at DME was found to be retarded by a non ionic surfactant Triton® X 100 and to shift the uranium wave to more negative potentials. Advantage was taken of this fact to determine the elements Hg(II), Fe(III), V(V), As(III), Sb(III), and Ti(IV) either individually in the presence of U(VI) or simultaneously in mixtures, a supporting electrolyte of 1 M H2SO4 containing 0.01% Triton® X 100 was used. The i1/C results gave excellent correlations in each case, as was indicated from the least squares regression analysis. The outcome results suggest the method validity as a quantitative method for determination of the studied elements.
Photoreduction of Aromatic Ketones in Hexamethylphosphoric Triamide (HMPA): Formation of Stable Coupling Products with HMPA
Authors: Kohmoto Shigeo , Kreher Thomas , Yamamoto Makoto , Yamada Kazutoshi 
Published: July 2006

Abstract
Irradiation of aromatic carbonyl compounds in hexamethylphosphoric triamide (HMPA) resulted in the cross-coupling of ketyl radicals with the HMPA-derived radical generated via hydrogen abstraction from it. The results on acetolysis, methanolysis, and the reaction with thionyl chloride of the resulting coupling products are described.
Thermal Decomposition and Mass Spectra of Phosphoramidate Esters
Authors: Shimasaki Choichiro , Mutou Yoshinori , Tsukurimichi Eiichi , Yoshimura Toshiaki 
Published: July 2006

Abstract
Thermal decomposition of diphenyl phosphoramidate (1)and phenyl phosphordiamidate (2) was investigated by DTA-TG, IR, 1H NMR, 31P NMR, mass spectroscopy, and TG-GC/MS. The DTA-TG/DTG curve showed that the thermal decomposition of 1 occurred in one stage. Compound 1 melted at about 150°C and decomposed to polyphosphates accompanied with a weight loss of about 60% in the temperature region of 200 to 350°C. It was confirmed from the results of IR, 1H NMR, and TG-GC/MS that this weight loss in TG of 1 is attributed to the liberation of ammonia and phenol and to the production of an insoluble polyphosphate through triphenyl phosphate or a soluble oligophosphate. The fragment ions of diphenyl ether (m⁄z 170) and aniline (m⁄z 93) were recognized in the mass spectrum of 1. This result indicates that phenyl radical and hydrogen atom in both samples transfer between three oxygen atoms and a nitrogen atom around a phosphorus atom. The activation energy of the thermal decomposition was estimated to be 151 kJ mol−1 for 1 and 220 kJ mol−1 for 2. From the DTA-TG/DTG curve of 2, the decomposition in TG showed two stages and proceeded in a similar process to 1. The cleavage of 2 by the electronic impact was also similar to that of 1.
Synthesis of Ferrocenyl-Substituted 3-Cyano-2-methylpyridines
Authors: Shibata Katsuyoshi , Katsuyama Isamu , Matsui Masaki , Muramatsu Hiroshige 
Published: July 2006

Abstract
Ferrocenyl-substituted 3-cyano-2-methylpyridines were easily prepared by the sonication of α,β-unsaturated carbonyl compounds substituted by ferrocenes in acetonitrile in the presence of potassium t-butoxide.
Chemical Behavior of Coenzyme PQQ toward Aminoguanidine: Redox Reaction and Adduct Formation
Authors: Mure Minae , Nii Kazumi , Itoh Shinobu , Ohshiro Yoshiki 
Published: July 2006

Abstract
The reaction of coenzyme PQQ with aminoguanidine, which is known as an inhibitor of quinoprotein amine oxidases, was investigated in vitro. The redox reaction predominantly proceeded at pH 10.0 to give PQQH2 (quinol), whereas deactivation of PQQ occurred at pH 6.7 to give the triazine adduct. In the case of semicarbazide or acetohydrazide as the substrate, azo adduct formation was mainly observed even at pH 10.0. Importance of the C-5 carbinolamine-type intermediate a is discussed.
Synthesis of Layered Polysilicic Acid–Acrylamide Intercalation Compounds and Polymerization in the Interlayer Spaces
Authors: Yanagisawa Tsuneo , Yokoyama Chika , Kuroda Kazuyuki , Kato Chuzo 
Published: July 2006

Abstract
Layered polysilicic acid–acrylamide intercalation compounds were synthesized by the reaction of H-magadiite (H2Si14O29·xH2O) and H-kenyaite (H2Si20O41·xH2O) with acrylamide saturated aqueous solutions. The formation of the intercalation compounds were ascertained by X-ray powder diffraction, IR, 13C-CP MAS NMR, DTA, and chemical analysis. However, when H-magadiite was used, a part of the intercalated acrylamide molecules was oligomerized during the intercalation. A heat treatment of the layered polysilicic acid–acrylamide intercalation compounds led to a polymerization of the acrylamide in the interlayer spaces.
The Reflectance Spectra of (BEDT-TTF)5Hg3Br11 and (BEDT-TTF)HgBr3. The Estimation of Effective On-Site Coulomb Interaction
Authors: Tajima Hiroyuki , Tamura Masafumi , Kuroda Haruo , Mori Takehiko , Inokuchi Hiroo 
Published: July 2006

Abstract
The reflectance spectra of (BEDT-TTF)5Hg3Br11 and (BEDT-TTF)HgBr3 were measured by using the microspectrophotometric technique in the spectral range from 450 cm−1 to 25000 cm−1. In the former salt, the gap formation due to a metal-insulator transition was observed in the reflectance spectrum at 100 K. In the latter salt, the effective Coulomb interaction and the intra-dimer transfer integral were estimated and compared with the corresponding values of BMDT-TTF and TTF.
The Ionization Constants of Nitrobenzoic and Benzoic Acids in Water-Ethanol Mixture at 25 °C from Conductance Measurements
Authors: Niazi M S K , Khan M Zafar Iqbal , Ali J , Ahmad M 
Published: July 2006

Abstract
Molar conductances of dilute solutions of 2-, 3-, 4-nitrobenzoic and benzoic acids are reported at 25°C in ethanol–water (EtOH–H2O) mixtures over composition range from 0 to 70 wt% of ethanol. The ionization constants and limiting molar conductances of these acids have been computed from the data using Fuoss 1978 conductance equation. Solvent effect on the ionization of acids in EtOH–H2O mixtures has been discussed in terms of free energy of transfer of respective anions of the acids from H2O to EtOH–H2O mixtures. It is found that the order of ionization of these acids in EtOH–H2O system is 2-nitrobenzoic acid&gt;3-nitrobenzoic acid \simeq4-nitrobenzoic acid&gt;benzoic acid.
Magnetic Studies of Some Benzamide Derivatives
Authors: Abdel-Kader M M 
Published: July 2006

Abstract
The diamagnetic susceptibilities of benzamide, methylbenzamides, and hydroxybenzamides have been accurately measured. From these measurements and the calculated values of the in-plane susceptibilities, the semi-experimental anisotropies have been obtained. The magnetic data are correlated with the arrangement of these molecules in the crystals.
The Reductions of Azido–, Thiocyanato–, and Isothiocyanato–pentacyanocobaltate(III) Anions by Titanium(III) in Aqueous Acidic Solution
Authors: Oyetunji Olayinka , Olubuyide Olusegun , Ojo J Folorunso 
Published: July 2006

Abstract
The reductions of azido–, thiocyanato–, and isothiocyanato–pentacyanocobaltate(III) anions by aquatitanium(III) have been studied in aqueous solution with I=1.0 mol dm−3 (LiCl) T=25°C. The reactions are found to have inverse acid dependence of the form: kobsd=kK⁄(K+[H+]).The estimated values of k and K are 1.47 dm3mol−1 s−1 and 1.0×10−2 mol dm−3 for the azido complex and 4.85 dm3mol−1s−1 and 6.0×10−3 mol dm−3 for the thiocyanato complex. Various criteria including the kN3−⁄kNCS− and kSCN−⁄kN3− ratios among others are used to suggest inner-sphere mechanism for these reactions.
Extraction–Spectrophotometric Determination of Chromium(VI) with Hydroxyamidines
Authors: Golwelker A , Patel K S , Mishra R K 
Published: July 2006

Abstract
A new, simple, rapid, and selective spectrophotometric method for determining Cr(VI) by extraction with hydroxyamidines in chloroform over 0.2–0.8 M HCl is described. The molar extinction coefficient of the complexes of Cr(VI) with 10 different hydroxyamidines lie in the range of (1.30– 1.52)×104 l mol−1 cm−1 at λmax 390–400 nm. Of these, the simplest compound, N-hydroxy-N,N′-diphenylbenzamidine (HDPBA) has been chosen for the detailed studies. The limit for detection is 0.1 μg Cr/cm3. The composition of the complex, and the effect of solvents, acids and diverse ions on the extraction of the metal are discussed. The method is free from interference of most of the metal ions except Mn(VII) which is removed by reducing with sodium nitrite. The method has been applied for determination of chromium(VI) to water samples containing the metal at ppb levels.
Mechanism of the Copolymerization of Silicic Acid and Metal Ions in Aqueous Media
Authors: Mizutani Tadashi , Fukushima Yoshiaki , Kamigaito Osami 
Published: July 2006

Abstract
The mechanism of copolymerization of silicic acid and metal ions was found to depend on the magnitude of the hydrolysis constant of the aqua-metal cations. It was also demonstrated that the pH of the solution is the major factor governing the Si/metal ion ratios in the solid phases.
Synthesis and Spectral Properties of 5,5′-Di(4-pyridyl)-2,2′-bithienyl as a New Fluorescent Compound
Authors: Nakajima Riichiro , Iida Hiroyuki , Hara Tadashi 
Published: July 2006

Abstract
A new type of fluorescent compound, 5,5′-di(4-pyridyl)-2,2′-bithienyl, has been synthesized and its fluorescence intensity measured at 510 nm in a 40% aqueous methanol (pH&lt;3.0) with excitation at 425 nm. The quantum yield was found to be 0.52. The thienylpyridine skeleton was found for the first time as a new fluorophore.
One Pot Synthesis of Substituted Tropones from 7,7-Dihalo-2,3-(or 3,4-)epoxybicyclo[4.1.0]heptane Derivatives
Authors: Kato Masahiko , Yamamoto Shigeyuki , Nomura Shigeki , Miwa Toshio 
Published: July 2006

Abstract
In order to obtain a scope and limitations of the reaction for newly developed tropone synthesis, some substituted 2,3- and 3,4-epoxy-7,7-dihalobicyclo[4.1.0]heptanes have been prepared and treated with several acids. We found that (1) the epoxy-carbons of starting materials should have, at least, one substituent which may stabilize the carbenium ion formed by cleavage of the epoxide with acid, (2) as halogens in the starting materials, bromine is superior to chlorine, (3) use of 20 molar equivalent of TFA to a substrate in chloroform at refluxing temperature or use of each 5 molar equivalent of TCA and water to a substrate in toluene at 100°C is recommended.