Toshiaki Yoshimura

Determination of melamine derivatives, melame, meleme, ammeline and ammelide by high-performance cation-exchange chromatography

Abstract The thermal decomposition of melamine produces melame and meleme, while alkaline hydrolysis of melamine produces ammeline and ammelide. These four melamine derivatives were determined by high-performance cation-exchange chromatography using phosphate buffer as the eluent. The elution behavior during the isocratic and gradient elutions was examined and the determination was simultaneously achieved using photodiode array UV–Vis detection. An isocratic elution with 50 mM phosphate buffer (pH 2.5) seemed most suitable for the rapid and quantitative analysis. Three types of gradient elutions involving phosphate- and NaCl-concentrations, and pH also showed satisfactory separations for the melamine derivatives.

[2+1] Cycloaddition of Nitrene onto C60 Revisited: Interconversion between an Aziridinofullerene and an Azafulleroid†

It is known that organic azides react with a [6,6] bond of C60 through a 1,3-dipolar [3+2] cycloaddition to afford triazolines. Thermolysis of a triazoline, followed by concomitant loss of nitrogen, gives rise to a [1,6]azafulleroid 1 and a [1,2]aziridinofullerene 2 (Scheme 1). Both 1 and 2 can also be obtained directly from the reaction of C60 and azides at higher temperatures, but the ratio of 1:2 depends on the nature of the substituent. Furthermore, azides have major associated problems in regards to toxicity and explosibility. Thus, new useful methods for the preparation of azafulleroids and aziridinofullerenes are expected. Sulfilimines are known to generate an N-substituted nitrene in thermal and photochemical reactions. Recently, it has been reported that N-sulfenylsulfilimine generates a sulfenylnitrene under mild conditions. Nitrenes readily react with alkenes to afford the corresponding three-membered aziridines. In this context, a nitrene is expected to be a key intermediate, instead of an azide, in the aziridination of fullerene. In the course of our study on the development of synthetic methodology for the preparation of [1,2]aziridinofullerene, we carried out the photoreaction of C60 with an N-p-toluenesulfonylsulfilimine having a dibenzothiophene structure (3 ; Scheme 2) to accomplish the regioselective

Effect of the fire-retardant, melamine, on the combustion and the thermal decomposition of polyamide-6, polypropylene and low-density polyethylene

Abstract Combustion tests show that polyamide-6 (PA-6) mixed with melamine is self-extinguishing. The thermal degradation process in PA-6 is modified strongly by the presence of melamine, so that the temperature of decomposition is lowered and the composition of the resulting volatile products is changed. On the other hand, melamine is not effective for either polypropylene (PP) or low-density polyethylene (LDPE). Activation energies based on thermogravimetry (TG) curves for the thermal decomposition of each sample at different heating rates are in the range of about 88.1 to 263 kJ mol −1 . The fluctuations found in activation energies indicates that a charring mechanism may contribute to the overall process. Minor amounts of thermal decomposition products other than ϵ-caprolactam were also evolved from the pure PA-6, their formation being suppressed in mixtures with melamine. The charring process occurs in parallel with the volatilization of decomposition products of PA-6, on which melamine seems not to have a significant effect. It appears evident that, compared with PP and LDPE, PA-6 is much more susceptible to thermal decomposition in the presence of melamine.

Generation of Nitrene by the Photolysis of N-Substituted Iminodibenzothiophene

To evaluate the ability of dibenzothiophene N-substituted sulfilimines as photochemical nitrene sources, their photolyses in the presence of several trapping reagents, such as sulfides, olefins, and phosphorus compounds, were performed. In the reactions, the corresponding imino-transfer compounds, namely sulfilimines, aziridines, and iminophosphoranes, were formed in good yields, indicating dibenzothiophene N-tosyl and N-acylsulfilimines have a potent nature as nitrogen sources.

A new method for the preparation of fluoro-λ6-sulfanenitriles: reaction of sulfimides with Selectfluor™

Several diaryl(fluoro)-λ 6 -sulfanenitriles 3 were synthesized by the reaction of S , S -diarylsulfimides 1 with Selectfluor™. This reaction also allows the first preparation of heterocyclic fluoro-λ 6 -sulfanenitrile, 5-fluoro-10,10-dioxo-5,10-dihydro-5λ 6 ,10λ 6 -thianthren-5-nitrile ( 5 ) and its molecular structure was determined by X-ray crystallographic analysis.

Continuous flow photocatalytic treatment integrated with separation of titanium dioxide on the removal of phenol in tap water

We studied the continuous flow photocatalytic treatment integrated with separation/reuse of titanium dioxide on the removal of phenol (20 mg l(-1)) in electrolytes containing tap water. A circulative flow tubular photoreactor and a separation tank were used, where inflow of phenol continuously flowed into a mixing tank (for titanium dioxide suspension) and treated water overflowed from the separation tank. Black light and sunlight were used by turns as the light source on the photocatalytic treatment. Photocatalytic removal of phenol was maximum at the circulative flow rate of 600 ml min(-1) and the transmittance of 0.3%. Integration of circulative photocatalytic treatment and titanium dioxide separation and continuous use of titanium dioxide could be performed effectively at low inflow of 10 ml min(-1). The titanium dioxide slurry sedimented spontaneously by standing was continuously used for at least 72 h without decreasing the efficiency of the photocatalytic treatment. The used titanium dioxide can be replaced with a fresh one by draw and fill method without interrupting the treatment.

Highly regioselective synthesis of bis-aziridino[60]fullerene with sulfilimine.

In the course of our study of the development of a synthetic methodology for the aziridination of fullerenes, we recently reported the photochemical [2+1] cycloaddition reaction of nitrene onto C(60) generated from sulfilimine. Sulfilimines with an electron-donating group on the N atom are well known to undergo Michael-type reactions, followed by concomitant elimination of sulfide to afford the corresponding aziridines. In these reactions, sulfilimines act as a nucleophile to the electrophilic olefins. Furthermore, C(60) has characteristic features of a low LUMO level and electron-accepting properties. Therefore, it can be an electrophilic olefin. In this context, sulfilimines might react with C(60) to afford the corresponding aziridinofullerenes. We have studied the thermal reaction of (S,S)-diphenylsulfilimines with C(60) and regioselectively synthesized bis- and tris-aziridinated fullerenes. These structures were determined through spectroscopic analyses. Among these, the structure of bis-aziridinated[60]fullerene, C(60)(NCH(3))(2), was determined using single-crystal X-ray analysis. Results show that the multi-aziridination occurs exclusively at the same six-membered ring of C(60) to afford one isomer of the bis-adduct and tris-adduct.

Formation of S,S-diphenyl-S-methoxythiazyne Ph2S(OMe)(≡N) in the alkaline hydrolysis of S,S-diphenyl-N-halosulfilimines

Abstract The structure of a compound formed during the alkaline hydrolysis of S,S-diphenyl-N-halosulfilimines to the corresponding sulfoximine in methanol was assigned to PhS(OMe)(≡N)Ph, S,S-diphenyl-S-methoxythiazyne, on the basis of spectroscopic analyses and chemical reactions.

Synthesis, structure, and reactivity of iminosulfonium ylides bearing an α-carbonyl group

Abstract Treatment of methyl(methylimino)diphenylsulfonium tetraphenylborate ( 3 ) with NaH and subsequent acylation produced a new type of iminosulfonium ylides bearing an α-carbonyl group 5 . The molecular structure of iminosulfonium phenacylide 5a was determined by X-ray crystallographic analysis. The ylide 5 reacted further with methyl triflate affording the corresponding novel alkylidenesulfonium salts 6 .

The structures of [Ph2XSNSPh2NH]+ cations (XNH, O)

Abstract Diphenyl(diphenylsulfodiimidoyl)(nitrido)sulfur(VI) (2) and diphenyl(diphenylsulfoximidoyl)(nitrido)sulfur(VI) (3) (Ph2XSNSNPh2N, X=NH, O) were prepared by the reaction of diphenyl(fluoro)(nitrido)sulfur(VI) (Ph2FSN) with sodium salts of diphenyl-sulfodiimide (Ph2S(NH)2) and -sulfoximide (Ph2OSNH). The nitrido-sulfur complexes 2 and 3 are considerably basic (pKa=7.86 and 7.60, respectively). Treatment of 2 and 3 with perchloric acid afforded quantitatively the corresponding μ-aza-bis[diphenyl(imido)sulfur(V)] perchlorate (4) and μ-aza-[diphenyl(imido)]-[diphenyl(oxo)]disulfur(V) perchlorate (5) ([Ph2XSNSPh2NH]+[ClO4]−, X=NH, O). The crystal structures of 4 and 5 were determined by X-ray crystallographic analysis. The former has essentially C2 symmetry with an SNS bond angle of 120.3(2)°, bridging SN bond lengths of 1.595(3) and 1.604(3) A, and terminal SN bond lengths of 1.509(3) and 1.497(3); the latter cation is an unsymmetrically substituted oxygen analog with an SNS bond angle of 123.1(2)°, and bridging SN bond lengths of 1.607(4) and 1.568(4) A, terminal SN and SO bond lengths of 1.501(3) and 1.438(2) A. Single-point ab initio calculations were also carried out using the data from the crystal structures of 4 and 5.