New synthetic reaction by electrolysis. III. α-acetoxylation of sulfide

Sulfides are directly converted effectively to the corresponding α-acetoxy sulfides by electrolysis in acetic acid.     

Facile synthesis of p-chloromethylated styrene by elimination reaction of p-(2-bromoethyl)benzylchloride using potassium hydroxide as a base under phase transfer catalysis

Phase transfer catalyzed elimination reactions of $\text{p}$-(2-bromoethyl)-benzylchloride with potassium hydroxide gave $\text{p}$-chloromethylated styrene in high yield.     

Supramolecular dioxygen receptors composed of an anionic water-soluble porphinatoiron(II) and cyclodextrin dimers

Three types of per-O-methylated β-cyclodextrin dimers, Im2CD, Im3NHCD and Py3NHCD, were prepared as globin models. Im2CD was synthesized by the condensation reaction of mono(2(A)-amino)-per-O-methylated β-cyclodextrin with 3-(1H-imidazol-1-yl)pentanedioic acid. Im3NHCD and Py3NHCD were obtained through the S(N)2 reactions of mono(2(A),3(A)-epoxy)-per-O-methylated β-cyclodextrin with 3-(1H-imidazol-1-yl)pentane-1,5-diamine and 3,5-bis(aminomethyl)pyridine, respectively. These cyclodextrin dimers formed 1:1 supramolecular inclusion complexes of tetrakis(4-sulfonatophenyl)porphinatoiron(II) (Fe(II)TPPS) in aqueous solution. The supramolecular complexes bound dioxygen (O(2)), with the O(2) affinity of the Fe(II)TPPS/Im3NHCD complex (P(1/2)(O2) = 1.5 ± 0.1 Torr) being much higher than those of the Fe(II)TPPS/Im2CD (36 ± 2 Torr) and Fe(II)TPPS/Py3NHCD complexes (70 ± 5 Torr). On the basis of the results of the present study and previous results, it is concluded that the imidazole axial ligand at the linker attached at the 3- and 3'-positions of the cyclodextrin units causes higher O(2) affinity as compared with the imidazole ligand at the 2- and 2'-positions and the pyridine ligand at the 2,2'- or 3,3'-positions. The electron donating ability and orientation of the axial ligand may control the O(2) affinity of a supramolecular receptor.     

Microgravity experiments of single droplet combustion in oscillatory flow at elevated pressure

An experimental study for 1-butanol single droplet flames in constant and oscillatory flow fields was conducted under microgravity conditions at elevated pressure. In the constant flow experiments, flow velocities from 0 to 40 cm/s were tested. Using obtained data of d², the burning rate constants were evaluated. The burning rate constant in the quiescent condition was also calculated successfully at high pressure by the extrapolation method based on the Frössling relation. In the oscillatory flow experiments, the flow velocities were varied from 0 to 40 cm/s at the frequencies of 2–40 Hz. Results showed that the burning rate constant during the droplet lifetime varied following the quasi-steady relation at 0.1 MPa; however, in the conditions with higher frequencies at 0.4 MPa, the average burning velocity became larger than that for the constant flow case with the velocity equivalent to the maximum velocity in the oscillatory flow. Under the condition where the burning rate constant increased, it was observed that the flame did not sufficiently move back upstream, leading to enhancement of the heat transfer from the flame to the droplet surface. Therefore, the instantaneous burning rate constant increased. To investigate the mechanism of such flame behavior, the ratio of two characteristic times, τ_f/τ_D (τ_f: flow oscillation characteristic time, τ_D: diffusion characteristic time), were compared. As the flow oscillatory frequency increased, τ_f/τ_D becomes smaller. τ_f/τ_D also became smaller at high pressure. If τ_f/τ_D is small due to the small mass diffusion rate, the droplet flame could not move back to the appropriate position for the minimum velocity in steady flow, leading to an increase of the burning rate constant, especially in the case of higher frequency at high pressure.     

Preparation of polymers containing the 1,3,4-oxadiazoline-5-thione structure and their application to the activation of N-protected α-amino acids

Two new monomers with pendent 1,3,4-oxadiazoline-5-thione structures were prepared. Homopolymerization of 2-isopropenyl-1,3,4-oxadiazoline-5-thione (V) and copolymerization with styrene (M₁)(r₁ = 0.02, r₂ = 1.56, Q = 4.12, e = 1.06) were examined. Further, 2-(4-methacryloylaminophenyl)-1,3,4-oxadiazoline-5-thione (VIII) having a phenylcarbamoyl group between the isopropenyl and 1,3,4-oxadiazoline-5-thione ring as a spacer was also synthesized and polymerized. The resultant polymers were allowed to react with N-protected α-amino acids such as Z-AlaOH, Z-LeuOH and Z-PheOH by the DCC method. The polymers containing amino acids thus obtained were reacted with ethyl glycinate to give the corresponding dipeptides in excellent yields without racemization.     

Alkoxycarbene complexes of nickel(II)

Alkynylnickel complexes trans-C₆Cl₅Ni(PPhMe₂)₂CCR (IIIa, R  H; IIIb, R  Me; IIIc, R  Et; IIId, R  CH₂OH; IIIe, R  CH₂CH₂OH; IIIf, R  Ph; IIIg, R  C₆H₄OMe-p) have been prepared from trans-[C₆Cl₅Ni-(PPhMe₂)₂L]ClO₄ and monosubstituted acetylenes in the presence of triethylamine, and their reactions with alcohols in the presence of perchloric acid were studied. Complexes IIIa and IIIe afforded alkoxycarbene complexes trans-[C₆Cl₅Ni-(PPhMe₂)₂{C(OR′)Me}]ClO₄ (IVa, R′  Me; IVb, R′  Et; IVc, R′  n-Pr) or trans-C₆Cl₅Ni(PPhMe₂)₂{$\text{C(CH}{}_2\text{)}{}_3\text{O}$}]ClO₄(IVd), respectively, but IIIb either decomposed or afforded trans-C₆Cl₅Ni(PPhMe₂)₂CHC(OMe)Me, depending on the amount of acid used. Treatment of IVaIVd with amines resulted in deprotonation to give α-alkoxyvinyl complexes, trans-C₆Cl₅Ni(PPhMe₂)₂C(OR′)CH₂ (VIaVIc) or trans-C₆Cl₅Ni(PPhMe₂)₂$\text{CCHCH}{}_2\text{CH}{}_2\text{O}$ (VId), the reaction being reversible. A ¹H NMR study indicated: (i) that the carbene methyl and the vinyl protons IV or VI are D-exchangeable by MeOD without catalyst; (ii) that the basicity of VIa is comparable to those of amines; (iii) that the carbene complexes IVaIVc have two isomers due to hindered rotation about the C(carbene)O bond in solution, IVb existing in the Z-form in the solid state; (iv) that the rotationalbarriers (°G^≠) about the C(carbene)O bond in IVb and the NiC-(carbene) bond in IVd are 20 (or more) and 11.7 kcal/mol, respectively. These results are explained in term of double bond character of the carbene carbon and its surrounding atoms.