Yasuo Kubo

Control of photophysical properties and photoreactions of aromatic imides by use of intermolecular hydrogen bonding.

The effect of addition of alcohols on the photophysical properties and the photoreactions of N-methylphthalimide (1), N-methyl-1,8-, -2,3-, and -1,2-naphthalimide (2-4), and N-methyl-9,10-phenanthrenedicarboximide (5) has been investigated. The UV and IR spectra of aromatic imides 1-5 showed the presence of the intermolecular hydrogen bonding between the carbonyl group of the aromatic imides and the alcohols in less polar solvents. The equilibrium constants K for the hydrogen bonding were determined by the UV spectra. The fluorescence intensities of 2 and 1 were found to be remarkably and moderately enhanced by the addition of alcohols, respectively, though those of 3-5 were little enhanced by the addition of alcohols. On the other hand, photochemical cyclobutane formation of 2 with styrene (6) was found to be enhanced by the addition of 2,2,2-trifluoroethanol in benzene. Enhancement of the fluorescence quantum yields Phi(f) and the photoreaction of 2 by the hydrogen bond formation was explained by the decrease of the efficiency of the intersystem crossing from (1)(pi pi*) to (3)(n pi*), whose energy was increased by the hydrogen bonding.

Separation of lighter rare earth metal ions by centrifugal countercurrent type chromatography with di-(2-ethylhexyl)phosphoric acid

Abstract A centrifugal countercurrent type chromatography (Centrifugal Partition Chromatography) was applied to separations of lighter rare earth metal ions (LaCl3, CeCl3, PrCl3, NdCl3, SmCl3 and EuCl3) first time. The results obtained by using di-(2-ethylhexyl)phosphate (D2EHPA) showed that this technique is successfully usable for the laboratory-scale separations, though the numbers of theoretical plate calculated from the chromatograms were considerably lower than expected. The values of separation factors for the adjacent RE ions were found to be substantially parallel to those obtained by single stage extraction method, indicating that our chromatography involves a multi-stage extraction process as in the cases of organic samples.

Carrier-aided centrifugal partition chromatography for preparative-scale separations

Centrifugal partition chromatography is a highly attractive technique for economic preparative-scale separations of a variety of compounds. The technique has been improved by adding a carrier compound to the stationary phase. The separation of alkali metal picrates by using dibenzo-18-crown-6 in chloroform-butan-1-ol as the stationary phase and water as the mobile phase. The retention volumes were found to correlate almost linearly with K(extraction) values, and the separation factor for K+/Na+ was 1.99 with 150 microcells. With suitable carriers the technique should be widely applicable to a variety of samples. The advantages and limitations, together with an outline of the physico-chemical background of carrier-aided chromatography, are reported.

Photochemical [2+2]- and [4+2]cycloadditions of N-methylphthalimide to allyltrimethylsilane

Irradiation of N-methylphthalimide (1) with allyltrimethylsilane gave a [2+2]cycloadduct possibly from the singlet excited state of 1 together with [4+2]- cycloadducts from the triplet excited state of 1

Further Results on Behaviors of Rare Earth Metal Ions in Centrifugal Partition Chromatography with DI(2-Ethylhexyl) Phosphoric Acid

Abstract In centrifugal partition chromatography (CPC) of rare earth metal ions (RECl3) by the use of di(2-ethyl-hexyl)phosphate (D2EHPA) as “separator” in the stationary phase, effects of number of microcells and stationary solvent were investigated for improving separation. By increasing the number of microcells from 1200 (3 cartridges) to 2400 (6 cartridges), the peak resolution value (R) for the separation of PrCl3 versus NdCl3 was improved from 0.37 to 0.62. Heavier RE ions (ErCl3 and YbCl3) was able to separate almost completely by using CHCl3 as stationary solvent. This result suggests that by adjusting these two factors, in addition to adjusting [HC1] in the mobile phase (previously reported), almost whole series of adjacent couples of RE ions will be effectively separated by CPC with acidic D2EHPA. In contrast, neutral tri-n-butyl phosphate (TBP) was found to be a poor separator.

Diastereoselective [3+2]-photocycloaddition of chiral 1,4-naphthalenedicarboxylic esters to alkenes

Abstract [3+2]-Photocycloaddition of di-(−)-menthyl, di-(−)-8-phenylmenthyl, and di-(−)-bornyl 1,4-naphthalenedicarboxylates to alkenes, such as isobutene, styrene, and α-methylstyrene, proceeded with diastereoselectivity, up to 62% diastereomeric excess (de), largely depending on the concavity of the auxiliary, steric bulk of the substituents of the alkenes, and reaction temperature. The de values remarkably increased with decrease of the reaction temperature, and linear dependence of In(diastereomeric ratio) on 1/T was observed.

Miscibility of Semirigid Liquid‐Crystalline Polycarbonate with Poly(vinyl alcohol), Partially Saponified Poly(vinyl acetate) or Poly(vinyl acetate)

The miscibility in blends of semirigid liquid-crystalline polycarbonate (LCPC) with poly(vinyl alcohol) (PVA), partially saponified poly(vinyl acetate) (PVAc75) and poly(vinyl acetate) (PVAc) was investigated by means of differential scanning calorimetry and scanning electron microscopy. These measurements suggested that LCPC forms partially miscible blends with PVA and PVAc75. Blends of PVAc are immiscible. The side-chain hydroxy groups play an important role in improving the miscibilities of the blends.

3+2-PHOTOCYCLOADDITIONS OF DICYANONAPHTHALENES TO ALKENES

Abstract [3+2]-Photocycloadditions of 1,2-, 1,3-, and 2,3-dicyanonaphthalenes to alkenes were found to proceed at the 1,8-, 4,5-, and 1,8-positions of the naphthalene ring of dicyanonaphthalenes, respectively. In the photoreactions of the 1,3- and 2,3-isomers [3+2]-adducts were obtained in oxidized forms and addition of Cu(OAc) 2 considerably improved the yields of the adducts. The observed addition sites of the alkenes are rationalized on the basis of the spin and charge densities of the radical anions of dicyanonaphthalenes.

Liquid-Membrane Transport of Rare Earth Metal Ions Facilitated by Di(2-Ethylhexyl) Phosphoric Acid: Comparison with the Results of Corresponding Centrifugal Partition Chromatography

Abstract Selective liquid-membrane transport of rare earth metal ions were found to be effectively attained by the use of di(2-ethylhexyl)phosphoric acid (D2EHPA) carrier. This finding was obtained on the basis of the idea that liquid-membrane transport phenomena would be basically correlated with those of “separator-aided centrifugal partition chromatography”, a separation technique based on the counter-current continuous extraction method. For the rare earth metal ion samples direct comparison of liquid-membrane transport with the corresponding centrifugal partition chromatography by employing the same two-phase liquid systems both containing D2EHPA showed that a close parallelism in the results obtained with the two separation systems.

Photochemical reaction of N-methylnaphthalene-1,8-dicarboximide with alkenes, dienes, and furans. Cyclobutane and oxetane formation

Irradiation of benzene solutions of N-methylnaphthalene-1,8-dicarboximide (1) in the presence of alkenes (2b–k) and dienes (9a–c) give the cyclobutanes (3b–j), (4c,e,f,h,i), and (10a–c). Stereospecificity of cyclobutane formation was observed in the reaction with cis- and trans-but-2-ene (2h,i), and some endo-selectivity was observed in the reaction with styrene (2f). In contrast, irradiation of benzene solutions of (1) in the presence of trans- and cis-stilbene (2j,k), 2,5-dimethylbuta-2,4-diene (9d), and furans (14a,b) gave the fragmentation products (7a,b), (8), (13a,b), (16a,b), and (17a,b) arising via precursor oxetanes. In fluorescence quenching studies of the alkenes (2a–d) a linear relationship was found for log plots of their Stern-Volmer slopes (kqτ) and ionization potentials, and the furans (14a) and (9d) showed new emissions, possibly from exciplexes. A tentative mechanistic scheme for the two types of reactions involving two types of exciplexes generated by the reaction of the singlet excited state of (1) and unsaturated compounds is proposed.