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.     

Anion-exchange separation and spectrophotometric determination of cobalt in sea water

Summary Traces of cobalt in sea water have been preconcentrated by anion-exchange from acidified sea water in the presence of thiocyanate. Cobalt adsorbed on the resin column is stripped by elution with 2 M perchloric acid. Accompanying iron is removed subsequently by anion-exchange from 6 M hydrochloric acid medium. Cobalt in the eluate is determined spectrophotometrically with 4-(2-pyridylazo)resorcinol in the presence of EDTA and potassium cyanide. The anion-exchange — PAR method allows to determine cobalt very selectively in sea as well as non-saline waters on a 2 l sample basis. The method gives a coefficient of variation of ca. 10% at a cobalt level of 0.1–0.2 g per liter.

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Spektralphotometrische Bestimmung von Kobalt in Meerwasser nach Abtrennung durch Anionenaustausch

Zusammenfassung Kobaltspuren in Meerwasser wurden angereichert durch Behandlung des angesÄuerten Wassers mit einem stark basischen Anionenaustauscher in Gegenwart von Thiocyanat. Adsorbiertes Kobalt wird mit 2 M PerchlorsÄure abgelöst. Eisen wird anschlie\end durch Anionenaustausch aus 6 M salzsaurer Lösung entfernt. Kobalt wird im Eluat spektralphotometrisch mit 4-(2-Pyridylazo)resorcin in Gegenwart von ÄDTA und KCN bestimmt. Das Verfahren gestattet eine selektive Kobaltbestimmung in Meerund Sü\wasser bei Verwendung von 2 l-Proben. Der Variationskoeffizient betrÄgt etwa 10% bei 0,1–0,2 g Co/l.

     

Errata

A novel palladium compound, (Ph₃P)Pd(Cl)(CH₂SCH₃), was prepared in which the CH₃SCH₂ group acts as a chelate ligand; the stereochemically non-rigid property of (Ph₃P)Pd(CH₂SCH₃)[S₂CN(CH₃)₂] was also discussed in terms of the ligating effect of sulfur in this group.     

Preparation of nanoparticles by reducing intermediate radicals formed in sonolytical pyrolysis of surfactants

Metal nanoparticles with a narrow size distribution could be prepared by sonolysis of aqueous solutions of metal cations in the presence of surfactants such as sodium dodecyl sulfate, polyethylene glycol monostearate, etc. The role of the surfactans is not only to stabilize formed particles, but also to produce reductive radicals in pyrolysis or hydrogen abstraction of OH radicals from surfactants. Particles with a smaller size could be obtained in a faster reduction rate with dilute metal cations concentration. Pt(IV) is consecutively reduced in two steps to Pt(0)via Pt(II). By comparing the sonolytical reduction withγ-ray radiolysis, two kinds of organic reducing radicals are proposed to contribute to the reduction. One (R_ab) is an intermediate radical which is produced by hydrogen abstraction of OH radical from surfactant and effective only on the reduction of Pt(II) to Pt(0). The other (R_py) is also an intermediate radical which is produced by thermal decomposition of surfactant at the interface between the cavity and bulk solution and effective on the reduction of Pt(IV) to Pt(II).     

Microchemical determination of lodate and iodide in sea waters by flow injection analysis

A flow injection analysis method for iodate and iodide in sea water is described. The system involves spectrophotometric detection based on the catalytic, fading effect of either iodate or iodide on the indicator reaction of iron (III) thiocyanate and nitrite. With and without an anion-exchange column in the flow conduit, the system allows the determination of iodate and total iodine, respectively; iodide can be found by difference. Both iodate-iodine and total iodine can be determined in the range 0.75 to 150 g/1 on the sea water basis with analysis times of 20 min for iodate-iodine and 9 min for total iodine. The RSDs are within 1.3% for both iodate and iodide. Results are presented for the determination of iodate and iodide in sea waters and some brines associated with natural methane gas evolution.     

First-derivative spectrometric analysis of mixtures of peroxo complexes of titanium,vanadium, and molybdenum for respective metals

The application of first-derivative spectrometry to the simultaneous determination of titanium and vanadium; titanium and molybdenum; and vanadium and molybdenum in their mixtures with varying mass ratios has been described with hydrogen peroxide as color developing reagent. At a first-derivative isosbestic point for the peroxo complex of one constituent, the derivative absorbance of the other constituent is read and used for quantitation. The procedure does not require the solution of simultaneous equations. The first-derivative spectrometry is also feasible at 450.0 nm for the selective determination of titanium in the presence of vanadium, molybdenum, and tungsten.     

Carbocyclization by homolytic substitution (SH′ process). A new route to dihydroindole or dihydrobenzofuran

N-(4-Phenylthio-2-butenyl)-2-bromoaniline reacted with tributyltin hydride to give 3-vinyl-2,3-dihydroindole in 96% yield via hitherto unknown intramolecular S_H′ process, some other examples and remarkable dilution effect on these homolytic carbocyclizations were described.     

A novel synthesis of 2-arylaminothiazolo[4,5-d]pyridazinones

The reaction of 5(4)-amino-4(5)-chloropyridazin-3(2H)-ones 1 (9 ) with methyl dithiocarbamates 2 gave 2-arylaminothiazolo[4,5-d]pyridazinones 3 (10 ). Treatment of 5(4)-alkylamino-4(5)-chloropyridazin-3(2H)-ones 5 (12 ) with 2 afforded the corresponding 2-aryliminothiazolo[4,5-d]pyridazinones 6 (13 ). Cyclization of 1a with phenylisothiocyanate produced 2-amino- and 2-iminothiazolo[4,5-d]pyridazinones 3a and 16 .