Gallium alkoxides: Synthesis and properties

Compounds Ga(OR)₃ (R = Me, Et, Prⁱ, Buⁿ, C₂H₄OMe) were synthesized by exchange reactions between gallium chloride and alkali metal alkoxides, the reetherefication of Ga(OPrⁱ)₃ and Ga(OC₂H₄OMe)₃ by other ROH (R = Me, Et), and anodic dissolution of metallic gallium in the presence of a electroconductive additive (LiCl, Bu₄NBr). When solid GaCl₃ is introduced into an alcoholic solution of NaOEt, stable soluble gallium oxoalkoxyhalides are formed. The same reaction with a GaCl₃ solution in toluene or electrochemical synthesis produces nonvolatile Ga(OEt)₃ samples, which have the polymer zigzag configuration [Ga(OR)_4/2(OR)]_∞. Mass spectrometry shows that only Ga(OPrⁱ)₃ and freshly prepared X-ray amorphous Ga(OEt)₃ samples (produced by reetherefication) are transferred to the gas phase. The spectra of the latter contain ions generated by penta-and hexanuclear oxoalkoxide molecules, along with fragments of orthospecies [Ga(OEt)₃]_2?4. IR spectra are described for all compounds synthesized.     

1-Phenyl-1-halo-1-silacyclohexanes

The approaches to synthesis of 1-phenyl-1-halo-1-silacyclohexanes C₅H₁₀Si(Ph)X (X = F, Cl, Br) have been examined. 1-Phenyl-1-chloro-1-silacyclohexane has been prepared via the known reaction of phenyltrichlorosilane with dimagnesium derivative of 1,5-dibromopentane; up to 20% of 1-bromo-1-phenyl-1-silacyclohexane admixture is formed along with the target product. The minor product formation has been prevented using an alternative method of chlorination of 1-phenyl-1-silacyclohexane with N-chlorosuccinimide. 1-Phenyl-1-fluoro-1-silacyclohexane has been obtained in close to quantitative yield via the reaction of 1-phenyl-1-chloro-1-silacyclohexane with SbF₃ and in 70% yield via its reaction with HF. The synthesis of 1-phenyl-1-bromo-1-silacyclohexane via bromination of 1-phenyl-1-chloro-1-silacyclohexane with N-bromosuccinimide has given the target product as a minor one, the major product being disiloxane formed due to hydrolysis of the Si–Br bond.     

Transformations of diallylsilanes under the action of electrophilic reagents

Reactions of dimethyl-, diphenyl-, and (chloromethyl)methyldiallylsilanes with acetic, trifluoroacetic, triflic acids and complex BF₃ · 2AcОH are studied. Depending on the structure of the starting diallylsilane and the nature of the electrophilic reagent the following processes are realized: addition of an electrophile to one СС bond; expulsion of one or two molecules of propene with addition of the electrophile residue to the silicon atom; and rearrangement with elimination of one allyl group from silicon and its attachment to the second allyl group of diallylsilane. Quantum chemical calculations of all three types of transformations are performed on the example of the reactions of dimethyl- and bis(chloromethyl)diallylsilanes with HF, CF₃COOH, CF₃SO₃H, as well as of the intermediate carbenium and silicenium cations.     

Stereochemistry of the horner-emmons reaction of 3-functionalized 2-methyl-2-propenylphosphonates with aliphatic aldehydes. 2. Effect of size of the functional substituent in the phosphonate

Conclusions In the Homer-Emmons reaction of 3-functionalized phosphonates having the general formula (R¹O)₂P(O)CH₂C(CH₃)=CHR² with isovaleraldehyde the amount of the (2E, 4E) isomer in the final 3,7-dimethylocta-2,4-dienoate ester product increases as the size of the terminal functional group substituent R² in the phosphonate is reduced.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2382–2385, October, 1988.     

Analysis for actinides in tissue samples from plutonium workers of two countries

For more than 25 years, the United States Transuranium and Uranium Registries (USTUR) and the Dosimetry Registry of the Mayak Industrial Association (DRMIA) of the Russian Federation have, each independently, collected tissues at autopsy from workers with potential or confirmed body burdens of actinide elements resulting from occupational exposures. Tissues, thus obtained, were radiochemically analyzed for actinides for the purpose of evaluating the biokinetics of these elements in the human body. Scientists of these two organizations have recently begun a collaborative research program to compare, combine and analyze the data to verify or refine biokinetic models needed for radiation dosimetry.     

Effect of the Composition of the H2SO4-AcOH Binary Solvent on the Dissociation Kinetics of Metal Porphyrins

The kinetics and mechanism of dissociation of copper(II) complexes with octaethylporphyrin and of manganese(III) with tetraphenylporphyrin were studied in relation to the composition of an H₂SO₄-AcOH binary solvent. Concentration ranges of H₂SO₄ in the composition of the binary solvent, where the kinetics of dissociation of metal porphyrins obeys common kinetic regularities, were found using data for porphyrin complexes of transition metals and indium. The reaction order with respect to proton and the nature of the active form of this latter change in the range of solvent compositions, where the H ₀-c⁰ H ₂ SO ₄ dependence is nonlinear.     

Photosensitive protection of carboxyl group and the synthesis of three o-methyl derivatives of gibberellin a3

The methylation of p-methoxyphenacyl ester of gibberellin A₃ (5) and its isomeric monoacetates 6, 7 followed by the removal of p-methoxyphenacyl group gives rise to 3,13-O-dimethylgibberellin A₃14 and to the isomeric O-acetyl-O-methyl-derivatives 15 and 16; the latter afford 3-O-methylgibberellin A₃(17) and 13-O-methylgibberellin A₃18 upon Zemplén deacetylation. The removal of p-methoxyphenacyl group can be achieved either upon photolysis in abs ethanol or with zinc-acetic acid. This protective group survives the conditions of Koenigs-Knorr synthesis as well as oxidation with manganese dioxide. The limitations of this way of protecting the carboxyl group can be seen on the example of the enone ester 20.