Presence Of Borane Research Articles

Specific features of radical copolymerization of methyl methacrylate and n-butyl acrylate in the presence of the tributylborane–p-quinone system

Copolymerization of methyl methacrylate (MMA) and n-butyl acrylate (n-BA) in the presence of the tributylborane–p-quinone system has been investigated. Reactivity ratios of the monomers differ from the values known for conventional radical polymerization. The copolymerization proceeds in a controlled manner according to the reversible inhibition mechanism. The nature of p-quinone and the composition of the monomer mixture affect the realization of this mechanism. The microstructure of the copolymers obtained in the presence of borane and p-quinones depends on the nature of the latter.

Borane and alane mediated hydrogen release from silane and methylsilane

The dehydrogenations of silanes SiH4 and CH3SiH3 in the presence of borane and alane were investigated using density functional (B3LYP) and coupled-cluster (CCSD(T)/aug-cc-pVnZ) theories. The calculated results showed that the hydrogen release reactions are more favorable in presence of BH3. Our theoretical analyses have further revealed that the addition of an extra BH3 can lead to several low energy barrier pathways. This observation is important to understand the catalytic role of BH3 in such reactions (depending on its release mechanism). Overall, silane and its alkyl derivatives can be used as effective starting materials for H2 production.

Cationic Polymerization of Norbornene Derivatives in the Presence of Boranes

Cationic polymerization of 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene, dicyclopentadiene, and norbornadiene-2,5 in the presence of boranes was systematically studied. It was found that B(C6F5)3 in combination with caprylic acid, 1-phenylethanol or water was a highly active catalyst for the polymerization of 5-alkylidene-2-norbornenes. The corresponding cationic polymers were obtained with up to yields 95% and with high molecular weights (Mw ≤ 430 000). The activity of 5-alkylidene-2-norbornenes in the polymerization using B(C6F5)3 containing systems was the highest among the other monomers (5-vinyl-2-nobornene, dicyclopentadiene, and norbornadiene-2,5). BF3·O(C2H5)2 based catalysts turned out to be not so active for cationic polymerization of monomers compared with the systems containing B(C6F5)3. They produced polymers predominantly containing the addition (vinyl) units instead of isomerization units. The structure of the polymer main chain units depended on the nature of the monomers: in the case of norbornadiene-2,5, 5-methylene-2-norbornene, and 5-ethylidene-2-norbornene the transannular polymerization proceeded, while dicyclopentadiene and 5-vinyl-2-norbornene formed the addition type polymers under the studied conditions.

Elucidation of hydrogen-release mechanism from methylamine in the presence of borane, alane, diborane, dialane, and borane–alane

The mechanisms of hydrogen release from methylamine with or without borane, alane, diborane, dialane, and borane–alane are theoretically explored. Geometries of stationary points are optimised at the MP2/aug-cc-pVDZ level and energy profiles are refined at the CCSD(T)/aug-cc-pVTZ level based on the second-order Møller–Plesset (MP2) optimised geometries. H2 elimination is impossible from the unimolecular CH3NH2 because of a high energy barrier. The results show that all catalysts can facilitate H2 loss from CH3NH2. However, borane or alane has no real catalytic effect because the H2 release is not preferred as compared with the B–N or Al–N bond cleavage once a corresponding adduct is formed. The diborane, dialane, and borane–alane will lead to a substantial reduction of energy barrier as a bifunctional catalyst. The similar and distinct points among various catalysts are compared. Hydrogen bond and six-membered ring formation are two crucial factors to decrease the energy barriers.

Deoxygenation of Sulfoxides to Sulfides in the Presence of Zinc Catalysts and Boranes as Reducing Reagents

In the present study, the zinc-catalyzed deoxygenation of aliphatic and aromatic sulfoxides in the presence of boranes as reducing reagent has been explored. After investigation of different reaction parameters the abilities of catalytic amounts of Zn(OTf)2 has been demonstrated in the deoxygenation of various sulfoxides. Moreover, various experiments have been performed to shed light on the underlying reaction mechanism.

The effect of the NH2 substituent on NH3: hydrazine as an alternative for ammonia in hydrogen release in the presence of boranes and alanes

Potential energy surfaces for H(2) release from hydrazine interacting with borane, alane, diborane, dialane and borane-alane were constructed from MP2/aVTZ geometries and zero point energies with single point energies at the CCSD(T)/aug-cc-pVTZ level. With one borane or alane molecule, the energy barrier for H(2)-loss of approximately 38 or 30 kcal mol(-1) does not compete with the B-N or Al-N bond cleavage ( approximately 30 or approximately 28 kcal mol(-1)). The second borane or alane molecule can play the role of a bifunctional catalyst. The barrier energy for H(2)-elimination is reduced from 38 to 23 kcal mol(-1), or 30 to 20 kcal mol(-1) in the presence of diborane or dialane, respectively. The mixed borane-alane dimer reduces the barrier energy for H(2) release from hydrazine to approximately 17 kcal mol(-1). A systematic comparison with the reaction pathways from ammonia borane shows that hydrazine could be an alternative for ammonia in producing borane amine derivatives. The results show a significant effect of the NH(2) substituent on the relevant thermodynamics. The B-N dative bond energy of 31 kcal mol(-1) in NH(2)NH(2)BH(3) is approximately 5 kcal mol(-1) larger than that of the parent BH(3)NH(3). The higher thermodynamic stability could allow hydrazine-borane to be used as a material for certain energetic H(2) storage applications.

The microdetermination of hydrazino functional groups in boron hydride compounds

Summary Hydrazine and azide functional groups can be determined in the presence of boranes by a modified microgasometric procedure. Hydrazine groups are oxidized to nitrogen with an iodate solution and azides are converted to nitrogen by the use of a ceric solution. The evolved gases are passed through a heated zone of copper oxide in a stream of carbon dioxide, and the hydrogen evolved by the borane is coverted to water. The nitrogen evolved is collected and measured in an azotometer.

The Design of a Portable Instrument for the Detection of Atmospheric Pentaborane and Other Toxic Gases

A direct reading, automatic, and temperature insensitive instrument has been developed for the detection and recording of pentaborane in air down to and below 0.1 parts per million (ppm) sensitivity using the flame-emission principle. Toxic levels of many other volatile materials may also be detected with appropriate modification. A small hydrogen flame takes on a typical greenish cast in the presence of boranes, the radiation intensity being proportional to the pentaborane concentration. A multiplier phototube with an appropriate interference filter detects this energy and the amplified current at the multiplier anode is applied to a dc differential amplifying stage using field-effect transistors. A panel meter is applied to this circuit, and recorder and control outputs are provided. The hand-carried instrument can operate for an eight-hour period using a self-contained hydrogen supply and rechargeable silver-zinc batteries. An automatic battery charge and cutoff circuit is built into the device.