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Synthesis and characterization of methylammonium borohydride
Kathryn R Graham1, Mark E Bowden, Tim Kemmitt
1MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington, New Zealand. k.benge@irl.cri.nz
Inorganic Chemistry
|January 8, 2011
Summary
A new methylammonium borohydride was synthesized, showing significant hydrogen mobility. This compound decomposes similarly to ammonium borohydride, releasing hydrogen and forming a methylated diborane diammoniate.
Area of Science:
- Inorganic Chemistry
- Materials Science
- Hydrogen Storage
Background:
- Borohydrides are crucial hydrogen storage materials.
- Understanding their decomposition pathways is key for practical applications.
- Methylated analogues offer potential for tailored properties.
Purpose of the Study:
- Synthesize and characterize a new methylammonium borohydride, [CH(3)NH(3)](+)[BH(4)](-).
- Investigate its hydrogen mobility and decomposition kinetics.
- Explore the general applicability of the synthetic method.
Main Methods:
- Metathesis reaction using methylammonium fluoride and sodium borohydride.
- Room-temperature X-ray diffraction for structural analysis.
- In situ X-ray diffraction and solid-state (11)B NMR spectroscopy for decomposition studies.
Main Results:
- Successful synthesis of [CH(3)NH(3)](+)[BH(4)](-) with tetragonal unit cell and high hydrogen mobility.
- Decomposition occurs around 40 °C, forming [BH(2)(CH(3)NH(2))(2)](+)[BH(4)](-) without detectable intermediates.
- Analogous synthesis of dimethylammonium and trimethylammonium borohydrides confirmed method's versatility.
Conclusions:
- [CH(3)NH(3)](+)[BH(4)](-) is a promising material with high hydrogen mobility.
- The decomposition pathway mirrors that of ammonium borohydride.
- The synthetic route is broadly applicable for creating novel borohydride materials.
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In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
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Alkylation is one of the methods used to prepare amines. Direct alkylation of ammonia or a primary amine with an alkyl halide gives polyalkylated amines along with a quaternary ammonium salt through successive SN2 reactions. This process of making the quaternary salt through the direct alkylation method is called exhaustive alkylation.
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Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
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Strong bases like NaOH or KOH deprotonate the phthalimide to form the corresponding anion, which acts as a nucleophile. Further, the anion attacks an...
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