September 20, 2016
Purdue researchers’ discovery could lead to safer, cheaper production of amine-boranes
WEST LAFAYETTE, Ind. – Purdue University researchers have developed a way to produce amine-boranes that promises to be safer and cheaper, and could lead to new uses in medicine, energy storage, rocket propulsion and other technologies.
P.V. Ramachandran, professor of organic chemistry in the Department of Chemistry, and graduate assistant Ameya S. Kulkarni have discovered a way to produce amine-boranes in an open-air environment using cheaper and more plentiful chemicals that have not been used before. The result could provide a safer, cheaper and more plentiful compound, including those not made before, that has a multitude of uses.
The process and one of their applications in organic chemistry is detailed in separate articles by Ramachandran, which appear in a recent issue of Chemical Communications. Links to the articles are available here and here.
Diborane is a pyrophoric gas seldom used as is due to its toxicity and safety issues. Amines, on the other hand, are compounds consisting of a nitrogen atom, Ramachandran said. When amines are combined with borane, the result is non-toxic, air- and moisture-stable amine-boranes.
“Amine-boranes have long been prized for their potential for hydrogen storage,” he said.
According to a 2006 report from the U.S. Department of Energy, amine-borane complexes have great potential as a component in fuel sources due to their high hydrogen content. Hydrogen can be used in fuel cells to power electric vehicles and other electronic devices and can be used to propel spacecraft.
Producing amine-boranes by conventional methods has several safety concerns.
“Borane dimethyl sulfide, one of the reagents used in the process up to now, if opened to air, reacts with the moisture in the air, releasing hydrogen, a highly flammable gas, which could catch fire; so extreme caution needs to be used. Due to the chemicals and process involved in the reaction, only highly trained people could do the reaction. What we’ve done is to make that reaction more accessible.”
The new method of producing the compound removes many of the dangerous forms of borane and substitutes them with sodium borohydride and sodium bicarbonate (or baking soda), which are less dangerous. That allows water to be used as a reagent, meaning the process can be done in an open-air environment, Ramachandran said.
“This process also leads to higher amounts of amine-boranes being produced,” he said.
Since the product is more readily available, it should bring the cost down significantly.
“The new process can also lead to the production of other types of amine-boranes, some of which have not been researched at all, since these materials have not been available in the past,” he said. “So it’s really up to a chemist’s imagination.”
Medicines, batteries and rocket propellants are only some of the uses that are possible.
In the companion manuscript published by Ramachandran’s group, the application of the simplest of the amine-boranes, ammonia borane, for hydroboration has been described. This builds on the seminal work on hydroboration first noted by the late Purdue Nobel Laureate Herbert C. Brown, which earned Brown the Nobel Prize in Chemistry in 1979. Ramachandran worked with Brown for many years.
Hydroboration refers to the addition of a hydrogen-boron bond to carbon-based bonds.
“Hydroboration gave organic chemists a procedure to make millions of compounds that were more difficult to make otherwise,” Ramachandran said. Despite its widespread use, hydroboration utilizes pyrophoric, moisture-sensitive reagents posing a safety risk. The current work from Purdue describes the first open-to-air hydroboration protocol using air- and moisture-stable reagents. “We believe that the ability to carry out hydroboration without the need for inert conditions will have tremendous implications in industry and chemical education,” Ramachandran said.
Ramachandran has provisional patents filed through the Purdue Research Foundation’s Office of Technology Commercialization and the technology is available for licensing.
Writer: Curt Slyder, 765-588-3342, firstname.lastname@example.org
Source: P.V. Ramachandran, 765-494-5303, email@example.com
Note to Journalists: Copies of the published papers are available by contacting Curt Slyder at firstname.lastname@example.org
Amine-boranes bearing borane-incompatible functionalities: application to selective amine protection and surface functionalization
P. Veeraraghavan Ramachandran
Ameya S. Kulkarni
The first general open-flask synthesis of amine-boranes with inexpensive and readily available reagents, such as sodium borohydride, sodium bicarbonate, water, and the desired amines is described. Even amines bearing borane-reactive functionalities, such as alkene, alkyne, hydroxyl, thiol, ester, amide, nitrile, and nitro are well tolerated. Some of these novel amine-boranes represent stable molecules containing potentially incompatible electrophilic and nucleophilic centers in proximity. This convenient scalable synthesis provides a novel class of organic ligands for surface functionalization, as demonstrated by the formation of self-assembled layers of thiol- and alkoxysilane-bearing amine-boranes on gold silica surfaces, respectively.
A non-dissociative open-flask with ammonia borane: ready synthesis of ammonia-trialkylboranes and aminodialkylboranes
P. Veeraraghavan Ramachandran
Michael P. Drolet
Ameya S. Kulkarni
Under open-flask conditions, ammonia borane hydroborates olefins in refluxing tetrahydrofuran. Unlike conventional hydroboration, the Lewis base (ammonia) is not dissociated from the boron center. Terminal alkenes selectively provide ammonia-trialkylborane complexes. On the other hand, internal alkenes afford aminodialkylboranes via a metal-free hydroboration-dehydrogenation sequence. Alkaline hydrogen peroxide oxidation of the products provides the corresponding alcohols in high yields.