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Regenerating spent ammonia borane

26 march 2011 - Recycling

Ammonia borane (AB) is a potential hydrogen carrier for the hydrogen economy but regenerating spent AB fuel presents a challenge. When using a catalyst based on a transition metal and an N-heterocyclic carbene more than two equivalents of hydrogen are extracted leaving a residue called polyborazylene, an odd mix of compounds with formal formula BNH. In 2009 Dixon et al. described AB regeneration from BNH based on ortho-benzenedithiol (converting B-N bonds to B-S bonds) / tributyltin hydride (reducing agent) (DOI) but the tin reagent proved too expensive for industrial application. In 2011 Dixon has made a switch to hydrazine (Sutton et al. DOI).
Direct reaction of BHN with hydrazine yields the hydrazine-borane complex which in itself can be used as a hydrogen fuel if it wasn't for the even more obscure waste-product obtained than PB without even a remote chance of regeneration. An ammonia replacement reaction then. At room temperature the hydrazine-borane complex is unimpressed by the presence of liquid ammonia but with heat applied the ammonia-borane is regenerated with 85% efficiency. The overall reaction taking place is: 4BNH + 5 N2H4 -> 4H3N.BH3 + 5N2. Efficiency (>92%) is greatly improved by reaction of PB with hydrazine in liquid ammonia: hydrazine is displaced in-situ from the hydrazine-borane complex and available again as a reducing agent.
The only new problem to solve according of Dixon is the limited global production capacity of hydrazine but integration of BNH regeneration and hydrazine production is envisioned.

It is like printing gold

19 march 2011 - Formulation chemistry

The secret of cardridge ink.gifThis week, in a most enjoyable episode of the new Dutch television program "de rekenkamer" (Audit office) which exclusively deals with the costs of stuff, it was all about the price of toner cartridges (Link). We all know you can buy a printer almost for free but from then on you spend fortunes on new ink. The program calculates a liter of ink costs you over 3000 euro's (an average cartridge contains 5 ml) or quoting one of the experts on the show with ink it is like printing gold. No surprise the ink manufacturers are secretive about ink formulations and they will not even patent them, according to the show. In a way ink is a curious concoction: it is supposed to stay a liquid to infinity while in the cartridge but is supposed to dry out once past the printer head.
Nevertheless the program tracked down a scientist from Eindhoven University of Technology who was willing to share a recipe and here it is: water 75%, pyrrolidone 4.99% , trimethylolethane 12.37% (this compound is labeled EHPD , not sure why), the sodium salt of EDTA 0.10%, MOPS 0.03%, ethylene glycol 0.28% (the structural formula as shown in the show is that of the diacrylate, needs to be sorted out), 2,4,7,9-tetramethyl-5-decyne-4,7-diol 1.25%, benzisothiazolinone 0.21% (biocide?) and finally Brilliant Black BN with 4.23%. The total combined costs are only 300 euro's which suggests the big ink companies make a fantastic 1000% margin.
In the show we see the scientist patiently adding all ingredients at once to a little bottle. But wait a minute: if it is that simple ink companies cannot keep the recipe a secret. Any analytical laboratory can flesh out a ink composition when exposed to GC, HPLC or MS. This blog thinks the sting is in the exact order in which you add ingredients and what treatments (heat , stirring) are used. Significantly the TUE formulation was not field-tested in an actual printer and why did it contain insoluble particles? (all ingredients are water-soluble?).

In any event please stop whatever you are doing right now research wise and start producing cartridge inks. Except of course those of you involved in illegal drugs, the only business on the planet more profitable.

Target : Lysergic acid

16 March 2010 - Pd power

Lysergic acid synthesis 1  Lysergic acid is a biomolecule and precursor to many alkaloids. Derivatives are used as pharmacauticals, the notorious lysergic acid diethylamide one of them. Inuki et al. do not state an urgent reason for recreating the compound in the laboratory other than showing of some new chemistry, more specifically palladium-catalyzed cyclizations of allenes DOI. Tosyl protected Chiral 2-ethynylaziridine 1 (obtained from L-serine) reacted in a reductive coupling with formaldehyde to alcohol 2 (Tetrakis(triphenylphosphine)palladium(0), InI). Protection of the amino alcohol with benzylidene acetal (CSA) and (silver nitrate, NIS) then gave iodo-alkyne 3. Starting point for building block number two was 4-bromoindole which was reacted with allyl alcohol to alkene 4 (Tetrakis(triphenylphosphine)palladium(0), triethyl borane), then with tosyl chloride (protection) to N-tosyl 5. Oxidative cleavage (OsO4
/ NaIO4) gave aldehyde 6. Chunks 6 and 3 were then joined in a Nozaki-Hiyama-Kishi reaction followed by alcohol oxidation to ketone 7 using Dess-Martin periodinane and asymmetric reduction back to an alcohol but now chiral using Alpine borane. The allene 8 was formed next with nosyl hydrazine / Mitsunobu reaction conditions.
The key transformation was a complex Pd catalyzed domino reaction (Tetrakis(triphenylphosphine)palladium(0) / potassium carbonate) to tetracycle 14 involving an oxidative addition, aminopalladation, reductive elimination. The final reactions consisted of alcohol oxidation (Dess-Martin periodinane) and esterification (Trimethylsilyldiazomethane) to ester 14, followed by detosylation (Sodium naphthalenide) - sequence spoiled by epimerisation - and methylation (formaldehyde / sodium borohydride) to 15 and then reduction to lysergic acid (lithium aluminium hydride) 16



Destination reached! Palladium count: 3.

Gold nanorod mass-production

06 March 2011 - Nanotech

Gold nanorod Bullen 2011.gifIn one of the many applications envisioned for gold nanorods they are introduced into the human body, anchor themselves to an ugly cancerous tumor and kill it when illuminated by a laser beam they heat up and puncture holes in it. Obviously for such a noble cause more of these gold nanorods are needed and a group of Australian researchers have proposed a way to scale up nanorod production (Bullen et al. DOI). In their recipe a mix of chloroauric acid, cetrimonium bromide and reducing agent acetylacetone is mixed with a mix of cetrimonium bromide and silver nitrate buffered by sodium bicarbonate / sodium carbonate. The first mix will produce nanogold particles all by itself but the silver in the second mix is needed for the correct rod aspect ratio. For continuous production the researchers devised a reactor featuring a stainless steel rotating (up to 2000 rpm) cylinder for mixing and a 20 meter silicone tube for particle growth. Of course a lot of tinkering was required before getting acceptable results: rotation speed, reactor residence time, temperature and the gold to silver ratio. In the end the desired nanorods on average measure 6 nm by 20 nm with 300 micron thickness. Another novelty the researchers introduce is that the production is seedless. Now this might be tricky to monitor and this blog is having some doubts: if you are in nanoparticle research the laboratory will eventually be dusted with nanoparticles from top to toe and there will no longer be any need for additional seeding experiments.
In any event the researchers are confident and in their Chemical Communications report they state they will eventually reach 100 kg scale production required to hypothetically furnish every person on the planet with a single 10 nm thick, 2.25 cm square monolayer of particles. So for the near future watch your mailbox for a very tiny parcel with an even tinier postage stamp from Australia.