Update: Improving atom economy of dehydrogenative decarbonylation

“Selective Metal-Catalyzed Transfer of H2 and CO from Polyols to Alkenes” Verendel, J. J.; Nordlund, M.; Andersson, P. G. ChemSusChem, 2013, 6, 426-429. DOI: 10.1002/cssc.201200843

In a recent post I commented on the byproducts of dehydrogenative decarbonylation, namely H2 and CO.

1st reaction scheme

I wondered whether this gas mixture, syngas, could be used in a subsequent reaction. This would improve the atom efficiency of the reaction and potentially also improve the safety (of both the syngas-producing and syngas-using reactions). Both are goals of green chemistry and I especially appreciate avoiding rolling cylinders of toxic and/or flammable gases around the lab.

After some digging I found some cool stuff, the most recent being the work from the Andersson group at Upsalla wherein the syngas produced from polyol deoxygenation is used in a subsequent hydroformylation of styrene. In addition, I found Madsen’s excellent paper, which includes lots of interesting references (such as this, where the CO liberated from decarbonylation of cinnamyl alcohol is used in the Pauson-Khand reaction. Note that cinnamyl alcohol can trap the evolved H2! Neat!).

In Andersson’s work the syngas-producing step is catalyzed by [Ir(cod)Cl]2 with (S)-BINAP in Reactor A (similar to Madsen’s work). The hydroformylation is simultaneously catalyzed by a different molecule, Rh(H)(CO)(PPh3)3, in Reactor B.

2nd reaction scheme

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Green Chemistry on your Smart Phone!

“Incorporating Green Chemistry Concepts into Mobile Chemistry Applications and Their Potential Uses.” Ekins, S.; Clark, A. M.; Williams, A. J. ACS Sustainable Chem. Eng. 2013, 1, 8-13. DOI: 10.1021/sc3000509

We here at GreenChemBlog have not posted in a while, but still hope to post and are still looking for contributors to the blog. Posts might be a bit shorter going forward, though, in order for us to post more frequently.

I’ve expanded my reading recently to include a new ACS journal, ACS Sustainable Chemistry & Engineering. In the first issue is the above article, which highlights a few recent additions to the smart phone/tablet world that utilize green chemistry!

The focus of the above paper is mostly on “Green Solvents”, which the authors developed based on the ACS GCI Pharmaceutical Roundtable Solvent Selection Guide. It is freely available for iPhone, iPod touch and iPad. (I personally use the Android platform for which the very similar app “Lab Solvents” is available) The authors also cover a few other green chemistry apps, so read the paper for more info! I especially like the Process Mass Intensity feature of the Yield101 app, though this app is $5.

For Green Solvents, the app entry page features a list of common solvents displayed as their chemical structures. More desirable solvents are color coded with a green background; less desirable solvents are color coded with a brown background. Selecting a solvent molecule brings up a box that lists the chemical’s name, CAS number, as well as scores on a scale of 1 – 10 for each of the five following categories: safety, health, environment (air), environment (water), and environment (waste). The lower the number, the greener the solvent. In addition, the numbers are color coded with 1-3 displayed as green, 4-7 displayed as yellow and 8-10 displayed as red. Furthermore, the selection box includes easily chosen links to the ChemSpider Web site, the Mobile Reagents app, and the Mobile Molecular DataSheet for more information on the selected solvent.

figure1

The power of the app is how quickly one can obtain info that should impact solvent choices in lab or in the field (without having to retreat to your desk or a nearby computer). And it’s free!

In the future I hope to see these apps provide suggestions for alternative solvent choices (for example, this editorial provides an example of a table Pfizer uses for solvent selection). For instance, I already know dichloromethane is a poor choice of solvent from a green chemistry perspective. How about an alternative choice, Green Solvents app? Trifluorotoluene?

Rh-catalyzed Alcohol Deoxygenation

“Acceptorless Photocatalytic Dehydrogenation for Alcohol Decarbonylation and Imine Synthesis.” Ho, H-A.; Manna, K.; Sadow, A. D. Angew. Chem. Int. Ed. 2012, 51, 8607-8610. DOI: 10.1002/anie.201203556

The use of biorenewables as feedstock chemicals for commodity chemicals as well as fuels requires mild, selective removal of oxygen-containing functional groups. This is in direct contrast to the production of these chemicals from petroleum products, which, at least for highly functionalized target molecules, necessarily involves oxygenation of hydrocarbons.

There are a large amount of methods development currently underway and I highlight the recent report from the Sadow group on the decarbonylation of alcohols under Rh catalysis. I think the described reaction is a good example of green chemistry, as the reaction is high-yielding, selective, and performed at room temperature under photocatalytic conditions. One serious drawback is the use of benzene as the solvent, although toluene works as a solvent in at least some cases.

Reasoning that photolysis would prevent catalyst inhibition by CO binding, the researchers first screened Rh(I) catalysts under photocatalytic conditions with the test substrate cyclohexanemethanol. Unfortunately, no cyclohexane was observed under these reaction conditions. The group then tested Rh and Ir compounds known for C-H activation, such as Cp*Ir(CO)2 and Tp*Rh(CO)2, and did observe cyclohexane for one of the tested catalysts, albeit in low yield (36 % NMR yield with Tp*Rh(CO)2). CO and H2 were also observed, consistent with the targeted alcohol decarbonylation reaction. Interestingly, using their previously reported rhodium tris(oxazolinyl)borate complex ToMRh(CO)2 (1) improved the yield to > 95%. Furthermore, the related dihydride, ToMRh(H)2CO (2) was roughly three times slower and the Ir complex ToMIr(CO)2 was inactive for this reaction.

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Raging Hormones – Gram-Scale Synthesis of Prostaglandin PGF2α

“Stereocontrolled organocatalytic synthesis of prostaglandin PGF in seven steps” Coulthard, G.; Erb, W.; Aggarwal, V. K. Nature 2012, online view. DOI: 10.1038/nature11411

In my very un-scientific survey of the green chemistry-branded journals, I see way more new methodologies than I see total syntheses. I hope to single-handedly change this, and show how green a total synthesis can be by writing about the awesome recent synthesis of prostaglandin PGF by Aggarwal and coworkers. First, a few words on the target molecule. Being hormones, prostaglandins such as PGF are involved in tons of biological processes. Interestingly, instead of being synthesized by some important gland and acting in far-off regions of the body as are endocrine hormones, they are autocrine or paracrine hormones and are synthesized “on-site.” The first structural characterizations of prostaglandins came in the 1960s, some 30 years after their initial discovery. Soon after, they became the subject of numerous syntheses, the first of which was achieved by E. J. Corey in 1969. A series of syntheses followed, but even 40 years later, the structurally-related glaucoma drug latanoprost is synthesized in 20 steps using Corey’s 1969 prostaglandin strategy.

That’s right, the prostglandin structural motif is medicinally relevant. So, not only would an improved synthesis be cool from a fundamental science perspective, it might actually be moved into industrial production and have an immediate impact! Continue reading

Toxicity of Iron Nanoparticles

“Stabilization or Oxidation of Nanoscale Zerovalent Iron at Environmentally Relevant Exposure Changes Bioavailability and Toxicity in Medaka Fish” Chen, P-J; Tan, S-W; Wu, W-L. Environ. Sci. Technol. 2012, ASAP. DOI: 10.1021/es3006783

We’ve posted before on iron-catalyzed reactions (see here for a recent post) as greener alternatives to more traditional platinum group catalyzed reactions. However, even iron has toxicity concerns as described in this paper from National Taiwan University on the toxicity in medaka fish of  zerovalent iron (nZVI) nanoparticles (NPs). This is particularly pertinent research in light of the increased usage of iron(0) nanomaterials in remediation.

The study investigates the effects of four different iron dosing ‘solutions’ on the molecular, cellular and organismal health of medaka larvae: (i) carboxymethylcellulose stabilized nZVI (CMC-nZVI), (ii) non-stabilized nZVI (nZVI), (iii) magnetite NPs (nFe3O4), and (iv) soluble Fe(II).

They first characterize the dosing solutions. The sizes of their nanoparticles are 75 nm, 25-75 nm, and 27 nm for CMC-nZVI, nZVI, and nFe3O4 respectively. The zeta potentials were measured to show, not surprisingly, that the CMC-stabilized particles are much more stable to aggregation than the non-stabilized nZVI.

Interestingly, of the four iron dosing solutions, CMC-nZVI has the most significant impact on the level of dissolved oxygen, decreasing it to zero where it remained for 12 hours. Furthermore, this aerobic oxidation of CMC-nZVI leads to a release of 45 mg/L of soluble Fe(II) in 10 min from an initial concentration of 100 mg/L CMC-nZVI as well as an increase in reactive oxygen species (ROS). In contrast, nZVI and nFe3O4 are 20 – 40 % aggregated within 10 min and release less than 20 mg/L of Fe(II) during this time. Only nZVI induces the production of ROS with nFe3O4 and soluble Fe(II) showing no increase in ROS relative to the control. The following figure details these findings for CMC-nZVI; analogous graphs are found in the supplementary information for the other solutions.

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A “Designer” Surfactant for Cross Couplings of Hydrophobic Reagents in Room Temperature Water

“TPGS-750-M: A Second-Generation Amphiphile for Metal-Catalyzed Cross-Couplings in Water at Room Temperature” Lipshutz, B. H.; Ghorai, S.; Abela, A. R.; Moser, R.; Nishikata, T.; Duplais, C.; Krasovskiy, A.; Gaston, R. D.; Gadwood, R. J. Org. Chem. 201176, 4379-4391. DOI: 10.1021/jo101974u

I occasionally run reactions in water, and it is awesome. I LOVE not worrying as much about cancer. Unfortunately many interesting chemicals are simply too hydrophobic to allow reactions to be run in aqueous solution. As anyone who has ever scrubbed a greasy pan will know, one way to get around the solubility problem is with soap. Also called emulsifiers, surfactants, amphiphiles, a soap by any name is pretty much the same thing in my mind (though others will disagree I’m sure). Molecules with hydrophilic and hydrophobic ends can form micelles in water, creating variously-shaped and sized particles with hydrophobic cores. Using those hydrophobic cores as reaction media is a concept known as micellar catalysis. The Lipshutz group was not the first player in this arena, but they have been at it for some time. They recently teamed up with the medicinal chemistry company Kalexsyn and came out with a new amphiphile that caught my eye, dubbed TPGS-750-M. 

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