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Offline BrainScience

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"Green" Synthesis
« on: November 27, 2012, 12:05:21 PM »
Hey everyone, new to forums so i thought i would start with a little background on what has brought me here. I'm currently enrolled in a synthetic chemistry course at my university and for our last project we have been assigned a synthesis and instructed to suggest "Green" (http://en.wikipedia.org/wiki/Green_chemistry) alternatives for the various steps of the synthesis. I noticed that there are a couple steps that reduce an alkene to the alkane, but don't use the common H2/Pd catalyzed hydrogenation. At first i thought this was weird, but after doing a little research i found that the reason for this is that the compound i'm synthesizing has a sulfur atom in it, which poisons the catalyst and prevents catalytic hydrogenation. What i can't seem to find is if there is some other catalyst out there that isn't poisoned by sulfur and would still allow for catalytic hydrogenation? The reagents that were originally used are N2H4, H2O2, and Cu2+, so its not all that bad in terms of green principles since the byproducts are H2O and N2 gas, but i thought i would try and check out the possibilities of catalytic hydrogenation none-the-less.

I appreciate any help or suggestions!

cheers

Offline discodermolide

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Re: "Green" Synthesis
« Reply #1 on: November 27, 2012, 12:12:38 PM »
Remember there is no such thing as "green Chemistry".
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Offline BrainScience

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Re: "Green" Synthesis
« Reply #2 on: November 27, 2012, 12:29:48 PM »
Ya i thought about writing that for my assignment and just handing it in....but i doubt my prof will take kindly to that....

I'm not exactly sure what you mean when you say there is no such thing as green chemistry? I mean, obviously there will always be unwanted byproducts and other wastes, but there are certainly ways to minimize environmental impact.

Offline discodermolide

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Re: "Green" Synthesis
« Reply #3 on: November 27, 2012, 12:35:27 PM »
What ways can you minimise environmental impact?
I can't think of any. Green Chemistry is bulls&$#.
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Offline curiouscat

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Re: "Green" Synthesis
« Reply #4 on: November 27, 2012, 02:06:39 PM »
Pt + Pd bimetallic catalyst?

Offline discodermolide

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Re: "Green" Synthesis
« Reply #5 on: November 27, 2012, 02:19:35 PM »
What's green about that?
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Offline BrainScience

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Re: "Green" Synthesis
« Reply #6 on: November 27, 2012, 02:24:10 PM »
Well if you can use catalytic amounts of something compared to stoichiometric amounts your going to limit the amount of waste produced. 

Offline BrainScience

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Re: "Green" Synthesis
« Reply #7 on: November 27, 2012, 02:28:36 PM »
Pt + Pd bimetallic catalyst?

Thanks for the suggestion, i will definitely look into that!

Do you happen to have a reference or a reason why that wouldn't be affected by sulfur? (specifically an isothiazole?)

Offline IsotopeBill

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Re: "Green" Synthesis
« Reply #8 on: November 27, 2012, 03:53:41 PM »
The term "Green Chemistry" is misleading at best.  That being said, however, there are plenty of ways to minimize environmental impact (and thus ultimately save your company $$$).  One is to use nonchlorinated solvents when possible (easier and less expensive to dispose of, and generally less expensive to purchase anyway).  Chromatography generates vast quantities of solvent in general, so if you can reuse the eluent or, better yet, use an alternate purification method, you're saving solvent.  And time:  chromatography eats up a lot of labor.  Generally, your goal in any lab should be to increase efficiency in terms of labor and the chemistry itself, including the use and disposal of reagents and solvents - that in itself will help to minimize the impact.  You'll end up being a better, more valuable resource

Offline discodermolide

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Re: "Green" Synthesis
« Reply #9 on: November 27, 2012, 04:45:56 PM »
Pt + Pd bimetallic catalyst?

Thanks for the suggestion, i will definitely look into that!

Do you happen to have a reference or a reason why that wouldn't be affected by sulfur? (specifically an isothiazole?)

Usually Pd/Pt catalysts are poisoned by sulphur.
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Offline curiouscat

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Re: "Green" Synthesis
« Reply #10 on: November 27, 2012, 11:19:16 PM »
What's green about that?

Green: Nope. Nothing.

More S resistance: Maybe.

Offline curiouscat

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Re: "Green" Synthesis
« Reply #11 on: November 27, 2012, 11:27:19 PM »
Pt + Pd bimetallic catalyst?

Do you happen to have a reference or a reason why that wouldn't be affected by sulfur? (specifically an isothiazole?)

Hunch, yes. Specific reason no.

Will it work for you: No idea!

Navarro, R. M., et al. "Hydrogenation of aromatics on sulfur-resistant PtPd bimetallic catalysts." Journal of Catalysis 189.1 (2000): 184-194.

Yasuda, Hiroyuki, et al. "Confirmation of sulfur tolerance of bimetallic Pd–Pt supported on highly acidic USY zeolite by EXAFS." Catalysis letters 54.1 (1998): 23-27.

Jiang, Hong, et al. "Effect of palladium on sulfur resistance in Pt–Pd bimetallic catalysts." Catalysis today 125.3 (2007): 282-290.

Lee, Joeng-Kyu, and Hyun-Ku Rhee. "Sulfur tolerance of zeolite beta-supported Pd− Pt catalysts for the isomerization of< i> n</i>-hexane." Journal of Catalysis 177.2 (1998): 208-216.

« Last Edit: November 28, 2012, 12:14:27 AM by curiouscat »

Offline BrainScience

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Re: "Green" Synthesis
« Reply #12 on: November 28, 2012, 12:52:45 AM »
Pt + Pd bimetallic catalyst?

Do you happen to have a reference or a reason why that wouldn't be affected by sulfur? (specifically an isothiazole?)

Hunch, yes. Specific reason no.

Will it work for you: No idea!

Navarro, R. M., et al. "Hydrogenation of aromatics on sulfur-resistant PtPd bimetallic catalysts." Journal of Catalysis 189.1 (2000): 184-194.

Yasuda, Hiroyuki, et al. "Confirmation of sulfur tolerance of bimetallic Pd–Pt supported on highly acidic USY zeolite by EXAFS." Catalysis letters 54.1 (1998): 23-27.

Jiang, Hong, et al. "Effect of palladium on sulfur resistance in Pt–Pd bimetallic catalysts." Catalysis today 125.3 (2007): 282-290.

Lee, Joeng-Kyu, and Hyun-Ku Rhee. "Sulfur tolerance of zeolite beta-supported Pd− Pt catalysts for the isomerization of< i> n</i>-hexane." Journal of Catalysis 177.2 (1998): 208-216.

Thanks for the follow up CuriousCat.

Offline curiouscat

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Re: "Green" Synthesis
« Reply #13 on: November 28, 2012, 12:57:56 AM »
Usually Pd/Pt catalysts are poisoned by sulphur.

Not always. In Hydrodesulfurization for diesel they are being actively considered due to their relative resistance to S-poisoning. Not just academic research but millions of $$$ of refining R&D. Cost is prohibitive though; that's why hasn't taken of commercially yet.

Not sure how relevant that domain is to other hydrogenations though.

Offline discodermolide

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Re: "Green" Synthesis
« Reply #14 on: November 28, 2012, 02:01:13 AM »
Well if you can use catalytic amounts of something compared to stoichiometric amounts your going to limit the amount of waste produced.

Sure this may limit your waste products, but what about the manufacture's waste products in producing these catalysts. No to mention the energy requirement.
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