[victor]

Hi everyone, I just confuse about some metals which are used as a catalysts for some organic reactions. How can we select the proper catalyst for each reaction? is there any book that can help me to understand the type and characteristics of those catalysts?? (I really confuse with those metal catalyst)..

Example is like this:
During catalitic hydrogenation process, my book write that we should use Ni catalyst. Why? how about other metal like Cu, Pd, and others?
Or like this, during Friedel-Crafts alkylation on benzene, we should use Al metal to act as catalyst while other reaction like bromination on benzene suggest that we should use Fe metal as a catalyst...why?

any help would be appreciated
Regards,
Victor

[alphahydroxy]

I'm not sure there's a general answer to this question, like it sounds like you're looking for...

There are a number of books on the role of metals in synthesis, I suggest you google for them and then read reviews to establish their target audience and quality.

As far as deciding which metals and ligands are appropriate for particular reactions, searching the literature will help you in a practical sense - i.e. deciding what may or may not work.

Understanding the mechanism of a particular reaction, and the role the metals/ligand play in the catalysis is key here though...

[Will]

Hi everyone, I just confuse about some metals which are used as a catalysts for some organic reactions. How can we select the proper catalyst for each reaction? is there any book that can help me to understand the type and characteristics of those catalysts?? (I really confuse with those metal catalyst).

Hi Victor,

Organic Chemistry by Clayden, Greeves, Warren and Wothers is an excellent organic chemistry book, its like my bible!
It explains EVERYTHING very well and I haven't come accross anything that I don't understand in it yet.

Example is like this:
During catalitic hydrogenation process, my book write that we should use Ni catalyst. Why? how about other metal like Cu, Pd, and others?

There are 4 pages in the book above dedicated to catalytic hydrogenation, and explains what catalysts to use for what hydrogenation and explains why. Palladium is an excellent catalyst for hydrogenation (generally speaking), but of course platinum (oxide which is reduced to Pt during hydrogenation), rhodium, ruthenium and (Raney) nickel are all suitable catalysts in different situations, and pressure and heat is also needed for some hydrogenations. This is all very well explained in the book, I really recommend you get it, it was the best £35 I've ever spent.

Or like this, during Friedel-Crafts alkylation on benzene, we should use Al metal to act as catalyst while other reaction like bromination on benzene suggest that we should use Fe metal as a catalyst...why?

In these reactions a halogen-carrier (Lewis acid) is used, such as those you mentioned above as well as FeBr₃, and pyridine is also a very good catalyst for bromination. For Friedel-Crafts alkylations, AlCl₃ is normally the catalyst of choice. I'm not sure why this is the case for alkylation, but most lewis acids like these whould work fine; bromination is not very fussy, you can use any of the catalysts above.
To work out which catalyst is best, it is helpful to know the reactive intermediate that makes the reaction happen, then you can see if there are any compounds which help the formation of the reactive intermediate. Hope this helps .

[victor]

Thanks for all your answer and I think I'll search the book that you've suggested will17...
or...do I have to learn something first about inorganic chemistry sincee it deals with..mostly metals...in my college,  I only get basic chemistry and organic chemistry..so, I do not understand about the inorganic one such as complex ion formation, geometry of complex ions, etc..
I hope that I still want to join chemistry faculty right after I'm graduated from biology faculty...

about the book..let's search it first....<searching and searching>....WHAT !!! US$ 117 ?? oh my goodness...I think I wanna collapse for a while...and then re-think again about the purchasement..

[Will]

do I have to learn something first about inorganic chemistry since it deals with..mostly metals...in my college,  I only get basic chemistry and organic chemistry..so, I do not understand about the inorganic one such as complex ion formation, geometry of complex ions, etc..

There are bits of inorganic chemistry you need to know for organic chemistry such as the fact that in transition metals there are vacant spaces for electrons in their d-orbitals. Also knowing the common oxidation states of transition metals such as chromium, manganese, osmium etc. is useful when you come accross these elements in reactions. You don't need to know much about complex ions in organic chemistry, but I don't know how advanced your course is.

about the book..let's search it first....<searching and searching>....WHAT !!! US$ 117 ?? oh my goodness...I think I wanna collapse for a while...and then re-think again about the purchasement..

Its only £35.14 ($65.98) in the UK (it used to be £30 for a while!), you guys get ripped off! It'll only be $77.24 if you buy the new one from http://www.amazon.com/gp/offer-listing/0198503466/ref=olp_tab_new/102-2911424-2726523?%5Fencoding=UTF8&condition=new. Or if you don't trust that you could buy the book off the UK amazon website, and have it shipped to the US, I think it works out about $35 cheaper .

The book is recommended for 1^st and 2^nd years at university so it it has lots of advanced stuff in there that you may not be able to understand at first, but it does have all the basic stuff in there, and its very well explained.

[Donaldson Tan]

Metals are usually used as heterogenous catalyst in organic reactions. A variety of data is required to decide if a metal is suitable as a catalyst. The data includes the heat of absorption (of the reactants to the metal surface), the % d character and the rate constants corresponding to the metal. It is also crucial to know the nature of the catalyst. Eg. some metals promote the dissociation of hydrogen gas, but if the reaction I intend to catalyst does not involve the formation of H radicals, I will not use that catalyst.

[victor]

@will17
In my college, there are only 3 chemistry-related subjects that're taught. They are, basic chemistry, organic chemistry and biochemistry. Of course I'm not as advaced as the people here because I'm not a chemistry student, but I really love organic chemistry..

Oh, one more question, it's also related with those catalyst...why do chemical industries always have different opinion in using catalysts with those people who work in chemical laboratory??
example, if lab people use catalyst A for X reaction, then industry people will use catalyst B to run the same reaction...

[movies]

The most interesting organometallic chemistry today seems to be happening with homogeneous metal catalysis.  Lots of examples, but I wouldn't say that there is much of a pattern.  Some metals can do one thing, others cannot and vice versa.

By the way, AlCl₃ is not a catalyst in the F-C reaction, it's a reagent.  Since the products tend to be more Lewis basic than the starting material, you can't turn over the catalytic cycle.

[Donaldson Tan]

Oh, one more question, it's also related with those catalyst...why do chemical industries always have different opinion in using catalysts with those people who work in chemical laboratory??
example, if lab people use catalyst A for X reaction, then industry people will use catalyst B to run the same reactiion...

You have a good point there. Chemical reaction carried out in labatories are small-scale. It is okay to use expensive catalysts for laboratory experiments because only a small amount of catalyst is required. In chemical plants, a big quantity of catalyst is required, hence the catalyst used must be affordable (cheap). In order to aid the cheap catalyst, high pressure and temperature are used to furthur drive industrial chemical reactions to the product side. Moreover, industrial equipments are built to withstand high pressure and temperature, unlike laboratory equipments.

[movies]

Some catalysts are also patented and if industry wants to use them, they would have to pay extra.  Sometimes they do pay to use a patented catalyst, but often times it is cheaper to use one that is not under patent or, better yet, develop their own catalyst so that they own the patent.

[Will]

Some catalysts are also patented and if industry wants to use them, they would have to pay extra.

Or wait (upto) a cool 20 years for the patent to expire!

By the way, AlCl₃ is not a catalyst in the F-C reaction, it's a reagent. Since the products tend to be more Lewis basic than the starting material, you can't turn over the catalytic cycle.

So true, movies! I just got caught out by the damn A-Level syllabus . One question though, what would happen if you did the F-C reaction without a base to remove the proton form the intermediate? Couldn't a chlorine on AlCl₄^- do that job?

[movies]

Yes, because you restore aromaticity.  The problem is that the ketone that you get in the end complexes Al better than the acyl chloride starting material, so you can't get the Al to do a second acylation reaction.

[Will]

Yes, because you restore aromaticity.  The problem is that the ketone that you get in the end complexes Al better than the acyl chloride starting material, so you can't get the Al to do a second acylation reaction.

Thanks for explaining that movies  .

What about in F-C reactions which involve alkylation, rather than acylation?

[movies]

I don't know about that, actually.  I suppose you probably get the same problem where Cl binds up the Al, maybe that is the real culprit in acylation too.  Someone told me it was the ketone product though.

At any rate, I'm pretty sure that you can't use catalytic AlCl₃ for either alkylation or acylation.

[Will]

I finally found what I wanted in the  organic chem book. It says what movies said about F-C acylations, but with alkylations, AlCl₃ can be used in 'catalytic quantaties', apparently!