Takron
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Catalyzed Hydrogenation of Naphthalene to Tetralin
Now before I begin, I want to say why I needed to make this particular product. I have had issues finding some particular products every now and then
and you eventually get to the point where you just figure it will be easier to make, than continue to look for. This is one of those situations. I
know some of you might say, ''Get it at Alfa.'' or something. I don't have that luxury. I was in the process of trying to do the potassium catalytic
reduction process everyone was trying and then Nurdrage did his with Tetralin to make the potassium float and it was pure genius. Then I ran into not
being able to find it, so I started combing the knowledge-net for a workable procedure that could be done on a home lab scale.
I first found 'this' which describes information about the catalytic hydrogenation of naphthalene, so I decided this could be a decent way of doing it. Palladium
on Carbon catalysis was stated as being a favorable catalyst because the reaction stops at Tetralin. Plus, operation temperatures at 100*C are
completely doable. However; the 1000 psig is the stumbling point and other papers I have read state 20 atm for a reacting pressure which is around
300psi but need 600*K or more 'here' for the reactions to occur.
What I'm wondering about the whole thing is has anyone done this or anything similar that can lend some information or ideas to the direction I should
go with this before I begin? I feel I have found enough information to start the process but I just want to get some pointers or suggestions before I
start. The information regarding this is very scattered and the things I have found seem to be saying higher temps equal lower pressures or lower
pressures equal higher temps but a concise paper is difficult to find and Orgsyn doesn't seem to have a process on just this.
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Nicodem
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Making something relatively inexpensive and easily available like tetralin from naphthalene is not at all worth the effort unless you are taking it as
a challenge. Given that you decided to make it yourself, I can only assume that you don't need it any more as a solvent for the original purpose. So,
for the sake of amateurism, you are better off by doing a two-step reduction rather than using an autoclave based hydrogenation. In short, naphthalene
is easily reduced to 1,4-dihydronaphthalene by the Birch reaction under various conditions.* Then, you can hydrogenate the dihydronaphthalene to
tetraline with <1 mol% Pd-C under atmospheric pressure or CTH conditions. Ironically, you can even use a Ni(COD) catalysed disproportionation of
dihydronaphthalene into naphthalene and tetralin (Journal of Organometallic Chemistry 1990, 382, 273-293).
* A few examples of the Birch reduction of naphthalene:
Inorganic Chemistry 2010, 49, 9333-9342. (Na, Et2O, tBuOH, 3 h, rt, 68%)
Journal of the American Chemical Society 2009, 131, 9281-9286. (Na, THF, tBuOH, 3 h, rt, 86%)
Russian Journal of Organic Chemistry 2008, 44, 362-368. (Na, hexane, iPrOH, sonication, 70 °C, 3 h , 95%)
Justus Liebigs Annalen der Chemie 1895, 52-80. (Na, EtOH, 84%)
J. Org. Chem. 1981, 46, 788–792. (photochemical, NaBH4, MeCN, H2O, cat. m- or p-dicyanobenzene)
There are dozens of other examples in the literature where other, less friendly conditions and reagents are used (in solvents like liquid ammonia or
ethylenediamine). For many other examples of the synthesis of 1,4-dihydronaphthalene, see: The Birch reduction of aromatic compounds, Organic
Reactions 1992, vol. 42 or e-EROS under Birch-like reagents entries (Lithium-Ammonia, Sodium-Ammonia, Calcium-Ammonia, etc.).
Don't forget to post back any experimental results.
PS: Given the ease with which naphthalene forms anion radicals, I would be surprised, but not overly so, if the Birch reaction would actually work
well even with iodine activated magnesium turnings in refluxing isopropanol (calcium in ammonia is known to work). If you feel like you want to do
some actual research work, I suggest you to try it out. In years of experience, I realized that the most fulfilling discoveries occurs as consequence
of destined little ironical events (e.g., if you wanted tetralin to use it in a magnesium based reduction of KOH, then perhaps you can use magnesium
to reduce naphthalene to get tetralin, and thus make a contribution to science). Under such metal dissolving conditions, adding something like 0.1
mol% Pd-C might even cause in situ hydrogenation directly to tetralin.
[Edited on 4/2/2012 by Nicodem]
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Takron
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These are all great alternatives and I think I will definitely try these out first as they seem like a lot less work. I will keep you posted on the
ensuing results.
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