benzylchloride1 - 31-12-2008 at 08:51
I have found a fairly easy synthesis of heptylaldehyde in the Chemistry of Natural Products by Rapheal Ikan. Heptylaldehyde is used in Klutes
synthesis of nonalactone. The synthesis involves the distillation of castor oil with a small amount of pine rosin added as a catalyst. 150 mL of
castor oil is placed in a 500 mL flask. About 1 gram of rosin is added. The flask is attached to an air condenser with a receiver. The flask is heated
with a free flame until a small discolored residue remains. The residue must be removed before it cools because it is very difficult to remove
otherwise, a base bath would probably work to clean the flask. The distillate is separated from water and dried with anhydrous magnesium sulfate. The
mixture is then fractionally distilled, a small forerun of acrolein comes over which rapidly polymerizes. The heptanal is collected between: 140-160
c. The product can be redistilled for higher purity. The residue upon vacuum distillation yields about 20 grams of undecylenic acid. Yield of heptanal
about 25 grams. Be sure to run this in a fume hood!
Magpie - 31-12-2008 at 11:02
Very interesting. Thanks for posting this. Have you tried it yet?
I'm not sure where to buy pine rosin. I see that pine tar is readily available where horse remedies are sold. But that is different I imagine.
octave - 31-12-2008 at 13:01
The easiest source of pine rosin would probably be directly from a pine tree.
benzylchloride1 - 31-12-2008 at 17:24
I tried this synthesis about 2 months ago, it worked extremely well. The pine rosin that I used was the dried stuff that can be collected from spots
on pine trees where limbs are removed. The heptanal has a very strong odor and the synthesis produces acrolein which has a horrible smell. I used an
old style distillation flask for the pyrolysis step with rubber stopper connections. The residue is very hard to remove from the flask, its thicker
then molasses when cold and must be poured out of the flask as soon as the pyrolysis is complete. This is similar to the way heptanal and undecylenic
acid are produced industrially. Heptylaldehyde can be used to synthesize heptyl alcohol and heptanoic acid as described in Organic Synthesis.
Ebao-lu - 1-1-2009 at 08:49
Nice synthesis! What is the role of pine resin there? Is it a catalyst to decrease the required temperature for heptanal formation, or used for some
other purpose?
benzylchloride1 - 1-1-2009 at 14:08
The rosin used as a catalyst contains abietic and other rosin acids. The catalyst is acidic and serves to catalyze the breaking of the bonds in the
glycerol ester of ricinoleic acid of which castor oil is composed of. I am unsure of the mechanism of this reaction. The reaction mixture has to be
heated for about 20 minutes with a free flame before anything distills over; during this process, considerable water vapor is produced which causes a
disturbing noise when the water droplets that condense hit the extremly hot oil!
Ozone - 2-1-2009 at 07:19
This one is interesting both from the mechanistic and practical points-of view. It should be applicable to other sorts of unsaturated oils (linoleic,
for example) and is a nice segue into a biobased chemical platform.
The acidity no doubt serves to split the acids from the glycerol, although this would require a stoichiometric amount of water (hydrolysis) or alcohol
(EtOH works, transesterification).
What this does not explain is how the products, heptaldehyde and undecylenic acid (undec-10-enoic acid) form from what should be ~ 89.5 % ricinoleic
acid (12-hydroxydec-9-enoic acid). Rather, it does not explain the how the double bond moves and then is cleaved yielding a terminal olefin and an
aldehyde.
This could involve free radicals as the attached preview (Our damn library does not have JOCS:mad
suggests. They are using the rosin with a benzoyl peroxide or a,a-azobisbutyronitrile initiator. If anyone can get the
full text, that would be great.
I will have to try this when I can get back to the lab after the holidays. I can do the pyrolysis (I have not settled on whether to do the straight
distillation or to run it a over ball bearing packed quartz tube in the furnace) in the home lab, but will need to get samples to work for
characterization. I'll probably methylate the product mixture and run GC-MS on the aldehyde/FAME mixtures.
Cheers,
O3
Attachment: Trivedi 1989.pdf (133kB)
This file has been downloaded 3282 times
Have article, will attach
sparkgap - 2-1-2009 at 17:40
The authors do believe that radical cleavage happens.There is then a shift of sorts that happens to the 11-carbon fragment.
sparky (~_~)
Attachment: hucastor.pdf (372kB)
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Ozone - 2-1-2009 at 18:34
Thanks Sparky!
That helps quite a bit. It appears that their mechanism is a bit vague, as well...Last time I checked "free radical dissociation energy" was not a
step that would get you through a General exam. No matter, hydrogen abstraction at the hydroxyl is a reasonable starting place.
I'll need to study this a bit more before further comment.
Thanks again,
O3
Ebao-lu - 3-1-2009 at 13:57
The easiest suggestion concerning the mechanism is a usual retro-ene reaction. I'm not concerned about the radicals, probably they catalyse ene
reaction as well (my pc is havin some problems, so i cant view the pdf files attached, hopefully i'll amend it soon). The hydrolisis of glycerol ester
should require water, so aparently the role of rosin is different. Maybe, it protonates the double bond, and the carbocathion breaks into alkene and
protonated hyptanal (this is not a ene reaction then).