benzylchloride1 - 3-7-2009 at 22:12
I am currently working on synthesizing camphor from turpentine via a classic 5 step sequence of reactions. Pinene conveted to bornyl chloride by
addition of hydrogen chloride to the double bond. The bornyl chloride is then converted to camphene by elimination of HCl. The camphene is then
reacted with acetic acid and sulfuric acid to form isobornyl acetate which is hydrolysed to isoborneol with alcoholic KOH. The isoborneol is then
oxidized to camphor with Jones reagent; K2Cr2O7, H2SO4. Turpentine is predominantly alpha pinene, which can be isolated from the turpentine via
fractional distillation, collecting the fraction boiling between 154C to 160C. Anhydrous hydrogen chloride is passed into the purified pinene keeping
the temperature below 20 C until crystals of bornyl chloride form. The crystals are filtered off, pressed and recrystallized from methanol. I
conducted this part of the synthesis and obtained a product melting at 100C. Literature value is about 130C, residual pinene is very hard to remove
from the crystals. I obtained the product in a yield of about 25%. The product is also known as pinene hydrochloride. A method exists for making a
purer product is posted below, but requires chloroform which I am out of.
Attachment: pinene HCl.pdf (380kB)
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Several methods exist for converting bornyl chloride to camphene; hydrolysis with anhydrous sodium acetate and glacial acetic acid, hydrolysis with
40% KOH on methanol, and hydrolysis with sodium phenoxide. I attempted the hydrolysis with acetic acid and sofium acetate using 25g bornyl chloride,
25g anhydrous sodium acetate and 50mL acetic acid. This was refluxed for 6 hours with a mantle; the temperatue never rose above 130 C. The procedure
was adapted from Ikan, Natural Products, a Laboratory guide clamide that the mixture was refluxed in a 200C oil bath for 4 hours. The mixture was then
steam distilled and a product melting at 100C was obtained. This indicated that the reaction was unsucessful; camphene melts at 50C. I am considering
running the reaction with 10g of bornyl chloride as is given by Krishnaswamy, Chemistry of Natural Products. Both of these books can be obtained in
limited preview on Google Books. Both procedures can be viewed in these previews. From reading Chemistry of Essential oils and perfumes, hydrolysis of
bornyl iodide gives both camphene and a higher melting isomer. Hydrolysis of the chloride would procede much slower. An older organic chemistry book
which was located by searching for the hydrolyis of pinene hydrochloride gave conflicting results; upon hydrolysis, bornyl chloride gives borneol.
Different conditions of hydrolysis give different products. If the procedure for the hydrolyis of bornyl chloride to borneol could be located, it
would substantially make this synthesis more economical. I am working on the hydrolysis step currently; this appears to be the major hurdle in this
synthesis. Any help would be greatly appreciated.
More references:
Fisher, Laboratory Manual of Organic Chemistry, 1924. Available on Google Books. Gives a five step procedure for this synthesis, using sodium
phenoxide for the hydrolysis step.
Williamson, Macroscale and Microscale Organic Experiments, 2nd edition, gives a microscale procedure starting from camphene
[Edited on 4-7-2009 by benzylchloride1]
Here is a reaction scheme in ISIS Draw. This program can be downloaded for free from the publisher.
Attachment: Camphor Synthesis.skc (7kB)
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[Edited on 4-7-2009 by benzylchloride1]
User - 4-7-2009 at 04:39
I understand the challenge, but why would a mad scientist want camphor.
It is quite available right ?
benzylchloride1 - 4-7-2009 at 21:49
Camphor from a drug store is rather expensive; $50 per pound. Camphor has many interesting uses in organic synthesis as a chiral auxillary. Of course
the camphor produced in this synthesis is racemic, but could be resolved into the two enatiomers. Organic synthesis is not about the product, but the
method of getting there. I find it more enjoyable to make an interesting molecule such as this then to buy it. Take for instance the total synthesis
of strychnine by Woodward and others. This molecule is extremely complex. It is available fairly cheaply by extraction from a plant. The total
synthesis is not away of producing this compound in quantity, but a Nobel Prize was awarded for this accomplishment. This is true madscience;
chemistry for chemistry's own sake.
not_important - 5-7-2009 at 08:06
Have you looked at "American Production of Synthetic Camphor from Turpentine" - attached
I agree, these sorts of synthesis can be quite useful instructions in technique and procedure. They also can provide a useful way to evaluating
alternative methods, say doing the Jones oxidation of some of the isoborneol, then comparing yields against other oxidation processes - say perhaps
the nickle-hypochlorite one, or even doing a Oppenauer type oxidation.
Attachment: ie50294a002.pdf (513kB)
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bfesser - 5-7-2009 at 10:37
Household bleach (aqueous sodium hypochlorite, typically 5.25% if I recall correctly) and glacial acetic acid work wonderfully for oxidizing
isoborneol to camphor.
[Edited on 7/5/09 by bfesser]
JohnWW - 5-7-2009 at 18:37
For further info about the stuff, which is a tricyclic terpenoid and an aliphatic ketone, C10H16O, with the two bridgehead carbons being optically
active, originally obtained naturally from the wood and bark of the camphor tree; - including synthesis from alpha-pinene (from pine needle oil), and
derivatives such as camphene, camphol, and (with one less carbon) norcamphor, see:
http://en.wikipedia.org/wiki/Camphor
http://www.botanical.com/botanical/mgmh/c/campho13.html
http://www.britannica.com/EBchecked/topic/91313/camphor
http://www.3dchem.com/molecules.asp?ID=203
http://www.inchem.org/documents/pims/pharm/camphor.htm
http://chestofbooks.com/health/materia-medica-drugs/Botanic-...
[Edited on 6-7-09 by JohnWW]
