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cuprate
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I understand catalytic hydrogenation is not an option for you. How about other sources other than hydrogen gas? For example, NH4Cl/Pd/C in refluxing
methanol or hexadiene/Pd/C?
other option will be butyl lithium. Although you have alcohol in your molecule, you just need waste one extra equivalent butyl lithium, and then
quench it with water. However, depend on your molecule, elimination to ether might happen.
| Quote: | Originally posted by solo
Need a method to dehalogenate a chlorinated primary non -benzylic amino alcohol.....want to avoid the HgAl a well known OTC method.....also the
catalytic hydrogenation is out of the option, hence have thought of using Hypophosphorous Acid for the dehalogenation. I would welcome more
suggestions as I've thought of ZnCl +HCl but the yields are very low...........solo |
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Sandmeyer
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I stated in another speed thread that afromentioned dehalogenation will probably work if you reflux the hydrochloride salt of the chloride in formic
containing excess zinc. To skip one extra (albeit very easy) step the amino acid can be taken down directly with boran, and by UTFSE you'll find a
paper for in situ preparation of it from relatively OTC chemicals.
[Edited on 16-9-2006 by Sandmeyer]
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LSD25
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| Quote: | Originally posted by solo
In March's text 5th edition on page 1328 the following..................
----------------------------------------------------------------------------------------------------
When proton acids catalyze alcohol dehydration, the mechanism is El.(160 )The
principal process involves conversion of ROH to ROH^ and cleavage of the latter to
R+ and H2O, though with some acids a secondary process probably involves
conversion of the alcohol to an inorganic ester and ionization of this (illustrated for
H2SO4):
..........................H2SO4
ROH ••>>>>>>>>>>>>> ROSO2OH •--------->.• R+ + HSO4
Note that these mechanisms are the reverse of those involved in the acid-catalyzed
hydration of double bonds (15-3), in accord with the principle of microscopic
reversibility. With anhydrides (e.g., P2O5, phthalic anhydride) as well as with some
other reagents such as HMPA,(161) it is likely that an ester is formed, and the leaving
group is the conjugate base of the corresponding acid. In these cases, the mechanism
can be El or E2. The mechanism with A12O3 and other solid catalysts has been
studied extensively but is poorly understood.(162)
Magnesium alkoxides (formed by ROH + Me2Mg —>ROMgMe) have been
decomposed thermally, by heating at 195-340°C to give the alkene, CH4, and
MgO.(163) Syn elimination is found and an Ei mechanism is likely. Similar
decomposition of aluminum and zinc alkoxides has also been accomplished.(164)
REF:
(160) For reviews of dehydration mechanisms, see Vinnik, M.I.; Obraztsov, PA. Russ. Chem.
Rev., 1990,59,63; Saunders Jr., W.H.; Cockerill, A.F. Ref. 3, pp. 221, 317; Knozinger, H. in
Patai The Chemistry of the Hydwxyl Group, pt. 2; Wiley: NY, 1971, p. 641.
(161) See, for example, Kawanisi, M; Arimatsu, S.; Yamaguchi, R.; Kimoto, K. Chem. Lett.,
1972, 881.
(162) For reviews, see Beranek, L.; Kraus, M. in Bamford; Tipper, Ref. 3, vol. 20, 1978, p. 274;
Pines, H. Intra-Sci. Chem. Rep., 1972, 6(2), 1; see pp. 17-21; Noller, H.; Andreu, P.;
Hunger, M. Angew. Chem. Int. Ed Engl, 1971,10, 172; Knozinger, H. Angew. Chem. Int.
Ed. Engl., 1968, 7,791. See also Berteau, P.; Ruwet, M.; Delmon, B. Bull. Soc. Chim. Belg.,
1985, 94, 859.
(1 6 3)Ashby, E.C.; Willard, G.F.; Goel, A.B. J. Org. Chem., 1979, 44, 1221.
(1 6 4)Reference 163; Brieger, G.; Watson, S.W.; Barar, D.G.; Shene, A.L. J. Org. Chem., 1979,
44, 1340.
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..............so the alcohol converts to the ester, then the ester is reduced to the hydrocarbon and HSO4:Noting that when applied to a primary non
benzylic amino alcohol the amine won't be affected by the acidic environment, ...........through thermal decomposition( pyrolysis) ........but is it
too high to destroy a phenylalaninol?
................I guess I better check the references next................solo |
There are patents (ho, ho, ho and so on) where the sulfate ester is formed by heating the amino alcohol with ammonium sulfate or ammonium bisulfate
(eg. http://www.wikipatents.com/4597911.html), but it is unclear (to say the least) whether this works and of course also as to whether this is
applicable to either the primary amino alcohol or the corresponding benzylic variant.
Whhhoooppps, that sure didn't work
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solo
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There was some interesting stuff posted here i.e. 2-benzylaziridines, from primary amino alcohols, the ester with sulfuric acid and the ring made with
destillation over NaOH......all but to open the ring and maybe even methylate the amine if that's your pleasure.......solo
https://sciencemadness.org/talk/viewthread.php?tid=4654&...
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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LSD25
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I was thinking this may be of some minor interest:
http://v3.espacenet.com/origdoc?DB=EPODOC&IDX=gb509661&a...
Of course that patent only deals with the benzylic sulfate ester variant, but I was wondering if the same would work with the primary amino alcohol
sulfate ester?
Whhhoooppps, that sure didn't work
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dangator
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Or just using a hydride reductant?
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LSD25
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What hydride would you suggest?
I expect it is possible that that would only take the amino acid to the alkanolamine? Not to the alkylamine?
I mean, if you have a good reference and it seems legitimate, it 'MIGHT' be possible that some hydride reductant could do this (seems odd that it has
escaped notice by several thousand researchers - both serious professionals and interested amateurs), although I for one would probably take some
convincing. Nonetheless, if you could point me in the right direction, I am more than interested in sharing in such a momentous discovery.
Solo,
Read that patent, it seems to be a lot more realistic than some I have read. Granted this is no guarantee of reproducibility, but it seems like a
possibility. If that doesn't work, it is known that a tosyl group works (removed with ZnI IIRC), so it is entirely possible that a mesyl group would
do the job. Given that, the use of a sulfate ester doesn't seem such a stretch - it converts the horribly difficult to remove OH to a sulfate ester,
the same leaving group that adheres to the OH group with either tosyl/mesyl addition. Given that this is a good leaving group and doesn't cause
cyclization (at least it isn't mentioned in the various articles on the use of these in the reduction of tyrosine/phenylalanine via there amino
alcohols), it may be worthwhile looking into how to graft the sulfate ester (rather than the mesyl/tosyl) onto the primary alcohol function.
Whhhoooppps, that sure didn't work
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dangator
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Whoops, was looking at the original fifth post where we were going from a simple alkyl halide to alkane. My mistake.
[Edited on 26-1-2008 by dangator]
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