napoleon9
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wash 5-hydroxypentyltriphenylphosphonium bromide
5-hydroxypentyltriphenylphosphonium bromide was synthesis from 5-bromopentan-1-ol and triphenylphosphine in toluene solvent at 100 oC.
please give me some advice, wash 5-hydroxypentyltriphenylphosphonium bromide produce.
thanks
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woelen
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Did you do some research on the subject yourself? Please show us what you already know/found and then let others jump in to help you further with your
questions.
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Jor
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Just heat for 1 hour in toluene, and cool it. Your salt should be precitipated. Filter and wash a few times with a small volume of ether. But I don't
think you need any toluene solvent. Triphenylphosphine melts below 100C and so does 5-bromopenta-1-ol I think.
I once prepared benzyltriphenylphosponium chloride. This was done by heating a mixture of benzyl chloride and triphenylphosphine at 100-110C. After
about 20 minutes the mixture at once solidified. It was a not that hard to remove from the flask. I placed it on the Buchner , sucked dry, and washed
a few times with ether.
I used this to make pure 1,4-diphenyl-1,3-butadiene crystals in OK yeilds.
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napoleon9
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5-bromopenta-1-ol to 5-hydroxypentyltriphenylphosphonium bromide is not easy
when 5-bromo-1-pentanol was treated with triphenylphosphine in dry benzene and heated to reflux only the bis-phosphonium salt was obtained. It was
subsequently discovered that freshly distilled 5-bromopentanol contaned HBr and even after removal of the acid, more was found to be present several
hours later. Thus, the equilibrium generating tetrahydropyran and HBr and the subsequent process which converts the bromopentanol to the dibromide had
to the circumvented.
please give me some advices.
IS it difficult ?
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DJF90
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You ever heard of protecting groups...
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jon
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no i never have.
but it looks like you could just esterify it and put a stop to the reaction you are talking about and, then procedd on.
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DJF90
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Top marks to Jon - thats exactly what I mean by a protecting group. Using a protecting group adds two steps to the synthetic pathway and so addition
and removal need to be high yielding. The protecting group must remove the undesired reactivity of the functional group being protected - in this
case, the nucleophilicity of the oxygen atom. Perhaps a -TMS, -Tr, or -Bn protecting group would be more appropriate.
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jon
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yeah i was just playing stupid i do that all the time never seems to work, i mean ever.
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smuv
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There would be some irony to picking a thp protecting group in this case.
EDIT: also, you probably have to distill the stuff under a REALLY high vac, systems like this easily cyclicize on heating. See: http://www.orgsyn.org/orgsyn/prep.asp?prep=cv2p0571
[Edited on 4-6-2011 by smuv]
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napoleon9
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some people show me that I need use to acid scavenger (K2CO3) . A solution containing 2.84 g 5-bromopenta-1-o, 4.47 g triphenylphosphine in 15
ml MeCN was treated with 2.38 g K2CO3 and the suspension heated at reflux for 4 h. The cooled solution was filtered and diluted with
150 ml alhyd ether. The solid was collected, washal with ether and dried.
. If I use it for this reaction, what will It be effect with reagents ? explain ?
How will K2CO3 be effect ? MeCN is the dissolution of K2CO3.
reference : tetrahydron, vol 27 , pp.5979
thanks
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napoleon9
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after the reaction ends if based on the above process can not be separated from the phosphonium salt and K2CO3.
How you can help me suggest a few ways to separate out K2CO3. Usually, you use TLC to help you know the reaction product is formed phosphonium or not?
So you run in the cup is what resolution? I usually run in CHCL3: petroether (60:90).
please you give me some advices
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napoleon9
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if you use a protecting group by -OTHP. You can't be heat with phosphine, so it will give product as you want.
If it can give product, you can introduce for me some marazines or references
thanks
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Nicodem
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Threads Merged
6-4-2011 at 09:21 |
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