ORGLIST: Re: Everybody Digest, Vol 3, Issue 7,

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From: Lakshmipathi (plpathi$##$hotmail.com)
Date: Tue Dec 14 2004 - 12:52:43 EST


Subject; ORGLIST: Reductive amination with NaCNBH3 at low pH
Hi Jones

I doubt whether HCN can be formed at that pH, but you could do NaCNBH3
mediated reduction equally well in methanol by maintaining the pH with help
of methyl orange. Take the compound and NaCNBH3 along with a pinch of
methylorange in methanol at RT and add 12N HCl dropwise maintaining the
reddish pink color (kinda titrimetric way). Once the pink color persists,
continue stirring at RT for an hour till the reaction is complete. If the
reaction is not complete, add little more NaCNBH3 and continue with HCl
addition to maintain the pink color. I used this method for reducing oximes
to get hydroxylamines in nearly quantitative yields.

bon courage

Lakshmipathi

Email; plpathi$##$hotmail.com
         lakshmipathi.p$##$astrazeneca.com

----- Original Message -----
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To: <everybody$##$orglist.net>
Sent: Tuesday, December 14, 2004 10:32 PM
Subject: Everybody Digest, Vol 3, Issue 7

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> Today's Topics:
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> 1. Re: Suggestions (Christopher Joseph Gorman)
> 2. Pyridine-SO3 complex (Jos? Barros)
> 3. Reductive amination with NaCNBH3 at low pH (will jones)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 13 Dec 2004 16:48:43 -0500
> From: Christopher Joseph Gorman <cjgorman$##$sas.upenn.edu>
> Subject: Re: ORGLIST: Suggestions
> To: Jacobo Cruces <jacobo.cruces$##$galchimia.com>,
> everybody$##$orglist.net, cjgorman$##$sas.upenn.edu,
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> Mechanisms for name reactions, I believe, are the most useful reference
for
> advanced students of organic chemistry. Good luck on your project. Let
me
> know if you have any questions or need any further advice, All the Best,
>
> Chris J. Gorman
> Undergraduate Class of 2005
> University of Pennsylvania
>
>
> > Dear all,
> >
> > In the past years we have made available for the community of organic
> > chemists a number of documents in different formats which we believe can
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> ------------------------------
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> Message: 2
> Date: Tue, 14 Dec 2004 12:51:28 -0300 (ART)
> From: Jos? Barros <zerozero43$##$yahoo.com.br>
> Subject: ORGLIST: Pyridine-SO3 complex
> To: everybody$##$orglist.net
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>
> Dear Chen,
>
> There are 2 methods to make Pyridine-SO3 complex in
> Fieser:
>
> (a) Pyridine (1 mol) is slowly dropped with cooling
> and stirring into a mixture of crushed sulfur trioxide
> (1 mol) and carbon tetrachloride (4 parts), and the
> cristalline product is colected and washed with ice
> water to remove a trace of pyridine-H2SO4.
>
> (b) chlorosulfonic acid (0.5 mol) is dropped with
> cooling and stirring into a solution of pyridine (1
> mol) in carbon tetrachloride; the product is washed
> with ice water to remoev pyridine hydrochloride.
>
> 2 C2H5N + ClSO3H -> C5H5N.SO3 + C5H5N+HCl-
>
> Method (b) can be carried out with 6.17g of pyridine
> and 4.51 g of chlorosulfonic acid in 15 mL of carbon
> tetrachloride.
>
> Best regards
> J.C. BARROS
>
>
>
>
>
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> ------------------------------
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> Message: 3
> Date: Tue, 14 Dec 2004 16:27:29 +0000
> From: "will jones" <willjones46$##$hotmail.com>
> Subject: ORGLIST: Reductive amination with NaCNBH3 at low pH
> To: everybody$##$orglist.net
> Message-ID: <BAY102-F16EDADAC046390881F336FAEAC0$##$phx.gbl>
> Content-Type: text/plain; format=flowed
>
> Hi there
>
> I am wanting to reductively aminate a fluorophore into the reducing end of
> an oligosaccharide for subsequent reactions.
>
> I have dug up loads of stuff on this and they have all said pretty much
the
> same thing
>
> Dissolve fluorophore in 0.15M AcOH/H2O (3:17 v/v), add to oligosaccharide.
> Add NaCNBH3 (1.0M in DMSO)
> Incubate for 16 hours at 37 degC
> I was planning on testing for the lack of reducing end of the
> oligosaccharide by whether Cu(II) is reduced to Cu(I), which I have used
> before for presence of reducing end of oligosaccharides.
>
> My question is to anyone who has worked with NaCNBH3.
>
> Can you work below pH7 with it or will it give off HCN? The reason I ask
is
> I know that NaBH4 gives off H2 below pH7 when Ive used it for other
> reduction reactions.
>
> Ideal conditions quoted appear to be pH2.3 ish. Can someone promise me no
> HCN is going to be given off!!???
>
> Cheers
>
> Will
>
>
>
>
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