I have a concern with dehalogenation of iodated amine.....will the hydrogenation create HI hence produce an added pressure in the vessel?
I can certainly use NaBh4 for the dehalogenation but would like to explore the catalytic hydrogenation.....other halogenated amines reduce without any
problem but I'm second guessing the application with an iodine being removed......some comments would be appreciated before I attempt the
dehalogenation.......soloRosco Bodine - 21-12-2007 at 12:25
Couldn't you use a base to take up the byproduct as an iodide ?solo - 21-12-2007 at 13:52
I guess NaOH could be added and in turn, water and NaI might be the end product , but unlikely hence I2 might just precipitate out ........it may be
worth a try....I will keep my eyes on the pressure gauge to see if there is any unsolicited increase in pressure in the vessel during the
reaction.............also I will wait to see if there are any other suggestions before I proceed..............soloRosco Bodine - 21-12-2007 at 13:58
I'd look at silver too as an alternative . Maybe a diammine silver salt or an amalgam .
[Edited on 21-12-2007 by Rosco Bodine]garage chemist - 21-12-2007 at 19:02
What solvent is used?
Alcohols bind HI, HCl and HBr just as strongly as water, giving absolutely no pressure increase.Drunkguy - 22-12-2007 at 01:07
I also want to envelope hydrogenation into the synthetic repertoire of my organic chemistry. I've done it under atmorpheric pressure with a balloon in
university academia. At first I had thought that getting a cylinder of H2 would be a problem and was reading about the Brown hydrogenator that uses
NaBH4 as the hydrogen source. It seems now that the hurdle of obtaining a smallish cylinder of hydrogen is not as difficult as what I had previously
anticipated. A further drawback is the cost of platinum black seems to be more of an issue than I had appreciated.
There is a procedure for making Raney Nickel in Vogel. I think he uses a 50/50 Ni/Al alloy and when it is heated to 1000C it leaves behind a porous
Ni "sponge" with an aburdly high surface area. Anybody want to use this thread to chime into hydrogenation in general?
The prospect of eventually getting a Parr Hydrogenator is something that appeals to me but it seems like more of a pipedream than something that is
realistically on the cards for the forseeable future. However, purchasing a cylinder of hydrogen and pursuing balloon hydrogenations is quite feasible
and I think this is something that will happen for me at some stage.Jamjar - 22-12-2007 at 04:06
"Further, the reaction is desirably carried with the removal of hydrogen halide by-product. The hydrogen halide can be removed, for example, by the
passage of an inert gaseous material, such as nitrogen, through the reaction medium or by the use of a base. Suitable basic materials include alkali
or alkaline earth metal hydroxides, bicarbonates or carbonates; ammonia, e.g. in the form of ammonium hydroxide; or amines, including mono-, di- or
tri-(lower alkyl)amines or quaternary ammonium hydroxides, such as tetra-methyl ammonium hydroxide. Similarly, salts of carboxylic acids, especially
lower alkanoic acids, such as alkali metal salts, for example, sodium acetate can be used to remove hydrohalic acids released during the reaction."
"The alkali metal acetate is preferably employed in an amount of at least one molar equivalent. Greater amounts may be employed but are not necessary.
When insufficient amounts are employed, the excess HCl formed during the reaction will interfere with the catalytic process. The preferred alkali
metal acetate is sodium acetate."stoichiometric_steve - 22-12-2007 at 05:57
Quote:
Originally posted by DrunkguyI've done it under atmorpheric pressure with a balloon in university academia.
what substrate did you do try this on?
does anybody have an idea of how much pressure a toy balloon holds?Drunkguy - 22-12-2007 at 09:18
This was during the preparation of 7-azabicyclo[2.2.1]heptanes related to epibatidine total synthesis. The are constructed using Diels-Alder chemistry
which is facile.
We used N-BOC pyrrole as the diene and Br-CC-SO2Ph as the dienophile.
The bromine atom readily reacted to give a ketone in step 2 of the synthesis.
The hardest part was detosylation which could be effected by Al amalgam or by SmI2. Al amalgam is the dirty method but SmI2 is way to pricey and is
absurdly senstive to moisture. Fresh reagent in THF is deep blue, whereas it turns to a straw color over a period of a few weeks. I think it
decomposes with air as well sa moisture. Extremely reactive and totally unstable, but elegent and expensive.
Personally, I had liked the procdure reported by Trudell that used Br-CC-CO2Me as the dienophile. Then in step 4 after the hydrogenation you have an
alpha keto carboxyl group that is facile to remove.
Major drawbacks are that the starting dienophiles are too prohibitively expensive.evil_lurker - 22-12-2007 at 09:38
I've got a flask that I intend to use for catalytic hydrogenation, but as of yet lack of funds have prevented me from completing my manifold setup.
That got cured last week, as I managed to order the 316ss manifold and pressure gauge.
Will post more pics when I get it completed.
Magpie - 22-12-2007 at 11:01
Interesting looking flask, lurker. What is it's pressure rating?evil_lurker - 22-12-2007 at 11:29
Chemglass doesn't say, other than that the flask has been hydrostatically pressure tested to 150PSI before leaving the manufacturer.
My cost is around $70 for the flask, and another $30 for the bushing, and if one wants to go perflouro o-ring its another $31.
Nice thing is the connection on the bushing is pre-threaded to accept 1/4" MPT.
Flask capacity is about 420ml, just the right size for a 1 molar reaction from what I have been reading.
I plan to stick a cross on top with a 3" nipple, stainless steel 0-160PSI gauge on top, needle valve on the left port for bleed off and purging, and
on the right port a quick connect fitting to connect to one of those self recoiling air compressor hoses.
Other plans are to get a tee fitting, gauge, and needle valve to use as an on-demand chlorine generator flask using TCCA/HCl and as a storage flask
for liquid sulfur dioxide.
I have some smaller 15ml pressure tubes I plan to outfit with a pressure gauge and do some pressure testing of the willgerodt reaction... I'm hoping
they hold.
[Edited on 22-12-2007 by evil_lurker]Drunkguy - 22-12-2007 at 12:15
That looks like a really sweet set-up. I would be ill able to afford something as neat as that in the UK and it is doubtful even if I stumbled on its
ownership that I would have the credentials to know how to use it.solo - 22-12-2007 at 12:44
Quote:
Originally posted by garage chemist
What solvent is used?
Alcohols bind HI, HCl and HBr just as strongly as water, giving absolutely no pressure increase.
I'm happy to hear this as I'm not sure how the reaction will go by me adding NaOH .....the substrate is the all too familiar primary amino alcohol
....one thing I've learned about this alcohol is that reduction goes by easier if the HCl salt is used , hence avoids the violent reaction using the
base when one tries to halogenate and /or halogenate -dehalogenate with HI........soloSandmeyer - 23-12-2007 at 16:30
I'd like to know why they use Pd-BaSO4 during the hydrogenation, AFAICS there is no need to poison the catalyst since the product can't be reduced any
further under the conditions employed, you can simply use Pd/C and follow one of those protocols...evil_lurker - 27-12-2007 at 11:24
Alrighty, the fittings came in and now I have something more to show than just a flask and needle valve.
The big thing with the hose on the right is the flask and pressure manifold. Its pretty simple, just an air compressor quick connect fitting and hose,
tee, nipple, needle valve, and hose barb.
The idea is simple, you rig your hydrogen regulator up with a quick connect fitting (or permanent connection), hook it up to the flask, and then turn
on the gas. You adjust your pressure using the regulator. Once the flask is filled, you crack your needle valve to purge, and then your good to go.
You control how much hydrogen is being took up by shutting off the cylinder and monitor the pressure via the gauge on the regulator. Simple.
The other doo-dad is for gas storage such as hydrogen chloride, ammonia, and perhaps sulfur dioxide. This will take a bit of thinking to get rigged
up, but shouldn't be too difficult as long as the flask is kept near freezing.
I still need another pressure gauge as I intend to perform a willgerodt in the future and see what kind of pressures the reaction generates...
And most importantly, a blast shield in case it goes boom.solo - 27-12-2007 at 11:30
I suggest you do your purging with nitrogen or argon ....three times then introduce our hydrogen and hydrogenate.....you also need to find a way
shake it as the Parr Hydrogenator does...... also you already hava a pressure gauge....it will tell you the pressure in the vessel regardless of it's
source.........solo
Note
I included the picture so that you believe me when I say to purge in that way especially if you plan to use palladium........solo
[Edited on 27-12-2007 by solo]evil_lurker - 27-12-2007 at 12:20
Can't you use magnetic stirring in such a get up as mine?solo - 27-12-2007 at 13:21
I would try it as the larger hydrogenator hava a stirring mechanism as the Parr is a shacking movement.....the trial will say it all.......soloDrunkguy - 27-12-2007 at 20:46
Keep up the good work guys
At least with balloon hydrogenations a T-bore adapter is used. The flask is evacuated at the pump, then the vacuum is displaced with hydrogen from the
balloon. This operation is repeated twice more. Then the hydrogentaion is allowed to proceed overnight, and simple olefin reduction is almost
quantitative with platinum black catalyst using acetonitrile solvent from one of those clunky deoxygenated solvent machines.
