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Klute
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Functionalization of silica gel without silanes, solid supported TEMPO catalysts?
I'm starting to interest myself to silica-supported TEMPO catalysts, as a good application of 4-oxo-TEMPO, to afford a easily seperated and re-useable
catalyst.
The problem is, TEMPO derivatives can't just be absorbed onto silica, without leaching, and most of time are crafted onto functionalized silica with
the aid of organo-silanes.
Two major paths for attaching a TEMPO moeity onto functionalized silica exist: using a amine function, such as aminopropyl-silica, and performing a
reductive amination with 4-oxo-TEMPO with NaBH3CN, or using a anhydride, such as ethylphtalic anhydride silane, and reacting the anhydrides with
4-hydroxy-TEMPO (from NaBH4 reduction of 4-oxo-TEMPO).
The problem is these organo silanes are very expensive, and not really availble to home-chemists. So I was wondering about any other ways of
functionalizing silica.
I remembered silica sulfuric acid is readibly formed when silica gel is reacted with chlorosulfonic acid. SSA is a great catalyst in itself for
various condensations, but chlorosulfonic acid isn't easily attained, except if you call yourself Len1 or Garagechemist  .
Si-OH + ClSO3H = Si-O-SO3H + HCl
So i figured out, if the hydroxyl groups of silica readibly react with chlorosulfonic acid at RT and atm pressure, could they react with P2O5?
Si-OH + P2O5 = Si-O-PO2 + HO-PO3
The metaphosphates functions could then be reacted with 4-hydroxy-TEMPO
Si-O-PO2 + HO-TEMPO = Si-O-PO(OH)-O-TEMPO
And such a catalyst could then be used for an oxidation, and simply filtered off at the end..
that last acidic phosphate could perhaps be basified with a large tertiary amine or similar, and a semi-PTC species obtained, possibly favoring
exchange in 2 layer oxydations, trapping small droplets of the aq. solution and bringing the secondary oxidant in contact with the TEMPO more easily
(HOCl for example).
What do you all think? Has anybody got experience with functionalized silica and their derivation?
Any ideas why P2O5 wouldn't react with the hydroxyl groups of silica? Or any other means of introducing an anhydride or amine group on silica without
silanes?
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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not_important
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An important difference is that ClSO3H is a simple molecule that is a liquid and soluble in various inert solvents, while P2O5/P4O10 is a polymeric
solid soluble in a limited number of solvents. Also the phosphates tend to hydrolysis fairly quickly.
Perhaps use and excess of SO2Cl2, from SO2 + Cl2, in solution.
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Klute
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Hum, good point. But wouldn't sufuryle chloride form Si-Cl bonds rather thatn the sulfonic acid? I don't have much knowledge in the field of silane
chemistry...
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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chemoleo
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And I guess you are particulalry keen on silica as a support because of its unreactivity towards solvents, reagents etc, i.e. as in HPLC columns?
If this isn't an issue for your purposes, there are many more organic resins, such as those based on sepharose, which are functionalised very heavily
i.e. in ion exchange columns...
I.e. Diethylaminoethyl (DEAE sepharose) or Q (quaternary ammonium) material - which both could be functionalised quite easily (and found on ebay).
Just a suggestion.
[Edited on 23-5-2008 by chemoleo]
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Klute
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Well, it was much more becasue I already have some at hand, and these kind of resisn are prett expensive... I wouldn't need more than a few grams, and
wouldn't ahve much use for the rest of it..
Apparently, a "sulfonated" silica can eb maybe by reacting freshly precipitated silica with SO2Cl, followed by calcination:
Synthesis of solid superacid of silica treated with sulfuryl chloride
Catalysis Letters
Volume 8, Numbers 2-4, 269-271 (1991)
DOI: 10.1007/BF00764126
Abstract:
A solid superacid catalyst was synthesized from silica gel, which was obtained from the decomposition of Si(OC2H5)4 with HNO3 solution, by exposing to
SO2Cl2 followed by calcination in air at 673 K. The catalytic activity for ethanol decomposition was higher than that of SiO2-Al2O3.
I guess this corresponds prett wel to Si-OSO3Cl or the sulfonic acid. If the sulfonyl chloride can be directly isolated after treatment with SO2Cl2,
evaporation of excess reagent, followed by reaction with 4-hydroxy-TEMPO in presence of TEA should give the sulonate... The -SO3-TEMPO moeity should
be pretty lipophilic, and if there are exces sulfonic acid groups present on the silica, there should be some hydrophilic sites on the catalyst,
helping the reoxidation from aq. oxidants...
EDIt:
apparently silica chloride SiO2Cl is very usefull for preparting these types of catalysts:
Synthesis of morpholinated and 8-hydroxyquinolinated silica gel and their application to water softening
Here is a preparation of silica chloride using SOCL2 (if antyhing else..  ),
so I was wondering if chlorination in presence of red P couldn't do the trick, as this seems to be brute force chlorination, i don't think much SiCl4
would be produced at RT with Cl2/P.. Although i could be wrong.
This could save me buying/making SO2Cl2. How know, perhaps lenghty chlorination of silica gel could give a certain amount of Si-Cl bond here and
there, enough to make an active catalyst.
[Edited on 23-5-2008 by Klute]
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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not_important
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| Quote: | Originally posted by Klute
Hum, good point. But wouldn't sufuryle chloride form Si-Cl bonds rather thatn the sulfonic acid? I don't have much knowledge in the field of silane
chemistry... |
If
Si-OH + ClSO3H => Si-O-SO3H + HCl
happens, then I would expect
Si-OH + ClSO2Cl =>L Si-O-SO2Cl + HCl
to happen. A potential problem would be the reaction of both Cl- with Si-OH, which is why I suggested an excess of SO2Cl2 in solvent.
As for reacting Si-O-SO2Cl with 4-hydroxy-TEMPO, would you even need the TEA as you already have an amine there in a 1-to-1 ratio with the reactive
HO-.
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Klute
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Well, witht he 4-hydroxy-TEMPO it would be the nitrosyl radical, but I realized it would be better to react 4-hydroxy-2,2,4,4-tetramethylpipiridine
with the functionalized silica, and then oxidize the supported amine. In that case, yes, the teritary amine would capte the proton, good idea.
It would just require filtering, adding a weak base (carbonate) to free the amine, and the H2O2 to get the nitrosyl.
So I guess Si-SO3-TEMPO and Si-TEMPO could be formed, depending on how the Silica is chlorinated, SO2Cl2 or possibly PCl5. I haevn't found anything
on chlorinating silica at atm pressure and reasonable temp to get Si-Cl bonds, only industrial SiCL4 preprations involving strong temp and
pressures... I will check out the prices of aminopropylsilane or carboxylic acid-silanes at my supplier in any case, it might be worth it in small
quantities, but the reductive amination might be a little delicate with NaBH3CN.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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NERV
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Getting there......
I don’t have a lot of experience with silane chemistry, but I do have the necessary reagents to tinker around with it. As soon as I get around to
working up my 4-keto-TEMPO (it’s been sitting on my bench for a month now), and reducing it to 4-hydroxy derivative via borohydride I will have to
try to do some work on this silica support system it sounds very interesting to me. Fleaker, and I will hopefully get to this soon, but we have some
inorganic experiments to tidy up with before we get back to this one.
A picture to whet your taste buds a little bit  ……
[Edited on 22-9-2002 by NERV]
Vir sapit qui pauca loquitur.
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Klute
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Oh My! I'm so jealous of that chlorosulfonic acid!
I'm very glad this subject has interested someone else, and am looking forward to here about your experiments! I might try the SO2Cl2 method myself,
it should be pretty easy to reflux silica in sulfuryl chloride, but i would need to do some IR to check how well it sulfonated the silica.
I have noticed most of the similar catalyst discribed in the litterature have a somewhat long carbon chain between the TEMPO moeity and the silica,
possibly to leave the TEMPO moiety more accesable.
It might be interesting to fix ethylendiamine onto the sulfonated silica, and reducively aminate with 4-hydroxy-TEMPO, or with something like
3-hydroxypropanoic acid, chlorinate carboxylic acid of the formed ester with SOCL2/PCl5 to the acyl chloride, and react that with the 4-hydroxy-TEMPO.
There plenty of room for experimentation here!
EDIT: NERV, is that a triacetoneamine reaction mixture, or the oxydation product? I think it might be easier to prepare the catalyst from triacetone
amine, to 4-hydroxy-2,2,6,6-tetramethylpiperidine, attach that to the functionalized silica, and then oxydize the amine to the nitrosyl.
As not important suggested, this would swop up the liberated acid in the case of acylation, and the nitrosyl radical is said to dismute in acidic
conditions to the hydroxylamine and a nitroso salt IIRC.
EDIT2: I checked with my suppliers, the silanes are OUTRAGEOUSLY expensive, and neither aminopropyl or tetrahydrophtalic sialnes are availble.....
SO it will not be possible to follow the litterature.
On the second hand, this remarkable piece of work present the synthesis and use of PEG-supported TEMPO (maybe by williamson etherification with 4-hydroxy-TEMPO.
Althouhg not a "real" solid supported catalyst, because soluble in the reaction medium, it is easily precipitated from the filtered solvant by adding
ether, and thus easily recylced.
The synthesis of the catalyst is staright forward, doesn't require any exotic reageants (the Cesium carbonate used can surely be substitued with a
lesss effective base, costing a few % yield). 6000u PEG costs 35E a kilo, much cheaper than those silanes .
I'm wondering if it can be possible to skip the whole para-hydroxyphenylpropanol moeity, which I suppose is there to leave the TEMPO moeity more
accesable, and directly graft p-hydroxybenzyl alcohol on the PEG. Thsi could also be used as a substarte for p-hydroxybenzaldehdye, so then I could
finally make my raspberry ketone .
And why couldn't 4-hydroxy-TEMPO be directly attached to PEG? Apparently PEG-supported TEMPO is commercially availble (didn't dare looking at the
price at Aldrichi must say I'm surprised at how easily the 4-hydroxy-TEMPO is reacted with a benzylbromide to form the ether. this could be used in the
silica-supported approach, attaching 4-hydroxybenzyl alcohol to sulfonated silica, and then williamson with 4-OH-TEMPO. Would give a longer side chain
and easier acces to the nitrosyl.
I'm trying to find a way of contacting the author of this thesis, to here about the reasons of grafting such a side chain, if he is willing to share
them.
Sulfuryl chloride is more expensive 75E a liter, but it can be used for many other things, unlike 6000u PEG... I'm waiting to see what the solid
superacid article gives before choosing a direction.
EDIT3: Damn, 4-hydroxybenzyl alcohol is 100E 100g! So i won't be following the thesis... Maybe using mono-protected hydroquinone instead? And insert
an ethylenglycol between the diphenol and the OH-TEMPO?
Chlorosulfonic acid would cost me 25E for 250mL, so I guess i will follow the sulfonated silica route. Just need to decided what to put between the
sulfonate and the TEMPO
NERV, what was your plan? Directly attach the TEMPO to the sulfonic acid after converting it to the sulonyl chloride?
[Edited on 24-5-2008 by Klute]
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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NERV
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| Quote: | Originally posted by Klute
Oh My! I'm so jealous of that chlorosulfonic acid! |
It is a very beautiful thing is it not ? I wish I had access to more of it
though this is all I have for who knows how long (credit should be given to Fleaker for acquiring it sneeky bastard  ).
| Quote: | Originally posted by Klute
EDIT: NERV, is that a triacetoneamine reaction mixture, or the oxidation product? I think it might be easier to prepare the catalyst from triacetone
amine, to 4-hydroxy-2,2,6,6-tetramethylpiperidine, attach that to the functionalized silica, and then oxydize the amine to the nitrosyl.
As not important suggested, this would swop up the liberated acid in the case of acylation, and the nitrosyl radical is said to dismute in acidic
conditions to the hydroxylamine and a nitroso salt IIRC.
NERV, what was your plan? Directly attach the TEMPO to the sulfonic acid after converting it to the sulonyl chloride?
[Edited on 24-5-2008 by Klute] |
Yes that is a triacetoneamine reaction mix I prepared last month after seeing your fully illustrated preparation of TAA. I just couldn’t help myself
how could one pass up a synthesis where all I had to do was toss acetone, and ammonium in a flask forget about it, and wham bam boom you have this
neat little oxidation catalyst that has so much potential? Sadly I have lacked the time nessasary to get back to it due to several prior engagements
me, and Fleaker had to attend to. I am hoping to finally be able to get to it sometime this upcoming weekend (crossing fingers). My intention is to go
from TAA to 4-oxo-TEMPO via the H2O2 route (I have limited access to NH3 gas, and I really don’t care to work with it all that much plus H2O2, and
Na2CO3 are cheap and easy) I realize that there are extensive impurities formed during the aforementioned oxidation, but I have never been opposed to
column chromatography ! All that is left after that is to reduce it with
borohydride to 4-hydroxy-TEMPO, and then oxidize the amine to the nitrosyl after coupling with a functionalized silica.
I am on the fence currently on weather or not to simply go about directly reacting my 4-hydroxy-TEMPO to the sulphonated silica, or to place some
type of chain in between the silica, and the TEMPO. I am leaning more towards the latter since doing so would defiantly allow more access to the TEMPO
moiety in a reaction or so it would seem, and it seems to be a fairly common occurance throughout the literature....... Ah what the hell I might as
well attempt both routes since it wouldn’t be that difficult to synthesis both versions just split my final product in half and compare the
effectiveness of TEMPO directly bonded to the silica Vs. one that is bonded via an intermediate carbon chain. The real question here is exactly what
should I use as my link between the silica, and the TEMPO. I really liked your idea of fixing ethylenediamine to the sulphonated silica, but my
stopping factor on this procedure is that fact that I don’t have any NaCNBH3 which would be my first choice for a reductive amination if anyone has
any alternative methods with decent yields I would love to hear them because all I can think of is amalgamation and I personally just don’t think an
amalgam would work here at least with any appreciable amount success (I could be wrong though). I am very interested in the coupling of
4-hydroxybenzyl alcohol to the sulfonated silica. Correct me if I am wrong the way I am visualizing that reaction in my head would be to first to
react your 4-hydroxyBZOH with your Si-O-SO3H giving you Si-O-SO(OH)-O-PhCH2OH which is subsequently halogenated (Br coming to mind first) too
Si-O-SO(OH)-O-PhCH2X and from there it’s a simple Williamson ether synthesis the neucleophile being formed from your 4-hydroxy-TEMPO. It sounds like
a relatively easy synthesis to me it’s just a matter of digging up some good references with experimental details that may or may not exist…….
The hunt is on!
[Edited on 22-9-2002 by NERV]
Vir sapit qui pauca loquitur.
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Klute
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I don't think a couple weeks more will hurt the reaction, i forgot about for over 6 months
Apparently, the H2O2/CO3 2- oxydation is actually very clean! See the article KMnO4 retrieved, I attached it in the TEMPO thread! The not-too-clean
reaction is the formation of TAA.. but if the product is isolated as it's salt and recrysatllized, it should be fine! I was really surprised at the
work up o fth eoxydation the authors propose, crisatllizing the catalyst out of aq. solution with NaCl, thus purifying ti already enough for it the be
able to crisatllize at RT! A simple recristn would be suffisant I guess, but obviously a little column chromatography can't hurt
The 4-hydroxybenzyl alcohol procedure is detailed in the thesis I attached, with all the experimental details! But they link it to a PEG.
You need to protect the benzyl alcohol before sulfonating the phenol, they use ally bromide, but I'm sure something less expensive can be used. Then
unprotect, and brominate (they use CBr4/PPh3, but HBr should work fine), and a simple reflux with 4-hydroxy-TEMPO and K2CO3!
Considering how easily 4-oxo-TEMPO seems to form imines (from the review KMnO4 posted in the ref forum, check it out! it's excelmlent and very
complete!), I guess NaBH4 could be used for the reductive amination, especially with ethylenediamine which really forms imines easily. A dean stark
could be used to generate the imine, hoping the ethylendiamine will not polymerise too much if pet ether is used as solvent, but hopefully just
stirring at RT in anhydrous conditions should be enough.
Not too sure if it would be better to form the di-amine between 4-oxo-TEMPO and ethylenediamine first, and then react with the sulfonated silica, or
start the other way around? Using an excess ethylendiamine should avoid double-amination.
Unfortunaly, the 4-hydroxybenzyl alcohol is prohibitively expesnive, so i can't got this route, I'm trying to fina cheap di-functional benzyl alcohol,
considerign how easily it alkylates 4-hydroxy-TEMPO...
I have some ethylene glycol mono ethyl ether, and was wondering about reacting that with the sulfonated silica, dealkylating the ethyl ether, and
alkyalting then 4-oxo-TEMPO with the tosylate of the 2-hydroxyethyl sulfonate silica...
i'm not too sure how to dealkylate the ethyl ether without affecting the sulfonate... Any ideas?
Otherwise, I was thinking of Nylon-6 monomer, 6-aminohexanoic acid: form the sulfonamide with the sulfoanted silica, and the ester with 4-OH-TEMPO!
no need for any protection here. Just need a easy way of aquiring the monomer: i don't know if hydrolyzing Nylon 6 would be a viable option ..
Can't wait to get started!
I will definitively first make some 4-oxo-TEMPO, then some 4-hydroxy-TEMPO with the 10g of TAA.HCl I have...
After I can start to try and optimize the TAA synthesis a bit...
Hoping to here about your progress!
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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Fleaker
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Some references
Pertinent additional information:
TEMPO_1
TEMPO_2
TEMPO_3
EDIT: Forgot one (attached it)
[Edited on 26-5-2008 by Fleaker]
[Edited on 26-5-2008 by Fleaker]
Neither flask nor beaker.
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Klute
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Beautifull, thank you! These direct procedures still seem pretty out of reach though... If we could find a couple esterification procedure of
sulfoanted silica to the ester without DIC and DMAP, it would be nice. I haevne't found anything regarding formation of silica bounded sulfonyl
chloride, I'm scared such a species wouldn't be stable as the sulfonyl group would react with free hydroxyl groups on the silica..
Maybe with a salt of the sulfonated silica and a tosylate of 4-hydroxy-TEMPO? Or refluxing in a deans tark for extended periods, but that might
cause a certain amount of by products...
Found thisrather interesting article, dealing with the absorbtion of TEMPO derivatives on zeolite and subsequent exchange with ortho-methyldibenzyl
ketone.
They discuss the preparation of 15N 4-oxo-TEMPO from 15N-ammonium sulfate in 66% yield which could be pretty interesting considering the price of
15N labeled ammonium salts, they must have used a very optimized procedure.
The other interesting point is that they decrib a room temp esterification of 4-hydroxy-TEMPO with diphenyl acetic acid in 66% yield, which could be
evry interesting to us.
I have requested both referenced procedures.
Another good point is the preparation of 4-hydroxy-TEMPO from 4-oxo-TEMPO with NabH4 in 94% yield!
There is something I'm not sure about :
| Quote: |
2,2,6,6-Tetramethyl-4-[(diphenylacetyl)oxy]-1-piperidinyloxy
(3) was synthesized following a published procedure for
esterification at room temperature using 4-hydroxy-2,2,6,6-
tetramethyl-1-piperidinyloxy-15N and diphenylacetic acid in 66%
yield. It was recrystallized using ethyl acetate.
2,2,6,6-Tetramethyl-4-[(diphenylacetyl)oxy]-1-piperidinyloxy-
15N (3-15N) was synthesized following the procedure for
3, using 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine-15N, the
latter prepared by a reduction of 1-15N (15N-4-oxo-TEMPO) using sodium borohydride
in 94% yield.
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The say the N-oxyl ester (3-15N) was formed according to the same procedure used for 3, but with 15N- piperidine, not the oxyl radical? Is this an
ommison, or did they oxidize the amine afetr? I doubt so, there could possibility (although minimal because of the steric hindrance) amide formation
during esterification?
I ask this because I would like to know if they reduced 4-oxo-TEMPO or TAA with NabH4 in 94% yield!
1-15N is 15N-4-oxo-TEMPO, but the way they describ it it is unclear if the 4-hydroxy-TEMPO was obtained from the reduction, or if the nitrosyl was
reduced, and the amine re-oxodized to the nitrosyl... I think they woul dhave mentionne d if they had oxidized the product of the NabH4 reduction, so
I would like to think the 4-hydroxy-nitrosyl radical is obtained, which would go in the same direction as the review, ei the nitrosyl isn't reduced by
NaBH4..
I think there is another mistake as they describ the preparation of the unlabeled ester 3 with the 15N-4-hydroxy-TEMPO, an djust after described hte
preparation of the 15N ester with the same 15N 4-hydroxy-TEMPO! I guess the first one is meant to be unlabeled 4-hydroxy-TEMPO as they do not describ
it's preparation, it must ahev been a commercial product; the 15N musn't be commericallly availble, hence the preparation from NaBH4.
I have yet to find any details on the NaBH4 reduction, what solvant and what reaction time, and what molar excess of NaBH4. I hope the 4-hydroxy-
and the 4-oxo-TEMPO are easily differentiated by TLC.
EDIT: BTW Fleaker, the two last papers are the same I guess you must have
thought you forgot to add the last one while you had
EDIt 2: Argh.. the ref for the prepaation of 15N-TAA from 15N-(NH4)2SO4 is wrongly referenced, the paper doesn't mention TAA or 4-oxo-TEMPO, only
2,2,6,6-tetramethylpiperidine used to prepare a enolisation reagent... I'll double check the previous and second ref in the list in case thye jumped
a number or something... Apparently they must have published the paper in a hurry, considering the number of mistakes present.
[Edited on 26-5-2008 by Klute]
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Klute
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I've checked with my supplier, and DCC is quite affordable (24.20E for 100g), the DMAP is much more expensive (12.90E for 5g) but only needed in small
quantities and hopefully avalibale in small quantities.
I will try out trivial esterification methods first guess, and if need be switch the DCC/DMAP esterification, starting elegant reactions
The same procedure could be used to prepare PEG supported caatlyst, reacting PEG with adipic acid for example, and esterification with
4-hydroxy-TEMPO...
Aliced25 had a very good idea of using basic resins to graft the 4-oxo-TEMPO on, if we could find a cheap one with a nice primary amino group hanging
around, it might be easier than sulfonated silica. Of course, it would be interesting to compare the activity of the two catalyst, I think silica
would have a greater surafce than the resins...
I will try and find such resins locally, and see how much details can be found on their compositions..
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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Nicodem
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Sulfonated silica, being a mixed anhydride, hydrolizes quite rapidly and is of no use as a solid support for further functionalization.
Polymeric polystyrene solid supports with chloromethyl or aminomethyl groups are quite common and I don't think they are particularly expensive. Yet,
since you want to be original you could just buy acryloyl chloride, esterify 4-OH-TEMPO with it and polymerize it (the ester might even polymerize
spontaneously with the nitroxyl radical acting as the initiator?). Though perhaps you would have to make a crosslinked polymer with divinylstyrene in
order to prevent the polymer from being soluble in organic solvents like CH2Cl2.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
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Klute
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I'm surprised you say this as Silica Sulfuric Acid is very often used as a recycleable acid catalyst, keeping the same activity after sevral uses in
various uses... But it's true I haven't found anything on further recation of the catalyst itself...
By hydrolyse, do you mean the whole sulfate moiety hydrolyzing off, according to:
[Si]-O-SO3H + H2O --> [Si]-OH + HO-SO3H
In any case, after some though I was thinking of starting from silica chloride rather than silica sulfuric acid, and reacting it with an diamine, or
aminoacid to latter graft a TEMPO moeity on, similarily to this article.
After all, thionyl chloride is roughly the same price as chlorosulfonic acid, and I could avoid the use of DCC/DMAP by using SOCl2 to generate the
acyl chloride of the acid to react with 4-hydroxy-TEMPO..
I'm just wondering how well a primary amine would react, if di-alkylation would occur to a large extent.. I was thinking of grafting 6-aminohexanoic
acid on silica chloride, and then esterifying with 4-hydroxy-TEMPO.. silica chloride is also said to be a efficient esterification/transesterification
catalyst (source )
Any ideas, comments?
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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Nicodem
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| Quote: | Originally posted by Klute
I'm surprised you say this as Silica Sulfuric Acid is very often used as a recycleable acid catalyst, keeping the same activity after sevral uses in
various uses... But it's true I haven't found anything on further recation of the catalyst itself...
By hydrolyse, do you mean the whole sulfate moiety hydrolyzing off, according to:
[Si]-O-SO3H + H2O --> [Si]-OH + HO-SO3H |
Yes, that's what I mean. Being a mixed anhydride of a weak acid with a strong one, it must be susceptible to hydrolysis by definition. This does not
necessarily mean it will hydrolyze at the sight of water, but eventually it will, especially under basic conditions.
When you say that "silica sulfuric acid" is a recyclable catalyst, do you mean that you read it in some green chem ideological paper? Unfortunately
the reality of the green chemistry is not compatible with the real world chemistry. You also have to think if it was ever exposed to water? Besides,
if the authors did not report the retention of the catalytic efficiency after recycling they must surely bluffed.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
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Klute
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Well, there many articles from reputable publishers dealing with SSA use in very diverse applications, but I admit most of them are not done in
aqueous solutions, using only caatlytic amount of water (I haven't read all of them in detail, far from that), and a good amount of them are from a
same author, which could mean it has to be taken with a grain of salt.
A few examples:
[url=]http://www.mdpi.org/molecules/papers/71000734.pdf]Silica Sulfuric Acid/ NaNO2 as a Novel Heterogeneous System[/url]
Deprotection of Acetals and Ketals by Silica Sulfuric Acid and Wet SiO2
The Use of Silica Sulfuric Acid as an Efficient Catalyst for Deprotection of
<a href="http://acta.chem-soc.si/50/50-3-563.pdf">SILICA SULFURIC ACID/KBrO3/WET SiO2 AS AN EFFICIENT HETEROGENEOUS SYSTEM FOR THE OXIDATION OF
ALCOHOLS
UNDER MILD CONDITIONS</a>
Silica sulfuric acid as an efficient and reusable reagent for crossed-aldol condensation of ketones with aromatic aldehydes under solvent-free
conditions
I guess I will go with the silica chloride route. Nicodem, do you think a primary amine would be polyalkylated by silica chloride? Or could we safely
assume that two Si-Cl will never be close enough to both recat with a same nitrogen?
[Edit: Ramiel [fixed link with html vs imgboard markup]]
[Edited on 10-6-2008 by Ramiel]
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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LSD25
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Nicodem,
Is it possible to nitrate & then reduce Lignin to a primary amine resin? If so, could that be used as a support for 4-oxotempo through reductive
alkylation? Alternatively, work out how to put a halide onto the ring of the various lignin-phenylpropanoid units, then aminate that, finally
alkylation with 4-oxotempo?
I am not seeking to find out simply for the 'novel' idea, but because DVB is hard to find/source without a university/business account. Insofar as
existing resins could be used, it seems that very few have a primary amine, so it would be harder to alkylate them with the ketone, or so I believe
anyhow.
Whhhoooppps, that sure didn't work
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Nicodem
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Well, I do not know about lignine, but polystyrene is easily nitrated to give mostly para nitro substitution. The so obtained poly-p-nitrostyrene can
be reduced to poly-p-aminstyrene (let me know if references are needed). Attached is one example of polystyrene nitration:
The nitration of polystyrene
Aristides Philippides, Peter M. Budd, Colin Price, Cuncliffe, Anthony V.
Polymer, 34 (1993) 3509-3513. DOI: 10.1016/0032-3861(93)90483-Q
Attachment: The nitration of polystyrene.pdf (398kB)
This file has been downloaded 3573 times
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Klute
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Thanks for the article Nicodem, very interesting. I take it derivated polystyrenes are soluble in DCM? Hopefully they could be isolated by adding IPA
or methanol to the reaction mixture, keeping the oxidation products in solution..
Indeed, derivation of polystyrene could lead to a wide variety of functionalized polymers! Considering sulfonation, formylation, alkylation, etc etc
seems possible provided they don't damage the polymer to much.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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Nicodem
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Polystyrene is certainly soluble in DCM, but I don't have a clue what solubility properties would "poly-(p-TEMPO-ylamino-styrene)" have. If it could
be crushed out of solution with MeOH like polystryrene can be, it would be quite nice but it is after all less hydrophobic than polystyrene. By the
way, are secundary 4-amino-TEMPO derivatives useful as oxidation catalysts at all?
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Klute
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Yes, a very good example is the Silicat:
Silicat: Novel Silica Supported Catalysts
Silica Supported TEMPO Catalysts: Synthesis and Application in the Anelli Oxidation of Alcohols
Also see the articles Fleaker posted
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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LSD25
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Of some small interest might be this article:
http://pubs.acs.org/cgi-bin/abstract.cgi/jcchff/2001/3/i01/a...
| Quote: | J. Comb. Chem., 3 (1), 117 -124, 2001. 10.1021/cc000083f S1520-4766(00)00083-3
Web Release Date: November 28, 2000
Copyright © 2000 American Chemical Society
Polytetrahydrofuran Cross-Linked Polystyrene Resins for Solid-Phase Organic Synthesis
Patrick H. Toy, Thomas S. Reger, Patrick Garibay, Jayne C. Garno, J. A. Malikayil,# Gang-yu Liu, and Kim D. Janda*
Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla,
California 92037, Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, and Aventis Pharmaceuticals, Inc., 1041
U.S. Route 202-206, Bridgewater, New Jersey 08807
Received September 20, 2000
Abstract:
Currently, divinylbenzene cross-linked polystyrene (DVB-PS) is the polymer of choice for use in solid-phase organic synthesis (SPOS). While much
research has been directed toward the optimization of linker groups for the attachment of compounds to the polymer, the development of new polymers
themselves has been relatively neglected. In an attempt to overcome the shortcomings of DVB-PS and to develop new polymers with optimum properties for
use in organic synthesis, we have prepared a series of polystyrene polymers that incorporate flexible polytetrahydrofuran (PTHF) based cross-linkers.
The objective of incorporating PTHF into the polymers was to slightly increase the overall polarity of the polymer and thus render the resins more
organic solvent-like. Since the degree to which a resin swells in and absorbs a particular solvent correlates to how well substrates attached to the
polymer are solvated, we compared the swelling of our new resins to commercially available DVB-PS resins. In all cases, we found that our resins
swelled to a much greater extent than do DVB-PS resins, and their use should therefore allow for SPOS reaction conditions that more closely mimic
homogeneous solution-phase conditions. It was also found that the PTHF chain length of the cross-linker does not affect the level of swelling since
all of our cross-linkers afford resins with comparable levels of increased swelling. Furthermore, we have examined the utility of our resins in
directed ortho-metalation reactions and found that the increased swelling of our resins allows for isolation of reaction products in yields comparable
to what is achieved using standard solution-phase conditions. |
This gives a resin with a MeCl linking group, might be useful with the p-hydroxynitrostyrene? Reduction of which would give the amine group we need?
Seems a little complex, what about this article (attached) where the researchers claim to have modified PS resin using only NaOH to give hydroxyl
& CO2H groups which they then functionalised
Attachment: FunctionalizationPS.pdf (170kB)
This file has been downloaded 1077 times
Whhhoooppps, that sure didn't work
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LSD25
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Sorry about the double-post but I wanted to attach this one (attached) where the researchers claim to have transformed waste, expanded polystyrene
(from those white coffee cups) to cation (ie. acid resin) exchange resin using only 95% H2SO4... Now that seems likely to be within the reach of
home-chemists
Attachment: SulfonationWasteExpandedPS.pdf (416kB)
This file has been downloaded 1736 times
Whhhoooppps, that sure didn't work
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