| Pages:
1
2 |
El.Sorbos
Harmless
Posts: 2
Registered: 12-7-2018
Member Is Offline
|
|
In my second experiment strong cooling with water salt/ice solution was applied, so temperatures didn't rose over 10 degree. Also stirring was strong
enough, so no hot spots are noticeable. (mechanical stirring)
Your filter cake extract was also black, so i come to the thesis the solvent are react with the dichlorocynuricacid?
I think one of my errors was my extraction technique, because i worked sloppy. In my next try i will perform additional a slower addition of my
NaDCCA, maybe i underestimated the reaction kinetic and you a right with the temperature argument. 
|
|
|
JJay
International Hazard
Posts: 3440
Registered: 15-10-2015
Member Is Offline
|
|
When I was sorting through some old research recently, I ran across a paper saying that monochlorinated amino acids degrade irreversibly in the
presence of base to form aldehydes, while dichlorinated amino acids degrade to form nitriles.
If aldehydes are forming, that can hurt yields in at least a couple of ways - by using up the amino acid to produce side products - and by unwanted
chlorination of the product by unconsumed chlorine. I'm not sure how fast the degradation into an aldehyde is, but I'm pretty sure that water can
serve as the base, especially if the temperature is high enough. I guess that is why amino acid to aldehyde syntheses with TCCA or hypochlorite tend
to use such dilute conditions. I'll see if I can find the paper....
[Edited on 20-7-2018 by JJay]
|
|
|
AvBaeyer
National Hazard
Posts: 659
Registered: 25-2-2014
Location: CA
Member Is Offline
Mood: No Mood
|
|
JJay,
What you have mentioned is actually quite important for the success of the procedure I posted. The reaction I described uses the sodium salt of
phenylalanine and an aqueous solution of NaDCC. As a result, the pH of the reaction is always near neutrality which inhibits the formation of the
aldehyde product. Thus, N-dichlorination becomes the predominant pathway with subsequent formation of the nitrile as a slow step. As I have also
pointed out, careful temperature control is extremely important to inhibit the formation of dark colored by-products. I believe the good points you
have raised are covered in some of the references I cited.
AvB
|
|
|
JJay
International Hazard
Posts: 3440
Registered: 15-10-2015
Member Is Offline
|
|
Yep, quite likely. You really did some amazing work on this, BTW.
|
|
|
Loptr
International Hazard
Posts: 1348
Registered: 20-5-2014
Location: USA
Member Is Offline
Mood: Grateful
|
|
I found another paper regarding the bromodecarboxylation of alpha-amino acids that I haven't seen before. It discusses some of the reactions that take
place when using NBS that can lead to the expected nitrile, a nitrile of one less carbon, or an aldehyde.
Attachment: J. Biol. Chem.-1961-Stevenson-715-7.pdf (382kB)
This file has been downloaded 818 times
"Question everything generally thought to be obvious." - Dieter Rams
|
|
|
John paul III
Hazard to Others
Posts: 110
Registered: 28-4-2018
Member Is Offline
Mood: No Mood
|
|
What the puropse of washing the organic solution with K2CO3 and brine?
|
|
|
thioacetone
Harmless
Posts: 16
Registered: 15-12-2022
Member Is Offline
|
|
Hi just wondering a few things - if anyone can please help:
- Can I use diethyl ether instead of DCM?
- I don't have access to iodine/iodides for the starch test - is there any way to avoid it?
- Can I use sodium metabisulfite instead of bisulfite?
- Can I dry with anhydrous magnesium sulfate instead of sodium sulfate?
Thanks
|
|
|
MrDoctor
Hazard to Others
Posts: 249
Registered: 5-7-2022
Member Is Offline
|
|
I found an old bag of supplements so i gave it a try, its a pretty simple reaction. Its currently drying over magnesium sulfate, i dont have sodium,
otherwise everything is to scale and no other substitutions.
upon filtering, i was able to get about 80% of the liquid out before the buchner funnel filled up so, i let it finish to dryness, put the liquid into
the sep funnel, and then got to work on the last bit + washes, and something crazy happened.
when the DCM began to boil due to the hard vacuum pulled by my aspirator, at first i thought nothing of it, i cant regulate the pressure anyway since
its fed by a solenoid valve, then suddenly it got really steamy, violent, and hot to the touch, as well as dark. just spontaneously, while there was a
thin film of DCM and aqeuous solution on the bottom of the flask, the evaporation of the DCM would seem to have triggered some sort of runaway
reaction. Ill also note, while it had a chlorine-like smell, it at no point was letting off chlorine fumes after the reaction began, and, did not
cause any changes in my iodide-starch paper. I also checked to make sure the paper was fine, so, there was no oxidizer present, at least none that
could oxidize iodine-starch complex. when i cut the vacuum, it stopped darkening, and stopped getting hotter, quite a bit of time passed before i had
put it in a water bath to cool it off, whatever was happening was being driven forward by the DCM leaving the system.
While at no point it ever made darkened the iodine-starch, i still added a bit of very dilute bisulfite solution i had out in case of bleach spills.
Prior to this as well, i noticed the organic layer was kind of boiling and doing a whole lava-lamp thing, though i didnt think anything of it, since
it was DCM at room temp at -650mmHg or so.
Does anyone know what happened here?
I also have some other questions, like what specifically is the function of the potassium carbonate, and a 50% brine?
specifically, is there any reason its potassium? when i added it, it just instantly milked up with some sort of precipitate that was denser than the
water and wouldnt float out of the organic layer, and was the perfect emulsing particle size, but it filtered out fine.
normally sat sodium chloride solution is saturated, to pull water out, so i wonder what was behind the decision there?
Lastly,to answer some questions, like for thioacetone, and one i saw earlier about aldehyde formation, apparently thats pH dependent, you might be
able to find some info about this if you look into HOCl oxidation of amines on the forum, thats where i read it. simply altering the pH can switch it
from nitrile>aldehyde to aldehyde>nitrile, im just going off the top of my head but, its something pretty simple like that, i think it needs to
stay neutral, which NaDCCA naturally is, which is probably why it works so well. TCCA is poorly soluble but it is an acid and can drop the pH below 3.
I think ordinary bleach was shown to work modestly well in the presence of a phosphate or borate buffer, or something like that.
as for diethyl ether, i wouldnt, youll have density issues and it will all evaporate as you try washing it through the precip cake, the workup is not
compatible with a solvent like that, hell i lost like 20% of my DCM. chloroform might work just as well, its easy to make and a single bleach bottle
should make enough for this.
As for iodine, you do in fact have access. iodine tincture or povidone iodine is easily processed for this. you can make an A4 sheet or two of test
paper with mere milligrams of iodide.
buy some kelp from an asian imports store and burn it, $6 worth of kelp will yield a lifetime supply of iodine for this purpose. It doesnt even have
to be the good kind of kelp with the crazy high iodine, basically any will do.
Metabisulfite is bisulfite, or, it is when dissolved in water, its the dehydrated form. Lots of confusion exists as people selling and marketing it
dont quite understand the chemistry, especially when they call it metabisulfate, like my homebrew sanitizer says.
Lastly, sodium sulfate is better than magnesium, but at very least it doesnt react on contact with magnesium sulfate which is what im using.
|
|
|
AvBaeyer
National Hazard
Posts: 659
Registered: 25-2-2014
Location: CA
Member Is Offline
Mood: No Mood
|
|
I have spent some time going over your post trying to figure out what happened to your experiment. Following are some comments:
“I found an old bag of supplements...”
Was this pure phenylalanine or some formulated material containing who knows what? If not pure phenylalanine, then all bets are off. Please clarify.
” it’s a pretty simple reaction.”
In principle, yes. In practice it requires strict attention to detail. The stoichiometry, very careful temperature control, addition rate of the
sodium dichloroisocyanurate solution and ensuring the reaction is complete are all critical. I made many runs of this experiment to get to the
procedure that I posted at the beginning of this thread. Please provide detail on your temperature control and your source of sodium
dichloroisocyanurate. Was it the dihydrate and did you take this into account in the stoichiometry? Was the phenylalanine (if pure) carefully
converted to the sodium salt? Did you let the reaction go longenough to complete the decarboxylation?
I will speculate on the reaction that occurred during your filtration which released a good deal of heat. My thought on this is that some unreacted
N-chloro intermediate was decomposing rapidly and was being concentrated as the DCM evaporated leading to a runaway decomposition. I have experienced
this in related reactions. The intermediates have a chlorine-like smell and upon warming and/or concentration can decompose violently. This brings me
back to points I made above regarding temperature control and stoichiometry when you set up and ran the reaction. Keep in mind that the
decarboxylation of the N-chloro intermediate is relatively slow. If you did not achieve complete decarboxylation this would leave behind residual
N-chloro compound. Total reaction time to ensure reaction completion is an important variable.
“what specifically is the function of the potassium carbonate and a 50% brine?”
The reaction by product isocyanuric acid has a small solubility in DCM. This mild base wash removes any residual by product. Sodium carbonate would
also work and may even work better (Na salt vs K salt solubility). The brine wash is probably not necessary.
Other comments:
Sodium sulfate will work just fine as a drying agent. I used magnesium sulfate because it was at hand.
I used DCM because I wanted a low boiling solvent in which isocyanuric acid had minimal solubility. I think using hexane or low boiling petroleum
ether should work as phenylacetonitrile will be soluble and everything else will not be.
A technical note (i cant regulate the pressure anyway since its fed by a solenoid valve): You should install a bleed valve between your vacuum source
and filter flask to control vacuum level.
AvB
|
|
|
MrDoctor
Hazard to Others
Posts: 249
Registered: 5-7-2022
Member Is Offline
|
|
i rigged a heat exchanger up using a copper coil supplied cold water from a chiller i normally use to supply my condenser with cold water, as a result
the NaDCCA addition took a very long time, it struggled to keep the solution below 10C, i aimed for around 8C as somewhere i could reasonably keep it.
but addition took several hours without the temp rising too much, though that was also due to the fact it was extremely difficult to fine tune the
flow without it just stopping altogether for some reason as the level in the funnel dropped.
and yes the amino acid used was pure supplement, so food grade, not even the mixed isomer just L-phenylalanine, but it was purchased quite some time
ago and i dont know what 7-8 years will do to it. forming its sodium salt was done by adding hydroxide solution until it dissolved and also read high
pH on paper. It was filtered as a few specs didnt dissolve and i wanted to ensure there was only the slightest excess of hydroxide so as not to mess
with the chlorine stoichiometry.
DCM was boiling away and concentrating its contents i suppose, though i would not have expected that simple action to cause such a violent reaction as
it did.
My source of NaDCCA was pool chlorine, it was the dihydrate, and i used the same weight and volumes as you listed since you also mentioned there might
be some difficulties if a larger amount was used.
Lastly, thankyou for mentioning this, i keep forgetting to do so, getting a T adaptor and a bleeder valve to put inline with my aspirator.
|
|
|
MrDoctor
Hazard to Others
Posts: 249
Registered: 5-7-2022
Member Is Offline
|
|
I finally got around to distilling the crude product. my yield was aproximately 5.8-6g of a faintly yellow clear liquid, distilling at close to
-700mmHg mostly at about 130-138C in an oil bath of around 220C, i did not measure the boiling liquids temp only the vapor, it started at 108C and the
peak was 144C, but the condenser was getting overloaded so i slowed down after that. its hard to tell if it was just one thing or two sequential
fractions close together, due to the air leaking and things just not being at all smooth, in hind sight i should have vacuum tested this shortpath ive
never used before.
I ordered some fluorescent dyed TLC plates, because im long overdue to begin doing TLC, in the mean time i might improvise some, i think you can use
calcium sulfate as a binder and some regular pottery grade silica, or alumina, to produce a somewhat useable TLC plate from microscopy slides, which i
have in abundance.
It also occured to me, theres many reactions you can only do if you monitor them by TLC, like a lot of buffered permanganate oxidations that can yield
next to nothing if you arent looking at what you are doing.
While i cant say for sure until i prove the purity of the nitrile, this is a fantastic method here, especially if it applies just as easily and high
yielding to many other amino acids.
i used the same quantities as you did, but i also didnt cool it quite as well, my phenylalanine is old, and i had that lil exothermic burst during
filtration, so, i can see that accounting for a lost gram or two. actually its rather forgiving as far as these kinds of reactions seem to go.
|
|
|
MrDoctor
Hazard to Others
Posts: 249
Registered: 5-7-2022
Member Is Offline
|
|
I did another one, and this time it decomposed in the sep funnel, and id say, explosively, this time. I consulted grok, and it directed me to a paper
on wastewater processing, that seems to match what i managed to squeeze out of the AI, which in short is that, a slight excess of chlorine is required
to drive the reaction to completion, and the products of under-chlorination can decompose violently, they also will be accompanied by, given enough
time, a solution absolutely depleted of free chlorine, which mine was, even after a full day of stirring at room temp and the night before.
Since baeyers solution reacted faintly positive on iodide-starch, i think it is conceivable that they ran their reaction to a slight excess needed for
things to absolutely complete. some extra chlorine or chlorite, is required it seems, for the chloro-aldimines to fully decarboxylate and dechlorinate
too, or maybe just to buffer the released chlorination products so they can be re-used. In any case all i have to go on is that mine decomposed
violently this time, and, my solution had no detectable free chlorine, so ill try it one more time, this time titrated, and, with a <1% excess.
Unfortunately i already discarded the washes but, upon adding the bisulfite solution to the organic phase it rapidly solidified before turning fluid
again, making me wonder, since chlorophenylacetylaldimine decomposes to phenyalcetaldehyde, could a substantial portion exist at this time, enough to
form an adduct and solidify for a moment? But that adduct is water soluble too right? would it have dissolved into the dilute bisulfite solution?
Im going to do the reaction one more time, since i still have 12g of phenylalanine and this is getting very interesting, but that one is going to wait
until i have TLC, because then i can test my hypothesis about using a slight excess properly, in a small test tube volume and not waste materials at a
full scale reaction.
|
|
|
| Pages:
1
2 |
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
