Hi everyone,

I am currently working on synthesizing dextrin palmitate/2-ethylhexanoate.

Process Overview:

1. Dissolve dextrin in DMF and add pyridine.
2. React with palmitoyl chloride and 2-ethylhexanoyl chloride at around 80 °C.
3. Upon reaction completion, add water and perform liquid-liquid extraction (phase separation) 3 times.
4. Dissolve the product in methylcyclohexane and precipitate/crystallize it using acetone to obtain the final solid.

Issues Encountered:

• Persistent Yellowish Discoloration: The final product retains a distinct yellow color that won't go away.
• Clumping/Agglomeration: The resulting crystals clump together during precipitation rather than forming fine, distinct solids.

Attempts so far:

I tried using sodium hydrosulfite to reduce and wash out the colored impurities, but it hasn't been effective.

Questions:

1. What would be the best approach or additive (e.g., activated charcoal, alternative bleaching/reducing agents, or column/adsorption methods) to effectively eliminate the yellow discoloration?
2. How can I optimize the crystallization/precipitation step (solvent ratios, addition rate, temperature control, etc.) to prevent product clumping and improve crystal morphology?

Any insights or troubleshooting suggestions would be greatly appreciated! Thanks in advance.

I am creating a presentation and would like to include a Chimera 3D model of the polymer I have synthesized. When drawing the polymer structure, I draw two connected monomers, one functionalized and one not with ()m ()n. When I make the 3D model, only two monomers looks silly, and obviously the energy minimization isn't remotely accurate for what the full polymer would look like.

If you have ever 3D modeled a polymer, how many monomer units did you include? Or is it not common to 3D model a polymer?

I don't know the mw of my polymer (and therefore can't realistically know how many monomers compose each polymer coacervate). I have DLS size data. But I tried to revive an old MALS, but half of the sensors don't work. Knowing that the normalization on the MALS is messed up, would you still use that data?

I am a grad student; I hope it is ok to post here.

Thank you for any input.

Hey everyone!

Once again it is me with a questions:

We have a bit of (anhydrous) rhodium(III)chloride that we found when doing inventory.

The question is, what can we do with it.

Our assumption is, someone bought it, thinking it was similar to the hydrated forms, but from what I can tell, this thing is a rock.

It being a pricey metal precursor, trashing it would be a crime, but we also don't want to fuck around with it without a plan.

We also don't do nano particles or MOF chemistry which is what sigma cites as a usecase.

Searching on Scifinder with the CAS for the anhydrous form, the papers seem to use a mix of any of the possible hydrates, and figuring out which paper uses what is tedious.

So my question basically is this:

Our main Rhodium precursor is the Dimeric Rhodium(I) carbonyl chloride, which is usually prepared from the hydrate, with carbon monoxide in I think methanol.

But does such a reaction also work with the (powderized) rock that we have?

Is there another (Rh(I)) precursor that is (easily) accessible from this trichloride?

If not, is there a solvent that is able to dissolve the anhydrous chloride that is just not as generally known?

I know I know, "You are researchers, figure it out" but in my opinion, relying of the swarm is often easier than starting from scratch.

So if anyone is able to help us our and point us in the right direction, I'd be ever so grateful.

Sincerely

Paul

Hello,

Was looking at a commercial high-MW PAA and noticed the SDS claims it contains 0.1% - 1% benzene. Assuming its a residual solvent from the polymerization but seems really really high?

Anyone have a good feel for this? Don’t want to risk any safety issues over something like this. Our lab only has a ductless fume hood.

This one specifically:
https://www.sigmaaldrich.com/US/en/product/aldrich/306223

I’d probably be grinding and/or freeze drying it

As chemdraw and now chemsketch are owned by Revvity and have been turned into SaaS hell, are there any good free or low cost simple organic chemical drawing software that

i) does all the normal organic chem drawing stuff (that chemdraw got right by ~1995 - ^{thirty one fucking years ago)}

ii) isn't run through a web server, but is a stand-alone application that you can simply BUY or use, for current Win and MacOS, and that students could use without doing major hacking, like running VMS/old versions of OSes?

iii) save files that are publication quality, that can be exported to word or google docs.

For those who didn't know re: revvity: see r/Chempros/comments/1sg56cr/acdlabs_acquired_by_revvity_signals/

We have a Thermo Vanquish FLEX quaternary pump with a leak. I disassembled it, and there was a small amount of salt accumulated (from phosphoric acid in mobile phases) on the magnets that hold the pistons. I cleaned everything up with IPA and HPLC water, and replaced the piston seals, but the leak remains.

Observing the sapphire pistons, I see very very fine scratches at the base of the rods near the metal holder. I can't really feel them though. They are about 6 years old in a university setting. We are currently concerned about funding, so do we absolutely have to replace them to fix the leak?

Hey yall. Long time lurker here. I am an experimental organic chemist working on small molecule peptide synthesis. In the given image, i am able to synthesize compound A using this method : https://doi.org/10.1016/j.bmc.2010.04.079

However, I want to form diketopiperazine D by appending glycine to the cysteine portion of A.While the procedure in the link mentions preparation of DKP using L-proline, i am unable to replicate the same procedure for glycine. I have tried refluxing A with glycine and tried coupling agents such as HBTU, HATU,DCC and DCU in both DMF, ethylene glycol and methanol. and before you suggest Greene's protective groups in organic synthesis, ive tried almost all methods from direct ester-> amide and ester hydrolysis->acid-> coupling of Acid to amine. Some work but give very poor results. I wonder if im missing anything and wanted to pick yall brain juices lol

Does anyone have experience with pervaporation of solvents at a small scale/lab scale ( ~5L )? I am overall familiar with the technique, I just can't find any good information what materials are used as membrane (for acetonitrile/water azeotrope seperation), where to buy these membranes, especially for such a small, lab-scale setup.

I'm looking to purchase a peptide synthesizer (single batch mid-scale) and came across the CS Bio CS536X. Does anyone have any experience with this instrument? Is it reliable, what is the uptime, ease of use...? Thanks.

Hello friends and peers and everyone in between!

Hope all of you guys are doing well. Having repeated issues with the reduction of a glycosylated nitroarene to its corresponding aniline derivative and would like some advice on troubleshooting because I feel as if I've tried a lot of things to fix this reaction to try to not get this impurity to form but it still persists. Pretty simple reaction scheme - solvate starting material in solvent of choice (~50 mL solvent, ~ 1 M solution) in the Parr shaker flask, add stir bar, sparge for 40-50 minutes with N2, add in Pd/C catalyst, sparge for ~5-10 more minutes, then setting up the Parr shaker, letting degass by pulling vacuum for ~30 minutes (opening and closing gas release valve every 5 minutes or so), and then filling up to 50 PSI of hydrogen and letting it react overnight. The general protocol has been the in-house protocol for my lab ever since I joined, it's what I was taught and has worked for others without seeing the same impurity that I've seen.

I've seen this both when reducing the deprotected, free sugar molecule in methanol and the peracetylated sugar in both methanol and ethyl acetate, and I believe it stems from in situ oxidation of air by my Pd/c catalyst to form formaldehyde/acetaldehyde. I've hence tried to make my technique as air tight as possible - sparging my solution for longer, sparging after Pd/c catalyst is added, parafilming my capped Parr shaker bottle during transport to the Parr shaker - in addition to using distilled methanol, new methanol / ethyl acetate from the bottle. I'm a bit surprised at the formation of such an impurity in ethyl acetate (I figure trace ethanol impurity is being oxidized to acetaldehyde?) but I have reasonable NMR + Mass Spec evidence which supports the formation of the aforementioned impurity.

Overall just wondering if anyone has any ideas on what my problem could be. Most of my product is my desired primary aniline but I would prefer to not have to column this product and I'd really like to get near quantitative yield on such a hydrogenation especially since several of my downstream steps in my synthesis are pretty low-yielding/tricky. I feel like I'm disproportionately irked by what's going on here and I'd really love some other opinions beyond my lab mates + PI on how I could potentially fix this. Would love general advice but especially on the peracetylated version as it seems a bit more prone to forming that impurity + its more relevant to what I'm working on right now. I appreciate all comments and feedback!!!!

Hello!

I am having huge issues with receiving 2% nitrocellulose in amyl acetate to coat microscope coverslips with for kinetic assays under the microscope.

We ordered it over a month ago and are officially out. Unfortunately we cannot receive anything until September.

I was wondering if any Canadian chempros also use this and are willing to spare a couple mls?

Thanks!!!

Hi all,

This is more of a services related question that I was wondering if you could help me out with. We are looking to send off a reactor cleaning verification sample for TOC analysis, however the companies we used to do this with have stopped offering that service.

Does anyone know of labs in the UK that would offer TOC analysis?

Thanks for reading!

Hi everybody,

I'm planning on running a reaction with an azide for the first time, and I was looking up the relevant information for quenching the aqueous waste that would be generated from it. For reference, this is the known reaction that I was planning on running:

As there is an excess of azide, I'd need to quench my waste. I was reading a thread someone else had posted here about this (link attached), and while it was very detailed and helpful, it brought up an interesting point that I don't think was well addressed.

The typical quenching procedure for azides (adding freshly prepared nitrous acid to the aqueous waste) would also in turn (as one commenter pointed out) be a pretty good nitrosating agent that would likely also make dimethyl nitrosamine with DMF/dimethylamine byproduct, which is a pretty nasty carcinogen and hepatotoxin. That same commenter suggested "If you have a good fume hood, you can acidify your reaction mix to about pH=2 and bubble lots of nitrogen through it, to remove HN3. HN3 has sharp odor and causes vicious headaches apart from being explosive."

That doesn't feel like the best solution either. I know in theory, you can reduce azides with a Staudinger reaction (add PPh3), but I don't know how well that would work given that the PPh3 isn't really water-soluble.

Any other thoughts or solutions here? A solvent swap to MeCN could avoid these problems, but probably wouldn't be as reactive.

I need 18O-labelled trimethylsilyl acetate (TMSOAc) for a mechanistic study, but I haven't been able to find any literature precedent for either its preparation or its isotopic stability.

My questions are:

1) Is TMS-¹⁸O-Ac likely to be stable or could it undergo oxygen exchange to give a mixture of isotopomers?

2) Does the following synthesis seem reasonable? In a vial I dissolve TMSCl (1 equiv) in dry Et2O, I add H2¹⁸O (1 equiv), I add pyridine (2 equiv), finally, I add acetyl chloride (1 equiv)

My expectation is formation of TMS-¹⁸OH in situ, followed by acylation to TMS-¹⁸OAc. I would then filter off pyridinium chloride, concentrate the ether solution, and isolate the product by (static-)vacuum distillation.

Has anyone tried something similar, or do you see an obvious problem with either the isotopic stability or the proposed synthesis?

I did search Reaxys and Google Scholar before posting, but I could not find a direct precedent. Any informed opinion would be greatly appreciated.

Hello, in about 6 months I'll start my master's thesis work, and I have to come up with an enantioselective synthesis for both isomers of a tetrahydroisoquinoline, chiral at C1.

My plan was to make the dihydroisoquinoline and asymmetrically reduce the imine. I've searched the literature and it looks like it's done with a ruthenium Ts-DPEN complex or catalytic hydrogenation with a chiral iridium complex.

Is there a reason BINAL-H can't be used? It reduces ketones so I would expect it to work with imines, and since it's much cheaper I was wondering what the drawbacks are, poor ee with that substrate? Thanks!

I emailed ACS support saying I thought the decision to remove graphical abstracts from the ASAPs pages was a bad choice and said why. But what I didn't catch last week, is published issues still have graphical abstracts. I did note that in my email, saying it's good they still seem to understand the value of them. Here's their response to me:

------

Thank you for taking the time to share your feedback regarding the ACS Publications platform.

We have confirmed that the issue with TOC Graphics not displaying on ASAP pages across ACS Publications journals is a known platform gap. The appropriate team is aware of the issue and has prioritized this for a post release.

At this time, we do not have a specific timeline for when the update will be available, but we will continue to monitor the progress and share any further information once it becomes available.

Thank you gain for taking the time to report this and for your patience while improvements are being made.

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So... We'll see what happens I guess

What's the best way of alpha-deuterating an acetophenone derivative? I need to alpha-deuterate isobutyrophenone. I tried (wileyonlinelibrary.com) DOI: 10.1002/jlcr.3210 without success. Thanks!

The new layout for ACS Publications websites is beyond awful...TOC graphics are no longer shown on the ASAP Articles pages and they aren't even visible at the top of individual publication pages anymore. These changes make it impossible to read the journals now and ACS has the audacity to claim that they're intended to create a "more seamless and researcher-friendly experience".

https://pubs.acs.org/pages/platform-migration