Keeping moisture-sensitive chemicals dry

  • Thread starter Thread starter MATLABdude
  • Start date Start date
  • Tags Tags
    Chemicals
Click For Summary

Discussion Overview

The discussion revolves around methods for keeping moisture-sensitive chemicals dry, particularly isothiocyanates, carbodiimides, and succinimides. Participants explore various storage techniques and materials, addressing both theoretical and practical aspects of moisture control in laboratory settings.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant discusses their progression from using a vacuum desiccator to heat-sealed Ziplocs and then to moisture barrier bags, expressing concerns about the effectiveness of these methods over time.
  • Another participant suggests that using oil can sometimes be a solution for water-sensitive materials, but acknowledges this may not apply to powdered compounds.
  • It is noted that moisture-sensitive compounds react with water, and storing them at low temperatures may slow hydrolysis, but caution is advised regarding condensation upon warming.
  • A suggestion is made to use indicating Drierite in a mayo jar for storing carbodiimides, with a warning that freezing may lead to moisture issues due to dew point concerns.
  • One participant emphasizes the inadequacy of polyethylene bags and vacuum food bags for moisture control, recommending the use of storage schlenks or ampules for better long-term storage.
  • A later reply mentions using a food vacuum sealer with moisture barrier bags, indicating that this method has been effective for them so far, while questioning if their concerns are overly cautious.

Areas of Agreement / Disagreement

Participants express a range of views on the effectiveness of different storage methods and materials, with no consensus reached on the best approach. Some methods are supported by multiple participants, while others are contested or questioned.

Contextual Notes

Participants highlight limitations in their current storage setups, including the lack of a high-quality glove box and the potential for moisture ingress when transferring chemicals. The discussion also reflects varying degrees of experience and confidence in the proposed methods.

Who May Find This Useful

This discussion may be useful for chemists and researchers working with moisture-sensitive chemicals, particularly those seeking practical advice on storage techniques and materials.

MATLABdude
Science Advisor
Messages
1,663
Reaction score
6
For a while, I've been stepping outside my comfort zone a bit and working with really moisture-sensitive chemicals (isothiocyanates, carbodiimides, succinimides, etc.: stuff that rapidly hydrolyzes and loses functionality). Even though we only purchased a tiny amount each time, we only used a tiny, tiny amount, leaving us with excess. That and the cost of these chemicals meant that we wanted to try to keep them around beyond one round of experiments.

In any case, we moved up from vacuum desiccator (we felt that the moisture requirement was more important than the "keep frozen" one), to heat-sealed Ziplocs with desiccant packs (these really don't work long-term: like beyond a month or so, at least according to the humidity indicator cards) to the heat-sealed moisture barriers used for SMT electronics. Unfortunately, we don't have a very good glove box to create a high-quality inert environment in (we can nitrogen purge bottles, which we do, but not sealed bags).

For the last while, we've just tried to squeeze out as much air out of the moisture barrier bag as possible prior to sealing with a few packets of desiccant and a humidity indicator card. In any case, I had an idea to use one of the food vacuum sealer units to even further reduce the humidity sealed in with the pouches. Does anybody have any experience with this, or know, back-of-the-envelope whether or not that's a whole lot of effort for not very much gain?

Thank you!
 
Chemistry news on Phys.org
I'm sure sometimes you can just use oil if it is water sensitive, but I don't think taht was what you were asking.
 
Kracatoan said:
I'm sure sometimes you can just use oil if it is water sensitive, but I don't think taht was what you were asking.

No, I've seen that done for larger samples of alkali metals (lithium, sodium, etc.) but I don't think that'll work particularly well for my powdered compounds...
 
Most moisture sensitive compounds are moisture sensitive because they react with water. In addition to keeping moisture out, storing at low temperature (e.g. in the freezer) can slow the rate of hydrolysis. Just remember to let the bottles warm to room temperature before opening to prevent water from condensing on your compounds once you open the bottle.
 
I would store my carbodiimides in an old empty mayo jar 1/3 full with indicating Drierite. Putting water-sensitive stuff in the freezer is asking for trouble since most of the time the environment inside is at dew point. Take it out and the entire thing is immediately coated with water... sort of like warming it under a stream of warm water. Polyethylene (ziplock) is a terrible barrier to moisture and I wouldn't trust the vacuum food bags either. They were designed to keep air out not moisture. If you want the ultimate in moisture barriers learn about storage schlenks. You can purchase them or have your glassblower make them using thick-walled round bottoms and glass stopcocks. These will last a lot longer but if you are really using small amounts, you should transfer all of your compounds into ampules when you first use them and seal them with a torch. This is done using schlenk line techniques and is suitable for even pyrophoric boranes. Purchasing those chemicals in small quantities with, for example, an Aldrich SureSeal septa is the best way to buy them but you should always be aware that these are likely stored on a shelf at your supplier's warehouse for some time before shipment. You will need to confirm activity before you begin if purity is a critical thing.
 
Thanks for the responses! I was hoping to use the food vacuum sealer not with the bags it comes with but rather moisture barrier bags (ones designed for electronics and which have very low moisture permeability). We have been freezing the (heat-sealed and bagged) vials after hopefully giving the desiccant time to scavenge the moisture inside. Thus far, it's worked so perhaps I'm being overly paranoid...
 

Similar threads

Mathematica This Week's Finds in Mathematical Physics (Week 241)
  • · Replies 8 ·
Replies
8
Views
5K