I will do it and post the ref here.

Sigma may have had another reason to call for storing under inert gas. Some versions of DCM are sold as “anhydrous” which means a very low water content, minimal O2 and CO2, and absence of common stabilizers like ethanol. If air is allowed to enter the bottle the solvent loses its value as “anhydrous” and is less useful in the lab.

BTW, I know about DCM decomposition from personal experience as well. Back in graduate school I came across a half-full 4L bottle of DCM that was several years old. When I opened it a puff of white smoke came out. This was probably HCl gas or phosgene reacting with moisture in the air (it was July in KS). The solvent tested as acidic with a wet indicator paper.

Slawomir Janicki, Ph.D.

Thank you. This is a great example of crowdsourcing for information. Importantly, the storage under an inert gas is not primarily for safety purposes.

Assuming this is the best answer to Ralph’s question, could someone please add this information to Wikipedia or ChemSpider? (It may already be on ChemSpider somewhere.)

Pete Reinhardt, Yale EHS

Dichloromethane can react with air moisture and oxygen and produce some nasty impurities like phosgene, hydrogen chloride, chloroform and 1,1,2,2-tetrachloroethane. DCM is more stable than chloroform, but not stable enough to leave it without inerting for storage.

If you google “dichloromethane decomposition” you will get many references with more details.

Slawomir Janicki, Ph.D.

From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**MED.CORNELL.EDU] On Behalf Of Monona Rossol
Sent: Saturday, April 12, 2014 7:03 AM
To: DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU
Subject: Re: [DCHAS-L] Dichloromethane storage?

Sigma Aldrich has a SDS that says, "Heat sensitive. Store under inert gas" I 

don't agree with that statement but thought you should know about the ref. My 

experience says the inert gas recommendation is to prevent it from evaporating 

while storing. A liquid seal cap should negate the need for the inert gas too I 

think. 

Sent from my iPhone

> On Apr 11, 2014, at 12:39 PM, "Ralph B. Stuart" <ralph.stuart**At_Symbol_Here**CORNELL.EDU> 

wrote:

> 

> A lab tech noticed a statement on a Dichloromethane bottle that said "store 

under an inert gas". He would like to know if this is a safety recommendation or 

designed to maintain the quality of the chemical by avoiding exposure to 

environmental gases. From what I can find, it appears to be the latter, but I 

thought I would ask DCHAS-L to see if anyone knows of a safety reason for this 

recommendation.

> 

> Thanks for any help with this.

> 

> - Ralph

> 

> 

> Ralph Stuart CIH

> Chemical Hygiene Officer

> Department of Environmental Health and Safety

> Cornell University

> 

> rstuart**At_Symbol_Here**cornell.edu