LaBTop (Daddy)
09-05-01 10:54
No 210273
      Test on Peroxides in solvents  Bookmark   

A simple test for peroxides in water-immiscible solvents:

Shake 2 ml of solvent with 1 ml of a freshly prepared KI solution (10% in water) and a drop of starch indicator solution, a blue color is rapidly developing if peroxides are present (a  faint yellow/brown color after addition of KI indicates low levels of peroxides).

Diethyl ether, dioxan, isopropyl ether and tetrahydrofuran form peroxides on storage and must be kept in dark bottles or in dark areas. These solvents should be  routinely tested to prove that peroxide levels are kept low before use. It must be emphasized that peroxides, even at low levels, may present an explosion hazard after concentration of solvents by evaporation or distillation.

Chloroform is a popular solvent, it is not very stable, forming phosgene and HCl in air, it should be stored in brown bottles. It is sold after addition of preservatives, ethanol, amylene or cyclohexene.  Dichloromethane (or methylene dichloride) is a similar extractant but less oxidizable. Chloroform and dichloromethane are currently stabilized by addition of ethanol (up to 1%) or methyl-2-butene-2 (about 20 mg/l).

Evaporation of solvents: When a large amount of solvent must be evaporated, it should be done in a rotary film evaporator, the flask containing the extract being maintained at no more than 50C with a water bath. The reduced pressure must be generated by a pump running without oil (motorized pump with metallic or Teflon membranes, diaphragm pumps) or conveniently with a water aspirator achieving a vacuum of 10-20 mm Hg. Last traces of water may be removed by adding 1 or 2 ml ethanol and evaporating again. LT/

(Hive Addict)
09-05-01 18:41
No 210384
      Re: Test on Peroxides in solvents  Bookmark   

So, what about a test for water misible ethers? like THF. or will the one above work for THF as well

nother question, if after say a Beaker like alkene >> alkane synthesis using IPA and THF and NaBH4, could it be assumed that there isd eneough IPA

A) in the distillation flask
B) co-distilling during simple distillation

to asume we needn't worry?

how frequently should these tests be conducted and any ghetto stabilization ideas for THF?

we use ethanol and NaOH for our diethyl etyher, same shit here? seems easier to simply make sure things are stabilized rather than constantly checking to see if they are about to go postal.

"All those memories lost like rain..."
(Hive Addict)
09-05-01 18:43
No 210385
      Re: Test on Peroxides in solvents  Bookmark   

In the chemistry links thread there is a great article about THF, its peroxides, how to measure them and how to prevent and get rid of them

Do Your Part To Win The War
09-06-01 11:33
No 210684
      Re: Test on Peroxides in solvents  Bookmark   

""seems easier to simply make sure things are stabilized rather than constantly checking to see if they are about to go postal.""

Easiest method, told before, add a pinch (knifepoint) of any ferro-salt to your distillation and/or stored suspected peroxide solvents. Gone! LT/