On the turbidity of toluene at low temperatures
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During the recrystallization experiments, as well as those to determine the solubility of the sample in toluene, the experiments proceeded normally at temperatures above 5 degrees. However, when the temperature dropped below 5 degrees, turbidity appeared in the test tubes. Even when the volume ratio of toluene to sample was greater than 80, the solution remained turbid, which led to suspicions that there might be an issue with the toluene itself. When toluene was used alone, it became turbid at 5, 0, -5, and -15 degrees, while remaining transparent at higher temperatures (normal behavior); when toluene from another manufacturer was used, turbidity occurred as well. I want to know if this is a normal phenomenon for toluene, or if there might be some issue somewhere.
Since the melting point of benzene is 5.5°C, the turbidity may be caused by benzene; check the benzene content in the sample or reagent.
With other solvents, including DMF, n-hexane, and petroleum ether, no turbidity was observed in 2# sng1107.
Before investigating the reagent as the cause, rule out instrument-related issues first
4# scene000: I’m not sure which type of instrument issue you’re referring to. The test tubes are all cleaned and dried in the same way; experiments are conducted under identical conditions as with other solvents, and it is only with toluene that this phenomenon occurs.
I’ve encountered the same problem with ethanol reagents I bought before as well.
It is likely caused by the precipitation of trace amounts of water mixed in with toluene. Some people upstairs say it’s benzene escaping – that’s absolutely a mistake.
7# ahhooyang: Toluene (analytical grade) treated with molecular sieve, but it remains turbid; I’m confused.