[levis123]

What to recrystallize methyl 3,5-dibromobenzoate from?

Literature says ethanol but it doesn't work. Compound precipitates and does not crystallize.

Melting point is 63 C.

I have also tried DCM, or DCM/hexane and the same thing happens.

[jeffmoonchop]

No-one ever tries water. If its precipitating the cooling or evaporation is too rapid. You need to control the conditions more. Add a solvent where the solubility of the compound is higher, and cool slower.

I discovered 4 new cocrystals, all polymorphs of each other by using water as the solvent.

[wildfyr]

Lit "ethanol" is a tricky beast. Ethanol often is 5% water. Did they mean wet ethanol? Is it reagent ethanol that has water, methanol, MEK, etc in it? Or do they mean anhydrous absolute ethanol?

These factors can have a surprisingly large effect.

Also jeff is right about trying to slow down the temperature slope as a good tactic. n-propanol is a similar but higher boiling solvent.


Also, I try water! Eventually. One time I was struggling to purify with this cyclic phosphate ester that I had turned into an alkyne for like a month. Column not an option. Eventually I recrystallized from boiling water. Beautiful crystals in hours. Dead pure. Nearly cried.

[levis123]

No-one ever tries water. If its precipitating the cooling or evaporation is too rapid. You need to control the conditions more. Add a solvent where the solubility of the compound is higher, and cool slower.

I discovered 4 new cocrystals, all polymorphs of each other by using water as the solvent.

Ok, thanks! I'll try water as well.

[levis123]

Lit "ethanol" is a tricky beast. Ethanol often is 5% water. Did they mean wet ethanol? Is it reagent ethanol that has water, methanol, MEK, etc in it? Or do they mean anhydrous absolute ethanol?

These factors can have a surprisingly large effect.

Also jeff is right about trying to slow down the temperature slope as a good tactic. n-propanol is a similar but higher boiling solvent.


Also, I try water! Eventually. One time I was struggling to purify with this cyclic phosphate ester that I had turned into an alkyne for like a month. Column not an option. Eventually I recrystallized from boiling water. Beautiful crystals in hours. Dead pure. Nearly cried.

Paper is from 1895 and I can't access it online, but reaxys says "ethanol" in the solvent column for melting point - so I really don't know. I will definitely try water.

[jeffmoonchop]

Not sure why you'd need melting point.

[wildfyr]

If you have access to scifinder its been made hundreds of times in the modern literature. I see columns being used (DCM/hexane). Cculdn't find a recrystallization quickly but its a good place to look.

[AWK]

Paper is from 1895 and I can't access it online, but reaxys says "ethanol" in the solvent column for melting point - so I really don't know. I will definitely try water.

Esters with such a low melting point are difficult to crystallize. Try extraction with CH₂Cl₂, purify extract with Na₂CO₃ and after drying the extract evaporate the solvent. Maybe you can get crystals after partial evaporation and freezing.