Saturday
December 20, 2014

Homework Help: Polarity

Posted by Sheryl on Tuesday, September 26, 2006 at 9:34pm.

Benzyl alcohol is not a good sovent with which to crystallize fluorenol. The melting point looks okay so I'm assuming that polarity is the problem. Benzyl alcohol looks polar to me because it has an OH but it is only partly soluble in water. Couldn't find much on fluorenol.

Help please.

Shery


I wouldn't expect benzyl alcohol to be very polar. It has such a large aryl ring so it is more like an aryl (benzene, toluene, etc) than an alcohol. I'm not sure how you are comparing m.p. versus what makes a good solvent. The m.p. of benzyl alcohol is about -16 C (b.p. about 210 or so). I could not find fluorenol listed in The Merck Index but I did find it on a Google search. The m.p. of fluorene is listed there as 153-154 C. I searched for solvents for fluorenol and found a couple of experiments in which photolysis was being conducted in polar versus non-polar solvents but these were not common solvents and the papers talked about half-lives of the order of nanoseconds. I didn't think that would be of much help. I also lucked onto a site which I was forbidden to see but they gave an intro I could read that said something like "You did a mixed solvent recrystallization of fluorenol with methanol-water mixture. Fluorenol is .......not very soluble in water, even hot water.".....etc. But that was the end of the intro and I couldn't access the full paper. At any rate, I would think methyl alcohol/water might be worth a shot if you are searching for a starting place. I hope this helps.


I made a typo below which I have corrected in bold.
I wouldn't expect benzyl alcohol to be very polar. It has such a large aryl ring so it is more like an aryl (benzene, toluene, etc) than an alcohol. I'm not sure how you are comparing m.p. versus what makes a good solvent. The m.p. of benzyl alcohol is about -16 C (b.p. about 210 or so). I could not find fluorenol listed in The Merck Index but I did find it on a Google search. The m.p. of fluorenol is listed there as 153-154 C. I searched for solvents for fluorenol and found a couple of experiments in which photolysis was being conducted in polar versus non-polar solvents but these were not common solvents and the papers talked about half-lives of the order of nanoseconds. I didn't think that would be of much help. I also lucked onto a site which I was forbidden to see but they gave an intro I could read that said something like "You did a mixed solvent recrystallization of fluorenol with methanol-water mixture. Fluorenol is .......not very soluble in water, even hot water.".....etc. But that was the end of the intro and I couldn't access the full paper. At any rate, I would think methyl alcohol/water might be worth a shot if you are searching for a starting place. I hope this helps.


The exact question is: Benzyl alcohol (bp 205 degree C) was selected by a student to crystallize fluorenol (mp 153-154 degrees C) because the solubility characteristics of this solvent are appropriate. However, this solvent is not a good choice. Explain.

So the melting point looks okay and both would seem to be nonpolar, according to your researches. What else could it be?

Sheryl


I must be getting tired. Of course, two nonpolars are soluble in each other. Sorry.

Sheryl


Please skip my previous message. There is still an unanswered problem

Sheryl


I am batting zero. I'm having lunch tomorrow with a good friend of mine (an organic chemist). I will ask him. Of course, you probably need this by tomorrow.


I don't need it by tomorrow. Am getting ahead on my work.

Have a nice lunch.

Sheryl

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