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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: yg7s7 on March 31, 2009, 11:19:10 PM

Title: melting point range of mixture of cholesteryl benzoate and cholesterol??
Post by: yg7s7 on March 31, 2009, 11:19:10 PM

Cholesterol has melting point range of 147-150 C, and so does cholesteryl benzoate, but when I mixed those two and measured the melting point range in my teaching lab, the melting point range was much lower (120-125 C). I'm sure I used pure compounds, so how would I explain this?? ???

Title: Re: melting point range of mixture of cholesteryl benzoate and cholesterol??
Post by: nj_bartel on April 01, 2009, 12:51:43 AM

When a compound is melted with an impurity, do you expect a lower or higher melting point for that substance?  A broader or tighter melting point range?

Title: Re: melting point range of mixture of cholesteryl benzoate and cholesterol??
Post by: gfunk on April 01, 2009, 09:17:37 AM

Look into colligative properties.

Also, interesting to note is that those two compounds actually have two separate melting points.  They both have a transitional liquid-crystalline phase upon heating from solid to liquid.  For cholesteryl benzoate, it melts at 145*C (cloudy liquid) and 175*C (clear liquid) or so.

Title: Re: melting point range of mixture of cholesteryl benzoate and cholesterol??
Post by: typhoon2028 on April 01, 2009, 10:44:26 AM

Is it possible the two compounds are forming an eutectic mixture?