The Vespiary

The Hive => Newbee Forum => Topic started by: Pimpo on October 11, 2003, 10:54:00 AM

Title: reflux and reactivity?
Post by: Pimpo on October 11, 2003, 10:54:00 AM

I've never read or heard about this, so I'll just try and ask it here. Does refluxing have any particular influence on chemical reactions, except constantly maintaining a certain temperature? E.g. could a reaction that normally is conducted in refluxing toluene (b.p. 110-112 °C) be done in xylene (b.p. 137 - 144 °C), being held as constantly as possible at a temperature of 110 °C or so?

Title: Convenience
Post by: lugh on October 11, 2003, 04:47:00 PM

Generally speaking, refluxing is used as a convenient means of controlling the temperature, since heating accelerates the rate of most chemical reactions by increasing the average kinetic energy of the molecules  :)  These principle were first quantified by van't Hoff in 1884, d ln k/dT = Q/RT²  8)  The system you propose would bee inconvenient in practice, though of course possible  ;)  One would normally reflux the xylene to increase the reaction rate, though naturally, this could bee counterproductive in certain cases  ;D

Title: If I remember correctly the aproximate rule of
Post by: foxy2 on October 12, 2003, 03:26:00 PM

If I remember correctly the aproximate rule of thumb is that for every 10C increase in temperature the reaction rate doubles.

Title: Thank you bees
Post by: Pimpo on October 14, 2003, 05:15:00 AM

This was helpful. I guess I'll go the easy way first and use a higher reflux temperature, if that seems harmful, I'll try to constantly maintain a lower temperature (I might check into thermostates anyway, they can be useful for one or the other reaction).

Title: reflux = free stirring
Post by: Rhodium on October 14, 2003, 05:45:00 AM

When you reflux you automatically get great stirring - if you are heating xylene to 110°C you should compensate for that with good magnetic or overhead stirring.