[GSR]

Hi,

can anybody suggest how to do the reactions at - degrees( for ex: dry ice -70 degrees) for long hours

-70, -100, -120 etc..

thanks in advance

[HP]

Using Duar flask is one hint. Once i used his coisin - the tea thermos made in China and the result was the same;) of course from time to time may add cooling agent as dry ice or some ice/salt mixture(i have tried ice/CaCl2/acetone)...

[movies]

Dry ice/acetone will get you about -78 degrees C and will last about 4 hours in a regular Dewar flask.  You can keep it going longer if you watch it more closely.  You can get -40 degrees C with dry ice and acetonitrile, but it kinda sucks.  For -100 degrees C you make a slush of diethyl ether and liquid nitrogen.  It's a pain to deal with.

Another good one to know is ice + NaCl + methanol, that will usually get you about -15 degrees C, but it won't last too long once the ice melts.