Author Topic: POCl3 Preparation  (Read 592 times)

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POCl3 Preparation
« on: March 27, 2002, 08:28:00 PM »
at the moment in more than one thread SOCl2 and POCl3 preparation is discussed. Uemura comes up with a translation from Jander-Blasius: Lehrbuch der anal und präp. anorganischen Chemie on the preparation of POCl3 and SOCl2.

Thionylchloride: SOCl2 mp=-105DegC bp=76DegC
Phosphoroxychloride: POCl3 mp=1DegC bp=105DegC

PCl5 + SO2 -> POCl3 + SOCl2

This rxn has to bee performed in a hood. In a 2 neck flask 100grm PCl5 are added. The flask is equipped with a reflux condenser which ends with a CaCl2 drying tube which goes directly into the vent of the hood.

Into a glas tube leading almost to the bottom of the flask, SO2 will be introduced.  The SO2 is dryed in two wash bottles filled with conc H2SO4 before it enters slowly the flask. A light yellow liquid builds up. When all PCl5 has dissolved the rxn is over.

The seperation of the SOCl2 - POCl3 mix is done via fractional destillation in a very well dried apparatus with a vigreux column.  On the receiver adapter a drying tube is connected. The following fractions are collected:
F1 up to 85C, F2 up to 92C F3 up to 105C F4 up to 152C. F1 is almost already pure SOCl2, F4 almost pure POCl3. F2 and F3 are a mix, both are put together and the destillation is repeated. Finally all added F1 (F4) fractions are destilled and the prodcut coming over between 78-79C (106-108C) are collected.

Another one:

2PCl3 + O2 (=dried air) -> 2POCl3

Uemura's favorite reactions to produce POCl3 are however the following two:

1) 3 PCl3 + KClO3 -> 3 POCl3 +KCl and
2) 3 PCl3 + P2O5  -> 5 POCl3   <=== He likes this one best

no stinking side products!
Carpe Diem