Laboratory Methods of Inorganic Chemistry, 2nd English Ed. 1928

SULPHUROUS ACID CHLORIDE. 205

As soon as all the phosphorus pentachloride is dissolved, stop the

flow of gas at once, and subject the resulting mixture of thionyl-

chloride and phosphorus oxychloride to a careful fractional dis-

tillation.

Through the cork in the neck of a round-bottomed flask fit a

fractionating tower, 35 cm. high, containing a 30-cm. column of

coarse glass beads. Connect the side arm of the tower with a

condenser and insert a thermometer through a cork placed in the

top of the tower. On the first distillation collect four fractions:

(1) all that distils up to 82°; (2) between 82° and 92°; (3) between

92° and 105°; (4) between 105° and 115°. The quantity of the

fractions varies from 110 to 180 grams. Distil each one of these

portions separately in the same apparatus — except that a

smaller flask is now used — observing the following plan of pro-

cedure: pour fraction (1) into the distilling bulb and place the same

flask in position again as receiving vessel. Distil until the tem-

perature reaches 82°, add the contents of receiving flask (2) to

the bulb and distil again. Continue to collect in receiver (1)

until the temperature again reaches 82°, then exchange this flask

for the now empty receiver (2). When the temperature reaches

92° add the contents of receiver (3) and continue to distil into

receiver (2) until 92° is again reached; then exchange this flask

for receiver (3). At 105° add the contents of receiver (4) and

continue to distil into receiver (3) until 105° is once more reached;

then change the receivers and collect the distillate in (4) until

115° is reached. It will be found that the middle fractions of

the second series of distillations are smaller than in the first

series. Repeat the fractionation, whereby the middle fractions

become still smaller with a corresponding increase of the end

fractions. Finally use only the two end fractions; distil each by

itself from the same apparatus after it has been cleaned, and reject

a small amount of each both at the beginning and the end of the
distillation. About 165 g. of thionyl chloride of boiling-point
77° to 79° and about 180 g. of phosphorus oxychloride of boiling-
point 109° to 111° are thus obtained. The yield of thionylchlo-

ride amounts to 55-60% of the theoretical, the percentage yield

is much lower when smaller quantities are prepared because of

the losses incidental to the fractionation: these losses are rela-

tively less in preparing larger quantities. The preparation is not