A.
o-Bromobenzenediazonium hexafluorophosphate. A solution of
95 ml. of 12N hydrochloric acid in 650 ml. of water is added with stirring to
60 g. of o-bromoaniline (0.35 mole; (Note 1)) in a
2-l. three-necked flask equipped with
stirrer and
thermometer. Solution is effected by heating the mixture on a
steam bath (Note
2). A solution of
29 g. (0.42 mole) of sodium nitrite in 75 ml. of water is added with stirring while the mixture is maintained at −5° to −10° by means of a
bath of ice and salt or of dry ice and acetone. At the end of the addition there is an excess of
nitrous acid, which can be detected with starch iodide paper.
Seventy-four milliliters (134 g., 0.60 mole) of 65% hexafluorophosphoric acid (Note
3) is added in one portion, with vigorous stirring, to the cold solution of the diazonium salt. Cooling and slow stirring are continued for an additional 30 minutes, and the precipitated diazonium hexafluorophosphate is then collected on a
Büchner funnel. The diazonium salt is washed on the funnel with 300 ml. of cold water and with a solution of
80 ml. of methanol in
320 ml. of ether (Note
4). The salt is partly dried by drawing air through the funnel for 2 hours. It is then transferred to a pile of several filter papers, powdered with a
spatula, and dried at about 25°/1 mm. for at least 12 hours. The dried
o-bromobenzenediazonium hexafluorophosphate is cream-colored; weight
108–111 g. (
94–97%); m.p.
151–156° (dec.) (Note
5).