Brown-black, crystalline powder. Very hygroscopic. Readily
soluble in water giving a brown solution which turns gradually green
in air. Also soluble in absolute ethanol; insoluble in benzene,
CCl4, CS2. d4.2.
Formed when metallic V and I2
are heated at 300°C under the
vapor pressure generated by the latter.
V + 3/2I2 = VI3
Vanadium metal (turnings or powder) and excess I2 are placed
in a hard glass or fused quartz tube, closed at one end; the tube
contents are cooled to — 80° C; the tube is thoroughly evacuated and
then melt-sealed to a short total length. A vigorous reaction sets
in on heating. The entire tube is heated for a while at temperatures
up to 300°C in order to achieve product uniformity. The excess I2
is then allowed to distill off into a somewhat cooler zone, and the
tube is quickly cooled and opened.
