DINITBITOTETRAMMINECOBALTIC SALTS. 179
Aquopentamminecobaltic chloride changes slowly on long keep-
ing into chloropurpureocobaltic chloride.
- Dibromotetramminecobaltlc Bromide, [Co(NH3) 4 Br 2 ]Br
(Dlbrompraseo Salt).
Place 20 g. of carbonatotetramminecobaltic nitrate in a flask,
shake it with 80 g. of concentrated hydrobromic acid (cf. No. 35)
and continue to shake while heating slowly over a free flame.
The mass evolves a large amount of carbon dioxide and changes
at first to reddish-brown, then pale-brown, and finally to a dull-
green. When the color ceases to change, allow the mixture to
cool to room temperature and add 50 c.c. of cold water, which
serves to dissolve a little admixed bromoaquotetramminecobaltic
bromide. Drain the precipitate on a hardened filter and wash
it with cold water until the filtrate is no longer reddish-violet but
comes through colorless. Yield, 24 grams of a very fine, light-
yellowish-green, difficultly-soluble powder.
Dissolve a portion of the powder in warm, dilute ammonia,
acidify with hydrobromic acid, and heat for half an hour on the
water-bath. The salt is thereby transformed into bromopent-
amminecobaltic bromide, [Co(NH 3 )5Br]Br 2 , which is a very finely
granular, reddish-violet precipitate.
- Dinitrltotetramminecobaltic Salts, [Co(NH 3 ) 4 (NO 2 ) 2 ]X
(Flavocobalt Salts).
Flavocobalt Nitrate, [Co(NHt)4(NOz)t]NOi. Dissolve, without
heating, 10 g. of carbonatotetramminecobaltic nitrate in a mixture
of 100 c.c. water and 14 g. of 40% nitric acid (sp. gr. 1.25), where-
by a blood-red solution of diaquotetramminecobaltic nitrate is
obtained. Add 20 g. of crystallized sodium nitrite to this solution,little by little, and place the flask containing the mixture in a
bath of boiling water for 7-8 minutes, or until the color of the
solution has become deep brownish-yellow, then immediately
cool under the water tap and add 130 c.c. more of the 40% nitric
acid. This causes foaming and a strong evolution of nitric oxide.
The next morning, drain off the precipitate of mixed acid and
neutral flavonitrate and wash it first with a little nitric acid and
then with alcohol. Yield, 8-9 grams.