trivalent Cr oxide is Cr203. it is green, insolH2O, slowly sol HCl, giving CrCl3. should have mentioned earlier that Cr+HCl=CrCl3 only with air contact of the sol., or else CrCl2 happens in a predominately HCl atm. dilute H2SO4 works the same way. HNO3 or conc H2SO4 wont dissolve Cr.
roasting the Cr2O3 in air with carbonate will give chromate but this can suck as fused Cr203 is very hard and resistant to acids. should be spread v thin for roasting, the chromate is leached out w/H2O. this oxidation does not happen very fast and nitrate or chlorate will help, just like in the making of KMnO4 from MnO2.
if you add a base to a +3 salt, you get the hydroxide. adding more base will dissolve it, giving the chromite. you can add the H202/OH to this, but thats a lot of OH to expose to the air to (and clean up), so its usually oxidized as the precipitate.
you can also fuse a +3 salt with nitrate(turns into nitrite) and alkali carbonate to get the chromate.
Cr203 that hasnt been fused (or CrCl3) can be converted to chromyl Cl by heating in a current of Cl2. look up the Etard reaction for typical use. the usual way to make it is by heating (di)chromate with H2SO4 and NaCl or other H2SO4 transposable chloride.
the CrO2Cl2 sublimes. this is very useful stuff, but like most everything very useful Very! Nasty! stuff. it fumes (very low mp) and the fumes, well, of course you have a fume hood. because otherwise you could die. there is more in TFSE.
Cr+6 can also be made by adding Cr+3 and an oxidizer such as ClO3- to alkaline alkali peroxide soln such as NaO2.
for Cr03, pure dry dichromate is slowly heated w/H2SO4. the 93% is ok. the hydrated bisulfate will melt round 160C. at 200C the CrO3 is molten and all on the bottom. remove heat very fast because the dec. point and mp are the same. tap the CrO3 molten or skim off the bisulfate then cool the CrO3 container in ice water fast.
no warranty expressed or implied
if you heat to 900-1100C any Cr cpd that is finely ground with the (bi)carbonate of K or Na +an oxidizer(nitrate, nitrite, chlorate...) you get the chromate.
i would rather put the HCl/Cr203 out on the back porch and wait patiently. once you precipitate the hydroxide its all downhill.
just beware Cr dusts and all +2 and +6 cpds.
..but we're all fucking peasants, as far as i can see...
yes, it is. you will turn green, people will stare. your skin will have good resistance to the elements, tho.
.. a working class hero is something to be...
Post 484576 (https://www.thevespiary.org/talk/index.php?topic=6544.msg48457600#msg48457600)
(sYnThOmAtIc: "Reuse?", Chemistry Discourse)
ning: I am very well aware of it's nastiness! And it's expense. That is why this thread is so long. It is almost entirely about the regeneration of the Cr species for reuse. The main point was answered by terbium.
That being said, would you like to post a method of producing aldehyde from anethole? Cause I would damn sure appreciate it.. No, really!! Prefferably not on the 10g scale either. So if you have a method with reference for oxidation of anethole on the 50-200g level please post it...
20 g anise oil was suspended in a mixture of 150 mL water and 30 mL conc. sulfuric acid; addition of 55 g sodium bichromate at such a rate that the temperature did not exceed 40°C. The reaction mixture was extracted with 4 x 125 mL toluene and the solvent evaporated. The residual oil was vacuum distilled to yield 9.1 g anisaldehyde.
Know of a better way? With specific results of anisaldehyde.
https://www.thevespiary.org/rhodium/Rhodium/chemistry/benzaldehydes.kmno4.html (https://www.thevespiary.org/rhodium/Rhodium/chemistry/benzaldehydes.kmno4.html)
https://www.thevespiary.org/rhodium/Rhodium/chemistry/alkene2aldehyde.kmno4-thf.html (https://www.thevespiary.org/rhodium/Rhodium/chemistry/alkene2aldehyde.kmno4-thf.html)
Post 474827 (https://www.thevespiary.org/talk/index.php?topic=9658.msg47482700#msg47482700)
(hypo: "wanted:otc _and_ largescale PhCH=CHCH3 -> PHCHO", Methods Discourse)
Post 444195 (https://www.thevespiary.org/talk/index.php?topic=9307.msg44419500#msg44419500)
(GC_MS: "Contest: anise oil as MDMA precursor", Methods Discourse)
I don't think it's fair of you to expect an article giving the exact conditions for your exact oxidation in exactly the scale you want, with no experimentation on your part. Especially when you are willing to do all kinds of experimentation to make dichromate.
Clandestine chemistry can be green chemistry too.
I wouldn't want to trip on anything that caused the poisoning of a river somewhere. Bad karma, ya know?
I will continue to explore beilstein for interesting articles related to this.
If you were going to process enough material to make chromium recycling worthwhile, I think an ozone generator would bee a worthy investment. Think about the cost of the precursor chemicals (-->$0). Ozonolysis yields are supposed to be quite good.