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Author: Subject: Symbol for hexavalent uranium?
chornedsnorkack
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[*] posted on 28-9-2022 at 21:32


Quote: Originally posted by teodor  
and there is a little point in an experiment if there is no hypothesis to check.

It is not only experiments that hypotheses are good for.
Hypotheses are also good for literature searches.

For example, some rules of thumb - expectations from theory about fluorides:
Most metals, indeed most elements but with significant exceptions, form fluorides by simple reaction with element fluorine. With fluorine excess, it is normally the higher fluoride. But fluorine is inconvenient to handle.

Among metals, the exceptions are those which form protective layer.
HF is a nonoxidizing acid, and weak at that. It may form fluorides, but then it would be the lower ones. Also since many fluorides are insoluble in water, even metals that dissolve in dilute HCl may resist dilute HF.
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teodor
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[*] posted on 28-9-2022 at 23:18


I think it is a good idea for an amateur chemist to have a table of dangers associated with different compounds.
It is almost of the same level of usefulness as the periodic table.

This is a small fragment from my personal table.

H2S 100 20
isopropyl bromide 10
benzene 500 10
naphthalene 250 10
CCl4 200 10
Acetic acid 50 10
pyridine 1000 5
phenol 250 5
SO2 100 5
aniline 100 5
dimethylaniline 100 5
Formic acid 30 5
Hcl and hydrochloric acid 50 5
Acetyl chloride 5
NO2, N2O3 20 5
Phenylhydrazine 15 5
HF 30 3

The first number is IDLH in ppm and the second is OSHA PEL.

When planning my amateur way to practically study reactions and choose what I will do as the next one I always consult with this table trying to get as much experience with compounds (or byproducts) from the top of the table before going down.
There are a lot of nice experiments with H2S, which has more or less satisfactory warning properties.
Isopropyl and other organic bromides open the world of Grignard reactions, also this is the way of water-free chemistry practice.
HCl in its gaseous form has many interesting properties, but it is less nasty than WF6 or BF3 and there is no much danger of doing experiments with it. If you will mess up with it you will feel it immediately.
Acetyl chloride is a nice beast with a broad usage in organic chemistry and also it could be used for making anhydrous transition metal halides. It works for some of them and doesn't work for others.
NO, NO2, N2O3, N2O4, N2O5 is a more "advanced" family of compounds with very interesting water-free chemistry.
And after managing those (which include practice in all things like apparatus design, glassblowing, heating, cooling, distillation, vacuum, and fume hood building) it is wise (in my opinion) to go to the BF3 family of compounds and then to other fluorides.
But OK, it is just the way how I do it.
I know some scientists are associated with fluorine chemistry only.

[Edited on 29-9-2022 by teodor]
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chornedsnorkack
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[*] posted on 28-9-2022 at 23:51


Quote: Originally posted by teodor  
I think it is a good idea for an amateur chemist to have a table of dangers associated with different compounds.
It is almost of the same level of usefulness as the periodic table.

This is a small fragment from my personal table.

H2S 100 20
isopropyl bromide 10
benzene 500 10
naphthalene 250 10
CCl4 200 10
Acetic acid 50 10
pyridine 1000 5
phenol 250 5
SO2 100 5
aniline 100 5
dimethylaniline 100 5
Formic acid 30 5
Hcl and hydrochloric acid 50 5
Acetyl chloride 5
NO2, N2O3 20 5
Phenylhydrazine 15 5
HF 30 3

The first number is IDLH in ppm and the second is OSHA PEL.


A suggestion here: IDLH and PEL are different, but still somewhat duplicating in the meaning... How about adding the room temperature vapour pressure (in the ppm units)? This way you can immediately recognize which substances are nonvolatile and safe unless sprayed, and which need only slight dilution to reach safe levels.
Soluble vapours would need more complex handling in how the vapour pressure depends on concentration.
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teodor
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[*] posted on 29-9-2022 at 00:00


A good point. A very good point. But well, I can imagine vapor pressure by experience for most of them. The extreme case is distillation or reflux and it is used very often for many types of compounds.

As for triffic acid, in my collection there are those publications:
https://sci-hub.se/https://doi.org/10.1039/JR9560000173
https://sci-hub.se/https://doi.org/10.1039/JR9540004228
https://sci-hub.se/https://doi.org/10.1039/JR9570004069
All of them are pre - 1960.

Please inform me if there are modern reviews of new discoveries here after 1960.

[Update]. OK, I found 2 reviews after 1960:
1. Senning dit it in 1965 (A. Senning is also known as the editor of 4 volumes set "Sulfur in Organic and Inorganic Chemistry", but these books which are covering many possible sulfur compounds don't cover for some reason the compounds with S-C bond).
2. https://sci-hub.se/https://doi.org/10.1021/cr60305a005 - this is probably the last (Wikipedia points to it). It was done in 1977.

So, this is just to illustrate my theory that the priorities in the "official science" were changed in the mid of 1970s.


[Edited on 29-9-2022 by teodor]

[Edited on 29-9-2022 by teodor]

[Edited on 29-9-2022 by teodor]
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Bedlasky
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[*] posted on 29-9-2022 at 12:54


Quote: Originally posted by chornedsnorkack  
Among metals, the exceptions are those which form protective layer.
HF is a nonoxidizing acid, and weak at that. It may form fluorides, but then it would be the lower ones. Also since many fluorides are insoluble in water, even metals that dissolve in dilute HCl may resist dilute HF.


Mixture of HNO3 and HF is very good for dissolving some really resistant metals like Nb, Ta, Zr and Hf. Nb and Ta can be dissolved only in this acid mixture.

[Edited on 29-9-2022 by Bedlasky]
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[*] posted on 29-9-2022 at 23:02


Quote: Originally posted by Gammatron  
One of the many cool aspects of uranium is that the complexities of it's compounds varies from extremely simple to insanely complex and reaching that realm of extremity is what motivates me to try to understand everything I am doing and desire to do. UF6 is definitely on the list of aspirations but I know my understand is far too behind to attempt such a synthesis.


It is not only a matter of understanding. Another is a matter of equipment. It would also be a big achievement of understanding if you understood exactly what equipment you would need to handle UF6, and why (equipment that you do not have).
The trivially simple approach which is used industrially to produce UF6 and WF6 industrially is simply to add gaseous fluorine either to the metal or to a lower fluoride:
W+3F2=WF6
UF4+F2=UF6
These require fluorine and apparatus to handle it.
Looking around other synthetic routes to fluorides?
A standard route is metathesis of oxides. But this is mostly suitable for lower fluorides:
CaO+2HF=CaF2+H2O
Goes to completion, easy way to get CaF2 or get rid of HF. CaF2 is perfectly stable and safe staying around in water or moist air or soil.
SiO2+4HF<>SiF4+2H2O
That reaction also happens easily, HF etches glass (which is why it is hard to handle) - but unlike CaF2, it is easily reversed. SiF4 reacts with excess of water and gives back HF and SiO2
Likewise
UO2+4HF<>UF4+2H2O
Standard way to produce UF4, but unlike CaF2, UF4 left lying in moist air slowly hydrolyses and gives off poisonous and corrosive HF fumes.
UO3+6HF<UF6+3H2O
You cannot get UF6 by simply reacting UO3 with HF. Because this reaction goes entirely in the direction of HF from UF6. (Maybe you could get UO2F2, but not all the way to UF6).
This is an issue with higher fluorides and other halides. Since the elements in higher coordination number prefer one oxygen to two halogens, they have tendency to exchange towards bonding to oxygen. If what you want is the element coordinated to halogens only, one thing you need to consider is excluding sources of oxygen like water or even HNO3.
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