Sciencemadness Discussion Board

Materials impervious to hot phosphoric and metaphosphoric acids

CobaltChloride - 21-4-2018 at 14:09

So I've heard that heating phosphoric acid to high temperatures makes it lose water and become metaphosphoric acid, which is an excellent dehydrating agent, but hot phosphoric acid corrodes glass quite a lot. Is there any material more resistant to these acids in these conditions besides borosilicate glass? PTFE should chemically resist them, but the high temperatures cause it to degrade.

BromicAcid - 21-4-2018 at 15:25

Check out this thread on metaphosphoric acid

http://www.sciencemadness.org/talk/viewthread.php?tid=4409

I think there is at least one other as well since everything I remember is not in that thread. Of note is that nickel had a catestropic failure. I had some success with copper as did another member but there was some attack on the vessel.

CobaltChloride - 22-4-2018 at 07:44

Of what I read there, gold plated copper crucibles sound the best. Now I just need to find a good way to do it.

Melgar - 22-4-2018 at 08:04

Okay, first of all, the corrosive effect of metaphosphoric acid comes from its similarity to glass. Phosphorus is right next to silicon on the periodic table, and forms a glassy substance that is slightly miscible with the stuff your glassware is made of. It doesn't exactly eat away at it, it's more like the substances are similar enough for them to mix a bit at high temperatures.

One solution is just to use cheap glassware, since the glass needs to be near its glass transition temperature in order for this to happen at an appreciable rate. Beakers and flasks are a couple bucks each when you buy them by the case. You can also use graphite or something, if you have a ton of money. However... you should try using an aluminum vessel. Hear me out. Aluminum phosphate is one of the most frustratingly insoluble, unreactive substances there is, and my educated guess is that as long as the aluminum doesn't melt, the phosphoric acid would form a passivating aluminum phosphate layer.

S.C. Wack - 22-4-2018 at 08:41

For ethylene from ethanol Weygand (1945) first dehydrates the stirred acid on porcelain, at 160-200C, Weygand/Hilgetag (1972) just heats 85% acid to 200-230C in a RBF and starts dripping in the alcohol. Is the product suitable for methaqualone though you wonder. Who knows.

Texium - 22-4-2018 at 15:48

Quote: Originally posted by S.C. Wack  
Is the product suitable for methaqualone though you wonder. Who knows.
Why would you assume that he's wondering that?

clearly_not_atara - 22-4-2018 at 17:34

Aluminium's compatibility with phosphoric acid is rated as "C-Fair". Sounds good to me. Will probably develop a patina but continue to work, as long as you only use the vessel for metaphosphoric acid it's fine.

S.C. Wack - 22-4-2018 at 18:17

Quote: Originally posted by Texium (zts16)  
Why would you assume that he's wondering that?

Was it not a perfectly nonspecific you, you being the reader? I wonder, because this is SM. Since you bring it up BTW what other threads has he started...phthalic anhydride just happens to be 2 steps away from anthranilic acid...

Amos - 22-4-2018 at 18:35

Quote: Originally posted by S.C. Wack  
Quote: Originally posted by Texium (zts16)  
Why would you assume that he's wondering that?

Was it not a perfectly nonspecific you, you being the reader? I wonder, because this is SM. Since you bring it up BTW what other threads has he started...phthalic anhydride just happens to be 2 steps away from anthranilic acid...


That's quite potentially because those are two reagents I've been discussing with him a lot in our group conversations on skype. Phthalic anhdyride I'm buying and selling, and metaphosphoric acid I have interest in for oleum. They're both extremely versatile reagents, I wonder why you thought of drugs first thing :thinking:

Melgar - 22-4-2018 at 20:03

Yeah, I mean, if I wanted anthranilic acid, I'd just buy methyl anthranilate on Amazon and cleave the ester. In the last year or so there have been some good finds on Amazon. They even had sodium borohydride at a really good price for a while. Got some benzaldehyde too, and even some phosphorous acid.

CobaltChloride - 22-4-2018 at 23:26

Quote: Originally posted by S.C. Wack  
Quote: Originally posted by Texium (zts16)  
Why would you assume that he's wondering that?

Was it not a perfectly nonspecific you, you being the reader? I wonder, because this is SM. Since you bring it up BTW what other threads has he started...phthalic anhydride just happens to be 2 steps away from anthranilic acid...

I am interested in phthalic anhydride because I consider the oxidation of naphthalene an easy beginner's oxidation and the phthalic anhydride can be used to make phenolphthalein and some fluorescent dyes. And I want to make metaphosphoric acid because I want to experiment with its properties and maybe make some oleum. I am NOT in any way interested in making anything illegal. Please don't assume the worst of people before you even have the chance to know them well.

CobaltChloride - 22-4-2018 at 23:36

Anyway, I'll tell you how the aluminium crucible works when I get my phosphoric acid.