Sciencemadness Discussion Board - naphtol - alkali fusion - water?

naphtol - alkali fusion - water?

learningChem - 19-11-2012 at 21:38

This is from Gatterman

Quote:

MATERIALS required: 70 g. (0-3 mole) of sodium naphthalene-
3-sulphonate, 210 g. of sodium hydroxide, 20 c.c. of water.

The sodium hydroxide is powdered and, along with the water, is heated with stirring in a copper or nickel crucible to 280°.

As soon as the temperature has reached 280° the sodium
naphthalenesulphonate is added rather rapidly with stir-
ring ;

My question : what's the point of adding water? Wouldn't all the water be gone when the water/NaOH mix is heated? Surely at 280C all the water is gone?

rest of the procedure

Quote:

heating is continued with a somewhat smaller flame and the temperature is maintained between 260° and 280°. After all the salt has been added, the flame is raised somewhat, causing the molten material to become more viscous as steam is evolved and bubbles are formed. Finally, at 310°, the reaction proper sets in. After the temperature has been kept at 310°-320° for about five minutes the material becomes more mobile and the reaction is over.

Magpie - 19-11-2012 at 22:37

Quote: Originally posted by learningChem

...the flame is raised somewhat, causing the molten material to become more viscous as steam is evolved ....

learningChem - 19-11-2012 at 23:16

Yes, I saw that, but I'm not sure how it answers my question?

As far as I can tell, the first step is to add 10% of water to the NaOH, and then heat the mix to 280C - Wouldn't the water boil off?

watson.fawkes - 20-11-2012 at 05:22

It looks like the water may act as a mixing agent, bringing the reagents in more intimate contact with each other. The mention of the viscosity of the melt as the water leaves is a hint that melting first and mixing second doesn't work nearly as well.

learningChem - 20-11-2012 at 12:58

But as I understand the instructions, first NaOH and water are heated alone. Will the NaOH be molten at 280? (MP is 318...)

Anyway, I'm going to try it now.

(What I thought after making my 2nd post is that perhaps 'wet' NaOH won't get 'dry' at 280 and the MP of 'wet' NaOH is lower than 318?)

[Edited on 20-11-2012 by learningChem]

Magpie - 20-11-2012 at 16:10

You also might want to check out the procedure shown in Fierz-David, p. 188, in the forum library.

NaOH fusions are interesting, and challenging due to the high temperature required. I was only partially successful at making resorcinol from sodium benzene m-disulfonate even though I had proof that my homemade disulfonate was quite pure. I made a small molten metal bath for this purpose.

I would also like to make beta-naphthol via NaOH fusion. Please report your results.

[Edited on 21-11-2012 by Magpie]

[Edited on 21-11-2012 by Magpie]

learningChem - 20-11-2012 at 21:56

Magpie, thanks for the pointer! I had downloaded that book but forgot about it - I'll check it now.

Anyway, first attempt : mostly a failure.

I used 7g NaOH, ~1g H2O, 2.1g Na sulphonate.

I used a stainless steel cup as crucible. The amount of NaOH was too small and it barely covered the bottom of my crucible.
I put the thermometer in a copper tube closed at one end, but didn't realize that it wouldn't be easy to handle because the tube gets...hot. Also, Gatterman says to put a bit of oil inside the tube, but the only oil I have at hand is sunflower oil. I'm not sure if it can take ~320C(I'll check that tomorrow), so I skipped that part. Also the molten hydroxide barely covered the tip of the tube.

Long story short, I wasn't able to stir things easily or get accurate temperature readings.

The NaOH - 10% water mix is a slurry at room temperature. At ~220 - 250 it seems to melt somehow. The melt got yellow. I suppose something in the crucible is reacting with it...damn.

Anyway, I added the sulphonate when the thermometer reached ~280. In something like 30 seconds (I think) there was a grey oil floating on top of the NaOH. I let it cook for 3 or 4 minutes more but didn't see any frothing. The oil started to get darker so I removed the flame. I thought it was getting charred.

I let the melt cool in the crucible and then dissolved it in 50ml of water (or more). I got a brown mess that seemed to contain some kind of suspension. Neutralized it with HCl, the water moslty cleared and a dark brown precipitate appeared. I don't think it's naphthol though. Or maybe there's a bit of naphthol but most of it is charred.

Anyway, I'm going to try again tomorrow with a proper thermometer setup (picture) and a bigger batch.

learningChem - 21-11-2012 at 00:01

reaction