Sciencemadness Discussion Board - quaternary ammonium salt reaction

quaternary ammonium salt reaction

Magpie - 5-7-2011 at 19:29

I have a generic question, based on a JACS paper* I have been reading.

The paper states that S-benzylthiuronic chloride, a quaternary ammonium salt, will react with sodium benzenesulfonate, a salt, to form a 3rd salt. This derivative then can be obtained by crystallization. It has a melting point that can be used in the identification of the benzenesulfonate (and other arylsulfonates, for that matter).

This is something new to me, ie, two organic salts reacting to form an apparently less soluble, 3rd organic salt. I wasn't sure just what the product formula was, the paper not specifying same. But after doing a little math I have come to these conclusions:

1. All 3 hydrogens of the quaternary amine functional group (R1-NH3+) are retained, as well as its positive charge.
2. The R2-SO3- functional group also retains its negative charge.
3. The dried salt, of course, is electrically neutral.

Is this interpretation correct, or does it sound reasonable?

*"The Identification of Sulfonic Acids" by Chambers & Watt, November 8, 1940

[Edited on 6-7-2011 by Magpie]

Paddywhacker - 6-7-2011 at 00:28

Quote: Originally posted by Magpie

... two organic salts reacting to form an apparently less soluble, 3rd organic salt...
[Edited on 6-7-2011 by Magpie]

and sodium chloride.

497 - 6-7-2011 at 03:58

I don't see how S-Benzyltiuronium chloride which is what I'm assuming they meant is a quaternary ammonium salt.

ScienceSquirrel - 6-7-2011 at 04:52

Quote: Originally posted by 497

I don't see how S-Benzyltiuronium chloride which is what I'm assuming they meant is a quaternary ammonium salt.

That is easy, the proton should be attached to the nitrogen and not the chlorine.
The salt is similar to urea nitrate.

Magpie - 6-7-2011 at 06:38

Quote: Originally posted by ScienceSquirrel

That is easy, the proton should be attached to the nitrogen and not the chlorine.
The salt is similar to urea nitrate.

Yes, that's my understanding:

497 - 6-7-2011 at 21:29

I always thought they were more along the lines of this:
http://en.wikipedia.org/wiki/Quaternary_ammonium_cation

Magpie - 7-7-2011 at 05:00

Quote: Originally posted by 497

I always thought they were more along the lines of this:
http://en.wikipedia.org/wiki/Quaternary_ammonium_cation

That's what SS and I are saying. The graphic I show (copypasta) is an inaccurate representation as it shows the proton as part of HCl.

not_important - 7-7-2011 at 09:35

Quote: Originally posted by Magpie

Quote: Originally posted by 497

I always thought they were more along the lines of this:
http://en.wikipedia.org/wiki/Quaternary_ammonium_cation

That's what SS and I are saying. The graphic I show (copypasta) is an inaccurate representation as it shows the proton as part of HCl.

But subject compound is RNH3(+), not RR'R''R'''N(+) - which is a quant salt. S-Benzyltiuronium chloride is a substituted ammonium chloride, used to prepare derivatives of acids (carboxylic, sulfonic, ...) for identification purposes. When reacting with a sulfonic acid, HCl is liberated as the benzyltiuronium salt of the sulfonic acid is formed.

http://pubs.acs.org/doi/abs/10.1021/ja01260a501

Magpie - 7-7-2011 at 11:19

Yes, I see. So the subject compound is a primary ammonium salt, correct? And it would lose its proton under sufficiently basic conditions, yielding an amine?

not_important - 7-7-2011 at 11:57

I assume so, but ...

the S-benzyltiuronium R-S-C(=NH)(NH3) is a derivative of thiourea S=C(NH2)2. I'm not at all sure what the C=NH will do on neutralisation. Note that salts such as Me-S(+)=C(NMe2)2 can be formed, or compounds that have resonance structures like that plus Me-S-C(=NMe2)(NMe2) (+).

Magpie - 7-7-2011 at 12:43

Quote: Originally posted by not_important

I'm not at all sure what the C=NH will do on neutralisation.

The JACS paper I referenced lead me to believe that only the -NH3+ group is affected. I deduced this by calculating %N and %S in agreement with the values in the paper.

Here's the paper:

http://pubs.acs.org/doi/abs/10.1021/jo01203a002

-------------------------------------

Correction: This reagent is covered in Vogel. The form represented there does not define where the proton attaches, ie, at the -NH2 or the =NH. In fact, I wonder if this is the reason for the two isomers that have different melting points.

[Edited on 7-7-2011 by Magpie]