Absolutely. I remember you wrote a good answer for the chromate-dichromate equilibrium using a mechanism-based approach. I'm all ears for something similar here :D

@AniruddhaDeb Ok then

Initially the steps would be similar, as in, we should try and get a molecular formula of the form (SxOyClzNa)3

But instead of trying to put in values of the variables, we will try and use this formula as a guide to verify what we get after proposing a mechanism

Initially, if you try and analyse the structures of some of the other common trimers we have, like $\ce{S3O9}$ and $\ce{Si3O9^6-}$ , we can observe some general trends:

In the monomers for each of these guys, that is, $\ce{SO3}$ and $\ce{SiO3^2-}$ , the central atom (which is a 2nd period element) only occurs once. Also, in the complete trimer, the oxygen is present as an "outlying atom"( that is, it is not present as a part of the ring), hanging outside the ring in a double or single bonded fashion as the case maybe( in the former, it also functions as a connecting atom but that is an additional property along with the two "outlying" oxygens)

Also, the three monomers can combine in the following fashion to form the trimer( I will be making it out for $\ce{S3O9}$ as it is a neutral molecule and therefore more relevant to the case we have at hand, but a similar pathway can be made for the silicate anion as well:

So, keeping this in mind, we can now look at the reagents

$\ce{SOCl2}$ and $\ce{NaN3}$

$\ce{SOCl2}$ as a reagent is famous for chlorination, and follows an addition-elimination mechanism as follows:

But the more interesting and perhaps, the major directing reagent in the reaction is sodium azide

As a reagent, azides are pretty famous for releasing nitrogen gas, and supplying a nitrogen in whatever reactions they are involved

This can be the basic scheme for almost all reactions, and it provides us a basis for guessing the initial stoichiometry of the reactants

One guess for the number of coefficients of the reagents can be 3 $\ce{SOCl2}$ and a single mole of $\ce{NaN3}$

I got the trimer part but still didn't understand how sodium azide would be able to take part in that reaction. The reaction you're showing is a curtius rearrangement (if I recall correctly)

Yeah I will explain that once I actually start making out the mechanism

so Na+[-N=N+=N-] + O=SCl2 is the mechanism in question

But right now, what you need to realise about azide reacting is that: a single mole of azide can only supply a single nitrogen, while it releases the other two nitrogens as gas

yep I got that part

Yeah, but see, this nature of azide as a reagent will cause problems in taking the coefficients as 3 and 1

I cant seem to find a suitable resonance structure of azide that explains this

Ideally were

That the azide releases nitrogen gas?

I am sorry, i guess i didn't follow what you're trying to explain

Ideally we're looking for a structure like N≡N->N-

what Im trying to do is instead of having an R-OH in the reaction with SOCl2, Im trying to see if I can make that reaction happen with an azide molecule

Yes that's what I will be doing, and that will give us what we want eventually, but we will have to tweak the stoichiometry to ge there

My point was that only: you can't use a single azide molecule to get all the three monomers required for the trimerization

even tho stoichiometrically it would make sense

because an azide molecule wastes 2 nitogens as gas

so you have to take 3 $\ce{SOCl2}$ and also 3 $\ce{NaN3}$

Ah ok I realize now. Ill have to tweak that reaction in that case

To get the 3 monomers

On a different note, thanks for the answer for the gauche ethanol question

Yep, now to the actual mechanism, I will ask you to try it out with arrow pushing diagram yourself while I make it out and send it. These are enough hints I guess to get started on it, the way I made mechanisms in the chromate question

You're welcome :)

Yep Im trying on my end as well

Ok I am done with the monomer formation. Should I send the image or are you still trying? @AniruddhaDeb

Ok since I am short on time,I am gonna go and upload what I have made here with my reasoning. You can see after trying and tell me if you agree or diagree

This is pretty much using the organic mechanisms analogies that I had sent above. In the same manner, 3 $\ce{SOCl2}$ molecules will react with 3 $\ce{NaN3}$ molecules to give rise to 3 monomers. These monomers can then trimerize as follows:

This now holds a few points of interest: why did I trimerize in this way only? Firstly, because nitrogen is generally more nucleophilic than oxygen due to electronegativity concerns, so I used nitrogen to attack on sulphur. You may try to counter this argument by pointing out the -I effect of the chlorine, but I would say it's a minor concern, and on top of that, if you recall the initial observation we had made with the $\ce{SO3}$ and $\ce{SiO3^2-}$ trimers, about how the oxygen atoms tend to..

..be the "outlying" atoms bonded to the central atom by double or single bonds. Using that observation, I could say that in the particular way of trimerization shown above, oxygen atom would become the "outlier" which has already been observed in a few previous known cases, and so it's more likely to happen. Rest is pretty simply observing that sulphur has only five bonds in the second step while it's maximum capacity is six, while on the other hand nitrogen is bearing a formal positive charge..

..due to the extra bond. So a simple [1,2] rearrangement will yield a neutral yet aromatic compound for the answer. Now it can be verified using the initial variable formula which was generated and also using the mass percentage of chlorine provided in the question

I had come up with a different structure and was debating the feasibility of it.

Yours seems way more logical than mine. I also didn't think of the 1,2-shift during trimerization.

@AniruddhaDeb Okay.. Well, do you have any questions for me? I just felt this is a better way than what you had put up in your blog,you would have been stuck in an endless loop if your answer hadn't matched with the mass percent when you put all coefficients as 1(no offence intended) :)

None taken :)

I'm still not completely convinced of the 1,2 shift of the Cl atoms though. I'll do a bit more research on that.

Thanks a lot for reaching out. I'll update my blog with this mechanism and give you a mention as well

Well, it's not exactly something definitive... But the thing is, pericyclic reactions tend to happen quite easily in close quarters,esepecially rearrangement which lead to more stable configurations as the energy is compensated in this case

You see, the [1,2] hydrogen shifts also happen because the intramolecular rearrangement can happen very closely,so the collision of the concerned part of the molecule(the intended bonds) is very easy as they are adjacent

So as such if you think about it,such rearrangements might not be a surprising thing even in a normal state of a molecule,as it may keep occuring and reversing dynamically

That does make sense.

Altho yes,it can only be testified or rejected by proof,but hust as good a probable method to solve the question as any :)

Better to have some hint at a mechanism than simply waiting for proof and not have any logic,is what I say :)

this article seems to mention a chlorine shift but is behind a paywall :?

Enter the doi at this website to get behind the paywall

holy crap thats awesome lol

Yeah, neat little trick.. Don't need to worry about firewalls

*paywalls xD

Altho i removed the name since i guess it's not exactly liked by the scientific community

You got the name right?

Yeah I got it

One wonders why do they have paywalls in the first place

Because it's proprietary work I guess ,and the authors want citations or whatever.. Anyway,I don't wanna get in the politics of it :)

[Aaron Swartz] (en.wikipedia.org/wiki/…), if you've heard of him, was very involved in removing this stuff.

No I hadn't heard of him,but yeah,seems like he got into a lotta trouble :)

Anyway nice talking to you. We'll meet again on chat, I'm sure

See ya around :)

Yeah, and I guess you should put this IcHO questions up on the mai site where I can answer it in the way I showed you

Might help a few other people as well :)

@AniruddhaDeb See ya :)

I updated the article. You can check it out here. The Chlorine shift makes more sense when you draw the negative charges on the Sulphur atoms..

So sulphur ends up donating it's lone pair to Chlorine, which donates the bond pair electrons back to Nitrogen.

I noticed that you currently study at IISER. If you don't mind me asking, which one?

@AniruddhaDeb Ah yes, that makes sense :)

IISER Kolkata