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Author: Subject: Preparation of SCl2
Magpie
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[*] posted on 17-11-2017 at 16:23
Preparation of SCl2


Preparation of SCl2 (Sulfur Dichloride) November 17, 2017

A. Introduction
This procedure follows the method of Len1 (ref 1) at 0.57 scale.

TCCA + 3HCl --→ 3Cl2 + cyanuric acid

S2Cl2 +Cl2 --→ 2SCl2

B. Reagents
118g S2Cl2
115.5g TCCA (C3N3Cl3O3) (10% excess)
17.6g HCl (10% excess) as a 15wt% aqueous solution
CaCl2 pellets
0.1g steel wool
perfluoropolyether grease, eg, Krytox

C. Apparatus
a. Reactor
1. Place the S2Cl2 in a 1000ml 2-neck rbf (the reactor) installed in an ice-water bowl.
2. Add 0.1g of steel wool. This forms a small amount of FeCl3 catalyst which substantially enhances the absorption of chlorine (see ref 1).
3. Install a sparge tube in the side-neck of the rbf with opening located a few mm above the bottom of the reactor.
4. Install a reflux condenser on ice-water in the center neck.

b. Chlorine Generator
1. Construct a chlorine generator using a 500ml 2-neck rbf.
2. Attach a 120mL p-e funnel to the center neck of the rbf.
3. Attach an outlet hose to the side-neck. Connect this hose to the sparge tube of the reactor via a drying tube with CaCl2 pellets.

Grease all ground-glass connections with perfluoropolyether (Krytox) grease to prevent the formation of difficult to remove white crud.

The complete apparatus is shown here:

SCl2 apparatus.JPG - 150kB

D. Procedure
1. Add the 15% HCl at 1-2 drop/s which will generate chlorine at 150-300mL/min. This will take about 36 minutes.

SCl2 pot.JPG - 138kB

From Len1 at full scale: “After approximately 400mL of HCl has been consumed in the chlorine generator, substantial reflux commences in the reagent flask due to the consumption of S2Cl2 and a corresponding drop in the boiling point of the mixture, with chlorine gas starting to appear at the condenser. Chlorine generation is now stopped and the weight of the deep red liquid product is found to be 324.5g, corresponding to a 100% yield of SCl2....”

2. Filter the product SCl2 to remove the undissolved steel wool and any elemental sulfur.

E. Results
My yield of SCl2 is 135.5g for a %yield of 75.3%.

F. Discussion
I forgot to install a CaCl2 drying tube in the Cl2 feed to the reactor. This resulted in a small amount of the S2Cl2 being converted to elemental sulfur per the following reaction:

2S2Cl2 + 2H2O --→ SO2 + 4HCl + 3/8S8

The following photo shows this sulfur floating on the surface.

SCl2 pot with sulfur.JPG - 112kB


The picture in Len1’s book, p. 194, is incorrect for this synthesis. I will place a tiny amount of blame on this for my not installing the gas drying tube.

G. Reference
1. Small-Scale Synthesis of Laboratory Reagents, p. 194, by Leonid Lerner, 2011, CRC Press

Corrections, questions, and comments are welcomed.

























[Edited on 18-11-2017 by Magpie]

[Edited on 18-11-2017 by Magpie]

[Edited on 18-11-2017 by Magpie]

[Edited on 18-11-2017 by Magpie]

[Edited on 18-11-2017 by Magpie]




The single most important condition for a successful synthesis is good mixing - Nicodem
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AvBaeyer
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[*] posted on 17-11-2017 at 20:19


Magpie,

Nice experiment and write up, as usual. You continue to exceed expectations!

AvB

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Magpie
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[*] posted on 17-11-2017 at 20:47


Thank you AvB. I have some more interesting syntheses planned but first must get my new stepper motor electronics repaired.



new stpper motor.JPG - 164kB




The single most important condition for a successful synthesis is good mixing - Nicodem
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