Electrochemical Synthesis of Organic Polysulfides from Disulfides by Sulfur Insertion from S8 and an Unexpected Solvent Effect on the Product Distribution

Abstract An electrochemical synthesis of organic polysulfides through sulfur insertion from elemental sulfur to disulfides or thiols is introduced. The highly economic, low‐sensitive and low‐priced reaction gives a mixture of polysulfides, whose distribution can be influenced by the addition of different amounts of carbon disulfide as co‐solvent. To describe the variable distribution function of the polysulfides, a novel parameter, the “absorbance average sulfur amount in polysulfides” (SAP) was introduced and defined on the basis of the “number average molar mass” used in polymer chemistry. Various organic polysulfides were synthesized with variable volume fractions of carbon disulfide, and the yield of each polysulfide was determined by quantitative 13C NMR. Moreover, by using two symmetrical disulfides or a disulfide and a thiol as starting materials, a mixture of symmetrical and asymmetrical polysulfides could be obtained.


General information
All reactions were carried out under atmospheric conditions. The used solvents were purchased in high purity (HPLC grade). Commercially available chemicals were used without further purification. Electrolysis were executed in undivided under constant current (drawing/photo see Figure S1). Therefore, a laboratory power supply from Aim TTi MX100T Triple Output Multi-Range DC Power Supply (35 V, 3 A) was used. As electrode materials platinum plates (dimensions 35 mm x 10 mm x 0.5 mm, purity min. 99.95%), glassy carbon plates (dimensions 35 mm x 10 mm x 0.5 mm), carbon roving (6 k, 400 tex), copper (Cu-DHP according to ENCW024A, dimensions 35 mm x 10 mm x 0.5 mm) and stainless steel (material number 1.4571 according to EN10027-2, dimensions 35 mm x 10 mm x 0.5 mm) were utilised.
NMR spectra were recorded on a Bruker Avance III spectrometer utilising pre-set pulse programs. The measurements were performed at room temperature. The chemical shifts are given in parts per million (ppm). Calibration was done by referring to the residual solvent signal (CDCl3: 1 H NMR 7.26 ppm, 13 C NMR 77.16 ppm) in relation to tetramethylsilane. Quantitative 13 C NMR spectra were measured with a relaxation time of 30 s per scan.
HPLC-UV spectra were recorded on an Agilent 1220 infinity II with a reverse phase (EC-C18) column poroshell 120 (4.6 mm x 150 mm, 2.7 μm particle size). A UV-Vis detector was used at a wavelength of 248 nm. As mobile phase, methanol at a flow rate of 0.5 mL/min was used.
HR-MS (High resolution mass spectra) were recorded on a Thermo Scientific DFS spectrometer using electron ionization (EI) at an energy of 40 eV.
GC-MS measurements were performed on a Shimadzu GCMS-QP2020. As capillary column an Optima 5 HT from Macherey-Nagel was used (length 30 m, inner diameter 0.25 mm, film thickness 0.25 μm). The ionisation was accomplished by electron impact (EI) with an energy of 70 eV.
GC-FID measurements were carried out on a Shimadzu GC-2010 Plus gas chromatograph with an Optima 5 MS capillary column from Macherey-Nagel (length 15 m, inner diameter 0.25 mm, film thickness 0.25 μm).
CV (Cyclic voltammetry) measurements were carried out on a BAS C3 cell stand and a BAS 100 electrochemical analyzer using a glassy carbon disk working electrode (2.0 mm diameter) and platinum wire counter electrode (0.5 mm diameter). Potentials were referred to a saturated Ag/AgCl (3 M NaCl) reference electrode.        Figure S2: 1 H NMR of di-n-butyl disulfide (1a) in CDCl3 at 500 MHz and rt.                    : 1 H NMR of the di-p-methoxyphenyl polysulfide mixture (5b-5f) in CDCl3 at 500 MHz and rt. Figure S23: 13 C NMR of the di-p-methoxyphenyl polysulfide mixture (5b-5f) in CDCl3 at 126 MHz and rt. Figure S24: 1 H NMR of the di-n-dodecyl polysulfide mixture (6a-6f) in CDCl3 at 500 MHz and rt. Figure S25: 13 C NMR of the di-n-dodecyl polysulfide mixture (6a-6f) in CDCl3 at 126 MHz and rt. Figure S26: 1 H NMR of the di-n-butyl polysulfides (1b-1f), the dicyclohexyl polysulfides (2b-2f) and the nbutylcyclohexyl polysulfides (7a-7e) in CDCl3 at 500 MHz and rt. Figure S27: 13 C NMR of the di-n-butyl polysulfides (1b-1f), the dicyclohexyl polysulfides (2b-2f) and the nbutylcyclohexyl polysulfides (7a-7e) in CDCl3 at 126 MHz and rt. Figure S28: 1 H NMR of di-n-dodecyl polysulfides (6b-6f), the dicyclohexyl polysulfides (2b-2f) and the cyclohexyl-n-dodecyl polysulfides (8a-8f) in CDCl3 at 500 MHz and rt. Figure S29: 13 C NMR of the di-n-dodecyl polysulfides (6b-6f), the dicyclohexyl polysulfides (2b-2f) and the cyclohexyl-n-dodecyl polysulfides (8a-8f) in CDCl3 at 126 MHz and rt. Figure S30: Quantitative 13 C NMR spectrum of the di-n-butyl polysulfides (1b-1j) from setup A (solvent DCM) at 126 MHz and rt with benzophenone as internal standard. The integral of benzophenone is set the way that the integral of each polysulfide represents its absolute yield. Figure S31: Quantitative 13 C NMR spectrum of the di-n-butyl polysulfides (1b-1j) from setup B (solvent DCM + 10% (vol.) CS2) at 126 MHz and rt with benzophenone as internal standard. The integral of benzophenone is set the way that the integral of each polysulfide represents its absolute yield. Figure S32: Quantitative 13 C NMR spectrum of the dicyclohexyl polysulfides (2b-2f) from setup A (solvent DCM) at 126 MHz and rt with benzophenone as internal standard. The integral of benzophenone is set the way that the integral of each polysulfide represents its absolute yield. Figure S33: Quantitative 13 C NMR spectrum of the dicyclohexyl polysulfides (2b-2f) from setup B (solvent DCM + 10% (vol.) CS2) at 126 MHz and rt with benzophenone as internal standard. The integral of benzophenone is set the way that the integral of each polysulfide represents its absolute yield. Figure S34: Quantitative 13 C NMR spectrum of the diphenyl polysulfides (3b-3d) from setup A (solvent DCM) at 126 MHz and rt with benzophenone as internal standard. The integral of benzophenone is set the way that the integral of each polysulfide represents its absolute yield. Figure S35: Quantitative 13 C NMR spectrum of the diphenyl polysulfides (3b-3d) from setup B (solvent DCM + 10% (vol.) CS2) at 126 MHz and rt with benzophenone as internal standard. The integral of benzophenone is set the way that the integral of each polysulfide represents its absolute yield. Figure S36: Quantitative 13 C NMR spectrum of the di-p-tolyl polysulfides (4b-4g) from setup A (solvent DCM) at 126 MHz and rt with benzophenone as internal standard. The integral of benzophenone is set the way that the integral of each polysulfide represents its absolute yield. Figure S37: Quantitative 13 C NMR spectrum of the di-p-tolyl polysulfides (4b-4g) from setup B (solvent DCM + 10% (vol.) CS2) at 126 MHz and rt with benzophenone as internal standard. The integral of benzophenone is set the way that the integral of each polysulfide represents its absolute yield. Figure S38: Quantitative 13 C NMR spectrum of the di-p-methoxyphenyl polysulfides (5b-5f) from setup A (solvent DCM) at 126 MHz and rt with benzophenone as internal standard. The integral of benzophenone is set the way that the integral of each polysulfide represents its absolute yield. Figure S39: Quantitative 13 C NMR spectrum of th edi-p-methoxyphenyl polysulfides (5b-5f) from setup B (solvent DCM + 10% (vol.) CS2) at 126 MHz and rt with benzophenone as internal standard. The integral of benzophenone is set the way that the integral of each polysulfide represents its absolute yield. Figure S40: Quantitative 13 C NMR spectrum of the di-n-dodecyl polysulfides (6a-6f) from setup A (solvent DCM) at 126 MHz and rt with benzophenone as internal standard. The integral of benzophenone is set the way that the integral of each polysulfide represents its absolute yield. Figure S41: Quantitative 13 C NMR spectrum of the di-n-dodecyl polysulfides (6a-6f) from setup B (solvent DCM + 10% (vol.) CS2) at 126 MHz and rt with benzophenone as internal standard. The integral of benzophenone is set the way that the integral of each polysulfide represents its absolute yield.

Definition of SAP248 and dispersity Đ
According to the number average molar mass in polymer chemistry, we define the "absorbance average sulfur amount in polysulfides at 248 nm" (SAP248) as (1) ,248 : referenced HPLC-integral of polysulfide at 248 nm (S): number of sulfur equivalents in polysulfide The SAP248 is based on the specific absorption-wavelength of organic polysulfides (248 nm). The SAP248 gives the average amount of sulfur atoms in polysulfides calculated on referenced HPLC-UV-spectra. The SAP therefore depends on the absorption coefficients and their ratios of a polysulfide. The SAP is suitable for comparison of a single polysulfide, not for comparison of different polysulfides nor for giving the absolute average sulfur amount.
Based on the mass average molar mass and following from (1) applies ,248 : referenced HPLC-integral of polysulfide at 248 nm (S): number of sulfur equivalents in polysulfide With (1) and (2) the dispersity is defined as