A Convenient Synthesis of Thiol, Trithiocarbonate and Disulfide

<div>Synthesis of unsymmetrical trithiocarbonate sulfonate salt, along with disulfide, thiol and</div><div>symmetrical trithiocarbonate from 3-mercapto-1-propane-sulfonicacid, sodium salt with, without</div><div>of phase transfer catalyst and under various reaction conditions are described. The obtained</div><div>compounds having divergent usefulness in RAFT polymerization, sulfonyl preparation and</div><div>having capable of binding in a multidentate fashion to soft transition metal ions.</div>


INTRODUCTION
The industrial demand for novel synthetic materials with specific properties is constantly growing. From an academic point of view, this has resulted in tremendous effort being put into the research and development of new methods of polymerization that yield polymers with tailored structures and the desired properties. Preparation of polymers with controlled architectures can be achieved by making use of controlled polymerization 1-2 techniques such as ionic polymerization, nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP), and lately, (RAFT) reversible addition fragmentation chain transfer polymerization. 3 Of all these methods, RAFT polymerization is often reported as being the most versatile, as it is fairly tolerant to impurities and can be used with a wide range of monomers.
When bromo compounds not having beta phenyl group (2h-2j) gives unsymmetrical trithiocarbonate salt (3h-3j). Under this condition, it is observed that nitrile (4d) was hydrolyzed to amide and the methyl ester (4f) was saponified to corresponding acid. (Table-1).  (6). The compound 6 is freely soluble in water, and its structure is confirmed by single crystal data. (Table-2).  To understand the formation of sulfonate salt polymer 6 and its affecting the overall stability of unsymmetrical trithiocarbonate 3, and symmetrical trithiocarbonate 5. we carried out reaction by using one carbonless, ethane mercaptan sulfonate sodium salt as starting material and repeated the same sequence of reactions. After obtaining the stable intermediate 8, we treated with substrate 2b,2e and 2h in presence of PTC and obtained expected thiol 4b,4e and 9h in good to excellent yields. However, in absence of PTC, the substrates 2b and 2e (having acid group) gives stable unsymmetrical trithiocarbonate 9b and 9e in excellent yield. The phenyl substrate 2h gives 5h in 60% yield along with 11% undissociated 9h. (Table-4 All new compounds were isolated as air and moisture-stable solids. All compounds were fully characterized using 1 H and 13 C NMR spectroscopy and elemental analysis. Organic salts are freely soluble in polar organic solvents DMSO and DMF and moderately soluble in methanol and ethanol, and insoluble in most organic solvents. The compound 6 is freely soluble in sat. NaHCO3, pH = 9, 10% HCl, water and dmso. Sodium salt of Trithiocarbonate (3) can be useful for transfer surfactants in emulsion polymerizations and symmetrical trithiocarbonate (5) for sulfonyl chloride synthesis 21 . These compounds (5 and 7) possess multiple sulfur atoms and are thus capable of binding in a multidentate fashion to soft transition metal ions. 22-24 A reaction of these ligands with late transition metal ions is a current focus in our laboratory.

Conclusions
We have prepared a series of new unsymmetrical and symmetrical trithiocarbonate, thiol and disulfide compounds containing different other functional groups by using of commercially available, water soluble, mercaptan salt. The synthetic procedure is straightforward, and the products are obtained in good to excellent yields without any chromatographic purification.
Excellent solubility properties and the presence of electron donor groups on arms of trithiocarbonate described herein may be advantageous in applications RAFT polymerization and ligand preparation using transition metals.

ACKNOWLEDGMENTS
The authors thank the National Science Foundation and the Welch Foundation for support of this work. S.R.G is thanks to Professor Brent Sumerlin for supporting to complete the project.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests.

Data and materials availability: Requests for materials should be addressed to Sudershan
Gondi (gondisr@gmail.com)

EXPERIMENTAL SECTION:
3-mercapto-1-propane-sulfonicacid, sodium salt and carbon disulfide were obtained from Acros and Aldrich respectively. All other materials were reagent grade unless otherwise specified. All reactions were carried out in a dry nitrogen atmosphere. 1H and 13C NMR spectra were obtained on a 400-MHz Bruker Avance NMR spectrometer. Infrared spectra were obtained on a Nicolet Magna-IR 560 spectrometer E.S.P. Elemental analyses were obtained with a CE Elantech Thermo-Finnigan Flash 1112 CHN elemental analyzer. Melting points were collected on a TA Instruments DSC 2010 Differential Scanning Calorimeter using a heating rate of 108 o C/min and nitrogen as a purge gas.