A simple and rapid route to novel tetra(4-thiaalkyl)- ammonium bromides† Richard A. O'Brien, * a Christy Wheeler West, * b Brian E. Hollingsworth, b Alexandra C. Stenson, a Codey B. Henderson, a Arsalan Mirjafari, c Niloufar Mobarrez, a Kevin N. West, b Kaila M. Mattson, d E. Alan Salter, a Andrzej Wierzbicki a and James H. Davis, Jr. a A simple approach for the preparation of symmetrical quaternary ammonium bromides employing thiol– ene click chemistry is used to synthesize tetra(4-thiaalkyl)ammonium bromides. This approach allows the incorporation of a variety of alkyl moieties onto the nitrogen center with a one-step synthesis involving easy work-up, no side reactions and environmentally friendly reagents. To elucidate information regarding the behaviour of this novel class of compounds, comparisons to tetraalkylammonium analogues have been made. These include melting points, activity as phase-transfer catalysts, and conformational predictions from computational modelling. All results are consistent in indicating stronger bonding between the quaternary cation and the anion for the salts with 4-thiaalkyl chains as compared to those with n-alkyl chains. Introduction Quaternary ammonium salts or “quat salts” have been the mainstay of research and industrial use for phase transfer catalysis for over forty years beginning with the pioneering work of Starks, 1 Makosza 2 and Brandstrom. 3 In addition, the pub- lished literature since then has described a multitude of uses for quat salts, 4 including preparation of ionic liquids, 5 antimi- crobial agents, 6 disinfectants, 7 surfactants, 8 fabric soeners, 9 antistatic agents, 10 wood preservation, 11 osmolytes, 12 chemical capacitors, 13 electrolytes for batteries, 14 capping agents for copper nanoparticles, 15 and plant growth retardants. 16 Quaternary ammonium compounds are typically prepared by quaternization of tertiary amines with alkyl halides and by anion exchange reactions on commercially available salts. 17 Such a synthetic route poses a limit on the variety of quat salt structures based on availability of amines and alkyl halides. Under neutral or acidic environments, quat salts are generally stable up to 150  C. 18 Conversely, under basic conditions, their susceptibility to Hofmann elimination and thermal decompo- sition at temperatures above 100  C limit the utility of quat salts in applications requiring alkaline environments. 19 Previous work in our group 20 described the thiol–ene click reaction with tetraallylammonium bromide and 1-thiogylcerol to prepare a polyhydroxylated tetra(4-thiaalkyl)ammonium bromide with subsequent metathesis to form the correspond- ing ionic liquid. The use of the thiol–ene reaction to add four alkyl appendages to the ammonium cation was modelled aer the approach by Hawker et al. for the thiol–ene based assembly of functionalized dendrimers. 21 Since the introduction of the principles of click chemistry by Kolb et al. in 2001, 22 researchers in the areas of synthetic and materials science have strived to incorporate these into drug discovery, and into syntheses of small molecules, polymers, and advanced materials. According to these guiding principles, 23 click chemistry includes syntheses that: (a) are modular, (b) have high yields, (c) have by-products that are removable by non-chromatographic processes, (d) are stereospecic, (e) are insensitive to oxygen or water, (f) can be accomplished with readily available starting materials and reagents, (g) can be performed without solvent or in environmentally benign media, and, (h) are wide in scope. Our intent was to incorporate as many of these principles as possible into a synthetic route for a new class of quaternary ammonium salts and to investigate their use as phase transfer catalysts. a Department of Chemistry, University of South Alabama, Mobile, Alabama, USA, 36688. E-mail: robrien@southalabama.edu; Fax: +1 251-460-6370; Tel: +1 251-460- 7427 b Department of Chemical & Biomolecular Engineering, University of South Alabama, Mobile, Alabama, 36688, USA. E-mail: cwwest@southalabama.edu; Fax: +1 251- 460-1485; Tel: +1 251-460-7463 c Department of Chemistry and Physics, Florida Gulf Coast University, Fort Myers, Florida, 33965, USA d Department of Chemistry & Biochemistry and Materials Research Laboratory, University of California-Santa Barbara, Santa Barbara, California, 93106, USA † Electronic supplementary information (ESI) available: Chemical shi data for the NMR and ESI-MS analyses performed on the compounds synthesized. See DOI: 10.1039/c3ra44042g Cite this: RSC Adv., 2013, 3, 24612 Received 31st July 2013 Accepted 7th October 2013 DOI: 10.1039/c3ra44042g www.rsc.org/advances 24612 | RSC Adv., 2013, 3, 24612–24617 This journal is ª The Royal Society of Chemistry 2013 RSC Advances PAPER Published on 14 October 2013. Downloaded by University of South Alabama on 16/12/2014 16:39:32. View Article Online View Journal | View Issue