Carbon–Sulfur Bond Cleavage During Adsorption of Octadecane Thiol to Copper in Ethanol

Abstract

The effect of the solvent on the formation of thiol self-assembled monolayers (SAMs) on oxide-covered, reactive metals is more involved than in the well-studied gold-thiol system. In this work, copper covered with a native oxide was modified with 1-octadecanethiol (ODT) in either tetrahydrofuran (THF) or ethanol. Infrared (IR) spectroscopy indicated the formation of crystalline chain packing of alkyl chains from both solvents. Surface coverage was approximately equal in both systems, with differences in tilt angles of the chains. A detailed analysis by X-ray photoelectron spectroscopy (XPS) showed the formation of Cu 2 S and copper-bound carbon when the adsorption was carried out in ethanol. This observation can be explained by the cleavage of the 1 C-S bond in ODT during adsorption. Based on the analogy of preparations, we reason that the solvation of ODT in ethanol must be such that it weakens the C-S bond in ODT, thus enabling the cleavage of this bond. Based on the evidence presented here, it is not possible to distinguish between surface solvation and bulk solvation.Electrochemical linear sweep voltammetry show that SAMs from both solvents have an enhancing protective effect compared to the native oxide layer. The results from this work show interesting possibilities for the preparation of adsorbed monolayers with chemical interaction to reactive metals, with some similarities to carbene-based SAMs.

Mechanistic Framework for the Formation of Different Sulfur Species by Electron Irradiation of n-Dodecanethiol Self-Assembled Monolayers on Au(111) and Au(100)

“…For instance, with regards to the tendency to produce atomic sulfur, which was confirmed for many metals, [84][85][86][87] but for Au(111). Moreover, slight changes in the organic backbone can induce the breaking of S-Au bond, 65 which highlights that also the chemical nature of the thiol matters.…”

“…Although comparisons of many two-dimensional molecular layers with them have been very useful, our study represents an example of how this approach is usually overestimated. It has been shown that the surface chemistry of thiols on many metals is different than that found on Au(111), for instance, with regard to the tendency to produce atomic sulfur, which was confirmed for many metals − but for Au(111). Moreover, slight changes in the organic backbone can induce the breaking of the S–Au bond, which highlights that also the chemical nature of the thiol matters.…”

Atomic Sulfur Formation Mechanism on 3-Mercaptopropanoic Acid Derivative Self-Assembled Monolayers: Understanding the C–S Bond Cleavage

“…Contrary to the idea that atomic sulfur comes from contamination, 20 it can be formed along with the SAM formation, or as a consequence of thiolate degradation. 18,21 Indeed, the C-S bond breaking of alkanethiolates has been reported for many metals with distinguishing catalytic properties as Pd 22 , Ni 21 , Cu 23 , and Pt 24 . On the other hand, long-chained alkanethiols only lead to alkanethiolate species when are chemisorbed on Au.…”

“…Looking closely to the SAMs’ degradation processes, there are several factors that influence the extension of a possible C–S bond breaking. Among them are the composition and structure of the substrate, the temperature, the solvent, and the chemical nature of the thiol. ,,, Then, to understand the SAMs’ degradation mechanism, many variables must be considered. More importantly, during and after C–S bond scission, the roles of the different chemical bonds in the whole thiol have to be considered.…”

Atom Probe Study of 1-Octadecanethiol Self-Assembled Monolayers on Platinum (111) and (200) Surfaces

“…Another study investigated the C-S bond scission of ODT on Cu substrates covered with a natural oxide layer. It was assumed that the solvation of ODT in ethanol weakens the C-S bond and therefore make the bond scission possible (Rechmann et al, 2019). Another work reported the C-S bond cleave on Ni(111), also known for its strong catalytic activity, at room temperature and therefore a considerable amount of atomic sulfur in their measurements (Blobner et al, 2015) is reported.…”