Using a Hydrazone-Protected Benzenediazonium Salt to Introduce a Near-Monolayer of Benzaldehyde on Glassy Carbon Surfaces

Abstract

A methodology is described for introducing a thin layer of covalently attached benzaldehyde on glassy carbon surfaces using aryl diazonium chemistry. Usually the electroreduction of aryl diazonium salts leads to the formation of an ill-defined multilayer because of the involvement of highly reactive aryl radicals that can add to already-grafted aryl groups. However, in this study we used a two-step "formation-degradation" procedure to solve this problem with the first step consisting of an electrografting of an aryl diazonium salt of a long-chain and bulky alkyl hydrazone onto a glassy carbon surface. The design of the hydrazone group serves to minimize multilayer formation by greatly diminishing the grafting rate after the first-layer formation and at the same time preventing radical additions from taking place at the inner aryl ring. Another valuable property of the hydrazone group is that it easily can be deprotected to the corresponding aldehyde by acid hydrolysis (i.e., the degradation step). In this manner, a thin and well-defined film of covalently attached benzaldehyde with an estimated coverage of 4 x 10(-10) mol cm(-2) was formed. The electrochemical responses of benzaldehyde were highly reproducible and largely independent of grafting medium (water or DMSO) and along with that also the thickness of the initially grafted film. AFM and contact angle measurements support the findings. The "formation-degradation" approach thus lays the foundation for carrying out further functionalization reactions in a controlled manner.

Amino functionalized thin films prepared from Gabriel synthesis applied on electrografted diazonium salts

“…The second method described as a ''formation-degradation'' process allows via the electrochemical grafting to fabricate monolayer or thin film on the electrodes with anchoring functions. Indeed, this was realized by cleavage of the protecting reactive group (such as a diaryl disulfide [23], a hydrazone group [24] or a function [25,26]) inside the thick electrografted film that remove the multilayer films and give free function (a thiol, an aldehyde or an ethynyl function were respectively obtained after electrochemical oxidation, acid hydrolysis or ammonium fluoride) for post-functionalization reactions.…”

Attractive double-layer forces and charge regulation upon interaction between electrografted amine layers and silica

“…In many technological applications, robust surface coatings that are resistant to harsh environments are a prerequisite, and an alternative way to prepare robust surface layers is to covalently bind functional groups on conducting surfaces by electrografting via electrochemical reduction of aryl diazonium salts [31] and aryl iodonium salts [32][33][34]. This technique has been applied to immobilize various functional groups such as alkylamine, thiophenolates, hydroxy and aldehydes [35,36] on surfaces such as glassy carbon (GC) [33,34] and metal oxides [37]. It has been shown that under certain conditions, aryl films formed from reduction of diazonium salts are even more strongly bound to gold surfaces than the thiol analogues [38].…”

Electrografting of calix[4]arenediazonium salts to form versatile robust platforms for spatially controlled surface functionalization

“…However, an undesirable counterback is the chemical inertness of these molecules, which precludes further functionalization. To remedy this problem, aryldiazonium salts bearing a pendant function masked by a protecting group exhibiting steric hinderance [28][29][30][31] and electronic shielding 29 properties have been used (Fig. 1d).…”