mercaptosilanes

Mercaptosilanes, or mercapto silanes, are a class of organosilicon compounds that feature both a thiol (mercapto) group and a hydrolyzable silicon substituent. Their typical structure comprises a silicon atom bearing alkoxy (or other hydrolyzable) groups and a hydrocarbon chain ending in a thiol group, such as (RO)3Si-(CH2)3-SH, where R is an alkoxy group (for example methoxy or ethoxy). The thiol end provides reactivity toward metals and organic functionalities, while the silane end enables grafting to inorganic substrates through hydrolysis and condensation to form siloxane networks.

Preparation and reactivity of mercaptosilanes generally involve introducing a mercaptoalkyl group onto a silicon center bearing hydrolyzable substituents. The most common representative is 3-mercaptopropyltrimethoxysilane (MPTMS). In moisture, the alkoxy groups hydrolyze to silanols and subsequently condense to create Si-O-Si linkages, allowing the molecule to bond covalently to glass, silica, or other oxides and to be incorporated into polymer matrices. The thiol group remains available for further reactions, such as bonding to metals (notably gold) or participating in thiol-ene chemistry, oxidation to disulfides, or complexation with metal ions.

Applications of mercaptosilanes include serving as adhesion promoters and coupling agents for primers, coatings, sealants, and sealant systems, where they enhance bonding between inorganic substrates and organic polymers. They are used in surface modification of glass, silica, and metal surfaces, in the preparation of self-assembled monolayers on metals, and as intermediates in the synthesis of thiol-containing polymers and networks. Common examples include 3-mercaptopropyltrimethoxysilane (MPTMS) and 3-mercaptopropyltriethoxysilane (MPTES). Safety considerations include odor and sensitivity to oxidation, which can form disulfides and reduce reactivity.