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Preparation of functionalized alkoxysilanes via the thiol-alkene reaction
2025-10-20
I. Research Background
1.1 Silicone materials combine the properties of both inorganic and organic materials.
1.2 Thiol-ene Reaction
Free Radical Step-Growth Polymerization Mechanism
Features:
1. Does not use heavy-metal catalysts
2. Mild reaction conditions
3. The reaction is unaffected by oxygen and water.
4. Quick and efficient response
1.3 Introduction to Silane Coupling Agents (Alkoxy Silanes)
Silane coupling agents are produced by the addition reaction between trichlorosilane (HSiCl₃) and unsaturated olefins bearing reactive groups, catalyzed by chloroplatinic acid, followed by alcoholysis.
Usage:
1. Surface Modification
2. Preparation of organic-inorganic hybrid materials
3. Preparation of room-temperature vulcanizing silicone rubber, organic silicon sealants, and more
4. Preparing the chromatographic column
II. Project Content
Select different organic compounds containing carbon-carbon double bonds, and use dibenzoylmethane peroxide (DMPA) as a catalyst to react them with (3-mercaptopropyl)trimethoxysilane under UV irradiation, thereby preparing functionalized alkoxy silanes. Through IR and 1H NMR analysis, investigate the reaction progress of the thiol-double bond system over time, and determine the reaction duration required for the complete disappearance of the double bonds.
2.1 Reaction of Mercaptopropyltrimethoxysilane with Vinyltrimethoxysilane
Reaction conditions: [SH]/[C=C] = 1:1; DMPA 2% by weight; irradiate under UV light for 30 minutes
Using infrared detection, compare the effect of the catalyst's presence on the reaction rate.
2.2 Reaction of Mercaptopropyl Trimethoxysilane with Allyl Polyether
Reaction conditions: [SH]/[C=C] = 1:1; DMPA; irradiate under UV light for 30 min
2.3-Mercaptopropyltrimethoxysilane reacts with oleic acid
Reaction conditions: [SH]/[C=C] ratios of 1:1, 1.2:1, and 1.5:1; irradiate the reaction under a UV lamp for 120 minutes.
III. Experimental Results and Discussion
3-1 (3-Mercaptopropyl)trimethoxysilane reacts rapidly with the double bond under UV irradiation in the presence of DMPA as a catalyst. Infrared spectroscopy (IR) analysis reveals that the characteristic peak of the double bond (1640 cm⁻¹) is completely consumed after just 8 minutes of reaction.
Under conditions without DMPA as a catalyst, the thiol-double-bond reaction is significantly slower compared to when a catalyst is added; however, 1H NMR analysis shows that the double bond can react completely within 30 minutes.
3-2 When using DMPA as a catalyst under UV irradiation, (3-mercaptopropyl)trimethoxysilane reacts more rapidly with allyl polyethers AEM-6 and AEM-7. 1H NMR analysis shows that the vinyl groups on the polyether can fully react with the thiol group within just 30 minutes.
The 1H NMR spectrum of the reaction between (3-mercaptopropyl)trimethoxysilane and vinyltrimethoxysilane after 30 minutes of illumination without DMPA.
The 1H NMR spectrum of the reaction between (3-mercaptopropyl)trimethoxysilane and allyl polyether after 30 minutes of UV irradiation at 2% wt DMPA.
3-3 In the case of oleic acid, where the double bond is located between two molecular segments, the reactivity of the C=C double bond is significantly lower than that of a vinyl group due to the molecular structure and steric hindrance effects. Consequently, its reaction with a thiol group under the same conditions is also much slower. This clearly demonstrates that the radical addition to the thiol double bond is closely related to the reactivity of the C=C double bond.
To ensure complete reaction between the thiol group and the double bond, it is necessary to increase the amount of thiol used and extend the reaction time.
When the thiol/oleic acid ratio is 1.5:1 and the mixture is exposed to UV light for 2 hours, the double-bond peak in the 1H NMR spectrum completely disappears.
- Conclusion and Outlook
For terminal double bonds (such as vinyl and propyl groups), they can undergo complete reaction under UV irradiation without a catalyst when the [SH]/[C=C] ratio is 1. The presence of a catalyst, however, significantly accelerates the reaction process.
Compared to terminal double bonds, internal double bonds (RHC=CHR), due to their lower reactivity and steric hindrance, undergo the mercapto-double-bond UV irradiation reaction at a slower rate. In the presence of a catalyst, complete conversion of the double bond can only be achieved by extending the reaction time under conditions where SH is present in excess.
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