Mechanism of esterification of alcohols with surface silanols and hydrolysis of surface esters on silica gels

Utsugi, Hiroshi; Horikoshi, Hideo; Matsuzawa, Toshiharu

doi:10.1016/0021-9797(75)90262-3

Cited by 44 publications

(15 citation statements)

References 6 publications

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“…Moreover, the proposed reaction mechanism should in principle also be applicable with other reactive groups besides carboxyl groups, for example, alcohols. [52][53][54][55] Regarding the stability of the formed link, it should be noted that the ester bond can in principle be hydrolyzed again in basic or in alkaline solution. First experiments, where we increased the pH value to 7.4 after ester bonds were formed at pH 2.0, show that these bonds are stable under nearly neutral conditions.…”

Section: Resultsmentioning

confidence: 99%

“…This may considerably simplify the coupling chemistry for immobilizing organic molecules on inorganic surfaces: In standard coupling protocols, the carboxylic acid is first activated with EDC and NHS, before it is linked to an amino group of the surface linker. Moreover, the proposed reaction mechanism should in principle also be applicable with other reactive groups besides carboxyl groups, for example, alcohols. − Regarding the stability of the formed link, it should be noted that the ester bond can in principle be hydrolyzed again in basic or in alkaline solution. First experiments, where we increased the pH value to 7.4 after ester bonds were formed at pH 2.0, show that these bonds are stable under nearly neutral conditions.…”

Section: Resultsmentioning

confidence: 99%

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Simple Coupling Chemistry Linking Carboxyl-Containing Organic Molecules to Silicon Oxide Surfaces under Acidic Conditions

et al. 2010

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The coupling chemistry of carboxymethylated amylose with organo-silanized silicon oxide surfaces at pH 7.4 and 2.0 was investigated using atomic force microscopy (AFM) based single-molecule force spectroscopy. At close to neutral pH, carbodiimide activation of a carboxylic acid affords formation of an amide bond with an amino surface linker. At pH 2.0, no activation with carbodiimide was required to anchor carboxymethylated amylose between an AFM tip and a glass substrate. At the same time, the mean bond rupture force f(r) dropped from 1.65 ± 0.37 nN at pH 7.4 to 1.39 ± 0.30 nN at pH 2.0 without carbodiimide, indicating that a different link to the surface can be formed at low pH. The coupling mechanism at pH 2.0 was elucidated by a series of experiments, in which the surface was functionalized with four different organosilanes, each containing characteristic functional groups. The results are rationalized with an acid-catalyzed ester condensation between a carboxyl group and a free, unreacted silanol group in the surface anchor or on the surface.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Simple Coupling Chemistry Linking Carboxyl-Containing Organic Molecules to Silicon Oxide Surfaces under Acidic Conditions

et al. 2010

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“…Possible reaction mechanisms for esterification of surface silanols are discussed by Low et al [600]. Utsugi et al [601] concluded from the retention of optical activity on esterification with chiral secondary alcohols that the OR groups of the silica, not of the alcohol, leave in the form of water.…”

Section: B) Surface Esters and Surface Amidesmentioning

confidence: 99%

Nature and Estimation of Functional Groups on Solid Surfaces

1983

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“…The assumption of the presence of ethoxy groups in the RMF phase is based on a similar mechanism described elsewhere for other alcoholic systems with aromatic molecules, including melamine 60 and hydroxymethylfurfural, 61 similar to the esterification mechanism also observed in silica, with the replacement of terminal O–H groups by surrounding R-OH alcohols. 62 This means that care has to be taken not to restrict the interpretation of the presence of ethoxy groups as forcibly being part of the silica surface.…”

Section: Resultsmentioning

confidence: 99%

Silica–Resorcinol–Melamine–Formaldehyde Composite Aerogels as High-Performance Thermal Insulators

et al. 2022

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Here, we report the gelation and supercritical drying of ethanol-based silica–resorcinol–melamine–formaldehyde (RMF) composite aerogels with relative concentrations of initial reagents ranging from neat silica to neat RMF alcogels. The as-prepared materials are subsequently supercritically dried with carbon dioxide. Their properties include a thermal conductivity in the 15–20 mW·m –1 ·K –1 range even with a silica content as low as 20% wt . The possible reasons behind this interesting insulation performance and the mechanisms leading to the underlying gel structure are discussed in depth. A focus is made on the different gelation modes happening between the RMF and silica phases, from a coating of silica surfaces with RMF species to discontinuous RMF particles within a silica backbone and a continuous RMF backbone with isolated silica particles. The implications in terms of mechanical properties and thermal conductivity are elaborated upon. The initial ratio of silica–RMF species in this ethanol-based synthesis affects the micro- and macrostructure of the composites, resulting in materials with drastically different pore structures and thus an interesting array of possibilities for a new class of silica-organic composite aerogels, based on a sol–gel process.

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Mechanism of esterification of alcohols with surface silanols and hydrolysis of surface esters on silica gels

Cited by 44 publications

References 6 publications

Simple Coupling Chemistry Linking Carboxyl-Containing Organic Molecules to Silicon Oxide Surfaces under Acidic Conditions

Simple Coupling Chemistry Linking Carboxyl-Containing Organic Molecules to Silicon Oxide Surfaces under Acidic Conditions

Nature and Estimation of Functional Groups on Solid Surfaces

Silica–Resorcinol–Melamine–Formaldehyde Composite Aerogels as High-Performance Thermal Insulators

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