Preparation of octadecyl modified column gels using heat-treated silicas and their retention behaviour in high-performance liquid chromatography

Summary The effect of silanol groups on three types of octadecylmodified column gels using heat-treated silicas by calcination has been studied by high-performance liquid chromatography. After heat-treating at 180°C, 500°C and 950°C, the silicas treated with octadecyldimethylchlorosilane were used for the measurement of physical and chemical analysis. From elemental carbon analysis data, the reactive silanol group concentrations, _OH(s), were determined to be 2.0 in the 180°C treated silica, 2.1 in the 500°C treated silica and 1.6 in the 950°C treated silica, respectively (original silica: mean pore diameter 116 Å, specific surface area 298 m²/g, pore volume 1.22 ml/g, particle size 5.0 m). The separation factors, , of pyridine versus phenol were measured to be 0.79 on 180°C treated silica, 0.91 on 500°C treated silica and 1.98 on 950°C treated silica, using acetonitrile-water mixtures as the eluent. And then, on the basis of the physico-chemical and chromatographic data, the three types of octadecyl modified column gels using heat-treated silicas by calcination have been compared.     

HMDS预处理系统

讲述了HMDS预处理工艺过程,HMDS预处理系统的优越性及该系统的工作原理与结构。     

[Sn(TPP)(BF4)2]: An efficient and reusable catalyst for chemoselective trimethylsilylation of alcohols and phenols with hexamethyldisilazane

Tin(IV)tetraphenylporphyrinato tetrafluoroborate, [Sn^IV(TPP)(BF₄)₂], was used as an efficient catalyst for trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS). High-valent [Sn^IV(TPP)(BF₄)₂] catalyzes trimethylsilylation of primary, secondary and tertiary alcohols as well as phenols, and the corresponding TMS-ethers were obtained in high yields and short reaction times at room temperature. While, under the same reaction conditions [Sn^IV(TPP)Cl₂] is less efficient to catalyze these reactions. One important feature of this catalyst is its ability in the chemoselective silylation of primary alcohols in the presence of secondary and tertiary alcohols and phenols. The catalyst was reused several times without loss of its catalytic activity.     

Efficient and practical protocol for silylation of hydroxyl groups using reusable lithium perchlorate dispread in silica gel under neutral condition

A very efficient and mild procedure for the trimethylsilylation of a wide variety of alcohols, including primary, allylic, benzylic, secondary, hindered secondary, tertiary, and phenols with hexamethyldisilazane on the surface of silica gel dispersed with LiClO₄ in room temperature at few minutes in excellent yields under neutral conditions is reported. This procedure also allows the excellent selectivity under LP-SiO₂ system for silylation of alcohols in the presence of amine and phenolic hydroxy groups.     

A novel and highly efficient method for the silylation of alcohols with hexamethyldisilazane (HMDS) catalyzed by recyclable sulfonic acid-functionalized ordered nanoporous silica

Silylation of alcohols with hexamethyldisilazane (HMDS) in dichloromethane provides the corresponding silyl ethers in almost quantitative yields at room temperature using 1-3 mol % of sulfonic acid-functionalized silica. Additionally, the catalyst displays a high activity and thermal stability (up to 240 °C) and it can be easily recovered and reused for at least 20 reaction cycles without loss of reactivity.     

p-Toluenesulfonyl Chloride (p-TsCl)-Catalyzed Trimethylsilylation of Hydroxyl Groups Using Hexamethyldisilazane and Their Regeneration Under Mild Conditions: The First Example for Catalytic Application of p-Toluenesulfonyl Chloride

The first catalytic application of p-toluenesulfonyl chloride (p-TsCl) for the efficient and selective trimethylsilylation of various types of hydroxyl groups with hexamethyldisilazane (HMDS) in dichloromethane and desilylation of these compounds in water is reported. The reactions were carried out at room temperature and were found to proceed in good to excellent yields.     

Iron(III) trifluoroacetate [Fe(F3CCO2)3] as an easily available, non-hygroscopic, non-corrosive, highly stable and a reusable Lewis Acid catalyst: Efficient O-silylation of α-hydroxyphosphonates, alcohols and phenols by hexamethyldisilazane (HMDS) under solvent-free conditions

O-Silylation of hydroxyl groups of α-hydroxyphosphonates, primary, secondary tertiary-alcohols and phenols with HMDS was achieved in high to excellent yields using iron(III) trifluoroacetate [Fe(F₃CCO₂)₃] as an easily available and a cost effective, non-hygroscopic, non-corrosive, highly stable and an efficient catalyst under solvent-free conditions. As a typical reaction, we have scaled up silylation of diphenyl methanol to 20 mmol of the substrate in order to show that the catalyst is quite effective for scaled up operation. The catalyst was easily isolated by simple filtration and recycled for silylation of diphenyl methanol for several runs without loosing its catalytic activity.     

Novel and Highly Effective Method for the Trimethylsilylation of Alcohols and Phenols with Hexamethyldisilazane (HMDS), Catalyzed by I2 Generated in situ Using Fe(NO3)3⋅9 H2O/NaI under Heterogeneous and Neutral Conditions

Structurally diverse alcohols and phenols were trimethylsilylated in a clean and efficient reaction with hexamethyldisilazane (HMDS) based on the use of I₂ generated in situ from Fe(NO₃)₃?9 H₂O/NaI. The reaction occurs very rapid in good‐to‐high yield in CH₂Cl₂ at room temperature, and the use of toxic and corrosive molecular I₂ is avoided.     

Silylation of Cellulose with Hexamethyldisilazane in Ammonia – Activation, Catalysis, Mechanism, Properties

Synthesis of trimethylsilylcellulose (TMSC) from cellulose and hexamethyldisilazane (HMDS) in liquid ammonia is reviewed, with emphasis on the scope of the reaction and mechanistic features. Conditions for complete and for controlled stoichiometric partial silylation have been established. Stoichiometric desilylation of TMSC is also possible in tetrahydrofuran containing ammonia as hydrogen bond donor. The activating effect of ammonia, solubility of reactants, catalysis and kinetics of the heterogeneous reaction are discussed. Silylation follows first order kinetics in the presence of saccharin as the catalyst, indicating that the accessibility of hydroxy groups is not the rate-determining factor. TMSCs have a solubility window in THF with a DS from 1.6 to 2.6. This window is narrower for higher molecular weight TMSC.     

Efficient Trimethylsilylation of Alcohols and Phenols with HMDS in the Presence of a Catalytic Amount of 1,3‐Dibromo‐5,5‐Dimethylhydantoin (DBDMH) as a Safe and Cheap Industrial Chemical

1,3‐Dibromo‐5,5‐dimethylhydantoin (DBDMH) is found to be an effective catalyst for trimethylsilylation various alcohols and phenols with hexamethyldisilazane (HMDS) in dichloromethane at room temperature.