Al(OTf)3 as a highly efficient catalyst for the rapid acetylation of alcohols, phenols and thiophenols under solvent-free conditions

Insight into the Mechanism of the Acylation of Alcohols with Acid Anhydrides Catalyzed by Phosphoric Acid Derivatives

Insight into the mechanism of a safe, simple, and inexpensive phosphoric acid (H₃PO₄)-catalyzed acylation of alcohols with acid anhydrides is described. The corresponding in situ-generated diacylated mixed anhydrides, unlike traditionally proposed monoacylated mixed anhydrides, are proposed as the active species. In particular, the diacylated mixed anhydrides act as efficient catalytic acyl transfer reagents rather than as Brønsted acid catalysts simply activating acid anhydrides. Remarkably, highly efficient phosphoric acid (1-3 mol %)-catalyzed acylation of alcohols with acid anhydrides was achieved and a 23 g scale synthesis of an ester was demonstrated. Also, phosphoric acid catalyst was effective for synthetically useful esterification from carboxylic acids, alcohols, and acid anhydride. Moreover, with regard to recent developments in chiral 1,1'-bi-2-naphthol (BINOL)-derived phosphoric acid diester catalysts toward asymmetric kinetic resolution of alcohols by acylation, some phosphate diesters were examined. As a result, a ³¹P NMR study and a kinetics study strongly supported not only the acid-base cooperative mechanism as previously proposed by other researchers but also the mixed anhydride mechanism as presently proposed by us.

Molybdenum-modified mesoporous SiO2 as an efficient Lewis acid catalyst for the acetylation of alcohols

A suitable, expeditious and well-organized approach for the acetylation of alcohols with acetic anhydride in the presence of 5%MoO₃–SiO₂ as an optimum environmentally benign heterogeneous catalyst was developed.

Iron (III) chloride hexahydrate as a highly efficient catalyst for acetylation of protic nucleophiles with acetic anhydride under solvent-free conditions

Background:

Acetylation of protic nucleophiles is used to protect these functional groups. Most of the methods described in the literature use solvents, one equivalent or more of toxic bases or expensive and toxic catalysts. Therefore, new methodologies are still in demand, above all, greener and more economical procedures.

Objective:

An eco-efficient method developed for acetylation of alcohols, phenols, thiols, amines and carbohydrates, using acetic anhydride and a catalytic amount of the environmentally benign and inexpensive FeCl3.6H2O under solvent free conditions.

Methods:

Acetylation of a variety of protic nucleophiles was performed using 0.2 mol % of FeCl3.6H2O as the catalyst, and 1.2 equiv. as the acetylating agent at room temperature and under solvent free conditions.

Results:

Our procedure appears to be highly efficient and promoted rapid and quantitative acetylation under simple and minimum manipulation. Chromatography or recrystallization were generally not necessary for the purification of products.

Conclusion:

This eco-friendly protocol appears to be potentially universally applicable in organic design to protect protic nucleophiles and potentially scalable for industrial fields.

Acetylation of Alcohols, Amines, Phenols, Thiols under Catalyst and Solvent-Free Conditions

In the present study, an easy and an efficient approach is reported for the acetylation of alcohols, amines, phenols, and thiols under solvent- and catalyst-free conditions. The experimental conditions were milder than conventional methods and the reactions were completed in shorter reaction time. The examined substrates afforded higher yields of the acetylated products under the short reaction time. Comparison of this work with earlier reported procedures reveals that this method offers some advantages than with reported catalysts and solvents. The as-synthesized products were characterized by 1H-NMR and GC-MS techniques to ensure their purity and identity. In addition, a possible mechanism was also proposed for this reaction.

Diazepinium perchlorate: a neutral catalyst for mild, solvent-free acetylation of carbohydrates and other substances

Diazepinium perchlorate-promoted acetylation of free as well as partially protected sugars, phenols, thiophenols, thiols, other alcohols and amines is described.

Oxidative Acetoxylactonisation of Alkenoic Acids Using H2O2 in Acetic Acid Catalysed by KI

In the presence of a catalytic amount of KI in combination with H2O2, a convenient catalytic procedure has been developed for the direct preparation of acetoxylactones from alkenoic acids in acetic acid at room temperature which provides the corresponding cyclic products in good yields. This novel methodology mediated by an in situ generated hypervalent iodine intermediate extends the catalytic application of KI in organic synthesis.

M, Somani RS. Synthesis of aluminium triflate-grafted MCM-41 as a water-tolerant acid catalyst for the ketalization of glycerol with acetone

An aluminium triflate species grafted over MCM-41 (Al(TF)–MS) was synthesized by a novel route as an inexpensive and water-tolerant solid acid catalyst for the ketalization of glycerol with acetone to solketal (solketal synthesis).

The first vinyl acetate mediated organocatalytic transesterification of phenols: a step towards sustainability

A practical and efficient method for vinyl ester based transesterification of phenols under organocatalytic conditions has been described.

Melamine trisulfonic acid (MTSA): an efficient and recyclable heterogeneous catalyst in green organic synthesis

Melamine trisulfonic acid (MTSA) as a highly efficient heterogeneous solid acid catalyst catalyzes various organic transformations.

Vinyl esters as effective acetaldehyde surrogates in [4 + 1] cycloaddition based multicomponent cascade

A new multicomponent cascade has been designed by utilizing vinyl esters as effective acetaldehyde surrogate.

Efficient and Rapid Solvent-Free Acetylation of Alcohols, Phenols, and Thiols Using Catalytic Amounts of Sodium Acetate Trihydrate

Under solvent-free conditions, different alcohols and phenols were efficiently acetylated at room temperature within short time periods by using acetic anhydride in the presence of catalytic quantities of sodium acetate trihydrate, which is a very inexpensive and mild reagent. Thiols were also shown to behave equally well under the same conditions. Chemoselective protection of less hindered alcohols in the presence of bulkier homologues and phenols in the presence of alcohols was achieved using competitive experiments.

Highly efficient solvent-free acetylation of alcohols with acetic anhydride catalyzed by recyclable sulfonic acid catalyst (SBA-15–Ph–Pr–SO3H) — An environmentally benign method

The catalytic activity of highly thermal stable, hydrophobic, and complete heterogeneous propylsulfonic acid functionalized nanostructured SBA-15 for excellent acetylation of alcohols and phenols with acetic anhydride at ambient temperature in solvent-free conditions was examined under environmentally benign reaction conditions. The salient features of this protocol are the absence of solvent, a green experimental procedure, and simple reusability of the catalyst (at least five reaction cycles).

An efficient synthesis of bis(indolyl)methanes and evaluation of their antimicrobial activities

A versatile and efficient method has been developed for the synthesis of bis(indolyl)methanes by using aluminium triflate (0.5 mol%) as a novel catalyst. Further, some of the synthesized compounds were evaluated for their efficacy as antibacterial and antifungal activities. Most of the compounds have shown moderate to good inhibitory activity.