Abstract
The synthesis of esters is one of the most fundamental and significant subjects in organic chemistry and chemical industry because they are used in high-value products such as cosmetics, biofuel, pharmaceuticals, surfactants, and food ingredients. In this study, an efficient, economic, sustainable, and green protocol for oxidative esterification reaction has been developed. A one-pot direct transformation of aliphatic, aromatic, and unsaturated aldehydes into esters in the presence of oxygen has been carried out over mesoporous organosilica-supported palladium nanocatalyst (Pd-Cyt@SBA-15) under ambient conditions. Pd-Cyt@SBA-15 efficiently catalyzed selectively large-scale conversion of aldehydes into esters in high yields and large turnover numbers (TON = 98,000). Pd-Cyt@SBA-15 nanocatalyst demonstrated excellent reusability and stability and could be recycled up to ten times without loss of significant reactivity. ICP-AES analysis showed that no leaching of active palladium species occurred during the recycling process of the heterogeneous Pd-Cyt@SBA-15 nanocatalyst.
Highlights
We have investigated the possibility of developing a more general method that is effective for converting a wide range of aldehydes to corresponding esters and report the catalytic activity of recycling-supported cytosine–palladium complex nanomaterial in the direct esterification of aldehydes with alcohols under aerobic conditions
In order to optimize various parameters such as catalyst loading, oxidant, reaction time, and temperature, a preliminary screening of the catalytic activity of Pd-Cyt@SBA-15 nanomaterial in the model oxidative esterification reaction of benzaldehyde and methanol was conducted under different conditions included in Table 1 (Scheme 2)
When a similar oxidative esterification reaction was conducted in the presence of 0.002 mmol of Pd-Cyt@SBA-15 as catalyst, methyl benzoate was obtained at 48% yield
Summary
For these reasons and following recent efforts from the group in the design of supported nanocatalysts for green and sustainable chemical transformations [14,15,16], we have studied the possibility of developing a green and versatile alternative protocol for one-pot conversions of various aliphatic and aromatic aldehydes with common alcohols using a palladium bearing a functionalized cytosine on the surface of mesoporous silica materials (Pd-Cyt@SMA-15) as an efficient and selective reusable nanocatalyst (Scheme 1) In this regard, we have investigated the possibility of developing a more general method that is effective for converting a wide range of aldehydes to corresponding esters and report the catalytic activity of recycling-supported cytosine–palladium complex nanomaterial in the direct esterification of aldehydes with alcohols under aerobic conditions.
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