Caffeine gold complex supported on magnetic nanoparticles as a green and high turnover frequency catalyst for room temperature A³ coupling reaction in water

Abstract

A new heterogeneous catalyst derived from gold (III) and supported on caffeine‐coated magnetic nanoparticles, Fe3O4@Caff‐Au, has been prepared and characterized using different techniques. This magnetic gold composite shows high catalytic activity in A3 coupling reactions of terminal alkynes, aldehydes and secondary amines. Using this green catalyst, propargylamines are obtained in high turnover frequency in short reaction times using water as solvent at room temperature. This stable and ready accessible catalyst can be easily recycled magnetically for at least nine consecutive runs without significant loss of activity and with slight aggregation of Au species.

QbD approached comparison of reaction mechanism in microwave synthesized gold nanoparticles and their superior catalytic role against hazardous nirto‐dye

“…Furthermore, addition of catalyst gold nanoparticles to the reaction mixture leading to change in the color of reaction as well as loss of absorbance intensity at 403.50 nm. Consequently, emergence of peak at 313 nm, was another evidenced of activated Au NPs mediated reduction of hazardous 4‐NP dye into safer 4‐AP as byproducts (Figure ) …”

“…To simulate the conditions of reduction for comparative analysis; In order to reduce toxic 4‐NP into relatively safe 4‐AP, an attempt to grid search was made. Briefly; according to standard procedure, freshly prepared 1.7 ml of 0.2 mM 4‐NP solution and 1 ml of 20 mM NaBH 4 (Sodium borohydrate) solution were mixed at 30 O C while gold nanoparticles acts as heterogeneous catalyst for their reduction into safer 4‐AP derivatives …”

“…While, gold nanoparticles as a catalyst; recently emerged as an alternative and facile choice among the novel catalysts, in many of chemical reactions which includes but not limited to trans‐esterification, ring opening, polymerization, polymerase chain reaction, condensation . Another reasons for growing interest of researchers of different disciplines for these nanoparticles are due to reusability and higher efficiency of these metallic nanoparticles, including gold nanoparticles, in catalytic reduction of environmental hazardous materials; such as nitro containing environmentally hazardous organic dyes (4‐ Nitrophenol: 4‐ NP) into safer amino analogues (4‐ AP: 4‐ Amino phenol) . However, due to advocacy of environmental activists and strict regulatory caveats related to biocompatibility and toxicity of conventional reducing reagents being used to synthesized metallic nanoparticles, shifts are focusing towards judicious adaptation of green chemistry approach which additionally favoring the final performances in terms of stability, toxicity and catalytic activities .…”

“…Consequently, textile and some chemical industries either use or in‐process generate dyes and dyestuffs mediated environmental pollution. 4‐ Nitrophenol is one of the most abundant but non‐biodegradable in nature so being accumulated in the biosphere and biomagnified over the time . So, due to their high toxicity, carcinogenicity, mutagenicity and posing direct threat to our life by leading into irreparable damage to skin, liver, kidney and other vital organs .…”

“…[7,8] Another reasons for growing interest of researchers of different disciplines for these nanoparticles are due to reusability and higher efficiency of these metallic nanoparticles, including gold nanoparticles, in catalytic reduction of environmental hazardous materials; such as nitro containing environmentally hazardous organic dyes (4-Nitrophenol: 4-NP) into safer amino analogues (4-AP: 4-Amino phenol). [9] However, due to advocacy of environmental activists and strict regulatory caveats related to biocompatibility and toxicity of conventional reducing reagents being used to synthesized metallic nanoparticles, shifts are focusing towards judicious adaptation of green chemistry approach which additionally favoring the final performances in terms of stability, toxicity and catalytic activities. [10,11] Furthermore, in past, some antioxidant containing plant extracts, emerged as promising reducing agents but due to their inherent low shelf-life owing to antioxidants; they inherent possess challenges hence their scope and suitability at industrial scale are quite limited.…”