Efficient and scalable synthesis of bis(indolyl)methanes via functionalized asphaltene

• A novel reusable catalytic system comprising asphaltene sulfonic acid decorated with L-proline was successfully synthesized and characterized. • Detailed spectroscopic analysis confirmed the structure and composition of the prepared functionalized asphaltene catalyst. • The catalytic efficacy of Asph-SO3H@pro was investigated for the green synthesis of bis(indolyl)methane derivatives. • The protocol offers several advantages, including waste utilization as a novel catalyst, low catalyst loadings, and the ability to achieve moderate to excellent yields. • The functionalized asphaltene catalyst demonstrated remarkable recyclability, maintaining its activity for six consecutive cycles without significant loss. Asphaltenes are the heaviest and most aromatic fractions of crude oil and bitumen, typically regarded as low-value by-products in the petroleum industry. Due to their complex polyaromatic structure, abundance of heteroatoms, and surface-active functional groups, asphaltenes offer significant potential as low-cost precursors for functional materials and heterogeneous catalysts. Herein, a novel reusable catalytic system comprising asphaltene sulfonic acid (Asph-SO 3 H) decorated with L-proline (Asph-SO 3 H@pro) has been successfully synthesized and characterized. Detailed spectroscopic analysis confirmed the structure and composition of the prepared asphaltene. The catalytic efficacy of Asph-SO 3 H@pro was investigated for synthesizing bis(indolyl)methane derivatives. The protocol offers several advantages, including waste utilization as a novel catalyst, operation under room-temperature conditions, low catalyst loadings, and the ability to achieve moderate to excellent yields. Notably, the catalyst demonstrated remarkable recyclability and maintained its activity for six consecutive cycles without significant loss. This sustainable catalytic system presents a valuable contribution to the field of organic synthesis, offering an efficient, and environmentally friendly approach for the synthesis of bis(indolyl)methane derivatives.