Abstract
In this work, the effect of pretreatment conditions (10% H2/Ar flow rate 25 mL/min and 400 °C, 3 h or 600 °C, 17 h) on the catalytic performance of 1 wt.% Pd/γ-Al2O3 has been evaluated for hydrogenation of 2-methyl-3-butyn-2-ol in continuous-flow mode. Two palladium catalysts have been tested under different conditions of pressure and temperature and characterized using various physicochemical techniques. The catalytic performance of red(400 °C)-Pd/γ-Al2O3 and red(600 °C)-Pd/γ-Al2O3 are affected by the coexistence of several related factors like the competition between PdH and PdCx formation during the reaction, structure sensitivity, hydrogen spillover to the alumina support and presence or absence of Pd–Al species. High-temperature reduction leads to formation of Pd–Al species in addition to pure Pd. The Pd–Al species which reveal unique electronic properties by decreasing the Pdδ− surface concentration via electron transfer from Pd to Al, leading to a weaker Pd–Alkyl bonding, additionally assisted by the hydrogen spillover, are the sites of improved semi-hydrogenation of 2-methyl-3-butyn-2-ol towards 2-methyl-3-buten-2-ol (97%)—an important intermediate for vitamin A synthesis.
Highlights
Many chemical conversions in the pharmaceutical industry involve stoichiometric amounts of reagents and, generate large amounts of waste [1]
Based on the literature data [42,43,44], the selective alkyne to alkene hydrogenation on palladium catalyst is possible only when carbon occupies interstitial lattice Pd sites and excludes H from populating the subsurface region and prevents total hydrogenation of substrate. As it is independent of the temperature and pressure, red(400 °C)-Pd/γ-Al2O3 produces 2-methyl-2-butanol as the main product (Figure 10) in contrast to Pd/γ-Al2O3 reduced at 600 °C (Figure 11), it could be assumed that the rate of C dissolution in red(400 °C)-Pd/γ-Al2O3 is too low to affect MBE
As it is independent of the temperature and pressure, red(400 ◦ C)-Pd/γ-Al2 O3 produces 2-methyl-2-butanol as the main product (Figure 10) in contrast to Pd/γ-Al2 O3 reduced at 600 ◦ C (Figure 11), it could be assumed that the rate of C dissolution in red(400 ◦ C)-Pd/γ-Al2 O3 is too low to affect MBE
Summary
Many chemical conversions in the pharmaceutical industry involve stoichiometric amounts of reagents and, generate large amounts of waste [1]. Implementation of catalytic methods (especially in the continuous-flow mode) in this highly competitive industry increases the process efficiency, improves energy efficiency and recyclability, reduces costs and improves sustainability. The continuous method allows fine-tuning of the contact time between intermediates and the active catalytic phase, which may result in high selectivity without using additives or a purification step, and turns into a decrease of the E-factor (kg of generated waste/kg of product) [2,3]. One of the desired products in the pharmaceutical industry is 2-methyl-3-buten-2-ol (MBE) which is obtained by means of partial reduction of 2-methyl-3-butyn-2-ol (MBY) (Scheme 1). MBE is an important intermediate for the industrial synthesis of vitamins A (Scheme S1) [6] The pharmaceutical industry’s application of continuous-flow practices is considered one of the most strategic fields of innovation towards greener manufacturing methods, and complies with twelve principles of green chemistry [2,4].
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call