An improved practical synthesis of liquid crystals of trans-cyclohexyltolans by Sonogashira cross-coupling reaction of 1-iodo-4-(trans-4-alkylcyclohexyl)benzene with aromatic terminal alkynes in the presence of Pd/C (palladium on activated carbon) as low as 0.03 mol% of Pd and CuI (2 mol%) in a mixture solvent of acetone-water (5 : 2 in volume) is described. The liquid crystals could be obtained in high yields as a solid with excellent purity by simple filtration, and the filtrate could be reused several times while still retaining high catalytic activity.

A microreactor system consisting of membrane-dispersion tube-in-tube microreactors and delay loops was developed for the continuous synthesis of 1-ethoxy-2,3-difluoro-4-iodo-benzene. Because of the high mass and heat transfer in the microreactor system, ortho-and halogen-lithiation could be performed at −40 and −20 C, respectively, which are much higher than the temperature required (−70 C) for the batch reaction. In stirred tanks, the yield of 1-ethoxy-2,3-difluoro-4-iodobenzene reaches 91.0% in 70 min. Nearly the same yield of 91.3% was achieved within a shorter time of 16 min in the microreactor system. Furthermore, the kinetics of ortho-lithiation calculated by the Gaussian software, were used for the computational fluid dynamics (CFD) simulations of the reaction process in another microreactor system. Thus, a Gaussian-CFD-coupled-method for efficiently predicting reaction kinetics and yield without experiments could be established. The predicted yield reached 88.7% at 1000 s, which is comparable with the experimental yield of 90.1% at 960 s.

An Improved Practical Pd/C-Catalyzed Sonogashira Cross-Coupling Reaction for the Synthesis of Liquid Crystals of trans-Cyclohexyltolans (III). -(SHANG, H.; HUA*, R.; ZHENG, Q.; ZHANG, J.; LIANG, X.; ZHU, Q.; Appl. Organomet.