We describe our attempts to fine‐tune the reactivity and selectivity of N‐fluorobenzenesulfonamide in fluorination reactions by changing the substituents on its phenyl rings. A series of N‐fluorobenzenesulfonamides bearing substituents at the ortho, meta, and para positions were prepared, and were used in the enantioselective fluorination of 2‐oxindoles catalysed by chiral palladium complexes. Fluorinating reagents 1b, 1c, 1d, 1e, 1h, 1i, and 1j gave similar results to 1a, while 1f, 1g, and 1n gave worse yields and selectivities. Under mild reaction conditions, a series of 3‐fluoro‐2‐oxindoles were obtained in excellent yields (up to 98 %) and enantioselectivities (up to 99 % ee) using N‐fluoro‐4,4′‐difluoro‐benzenesulfonamide as the fluorination agent.

A series of N‐fluorobenzenesulfonamides such as (I) is synthesized and screened in the enantioselective fluorination of oxindole (IIa).

To reduce the failure probability of rigid supporting structures caused by large deformation of deeply buried high-stress soft rock roadways, the mechanical properties and failure features of basalt fiber-rubber granular concrete (BFRGC) are investigated based on triaxial compression tests. The post-peak strain softening equations of BFRGC, based on the Mohr–Coulomb yield criterion, are deduced and then compiled in the finite-difference software (FLAC3D) to simulate the post-peak strain-softening process of BFRGC. Combined with practical engineering, the supporting effects of BFRGC with different proportions are evaluated by FLAC3D. The results of compression tests show that the yield strength of the BFRGC increases significantly when the mass percentage of basalt fiber is 0.4%. Moreover, mixing basalt fibers into both the plain concrete and rubber concrete can effectively restrain the development of the fractures under three-dimensional stress. The numerical results show that when the mass fractions of basalt fibers and rubber particles are 0.4% and 5–10%, respectively, both the plastic zone in the surrounding rocks and the deformation of the rigid supporting structures decrease obviously. It is indicated that the optimal ratio of BFRGC can effectively reduce the stress concentration around the roadway and improve the overall bearing capacity of the supporting structures.

An adjustable foaming machine that consisted of air feeding system, liquid feeding system, foaming device, and control system was designed to satisfy various demands on foam density and foam diameter in the preparation of foam concrete. The air-liquid ratio was adjusted by controlling the foaming liquid flow, and the adjustment of foam density was achieved. An adjustable single-foam tube structure was adopted to realize the controls of foam density and pore size by adjusting the packing density of the foaming medium in the foaming tube. By using the singlechip as the digital processing core, the communication between singlechip and frequency converter was established through the RS485 interface, thereby realizing the automatic control in the working process of the adjustable foaming machine. The experimental result indicated that the foaming process of this machine was stable and highly efficient, and foam density and foam diameter were easy to adjust and control, which improved the usability.

No abstract