中文
Pyridine hydrobromide (CAS 18820-82-1), molecular formula C₅H₅N·HBr, molecular weight 160.01 g/mol, EC number 242-600-7, is a white to off-white hygroscopic crystalline solid that melts around 216–219 °C with decomposition. It is prepared by the classic equimolar acid-base neutralization:C₅H₅N + HBr → [C₅H₅NH]⁺ Br⁻
Under an ice bath, hydrobromic acid is added dropwise to a solution of pyridine in diethyl ether or ethanol, whereupon the target crystals precipitate. As a functional reagent in the ring-expansion step of 7-ADCA — the key intermediate behind cephalosporin antibiotics — its purity and hygroscopicity directly govern the process robustness of downstream products such as cephaloridine, cefapirin and ceftazidime. This is precisely why Shunxiang Pharmaceutical has long treated this grade as a priority quality-control item.
Benchmarked against international reagent specifications, TCI (P1666) and Thermo Fisher (AC442132500) typically certify ≥98% (HPLC), while Santa Cruz Biotechnology requires ≥97%. The numerical gap looks narrow, yet trace organic-amine impurities carried over from a recycled-pyridine route compete with the β-lactam ring for protonation sites, causing the ring-expansion isomer ratio to drift. Published experimental data show that adding 0.5 equivalent of high-purity pyridine hydrobromide shortens the condensation cycle to about 1 hour, lifts yield above 92%, and cuts polymer-type by-products by roughly 80%.
A second widely used route generates pyridinium bromide perbromide (CAS 39416-48-3) in situ with elemental bromine:[C₅H₅NH]Br + Br₂ → [C₅H₅NH]Br₃
Taking 4-chloroacetophenone as substrate, with acetic acid as solvent, 90 °C and a substrate-to-brominating-agent molar ratio of 1:1.05, 4-chloro-α-bromoacetophenone is obtained with high selectivity — avoiding the polybromination side reactions that occur when liquid bromine is used directly.
Whether deployed in 7-ADCA ring expansion or as an in-situ brominating precursor, the real bottleneck lies in moisture control and batch-to-batch consistency. Around this product, Tengxiang Import & Export has built an end-to-end QC workflow that spans raw-material pyridine source traceability, inert-gas packaging, and pre-shipment moisture re-testing — delivering stable purity to downstream cephalosporin and fine-chemical customers.