A novel method for the regioselective C2-chlorination of heterocyclic N-oxides has been developed. PPh3/Cl3CCN were used as chlorinating reagents and the desired N-heterocyclic chlorides were obtained smoothly in satisfactory yields. The reactions proceeded in a highly efficient and selective manner across a broad range of substrates demonstrating excellent functional group tolerance. In addition,
Comparative Study of Holmium (III) Selective Sensors Based on Thiacalixarene and Calixarene Derivatives as an Ionophore
作者:Sanjay Singh、Geeta Rani
DOI:10.5012/bkcs.2012.33.7.2229
日期:2012.7.20
The two chelates based on calix[4]arene and thiacalix[4]arene have been synthesized and used as neutral ionophores for preparing PVC based membrane sensor selective to $Ho^3+}$ ion. The addition of potassium tetrakis(4-chlorophenyl)borate (KTpClPB) and various plasticizers, viz., NDPE, o-NPOE, DOP, TEP and DOS have been found to improve significantly the performance of the sensors. The best performance was obtained with the sensor no. 6 having membrane of $L_2$ with composition (w/w) ionophore (2%): KTpClPB (4%): PVC (37%): NDPE (57%). This sensor exhibits Nernatian response with slope $21.10\pm}0.3mV/decade$ of activity in the concentration range $3.0\times}10^-8}-1.0\times}10^-2}M\;Ho^3+}\;ion$, with a detection limit of $1.0\times}10^-8}M$. The proposed sensor performs satisfactorily over a wide pH range of 2.8-10, with a fast response time (5 s). The sensor was also found to work successfully in partially non-aqueous media up to 25% (v/v) content of methanol, ethanol and acetonitrile, and can be used for a period of 4 months without any significant drift in potential. The electrode was also used for the determination of $Ho^3+}$ ions in synthetic mixtures of different ions and the determination of the arsenate ion in different water samples.