Analysis of citrates and benzoates used in poly(vinyl chloride) by supercritical fluid extraction and gas chromatography

Supercritical fluid extraction (SFE) has been demonstrated to be a useful tool in the determination of additives in polymeric materials. This paper describes the determination of some citrates and benzoates in poly(vinyl chloride) blended with 33–34% of plasticizer using off-line SFE followed by gas chromatography. Experimental factors affecting SFE have been studied by gravimetric analysis, followed by analysis of the extracts using a gas chromatograph equipped with a flame ionization detector. The extraction process is governed by the solubility of the plasticizers in the supercritical fluid or by their diffusion through the polymer matrix, which depend on the pressure and temperature used. Maximum extraction (>99%) is obtained at pressures and temperatures higher than 40 MPa and 80 °C, respectively. Due to purge losses, the collection efficiency of plasticizers into a liquid solvent ranges from 85 to 90%. The applicability of the SFE method is demonstrated using real samples and comparing the results with those obtained by conventional Soxhlet extraction.     

Synthesis,Crystal Structures,and Characterization of Two 3d‐3d Heterometallic Coordination Frameworks: [ZnCo(Hcit)Cl] and [ZnCo(Hcit)Br]

Reactions between CoO, ZnCl₂ (or ZnBr₂), and molten citric acid (Hcit) led to the formation of two 3d‐3d heterometallic coordination frameworks: [ZnCo(Hcit)Cl] ( 1 ) and [ZnCo(Hcit)Br] ( 2 ). X‐ray structure analyses show that both compounds 1 and 2 crystallize in the monoclinic space group P2₁/n [ 1 : a = 5.8699(5) Å, b = 17.7963(13) Å, c = 9.2152(8) Å, β = 106.806(4) °, Z = 4, V = 921.53(13) Å³; 2 : a = 5.909(3) Å, b = 17.798(8) Å, c = 9.302(5) Å, β = 106.374(7) °, Z = 4, V = 938.6(8) Å³]. The structures of the two compounds are almost the same except for the terminal halogen ligand. Both of them are 3D frameworks based on citric acid bridging ligands and a 1D backbone chain built of corner‐shared {CoO₆} and {ZnO₃Cl} polyhedra. Photoluminescence and thermal stabilities of the compounds were studied.     

Crystal Structure,Synthesis, and Properties of tri‐Calcium di‐Citrate tetra‐Hydrate [Ca3(C6H5O7)2(H2O)2]·2H2O

From hydrothermal synthesis needle‐shaped crystals of [Ca₃(C₆H₅O₇)₂(H₂O)₂] · 2H₂O were obtained. The crystal structure was determined by single‐crystal X‐ray experiments and confirmed by powder data (P$\bar{1}$ (no. 2) a = 5.9466(4), b = 10.2247(8), c = 16.6496(13) Å, α = 72.213(7)°, β = 79.718(7)°, γ = 89.791(6)°, V = 947.06(13) Å³, Z = 2, R1 = 0.0426, wR2 = 0.1037). The structure was obtained from pseudo merohedrically polysynthetic twinned crystals using a combined data collection approach and refinement processes. The observed three‐dimensional network is dominated by eightfold coordinated Ca²⁺ cations linked by citrate anions and hydrogen bonds between two non‐coordinating crystal water molecules and two coordinating water molecules.