Solubilities of Some 2H-Chromene Derivatives in Supercritical Carbon Dioxide Naader Bahramifar, † Yadollah Yamini,* ,† Ali Ramazani, ‡ and Nader Noshiranzadeh ‡ Department of Chemistry, Tarbiat Modarres University, Tehran, Iran, and Department of Chemistry, Zanjan University, Zanjan, Iran The equilibrium solubilities of four recently synthesized 2H-1-benzopyran (2H-chromene) derivatives have been measured at temperatures ranging from 308 K to 348 K and pressures from (12.2 to 35.5) MPa in supercritical carbon dioxide. The data were obtained by using a simple static sampling apparatus, which was tested by measuring the solubility of naphthalene in supercritical carbon dioxide. The measured solubilities were correlated using a semiempirical model. The calculated results show satisfactory agreement with the experimental data. 1. Introduction Recent studies have shown that the use of supercritical fluid as an extraction medium provides a powerful alterna- tive to traditional extraction methods. 1,2 The potential benefits of supercritical fluid extraction (SFE) include faster analysis; reduced sample handling; protection from degradation by light, heat, or oxygen; high load ability of samples and possibility of trace analysis; easy separation of extracts from solvent after extraction; elimination of hazardous and/or expensive solvents; and analysis of aqueous samples (serum, urine, and saline solution) with- out introducing organic solvents. As a consequence of two decades of development of supercritical fluid extraction in food industries, there is at the moment a widespread interest in the application of supercritical fluids (SCFs). This is also the case for the pharmaceutical industry. SFE is a potential technique for the purification of pharmaceutical products containing residual solvents. A common element of any application of SCFs technology being considered in current research is the requirement of a thorough understanding and knowledge of the solubility of solids in the SCFs. This knowledge is essential for evaluating the feasibility of the supercritical separation process and for establishing optimum conditions of opera- tion. 2H-1-Benzopyran derivatives and naphthopyrans (chro- menes) are important heterocycles in bioorganic chemistry and are present in many natural products and pharma- ceuticals. 3,4 In the present study the solubilities of four 2H- chromene derivatives, recently synthesized by this research group, 5-7 were determined in supercritical carbon dioxide over wide ranges of temperatures and pressures. The measured solubilities were successfully correlated by using a semiempirical model. 2. Experimental Section 2.1. Materials. HPLC-grade chloroform, methanol, and ethanol (all from Merck) were used as received. Carbon dioxide (Sabalan, Tehran, 99.99%) was used for all extrac- tions. The 2H-chromene derivatives, namely, dimethyl 2H- 1-benzopyran-2,3-dicarboxylate (A 1 ), di-tert-butyl-3H-naph- tho[2,1-b]pyran-2,3-dicarboxylate (A2), dimethyl 6-bromo- 2H-1-benzopyran-2,3-dicarboxylate (A 3 ), and dimethyl-3H- naphtho[2,1-b]pyran-2,3-dicarboxylate (A 4 ), were synthesized and purified as described before. 5-7 The purities of the 2H- chromene derivatives were confirmed by spectroscopic data and elemental analysis. The purities of the 2H-chromenes were higher than 99 mass %, and no further purification was made before use. However, prior to the measurement of solubilities, small quantities of volatile impurities were extracted by dynamic SFE at P ) 12.2 MPa and T ) 308 K for a duration of 10 min at the SCFs flow rate 0.30 mL/ min. The impurities were only present during the extrac- tion of the first 2-4% of the material charged into the extraction vessel. After making sure that no impurities existed in the extract, solubility measurements were done. The physical properties of the 2H-chromene derivatives (A 1 to A 4 ) used are shown in Table 1. 2.2. Equipment and Procedure. A Suprex (Pittsburgh, PA) MPS/225 system equipped with a modified static system for solubility determination in the SFE mode was used. A detailed description of the equipment and operating procedures has been given previously. 8,9 In this system, contact between the species and the fluid is established. After the equilibrium is reached, a known volume of the saturated fluid of the species is chosen and the amount of the solute is measured. Then, the solubility is calculated. Solubility measurements were accomplished in the pres- sure range from (12.2 to 35.5) MPa, at the temperatures (308, 318, 328, 338, and 348) K, each for a duration of 30 min. It should be noted that, by monitoring the solubility data versus time, 30 min was found to be adequate to ensure the attainment of equilibrium. The equilibrium temperature and pressure were measured to accuracies of (1 K and (0.1 MPa, respectively. The solid solutes (100 mg) were mixed well with a proper amount of glass beads and packed into a 0.5-mL extraction vessel. This procedure prevents channeling, increases the contact surface between the sample and the supercritical fluid, and, consequently, reduces the equilibration time. Sintered stainless steel filters (5 µm) were used to prevent any carry-over of the * Corresponding author. Fax: +98-21-8006544. E-mail: yyamini@ modares.ac.ir. † Tarbiat Modarres University. ‡ Zanjan University. 1104 J. Chem. Eng. Data 2003, 48, 1104-1108 10.1021/je0201875 CCC: $25.00 © 2003 American Chemical Society Published on Web 08/19/2003