EXPERIMENT 4 Solvent Extraction

Vogel s Textbook of Practical Organic Chemistry, 5th ed.  

Zubrick, J. W. The Organic Chem Lab Survival Manual, 7th ed. Wiley N ewYork, 2008. 

Determination of a Partition Coefficient for the System Benzoic Acid, Methylene Chloride, and Water 

Purpose. This exercise illustrates the general procedures that are used to determine a partition coefficient at the microscale level. Experience in weighing milligram quantities of materials on an electronic balance, the use of automatic delivery pipets for accurately dispensing microUter quantities of liquids, the transfer of microHter volumes of solutions with the Pasteur filter pipet, and the use of a Vortex mixer, are techniques encountered in this experiment. 

Weighing of Solids in Milligram Quantities (p. 39) Technique 4 Solvent Extraction 

---

Solvent Extraction Experiments. Solvent extraction studies were done on two feed samples representing dissolved hydroxide cake (SSA) and evaporator supernate (SSB). SSA was prepared by dissolution of hydroxide cake with slow addition of concentrated HN03, adjustment of the final acidity to 0.5 N by addition of water and/or HN03, and clarification by filtration. To prepare SSB, some supernate liquid from the evaporator was titrated, acidity adjusted to 0.5 N by NaOH and water addition, then clarified by filtration. No appreciable solids were observed on the clarification filters for either solution. Compositions of these feeds are listed in Table III. 

Solvent extraction experiments. Solvent extraction (SE) batch experiments were conducted in order to identify the best extractant-trapping agent couple. The extraction mechanism of Cd " with D2EHDTPA (noted AH) is a cationic exchange type ... 

The study of carbonate complexes of Pu is complicated by various experimental difficulties. The low solubility of many carbonates (7), leaving a very dilute Pu concentration in solution, results in difficulties to the experiments with electrochemical or spectrophotometric methods. However, the radiometric method with solvent extraction or solubility measurement is easily applicable for the purpose. Unlike the solution with anions, like Cl, N03 etc., the concentration of which can be varied at a constant pH, the preparation of solutions with varying carbonate concentration accompanies indispensably the change of pH of the solution. As a result, the formation of carbonate complexes involves accordingly the hydrolysis reactions of Pu ions in solutions under investigation. It is therefore prerequisite to know the stability constants of Pu(IV) hydroxides prior to the study of its carbonate complexation. 

Bioreactors containing an nndefined anaerobic consortinm rednced TNT to 2,4,6-triaminotoluene (TAT) in the presence of glncose (Dann et al. 1998). The sorption of TAT to montmorillonite clay was irreversible, and the snbstrate conld not be released by solvent extraction or by acid or alkaline treatment. Similar resnlts were obtained with humic acids in which covalent reactions with carbonyl or activated C=C bonding presumably occurred. Results from laboratory experiments nsing i C-labeled TNT in reactors to which... 

For pesticide residue immunoassays, matrices may include surface or groundwater, soil, sediment and plant or animal tissue or fluids. Aqueous samples may not require preparation prior to analysis, other than concentration. For other matrices, extractions or other cleanup steps are needed and these steps require the integration of the extracting solvent with the immunoassay. When solvent extraction is required, solvent effects on the assay are determined during assay optimization. Another option is to extract in the desired solvent, then conduct a solvent exchange into a more miscible solvent. Immunoassays perform best with water-miscible solvents when solvent concentrations are below 20%. Our experience has been that nearly every matrix requires a complete validation. Various soil types and even urine samples from different animals within a species may cause enough variation that validation in only a few samples is not sufficient. 

Work is in progress to validate the MAE method, proposed for EPA, in a multi-laboratory evaluation study. Nothing similar has been reported for additives in polymeric matrices. Dean el al. [452] have reviewed microwave-assisted solvent extraction in environmental organic analysis. Chee et al. [468] have reported MAE of phthalate esters (DMP, DEP, DAP, DBP, BBP, DEHP) from marine sediments. The focus to date has centred on extractions from solid samples. However, recent experience suggests that MAE may also be important for extractions from liquids. 

Solvent extraction experiments were performed on all processed homopolymers and blends. The samples were first weighed then immersed in 20 mL acetone for 24 hours at room temperature. The remaining solid rod was removed from the acetone, vacuum dried and reweighed. The remaining experimentation was performed only on samples from (A) and (D) above. 

Data on the DFR of chlorothalonil on carnation crops in previous studies indicated an increase in DFR of 10 to 20% with solvent extraction (unpublished data). However, in all of the current experiments, no differences were observed between dislodgeable foliar residue and solvent-extracted foliar residue for the pesticides methiocarb and thiophanate-methyl. 

During our early experiments on chemical gels, when first observing the intermediate state with the self-similar spectrum, Eq. 1-5, we simply called it viscoelastic transition . Then, numerous solvent extraction and swelling experiments on crosslinking samples showed that the viscoelastic transition marks the transition from a completely soluble state to an insoluble state. The sol-gel transition and the viscoelastic transition were found to be indistinguishable within the detection limit of our experiments. The most simple explanation for this observation was that both phenomena coincide, and that Eqs. 1-1 and 1-5 are indeed expressions of the LST. Modeling calculations of Winter and Cham-bon [6] also showed that Eq. 1-1 predicts an infinite viscosity (see Sect. 4) and a zero equilibrium modulus. This is consistent with what one would expect for a material at the gel point. 

Between pH values of ca. 6 and 12 aqueous solutions hold very little dissolved beryllium because of the low solubility of Be(OH)2. When the pH is raised above 12, the hydroxide begins to dissolve with the formation of, first, Be(OH)3 and then, at even higher pH values, Be(OH) (52). The presence of these species in strongly alkaline solutions was confirmed by means of solvent extraction experiments (90) and infrared spectroscopy (31). A speciation diagram is shown in Fig. 7, which was constructed using the values of log /33 = 18.8 and log /34 = 18.6 critically selected from Table III. The diagram illustrates clearly the precipitation and dissolution of Be(OH)2. 

Leo Weitzman received his Ph.D. in chemical engineering from Purdue University. He is a consultant with 30 years of experience in the development, design, permitting, and operation of equipment and facilities for treating hazardous wastes and remediation debris. Dr. Weitzman has extensive experience in the disposal of hazardous waste and contaminated materials by thermal treatment, chemical reaction, solvent extraction, biological treatment, and stabilization. He has published over 40 technical papers... 

Figure S. TLC of the fish and soil extractable radioactivity and water from the 14C-DDT experiment. Solvent system used was petroleum etheridiethyl ether...

The many uses of solvent extraction make the subject important for university students of chemistry and chemical technology. Some universities offer special courses in solvent extraction, whereas others include it as a minor topic in more comprehensive courses. Pilot-scale experiments on solvent extraction are common in chemical engineering curricula. Because of the breadth of the subject, the treatment in such courses is often scanty, and a satisfactory text is difficult to find in a form suitable for use directly with students. 

The primary parameter in solvent extraction is the measured distribution ratio, where it is up to the writer to define what is being measured, indicating this by an appropriate index. In the Nernst distribution experiment described earlier, the analytically measured concentration of benzoic acid is in the aqueous phase [Bz]aq,tot = [HBz]aq + [Bz ]aq, and in the organic phase [Bz] , tot= [HBzJorg + [HjBzjlo . Thus the measured distribution ratio, abbreviated Z)bz, becomes... 

The industrial application of solvent extraction is a mature technique, and it is now possible to move from laboratory experiments on a new extraction system to full industrial practice with little technological risk. There is a sufficient variety of large-scale equipment available to cope with most problems encountered in application, although much of the equipment remains rather massive. Attempts to miniaturize, for instance, by using centrifugal forces to mix and separate phases, still has to be developed further. 

Migration experiments have shown that the hydrated cations not only carry with them the water in the inner coordination sphere, but also one or more shells of additional water molecules, for typical total values of 10-15. When the metal ion leaves the aqueous phase in the solvent extraction step, this ordered coordinated water returns to the bulk water structure, contributing an additional factor to consider in evaluating the thermodynamics of extraction. 

The centrifugal separator of the AKUEVE system is also used for phase separation in the SISAK technique [84]. SISAK is a multistage solvent extraction system that is used for studies of properties of short-lived radionuclides, e.g., the chemical properties of the heaviest elements, and solvent extraction behavior of compounds with exotic chemical states. In a typical SISAK experiment, Fig. 4.34, radionuclides are continuously transported from a production... 

In the rapid determination of whether an extractant may be useful for the extraction of a particular substance or to determine the best extractant in a series of extractants, an approach known as screening may be employed. Much of the usefulness of this approach depends on the investigator s knowledge and experience of solvent extraction, since the tests carried out are minimal and are generally based on the relative properties of an extractant. 

Experience in solvent extraction processes has shown that such processes can be scaled up from pilot plant—or even bench-scale—data quite reliably. This is particularly evident in processes employing mixer-settlers. However, scale-up will only be as reliable as the data on which it is based, and time spent in obtaining the correct and relevant data will always pay dividends. 

---