Recovering Solvent from Iodine Solutions After reading the note "A Convenient Method to Recover the Solvent from ~ a l o ~ e n - c c 1Mixtures"1, 4 readers unfamiliar with iadine chemistry might draw the conclusion that the removal of iodine from this solvent is a difficult process that requires a specific reagent such as NaBHa. Quite the contrary, extraction of iodine from most solvents can be easily achieved with a wide variety of products, some of them safer and cheaper than NaBH4, and thus, mare appropriate. In our laboratory of general and inorganic chemistry we use iodine salutions in a variety of solvents, most frequently water"irnmiscible"(CHzClz,CHCla, CCa, CSHM,C6H6, PhCK?, EtzO, CSZ).Themethod we prefer to extract the halogen and recover the solvent is as follows. We add 100-200 mL of an aqueous solution of NazSzOa.5HzO (10% wlw) to 1-2-L batches of iodine solution. After viearous stirrine. -. the discolored solvent is decanted and further purified hv standard methods, and the aaueous laver is reused to exhaustion. We have selected this way of operation based on the following considerations. (1) The reaction is well-known to proceed quantitatively according to
(2) The reaction is rapid and safe. Less than 1min of vigorous shaking - is required (alternativelv the mixture can be jrirrrd overnighr . N~,gasesnrrevolved, and nnrlAmific3nrthermal e%ct I S inwlwd. 13 Sorhnm th~osulfateis n rhrnp and common rtagcnr in chemistry laboratories 4 Using the stn~hlometr! and the similar rnolccular weights. estirnntiunr of the, nro--;gar). amount of th~osulfntrneeded arc rasllv made from rhr amount or iodnne prertnt. 5, Moreover, the mild nature of this reagent, a s well as the products ofthe reaction, make it very easy to clean accidental soills of iodine on elothine and skin. Ifshaking and drrnntmgare undri~rable.we suggest as alternatives: Prolonged sttrnnz uf iodine solurwns wnh .i large cxwii of adid sodlurn thiosnlfate, or p a ~ l n gthe iodine solutmn through n column chargco with snlrd sodlurn ifnereat thmsultbtr In thelatter, r h r w u a l dI;w nfcdwd~schnrgrisatrrartivr, nnd the proreis i~rapec~alb.dT~.rti\r volume of dilute iodine solution is involved. It should be n k d , however, that in our experienck the color discharge stops when less than 10% of charged sodium thiosulfate has been consumed. These alternatives are also valid to extract iadine from most miscible aqueous solvents, hut distillation can be necessary because the solubility of the salts, especially sodium iodide, is in some cases very large. ~
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'Sabol, J. E.; Kurtz, D. W. J. Chem. Edue. 1990,67,532.
Francisco J. Arnaiz and Juan A. Casares Departamento de Qulmica lnorganica Coiegio Universitario de Burgos 09002 Burgos, Spain
516
Journal of Chemical Education
