Rio de Ja ne i ro, June 27, 1998 Dear sir:
The pa per “Spec trop ho to me tric De ter mi na ti on of Io da te in Tal be Salt”, wro te by Rosa Lina G.N.P. Sil va, A. Fer -nan do de Oli ve i ra, and Edu ar do Alme i da Ne ves that ap pe a red in J. Braz. Chem. Soc. 1998, 9(2), 171 has cal led my at ten ti on be ca u se of the mo lar ab sor ti vi ti es found by the se aut hors for the ion I3- at the wa ve lengths 288 and 352 nm. As can be seen from the ta bles pre sen ted be low, the se va lu es are much hig her than tho se ob ta i ned by ot her aut -hors.
As the io da te con tent in the ta ble salt is me a su red by the UV-Vis spec tros copy at the se wa ve lengths it would be con ve ni ent for the se aut hors to jus tify why the ir mo lar ab -sor ti vity va lu es are so dif fe rent.
Res pect fully,
Ro ber to de Bar ros Fa ria
De par ta men to de Qu í mi ca Inor gâ ni ca Uni ver si da de Fe de ral do Rio de Ja ne i ro.
References:
1. Awtrey, A.D.; Con nick, R.E. “The Absorp ti on Spec -tra of I2, I3-, I-, IO3-, S4O6-2 and S2O3-2. Heat of the Re ac ti on I3- = I2 + I-”, J. Am. Chem. Soc1951, 73, 1842-1843.
2. Allen, T.L.; Ke e fer, R.M. “The For ma ti on of Hypo i o -dous Acid and Hydra ted Io di ne Ca ti on by the Hydroly sis of Io di ne”, J. Am. Chem. Soc1955, 77, 2957-2960.
3. Pal mer, D.A.; Ra met te, R.W.; Mes mer, R.E. “Tri i o di de Ion For ma ti on Equi li bri um and Acti vity Co ef fi ci -ents in Aque ous So lu ti on”, J. So lu ti on Chem1984,
13(9), 673-683.
4. Troy, R.C.; Kel ley, M.D.; Nagy, J.C.; Mar ge rum, D.W. “NonMetal Re dox Ki ne tics: Io di ne Mo no bro -mi de Re ac ti on with Io di de Ion and the Hydroly sis of IBr”, Inorg. Chem.1991, 30(25), 4838-4845. 5. Tho mas, T.R.; Pen ce, D.T.; Hasty, R.A. “The Dis pro
-por ti o na ti on of Hypo i o dous Acid”, J. Inorg. Nucl. Chem.1980, 42, 183-186 (note that the cor rect ε va lue for the 353 nm band is equal to 2,58 x 104 and not 2,58; it can be ob ta i ned from Eqs. (1) and (2)).
Author’s Replay
Our mo lar ab sor ti vity data, ε, are cor rect and are re fer -red not exactly for the I3- ani on but in di rectly for IO3- as they are the slo pes of analy ti cal cur ves for io da te in salt NaCl. The re por ted data are ba sed on the fol lo wing re dox re ac ti on that ta kes pla ce bet we en io da te with io di de in aci -dic me di um:
IO3- + 5 I- + 6 H+→ 3 I2 + 3 H2O 3 I2 + 3 I-→ 3 I3
-IO3- + 8 I- + 6 H+→ 3 I3- + 3 H2O
On this ba sis it is cle ar that 1 IO3- ion ge ne ra tes 3 I3-. Thus our in di rect io di de ε data should be di vi ded by 3 when re fer red to I3-:
At 352 nm, ε = (73 200 / 3) = 24 400 L mol-1 cm-1 At 288 nm, ε = (110 300 / 3) = 36 767 L mol-1 cm-1 The se va lu es are col se to tho se from the li te ra tu re, 40 000 or 38 790 at 288 nm and 26 400 or 25 800 at 352 nm. Small dif fe ren ces are ac cep ta ble due to dif fe rent ex pe ri -men tal con di ti ons, viz. io nic. strength and the pre sen ce of chlo ri de ion in our wor king sou ti ons which can com pe te to some ex tent with io di de to form a com plex like I2Cl-.
Edu ar do Alme i da Ne ves Co-author
DQ-UFSCar São Car los - SP Cor res pon den ce
J. Braz. Chem. Soc., Vol. 9, No. 5, 514-514, 1998. © 1998 Soc. Bras. Qu í mi ca
Prin ted in Bra zil. 0103 – 5053 $6.00 + 0.00
Ta ble 1.
λ / nm ε/M-1 cm-1 Ref.
287.5 40 000 1
288 40 000 2
288 38790 3
288 40 000 4
288 1.103 x 105 Sil va et al.
Ta ble 2.
λ / nm ε/M-1 cm-1 Ref.
350 25 750 3
351 27 000 4
352 26 400 2
352 7.320 x 104 Sil va et al.
353 26 400 1
