The Blue Bottle Experiment Revisited How Blue? How Sweet? A. Gilbert Cook, Randi M. ~ o l l i v e rand , ~ ~Janelle ~ E. ~illiarns'*~ Valparaiso University, Valparaiso, IN 46383 The "Blue Bottle" experiment was first popularized by Campbell with his article in this Journal in 1963 (1)and later in his book (2).The reaction consists of a flask about half full of a colorless liquid that, when shaken, turns blue. When left to stand the liquid turns colorless again. The cyclic process--being shaken, turning blue, being leR to stand, and turning colorless+an be repeated many times. By making a series of guided observations with this simple but colorful system, the student can determine a rate law and a plausible mechanism for the reaction without ever knowing the contents of the flask. The activation energy of the reaction can also be measured by making observations a t various tem~eratures.This ~ o ~ u lex~eriment ar has been carried out b; general c h e m i i t j studenis at Valparaiso University since 1963 with p e s t success. The Reaction The contents of the flask are an aqueous solution of sodium hydroxide, glucose, and methylene blue. The relative amounts of each of these needed to make the solution is approximately 20 g of sodium hydroxide, 20 g of gluwse, and 1mL of 1% alcoholic methylene blue solution per liter of water. The rate law for the reaction is
Table 1. Dye Structures Thfazines
R4
y&*
R1
R3
R i = (CH3)2N,R2 = (CH3)zN' RI = NHz, R2 = (CH3)zNi RI = (CHdNH,Rz = (CH3)Nf RI = (CH3)zN.R2 = (CH3)N.R6 = CH3 RI = CzHsNH. R2 = CzH5NHf. R4 = R5 = CH3 Ri = HzN, Rz = HzNt Rx = HzN, Rz = H2Nt, Rs = CH3 R i = (CH3)2N,R2 = (CH3)2N', R3 = NO2
Ri = (CH3)zN.R2 = 0 Oxazines
rate = k[D,I[CHI[OHI where Do, is the oxidized (blue) form of methylene blue, and CH is the carbohydrate, glucose. The following is a simple mechanism for this reaction.
fast D, O,+D d
R3 Ri=NaO,Rz=O,R7=0 Ri = (CzH5)2N,R2 = HzN,' Rs = CH3 Ri = H2N, R2 = HzNt, Rs and Re = fused benzene Ri =OH, R2 = (CzH5)2N,R3 = OH, R4 = HzNCO Azines
where D is the reduced (wlorless) form of the dye methylene blue, and X- represents the oxidation products from the glucose (arabinoic, formic, oxalic, and erythronic acids (3,411.The enthalpy of the reaction has been reported to be 5.5 kcal/mol(5). How Blue? Are other colors beside blue possible for this reaction? Methylene blue is a thiazine dye (structure 1 shown in Table 1).There are manv other dves in the thiazine dve family that might be usckd, as wcil as dyes in the related oxazine and azme dye families. Wc havc found that many Preliminary report presented at the 106th Annual Meeting of the Indiana Academy of Science, 1990. 'PRISMS Program (Precollege Research In the Sciences for Minority Students)participants during summers of 1990and 1991. Program cosponsored by GTE and Valparaiso University. 'Theodore Roosevelt High School. Gary, IN 46407. 3West Side High School, Gary, IN 46406.
160
Journal of Chemical Education
- . R = H except where noted.
of these other dyes also catalyze the oxidation of an alkaline aqueous solution of glucose when mixed with oxygen. However, the rates of reaction and sometimes the wlors of the oxidized dyes vary from that observed with methylene blue. The color of the oxidized form of the dye in aqueous base and the relative rates of oxidation of glucose are shown in Table 2. Two of the oxazine dyes (cresyl violet acetate and resazuriu) fluoresce red in their oxidized states when excited by a 365-11111 U V lamp, whereas fluo-
