REEL QuASI Lab

Name: Richard Bowles Teaching Assistant: Jake Dumbleton

Lab: W/F 8:30-11:18 am – 430 CE Submitted: March 11, 2011

Lab Partner: Alicia Buxton Hood Number: 3

Purpose: To synthesize a dye that changes color in the presence of concentrated anions in solution.

Reaction Scheme: ¹

Synthesis of 4-NA-ND Procedure: ¹

12M, 37% Hydrochloric acid (3 mL) was added to large test tube and cooled in an ice bath. 4-Nitranaline (NA) (0.617g, 4.44 mmol) was added to test tube and heated until solids dissolved. Solution was cooled in ice bath and Sodium Nitrite (0.157 g, 2.27 mmol) and a small ice chip was added to the NA. A solution of Napthalene-1,8-Diamine (ND) (0.3319 g, 2.10 mmol) and glacial Acetic acid (0.5 mL) was added to a separate test tube and added to the NA via Pasteur pipette. Solution was set for 15 minutes, than 3M Sodium Hydroxide (9 mL) was added until solution was tested basic. Solids were recrystallized and collected via vacuum filtration, washed with Hydrochloric acid and then recrystallized with water. Solution was set out to dry overnight in Buchner funnel.

UV-Vis Procedure: ¹

Small sample of dye is dissolved in water (10 mL) in a 100-mL beaker. If not water soluble, dissolve dye in 95% ethanol. Solution (~1 mL) is added to test tube (tt-#1-acid) and acidified with 0.01 M methanesulfonic acid (~1 mL). Solutions pH is tested to be acidic and then UV-vis is taken to record λ_max and wavelength. Acidic solution (~ 1 mL) is added to clean test tube (tt-#2-acid-Cl) and 0.010 M NaCl solution (~0.25 mL, 5 drops) is added. UV-vis is taken recording λ_max and wavelength. 0.2 M NaOH (~0.1 mL, 2 drops) is added to test tube (tt-#2-acid-Cl) to form (tt-#2-base-Cl). UV-vis is taken recording λ_max and wavelength. Acidic solution (tt-#1-acid) is added to a clean test tube (~1 mL). 0.01 M NaBr (~0.25 mL, 5 drops) is added (tt-#3-acid-Br) and UV-vis is taken recording λ_max and wavelength. 0.2 M NaOH (~0.1 mL, 2 drops) is added to (tt-#3-acid-Br) to form (tt-#3-base-Br) and UV-vis is taken recording λ_max and wavelength.

Discussion:

The 4-NA-ND dye was a purple dye but the solid turned yellow when recrsytalized with water. This color change is most likely due to a higher concentration of electrons on the nitrite anion when protonated with water. The solid itself was very soluble in ethanol but only slightly soluble in water. One of the limitations of this experiment was an attempt to standardize every possible azo dye with the same procedure. It is very likely that not every dye will have the exact same properties and therefore may require slight adjustments in equivalents of catalysts and other requirements in the procedure to yield a pure sample.

Analysis of the cumulative 4-NA-ND for the class, it’s clear that there is a strong difference in wavelength between an acid and acid Cl solution, as well a difference between the Br acid and Cl acid solution. When solution is basic, an electron difference is barely detectable by UV-Vis analysis and therefore not useful in determining a difference in wavelengths between the presence of bromine and chlorine. Overall, 4-NA-ND is a fairly good indicator between the bromine and chloride due to a consistent difference between the wavelengths of chloride and bromine.

Overall, the most wavelength difference was found in samples that were in the fourth substituent. This is most likely due to the stability of the fourth substituent. Being more stable allows for the anions to accept a halide easier which in turn increases the electron density and changes the UV-Vis wavelengths.

References:

(1) Paul, N. M. The Search for a Quantitative Anion Selective Indicator (QuASI) for Aqueous Solutions. Chemistry 255 Handout. 2011, p. 1-14.

Ramblings of the QuASI

These are the discussion questions to go with the QuASI REEL lab report due next week. Its some food for thought.  Ill post my idea/thoughts/responses to each of these sometime in the next week.  I need to really do some research first to get all my facts straight.

Discussion Questions ¹

1. The synthesis of these new azo dyes using a procedure adapted from methyl orange was not as easy as it sounds. The solubility of the starting materials we a big issue. What steps would you take to modify the procedure to overcome some of your synthetic difficulties and the uncertainty that resulted?

2. Some of the compounds that were tested were recrystallized and some were not. Why could this be a problem? Why doesn’t Dr. Paul care if what we tested was pure or not? On the other hand, discuss the benefits of working with pure molecules?

3. The “A” in QuASI is for “aqueous”, and some of your products were not soluble enough in water to analyze their properties. Propose changes to the dye molecules structure that might make them more soluble in water without affecting their ability to detect anions.

4. Anions are extremely soluble in water because water strongly hydrogen bonds to these atoms to stabilize their concentrated charges. Would you expect complexing/associating an anion with an organic molecule would be difficult in the presence of so much water? What would you have to do to make your dye molecule a better “life raft” or “seat cushion” for the halides to sit down on?

5. Why would you expect a halide to change the color of an organic molecule in solution?

6. A majority of the UV‐vis analysis studies did not record a significant change in λmax between chloride and bromide containing solutions, yet this may not be a problem with our hypothesis. Consider as many aspects of the experiment that might factor into this negative result. Why did so many people see no change?

References:

(1) Paul, Noel. "Anion Selective Indicator (QuASI) for Aqueous Solutions." Chemistry 255 Research Experience to Enhance Learning. (2011): Print.