Objective

To determine the solubility of 2-naphthaldehyde, 4-hydroxybenzaldehyde, 4-nitrobenzaldehyde, o-vanillin and piperonal in methanol by UV-Vis spectroscopy using molar absorptivities (ε) obtained from NIST database.

Procedure

Saturated solutions of 2-naphthaldehyde, 4-hydroxybenzaldehyde, 4-nitrobenzaldehyde, o-vanillin and piperonal in methanol were prepared in one dram vials and left to equilibrate for 24 hours. The supernatant from each solution was then decanted in to a different vail and subjected to dilutions until UV absorbance for them fell between 0.5-2.0 absorbance units. Using ε values obtained from NIST database for each aldehyde, concentration of their saturated solution was calculated.

Results

Saturated solutions-day1
Saturated solutions -day2
After decanting

2-naphthaldehyde
ONSExp023A-3
ONSExp023A-3'
ONSExp023A-3a
ONSExp023A-3b
ONSExp023A-3c
ONSExp023A-3d
ONSExp023A-3e
ONSExp023A-3a-e

[Where is the Spreadsheet with the calculations? JCB]

Discussion


NIST UV spectral data [NIST doesn't report the solvent so you'll have to look up the references to find out - also look on Beilstein for methanol and these solutes JCB]
Aldehyde
Wavelength nm
Log ε
ε
2-naphthaldehyde
246.9
4.361005
22961.75

282.7
3.9638
9200.258

339.9
3.2636
1834.848
4-hydroxybenzaldehyde
93.5
4.259
18155.16
4-nitrobenzaldehyde
260
4.1982
15783.38

300.6
3.3212
2095.077

338.7
2.413
258.8213
o-vanillin
220
4.226
16826.74

265.1
3.99696
9930.246

348
3.3589
2285.073
piperonal
233.4
4.04501
11092

274.2
3.8012
6327.032

313
3.92295
8374.329




Conclusion

Experiment aborted.

Log


2009-01-03

11:00 Made-up saturated solution of 2-naphthaldehyde, 4-hydroxybenzaldehyde, 4-nitrobenzaldehyde, o-vanillin and piperonal in methanol. This was done by vortexing each of them for 10 min after it appeared like the solution had become saturated.
Solutions of piperonal and o-vanillin continued to become clear after vortexing, however once they were left undisturbed for 15-20 they started recrystallizing. Therefore they had to be revortexed, they formed clear solution again...after repeating this process 3 times..the clear solutions were left in the hood...soon after they started to recrystallize, with some supernatant in them..it is assumed that this supernatant solution is the saturated solution.

[Do you have any way to record ambient temperature (and its fluctuations) in the vicinity of your hood? Or any way to ensure that the solutions remain at a constant temperature? It seems to me that solubility data should always come with temperature anyway... -BH]

11:20 The solutions were left in the hood to equlibrate.
18:40 Obtained a picture of the solutions.

2009-01-04

12:30 Centrifuged the vials for 1min, obtained a picture. [saturated solutions-day2]
12:40 Decanted the supernatant from the vials in to 5 new one dram vials labeled 1-5. Obtained a picture. [After decanting]
15:00 Performed dilutions of the saturated solution of 2-naphthaldehyde in methanol as described below
Solution ID
Description
23A
Saturated solution
23A-1
100uL 23A in a 10mL Volumetric flask
23A-2
100uL 23A-1 in a 10mL Volumetric flask
23A-3
100uL 23A-2 in a 10mL Volumetric flask
23A-3a
125uL 23A-2 in a 10mL Volumetric flask
23A-3b
150uL 23A-2 in a 10mL Volumetric flask
23A-3c
175uL 23A-2 in a 10mL Volumetric flask
23A-3d
200uL 23A-2 in a 10mL Volumetric flask
23A-3e
225uL 23A-2 in a 10mL Volumetric flask