Objective

To measure the solubility of benzoic acid (Chemspider) and 4-chlorobenzaldehyde (Chemspider) in different solvents. For a justification of this project see here.

Procedure

Saturated solutions are made of benzoic acid (Chemspider) and 4-chlorobenzaldehyde (Chemspider) by charging a one dram vail with 900ul of the solvent. The solute is then added until the solution is saturated. Each vial is vortexed for 30s. Also each vial is centrifuged for 1-2minutes. 300ul of the liquor is then pipetted into half dram preweighed vials. The solution is weighed and entered into the speedvac. The solution is then reweighed after all of the liquid has evaporated off. The results can be found in the Spreadsheet.

Results

The results can be found in the Spreadsheet. Yes looks good - all you are missing in the spreadsheet are values from the literature JCB
Benzoic Acid in methanol is 2.70 M.
Benzoic Acid in ethanol is 2.44 M. Benzoic Acid inTHF is 3.65 M. Benzoic Acid in acetonitrile is 0.76 M.
4-chlorobenzaldehyde in ethanol is 2.81 M.
4-chlorobenzaldehyde in THF is 5.28 M. Finally 4-chlorobenzaldehyde in acetonitrile is 5.85.
add pics 1 and 2 JCB

Discussion

The main concern when determining solubilities using the evaporation technique, is the possible evaporation of solutes at reduced pressure. Thus the b.p. of the solutes must be determined at the lowest possible pressure the sppedvac can accomodate. Also keeping check of the pressure using a pressure meter helps. The boiling point of benzoic acid at 1atm is 249C, the speedvac can achieve as low was 0.1mmHg. The boiling point of benzoic acid at 0.1mmHg is 45C. The b.p. of 4-chlorobenzaldehyde at 1atm is 214C, and the b.p. at 0.1mmHg is 20C. This raises a red flag for the experiment. However the noted pressure inside the speedvac during evaporation did not fall below 5mmHg. Since the pressure did not fall below 5mmHg, the predicted b.p. of 4-chlorobenzaldehyde is now 80C. Thus the results achieved are still okay to use.
4-chlorobenzoic acid was also considered for this experiment. Initially I thought it sublimed at R.T. and thus does not make a good candidate for using it in the speedvac. Another method like UV/VIS will be used for its solubility determination. However it doesnt sublime at R.T. (give the b.p. at 1 atm you used for your calculations. JCB) The boiling points of this acid at 0.1 Torr is63C, and at 5 Torr is 122C. [good reasoning. -- BH]
Have you found any of these measurements in the literature? JCB will be adding them as I find them in my paper.

Log

2008-11-11

11:30 Charged one dram vials with 900ul of solvent
11:45 Charge each vial with solute, and agitated each for 30s until solution was saturated.
12:15 Centrifuged each solution for one minute.
12:30 Took picture of solutions. Picture 1
12:45 Weighed empty half dram vials.
13:00 Charge each half dram vial with corresponding solution (300ul)
13:15 Weighed vials without cap.
13:30 Entered vials into speedvac, turned on machine.
14:00 Stopped speedvac.
14:10 Weighed vials
14:15 Took picture of vials. Picture 2


Tags


Compounds
InchiKey
Inchi
Benzoic Acid
WPYMKLBDIGXBTP-UHFFFAOYAD
InChI=1/C7H6O2/c8-7(9)6-4-2-1-3-5-6/h1-5H,(H,8,9)
4-chlorobenzaldehyde
AVPYQKSLYISFPO-UHFFFAOYAQ
InChI=1/C7H5ClO/c8-7-3-1-6(5-9)2-4-7/h1-5H
THF
WYURNTSHIVDZCO-UHFFFAOYAI
InChI=1/C4H8O/c1-2-4-5-3-1/h1-4H2
methanol
OKKJLVBELUTLKV-UHFFFAOYAX
InChI=1/CH4O/c1-2/h2H,1H3
ethanol
LFQSCWFLJHTTHZ-UHFFFAOYAB
InChI=1/C2H6O/c1-2-3/h3H,2H2,1H3
acetonitrile
WEVYAHXRMPXWCK-UHFFFAOYAJ
InChI=1/C2H3N/c1-2-3/h1H3