Solubility of Benzoic Acid in Chloroform using 1H NMR

Researcher
David Bulger

Objective
To confirm the solubility of benzoic acid in chloroform using 1H NMR.

Method

NMR experiments were conducted on a JEOL_300MHz_NMR equipped with a 5_mm NMR_tube capped with a single seal cap. All experiments were carried out at approximately 293.2 K using auto-gain with spin off. The proton spectra were acquired using a 45-degree pulse with a relaxation delay of 5 seconds, 1 scan with a resolution of 77.97 mHz. Shimming of spectra used JEOL automatic gradient shimming with deuterated chloroform spinning at 15 Hz. Mass determinations were performed using a 0.1 mg accuracy Sortorius balance. A saturated solution of benzoic acid (ChemSpider) in protonated chloroform (ChemSpider) was made and the supernatant was transferred to 3 NMR tubes using Pasteur_Pipet followed by addition of capillary tubes filled with 94 uL water using a Microsyringe (NMR_external_reference_setup). Reference NMR run performed first with deuterochloroform, then with protonated chloroform.

Results

Identification of Peaks on Solubility_35:
Identification Spectrum

Spectra:
Solubility_15
Solubility_34
Solubility_35
Raw JCAMP-DX file for Solubility 15
Raw JCAMP-DX file for Solubility 34
Raw JCAMP-DX file for Solubility 35

Spreadsheet:
EXP031 Spreadsheet

Photos of Equipment:
300_MHz_NMR_1
300_MHz_NMR_2
300_MHz_NMR_3
300_MHz_NMR_4
NMR_Tubes
NMR_Caps
Weighing_Table
Analytical_Scale_1
Computer_with_Delta
Pasteur_Pipet
Microsyringe
NMR_external_reference_setup
NMR_external_reference_setup_close_up
Benzoic_Acid
Benzoic_Acid_top

Spectrum
Proton
SAMS Solubility (M)
External Standard Solubility (M)
Solubility_15
Ha
1.8889
1.8893
Solubility_15
Hb
1.5685
1.5682
Solubility_15
Hc
1.4970
1.4968
Solubility_15
Hd
1.4926
1.4928
Solubility_34
Ha
1.9043
1.9045
Solubility_34
Hb
1.5130
1.5135
Solubility_34
Hc
1.5033
1.5029
Solubility_34
Hd
1.4747
1.4750
Solubility_35
Ha
1.7483
1.7479
Solubility_35
Hb
1.5440
1.5441
Solubility_35
Hc
1.4649
1.4647
Solubility_35
Hd
1.5183
1.5181
Table 31.1: Solubility Results for Benzoic Acid in Chloroform

Discussion
The solubility of benzoic acid in chloroform was measured by NMR with three replicates using the SAMS method with and without an external standard (Table 31.1). Both methods were shown to give almost identical results: 1.59 +/- 0.16 M for SAMS and 1.59 +/- 0.16 M for External Standard.

Conclusion
The solubility of benzoic acid in chloroform was measured to be 1.59 +/- 0.16 M by both SAMS and External Standard methods.

Log

1.23.09 CST

11.30 - Reference sample preparations
11.40 - Weighed benzoic acid (0.116 2 g)
11.45 - Weighed deuterated chloroform (1.306 6 g)
11.50 - Mixed by hand
11.55 - Capillary tube filled with water using microsyringe
11.57 - NMR run (Solubility_12)
Note: This reference was not used because it used deuterated chloroform.

17.26 - Filled 3 capillary tubes with water
17.31 - Labeled 3 NMR tubes
17.47 - Weighed vial (48.046 6 g)
17.49 - Added benzoic acid and weighed (49.149 7 g)
17.52 - Added protonated chloroform and weighed (52.141 0 g)
17.55 - Added benzoic acid and weighed (53.313 7 g)
18.04 - Added chloroform and weighed (57.445 8 g)
18.08 - Added benzoic acid and weighed (58.263 6 g)
18.10 - Added chloroform and weighed (61.104 4 g)
19.09 - Shimmed (Z1 = (-1 279), Z2 = (-981), Z3 = (-159), Z4 = (790))
19.11 - Transferred supernatant to NMR tubes and capillary tubes added
19.23 - NMR run Solubility 15
19.30 - NMR run Solubility 34
19.42 - NMR run Solubility_35
20.30 - Photos taken of equipment and reagents

1.30.09 CST

16.06 - Added 94 uL water to capillary tube using microsyringe
16.50 - Photos of equipment
16.54 - Automatic gradient shim using pre-made deuterated chloroform sample (Z1 = (-1 279), Z2 = (-977), Z3 = (-293), Z4 = (936))
16.58 - Weighed empty NMR tube (3.086 8 g)
17.01 - Added benzoic acid and weighed (3.099 7 g)
17.02 - Added benzoic acid and weighed (3.114 3 g)
17.04 - Added protonated chloroform and weighed (4.627 6 g)
17.12 - Sonicated for 10 min
17.24 - Added capillary tube and NMR run (Gain = 6) with zero_region (Benzoic Acid Reference)

References

1) Lin, M., Tesconi, M., Tischler, M., Use of H NMR to Facilitate Solubility Measurement for Drug Discovery Compounds, International Journal of Pharmaceutics (2008), doi:10.1016/j.ijpharm.2008.10.038

[Please also add measurements like these directly in to the **SolubilitySum spreadsheet** as well. That way you can refer to all references for a solubility with a link like this: **http://oru.edu/cccda/sl/solubility/ugidata.php?solute=salicylic%20acid&solvent=ethanol** JCB]They should be added now.

Solubility of benzoic acid in chloroform (solubility data viewer)

Acknowledgements:

The auther wishes to thank Dr. Robert Stewart for his advice throughout the course of the experiment including reference #3 and for the use of the NMR and other equipment, Dr. Jean-Claude Bradley for his help with the interactive NMR spectra, Dr. Reed for the use of the department camera, and Dr. Antony Williams for reference #1.
Past Material





Calculations

The solute and the chloroform peaks' integrations were analyzed against the external water reference integration per hydrogen as follows: (area / # H's) / (water area / 2 H's).

Weight Percent (wt%) of entire solution = total mass of solid added / total mass of solution * 100%.

Integral ratio was calculated for the unsaturated reference spectrum as follows:

Integral Ratio = wt% of unsaturated reference / (unsaturated solute peak against water peak / unsaturated chloroform peak against water peak).

The solubility is calculated in wt% as follows:

wt% observed = Integral Ratio of unsaturated reference * (saturated solute peak against water peak / saturated chloroform peak against water peak).

Interactive Spectra (these are very large files (800K) and may require increasing JAVA memory and closing all browser windows before attempting to view each spectrum) and Interactive Spectra Screenshots of Integrations (Benzoic Acid Reference: Minimum Y = 0, Integral Factor = 150, Integral Offset = 0; Solubility 15, 34, 35: Minimum Y = 0.1, Integral Factor = 50, Integral Offset = 0):



Benzoic Acid Reference
Solubility 15
Solubility 34
Solubility_35

015Ha
034Ha
035Ha
BARHb_a
015Hb_a
034Hb_a
035Hb
BARHb_b
015Hb_b
034Hb_b


015Hc_a
034Hc_a
035Hc_a

015Hc_b
034Hc_b
035Hc_b

015Hd_a
034Hd_a
035Hd_a

015Hd_b
034Hd_b
035Hd_b
BARHe_a
015He_a
034He_a
035He_a
BARHe_b
015He_b
034He_b
035He_b
BARHf_a
015Hf_a
034Hf_a
035Hf_a
BARHf_b
015Hf_b
034Hf_b
035Hf_b



[Well done on finding a reference #2 for the solubility of benzoic acid in chloroform - how does your measurement compare? JCB]
The weight percent was found to be 16.5 wt% at 22 degrees Celsius. This is greater than the 12.5 wt% from the "Solubilities of Inorganic and Organic Compounds" (Reference 3) at 25 degrees Celsius. Reference 2 showed the solubility at 20 degrees Celsius to be 12.5 g/ 100 mL. The Merck Index showed the solubility to be 22 g/ 100 mL at room temperature.

[Could you mention exactly how (and how long) you mixed the solutions? We have found that mixing must be very thorough to get reproducible values. JCB] The solution was mixed by hand for approximately 3 min after each of the chloroform additions.[That is not enough mixing - in the future you should vortex (or sonicate) for at least 10 mins after the last addition of solute.JCB]

[The log doesn't say how much water was added - are you assuming that the water and the entirety of your sample are being integrated?] The capillary tube was filled to about half an inch from the top of the capillary tube. This prevented the water from changing the solubility while providing an external reference to compare the sample peaks with. Both the water and the sample were integrated manually. The microsyringe measured the amount of water inserted into the capillary tube to be 94 uL.


The solubility of benzoic acid in chloroform was determined to be approximately 16.5 g benzoic acid/ 100 g solution of protonated chloroform and benzoic acid. [Please explain to me what you mean by wt%, how/whether this is different from g solute/100g solvent and why you are reporting 16.5 wt% three paragraphs above and 12.5g/100g here? Finally, is there a reason not to convert g/100g to molarity? -BH] Thank you for pointing that out. I copied the wrong number from the discussion and stated the solvent rather than the solution. What I mean by weight percent is really just g solute/ g solution * 100%. 16.5 g benzoic acid/ 100 g solution with protonated chloroform is the same as 16.5 wt%. I find weight percent a little more concise than g solute/ 100 g solution. The solubility was not converted to molarity because I did not measure the volume of the solution and do not know the density of the solution.
[Note that the primary format of reporting our solubilities is molar so you should design your experiment to report it that way. You can do that if you transfer over a measured volume of saturated solution to the NMR tube and add an internal standard. Since you didn't do that you'll have to convert over from mass solute/mass solution to molar using some approximations.
The SolubilitySum spreadsheet already has columns ready to process that conversion when necessary - but if you are designing the experiment you shouldn't have to JCB]