Objective

To ascertain the solubility of crotonic acid in acetonitrile, chloroform, ether, DMSO, and n-hexane by NMR spectroscopy using an internal standard.

Procedure

Saturated solutions of crotonic acid were prepare in acetonitrile, chloroform, ether, DMSO, and n-hexane solvents. The solutions were prepared by mixing together the solute and 1mL of the solvent into a vial. With subsequent additions of solute, and bouts of vortexing; which consisted of 2-3 minutes stints. Once the solution showed an excess of solute, the vials were vortexed for 10 minutes. Solutions were then left to equilibriate. The supernatants from each saturated solutions was cautiously collected into separate vials. 100μL of the supernatants were dissolved into NMR tubes containing 700μL of deuterated chloroform (CDCl3) and 10μL of dichloromethane; which was used as an internal standard for the NMR process. Proton NMR readings of the solutions were obtained with the use of a 500MHz instrument.

The NMR analysis was repeated using 1,2-dichloroethane as an internal standard, because of the concern that dichloromethane was evaporating out of the micropipette and thereby jeopardizing the future calculations due to an unknown volume of internal standard used.

Results


Spreadsheet ONSC-Exp064 (calculated using direct integration of solute to solvent - as explained here)
Sample
Solvent
Solute
Internal standard
HNMR
Solubility (M)
1
Acetonitrile
Crotonic acid
1,2-dichloroethane
HNMR

3.59
2
Chloroform
Crotonic acid
1,2-dichloroethane
HNMR
7.6
3
Chloroform
Crotonic acid
1,2-dichloroethane
HNMR
6.88
5
DMSO
Crotonic acid
1,2-dichloroethane
HNMR
7.76
6
n-Hexane
Crotonic acid
1,2-dichloroethane
HNMR
1.07
7
Chloroform
Crotonic acid
1,2-dichloroethane
HNMR
7.54

Spreadsheet (integration based on DCE)
Std Solution.
Crotonic Acid- in n-hexane-- (0.10189g in 2mL=0.898molal; 0.65M based on SAMS)

Solubility based on automated solubility measurement spreadsheet.
Spreadsheet Exp064B

Discussion

Originally the study underwent using dichloromethane (DCM) as the internal standard for the NMR analysis. However, based on the solubility results that were obtained from Exp062 the integrity of the results to be obtained here was questioned. It was believed that due to the volatility of DCM, the solvent was evaporating out of the micropipette used to obtain the 10μL needed for the NMR analysis. Therefore, 10μL of 1,2-dichloroethane (DCE) was also placed into the NMR tubes with the idea to use the DCE as the internal standard and also use the results obtained from its use to determine if the DCM solvent was indeed evaporating whilst micropipetting.


Sample
Solvent
Solute
internal Standard
HNMR
Solubility (M)
1
Acetonitrile
Crotonic acid
dichloromethane
HNMR

138.68
2
Chloroform
Crotonic acid
dichloromethane
HNMR
32.24
3
Chloroform
Crotonic acid
dichloromethane
HNMR
--
5
DMSO
Crotonic acid
dichloromethane
HNMR
50.96
6
n-Hexane
Crotonic acid
dichloromethane
HNMR
5.98
Spreadsheet (integration based DCM)

The table above shows solubility results obtained with the use of DCM as the internal standard. Based upon the above data table, the DCM was indeed evaporating (sample 3 shows no peak for DCM in the NMR spectra, which shows that it evaporated and therefore no solubility data could be extracted for the solute using DCM as the standard in this sample). These values should be discarded, and the results obtained from the use of DCE as the internal standard for the NMR analysis should be used. However, there is a significant difference in the results obtained for crotonic acid in cholorform solvent. Therefore, another assay for the chloroform solvent is proposed to verify the solubility results of crotonic acid in this solvent.

There is also an issue with the integration in the NMR analysis of the n-hexane sample. It appears that the ratio between the different protons (acid proton, vinyl proton, and methyl-group protons) is incorrect. An issue of relaxing time given to the sample during the NMR analysis is proposed. A known concentration of crotonic acid in n-hexane is to be used to determine which proton in the sampel should be used for integration.

Solubility of crotonic acid had also been calculated using SAMS method which does not require an internal standard to calculate solubility. This method assumes that the volume of the solute and solvent are additive.


Conclusion

The solubility of crotonic acid has been determined in acetonitrile, chloroform, and DMSO. The obtained data shows that crotonic acid is indeed capable of making 2M solutions for the Ugi product. Furthermore, this experiment shows that the use of dichloromethane as an internal standard for NMR analysis should not be used, because of its volatility, it may easily evaporate in micropipette tips and therefore threaten the integrity of solubility results.

No solubility data existed for crotonic acid in literature using the Beilstein database
[Well done - JCB]

Log

(includes Observations)

2009-02-20

13:11 Added 1mL of acetonitrile to a vial labeled "acetonitrile" and capped it.
13:13 Added 1mL of chloroform solvent to a vial labeled "chloroform" and capped it.
13:18 Added 1mL of ether to a vial labeled "ether" and capped it.
13:18 Added 1mL of DMSO to a vial labeled "DMSO" and capped it.
13:20 Added 1mL of n-hexane solvent to a vial labeled "n-hexane" and capped it.
13:29 Added crotonic acid solute to the "acetonitrile" vial, and briefly vortexed the vial.
13:32 Undissolved solute observed to accumulate in the "acetonitrile" vial.
13:33 Added solute to "chloroform" vial, vortexing in between additions till some solute was seen to remain undissolved.
13:35 The amount of undissolved solute in the "chloroform" vial was quite small, so more solute was added to the vial.
13:36 It was observed that the crotonic acid solute was accumulating at the top of the "chloroform" vial, due to it's low density compared to chloroform.
13:37 Added solute to the "ether" vial, and vortexed till solute no longer went into solution.
13:38 Added solute to "DMSO" vial.
13:39 Vortexed "DMSO" vial.
13:40 Added more solute to the "DMSO" vial and vortexed it.
13:44 Added solute to the "n-hexane" vial and vortexed it. Not much solute was added till none would continue into solution.
13:45 The addition of solute to all solvent appeared to be endothermic reactions, as the vials grew cold to the touch.
13:53 Vortexed the "acetonitrile", "chloroform", and "ether" vials for 10 minutes.
14:04 After the 10 minutes, undissolved solute remained in all 3 vials.
14:05 Vortexed the "DMSO" and "n-hexane" vials for 10 minutes.
14:16 After 10 minutes, undissolved solute remained visible in both vials.
14:17 All vials were left to equilibriate overnight.


2009-02-21

17:28 Cleaned 5 NMR tubes and caps with acetone, and placed them briefly in laboratory oven for evaporation of the solvent.
17:35 Added 700μL of deuterated chloroform to all NMR tubes.
17:50 Added 10μL of dichloromethane, as the internal standard, to all NMR tubes.
17:53 Capped and briefly vortexed the NMR tubes.
17:55 Retrieved the supernatants from the equilibriated vials, and placed them into corresponding new vials with the use of a Pasteur pipette.
18:43 Placed 100μL of the retrieved supernatant for acetonitrile and placed it into NMR tube "1."
18:44 Placed 100μL of chloroform supernatant into NMR tube "2."
18:45 Placed 100μL of ether supernatant into NMR tube "3."
18:46 Placed 100μL of DMSO supernatant into NMR tube "4."

18:47 Placed 100μL of n-hexane supernatant into NMR tue "5."
18:48 Briefly vortexed all NMR tubes.


2009-02-24

18: The accuracy of the micropipette was tested by weighing out 10μL of 1,2-dichloroethane (DCE) and comparing that obtained weight to a referenced value determined by using it's density (1.256g/mL). First, a capped half-dram vial was weighed using a top-loading balance. Then, 10μL of DCE was micropipetted into the vial and capped immediately (this was done to assure no evaporation of the sample occurred). The balance was tared and the capped vial was re-weighed. The difference obtained was taken to be the weight of the sample. By averaging the weight of the sample obtained from each trial, a value of 0.0125g was produced; giving a 99.52% accuracy to the referenced value of 0.01256g (10μL*1.256g/mL*1000). Therefore, it can be concluded that the micropippette in use for this experiment was able to accurately dispense the solvent.


Trial

Volume pipetted (μL)


Weight of vial (g)

Weight of vial with sample (g)

Weight of sample (g)

1
10
3.2714
3.2849
0.0135
2
10
3.2692
3.2804
0.0112
3
10
3.2738
3.2866
0.0128


18:32 10μL of 1,2-dichloroethane was added to all NMR sample tubes.
18:45
Obtained HNMR spectra all of solutions (except "ether" solution) on the 500MHz Varian Invoa instrument.
18:46 NMR tube containing the "ether" solution broke, and mistakenly another "chloroform" solution was drawn-up. An NMR spectra for that new sample of "chloroform" was obtained and no data for ether solution could be reported because it was lost.



2009-02-27

00:39 Micropipetted 1mL of chloroform into a vial labeled "CHCl3" and capped it.
00:42 A spatula was cleaned using acetone.
13:11 Added crotonic acid to the chloroform solvent and vortexed the vial. More solute was added to the vial if no undissolved solute remained after the stint of vortexing. This process was repeated until no more solute was observed to go into solution. It was observed that the process of mixing the solute and solvent together was an endothermic reaction, because the vials grew noticeably cold to the touch. Also, the crotonic acid collected at the top of the vial; which indicates that the density of the solvent is greater than that of the solute which is indeed true.
13:16 Vortexed the vial for 10 minutes.
13:28 Vial was left to equilibriate
13:30 An NMR tube was cleaned using acetone, which was then allowed to evaporate using a laboratory oven.
13:38 An NMR cap was cleaned and using acetone, which was then briefly evaporated in the oven.

2009-02-28

11:53 Collected the supernatant from the saturated chloroform solution using a Pasteur pipette into a new vial, labeled "sat. chloroform."
12:06 Pipetted 10μL of 1,2-dichloroethane into a NMR tube labeled "7 chloroform."
12:15
Pipetted 100μL of the supernatant from "sat. chloroform" into NMR tube "7 chlorform."
12:16 Vortexed the NMR tube.

12:26 Weighed 0.10189g of crotonic acid, which was then placed into a vial labeled "0.5M CA."
12:29 Added 2mL of n-hexane to the vial to make a 0.5M solution.[this is still not a 0.5M solution - remember the difference between molarity and molality JCB]
12:33 Vortexed the vial until no undissovled solute was left.
12:42 Cleaned an NMR tube and cap with acetone, and briefly evaporated off the solvent in a laboratory oven.
12:44 Added 700μL of deuterated chloroform to the NMR tube, which was labeled ".5M CA."
12:44
Added 200μL of the 0.5M crotonic acid in n-hexane solution to the NMR tube.
12:45 Vortexed the NM
R tube.

22:00 Obtained HNMR of the solutions ("7 chloroform" and ".5M CA").




Compound
Inchi Key
Inchi
Crotonic acid
LDHQCZJRKDOVOX-NSCUHMNNBH
InChI=1/C4H6O2/c1-2-3-4(5)6/h2-3H,1H3,(H,5,6)/b3-2
Acetonitrile
WEVYAHXRMPXWCK-UHFFFAOYAJ
InChI=1/C2H3N/c1-2-3/h1H3
Chloroform
HEDRZPFGACZZDS-UHFFFAOYAG
InChI=1/CHCl3/c2-1(3)4/h1H
Ether
RTZKZFJDLAIYFH-UHFFFAOYAB
InChI=1/C4H10O/c1-3-5-4-2/h3-4H2,1-2H3
DMSO
IAZDPXIOMUYVGZ-UHFFFAOYAR
InChI=1/C2H6OS/c1-4(2)3/h1-2H3
n-Hexane
VLKZOEOYAKHREP-UHFFFAOYAD
InChI=1/C6H14/c1-3-5-6-4-2/h3-6H2,1-2H3
Dichloromethane
YMWUJEATGCHHMB-UHFFFAOYAG
InChI=1/CH2Cl2/c2-1-3/h1H2