Evan Curtin and Jean-Claude Bradley
To determine the melting point of
discrepancies in melting point data
The sample of a few grams in a sealed bottle or tube was frozen then allowed to warm back up and an attempt to measure the melting point from the appearance of the sample was made.
Pic1 showing the bottle as received with 10g of 4-benzyltoluene
Pic2 showing the sealed bottle about to enter the 0C ice bath
Pic3 showing the sealed bottle with frozen contents and bath temp at -18C
Pic4 showing the tube with frozen sample and internal thermometer allowed to heat up
Pic5 showing the sample frozen at -14C after 16 days in freezer
Pic6 showing the still frozen sample in an ice water bath
HNMR of Sample
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Allowing the sample to warm to room temperature after freezing gave inconclusive results. Instead of a plateau at the melting point, the sample appeared to melt as low as about -10C but solid was still present at +7C.
Failure to solidify after 2 days at -15C suggested that the melting point should be below this value. However, after 16 days the sample did freeze and slow warming identified the melting point at about 4-6C.
An H NMR of the sample was consistent with the reported purity >98%. It was also consistent with the H NMR reported for compound 3b in (
). This compound was reported as yellow crystals melting at 97-98 C in that reference.
[Also take C NMR at some point to compare with above ref JCB]
After 2 days in the freezer the sample remains unfrozen at -15C. However, after 16 days the sample was found frozen at -14C. Immersion in an ice bath and very slow heating over a few hours revealed that complete melting happened at 4-6 C.
11:20 - Removed 4-benzyltoluene container from package, observed that it is a liquid at room temperature (25C) - pic 1
11:31 - Wrapped in parafilm, put in 0C bath. - pic 2
11:34 - No change in viscosity of the sample
11:52 - Moved sample to an acetone bath, slowly added dry ice. Sample was not frozen at -5C (bath temperature)
12:00 - unclear when sample froze but after letting heat up to -18C sample still frozen - pic 3
12:10 - Transferred ~2mL of sample into a test tube, put thermometer into the sample directly, wrapped the open end of the tube with parafilm (around the thermometer).
12:20 - Froze the sample inside the test tube, this happened completely around -30 to -35C. Removed from bath, observed as the sample warmed. Sample warmed too quickly to get accurate data.
12:41 started pic4 series of 6 about one per minute
12:51 - Froze sample again inside the test tube, observed some freezing around 0C. Let sample warm inside an acetone/dry ice bath. Sample was solid at -11C. Sample started melting at -9C. Over time, the sample melted, but the temperatures continued to rise.
11:00 put the sample in freezer
12:00 sample still liquid with internal thermometer reading of -15C
9:00 sample in freezer after 2 days still a liquid and not viscous - internal thermometer reading of -15C
11:55 - Sample in freezer is solid, internal temperature reading -14C.
11:56 - Took pic5 showing frozen sample
11:58 - Put sample in ice/water bath. Temperature of bath -1C internal temperature 2C
11:59 - Took pic6 showing still frozen sample at internal temperature 2C
12:04 - Internal temperature 2C, external temperature -1C
12:20 - Internal temperature 2.5C, external temperature 0C, sample is solid.
12:47 - Internal temperature 3C, external temperature 0C, sample is solid.
13:10 - Internal temperature 3C, external temperature 0C, sample still solid.
13:55 - Internal temp 3C external temp 0C. Sample solid.
14:05 - internal temp 4C external temp 0c some liquid formed.
14:14 - internal temp 4C external temp 0C some liquid, mostly solid in the sample.
14:43 - internal temp 4C external temp 0C some liquid, mostly solid in the sample.
14:54 - internal temp 5C external temp 0C. Slightly more liquid formed in the sample, but most of the sample is solid.
15:12 - Internal temp 5C external temp 3C. More liquid formed, still mostly solid.
15:19 - Internal temp 5.5C External temp 4C. The sample is roughly half liquid and half solid.
15:22 - Internal temp 6C, external temp 4C. The sample is nearly all liquid.
15:23 - Internal temp 6.5C. External temp 5C. The sample is completely melted.
11:36 - Mixed some of the sample with CDCl3, put in NMR tube.
12:53 - Took HNMR spectra using 300MHz varian NMR.
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