I've done some TLC plates using ethyl acetate with 0.5% glacial acetic acid as a solvent. The structure of these substances looks polar to me. I"m assuming that ethyl acetate is not very polar. Is this correct?
Acetaminophen barely travelled any distance while aspirin went 2/3s of the way up.
Sheryl
Thanks. That helped.
Sheryl
The polarity of a solvent can indeed affect the distance traveled by different compounds on a TLC (thin-layer chromatography) plate. In the case of ethyl acetate with 0.5% glacial acetic acid as a solvent, it can be considered a moderately polar solvent.
Ethyl acetate (CH3COOC2H5) is a relatively polar molecule due to the presence of a carbonyl group (C=O). This polarity is further enhanced by the oxygen atom, which makes ethyl acetate somewhat polar. However, compared to highly polar solvents like water or methanol, ethyl acetate is considered to be less polar.
The addition of 0.5% glacial acetic acid to ethyl acetate increases its polarity slightly. Glacial acetic acid (CH3COOH) is also a polar molecule due to the carbonyl group and the presence of an acidic hydrogen atom. This combination of ethyl acetate and glacial acetic acid makes the solvent moderately polar.
Now, let's relate this information to your results. Acetaminophen and aspirin are both polar compounds due to the presence of functional groups such as hydroxyl (-OH) and carboxylic acid (-COOH) groups. Both of these compounds have the potential to undergo hydrogen bonding and other polar interactions.
Since ethyl acetate with 0.5% glacial acetic acid is a moderately polar solvent, it has a greater affinity for polar compounds like acetaminophen and aspirin. As a result, these polar compounds tend to have a slower migration rate on the TLC plate, meaning they travel a shorter distance. Acetaminophen, which barely traveled any distance, has a higher affinity for the stationary phase on the TLC plate, while aspirin, which traveled around 2/3 of the way up, has a slightly lower affinity.
It's important to note that the interpretation of TLC results is not solely based on the polarity of the solvent. Other factors, such as the Rf value (ratio of the distance traveled by the compound to the distance traveled by the solvent), the composition and thickness of the stationary phase, and the specific interactions between the compound and the stationary and mobile phases, can also influence the migration behavior of compounds on a TLC plate.