acCAION SYNTH OF AN ESTER Post-Lab Questions 1. Propionic acid and methyl acetat

Question

acCAION SYNTH OF AN ESTER Post-Lab Questions 1. Propionic acid and methyl acetate are isomers. Which has the higher boiling point and why? Which one would have the greater R, value on TLC? Why? Thinking about your reasoning for the TLC question above, devise a way to separate unre- acted alcohol from your ester using column chro about w the ester. 2. matography. You do not need to be specific hich solvent system to use, etc., just give a general procedure for the purification of Polylethylene terephthalate), which is the commonly used polyester, Dacron, can be formed by an acid-catalyzed esterification between ethylene glycol (HOCH,CH,OH) and terephthalic acid (HOOC-CH,-COOH, para isomer). Show the polymerization reaction. id-catalyzed esterification to favor ester How would you change the reaction conditions of ac hydrolysis rather than ester formation? 4. 5. Give the structure of the product formed when adipic acid (HOOC-(CH,),-COOH) is reacted with a large excess of 1-propanol with a sulfuric acid catalyst. 6. Why was the reaction mixture from this experiment extracted with sodium carbonate? What gas is evolved during the addition? Write out the reactionís) and explain why it is necessary to do this extraction. If 1.0 g of isopentyl alcohol is reacted with an excess of acetic acid, and 1 mL of isopentyl acetate (d = 0.876) is obtained, what is the % yield? 7. 138

Explanation / Answer

TLC stands for Thin Layer Chromatography; it is an analytical technique in which we exploit each sample's affinity toward different polar/nonpolar solvents.

We use a stationary phase: a phase which does NOT moves, as the name implies. It is typically the "thin layer" or the "plate". It is commonly to use silica gel plates, which are polar, but any species could be used, such as paper.

We also use a mobile phase: as the name implies, this phase will "move" and will carry along the path all the components from the solvent. Many times, you will be able to split in several components the "mixture" of the sample. Therefore, they can be seen in the stationary phase (plate). Typically, we allow the mobile phase to go up to the "Rfinal" mark, or final reference. This is the distance travelled by the solvent (mobile phase). It starts at solvent level, it is R0, therefore.

Rf = distance traveled by sample / distance traveled by solvent

Then, "Rf" value allows us to understand the affinities of anaytes towards the solvent.

As Rf increases, this implies higher affinity toward the mobile phase ( since it is carried all along the mobile phase)

If Rf is low, this implies a low affinity toward the mobile phase; therefore higher affinity toward the stationary phase, since it sticks to the plate rather than travel upwards.

Therefore

Q1:

methyl acetate --> nonpolar, propionic acid --< polar

Rf depends on polarity, the least poalr remains low in Rf, sicne it will prefer the stationary phase

Rf for the nonpolar will be high, since Rf will go to the mobile phase, then it travels longer

Q2

unreacted alcohol --> polar

reacted ester --> nonpolar

therefore, we can use cromatography to explotis their polarities and separate the alcohol vs. ester

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.