Need help with this uestion A-E are sub questions You are given a light brown so
ID: 900673 • Letter: N
Question
Need help with this uestion A-E are sub questions
You are given a light brown solid sample with the information that it is an impure sample of an aromatic hydrocarbon– you are tasked with its purification. You ask for information about the suspected impurities, but it seems no one really knows exactly. So you ask for an IR spectra of the impure sample. Upon scrutinizing the IR spectrum carefully, you find several medium intensity signals at 3020 - 3040 cm-1 and 1510 cm-1, a small but distinct signal at 1730 cm-1, and a small broad peak centered at about 2700 cm-1. This confirms the presence of the aromatic hydrocarbon, and also gives you an idea about the nature of the impurity, but you know you need to further confirm it before finalizing your purification strategy. (Refer to the IR tables in the IR folder on Blackboard /an organic chemistry textbook / the techniques manual by Padias, to help you interpret this data.
A.What can you deduce about the nature of the impurity, based on the IR spectrum? Explain your reasoning, clarifying which IR signal(s) provided the clue(s)
B. What simple chemical test(s) could you perform to determine the correctness of your conclusions regarding the impurities? Explain your reasoning.
C. If you find that your conclusions are indeed correct, how would you plan and execute your purification task? Provide sufficient detail regarding your experimental strategy to earn full credit.
D. After recovering your product, you observe it closely: it looks like shiny, plate-like crystals that are light yellow in color. You carefully record its melting point, and believe you have completed the purification task. Explain how you might reach this conclusion from your observations.
E. When you give the purified sample to the synthetic chemists planning to use this substance in a synthesis, they tell you it cannot be pure, because the pure substance is supposed to be white, not light yellow. You bring it back to your lab and set to work again: what might you do to purify it further? Explain clearly.
Explanation / Answer
A. The impurity present here contains a carbonyl functionality, could be an aldehyde or a ketone (1730 cm-1). The broad peak at 2700 cm-1 suggests the impurity could be an aldehyde. Peaks in the region, 3020-3040 cm-1 and 1510 cm-1 shows presence of aromatic ring.
B. Aldehydes gives a very bright orange/yellw color precipitate on reaction with 2,4-DNP reagent (hydrazone derrivative). This could be thus used as a qualitative analysis test for the confirmation of presence of aldehyde group.
C. A simple column chromatography should be able to separate this impurity using ethylacetate-hexane as the mobile phase.
D. Sharp melting points suggests the compound is purified and is pure. A broad melting point range tells the compound is stil impure.
E. For a quick decoloration of the compound, take the compound is ethanol and add a pinch of activated charcoal to it. Boil the solution for few mintutes and filter hot through a pad of celite. The colored impurities should stick to charcoal and you should get pure white crystals from the filtrate upon crystallization.