Question

help with identifiying each unknown in extraction and washing experiment. the ir spectra are given below, along with data, and the lab sheet is attached.

Neutral Solid Primary amine (Aniline) 3403cm - NE presence Transmittance 60 3258cm 1 streren NOUD Streich 50 Ctretcher strator NH2 aromatto 11 NO2 aring 2-nitroaniline K LILI 3600 3200 2800 2400 2000 1800 1600 Wavenumber cm-1 1400 1200 1000 800 600

Answer 1

There are three neutral compounds in the unknown mixtures, 2-nitroaniline, naphthalene, and phenanthrene. The neutral unknown compound is 2-nitroaniline, because of the melting point range 71-72 oC from the experiments, also the IR spectra bands corresponding to amine stretching frequency at 3400 cm-1 along with nitro stretching frequencies at 1500 cm-1 range match, also aromatic double bond stretch at 1600 match as well. This cannot be other neutral aromatic compounds such as naphthalene or phenanthrene because we cannot explain IR spectra peaks at  3400 cm-1 for them. Also, the melting point range corresponding to naphthalene or phenanthrene is not a match to the observed melting point form the experiments. So it safe to say the neutral compound observed is 2-nitroaniline.

There are three acids in the list chloroacetic acid, benzoic acid, and 3-bromopropionic acid. In this three only one of them is aromatic and contains double bonds. The IR spectra for acidic compound indicates that it has aromatic C-H stretch and C=C stretch at 3100 cm-1 and 1500 cm-1 respectively. Also, the melting point observed is a close match to the expected mp of benzoic acid that is 122 oC. Considering the mp range mismatch for 3-bromopropionic acid and chloroacetic acids along with IR spectra mismatch we can safely disregard these two as options. So the correct choice for this is benzoic acid.

Finally, there is only one clear base in the solution, i.e. p-acetylaninline. This has aromatic ring and acetyl groups both these groups have clear IR stretching frequencies at 1500 and 1700 cm-1 respectively and the IR spectra match this information. Also, the observed melting point is a very close match to the actual melting point i.e 106 oC. We observed 110 oC this could be due to some impurities in the extracted compound by further purification these impurities can be removed.