# Help interpreting IR spectrum

Whilst attempting to create salicylic acid/2-hydroxybenzioc acid, one of our experiments produced a compound with a melting point of over $300^\circ\mathrm{C}$ ( as high as the machine would go) and the IR absorption spectra attached. Can anyone help us identify the compound we have produced?

We used:

• $4 \,\mathrm{g}$ of oil of wintergreen
• $100 \,\mathrm{mL}$ of $2 \,\mathrm{M}$ aqueous sodium hydroxide solution
• Sulfuric acid

The experiment was left for two weeks at which point the crystal pictured had formed.

I do believe something is wrong with this spectrum. I find it highly improbable that a compound would exhibit a single strong absorption peak at low wavenumbers, while showing no other absorbance whatsoever. The fact that there is no overtone of your band also shows me that there was some experimental error when recording this spectrum.

I second @Ezze, there is something fishy here and the spectral data recorded do not match with how a spectrum of your targeted material should look like:

(Notice that this spectrum was recorded in transmission mode with a pellet of KBr and hence differs slightly from the ATR-FTIR setup you likely deploy [the $\ce{CO2}$ bump]).

In addition, the melting point is far to high compared with literature data.

Recommended action Figure out the error with your spectrometer, record a spectrum of a compound you know about its identity and have access to a reference spectrum. Then record data of your compound (do not stop at 1000 1/cm, record if possible between 4000 to ca. 500 1/cm, as the displayed reference).

• I think sodium sulfate nails it.... – MaxW Mar 22 '17 at 5:54
• Yes we ran the experiment three times and the other two times the IR looked like it should and the melting point was in the normal range. The lab tech that ran the IR agreed she had never seen anything like it and our lecturer was also intrigued. The sample has now been destroyed so we have to attempt to work out what we have made with the data we have. Sodium sulfate seems a strong contender thanks @Buttonwood – Jessica Madden Mar 22 '17 at 13:01
• @JessicaMadden The ester was cleaved-off under basic conditions; yet aq. NaOH naturally will deprotonate both the acid and the phenolic OH and I speculate this disodium salt is much more water soluble, than expected. As both the pure starting material, as well as the pure product are colourless, perhaps you accidentally confused once the aqueous phase with the organic phase during and extractive workup? Perhaps you did not add enough acid (both for neutralization + acidification .and. thoroughly mixing .and. check) to the aq. phase prior back-extraction? I myself know both errors, too... – Buttonwood Mar 22 '17 at 22:30
• @JessicaMadden As an additional suggestion for future improvement, taking into account that there was a first lab class, and a second one about two weeks later -- maybe used to further purify the product by a slow recrystallization: ATR-FTIR spectroscopy does not consume a lot of sample material, does not require additional chemicals, and is rapidly recorded; just record IR data of your pre-purified product, prior to cleaning the work space. I do so after column chromatography, to confirm "the correct fraction", too -- often quicker, and much less expensive than to collect a H-NMR spectrum. – Buttonwood Mar 22 '17 at 22:35
• It probably is the spectrum of sodium sulphate...some things still seem a bit off though. webbook.nist.gov/cgi/… – Eashaan Godbole Mar 4 '18 at 19:43