VIdentification of an Unknown Drug Sample

Learning to identify unknown chemicals has myriad advantages, from simply checking the steps when synthesizing a chemical product, to chemical analysis of a potentially toxic environment. In particular, identifying unknown drug samples has very useful applications in pharmaceutical quality control, as well as forensics. From knowing whats exactly in a new medicine before distributing it for public consumption to something as dramatic as finding the cause of to an overdose, these are just a few examples of the importance of drug identification.

The objective of the experiment is to be able to identify a sample of an unknown drug. For this particular experiment, the unknown drug is identified from a list of six possible substances, namely Salicylamide, Paracetamol, 4-Aminosalicylic Acid, Benzocaine, 3-Aminoacetophenone, and 4-Hydroxy Acetophenone. The sample is identified using physical and chemical tests, such as appearance, acidity and solubility functional group tests and analysis of the samples Infrared and Ultra-violet spectra.
Other than the main objective, other supplementary skills developed in this exercise are determining the presence of functional groups which is useful for testing organic substances, extracting valid information from IR and UV spectra, and the critical thinking applied in the step-by-step elimination of the other possible answers.

Chemical Structures of Possible Drug Substances
Salicylamide

Paracetamol or
Aminophen
4-Aminosalicylic Acid
Benzocaine

4-Hydroxy Acetophenone
3-Aminoacetophenone

2. METHODS, RESULTS, and INFERENCE
A. Physical and Chemical Tests
MethodResultInferenceSmellOdourlessPossibly no ether presentAppearanceWhite powderNA(All are white powder)Heat on nickel foilCool (no heat)No reaction to nickelAction to damp blue litmusTurns redAcidicAction to damp red litmusNo reactionPossibly acidicSolubility in 6 drops distilled water                 UndissolvedInsoluble in H2OSolubility in 6 drops HCl (dil)                         DissolvedPossibly a weak baseSolubility in 6 drops NaOHPartially dissolvedAcidic, may contain acidic functional groupPresence of NitrogenRed to Blue Litmus,
Nitrogen is presentHas Nitrogen-containing functional groups
B. Functional Group Tests
MethodResultInferencePhenolic OH group testYellowNo phenolic OH groupCarbonyl group testYellow precipitateCarbonyl group present
Ester group testDark, almost brownish, redEster group presentAmide group testPinkNo amide groupPrimary aromatic amine group testDark red colorPrimary aromatic amine presentN-arylamide group testNANA

3. INTERPRETATION OF UV AND IR SPECTRA
 SHAPE   MERGEFORMAT 
A. Infrared Spectra 
Primary aromatic amine is distinguishable with the NH2 absorbance peaks (transmittance troughs) at 3300-3400cm-1 while an O-H stretching band can be seen between 3200-3600 cm-1 (rather broad). There are strong Aromatic CH bands at around 3000cm-1, while aliphatic CH stretching bands can be seen at 2850-2950cm-1. Theres a strong Carbonyl signal at around 1700cm-1 and the presence of the Ester group is confirmed by the absorbance peaks at around 1685cm-1 with CO stretching at 1280cm-1.

B. Ultra-Violet Spectra
In H2O, the ultra-violet spectra of the unknown sample peaks at 290nm, 220nm, and around 200nm. In HCl however, the peaks are at around 225nm and 270nm. Basing on the highest peaks, and because the wavelengths are not convergent, this is a hypsochromic shift. These peaks are rather expected though, because just basing on the solubility tests, it was shown that the unknown drug sample is insoluble in water while soluble in Hydrochloric acid.

4. DISCUSSION AND CONCLUSION
For the initial physical tests, while most of the possible substances are white powders, samples like 3-Aminoacetophenone can be outright eliminated as it is usually found to be light brown. This can be rather inconclusive though, for 4-Aminosalicylic acid which can be described as beige or off-white. The lack of an odour could also mean it was too slight as to be undetected rather than conclusive, but it does present the possibility than no ether group is present. The reaction of the litmus paper though, indicated a substance with a low pH, thus possibly eliminating the strong bases in the possible substances. The insolubility of the unknown in H2O eliminates Salicylamide since this is soluble in water. Now the presence of Nitrogen effectively eliminates 4-Hydroxy Acetophenone since this is the only substance of the five that has does not contain any Nitrogen. Now the functional group tests and Infrared spectra analysis are thus far the most conclusive. The lack of phenolic OH in itself would eliminate all the possible substances with OH in their respective chemical structures. Now with the elimination of all the other possible drug substances, plus the strong presence of the ester group and the UV spectra, it can thus be concluded that the unknown drug is Benzocaine.