Christopher Smith

Christopher Smith Chem 216 Sec 111 Discussion: Ex. #2

In experiment two, the primary alcohol octadecanol was oxidized by pyridinium chlorochromate (PCC) into an aldehyde. After the formation of the aldehyde, its

2,4-dinitrophenylhydrazine (2,4-DNP) derivative.

The formation of the initial aldehyde product took nearly two hours to react to completion. Two equivalents of PCC were used to speed this oxidation reaction. The reaction rate is expressed as r = k [octadecanol] [PCC]. TLC analysis of the reaction showed the amount of octadecanol and aldehyde product in the mixture solution alongside a solution of the original octadecanol. The aldehyde solid that was recovered had a powdery white appearance. There was a slight yellow appearance to the solid indicating that it was not completely pure. Having begun the oxidation reaction with 500 milligrams of octadecanol, the theoretical yield of aldehyde product was 496 milligrams.

262 milligrams was the amount recovered giving a 53% yield. The melting point of the solid aldehyde should have been 38oC but instead was 65oC. This observation was due to the fact that during the oxidation reaction of the octadecanol, a trimer was formed in addition to the aldehyde product. The IR spectrum still indicated that some aldehyde had been formed because an absorption peak at 1704.6 cm-1 corresponding to a C=0 aldehyde bond was present. A C—O bond from a possible trimer product may also have been present due to a small absorption peak in the range of 1000-1300 cm-1.

After formation of the solid aldehyde, its 2,4-dinitrophenylhydrazine derivative was created to test if the product was indeed an aldehyde. This is the basis for creation of the 2,4-DNP derivative. If the product is indeed a ketone or an aldehyde, then the

2,4-DNP derivative forms. Also, the melting points of aldehydes have wide melting ranges and are often low. By creating the 2,4-DNP derivative one can get a highly crystalline solid with a narrow melting range. Creating the 2,4-dinitrophenylhydrazine derivative of the reaction product formed above proved to be very difficult. The molarity of the 2,4-DNP reagent used was .101 M. Therefore, 11.1 mL (1.5 equivalents) of liquid reagent was used to react with 200 milligrams of aldehyde to form the derivative. When the solutions were mixed little instantaneous yellow precipitate was formed, and the majority of the product remained unreacted indicating that the solid was not an aldehyde but possibly a trimer. The suspended solid was suction filtered out of the 2,4-DNP solution and had a white-yellow appearance indicating some trimer and some 2,4-DNP derivative were present. The 2,4-DNP derivative was recrystallized because impurities in the solid were present. The percent yield of the recrystallization process was 43%.

An IR spectrum of the crystals presented an interesting result. While C=O and C

—H bonds were evident, a small broad band at 3431.7 cm-1 appeared. This spectrum leads to the hypothesis that through recrystallization, only the actual 2,4-DNP derivative of the small amount of aldehyde was actually recrystallized while the trimer remained in solution. The IR spectrum of the crystals correspondingly showed no indication of a

C—O bond present.