CHM243H5 Study Guide - Midterm Guide: Thin-Layer Chromatography, Column Chromatography, Molecular Sieve

The selective oxidation of a primary alcohol to an aldehyde using oxalyl chloride and DMSO at - 60 degree C, followed by triethylamine is referred to as the __oxidation. Key to the usefulness of Swern oxidation as a selective oxidant for the production of aldehydes from primary alcohols is k. PCC and CrO_5 are both Cr(VI) reagents. However, PCC/CH_2CI_2 is useful in oxidizing primary alcohols to aldehydes, while the analogous reaction with CrO_3/H_2 SO_4 will typically produce carboxylic acids. Why? Aldehydes are more reactive than ketones towards nucleophilic substitution because of both and electronic factors. Briefly explain

TEMPO Oxidation Post-Lab Questions Name: Consider the following three oxidation reactions. OH CrO3. H2SO H20 OH OH PCC CH2Cl2 OH TEMPO H20/ CH2Cl2 HWI. acid (1)? Specify what it is about a Jones oxidation (I) that drives the oxidation to the carboxylic HW2. In contrast, specify what is it about a PCC oxidation that only oxidizes the alcohol to the aldehyde and stops (I1) ?: HW3. Read the following excerpt from a TEMPO review article (Tojo, G. Fernandez, M.I. Oxidation of Alcohols to Carboxylic Acids A Guide to Current Common Practice, 2007 pg 82) "In 1987, Anelli et al. made a key contribution to TEMPO-mediated oxidations by showing that the very cheap reagent chlorine bleach (aqueous NaOCI) can function very effectively as a stoichiometric oxidant for alcohols in the presence of traces of 4-MeO-TEMPO. a reaction run at 0_C in a biphasic CH2C12-water mixture in the presence of excess of NaOCI, NaHCO3, KBr, and catalytic 4-MeO-TEMPO for oxidation to aldehydes. Under these conditions the oxidation to acids is quite slow. If the acid is desired, it is advisable to add a phase-transfer catalyst to speed up the oxidation." They established a protocol involving 209

CHEMICALS: benzyl alcohol, concentrated nitric acid (HNO_3, 15.7 M). HAZARDS: Nitric acid is highly corrosive and an oxidizer. Avoid contact with skin and wash immediately if it occurs. DISCUSSION: Primary alcohols can oxidized to aldehydes or carboxylic acids depending upon the reagent used. A gentle oxidizer such a cupric oxide (CuO) or pyridinium chlorochromate (PCC) will stop at the aldehyde. However the more common oxidizing agents, such as chromic acid (CrO_3) or permanganate (MnO_4^-), tend to proceed on to the carboxylic acid. Moreover, these reagents contain metals that may yield toxic by-products. In this exercise, a less common oxidizer, HNO_3, will be used to carry out the following reaction. Nitric acid, while highly corrosive, is relatively easy to handle, and the product nitrogen oxides (here represented by NO_2) can be easily absorbed by base. PRE-LAB: In addition to the usual items, pre-lab preparation for this experiment should include the following: Write balanced equations for both half-reactions of the redox. Combine them to determine the overall balanced redox equation. Determine the limiting reagent and calculate the theoretical yield of acid. Remember to take into account the concentration of the nitric acid solution. PROCEDURE: With increasing adoption of western lifestyles in Japan, the rates of CHD risk factors could approach those of Americans. Although the prevalence of smoking among men decreased from 80% in 1961 to 50% in the mid 1980s, it remains.