Question

2. Why is it safer to use NaOCI as the oxidant, rather than Cro. / pyridine? 3. Sodium hypochlorite is prepared by reacting Cl, through aqueous (excess) NaOH. Write a balanced equation for this; HINT: push electrons. 4. Looking a the reaction scheme in the background section of this lab, what mechanism(s) are involved in this reaction. Name them and indicate which reaction steps follow these mechanistic patterns. 130

Answer 1

2) Chromium trioxide in pyridine, AKA Collins' Reagent gives pyridinium chlorochromate, a controlled oxidizing agent, like NaOCl which does not oxidize alcohols all the way to acids but stops at the aldehyde stage. The chromium reagent is extremely hygroscopic and also is produced is a highly exothermic reaction, so rapid that the flask tends to inflame during preparation itself. Since sodium hypochlorite's preparation is neither rapidly exothermic nor highly hygroscopic, it is a safer alternative to the former.

3) When chlorine is passed through excess NaOH, it dissociates and reacts with NaOH to produce NaOCl and NaCl, giving water. When an aqueous NaOH solution is used, the result is aqueous sodium hypochlorite solution.

$2\;NaOH _{(aq)} + Cl_2 _{(g)} \rightarrow NaCl _{(aq)} + NaOCl _{(aq)} + H_2 O _{(l)}$