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92 Organic Chemistry Solutions Manual So, if the available concentrations of are about 25, the ratio of esters must be about 25 the other way with a 25-fold excess of MeCO₂R². The mixture contains about 96% and about 4% This is quite enough to make ester exchange a practical method. Problem 4 Write a mechanism for the reaction to give HCI on alumina. You do not need to consider the role of the alumina. CI 2HCI + + + CO CI on oxalyl chloride Purpose of the problem Practice at writing mechanisms of new reactions. Suggested solution The first step must surely be attack of water on one of the very reactive acid chlorides. + CI 0 H2O 0 0 + HCI H2O 0 CI 0 CI 0 CI This intermediate, which is half acid and half acid chloride, can now decompose to produce all 3 the products in a step greatly favoured by entropy. H 0 0 + H + CO₂ + co + CI 0 CI Problem 5 Propose a mechanism for the formation of the diazonium salt referred to in the chapter. The first step is the formation of nitrous acid HONO. N NH₂ N HCI 0-5 °C Purpose of the problem Practice at writing the complicated mechanism of an important reaction that we shall need later. Suggested solution The first step is the formation of HONO, we are told, and it is clear that the amine must be a nucleophile as amines can only play that role. HONO must be the electrophile so we had better combine them to form an N-N bond as that is present in the product. 0 H₂ H Pur NH₂ N 0 N N N N OH OH