Patent GB-658758-A (GB)
Title: Improvements in the manufacture of 11-bromo-undecy lic acid
IPC: C07C53/19
Filed: 1948-08-05
Abstract: 11-Bromo-undecylic acid is made by treating a solution of 10-11-undecylenic acid with a maintained excess of hydrobromic acid in a hydrocarbon or chlorinated hydrocarbon solvent which is substantially inert to hydrobromic acid, in the presence of an added gas containing free molecular oxygen at -10-+40 DEG  C., preferably 0-30 DEG  C., whilst avoiding the presence of Fe, Cu and Al and their compounds, which catalyse the production of the 10 isomer.  Benzene, toluene and pet. ether are specified solvents. Oxygen is supplied by bubbling air through the reaction medium and excess hydrobromic acid is maintained by gradually adding the undecylenic acid to hydrobromic acid in the solvent, by adding both acids simultaneously to the solvent, an excess of hydrobromic acid being used, and reacting the undecylenic acid in the solvent in counterflow with gaseous hydrobromic acid at rates to provide an excess of the latter. Hydrobromic acid may be made in any known fashion desirably by direct combination of the elements when, however, an excess of hydrogen is present, which favours the production of the 10 isomer of the desired acid.  No difficulties arise when using solutions of hydrobromic acid since hydrogen is not soluble in these solvents, otherwise the hydrobromic acid may be stripped from mixture with hydrogen by dissolving in acetic acid or anhydride at, e.g., 15 DEG  C. and volatilizing off at about 110 DEG  C.  In examples: (1) air is passed through a solution of hydrobromic acid in toluene whilst 10-11-undecylenic acid is gradually added over 30-40 minutes, the temperature meanwhile rising from - 8-+15 DEG  C., and the 11-bromo-undecylic acid isolated by fractionation is purified by recrystallization from ligroin; (2) air is passed through toluene to which is added simultaneously a solution of hydrobromic acid in toluene and 10-11-undecylenic acid, cooling to 30-40 DEG  C. being effected and the product isolated as in (1); (3) 10-11-undecylenic acid is reacted at 30-40 DEG  C. with hydrobromic acid in benzene, whilst air is passed through, the hydrobromic acid being freed from hydrogen by the above indicated solvent treatment, a counter-current extraction method with acetic acid or anhydride being illustrated; (4) also illustrates the separation of hydrogen from hydrobromic acid, subsequent steps being as in (1); and in (5) undecylenic acid in toluene is reacted at about 30 DEG  C. in counterflow with hydrogen-free hydrobromic acid whilst air is passed through the reaction zone, the product being isolated as in (1).ALSO:Hydrobromic acid made from bromine and hydrogen is purified from excess hydrogen by absorption in a solvent for the acid such as acetic acid or anhydride at about 15 DEG  C., the acid being liberated on heating at about 110 DEG  C. and the stripped solvent re-used.  An illustration is provided of countercurrent absorption of the acid in a downwardly-moving stream of acetic acid or anhydride in a vessel provided with a cooling device, hydrogen passing out at the top and solvent containing hydrobromic acid at the bottom.