Effect of oxygen and hydrogen nitride on prepared cobalt–bromide complex in benzonitrile has been studied. It has been found that destruction of cobalt – bromide complexes does not take place in a presence of oxygen, and composition does not change. On passage of the oxygen – hydrogen nitride mixture through the cobalt–bromide complex, these complexes degrade. The larger the volume fraction of hydrogen nitride within the oxygen – hydrogen nitride mixture, the higher the rate of bromide complexes destruction. Simultaneously redistribution of mole fractions of cobalt–bromide complexes takes place. The share of tri- and dibromide mixtures of complexes decreases, while he share of monobromide complex increases