▁most ▁common ▁organ oh al ides ▁in ▁nature , ▁even ▁though ▁the ▁concentration ▁of ▁b rom ide ▁is ▁only ▁ 0 . 3 % ▁of ▁that ▁for ▁ch lor ide ▁in ▁sea ▁water , ▁because ▁of ▁the ▁easy ▁ox id ation ▁of ▁b rom ide ▁to ▁the ▁equivalent ▁of ▁Br + , ▁a ▁pot ent ▁elect roph ile . ▁The ▁en zym e ▁b rom op ero x id ase ▁catal y zes ▁this ▁reaction . ▁The ▁o ce ans ▁are ▁estimated ▁to ▁release ▁ 1 – 2 ▁million ▁tons ▁of ▁b rom o form ▁and ▁ 5 6 , 0 0 0 ▁tons ▁of ▁b rom om eth ane ▁ann ually . ▁ ▁An ▁old ▁qual itative ▁test ▁for ▁the ▁presence ▁of ▁the ▁alk ene ▁functional ▁group ▁is ▁that ▁al ken es ▁turn ▁brown ▁a que ous ▁b rom ine ▁solutions ▁colour less , ▁forming ▁a ▁b rom oh yd rin ▁with ▁some ▁of ▁the ▁di b rom o alk ane ▁also ▁produced . ▁The ▁reaction ▁passes ▁through ▁a ▁short - l ived ▁strongly ▁elect roph il ic ▁b rom on ium ▁intermediate . ▁This ▁is ▁an ▁example ▁of ▁a ▁hal ogen ▁addition ▁reaction . ▁ ▁Occ urrence ▁and ▁production ▁ ▁B rom ine ▁is ▁significantly ▁less ▁abund ant ▁in ▁the ▁cr ust ▁than ▁flu or ine ▁or ▁ch lor ine , ▁compr ising ▁only ▁ 2 . 5   parts ▁per ▁million ▁of ▁the ▁Earth ' s ▁cr ust al ▁rocks , ▁and ▁then ▁only ▁as ▁b rom ide ▁sal ts