Careful monitoring of the product distribuQons of these reacQons, however, revealed an addiQonal effect of changing parQal pressure of CO and H2. Under the standard condiQons in which the Hammee analysis was conducted, small amounts (2 -10%) of hydrodebrominated side-products were observed for the most electron-deficient substrates. While similar amounts of these species were observed at low PH 2 their formaQon increased significant at low PCO, suggesQng that under CO limiQng condiQons hydrodebrominaQon takes over as compeQQve process to formylaQon (Table ). Prior work has invesQgated the effect of gas raQos in aryl bromide formylaQon under flow condiQons with opQmum yields and selecQvity found for 1:3 raQos of CO:H2. 10