First, I have to qualify my subject statement by saying that there are two types of sweet basil oil, one with high levels (>70%) of methyl chavicol (estragol) and one without. I believe that I am talking about the one with high levels. My experience is based on the sweet basil oil purchased from http://www.perfumersworld.com/listproducts.php?maingroup=Aroma%20Materials&secondgroup=A-Alifatic
(If I remember correctly, this company is in Korea. I had no problem with customs.). This sweet basil oil tastes similar to anise oil except more like root beer. Thus, substituting sweet basil oil for anise oil in any root beer recipe should improve the flavor. Amazingly, although sweet basil oil has been available for a long time, I have never seen it in any root beer recipe. However, I suspect that methyl chavicol is used in some commercial formulas.
According to http://www.thegoodscentscompany.com/data/es1006622.html
, the safety "Recommendation for sweet basil oil flavor usage levels up to : 20.0000 ppm in the finished product."
According to http://www.thegoodscentscompany.com/data/rw1013251.html
, the safety "Recommendation for estragole flavor usage levels up to : 50.0000 ppm in the finished product."