I just came across this claim and obviously this is something that sounds outright false. So why this question? After some digging I stumbeld upon a book called "Trading With the Enemy"

In this book it is claimed that the German war effort againsthe UK and the UssR as well as the Japanese war effort was only made possible in the first place by the US by trading 500 tons of Ethyl with them. However ... I do not quite trust them. The book has no sources (at least the online version of it that I found on a website that is littered with Red Stars...) and I do not find anything that confirms that this is true