You can buy proprietary brands of sugar syrup, or if you'd prefer to make your own, I recommend making a 'rich' two parts sugar to one part water (2:1)...
See step 3 - boiling sugar solution to thicken it. If boiling sucrose without an acid catalyst (or presence of an enzyme) did indeed cause sucrose to convert to glucose and fructose, then the sugar industry would have to find another way to produce sugar. Hope that helps.
https://www.sugar.org/blog/refining-and-processing-sugar-cane/
See step 3 - boiling sugar solution to thicken it. If boiling sucrose without an acid catalyst (or presence of an enzyme) did indeed cause sucrose to convert to glucose and fructose, then the sugar industry would have to find another way to produce sugar. Hope that helps.