2,4-D and glyphosate are not related chemicals. Their mode of action is different, with 2,4-D acting as a plant growth regulator and glyphosate preventing the production of an enzyme that is need to make proteins.
Agent Orange was a blend of herbicides, and was concocted long before Roundup was invented. It contained 2,4-D and 2,4–5-T, both selective broadleaf herbicides (in other words, plants with a single cotyledon, like rice or barley are not affected by it, but plants with leaves that exhibit bilateral symmetry, like trees and vines, are.) The object of using Agent Orange was to help bombers seek out jungle roads, and to eliminate the vegetative canopy where snipers could hide, all without harming the civilians’ rice and grain crops. 2,4–5T was banned in the 1970’s It was the bad actor in Agent Orange, because it is mutagenic and teratogenic in humans. In addition, its manufacture left traces of a dioxin
Roundup, Glyphosate, is non-selective, and kills every plant it contacts, given sufficient quantity.
The two products are not the same but they are still herbicide chemicals that aren't healthy to say the least.