2,4,6-Trimethyl-m-xylylene isothiourea dihydrochloride 64039-24-3 Pseudourea, 2,4,6-trimethyl-m-xylylenebis(2-thio-, dihydrochloride Pseudourea, 2,4,6-trimethyl-m-xylylenedithiodi-, dihydrochloride USAF EL-91