4-phenyl-1,2,4-triazoline-3,5-dione

Structural formula
General
Surname	4-phenyl-1,2,4-triazoline-3,5-dione
other names	4-phenyl-4,5-dihydro-3 H -1,2,4-triazole-3,5-dione ( IUPAC ) ; PTAD;
Molecular formula	C 8 H 5 N 3 O 2
Brief description	red solid
External identifiers / databases
EC number	224-191-7
ECHA InfoCard	100.021.993
PubChem	77913
Wikidata	Q905685
properties
Molar mass	175.15 g mol −1
Physical state	firmly
Melting point	165 ° C
safety instructions
GHS labeling of hazardous substances	no GHS pictograms
	no GHS pictograms
H and P phrases	H: no H-phrases
	P: no P-phrases
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

4-Phenyl-1,2,4-triazoline-3,5-dione ( PTAD ) is an azodicarbonyl compound. It was first presented in 1894 by Johannes Thiele and Otto Stange through the oxidation of 4-phenylurazole with red lead in sulfuric acid . However, the amount of substance presented was not sufficient for characterization. A synthetically useful synthesis was not published until 1971.

Extraction / representation

The synthesis starts from hydrazine and diethyl carbonate ( 1 ). These react to form ethyl hydrazine carboxylate ( 2 ), which is reacted with phenyl isocyanate ( 3 ). The 4-phenyl-1-carbethoxysemicarbazide ( 4 ) formed is cyclized with base to give 4-phenylurazole ( 5 ) , from which the PTAD ( 6 ) is finally formed by oxidation .

Synthesis route of PTAD ( 6 ) starting from hydrazine and diethyl carbonate ( 1 ). For details see text.

Chemical properties

PTAD is only stable in the absence of light and moisture; on contact with alkalis , immediate decomposition occurs. Water, alcohols and acids lead to slow decomposition. A melting or boiling point cannot be determined as the compound decomposes between 160 and 180 ° C without melting.

It is currently the most reactive dienophile known for Diels-Alder reactions . It is a thousand times more reactive than tetracyanoethene and even two thousand times more reactive than maleic anhydride . Simple cycloadditions take place at very low temperatures and even with cyclooctatetraene , which is not a suitable 1,3-diene for a Diels-Alder reaction because of its tub shape , it can react to form the expected cycloadduct. It is assumed that in this case the reaction does not occur in a concerted manner , but occurs via a homotropylium zwitterion .

use

In addition to its use in Diels-Alder reactions and other cycloadditions, it is also used as a trapping reagent for unstable molecules with conjugated double bonds because of its high reactivity and reaction speed . With PTAD the synthesis of the strongly strained prism was achieved for the first time .

Individual evidence

↑ ^a ^b ^c ^d Data sheet 4-Phenyl-1,2,4-triazoline-3,5-dione from Sigma-Aldrich , accessed on October 16, 2016 ( PDF ).
↑ Johannes Thiele, Otto Stange: About semicarbazide. In: Justus Liebig's Annals of Chemistry. 283, 1894, pp. 1-46, doi : 10.1002 / jlac.18942830102 .
^ ^A ^b R.C. Cookson, SS Gupte, IDR Stevens, and CT Watts: 4-Phenyl-1,2,4-triazoline-3,5-dione In: Organic Syntheses . 51, 1971, p. 121, doi : 10.15227 / orgsyn.051.0121 ; Coll. Vol. 6, 1988, p. 936 ( PDF ).
↑ Contacts. (Merck, Darmstadt) 2. 1985, 17.

[Sigma-1] Data sheet 4-Phenyl-1,2,4-triazoline-3,5-dione from Sigma-Aldrich , accessed on October 16, 2016 ( PDF ).

[2] Johannes Thiele, Otto Stange: About semicarbazide. In: Justus Liebig's Annals of Chemistry. 283, 1894, pp. 1-46, doi : 10.1002 / jlac.18942830102 .

[Organic_Syntheses-3] A ^b R.C. Cookson, SS Gupte, IDR Stevens, and CT Watts: 4-Phenyl-1,2,4-triazoline-3,5-dione In: Organic Syntheses . 51, 1971, p. 121, doi : 10.15227 / orgsyn.051.0121 ; Coll. Vol. 6, 1988, p. 936 ( PDF ).

[Kontakte-4] Contacts. (Merck, Darmstadt) 2. 1985, 17.