Triazene functionality

A smouldering bag in a pesticide warehouse, believed to be of this, led to an explosion, killing three firemen, and fire which took six days to extinguish (possibly because of caution concerning anti-cholinesterase toxicity). This is a moderately high energy compound by virtue of the triazene function. Other pesticides present were of less energetic structure. 

Azo functions are well known to initiate free radical polymerization and have been used previously in polymeric initiators [6]. However, triazene functions are only rarely used in free radical polymerization [7], and not much is known about their thermal decomposition mechanism. The comparison of the thermal characterisitics of two model compounds, 3 and 4 (see Fig. 3), for AMP and TMP has shown that the azo fimction is much more thermally labile than the triazene group. The maximum of decomposition in bulk for 3 is at 135 °C and for 4 at 270 °C. Decomposition of 3 and 4 in DMSO solution at 80 °C followed by UV spectroscopy led to complete decomposition of 3 after 600 min whereas only about 5 % of the triazene functions are destroyed at this time. 

The azo initiator was chosen in a way that the low molecular dinitrile radical formed after decomposition does not initiate fi ee radical formation. Therefore no homopolymer of the graft monomer in the graft products A-PC was found. However, in the case of the triazene initiator functions homopolymer formation can not be fully excluded in T-PC. Further studies on grafting efficiency, length and number of graft arms, and homopolymer formation, as well as on the initiator mechanism of the triazene functions are in progress. 

The chemical structures of the tested polymers TM1, TM2, MP1, and MP2 are shown in Scheme 3. TM1 and TM2 contain triazene functional groups,... 

Scheme 12-8 Linking functionalized aromatic monomers to polystyrene beads via the l-aryl-3,3-dialkyl triazene functional group. Reagents (a) dicyclohexylcarboiimide, 1-hydroxybenzotriazole, DMF, 25 °C, 48 h (b) sodium hydride, THF, 70 °C, 96 h (c) potassium carbonate, DMF, 0°C, 2 h. (d) n-propylamine, THF, 70 °C, ten days.

However, an evaluation of the observed (overall) rate constants as a function of the water concentration (5 to 25 % in acetonitrile) does not yield constant values for ki and k2/k i. This result can be tentatively explained as due to changes in the water structure. Arnett et al. (1977) have found that bulk water has an H-bond acceptor capacity towards pyridinium ions about twice that of monomeric water and twice as strong an H-bond donor property towards pyridines. In the present case this should lead to an increase in the N — H stretching frequency in the o-complex (H-acceptor effect) and possibly to increased stabilization of the incipient triazene compound (H-donor effect). Water reduces the ion pairing of the diazonium salt and therefore increases its reactivity (Penton and Zollinger, 1971 Hashida et al., 1974 Juri and Bartsch, 1980), resulting in an increase in the rate of formation of the o-complex (ik ). 

A variety of cleavage conditions have been reported for the release of amines from a solid support. Triazene linker 52 prepared from Merrifield resin in three steps was used for the solid-phase synthesis of aliphatic amines (Scheme 22) [61]. The triazenes were stable to basic conditions and the amino products were released in high yields upon treatment with mild acids. Alternatively, base labile linker 53 synthesized from a-bromo-p-toluic acid in two steps was used to anchor amino functions (Scheme 23) [62]. Cleavage was accomplished by oxidation of the thioether to the sulfone with m-chloroperbenzoic acid followed by 13-elimination with a 10% solution of NH4OH in 2,2,2-trifluoroethanol. A linker based on l-(4,4 -dimethyl-2,6-dioxocyclohexylidene)ethyl (Dde) primary amine protecting group was developed for attaching amino functions (Scheme 24) [65]. Linker 54 was stable to both acidic and basic conditions and the final products were cleaved from the resin by treatment with hydrazine or transamination with ra-propylamine. 

Schmiedenkamp, A. M., I. A. Topol, S. K. Burt, H. Razafinjanahary, H. Chermette, T. Pfatzgraff, and C. J. Michejda. 1994. Triazene Proton Affinities A comparison between Density Functional, Hartree-Fock, and Post-Hartree-Fock Methods. J. Comp. Chem. 875, 875. 

Having chosen to ignore amidoximes with the general formula R C(NR R )=N—OH legitimizes our decision to ignore in this chapter A-hydroxytriazenes with their functionality R N(OH)—N=N—R (or are they the tautomeric triazene A-oxides, R N(0)= N—NH—R ) because they are all A-substituted hydroxylamines. 

The reaction of iodo-substituted aryltriazenes 594 with /-PrMgCl LiCl afforded functionalized carbazoles 596. In this reaction, evaporation of i-Prl resulting from the 1/Mg-exchange is important before heating otherwise, unwanted cross-coupling products with i-Prl are observed. Mechanistically, this reaction could proceed with the formation of an arylmagnesium derivative 595 followed by intramolecular addition of the triazene onto nitrogen with the elimination of hydroxylamine (569) (Scheme 5.31). 

Magnesiated triazene derivatives like 96 can further be used for the preparation of functionalized carbazoles 97 (equation... 

Functionalization on the polymer bead has been demonstrated extensively. Acidic cleavage of the triazene resin yields the amine resin 10, which can be recycled, and the modified aryl diazonium salts 8-R which can be further transformed directly at the cleavage step in high yields (>90%) and purities (>90-95% according to GC, NMR, HPLC analyses) (Scheme 2). 

As pointed out above, acidic media (below pH 3) cleave the triazenes to give the diazonium salts. The diazonium salts can be further functionalized as exemplified in the case of the reduction to the hydrocarbon 17-H in THF with the aid of ultrasound11 through a radical pathway. A new reagent... 

The approach from Nicolaou [13] is similarly based on the activation of an aryl halide. Aryl bromides and iodides substituted with ortho-triazene react smoothly with phenols at 80 °C in the presence of K2CO3 and CuBr-Me2S to afford diaryl ethers in good yields (Scheme 2b). The use of this procedure requires the preformation of the requisite triazenes and the subsequent removal or transformation of this functional group. 

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