Aliphatische Azoverbindungen, I Darstellung und Thermolyse von 1.1′‐Dimethyl‐azocycloalkanen, 1‐Methylcycloalkyl‐azobenzolen und 1‐Methylcycloalkyl‐azo‐α‐cumolen
Abstract:Es wurden dargestellt die 1.1'-Dimethyl-azocycloalkane 2 b (n = 4-8) aus den entsprechenden Aminen mit JF5, die 1-Methylcycloalkyl-azobenzole 3 (n = 5-6) durch Kupplung der Grignard-Verbindungen mit Benzoldiazonium-tetrafluoroborat und die I-Methylcycloalkyl-azo-a-cumole 4 (n = 5 -6) aus den unsymmetrischen Harnstoffen iiber Diaziridinone, deren Hydrolyse und folgende Oxidation mit Queckdilberoxid. -Die Kinetik der Thermolyse dieser Azoverbindungen wurde gaschromatographisch oder UV-spektroskopisch verfolgt. D… Show more
“…The DSC data reveal that the 1,1′‐biscycloazo azo compounds decompose over a wide temperature range. These results are in line with previous publications describing the rates of decompositions of α ‐methylcycloalkylazo derivatives and those azonitriles derived from various cycloalkanones 19, 20. In both cases the order of thermal stability decreases from cyclobutyl > cyclohexyl > cyclopentyl >> cyclododecyl, and the striking differences in thermal stability has been attributed to differences in ring strain.…”
A number of symmetrical and unsymmetrical azoalkanes of the general formula R(SN ¼ NSR and related azoxy, hydrazone as well as azine derivatives have been synthesized in order to assess their potential as novel flame retardants for polypropylene alone or in combination with commercially available flame retardants such as alumina trihydrate (ATH), decabromodiphenyl ether (DecaBDE) and tris(3-bromo-2,2-bis(bromomethyl)-propyl)phosphate (TBBPP). The experimental results show that in the series of different sized azocycloalkanes the flame retardant efficacy decreased in the following order: R ¼ cyclohexyl > cyclopentyl > cyclobutyl > cyclooctanyl >> cyclododecanyl. Whereas in the series of aliphatic azoalkanes compounds the efficacy decreased in the following order: R ¼ n-alkyl > tert-butyl > tert-octyl. In addition, also some of the prepared azoxy, azine, and hydrazone derivatives provide flame retardancy to polypropylene films at already very low concentrations (0.25-1 wt%). Noteworthy is that in contrast to other halogen-free radical generators, the azoalkanes are also very effective as flame retardants in polypropylene thick moldings. Interestingly, it was found that 4,4(-bis(cyclohexylazocyclohexyl)-methane) shows a strong synergistic effect with ATH. Thus, in the presence of 0.5 wt% of azoalkane the ATH loading could be reduced from 60 to 25 wt% and still UL94 V-2 rating could be reached. Furthermore, the fire testing data reveal that azoalkanes show a synergistic effect with DecaBDE and when used in conjunction with very low loadings of TBBPP.
“…The DSC data reveal that the 1,1′‐biscycloazo azo compounds decompose over a wide temperature range. These results are in line with previous publications describing the rates of decompositions of α ‐methylcycloalkylazo derivatives and those azonitriles derived from various cycloalkanones 19, 20. In both cases the order of thermal stability decreases from cyclobutyl > cyclohexyl > cyclopentyl >> cyclododecyl, and the striking differences in thermal stability has been attributed to differences in ring strain.…”
A number of symmetrical and unsymmetrical azoalkanes of the general formula R(SN ¼ NSR and related azoxy, hydrazone as well as azine derivatives have been synthesized in order to assess their potential as novel flame retardants for polypropylene alone or in combination with commercially available flame retardants such as alumina trihydrate (ATH), decabromodiphenyl ether (DecaBDE) and tris(3-bromo-2,2-bis(bromomethyl)-propyl)phosphate (TBBPP). The experimental results show that in the series of different sized azocycloalkanes the flame retardant efficacy decreased in the following order: R ¼ cyclohexyl > cyclopentyl > cyclobutyl > cyclooctanyl >> cyclododecanyl. Whereas in the series of aliphatic azoalkanes compounds the efficacy decreased in the following order: R ¼ n-alkyl > tert-butyl > tert-octyl. In addition, also some of the prepared azoxy, azine, and hydrazone derivatives provide flame retardancy to polypropylene films at already very low concentrations (0.25-1 wt%). Noteworthy is that in contrast to other halogen-free radical generators, the azoalkanes are also very effective as flame retardants in polypropylene thick moldings. Interestingly, it was found that 4,4(-bis(cyclohexylazocyclohexyl)-methane) shows a strong synergistic effect with ATH. Thus, in the presence of 0.5 wt% of azoalkane the ATH loading could be reduced from 60 to 25 wt% and still UL94 V-2 rating could be reached. Furthermore, the fire testing data reveal that azoalkanes show a synergistic effect with DecaBDE and when used in conjunction with very low loadings of TBBPP.
“…Consistent with this explanation, the relative rates of reaction of the derivatives of alanine 67 and sarcosine 85a are nearly identical, since the extent of nonbonding interactions associated with planar conformations of the radicals 67 and 103 is very similar. Methyl pyroglutamate ( 63 ) reacts faster than the glycine derivative 16a , because the radical 104 can adopt planar conformations which are relatively free of nonbonding interactions and because formation of the radical 104 is favored by the relief of ring strain and by the release of steric interactions between the methoxycarbonyl substituent and the β-hydrogens. − 3 Nonbonding interactions associated with planar conformations of the radicals 20 , 67 , 93 , and 103 − 105 .…”
Section: A Intermolecular To Give
α-Carbon-centered
Radicalsmentioning
“…In the present report, we describe the free-radical chemistry of initiators 4 − 7 . Azoalkanes 5 − 7 are new, but 4 and two related compounds are already known. Mechanistic studies of 4 are lacking, despite the fact that this initiator affords two well-studied radicals: cumyl − and tert -butyl. − The cross reactions of these radicals are described herein.…”
Four tert-butylazocumenes (4-7) were prepared from the corresponding cyanobenzenes, and their nitrogen evolution kinetics and products were analyzed. In combination with TEMPO, the simplest compound, tert-butylazocumene (4), shows promise as a "one-radical" initiator of styrene polymerization. The ABNO-trapped cumyl radical 29 is a particularly stable trialkylhydroxylamine, whose thermolysis half-life is 2.1 h at 150 degrees C. Taking advantage of this stability, we trapped the cumyl radical centers from 7 to afford tris adduct 32a. While the behavior of the meta bisazoalkane 6 can be mostly predicted from that of 4, the para isomer 5 exhibits both unusual products and kinetics, attributed to the formation of quinodimethane 33 via azo-containing radical 34. In fact, flash vacuum pyrolysis of 5 allowed observation of the (1)H and (13)C NMR spectra of 33, whose persistence even at ambient temperature showed that this quinodimethane is far more stable than the parent 36. Finally, evidence is presented that 7 is an initiator of star polymerization.
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