Günther Rist

Time-resolved ESR and endor during the photolysis of ω,ω-dimethoxy-ω-phenyl-acetophenone

Abstract The ketone ω,ω-dimethoxy-ω-phenyl-acetophenone (DMPA) is an efficient initiator in UV-curing polymerization processes started by photochemically generated radicals. The short-lived radical intermediates created during the photolysis of DMPA have been investigated by time-resolved ESR and ENDOR spectroscopy taking advantage of a strong CIDEP effect.

Some aspects of a new class of sulfur containing phenolic antioxidants

Abstract The commercial sulfur containing antioxidant AO2 (Irganox 1520) is compared with other classical phenolic antioxidants, and its special autosynergistic profile, particularly under dynamic test conditions (Brabender, 160 °C), in commercial polybutadiene rubber is investigated. AO2 outperforms all other tested phenolic stabilizers. A tentative mechanistic explanation for the action of AO2 is given, consisting of either a concerted reaction or a ‘tandem reaction’ of the antioxidant with macroalkylperoxy radicals. Other mechanistic pathways, for instance the role of the phenoxy radical 8 or its C,Orecombination products with oxygen centered radicals (such as macroalkylperoxy radicals) and of the recently synthesized stable quinone methide 10 are discussed. CIDNP experiments, generating the radical 8 from AO2 , demonstrate that the main reaction between phenoxy radicals 8 is regioselective C,O-recombination, giving rise to the dimers 9a and 9b and no direct formation of quinone methide 10 and C,C-coupling products is observed.

ORGANIC PHOSPHORUS COMPOUNDS 771 SYNTHESIS AND PROPERTIES OF PHOSPHINOTHRICIN HOMOLOGS AND ANALOGS

Abstract The synthesis, chemical, and spectral properties of (3-amino-3-hydroxycarbonyl-propyl)phosphonous acid (2), bis(3-amino-3-hydroxycarbonylpropyl)phosphinic acid (5), (2-amino-2-hydroxycarbonylethyl)-methyl-phosphinic acid (6), (1-amino-2-hydroxycarbonylethyl)methylphosphinic acid (10), and of a structural isomer of phosphinothricin, (3-amino-2-hydroxycarbonylpropyl)-methylphosphinic acid (12) are described. While the phosphonous acid derivative 2 exhibited weak herbicidal activity, the acids 4, 5, 8, 10, and 12, showed no activity as herbicides. The phosphinic acid 12 showed weak plant growth regulator properties.

ORGANISCHE PHOSPHORVERBINDUNGEN 81 HERSTELLUNG VON HETEROCYCLISCH SUBSTTTUIERTEN PHOSPHINOXIDEN UND DEREN VERWENDUNG IN DER WITTIG-HORNER REAKTION

Abstract The reaction of dimethyl-chloromethylphosphinoxide with the alkali salts of imidazole, pyrazole, triazole, benztriazole, 2-methyIimidazole, benzimidazole, tetrazole, and indazole yields the corresponding dimethyl-heterocyclic substituted methylphosphine oxides 1a-1i (Table I). These phosphine oxides easily undergo a Wittig-Horner reaction when treated with aldehydes and ketones and give a cis/trans = 1:1 mixture of the corresponding olefines 2a, 2a′, 2b, 2d and 2f. Several of these can be separated by flash chromatography into the pure cis and trans isomers. It was observed that only the cis compounds exhibit fungicidal activity against Erysiphe graminis.

STABLE QUINONE METHIDES II: ADDITION OF THIOLS TO QUINONE METHIDES, SYNTHESIS OF BISALKYLTHIOSUBSTITUTED QUINONE METHIDES AND TRITHIO-ORTHOBENZOATES

Abstract Regioselective oxidation of the p-alkylthiomethylphenols 1 with K3[Fe(CN)6] to the monosubstituted p-quinone methides 2 followed by addition of thiols R3SH gives rise to the dithioacetals 3.1 This reaction sequence can be extended to introduce a third RS substituent by repeating the above mentioned reactions. Spectroscopic data, especially 1H-NMR and 13C-NMR data of the quinone methides 4 and the new trithioorthoesters 5 are discussed. The same regioselectivity as for the oxidation of la 1 is observed when compounds with two different activated benzylic positions e.g. 3a and 3b are oxidized with K1[Fe(CN)6]. The sequence 1 → 2 → 3 → 4 → 5 constitutes a new approach to trithio-orthoesters.

ESR- and CIDNP-investigation of industrial additives

ESR and CIDNP are applied to the investigation of the reaction mechanisms of several phenolic antioxidants and initiators of polymerization. It is shown how the ESR- and CIDNP-techniques complement each other.

New electroactive 2-n-octyloxy-5,6,11,12- tetrathiotetracene dodecylsulfate cation radical salt: Formation at the air-water interface and characteristic properties of Langmuir-Blodgett films

Abstract The formation and characteristic properties of the new electroactive 2-n-octyloxy-5,6,11,12-tetrathiotetracene dodecylsulfate cation radical salt 1 are described. The salt is prepared in monomolecular layers at the air-water interface according to the following steps: (a) neutral donor molecules of 2-n-octyloxy-5,6,11,12-tetrathiotetracene 2 are spread on an aqueous sodium dodecylsulfate solution, (b) the monolayer of 2 thus prepared is gradually oxidized by air under formation of cation radicals, while (c) the dodecylsulfate ions 3 present in the subphase are inserted in the monolayer as counterions of the cation radicals. This insertion is accompanied by an expansion of the monolayer by about 70% of the original area. The oxidized monolayers can be easily deposited on different substrates by the Langmuir-Blodgett (LB) technique. Characterization of the LB films by various spectroscopic methods such as UV-visible, IR and ESR spectroscopies indicates that the films consist exclusively of the cation radical salt 1. Electron spin resonance spectroscopy studies suggest that the tetrathiotetracene molecular plane is oriented perpendicular to the substrate plane. It is demonstrated by conductivity measurements and cyclic voltammetry that the LB films are poorly conducting but can be reversibly oxidized and reduced electrochemically.

1H-,2D- and 13C-CIDNP Investigation of Photoinitiators and Photoinduced Polymerization

The photochemistry of the polymerization initiators ω,ω-dimethoxy-ω-phenyl-acetophenone (A) and ω,ω-diethoxy-acetophenone (B) has been studied by 1H-, 2D- and 13C-CIDNP-experiments. In some radical scavenging experiments the competition between reactions among initiator radicals and reactions of initiator radicals with the monomer acrylic acid methyl ester was observed at low monomer concentrations. These experiments give insight into the first steps of the polymerization process.