Metallorganische Peroxide. VIII. Zum Mechanismus der Zersetzung von Bis-organoantimonyl-peroxiden. Teil II

Organometallic Peroxides. VIII. Mechanism of the Decomposition of Bis-organoantimony-peroxides. Part II Bis-(bromo-triphenylantimony)-peroxide ( 1a ) reacts with bromine or iodine in an analogous way as we suggested concerning the mechanism of decomposition of 1a , yielding singulet oxygen. Moreover, we found that triphenylantimony bisiodide catalyses the decomposition of 1a . Also bis-(chloro-triphenylantimony)-peroxide ( 1b ) easily decomposes in the presence of such additives releasing singulet oxygen.     

Zum Mechanismus der Stabilisierung von Emulsionen

Mechanism of Stabilization of Emulsions The known mechanisms of stabilization of emulsions by the use of interface-active substances are explained. In emulsions which contain relatively small proportion of the emulsifier, the latter is effective exclusively at the interface between the emulsion droplet and the continuous liquid. In this case the emulsifier causes the formation and stabilization of either an o/w-or a w/o-emulsion, depending on its constitution. The physical and chemical background of the aforesaid phenomenon is discussed. Based on these considerations one can explain the HLB-system as well as the Bancroft's rule governing the relationship between partition equilibrium of the emulsifier and the type of emulsion formed. In emulsions which contain relatively large proportions of the emulsifier, the type of emulsion and its stability may also be influenced by the formation of liquid crystalline mixed phases composed of all the components. A special case is the so called ?Micro-Emulsions”?, which can be considered as micellar solutions of solubilized polar and unpolar oil.     

Phosphororganische Antioxidantien. I. Kinetik und Mechanismus der Zersetzung von Alkyl-hydroperoxiden durch o-Phenylen-phosphite und -phosphate

Organophosphorus Antioxidants. I. Kinetics and Mechanism of the Decomposition of Alkylhydroperoxides by o-Phenylene Phosphites and Phosphates The reaction mechanism of 2-(2, 6-di-tert-butyl-4-methyl-phenoxyl)-1,3,2-benzodioxaphosphole ( 1 ) with cumyl and t-butyl hydroperoxide has been studied kinetically by means of ³¹P-n.m.r. spectroscopy and high pressure liquid chromatography. 1 reacts with cumyl hydroperoxide to give the corresponding 2-oxide ( 2 ) which with more hydroperoxide and/or water forms the open chained phosphate ester 5 . This acidic phosphate decomposes hydroperoxide catalytically. The kinetic parameters of the separate reaction steps are given. The ionic mechanism of hydroperoxide decomposition is accompanied by a homolytic one in a minor proportion.     

Zum Mechanismus der Photoreaktionen von 2-Chlorchinolin mit Nucleophilen

The Mechanism of Photoreactions of 2-Chloro Quinoline with Nucleophiles The photochemical reactions of 2-chloro quinoline with various nucleophiles in water or methanol are studied. The main products are: 1,4-dihydro quinolines (1,4-addition of the respective nucleophile) 1 , quinoline 2 , and quinolines substituted in 2-position by the nucleophile 3 . There is good evidence that the elementary step of the photochemical reactions is an electron transfer reaction from the nucleophile to the singlet or triplet excited 2-chloro quinoline. The results are discussed with regard to free enthalpie differences of the electron transfer and the character of radical pairs formed.     

Photokatalytische Systeme. XXI. Zum Mechanismus der Photoreduktion von Kaliumchromat in Alkoholen

Photocatalytic Systems. XXI. On the Mechanism of the Photoreduction of Potassium Chromate in Alcohols The photolysis of crown ether complexes of potassium chromate in several alcohols has been investigated by e.s.r.-spectroscopy. Two different relatively long-lived Cr(V) intermediates formed by different reaction pathways have been observed. Radicalic oxidation products of the alcohols (alkoxy and hydroxyalkyl radicals as well as fragmentation products) and of the crown ether have been detected by spin trapping.     

Phosphororganische Antioxidantien. II. Kinetik und Mechanismus der Zersetzung von Alkylhydroperoxiden durch Esteramide der phosphorigen- und Phosphorsäure

Organophosphorus Antioxidants. II. Kinetics and Mechanism of the Decomposition of Alkylhydroperoxides by Esteramides of Phosphorous and Phosphoric Acid The reaction mechanism of 2-amido-1,3,2-benzodioxaphospholes ( 1 ) with cumyl and t-butylhydroperoxide has been studied kinetically by means of ³¹P-n.m.r. and e.p.r. spectroscopy and high pressure liquid chromatography. 1 reacts with cumyl hydroperoxide to give the corresponding 2-oxides ( 2 ) which with more hydroperoxide and/or water form the phosphate esters 7 and 8 . These acidic phosphates decompose cumyl hydroperoxide catalytically giving phenol and acetone. All amides ( 1 ) react with t-butyl hydroperoxide stoichiometrically to give t-butanol. The ionic mechanism of hydroperoxide decomposition is accompanied in a minor proportion by a homolytical one.     

Zum Mechanismus der thermischen Abspaltung von Chlorwasserstoff aus Polyvinylchlorid. 9. mitt.: Zur struktur der verzweigungen in polyvinylchlorid

The reduction of PVC and of copolymers from vinyl chloride and 2-chloropropene with lithium aluminium hydride occurs in a nearly quantitative manner. A selective reduction of the tertiary chlorine atoms in the copolymers, using lithium deuteride, cannot be observed by means of n.m.r. spectroscopy. The amount of CH₃-groupins the reduced samples was determined by i.r. spectroscopic compensation against polymethylene. The number of methyl groups determined in the copolymers agrees well with the copolymer composition found by n.m.r. spectroscopy. The experimental results of the determination of branches and of the thermal degradation indicate no tertiary chlorine atoms in PVC; therefore, one can assume another structure of branches in PVC.     

Mechanismus der katalysierten Synthese von Kohlenwasserstoffen

On the mechanism of the catalysed synthesis of hydrocarbons . Recent results by independent research teams prove that, in hydrocarbon synthesis over metal catalysts in a reducing atmosphere, the dissociative adsorption of CO is of considerable importance. On the catalyst surface the two fragments, C_ads and O_ads, react swiftly with hydrogen to CH_x,ads and H₂O respectively. CH_x,ads can be either hydrogenated to methane or incorporated in growing chains. This process may be visualized as a cis insertion of a carbene CH_2,ads in a metal-alkyl bond. In the steady state the catalyst surface is predominantly covered with CO_ads, only a small fraction of the surface atoms carrying growing alkyl groups. These have been detected by ¹³C labelling as well as by IR spectroscopy.     

Photovernetzung von Siliconen. VII. Zum Einfluß der Siliconkette – eine kinetische Studie

Photocrosslinking of Silicones. VII. The Influence of the Silicone Backbone – a Kinetic Study The photo-induced radical crosslinking of silicone containing pendant acrylate groups was investigated by nanosecond flash photolysis and photocalorimetry. From the results of the flash photolysis is inferred that the photochemically formed benzoyl radicals react with the acrylate groups of the system. A possible H-abstraction from the methyl groups of the silicone backbone was not observed. The silicone backbone functions only as an internal solvent. Calorimetric measurements with model systems support these results. The polymerization process is inhibited by oxygen. From calorimetric results is inferred that oxygen both inhibits and terminates the polymerization process. Due to their high oxygen solubility the silicone units increase the oxygen influence on the crosslinking. The calorimetric measurements shows also that a direct bond between silicone backbone and the acrylate group reduces the oxygen influence. Also, in absence of oxygen a direct bonded acrylate group accelerates the polymerization rate.     

Untersuchungen zum Mechanismus der Chlorhydrinierung von Olefinen

Studies on the Mechanism of the Chlorohydrination of Olefins We studied the rate-determining and the product-determining steps of the chlorohydrination of olefins with Cl₂/H₂O and HOCl. In competitive kinetic experiments with 3-ethylpent-2-ene and cyclohexene we determined the relative rate constants k_rel = 1,5 (with Cl₂/H₂O) and k_rel = ∞ (with HOCl). This shows that the rate-determining steps of the chlorohydrination with Cl₂/H₂O and with HOCl are different. In order to investigate the product-determining steps we determined the proportion of alkyl-(2-chloroethyl)-ethers 3 and ethylene chlorohydrine 2 in the reaction of ethylene with Cl₂ and with HOCl in alcohol/water-mixtures. The proportion of both the reaction products 3/2 was independent of the chlorinating agent used. Also the proportion of MARKOVNIKOV and anti-MARKOVNIKOV products in the chlorohydrination of propylene with Cl₂/H₂O or HOCl was independent of the type of chlorinating agent. In the chlorohydrination of cyclohexene both agents (Cl₂/H₂O and HOCl) yielded only the trans-chlorohydrine. From the results obtained it may be concluded that the product-determining step of chlorohydrination is the same for both the chlorinating agents studied.