- Kinetische Untersuchungen zur Methanolyse von Acetalen
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It has been shown that the acid-catalyzed methanolysis of the diethylacetales RCH(OEt)2 of acetaldehyde (R=CH3), propionaldehyde (R = C2H5), butyraldehyde (R = C3H7) and caprylaldehyde (R = C7H15) at temperatures between 283 and 318 K proceeds as a consecutive reaction involving a reversible second step.The pseudo first order rate constants of the three reaction steps, their activation parameters and equilibrium constants were estimated by measuring the concentration-time-curves of starting product, intermediate and final product and using a large excess of methanol.There is a linear dependence be tween rate constants of methanolysis and concentration of the catalyst.
- Claus, P.,Berndt, T.,Scherzer, K.
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p. 1205 - 1216
(2007/10/02)
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- INDIRECT ELECTROCHEMICAL α-METHOXYLATION OF ALIPHATIC ETHERS AND ACETALS - REACTIVITY AND REGIOSELECTIVITY OF THE ANODIC OXIDATION USING TRIS(2,4-DIBROMOPHENYL)AMINE AS REDOX CATALYST
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The technically important α-methoxylation of aliphatic ethers and acetals to form mixed acetals respectively aldehydes or ortho-esters can be performed electrochemically at low potentials in methanol solution using an undivided cell and tris(2,4-dibromophenyl)amine as redox catalyst.The regioselectivity is usually considerably higher as compared with direct electrolysis in the abscence of a catalyst.Especially valuable is the method for the regioselective methoxylation of secondary carbon atoms in presence of primary or tertiary ones and of the acetal carbon in 1,3-dioxolanes.The redox catalyst is stable under the reaction conditions so that more than thousand turnovers could be obtained.
- Ginzel, Klaus-Dieter,Steckhan, Eberhard,Degner, Dieter
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p. 5797 - 5806
(2007/10/02)
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- Ozonolysis of Symmetrically 1,2-Disubstituted Ethylenes in HCl/Methanol Solutions: Acid Catalyzed Reactions of Primary Cleavage Products
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The ozonolysis of olefins in 1 M anhydrous solutions of hydrogen chloride in methanol at /= 0 deg C was investigated.Upon warm-up of the ozonolysis products, the peroxidic primary fragmentation products were converted into non peroxidic end-products by HCl-catalyzed reactions.Cyclopentene (1a) and cyclohexene (1b), e.g., afforded mixtures of the corresponding α,ω-dialdehydebis(dimethyl acetals) (8), dimethyl α,ω-dicarboxylates (9), and methyl ω-aldehyde dimethyl acetal carboxylates (10).Norbornene (1c) gave a mixture of the correspondingly substituted 1,3-cyclopentane compounds (8c - 10c), phenanthrene (22) gave a mixture of methyl 2'-formyl-2-biphenylcarboxylate (24a), 2,2'-biphenyldicarbaldehyde (24b), and dimethyl 2,2'-biphenyldicarboxylate (24c).A reaction scheme was advanced for the rationalization of the types and the distribution of the products.It was partly substantiated by model reactions.
- Griesbaum, Karl,Neumeister, Joachim
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p. 2697 - 2706
(2007/10/02)
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