4-Anilino-5,7-dinitrobenzofurazan – Untersuchungen zur Struktur und Reaktivität

4-Anilino-5,7-dinitrobenzofurazan – Studies on Structure and Reactivity 4-Anilino-5,7-dinitrobenzofurazan 3 reacts with gaseous ammonia at room temperature under elimination of aniline leading to 4 . Compound 3 may also be transformed into the isolable salt 6 by treatment with aqueous KHCO₃, whereas 4 reacts with KHCO₃ furnishing potassium 5, 7-dinitrobenzofurazan-4-olat 5 . As shown by X-ray analysis and CNDO/2 calculations of 3 , the case with which the nucleophilic substitutions proceed may be explained by the assumption of an azomethine structure in 4 and 6 .     

Struktur und Reaktivität heterosubstituierter Nitrile. XX [1]. Kinetik und Mechanismus der Addition primärer aliphatischer Amine an Arylcyanate

Structure and Reactivity of Heterosubstituted Nitriles. XX. Kinetics and Mechanism of the Addition of Primary Aliphatic Amines to Aryl Cyanates The addition rate of primary aliphatic amines to aryl cyanates in water/dioxane mixtures was measured by u.v.-spectroscopy. The second order rate constants give a linear correlation with the concentration of water. The rate of the addition is increased by growing electrophilicity of the aryl cyanates and decreased by steric hindrance of the amine substituents. The nucleophilicity of the amine has no influence on the reaction rate. The results are explained by a six-membered cyclic transition state, in which the nucleophilic attack and the proton transfer proceed with equal rate.     

Struktur und Reaktivität heterosubstituierter Nitrile. XIX [1]. Kinetik und Mechanismus der Addition sekundärer aliphatischer Amine an Arylcyanate

Structure and Reactivity of Heterosubstituted Nitriles. XIX. Kinetics and Mechanism of the Addition of Secondary Aliphatic Amines to Aryl Cyanates The N,N-dialkyl-O-aryl isourea formation by the addition of secondary aliphatic amines to aryl cyanates was studied by kinetic methods in dioxane and dioxane water mixtures. Linear relationships between the rate constants and the water concentrations, the basicity of the amines and the electrophilicity of the aryl cyanates have been found. These data and the activation parameters support two concurrent reactions, a direct nucleophilic attack of the amine to aryl cyanate and one involving a six membered transition state between a molecule of cyanate, amine and water.     

Struktur und Reaktivität heterosubstituierter Nitrile. XVIII [1]. Kinetik und Mechanismus der Alkohol-Addition an Arylcyanate in Gegenwart tertiärer Amine

Structure and Reactivity of Heterosubstituted Nitriles. XVIII. Kinetics and Mechanism of the Addition of Alcohols to Aryl Cyanates in Presence of Tertiary Amines The mechanism of the carbonic acid arylester imide or carbamic acid arylester formation by the addition of alcohols or water to aryl cyanates in the presence of tertiary amines has been studied. After a slow formation of an autocatalyst, an intermediate is formed in a fast equilibrium between this one and a molecule of aryl cyanate and tertiary amine. This intermediate is slowly alcoholyzed to carbonimidic acid diester which in part is fragmented by the base to phenole and alkyl cyanate. The alkyl cyanate undergoes further reaction with the alcohol and the amine to dialkyl ether and trialkyl ammonium cyanate in the reaction mixture.     

Struktur und Reaktivität heterosubstituierter Nitrile. XVII [1]. Kinetik und Mechanismus der Phenol-Addition an Arylcyanate in Gegenwart tertiärer Amine

Structure and Reactivity of Heterosubstituted Nitriles. XVII. Kinetics and Mechanism of the Addition of Phenols to Aryl Cyanates in Presence of Tertiary Amines The rate of carbonic acid diaryl ester imides formation by the addition of phenols to aryl cyanates in the presence of tertiary amines was determined by IR-spektroscopy. The rate constants are first order in aryl cyanates and correlate linear with [ArOH] [ArO⁻ ∥ R₃NH⁺]. The third order rate constants depend linear on the (σ + σ⁻)-values of the phenol substituents, the σ⁰-values of the aryl cyanate substituents, and the pK_a of the tertiary ammonium salts. These results support a transition state formed by the nucleophilic attack of a phenoxide trialkyl ammonium ion pair to an aryl cyanate phenol associate.     

Reaktivität und Toxizität homologer Brom- und Dibromalkane

Reactivity and Toxicity of Homologous Bromo- and Dibromoalkanes The rate constants of the reactions of 4-(4-nitrobenzyl)-pyridine (NBP) with ω,ω′-dibromoalkanes Br (CH₂)_n Br (n = 2–4), alkyl bromides C_nH_2+n1Br (N = 2–4) and allyl bromide in acetophenone were measured and compared with the LD₅₀-values of these compounds estimated on mice. The tested dibromoalkanes show a contrary graduation of reactivity and acute toxicity.     

Struktur und Reaktivität heterosubstituierter Nitrile. 24 Kinetik und Mechanismus der Reaktion von o-Phenylendiamin mit Arylcyanaten

Structure and Reactivity of Heterosubstituted Nitriles. 24. Kinetics and Mechanism of the Reaction of o-Phenylen diamine with Aryl Cyanates The second and third order rate constants for the reaction of o-phenylene diamine with aryl cyanates to 2-amino benzimidazole phenylester imide in water/dioxane have been determined by i.r. measurements. The reaction proceeds through a bimolecular and a trimolecular mechanism simultaneously. In the slow step of the bimolecular process an electrophilic attack of the aryl cyanate on o-phenylene diamine takes place in a seven membered cyclic transition state. The slow step of the trimolecular mechanism consists of a nucleophilic attack of the diamine on a phenole aryl cyanate associate by a six membered cyclic transition state. The final products of both reactions are formed by successive fast reactions.     

Darstellung und Reaktivität von 2,4-Diamino(bis-alkylamino)-1,3,5-triazin-6-yl-thioharnstoffen

Synthesis and Reactivity of 2,4-Diamino(bis-alkylamino)-s-triazine-6-thioureas 2,4-Diamino-s-triazine-6-thiourea ( 1a ) was prepared by treating cyanomelamine with hydrogen sulphide under pressure in aqueous ammonia. Addition was also performed indirectly by the reaction with thioacetamide. This method was further be used to get 2,4-bis-alkylamino-s-triazine-6-thioureas ( 1b – g ). s-Triazine-thioureas ( 1a – g ) were S-alkylated with methyl iodide or benzyl chloride to the compounds 2a – f , 3a . Hantzsch thiazole synthesis of s-triazine-thioureas with α-halocarbonyl derivatives gave 2,4-diamino(bis-alkylamino)-6-(thiazolamino)-s-triazines ( 5a – j , 6b , d – g , 7a – f ).     

Struktur und Reaktivität heterosubstituierter Nitrile. XVI[1]. Kinetik und Mechanismus der Arylcyanatbildung aus Bromcyan und Phenolen

Structure and Reactivity of Heterosubstituted Nitriles. XVI. Kinetics and Mechanism of the Formation of Arylcyanates from Cyanogen Bromide and Phenoles The first-order and second-order rate constants of the reaction of cyanogen bromide with phenoles in the presence of tertiary aliphatic amines were determined in absolute acetone. The first step of the reaction is the nucleophilic attack of the tertiary amine at the cyanogen bromide. By a fast equilibrium reaction an N-cyano-N,N,N-trialkylammonium bromide is formed, which is attacked by the phenol as a nucleophile or dissociates in the slowest steps of the reaction. The nucleophilicity and the steric hinderance of the tertiary amine, and the nucleophilicity of the phenole as well determine, which of these reactions is favoured.     

Zur Reaktivität des Methoxybutenons

Reactivity of Methoxybutenone (trans)4-Methoxy-but-3-en-2-one shows as a vinylen homologous ethyl acetate 4 functional groups: C,C-double bond, methyl, carbonyl, and methoxy group. Examples for the special reactivities are given. Cyclization reactions are reported mostly with the carbon atoms 4+2 and 4+3.