Zur Kenntnis der anomalen Reaktionen bei der Aminostickstoffbestimmung. VI Die Anomalie des Indols und seiner Derivate

Zusammenfassung Es wurde untersucht, warum Indol und viele seiner Derivate bei der Aminostickstoffbestimmung ein Gasvolumen liefern, obwohl sie keine primäre Aminogruppe besitzen. An Hand von präparativen Befunden wird gezeigt, daß die anomale Reaktion bei Indol in folgender Weise abläuft: Bei Einwirkung von salpetriger Säure bildet sich 3-Nitrosoindol, das sieh mit freiem Indol zu Indolrot polymerisiert. Gleichzeitig lagert sich die Nitrosogruppe zur Isonitrosogruppe um. Diese reagiert nun mit überschüssiger salpetriger Säure unter Entwicklung von Stickstoff und Distickstoffoxyd. Ist die Stellung 2 und 3 besetzt, so bleibt die anomale Gasentwicklung aus, da sich keine Isonitrosoverbindung bilden kann. Es wurde auch das Verhalten von 3-Methylindol und 3-Indolylessigsäure untersucht und die anomale Reaktion erörtert.

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Summary A study was made to learn why indole and many of its derivatives deliver a gas volume during the determination of the amino nitrogen, even though they contain no primary amino group. On the basis of preparative findings, it was shown that in the case of indole the anomalous reaction proceeds in the following fashion. When the nitrous acid reacts, 3-nitrosoindole is formed, which then polymerizes with free indole to indole red. At the same time, the nitroso group rearranges into the isonitroso group. The latter reacts with excess nitrous acid with evolution of nitric oxide and nitrogen dioxide. If positions 2 and 3 are occupied, there is no anomalous generation of gas, because no isonitroso compound can form. The behavior of 3-methylindole and 3-indylacetic acid was also studied and the anomalous reaction noted.

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Résumé Les auteurs ont recherché pourquoi l'indol et nombre de ses dérivés donnent lieu à un dégagement gazeux lors de la détermination de l'azote aminé bien qu'ils ne contiennent aucun groupement aminé primaire. Des constatations effectuées au cours de travaux de chimie préparative ont montré que la réaction anormale de l'indol a le cours suivant: lors de l'action de l'acide nitreux il se forme du nitroso-3 indol qui en présence d'indol libre se polymerise en rouge d'indol. Simultanément le groupement nitrosé se transpose en groupement isonitrosé. Ce dernier réagit alors avec l'acide nitreux en excès en donnant lieu à un dégagement d'azote et de protoxyde d'azote. Si les positions 2 et 3 sont occupées il ne se produit pas de dégagement gazeux anormal car la combinaison isonitrosée ne peut se former. Les auteurs ont également examiné le comportement du méthyl-3 indol et de l'acide indoyl-3 acétique et discuté leurs réactions anormales.

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I: Anomalie der Isonitrosoverbindungen¹; II: Anomalie der Verbindungen mit NH-CO-Gruppierung²; III: Anomalie der Verbindungen mit aktiven Methylengruppen³; IV: Anomalie von Glycin⁴; V: Anomalie der Phenole⁵.     

Determination and characterization of a transition structure for water–formaldehyde addition

Quantum mechanical calculations of the geometric, energetic, electronic, and vibrational features of a transition structure for gas-phase water–formaldehyde addition (FW1?) are described, and a new transition-structure search algorithm is presented. Basis-set-dependent effects are assessed by comparisons of computed properties obtained from self-consistent field (SCF) molecular orbital (MO) calculations with STO-3G, 4-31G, and 6-31G^** basis sets in the absence of electron correlation. The results obtained suggest that STO-3G-level calculations may be sufficiently reliable for the prediction of the transition structure of FW1? and for the transition structures of related carbonyl addition reactions. Moreover, the calculated activation energy for formation of FW1? from water and formaldehyde (?44 kcal mol^?1) is very similar in all three basis sets. However, the energy of formaldehyde hydration predicted by STO-3G (? ?45 kcal mol^?1) is about three times larger than that predicted by the other two basis sets, with the activation energy for dihydroxymethane dehydration also being too large in STO-3G. Calculated force constants in all three basis sets are generally too large, leading to vibrational frequencies that are also too large. However, uniformly scaled force constants (in internal coordinates) give much better agreement with experimental frequencies, scaled 4-31G force constants being slightly superior to scaled STO-3G force constants.     

Mechanisms of antioxidant action: Transformations of 4-hydroxy-2,2,6,6-tetramethylpiperidinoxyl (HTMPO) in polypropylene during processing

When 4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl (HTMPO) is processed in polypropylene in a closed mixer, almost 50% is converted to other products during the first few minutes whilst the applied torque in the mixer is high. There is associated formation of unsaturation and this fact, in conjunction with the almost complete regeneration of nitroxyl within five minutes, suggests that the corresponding hydroxylamine (HTMPOH), which can be qualitatively identified, is the major transformation product. A study of the UV stability of PP films fabricated from polymer processed for varying times shows that UV stability is related to the quantity of the redox couple (HTMPO + HTMPOH) remaining in the polymer. This is considerably reduced by severe processing. The redox capable has almost no thermal antioxidant (oven aging) activity.     

Excited-state proton-coupled electron transfer within ion pairs

The use of light to drive proton-coupled electron transfer (PCET) reactions has received growing interest, with recent focus on the direct use of excited states in PCET reactions (ES-PCET). Electrostatic ion pairs provide a scaffold to reduce reaction orders and have facilitated many discoveries in electron-transfer chemistry. Their use, however, has not translated to PCET. Herein, we show that ion pairs, formed solely through electrostatic interactions, provide a general, facile means to study an ES-PCET mechanism. These ion pairs formed readily between salicylate anions and tetracationic ruthenium complexes in acetonitrile solution. Upon light excitation, quenching of the ruthenium excited state occurred through ES-PCET oxidation of salicylate within the ion pair. Transient absorption spectroscopy identified the reduced ruthenium complex and oxidized salicylate radical as the primary photoproducts of this reaction. The reduced reaction order due to ion pairing allowed the first-order PCET rate constants to be directly measured through nanosecond photoluminescence spectroscopy. These PCET rate constants saturated at larger driving forces consistent with approaching the Marcus barrierless region. Surprisingly, a proton-transfer tautomer of salicylate, with the proton localized on the carboxylate functional group, was present in acetonitrile. A pre-equilibrium model based on this tautomerization provided non-adiabatic electron-transfer rate constants that were well described by Marcus theory. Electrostatic ion pairs were critical to our ability to investigate this PCET mechanism without the need to covalently link the donor and acceptor or introduce specific hydrogen bonding sites that could compete in alternate PCET pathways.

Electrostatic ion pairs provide a general method to study excited-state proton-coupled electron transfer. A PT_aET_b mechanism is identified for the ES-PCET oxidation of salicylate within photoexcited cationic ruthenium–salicylate ion pairs.     

Synthesis of an s-butyldibenz[a,h]acridine. Alkyl migration in the bernthsen reaction

The Bernthsen reaction between N-1-naphthyl-2-naphthylamine and 2-methylbutanoic acid and its anhydride at 200–230° for seven hours gives a low yield of 12- or 13-s-butyldibenz[a,h]acridine, instead of the expected 14-isomer. The parent molecule dibenz[a,h]acridine results from the same reaction conducted at 270° for thirteen hours. It is suggested that alkyl migration may have occurred in some other cases where the Bernthsen reaction was reported to yield 14-alkyldibenz[a,h]acridines.     

Trends in 19F-19F and 29Si-19F coupling constants in organosilicon derivatives containing SiF2 and Si2F4 units

Consideration of ¹⁹F-¹⁹F and ²⁹Si-¹⁹F coupling constants in a series of organosilicon derivatives containing SiF₂ and Si₂F₄ units reveals a number of trends which are useful for structural and stereochemical assignments. For example the vicinal ¹⁹F-¹⁹F coupling constants in a number of CSiF₂SiF₂C- derivatives (including straight chain compounds, disilacyclobutanes and disilacyclohexanes) show an apparent linear dependence on dihedral angle, varying in magnitude from near zero for small values of φ up to ca. 19 Hz for φ ～ 180°. This is particularly useful for stereochemical assignments [1,2]. In addition ²⁹Si-¹⁹F coupling constants appear to fall in quite distinct ranges (¹J_SiF > 300 Hz, 29 Hz < ²J_SiF < 55 Hz, ³J_SiF < 10 Hz). This is quite useful for structural assignments [1,6]. Reaction of SiF₂ with 1,3-cyclohexadiene gives two new silicon fluorine compounds: a disilabicyclo[2,2,2]octene and an HSi₂F₅-substituted cyclohexadiene.     

Über die anomale Reaktion von Glycin bei der Aminostickstoffbestimmung Nach Van Slyke

Zusammenfassung Es wurde die anomale Reaktion von Glycin mit salpetriger Säure erneut bearbeitet, da das vonAustin angegebene Reaktionsschema nicht zur Erklärung der anomalen Gasmengen ausreicht. Zunächst wurde wahrscheinlich gemacht, daß sich aus dem Carbeniumkation, das bei der Desaminierung von Glycin entsteht, unmittelbar Methylnitrolsäure bildet. Nitroessigsäure oder Nitromethan kommen als Zwischenprodukte nur in untergeordneter Menge in Betracht. Die Methylnitrolsäure ist Ausgangspunkt für die anomale Reaktion, die in zwei Konkurrenzreaktionen abläuft. Bei der einen Konkurrenzreaktion reagiert die Isonitrosogruppe von Methylnitrolsäure mit salpetriger Säure, wobei 1 Mol (N₂ + N₂O) sowie Nitroformaldehyd entstehen. Nitroformaldehyd reduziert salpetrige Säure zu N₂O und N₂ und wird zu Nitroameisensäure oxydiert. Letztere zerfällt unter CO₂-Entwicklung. Die zweite Konkurrenzreaktion wurde im Prinzip bereits vonAustin angegeben und von uns entsprechend den Ergebnissen über den Abbau von Isonitrosoverbindungen modifiziert. Demnach wird Methylnitrolsäure thermisch unter Bildung von Knallsäure und salpetriger Säure zersetzt. Knallsäure lagert Essigsäure an. Dieses Addukt wird von salpetriger Säure unter Entwicklung von N₂ und N₂O zu Ameisensäure zersetzt. Ameisensäure wird in geringer Menge noch zu CO₂ weiter-oxydiert.

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Summary The anomalous reaction of glycine with nitrous acid was reinvestigated because the reaction scheme given byAustin is not adequate to explain the anomalous amounts of gas. At the start it was made probable that methylnitrolic acid is formed directly from the carbenium cation which results from the deamination of glycine. Nitroacetic acid or nitromethane are involved to only a minor extent as intermediate products. Methylnitrolic acid is the starting point for the anomalous reaction, which proceeds in two competing reactions. In one of the competing reactions the isonitroso group of methylnitrolic acid reacts with nitrous acid, whereby one mol (N₂ + N₂O) and also nitroformaldehyde are produced. Nitroformaldehyde reduces nitrous acid to N₂O and N₂, and is oxidized to nitroformic acid. The latter decomposes with evolution of CO₂.The second competing reaction has previously been given, in principle, byAustin and modified by the present writers to correspond with the results of the degradation of the isonitroso compounds. Accordingly, methylnitrolic acid is decomposed thermally to produce fulminic acid and nitrous acid. Fulminic acid adds acetic acid. This adduct is decomposed by nitrous acid with generation of N₂ and N₂O and formic acid results. A slight proportion of the formic acid is also oxidized further to CO₂.

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Résumé Les auteurs ont à nouveau étudié la réaction anormale de la glycine sur l'acide nitreux car le schéma réactionnel donné parAustin ne permet pas de rendre compte des dégagements gazeux anormaux qui se produisent. II a tout d'abord été établi selon toute vraisemblance qu'à partir du cation carbénium qui se forme lors de la désamination de la glycine il se produit immédiatement de l'acide méthylnitrolique. L'acide nitroacétique ou le nitrométhane n'apparaissent comme produits intermédiaires qu'en quantités minimes. L'acide méthylnitrolique est le point de départ de la réaction anormale qui se partage en fait en deux réactions concurrentielles. Lors de l'une de ces réactions, le groupement isonitrosé de l'acide méthylnitrolique réagit avec l'acide nitrolique avec formation d'une molécule du mélange (N₂ + N₂O) ainsi que de nitroformaldéhyde. Le nitroformaldéhyde réduit l'acide nitreux en N₂O et N₂ tandis qu'il s'oxyde en acide nitroformique. Ce dernier se décompose avec dégagement de CO₂. La seconde de ces réactions a été déjà indiquée en principe parAustin et modifiée par les auteurs compte tenu des données relatives à la dégradation des composés isonitrosés. D'après cette réaction l'acide nitrolique se décompose thermiquement avec formation d'acide fulminique et d'acide nitreux. L'acide fulminique se fixe par addition sur l'acide acétique. Le produit obtenu est décomposé par l'acide nitreux avec dégagement de N₂ et N₂O et formation d'acide formique. L'acide formique s'oxyde ensuite en faibles proportions en CO₂.