Die Bestimmung von 1,5-Naphthylendiisoeyanat (Desmodur 15) in Luft

Zusammenfassung Bei einer früher publizierten Methode zur Bestimmung von 1,5-Naphthylendiisocyanat (Desmodur 15) ist die Kapazität der Absorptionsvorrichtung bei sehr großen Mengen Isocyanat nicht ausreichend und die Empfindlichkeit der Methode für hohe Ansprüche nicht genügend. Daher wurde eine neue Methode erarbeitet. Desmodur 15 wird aus Luft in üblicher Weise absorbiert, mit Wasser in schwach saurer Lösung quantitativ zu 1,5-Naphthylendiamin verseift, dieses diazotiert und in gepufferter Lösung mit Phenol zu einem Azofarbstoff gekuppelt, dessen Absorptionsmaximum bei 400 nm liegt. Der Farbstoff ist in n-Pentanol leicht löslich und kann aus der wäßrigen Phase in ein definiertes Volumen n-Pentanol ausgeschüttelt werden, wodurch eine wesentliche Steigerung der Empfindlichkeit erreicht wird. Die Verseifung des Isocyanates zu dem entsprechenden Amin verläuft in 10 Minuten quantitativ; das aus dem Isocyanat erhaltene Amin zeigt dieselbe Extinktion wie die äquivalente Menge 1,5-Naphthylendiamin. Das Lambertsche und das Lambert-Beersche Gesetz sind erfüllt. Die Absorption und die Kapazität des Absorbers wurden geprüft; diese beträgt 20mg 1,5-Naphthylendiisocyanat, das maximal zulässige Luftvolumen pro Probe 10001. Eine ausführliche Arbeitsvorschrift wird angegeben. Die Erfassungsgrenze beträgt 2 g Desmodur 15.

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Summary A previous paper described a method for determining 1,5-naphthylenediisocyanate (Desmodur 15). However, the capacity of the absorption arrangement is not adequate for very high amounts of isocyanate and the sensitivity of the method is not good enough for high demands. Accordingly a new method was worked out. Desmodur 15 is absorbed from air in the usual way, quantitatively saponified with water in weak acid solution to yield 1,5-naphthylenediamine, and the latter then diazotized and coupled in buffered solution with phenol to produce an azo dyestuff whose absorption maximum is at 400 nm. The dye is readily soluble inn-pentanol and can be shaken out of the aqueous phase in a definite volume ofn-pentanol, and a considerable increase in the sensitivity is attained in this way. The saponification of the isocyanate proceeds quantitatively to the corresponding amine in ten minutes; the amine obtained from the isocyanate shows the same extinction as the equivalent quantity of 1,5-naphthylenediamine. The Lambert and the Lambert-Beer laws are satisfied. The absorption and the capacity of the absorber were tested; the latter amounts to 20 mg of 1,5-naphthylenediisocyanate, the maximum permissible volume of air per sample is 1000 liters. The procedure is described in full detail. The limit of detection is 2 g Desmodur 15.

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Résumé Dans une méthode publiée antérieurement sur le dosage du diisocyanate de naphtylène-1,5 (Desmodur 15), la capacité de l'appareil d'absorption pour de très grandes quantités d'isocyanate, et, si l'on se montre plus exigent, la sensibilité de la méthode, sont insuffisantes. C'est pourquoi on a mis au point une nouvelle méthode. On absorbe de la manière habituelle le Desmodur 15 contenu dans l'air, on saponifie quantitativement, avec de l'eau en solution faiblement acide, en diamine de naphtylène-1,5 que l'on diazote et que l'on copule, en solution tamponnée, avec le phénol, ce qui donne un colorant azoïque dont le maximum d'absorption se situe à 400 nm. Le colorant est facilement soluble dans le pentanol-N et peut être extrait par agitation de la phase aqueuse dans un volume défini de pentanol-N, ce qui permet d'atteindre une augmentation importante de la sensibilité. La saponification de l'isocyanate en l'amine correspondante s'effectue quantitativement en 10 minutes; l'aminé obtenue à partir de l'isocyanate montre la même extinction que la quantité équivalente de diamine de naphtylène-1,5. La loi de Lambert et la loi de Lambert-Beer sont suivies. On a étudié l'absorption et la capacité de l'absorbeur; celle-ci s'élève à 20 mg de diisocyanate de naphtylène-1,5; le volume d'air maximal permis par échantillonage est de 1000 l. On donne un mode opératoire détaillé. On peut déceler jusqu'à 2 g de Desmodur 15.

     

Photooxygenation of the helimers of (-)-isocolchicine: regio- and facial selectivity of the [4 + 2] cycloaddition with singlet oxygen and surprising endoperoxide transformations

Photooxygenation of the helimeric mixture of (-)-(M,7S)/(P,7S)-isocolchicine (6) with the superdienophile singlet oxygen has been studied. Cycloaddition occurred with high regioselectivity at the 7a,11-positions of the alkaloid and predominantly at the diene face anti to the amidic substituent at the stereogenic center C-7, leading to two endoperoxides 7 (syn) and 8 (anti) with an 1:7 ratio. The structure of the minor product 7 was established by X-ray analysis. Investigation of the triethylamine induced transformation of the predominant endoperoxide 8 furnished a mixture of two isomers (M,7S)-10a/(M,7S)-10b in a 2:1 ratio possibly with constitutional interconversion and with (M,7S)-9 as plausible intermediate. Treatment of this mixture with silica gel/ethyl acetate at ambient temperature surprisingly led to an atropenantiomerically pure colchicinoid (M,7S)-12 characterized by an eightmembered oxocine B-ring, the structure and absolute configuration of which could be determined by X-ray analysis. For the unprecedented formation of the novel colchicinoid (M,7S)-12 a plausible reaction pathway is suggested, involving a complete transfer of the (M) helical asymmetry of the intermediate (M)-11 into (S) asymmetry of the newly formed carbon center of (M,7S)-12. Prerequisite for such a scenario is the configurational stability of the intermediate pseudobiaryl (M)-11, under the conditions employed, allowing to transmit the axial chirality onto the chiral center of the product (M,7S)-12.     

Polymer nanocomposite coatings based on polyhedral oligosilsesquioxanes: route for industrial manufacturing and barrier properties

A route to a large variety of functionalized POSS compounds by a two-step procedure has been developed. Up-scaling to high volume industrial applications is feasible. In the first step, an amino-functionalized silane such as 3-aminopropyltriethoxy silane is converted to amino-functionalized POSS (amine-POSS) by a sol–gel process. In the second step, the amine groups of amine-POSS are converted by state-of-the-art amine chemistry. A large number of reactants including carboxylic acids, esters, anhydrides, isocyanates, carbonates, epoxides, and acrylates as well as reactants suitable for nucleophilic substitution can be applied. Conversion of an amine-POSS with hexanoic acid leads to an amide-POSS. Amine chemistry can usually be performed under mild conditions, which suppresses degradation and/or cross-linking reactions of the amine-POSS during the conversion. MALDI-TOF mass spectroscopy and dynamic light scattering (particle size: 3–6 nm) have been applied to prove the conversion of an amine-POSS to an amide-POSS. ¹H-NMR and TGA-MS prove the presence of amide-POSS and its thermal stability. Gas barrier properties of nanocomposite coatings based on functionalized POSS are characterized.     

Studies on induced smectic phases (III). Fourier transform infrared and laser-raman spectral differences between isotropic and induced smectic phase of binary mixtures of nematogens with contrasting dielectric anisotropies

The S_E, S_B, S_A induced phase sequence was detected in binary mixtures of two nematogens, 4,4′-di-n-heptyl azobenzene (7AB) with 4-n-pentyl-4′-cyano biphenyl (5CB). The mixtures as well as the single components were studied by Fourier transform IR and laser-Raman spectroscopy at different temperatures. Charge redistribution of 5CB is demonstrated by the spectral differences found by the ratio-recorded IR spectra and also by integrating the intensities of some Raman lines. The spectra of the different phases of the 7AB—5CB mixture, built up from components of different length, indicate a population increase of the gauche conformers of 7AB in the smectic A phase.