Decomposition and disproportionation of hydrazyl radicals and hydrazo compounds derived from azo dyes

Abstract

6 G. Heijkoop et al. /Decomposition and disproportionation of hydrazyl radicals and hydrazo compoundsLes aldehydes et salicylates de methyle substitub sont tous des produits commerciaux utilisb aprts distillation ou recristallisation. de reaction est celui d'un melange equimoleculaire de benzaldehyde et d'acide salicylique, confirmant le fait que la saponification de. la fonction ester etait compltte. Mesures cinetiques A) Mkthodes cinktiques appliyukes aux acktals mkthoxycarbonyltsLa reaction d'hydrolyse de ces acetals aryles est suivie, par spectrophotometrie U.V., dans un milieu aqueux, tamponne, de force ionique p = 0,l et a une temperature maintenue B 25°C f 0,l par circulation d'eau dans des cuves a jaquette. Une etude spectrale de la solution cinetique en debut et en fin de reaction nous permet, pour chaque produit, de determiner la longueur d'onde optimale pour laquelle la variation de la densitt optique utilise la pleine tchelle de I'enregistreur. Une solution-mere d'acetal est prepark en solubilisant 5 pl de produit dans 5 a 10 ml d'ethanol absolu; 20 pI de cette solution sont ajoutes a I ml de tampon; la concentration en acetal de la solution obtenue est donc de l'ordre de 3 1 6 10-5M suivant les cas et permet d'observer une variation de la densite optique de 0,8 unitb environ au cours de la reaction. Le lissage de la courbe exponentielle obtenue est effectut sur ordinateur d'aprks la mtthode des moindres carrts et nous donne la valeur de kobq. B) Mkthodes cinktiques appliqukes aux acetals carboxylds (Ib-IXb)La reaction d'hydrolyse de ces acetals est suivie, comme pour leurs esters, dans un milieu aqueux, tamponne, de force ionique 0,l et a 25OC f 0,l. 20 pl de la solution-mere du sel de potassium de chaque acttal sont ajoutes a 1 ml de la solution tampon et la densitk optique du melange obtenu apres agitation est mesurke en fonction du temps.Le traitement des donntes cinttiques est similaire B celui indiqut dans le cas des acktals-esters. Abstract. The mechanisms of decomposition and disproportionation of hydrazyl radicals and hydrazo compounds, derived from azo dyes, have been studied by flash photolysis, flow experiments and fluorescence spectrometry. The hydrazyl radicals undergo a combined decomposition and oxidation process, resulting in the formation of amines and iminoquinones, and regeneration of part of the amount of dye used in their preparation. Hydram compounds are formed upon further photoreduction of hydrazyl radicals, and decompose in a similar fashion as the latter.

Radical mechanism of azo cleavage for monoazo reactive dyes, a QSPR study: the similarity between photoreduction on polyamide substrates and thermal reduction in aqueous dithionite solutions

“…In the case of disperse azo dyes, the fading ratio (K PA /K PET )(k 0,i /k R1 ) = K PA / (f i /f R1 ) was used because relative values to the reference were used [18][19][20]. To eliminate the photophysical factor from the K PA values, the K PA /f i values were calculated.…”

“…b k 1 (s À1 ) [rate constants for the first-order disproportionation of (MHN) in water at ca. [19,20] proposed that the oiminooxoquinones react further with (MHN) in a deactivation process, resulting in aminonaphthols, although the reaction may be thermochemically allowable. [19,20] proposed that the oiminooxoquinones react further with (MHN) in a deactivation process, resulting in aminonaphthols, although the reaction may be thermochemically allowable.…”

“…The other azo dyes with reactive anchors in the coupling component moiety, such as A4, A5, C1, C2, C4, and D1, exhibited similar phenomena: the spectroscopically same end products show the absence of amino groups. Heijkoop and van Beek [19,20] and Abbott et al [21,22] reported the formation of o-iminooxoquinones (see above). This behaviour was also observed in thermal reduction with aqueous dithionite, indicating deactivation terminated by the formation of o-iminooxoquinones; the fact that no progress in the diazotisation/ coupling reactions was observed for azo dyes when a reactive anchor was attached to the coupling component may indicate that o-iminooxoquinones are the end products of photo-and thermal reduction.…”

“…Thermochemical analysis for the rates of thermal reduction of food azo dyes Gemeay's data [18] for the dithionite reduction of G1 and G2 together with the data for G3-G7 of van Beek et al [19,20] were analysed using the RM1 and COSMO methods (RM1/H 2 O). The results of the thermochemical analysis are shown in Table 3 according to procedures used in previous papers are shown in Table 3 [30][31][32].…”

“…The absence of hydrazines has been confirmed indirectly in the study of the byproducts [10,11]. Thus, azo compounds may produce hydrazines via a charge transfer mechanism [16,17] and amines via a radical mechanism [18][19][20]. Thus, azo compounds may produce hydrazines via a charge transfer mechanism [16,17] and amines via a radical mechanism [18][19][20].…”