Hidrológiai Közlöny 1967 (47. évfolyam)

7. szám - A „Szervesanyag meghatározási problémák édesvizekben” című 1966. szeptember 25–28. között Tihanyben rendezett Szimpózium előadásai - Bidlo, Zdenek: Megjegyzések a vízben levő rezorcinol kimutaásához

Bidlo, Z.: A vízben levő rezorcinol Hidrológiai Közlöny 1967. 7. sz. 317 the whole reaction are two phenoxazine derivates. Their mutual ratio is dependent on the conditions under which the determination has been carried out. A great advantage of this mechanism is that it permits the explanátion of the two derivates produced and that it explains the unreactivity of phenols with free p-position. Approximately at the same time a paper by Umeda [4] was published, dealing with the analysis of reaction products of ANBN with both p-substituted phenols and with resorcinol. According to this author again phenoxazine derivates result; since however this author worked under milder conditions, he noticed the origin of one derivate only. For the reaction of ANBN with p-substituted phenols and resorcinol he assumes a similar mechanism as King and Newall. Comparing the results of the discussed papers with the results of our own studies, we see that with the greatest probability there will result again two phenoxazine derivates in the reaction between ANBN and resorcinol, which has alsó been confirmed by paper chromatographic determinations. If we investigate the reasons why in the described reaction Catechol or hydroquinon do not alsó react we find that it is probably because during the reaction the nitrogén from the ANBN molecule becomes attached to the most active position of the resorcinol molecule, i.e. in position 2 (this position is in relation to the two hvdroxyl groups in oposition) or in position 4 (o-position in relation to one and p-position in relation to the other hvdroxyl group). These favourable cdnditions do not exist in any other divalent phenol (naturallv with the exception of resorcinol derivates), since in these compounds the activation effects of the single hydroxyl groups interfere with each other. Quantitative determination of resorcinol using ANBN In the preceeding paragraphs the constitution of the red end-product produced iii the determination was discussed. Now we shall describe the single stages of the whole determination. For the determination 25 ml of water containing resorcinol or its derivatives are taken, but alsó larger quantities can be used, in this way increasing the sensitivity of the reaction; in such a case it is alsó necessary to use greater amounts of the other reagents. The sample is heated in a test tűbe or Erlenmeyer flask for 5 min. on a boiling water bath with 1% ANBN in ethanol solution. After 5 minutes nitric acid is added, after cooling, it is shaken with benzene and the benzene layer is reextracted in 50% sulphuric acid and this layer is measured at 550 m /i against a blank. The time of heating the sample with the reagent is not critical, a longer time of heating does not change the absorbance, as it is shown in Tab. 1. Another variable factor in the determination could be the quantity of the reagent added to the investigated solution. It was found that 0,2 ml of the reagent is quite sufficient even with relatively high contents of interfering substances; naturallv, Table 1. Efíect of time of heating Time of heating min. Absorbance 3 0.298 6 0.296 9 0.306 12 0.302 as long as there is a very small quantity of resorcinol in the sample compared with other polyhydric phenols, it is necessary to increase the reagent dosage In Tab. 2. the effect of the reagent quantity on the colour intensity is shown. Tab. 2. Effect of amount of reagent added Amount of reagent added to 25 ml of sample Absorbance 0.1 ml 0.463 0.2 ml 0.465 0.4 ml 0.468 0-6 ml 0.460 In a similar way alsó other variable factors of the determination were investigated and that the quantity of nitric acid, the concentration of sulphuric acid used for the reextraction of the colour from the benzene layer; in all cases and in the single stages of the whole determination alsó the stability of the colouring, which proved to be excellent, was observed. A very important factor for the satisfactorv application of the determination was the interference of other polyhydric phenols (monohvdric phenols can be on the whole easily removed from the originál sample by steam distillation). In Tab. 3. the effect of the other polyhydric phenols is shown. From Tab. 3. it clearly follows that the interference of the other polyhydric phenols present is very slight. These polyhydric phenols reduce in the majority of cases the absorbance of resorcinol but not to such a degree thatitwouldseriouslythreaten the possibility of quantitatiye determination of resorcinol in the presence of these other polyhydric phenols. The only exception here is phloroglucinol, the configuration of which is reallv the double configuration of resorcinol and here alsó a more serious interference could be expected. At this occasion we should liké to point out another interesting aspect of the whole determination. After the reaction between resorcinol and ANBN, we shake the reaction product with benzene; the extraction is possible only for the reason that it is done in slightlv acid médium. As soon as