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

Hidrológiai Közlöny 1967. 7. sz. 316 The analysis of resorcinol and its derivatives in water ZBÍSÉK BIDIO C. S C.» Phenols are organic compounds having attached one or more hydroxylic groups on the aromatic nucleus. This hydroxylic group is alsó responsible for the very high reactivitv of phenols themselves; it forms in the free p- and o-position respectively places of high electron densitv and therefore these places are the ones, where the aromatic or benzene nucleus is suhstituted. That is the case of the reaction of phenols with diazonium salts (e.g. the determination of monohydric phenols with p-nitraniline) or of the reactions, where indophenol compounds are förmed (e.g. the determination of phenols with 4-aminoantipyrine or with Gibbs' reagent). This statement is valid, of course, only for monohydric phenols, i.e. for such phenols, where the only hydroxylic group has a unique direction of electron pressure. It is therefore possible to determine all monohydric phenols with a single type of reaction, of course, with the exception of p-substituted phenols. Quite different is the situation with di- and polyhvdric phenols. Here the different mutual position of the hydroxv groups means that practicallv each polyhydric phenol represents an entirely different substance and only occasionally a certain analogy between various polyhvdric phenols can be found. The outlined analysis shows that whereas for monohydric phenols a whole number of suitable methods are available, there is no universal method for polyhydric phenols. Hence it seems that for the analysis of polyhydric phenols there are only two possible ways. According to the first it would be necessarv to abandon the possibilities of applying such reactions in which the vacant, unsubstituted * positions in the aromatic nucleus are attacked and to consider only those reactions in which the hydroxyl groups as such are attacked. Although these reactions would be non-selective and would require a certain pretreatment of the sample to remove interfering substances, they would have the advantage that they would include really all polyhydric phenols. An example of this type of determination is e.g. the acetylation of polyhydric phenols together with the removalof the excess of the acetylation reagent and the determination of the acetyl number. According to the second method it would be necessary for the determination of polyhydric phenols to select such reactions in which only a certain polyhydric phenol would react whereas the greatest possible number ot other polyhydric phenols present would not interfere with the determination. The method of the quantitative determination of resorcinol in water described in this paper is an example of the second method. Discussion oí the problem In the investigation of the quantitative determination of p-substituted monohydric phenols in water according to the Gerngross—Voss—Herfeld * Hydraulic Research Institute Prague, ŐSSR reaction [1—3] we noticed alsó the interference of polyhydric phenols. In this connection it was found that among the present polyhydric phenols resorcinol showed a strong interference and therefore we tried to modifv the reaction of l-nitroso-2naphthol (further ANBN) with resorcinol for the quatitative determination of resorcinol in water. The determination of resorcinol with ANBN has been recently described, although not from the point of view of water analysis, in a relatively little accessible Japonese journal [4]. According to all published papers dealing with the determination of p-substituted phenols or resorcinol by means of ANBN, the prodecure of the determination is basically always the same. The solution of the investigated phenol in water or acetic acid reacts with the ANBN solution in ethanol, acetic acid or sodium hydroxide under normál or elevated temperature, obtaining the colouration by adding an oxidation agent, usually nitric acid. In the past it was assumed that in the first stage of the determination nitric acid changes the nitroso-group in ANBN to the nitro-group, however it has beenproved that this is not the case. The favourable applieation of nitric acid is now being explained that it converts phenols with free p-positions to the corresponding nitro-derivates which no longer react with ANBN and so a selective determination is insured. The oxidative closure of the phenoxazine ring can alsó be achieved by using other oxidants rather than nitric acid such as manganese oxidé in acid médium atc. According to hitherto published studies dealing with the question the of configuration of the coloured product produced, there are mainly three different opinions. So for instance Anger and Ofri [5] assume that an acridine derivative is produced; this asssumption, however, is probably not quite correct and that for several reasons. So e.g. the stability of the acridine dyes contrasts strongly with the instability of the coloured product obtained in the determination of p-substituted phenols with ANBN, further according to their interpretation there should result only one compound, whereas in almost all other studies the formation of two derivates has been stated; in addition, according to the reaction scheme suggested by tlik above mentioned authors, it would not be possible to explain why the described reaction is obtained only with p-substituted phenols, etc. Another paper dealing with the study of the reaction products of ANBN with p-substituted phenols is by King and Newall [6] who according to our opinion found the best interpretation of the whole reaction mechanism. The structure of the reaction products suggested by them is supported by a number of further observations, by the analysis of the infra-red spectra of the products etc. According to this study the reaction mechanism is rather complicated, includes tautomeric rearrange— ments of uncyclized intermediates etc.; the result of