4- resorcinol, complexes with

Certain organic compounds form reversible gels with poly(vinyl alcohol). Congo red, for example, yields a red gel that melts sharply at about 40°C. Other organic compounds that form temperature-reversible complexes with PVA include a2o dyes, resorcinol, catechol, and gaUic acid (168—170). 

OPTICAL DENSITY DIFFERENTIATION FOR THE MIXTURES OF Cu, Zn, Co, Ni COMPLEXES WITH 4-(2-PYRIDYLAZO)-RESORCINOL... 

Concentration limits of the diphosphate-ion, admissible to determination of magnesium and cobalt, manganese and cobalt, zinc and cobalt by spectrophotometric method with application of the l-(2-pyridylazo)-resorcinol (PAR) are presented. Exceeding maintenance of the diphosphate-ion higher admissible supposes a preliminary its separation on the anionite in the H+-form. The optimum conditions of cobalt determination and amount of the PAR, necessary for its full fastening are established on foundation of dependence of optical density of the cobalt complex with PAR from concentration Co + and pH (buffer solutions citrate-ammoniac and acetate-ammoniac). 

Cobalt Complexation with 4-(2-thiazolylazo) resorcinol, adsorption on XAD-4, resin elution with methanohchloroform Graphite furnace AAS - [234]... 

Determination of Pb(II) ion by classical or reversed FIA consists of a preconcentration step either on columns packed with a chelating sorbent (PC-FIA) or on a mercury film, followed by spectrophotometric determination of the complex with 4-(2-pyridylazo)resorcinol (11, kmax 518 nm) in borate buffer solution RSD 3-6% at 0.01-1 pM. End analysis by ASV was also applied99. 

As a first step toward a dopamine-jS-hydroxylase mimic, basket-shaped receptor 17 was functionalized with two sets of bis-[2-(3,5-dimethyl-l-pyra-zolyl)ethyl]amine ligands to give compound 35 (see Scheme 5). Reaction of 35 with Cu(C104,)2-6H20 yielded complex 36 which was fully characterized [39], Ligand system 35 binds dopamine derivative 37 and phloroglucinol (1,3,5-trihydroxybenzene) with association constants of = 60 and 3500 respectively. The affinity of the Cu(I) analogon of 36 for 37 was very similar to that of 36 itself and amounted to Ka = 60 M L Resorcinol is bound in the cavity of the Cu(I) complex with a Xj-value of 2(XX) M". ... 

Any dialkyl lead present was determined spectrophotometrically as the dialkyllead 4(2-pyridylazo)resorcinol (P.A.R.) complex at pH 9. Trialkyl lead does not form a complex with P.A.R. therefore its concentration was obtained by conversion to the dialkyl lead form in iodine monochloride solution followed by determination as the P.A.R. complex. Any inorganic lead in solution was... 

The interaction of metallochromic indicators (Section 10.6.4) with metals has received a lot of attention since the resulting complexes are often solvent extractable. C. Woodward and H. Freiser73 have examined complexes of metals with sulfonated azo dyes with a view to their extraction by Aliquat-336. Vanadium in sea water can be determined at the 2 p.p.b. level by complexation with PAR (4-(2-pyridylazo)resorcinol) in the presence of CDTA and extracting the anion so formed into Zephiramine (tetradecyldimethylbenzylammonium chloride).74 The field has been reviewed up to 1971 by Ueno.2... 

In the photometric determination of copper, a coupling product formed between the diazonium salt from 2-amino-pyridine and resorcinol, or 4-(2-pyridinylazo)-l,3-benzenediol 21, has been used. Here the formed copper complex under acetate buffer exhibits an absorption peak at 520 nm, which is measured photometrically <2003KPU28>. Similarly for photometric determination of iron(ll), a coupling product formed between the diazonium salt of 2-amino-4,6-dihydroxypyrimidine and 8-hydroxyquinoline, or 6-hydroxy-2-(8-hydroxy-7-quinolinyl)azo-4(l//)-pyrimidinone 22, has been used. This reagent forms a blue complex with iron(n) ions with an absorption maximum at 625 nm that does not interfere with the presence of other metals <2003KD95>. 

Hazardous materials in trace amounts, such as metallic ions, find their way into the water system. It is necessary to be able to detect these materials in situ and in real time. Recently (12), such a method was found involving the SERS technique using optical fibers. The technique monitors the ions in aqueous solutions, measuring the changes in the Raman spectra of indicators, which form complexes with the metallic ions. The indicators used were Eriochrome Black T (EBT), 4-(2-pyridylazo)resorcinol (PAR), cresol red, methyl red and 4-pyridinethiol. 

Triazaphosphaadamantane forms complexes with phenol, catechol, resorcinol, and hydroquinone. These compounds are similar to those formed by hexamethylenetetramine, and were proposed as intermediates for the preparation of Bakelite-type resins (76MI1). 

Relationships between the structure and stability of phenol-starch complexes are not clearly understood. Apart from the complexes of phenols listed in Table XXXII, complexes of chlorocresols,712 three isomeric nitro-phenols,715 resorcinol, phloroglucinol, and rutin,716 have been reported. The formation of complexes with nitrophenols has been monitored by ultraviolet... 

Cineol (179) occurs widely (there is, for example, up to 50% in laurel oil ) and it is of interest to isolate it commercially. A new method consists of isolation of the mixture of 1,4-cineol and 1,8-cineol as the resorcinol complex. This mixture, when treated with thiourea, yields an addition compound (m.p. 172 °C)... 

Structural studies of two complexes with dimethylformamide (DMF) and dimethylacetamide (DMA) were reported. In the former, three types of solvent molecules are embedded in the crystal lattice first, disordered isolated molecules located just above the cavities formed by the resorcinol units second, clusters of four DMF molecules located between the calixarene layers and third, single DMF molecules located inside the layers close to the alkyl chains. The challenge for solid state NMR is to recognize and locate guest molecules in the lattice. CP/MAS, dipolar dephasing and variable contact-time exper-... 

The tetra-anion of macrocycles made from resorcinol allows likewise host-guest complexes with positively charged organic compounds, but also with neutral molecules like diethyl ether . 

TP and Ag + were found to react with 4-methoxyphenol and 3,5-dimethoxyphenol by 100% electron transfer (equation 2), whereas with TlOH the efficiency of electron transfer is only ca 75%. The ease of oxidation increases considerably in going from the neutral phenols to the phenolates even the weak oxidants Tl(OH)2 and Ag(OH)2 are able to oxidize the phenolates with 100% yield to give the corresponding phenoxyl radicals. In going from phenol to the dihydroxybenzenes the oxidizability increases hydroquinone and resorcinol are oxidized with 100% yield not only by TP but also by the weaker oxidant TlOH . Catechol forms a complex with Tl(II), which has the same structure as thaf produced by reaction of ortfjo-semiquinone radical with Tl or by reaction of ort/io-benzoquinone with XT . The rate constants for reaction of the Tl(II) and Ag(II) species are between 10 -10 M s (see Table 1). 

Unlike PAN, 4-(2-pyridylazo)resorcinol (PAR) (formula 4.2) is water-soluble and forms water-soluble complexes with metal ions [15,16]. In the range from 90% H2SO4 to pH 2 the following protonated forms are present HsR, H4R and H3R. The neutral PAR molecule exists between pH 2.1 and 4.2 (A,max 385 nm). The anion HR" (A,max 413 nm) occurs over the pH range 4.2-7. In alkaline solutions (pH 11-13) both hydroxyl groups are dissociated. The R form has Xmax 490 nm. 

The following review presents the selective, but rather insensitive methods based on the use of BPHA and 8-hydroxyquinoline, a moderately sensitive method involving 4-(2-pyridylazo)resorcinol (PAR), and a very sensitive method based on the ion-associate of a vanadium chelate complex with Brilliant Green... 

Another example of a metal ion separation on a weak-acid column is shown in Fig. 7.14. Here, spectrophotometric detection at 530 nm was used after post-column addition of pyridylazo resorcinol (PAR) as a complexing reagent. At highly alkaline pH values forms colored complexes with metal ions that are more stable than the eluent complexing reagent (Chapter 4). 

The second-order calibration example shown next is from the field of environmental analytical chemistry. A sensor was constructed to measure heavy metal ions in tap and lake water [Lin et al. 1994], The two heavy metal ions Pb2+ and Cd2+ are of special interest (the analytes) and there may be interferents from other metals, such as Co2+, Mn2+, Ni2+ and Zn2+. The principle of the sensor is described in detail in the original publication but repeated here briefly for illustration. The metal ions diffuse through a membrane and enter the sensor chamber upon which they form a colored complex with the metal indicator (4-(2-pyridylazo) resorcinol PAR) present in that chamber. Hence, the two modes (instrumental directions) of the sensor are the temporal mode related to the diffusion through the membrane, and the spectroscopic mode (visible spectroscopy from 380 to 700 nm). Selectivity in the temporal mode is obtained by differences in diffusion behavior of the metal ions (see Figure 10.22) and in the spectroscopic mode by spectral differences of the complexes formed. In the spectroscopic mode, second-derivative spectra are taken to enhance the selectivity (see Figure 10.23). The spectra were measured every 30 s with a resolution of 1 nm from 420 to 630 nm for a period of 37 min. This results in a data matrix of size 74 (times) x 210 (wavelengths) for each sample. 

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