Borax buffer

The diazotization of amino derivatives of six-membered heteroaromatic ring systems, particularly that of aminopyridines and aminopyridine oxides, was studied in detail by Kalatzis and coworkers. Diazotization of 3-aminopyridine and its derivatives is similar to that of aromatic amines because of the formation of rather stable diazonium ions. 2- and 4-aminopyridines were considered to resist diazotization or to form mainly the corresponding hydroxy compounds. However, Kalatzis (1967 a) showed that true diazotization of these compounds proceeds in a similar way to that of the aromatic amines in 0,5-4.0 m hydrochloric, sulfuric, or perchloric acid, by mixing the solutions with aqueous sodium nitrite at 0 °C. However, the rapidly formed diazonium ion is hydrolyzed very easily within a few minutes (hydroxy-de-diazonia-tion). The diazonium ion must be used immediately after formation, e. g., for a diazo coupling reaction, or must be stabilized as the diazoate by prompt neutralization (after 45 s) to pH 10-11 with sodium hydroxide-borax buffer. All isomeric aminopyridine-1-oxides can be diazotized in the usual way (Kalatzis and Mastrokalos, 1977). The diazotization of 5-aminopyrimidines results in a complex ring opening and conversion into other heterocyclic systems (see Nemeryuk et al., 1985). 

This preparative scheme leads to only 30% yield due to the side reactions between the meto-astatoaniline diazonium salt and astato-phenol, which cannot be eliminated even by continuous extraction of the product with n-heptane (167). All the astatophenols synthesized to date have been identified by either HPLC (99,104) or TLC (160,166,167). Their dissociation constants (KJ have been established from extraction experiments by measuring the relative distribution of compounds between aqueous borax buffer solutions and n-heptane as a function of acidity. On the basis of these derived values, the Hammett a-constants and hence the field (F) and resonance (R) effects have been estimated for these compounds (167) (see Table VI). The field effect for astatine was found to be considerably weaker than that for other halogens the resonance effect was similar to that for iodine (162). 

In vitro studies have indicated that 5-astatouracil is chemically stable over the pH range 1-11.5 at room temperature, and 1-7 at 50°C over a period of 20 hours these results are similar to those for the iodo analog. Heating to 50°C at pH > 11.5 resulted in loss of 20-30% of bound astatine after 20 hours. This has been attributed to direct attack of OH on the 5-position of the pyrimidine nucleus, as in the case of 5-iodouracil, Both halouracils are stable in the presence of S03 and H2O2 (170). From distribution studies utilizing benzene and aqueous borax buffers, the pK, of 8.97 has been established for 5-astatouracil at 0 C (167). 

The Co(II) -phenylthiourea-borax buffer system has been studied applying CSV at HMDE [69]. An irreversible peak observed at —1.5 V was attributed to the catalytic hydrogen evolution. The first reduction step, combined with the adsorptive accumulation of herbicide metribuzin at mercury electrode, has been used for its determination by adsorptive stripping voltammetry [70]. 

The I2O7 content of the periodates described is determined as follows The weighed sample is covered with 20 ml. of water, and 5 to 10 drops of 6N HC1 is added to hasten solution. No chlorine is liberated from the acid of this concentration. The solution is diluted to 100 ml., made just alkaline to phenolphthalein paper with borax, buffered with borax and boric acid (Muller and Wegelin Z. anal. Chem., 52, 755-759 (1913), and an excess of potassium iodide is added. Under these conditions, the periodate is reduced to iodate. The liberated iodine is titrated with 0.1N arsenite. 

The pH reference materials were selected also to cause small liquid junction potential < 0.01 in pH if the pH of the buffer solution prepared from this material is measured in cells with transference [12]. The molality of the primary buffer solutions are kept at < 0.1 mol kg-1 for the same reason [13]. Furthermore, the primary buffers have a long-time stability of stored solid material (>3 years), except solid borax buffer material. Borax buffer (0.1 mol kg-1) has a restricted stability of about 2 years only [14]. 

Solutions of periodic add and of sodium metaperiodate in water are quite stable at room temperature. The periodate content is readily determined by titrating, with standard sodium arsenite solution, the iodine liberated from iodide in neutral solution.49 103-197 Periodate also may be determined accurately in the presence of iodate, since in neutral solution periodate is reduced by iodide to iodate. The reaction in the presence of a boric add-borax buffer is shown by the following equation. 

An additional example for ion pair extraction of QTA (ipratropium) was described by Tang et al. mixing equine urine with alkaline saturated borax buffer prior to extraction with EE allowing to remove more lipophilic compounds. Subsequently, the EE layer was discarded and an alkaline potassium iodide-glycine solution was added to the aqueous phase. Afterwards, the ipratropium-ion pair complex was extracted twice with dichloromethane yielding in a recovery of 82 % [24] (Table 3). 

Fig. 12.1. Anodic deposition of FeOOH on Au from 5mM Fe(NH4)2S04 in (NH4)2S04 and borax buffer of pH 8.5 at 0.7 V (NHE). (a) Time course of A/ (b) Current density and d//dr and (c) Electrode potential. Arrows indicate switch off and open circuit potential...

Borax Buffer Dissolve 47.63 g of sodium borate decahy-drate in warm water. Cool to room temperature. Add 20 mL of 4 N sodium hydroxide solution, adjust the pH of the solution to 9.7 with 4 N sodium hydroxide, and dilute to 2 L with water. 

Procedure Equilibrate the Substrate Solution in a water bath at 37° 0.2° for at least 15 min. For active samples, transfer 1.0 mL of each sample to separate test tubes and equilibrate in the 37° 0.2° water bath. At zero time, add 2.0 mL of Substrate Solution, mix, and return to the water bath. After exactly 15.0 min, add 5.0 mL of Borax Buffer to each tube, mix, and remove from the water bath. 

For sample blanks, transfer, in sequence, 1.0 mL of each sample to separate test tubes, add 5.0 mL of Borax Buffer, and mix. Add 2.0 mL of Substrate Solution to each tube, and mix. 

Sc CA 65, 12854(1966) (Polarographic detn of NGu) 13) H. Opel Sc W. Ardelt, ZChem 7 (11), 439-40(1967) Sc CA 68, 46066(1968) [(Analysis of cyanamide derivatives. III. Determination of NGu) (Method is polarographic dilution titration with borax buffer and Na sulfite — compares well with titanous chloride method)]... 

Fig. 2. Effect of pH on the ultraviolet spectrum of phenobarb-itone. A, non-ionised barbiturate in 0.1 M hydrochloric acid B, mono-anion in 0.05M borax buffer (pH 9.2) C, di-anion in 0.5M sodium hydroxide (pH 13).

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