Complexation, boric acid effect

It was found in the first place that aliphatic, non-cyclic glycols without adjacent hydroxyl groups have no effect they cannot form cyclic complexes. But also most glycols with not more than two adjacent hydroxyl groups are inactive. I therefore assumed that only if two hydroxyl groups are favorably situated for the formation of a complex boric acid compound, will it be possible to observe an increase in the conductivity. 

PuUy hydroly2ed poly(vinyl alcohol) and iodine form a complex that exhibits a characteristic blue color similar to that formed by iodine and starch (171—173). The color of the complex can be enhanced by the addition of boric acid to the solution consisting of iodine and potassium iodide. This affords a good calorimetric method for the deterrnination of poly(vinyl alcohol). Color intensity of the complex is effected by molecular weight, degree of... 

The system has been used as an analytical tool (4), because the complex formed shows greater conductivity than the sum of the conductivities of the boric acid and the diol compound. Favorably situated diols have a pronounced effect in increasing the conductivity. cis-l,2-Diols fixed in position by molecular structure—e.g., o-dihydroxyphenols and cis-dicyclic polyols—are favorable structures. The reaction is depicted in Figure 2. 

Boric acid can form complexes with hydroxyl compounds. The control of the delay time requires control of the pH, the availability of borate ions, or both. Control of pH can be effective in freshwater systems [17]. However,... 

The effect of those ions most frequently present in soils on the boron determinations is shown in Table 12.1. The interference of iron at concentrations higher than 7xlO 5M can be eliminated as the chloro complex by extraction with methyl isobutyl ketone. The total elimination of iron III was not necessary as the phosphoric acid masked the residual iron III in the boric acid-curcumin reaction. 

We [47] further studied quantitatively the strain-induced complex formation in PVA films in dilute iodine solutions whose iodine concentration is lower than the threshold required for the complex formation. We were interested in the effects of degree of hydration D.H. of PVA films and the iodine concentration of the soaking solutions on the strain-induced complex formation. PVA films were stretched in iodine-KI soaking solutions whose iodine concentration was in the range of 2 x 10 9 x 10 mol/1. No boric acid was added to the solution. No complex forms in these solutions, and therefore films remain brown in color before extension. However, when stretched in the solution the color turns to blue at the points indicated by arrows on the stress-strain curves shown in Fig. 11, which shows the beginning of the formation of the complex. The strain-induced complex formation is also shown by the visible ray absorption spectra measured before and after extension in a solution of 3x 10 mol/1 iodine concentration at 30 °C as shown in Fig. 12. A broad peak of the complex with... 

Mercury(II) is also a very effective masking agent for Cl-, Br- and I- as well as S03 . Masking of fluoride ions is important analytically and this can be done effectively by transforming it into a variety of stable coordination compounds, e.g. boric acid yields BF4-, beryllium gives BeF42-and a number of stable octahedral complexes are formed with Al, Fe, Ti, Zr, Nb and Ta. 

Expressions VII and VIII are identical in form they differ only in the meaning of the constants they contain. In both cases an increase in the borate ion concentration would result in an increase in the diol-boric acid complex. Therefore, an examination of the effect of pH on the equilibrium concentrations of various components of the system cannot be used to determine which of the two boroxy species actually reacts with the diol. 

Borate complexes have been utilized by Brigl and Griiner47 to effect partial esterification. Anhydrous D-glucose and metaboric acid dissolved in acetone give a complex which exhibits the analysis of a diborate. Reaction of the latter with an excess of benzoyl chloride gives 2,6-di-O-benzoyl-D-glucose (XL). D-Mannitol likewise forms a diborate, which produces the 1,6-di-O-benzoyl derivative (XLI) upon benzoylation. In the presence of boric acid, D-glucose diethyl thioacetal yields the 6-benzoate (XLII). In the non-aqueous medium the formation of complexes... 

Until recently, very little had been reported on the important area of metal borate complexation in aqueous solution. The effect of salts on the ionization of boric acid (358, 375) has been mentioned above, and subsequent research suggests that complexation of borate with, for example, calcium ions can account for the enhanced acidity of H O Literature on cationic complexes of boron was reviewed in 1970 (376). 

The effect of neutral salts (e.g., NaCl) on the composition of borates precipitated from, or in equilibrium with, aqueous solutions doubtless arises from a reduction in water activity, metal borate complexation, and a shift in polyborate equilibria (Sections IV,A, B). The "indifferent or inert component method has frequently been used for the synthesis of borates. Potassium and sodium chlorides can be used to enhance the precipitation of specific nickel (48), aluminum (51), iron (49), and magnesium (151) borates. In the K20-B203-H20 system at 25°C (248), the presence of potassium chloride results in a reduced boric acid crystallization curve, lower borate solubilities, lower pH, and an extended B203 K20 range over which the pentaborate crystallizes. 

Catechol, boric acid complex, IV, 194 effect on conductivity of boric acid, IV, 191... 

Reduction of sugars into alditols is effected by treatment with sodium borohydride, and acetylation by treatment with acetic anhydride containing sulphuric acid (2%) at 80°C for 15 h [436] or for 4 h by refluxing with a mixture of acetic anhydride and pyridine (1 1) [437]. The excess of reducing agent is usually decomposed prior to the acylation by treatment with an acid. The boric acid so produced should be removed, as it forms a complex with alditols and retards the acylation. Polar stationary phases (e.g., Carbowax 20M), on which strong sorption and decomposition of the derivatives occur, are not very suitable for the GC separation of acetates. Carbowax 20M modified with terephthalic acid and XE-60 provides good results, but some derivatives do not separate. 

Fia. 24. Effect of temperature on the resolution of complex II. Complex II was suspended in a solution containing 30 mil/ Tricine, 100 mil/ boric acid, 20 mM succinate and S mM dithiothreitol. pH of the buffer was adjusted to 8.1 with NaOH. Complex II was resolved by addition of 1.0 M NaC10< at the temperatures indicated. After addition of NaClOi the concentration of complex II was 8 mg/ml. (a) Resolution at 0°, 10°, and 30°. (b) Increased resolution and reconstitution as the temperature was changed from (O) 0° to ( ) 30° and from 30 to 0°, respectively. Assays were performed at 38°. From Davis and Hatefi (1S9). 

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