Hydroxy-, titration

Calmagite l-(6-Hydroxy-m-tolylazo)- Hjin- (red) pK2 = 8.1 Wine-red Titrations performed with Eriochrome... 

Bromine titration has been applied to several heteroaromatic compounds, but it is not a reliable method. The assumption is often made that oxo structures react very slowly with bromine whereas the hydroxy forms react rapidly. Thus, 3,4-diphenylisoxazol-5-one when freshly dissolved in ethanol was found to react with 0.5 mole of bromine, but after standing it reacted with almost 1 mole. These observations led to the conclusion that the solid was in the CH... 

Fig. 2. Hysteresis loop in rapid titration of O.OOlM 2-hydroxy-6-methyl-pteridine with 0.01-M potassium hydroxide and back-titration with hydrochloric acid, and the equilibrium titration curve.

In systems such as the 2- and 6-hydroxypteridine series, rapid potentiometric or spectrophotometric pA determinations on neutral solutions usually give values near to the acidic pA of the hydrated series. (Exceptions include 2-hydroxy-4,6,7-trimethyl-, 6-hydroxy-7-methyl-, and 4,6-dihydroxy-pteridine, where the neutral solution contains comparable amounts of hydrated and anhydrous species. In such cases, rapid potentiometric titrations show two well-defined and separated curves, one for the hydrated, the other for the anhydrous, species.) Similarly, from solutions of the anion, an approximate pA value for the anhydrous species is obtained. For convenience, the anhydrous molecule is referred to as HX, its anion as X , the hydrated neutral molecule as HY, and its anion as Y, and the two equilibrium constants are defined as follows ... 

Solochrome black (eriochrome black T). This substance is sodium 1-(1-hydroxy-2-naphthylazo)-6-nitro-2-naphthol-4-sulphonate, and has the Colour Index reference C.I. 14645. In strongly acidic solutions the dye tends to polymerise to a red-brown product, and consequently the indicator is rarely applied in titrations of solutions more acidic than pH = 6.5. 

Patton and Reeder s indicator. The indicator is 2-hydroxy-l-(2-hydroxy-4-sulpho-l-naphthylazo)-3-naphthoic acid the name may be abbreviated to HHSNNA. Its main use is in the direct titration of calcium, particularly in the presence of magnesium. A sharp colour change from wine red to pure blue is obtained when calcium ions are titrated with EDTA at pH values between 12... 

Solochrome dark blue or calcon ( C.1.15705). This is sometimes referred to as eriochrome blue black RC it is in fact sodium l-(2-hydroxy-l-naphthylazo)-2-naphthol-4-sulphonate. The dyestuff has two ionisable phenolic hydrogen atoms the protons ionise stepwise with pK values of 7.4 and 13.5 respectively. An important application of the indicator is in the complexometric titration of calcium in the presence of magnesium this must be carried out at a pH of about 12.3 (obtained, for example, with a diethylamine buffer 5 mL for every 100 mL of solution) in order to avoid the interference of magnesium. Under these conditions magnesium is precipitated quantitatively as the hydroxide. The colour change is from pink to pure blue. 

Fast sulphon black F ( C.I.26990). This dyestuff is the sodium salt of 1-hydroxy-8-( 2-hydroxynaphthylazo) -2- (sulphonaphthylazo) -3,6-disulph onic acid. The colour reaction seems virtually specific for copper ions. In ammoniacal solution it forms complexes with only copper and nickel the presence of ammonia or pyridine is required for colour formation. In the direct titration of copper in ammoniacal solution the colour change at the end point is from magenta or [depending upon the concentration of copper(II) ions] pale blue to bright green. The indicator action with nickel is poor. Metal ions, such as those of Cd, Pb, Ni, Zn, Ca, and Ba, may be titrated using this indicator by the prior addition of a reasonable excess of standard copper(II) solution. 

B. l0-Bromo-ll-hydroxy-10,ll-dihydrofarnesyl Acetate [2,6-Dodeca-diene-1,11-diol, 10-bromo-3,7, -trimethyl-, 1-acetate, (E,E)-]. Farnesyl acetate (29 g., 0.11 mole) is dissolved in 1 1. of /erf-butyl alcohol (Note 4) contained in a 3-1. Erlenmeyer flask. Water is added (500 ml.), and the solution is cooled to about 12° using an external ice water bath. Maintaining this temperature, rapid magnetic stirring is begun, and more water is added until a saturated solution is obtained. The second addition of water may be rapid initially, but the saturation point must be approached carefully, like the end point of a titration. A total of about 1200 ml. of water is required for the above amounts of farnesyl acetate and ferf-butyl alcohol. The solution must remain clear and homogeneous at about 12°, and if the saturation point is accidentally passed by adding too much water, ferf-butyl alcohol should be added to remove the turbidity. 

Determination of hydroxy groups. Hydroxy groups are rarely titrated. Indeed, this titration is more complex and less accurate than carboxy-group determination. However, it is very helpful to know the hydroxy group content, for example in the case of reactions carried out with a great excess of add. In this case, the variations of the add concentration during the esterification are very small and are determined only with poor accuracy. 

Reaction of hydroxy groups with phenyl isocyanate and back titration of the excess isocyanate with dibutylamine. Both moisture and acidity interfere275. ... 

Carboxy-hydroxy reactions, 63 Carboxyl endgroup chemical titration, 94 Carboxylic acid-aryl acetate interchange reactions, 62, 63... 

Hydroxybenzylamine intermediates, 392 Hydroxybenzylamines, 389, 391, 416 thermal decomposition of, 392 Hydroxy-ester interchange reactions, 62, 65, 69-74, 84, 111 Hydroxy-functional crosslinkers, 214 Hydroxyl endgroup chemical titration, 94-95... 

Active matter (anionic surfactant) in AOS consists of alkene- and hydroxy-alkanemonosulfonates, as well as small amounts of disulfonates. Active matter (AM) content is usually expressed as milliequivalents per 100 grams, or as weight percent. Three methods are available for the determination of AM in AOS calculation by difference, the two-phase titration such as methylene blue-active substances (MBAS) and by potentiometric titration with cationic. The calculation method has a number of inherent error factors. The two-phase titration methods may not be completely quantitative and can yield values differing by several percent from those obtained from the total sulfur content. These methods employ trichloromethane, the effects from which the analyst must be protected. The best method for routine use is probably the potentiometric titration method but this requires the availability of more expensive equipment. 

Sodium hydroxyalkanesulfonates may be determined in the presence of an unsaturated hydrocarbon, including sodium alkenesulfonate. The sulfonates are converted to the free sulfonic acids using a slight excess of 2,4-dinitrobenzene-sulfonic acid. The hydroxyl group of the sulfonic acid liberated is acetylated in ethyl acetate solution by a known excess of acetic anhydride. The unconsumed anhydride is hydrolyzed by a pyridine-water mixture and the acids titrated potentiometrically with standard sodium hydroxide solution. The hydroxy-alkanesulfonate content is calculated after correction for any traces of acidity or alkalinity in the original sample. 

Alternatively, the 3- and 4-hydroxy sulfonates may be converted to the corresponding sultones by treatment with a strong mineral acid. An ether extract concentrates the organic components, sultones, and alkenesulfonic acid, which can be weighed and titrated potentiometrically with sodium hydroxide. 2-Hydroxyalkanesulfonate will not dehydrate to the sultone under these conditions and is not measured. 

Carbon dioxide is not a common oxidation product in periodate work, but it does appear in the oxidation of ketoses,49 a-keto acids,14,39 and a-hydroxy acids,14 39 and it is often a product23 141 of overoxidation. Carbon dioxide analyses have been carried out using the Plantefol apparatus,49 the Warburg apparatus,14 23 and the Van Slyke-Neill mano-metric apparatus,39 and by absorption in standard sodium hydroxide141 followed by back-titration with acid. A most convenient method is the very old, barium hydroxide absorption scheme.16 The carbon dioxide is swept from the reaction mixture into a saturated, filtered barium hydroxide solution by means of a stream of pure nitrogen. The precipitated barium carbonate is filtered, dried, and weighed. This method is essentially a terminal assay. The manometric methods permit kinetic measurements, but involve use of much more complicated apparatus. 

Consider a polyester prepared the polycondensation of a hydroxy acid. From the structure of the polymer it is known that this polyester has a carboxyl group for each molecule and when titrated one mole of sodium hydroxide is used per mole of polyester. To calculate the Molecular weight of the polyester, we have only to calculate how much polyester (in grams) gets neutralised by... 

Synthesis and characterization of well-defined, a,w-terminated difunctional siloxane oligomers are discussed. Detailed procedures on the preparation of primary amine- and hydroxy-terminated oligomers are given. Control of the average molecular weight (Mn) and also the possible variations in the backbone structure and composition are explained. The effect of these variations on the physical, thermal and chemical properties of the resulting materials are discussed. Characterization of these oligomers by FT-IR, NMR and UV spectroscopy, potentiometric titration and DSC are summarized. 

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