Mannitol titration

For the most part boric acid esters are quantitated by hydrolysis in hot water followed by determination of the amount of boron by the mannitol titration (see Boron compounds, boric oxide, boric acid and borates). Separation of and measuring mixtures of borate esters can be difficult. Any water present causes hydrolysis and in mixtures, as a result of transesterification, it is possible to have a number of borate esters present. For some borate esters, such as triethanolamine borate, hydrolysis is sufftciendy slow that quantitation by hydrolysis and titration cannot be done. In these cases, a sodium carbonate fusion is necessary. 

Weigh out accurately about 0.8 g of the purest acid and make up to 250 cm with water in a volumetric flask. Pipette 25.0 cm of the solution into a conical flask, dilute to 50 cm with water, add a few drops of phenolphthalein and 3.0 g mannitol. Titrate with standard O.I M NaOH until the first pale red colour is detected. Repeat to obtain concordant results and calculate from the average titre the concentration of the acid in mol dm ... 

Take approximately 0 5 g. of the finely powdered mannitol, using either a weighing bottle, or else weighing directly in the flask A as before. Heat on the water-bath for 60 minutes. During the titration with the NaOH solution, a fine precipitation of the hexacetyl-mannitol may occur, but will not affect the titration. The results are excellent. 

The apparent acid strength of boric acid is increased both by strong electrolytes that modify the stmcture and activity of the solvent water and by reagents that form complexes with B(OH) 4 and/or polyborate anions. More than one mechanism may be operative when salts of metal ions are involved. In the presence of excess calcium chloride the strength of boric acid becomes comparable to that of carboxyUc acids, and such solutions maybe titrated using strong base to a sharp phenolphthalein end point. Normally titrations of boric acid are carried out following addition of mannitol or sorbitol, which form stable chelate complexes with B(OH) 4 in a manner typical of polyhydroxy compounds. EquiUbria of the type ... 

Glycerol has been widely employed for this purpose but mannitol and sorbitol are more effective, and have the advantage that being solids they do not materially increase the volume of the solution being titrated 0.5-0.7 g of mannitol or sorbitol in 10 mL of solution is a convenient quantity. 

The method may be applied to commercial boric acid, but as this material may contain ammonium salts it is necessary to add a slight excess of sodium carbonate solution and then to boil down to half-bulk to expel ammonia. Any precipitate which separates is filtered off and washed thoroughly, then the filtrate is neutralised to methyl red, and after boiling, mannitol is added, and the solution titrated with standard 0.1M sodium hydroxide solution ... 

Procedure. To determine the purity of a sample of boric acid, weigh accurately about 0.8 g of the acid, transfer quantitatively to a 250 mL graduated flask and make up to the mark. Pipette 25 mL of the solution into a 250 mL conical flask, add an equal volume of distilled water, 2.5-3 g of mannitol or sorbitol, and titrate with standard 0.1 M sodium hydroxide solution using phenolphthalein as indicator. It is advisable to check whether any blank correction must be made dissolve a similar weight of mannitol (sorbitol) in 50 mL of distilled water, add phenolphthalein, and ascertain how much sodium hydroxide solution must be added to produce the characteristic end point colour. 

Other suggested experiments include titration of 0.05M Na2C03 with 0.1M HC1, and of 0.1M boric acid in the presence of 4 g of mannitol with O.lMNaOH. 

Analytical. Mannitol Hexanitrate can be hydrolyzed in basic soln and the soln acidified in the presence of NITRON to quanty ppt NITRON nitrate (Ref 16). A procedure is described for. the quant detn of nitrate esters, including Mannitol Hexanitrate, in the presence of aromatic nitro compds in Ref 17. It gives a yellow color when treated in et ale or acet with 5% aq K hydroxide, then 5% aq ammonia (Ref 24), It can be quanty detd by reduction with Devarda s alloy (Encycl 5, D-l 110) or A1 wire in aq et ale and titration of the evolved... 

Hypertonic sahne is actively excluded from an intact BBB and also acts to draw water into the intravascular space by the creation of a sodium gradient. Various concentrations have been evaluated, with continuous sodium chloride infusions ranging from 3% to 9%, and bolus infusions up to 23.4% administered over 20 minutes in a 30 mL solution. When a continuous infusion is used, the serum sodium is typically titrated to the 155-160 range. Sodium levels above this range raise the concern for seizures and other toxic side effects. Hypertonic saline may hold an advantage over mannitol, as it has been found in animal models to decrease edema in both... 

In the course of work on the potentiometric titration of some oxidizing acids, Malaprade1 found the existing method for determination of periodic acid in periodic-iodic acid mixtures too inaccurate for estimation of small proportions of one component. He discovered that mannitol will reduce only the periodic acid and, furthermore, that it only reduces the acid to iodic acid.2 The following general reaction appeared to take place. 

The complexes with boric acid and borates have been of more interest. The ability of D-mannitol to render boric acid more acidic is well known and forms the basis of an anal3rtical method allowing boric acid to be titrated as a monobasic acid. The boric acid complexes have been... 

The B2O3 content of borax may be determined by extraction into HCl solution followed by complexation with mannitol and titration with dUute NaOH. The Na20 content of horax may he measured by titration of an aqueous solution with dUute HCl. Boron and sodium metals in the acid extract of horax may be analyzed by atomic absorption or emission spectroscopy after appropriate dUution of the extract. In the solid phase B2O3 and Na20 may he measured nondestructively by x-ray techniques. 

Elemental composition B 17.50%, H 4.88%, O 77.62%. Boric acid may be analysed by adding calcium chloride (in excess) and sorbitol or mannitol to its solution, followed by acid-base titration using a strong base to phenolph-thalein endpoint. Elemental boron may be analyzed by AA or ICP spectrophotometry. 

Anaiysis. If a borate is treated with H2SO4 and methanol H3COH, methyl borate is produced. If a small amount of the mixture is introduced to a flame, a green flame color is produced. The test is sensitive to 20 ppm of B. Ba and Cu interfere, both of these also giving a green color. A spot test with curcumin will detect 5 ppm of B. Titration of H3BO3 in a mannitol solution... 

The hydroxy a-amino acids l-serine and l-threonine, used as models for the 2-amino-2-deoxy glyconic acids, have been complexed with Ni(II) at 37 °C in aqueous solutions of 0.15M potassium nitrate. Values for the stability constants were obtained from iso-pH titration data which were collected by alternate, small, incremental additions of metal ion and potassium hydroxide being made such that the pH of the solution remained nearly constant. The data were consistent with the predominance of MLn species, along with additional protonated and hydrolyzed complexes. There was no evidence for the involvement of the hydroxyl group in chelation. By the same iterative computations the complexes formed between borate and mannitol have been analyzed, and the stability constants have been calculated. Complexes with mannitohborate stoichiometries of I.T, 1 2, 1 3, and 2 1 were proposed. 

The titration data were analyzed by a computer program, which was a modification of the program SCOGS (17). The systems Ni(II) and L-serine or L-threonine, as analogs of amino-sugar acids, and boric acid and mannitol-borate were evaluated. For each of these systems it was convenient to refine first the formation constants for the simple complexes, such as ML and ML2, adding other more complex species later until the best fit to the data had been obtained. 

Example.—Mannitol.—The hexa-acetyl derivative (p. 259) is prepared and purified, and a quantity of it—about 0-2 gm.—along with 100 c.cs. of 10% benzene sulphonic acid solution placed in a steam distillation flask. The flask is connected to a condenser on one side and to an apparatus for the generation of pure steam on the other. A suction flask to serve as receiver is attached by a cork to the condenser, and to the side tube of the suction flask a soda-lime tube to prevent the entrance of carbon dioxide is attached. Steam is blown through the flask until (1-5—3 hours) the distillate passing over is neutral. The whole distillate is then titrated with standard baryta, using phenolphthalein as indicator. 

In the first cycle, the two mixer stages where the organic phase is mixed with ammonia-mannitol solution need special attention. The addition of the aqueous solution is controlled by a pH-electrode in the organic phase at the outlet from the second mixer stage connected to a titrator controlling the IE-feed pump. 

The ion does not combine with a proton since the boron is already exerting its maximum covalence of four, but it does bind II3O+ electrostatically. Boric acid can be titrated against NaOH in the presence of mannitol or glycerol for this reason. 

Ethyl orthoborate has a boiling point of 120°, a density of 0.86426, and a refractive index (n ) of 1.3721. It is readily hydrolyzed to ethanol and orthoboric acid. The ester may be analyzed for boron by dissolving a weighed sample in water, adding mannitol (about ten times the weight of sample taken), and titrating the boric acid to the phenolphthalein end point. This determination works best if the solution is protected from atmospheric carbon dioxide in the region of the end point. 

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