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By M. R. F. Ashworth

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This was done by adding the reaction mixture to a solution of 1 mg of phloroglucinol in a few ml of sulphuric acid, which yields a yellow or orange colour. Resorcinol or thymol can be used instead of phloroglucinol, but are less sensitive. The author preferred vanadium(V) to bromine. 1 33 OXIDATION METHODS West and Skoog (1959) determined glycerol in dilute aqueous solution by oxidation with acid vanadate reagent to formic acid through heating for 1 h on the water bath: C H (OH) 3 5 3 + 8V0 + 2 + 8H + 3HCOOH + 8 V 0 2 + + 5H 0 2 After cooling the solution they back-titrated with ferrous iron to the colour change from violet to green of the indicator N-phenylanthranilic acid.

100°C on the steam bath. Unused anhydride was then reacted with excess (25 ml) standard 0-9% aniline (ca. 0-1N) in benzene solution and 30 ml of glacial acetic acid; after 5 min the residual aniline from this was back-titrated with 0-1N perchloric acid-acetic acid to Crystal Violet indicator: (C H CO) 0 + C H N H -* C H CONHC H 2 D. 5 DIRECT 2 6 5 2 ESTERIFICATION 2 WITH 5 6 5 CARBOXYLIC + C H COOH 2 5 ACID This principle is seldom used. Bryant et al. (1940) determined alcohols, including glycerol, by reaction in dioxan with acetic acid containing dissolved boron trifluoride as catalyst for the esterification: CH3COOH + R O H - * C H C O O R + H 0 3 2 After 2 h at 67 + 2°C they added pyridine and titrated the water formed using the Karl Fischer reagent.

2h/100°C I U P A C methods (1973) 4 4 Siggia et al (1961) Also with acetic anhydride2 0 m i n / 5 0 + 1°C ethyl acetate-toluene-psulphonic acid (33 + 100 + 4 g) * The final titration was with alkali to phenolphthalein indicator, except in the three cases where it is stated otherwise. 2 GLYCEROL faster because the ester product does not have to be quantitatively hydrolysed in a following determining step. But care is needed here too during the removal of unused anhydride to ensure that the ester does not undergo hydrolysis.

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