Measurement of Mutarotation Reactions

Apparatus, polarimeters, light sources, and tubes are described in References 174 to 180. 

Jacketed, glass polarimeter tubes, 2 and 4 dm in length, are recommended. They should have a central side-tube for rapid filling and for holding a thermometer (inserted in a stopper) during the reaction. For reactions that may be catalyzed by glass, silica tubes may be 

For accurate determination of specific rotation, sugar samples must be adequately dried, or the content of solvent must be determined. In order to minimize the time required for dissolution, the sugars should be ground, and screened through a 80— 100-mesh sieve. 

For determinations of reaction constants, anomeric purity is not necessary, but for the determination of initial rotations, only one anomer can be present. Pure anomers can often be obtained by slow crystallization from a suitable solvent in the presence of nucleating crystals of the desired form and in the absence of crystals of other forms. For measurements in aqueous solution, use of mM potassium hydrogen phthalate as a buffer (pH 4.4) is recommended, to avoid variation in acidity during measurements. Precautions for purification, drying, and use of organic solvents have been described by Lowry and Baker. Anomeric impurities can be removed by lixiviation with a solvent (such as aqueous alcohol) in which both anomers are slightly soluble. 

To measure the mutarotation, the tube, with water at the desired temperature passing through the jacket, is placed in the polarimeter. The temperature should be controlled to about 0.01°. A known 

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