Simple mutarotation

Often, the sweetness of simple sugars is reported in the literature without any indication of anomeric specification, although the values recorded in some cases refer to an equilibrated solution. In other instances, they refer to some unstated, partially mutarotated solution. 

For some monosaccharides, the rate of mutarotation (K = k 3-kf) is found to obey a simple first-order rate law in which — d[a]/dt = A [a] — A2[P] (Scheme 1.4). Glucose, mannose, lyxose and xylose exhibit... 

The rate of mutarotation of some sugars (for example, D-glucose and D-xylose) obeys a simple, first-order law corresponding to an equilibrium between two species only. a-n-Glucopyranose and its anomer mutarotate... 

The mutarotations of the first group, designated simple mutarota-tions, can be expressed by equation 5, the exponential form of equation ... 

The following aldoses show simple mutarotation, arising in large measure from a,/3-D-pyranose anomerization a-D-xylose, a- and... 

When the two modifications of a sugar showing a simple mutarotation are known, the equilibrium proportions may be calculated from the equilibrium rotation and the initial optical rotation of the known crystalline modifications. In the event that only one modification is known in the crystalline form, the proportion of the second modification may be obtained from the initial and maximum solubilities of the first, as described on page 18. With sugars that show complex mutarotation, the proportions of the a- and /8-pyranose modifications may be estimated roughly from the extent of the slow mutarotation as compared to the optical rotations of the known a- and... 

With sugars that show simple a,j8-pyranose mutarotations, the proportions of the anomers may be estimated from optical rotations, as described on page 23 and given in Table III. Optical rotation data can be supplemented and confirmed by measurements of solubility and by evaluation of the data as described on page 18. 

The differential equations describing complex mutarotations resist explicit solution, and are usually solved numerically. Much mechanistic work has been done, however, on simple mutarotations monitored polarimetrically. Such reactions are can be treated as reversible first-order reactions, with the mutarotation rate constant corresponding to the sum of the ring-opening reactions of the two pyranose forms, which are the rate determining steps in each direction (Equation 1.2). 

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