Mutarotation experimental observation

Simulation of the mutarotation of arabinose closely followed the work on galactose, except that four components plus a central intermediate were included, and the / -pyranose was the starting anomer. The components were the a-pyranose (kt, k2), / -pyranose (k3, k4), a-furanose (k5, k6), and / -furanose (k7j kg). Table III shows sets of values for the k s which yield the experimentally observed half-times for the approach of the components to their equilibrium levels. 

We have seen that the form I —> form II interconversion may take place along different pathways depending on the solvent system, with differing over-all mutarotation kinetics. In acetic acid the apparent order of the forward mutarotation reaction is 1.33 (0). It will be seen from Eq. (8) that in this case K t) should decrease with time, in agreement with the experimental observations. When 0 = 1, the mutarotation proceeds with first-order kinetics. This behavior is seen in the reverse mutarotation of poly-L-proline II in acetic acid-propanol. When /3 < 1, K (t) increases with time. This situation obtains in the initial stage of the forward mutarotation in acetic acid-water solvent which proceeds with zero-order kinetics. 

The original experimental evidence for concerted acid-base catalysis of the mutarotation in benzene is now considered unsound133 134 and concerted acid-base catalysis has been difficult to prove for nonenzy-matic reactions in aqueous solution. However, measurements of kinetic isotope effects seem to support Swain and Brown s interpretation.135 Concerted acid-base catalysis by acetic acid and acetate ions may have been observed for the enolization of acetone136 and it may be employed by enzymes.1363... 

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