Lyxose rates

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 

Lemieux and Brice have measured the rate of exchange (in chloroform) of a large number of 1,2-trans sugar acetates with stannic trichloride acetate labeled with C. Their results are given in Table XVII. The low reactivities of the acetates of 8-D-ribose, a-D-lyxose, 8-D-allose, and a-D-mannose (rela- 

The isopropylidene group in methyl 2,3-0-isopropylidene-a-D-manno-pyranoside was hydrolyzed even more readily, with 0.01 N hydrochloric acid at 15°. The rates of hydrolysis of some isopropylidene derivatives of D-xylose, L-arabinose, D-ribose, and D-lyxose were examined,using 0.2 N oxalic acid at room temperature or at 65°. 

The similar polarographic behavior of semicarbazones, hydrazones, phenylhydrazones, and oximes of D-glucose, D-galactose, and n-mannose was described in another paper. For the aldoses studied, the equilibrium and rate constants for the formation of their oximes, semicarbazones, and hydrazones were determined at several different pH values, and it was found that their reactivity increases in the order D-glucose < D-galactose < D-mannose < D-xylose < n-arabinose < D-ribose < D-lyxose.  

On the grounds that furanosides anomerise and hydrolyse very much more readily than do the corresponding pyranosides. Bishop eind Cooper assumed that the first step in the glycosidation process is the methanol-ysis of the furanose form of the free sugar, and they visualised, without evidence, a unimolecular process proceeding by way of a stabilised cyclic ion (1). In support of this they observed 5) that for xylose, lyxose and ribose the furanoside formation rates (3,1,12 respectively) correlated with the furanoside contents at equilibrium (see Table 3) and hence, presum- 

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