ISSN:
0449-2951
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
On the basis of the rate data of Jones, Dimler, and Rist on the acid-catalyzed hydrolysis of isomaltotriitol it is shown that the kinetics can be described by rate equations derived by assuming a combination of two interdependent simultaneous (“parallel”) and consecutive reactions according to the scheme: where A is isomaltotriitol; (B), B, and B* are glucose; C is isomaltitol; D and (D) are sorbitol; and E is isomaltose present at any instant; k1 and k2 are specific rates at which the two glucosidic bonds are hydrolytically cleaved in isomaltotriitol; k3 is the specific rate of hydrolysis of isomaltitol (known); and k4 is the specific rate of hydrolysis of isomaltose (known). Values for the constants k1 and k3 have been computed from the experimental values of the composition of the hydrolysis reaction mixture and the known values for k2 and k4. The yields of glucose and sorbitol as well as the extent of hydrolysis have then been calculated using the values for k1 and k3 (computed) and k2 and k4 (known) by means of rate equations corresponding to the above scheme. They are in very good agreement with the experimental values. The kinetics of the acid hydrolysis of isomaltotriose can also be described by rate equations corresponding to a kinetic scheme: where A″ is isomaltotriose; (B″), B″, B″*, and B**″ are glucose; (C″) and C″ are isomaltose at any instant; k5 and k6 are the specific rates of hydrolytic cleavage of the two glucosidic bonds in isomaltotriose, and k4 is the specific rate of hydrolysis if isomaltose (known). Assuming that k5 = k4/1.3 and k6 = k4/1.5, values for the extent of hydrolysis (expressed in terms of glucosidic bond cleavage for 100 bonds) have been calculated by means of rate equations derived on the basis of the above scheme. They show good agreement with the experimental values. However, transposing the values for k5 and k6 does not alter the calculated values. Thus, only the following conclusions seem to be permissible: the glucosidic bonds in isomaltotriose most likely hydrolyze at a lower rate than isomaltose; the two bonds do not hydrolyze at the same rate; whether the rate of hydrolysis of the glucosidic link of the reducing unit is slower than that of the nonreducing unit or the reverse, remains to be established. Attention is drawn to the role of the theoretical carbohydrate structural chemist who may offer an explanation for the deductions of the kineticist in the field of both trisaccharide and disaccharide hydrolysis.
Additional Material:
3 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1964.100020526
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