Gluconolactone, hydrolysis

K a Volumetric oxygen transfer coefficient, h ki Michaelis constant for lactone production, g.L kp Gluconolactone hydrolysis rate constant, h ... 

Another example is the absence of oxygen exchange with solvent in the hydrolysis of gluconolactone. Simple acyclic esters usually undergo isotopic exchange at a rate that is conqietitive with hydrolysis. This occurs through the tetrahedral addition intermediate. 

Conversion of the gluconolactone to gluconic add occurs under certain conditions by spontaneous hydrolysis, though a rather specific lactonising enzyme is present in cells. 

Bromine oxidation of lactose followed by methylation and hydrolysis yields tetra-O-methyl-1,4-gluconolactone and the same galactose derivative as in (4). 

As shown in different works,41 65-71 the mechanism of glucose electrooxidation on platinum is similar to that on gold electrode. The primary and main reaction product remains 8-gluconolactone that is transformed into gluconate by hydrolysis. 

The reaction of D-gluconolactone 49 with 018-labeled hydroxide ion under stereoelectronic control (which is axial attack) will furnish 50. Note that the crc (, ri bond formed is antiperiplanar not only to an electron pair orbital on the resultant oxy anion, but also to the axial electron pair orbital on the ring oxygen. This reaction is reversible because the crc G n can also cleave very rapidly with the assistance of the same two stereoelectronic effects that facilitated its formation in the first place. Intramolecular proton transfer culminating in the transformation 50 —> 51 is also reversible. The ctc oh bond in 51 cannot cleave because it is antiperiplanar to only one electron pair orbital on the oxy anion [O ]- and, thus, 54 that retains the labeled oxygen will not form. In other words, if the hydrolysis reaction is interrupted (quenched by an aqueous acid) before completion and the unreacted D-gluconolactone is examined for the presence of O18, it will be discovered to be absent. 

An argument similar to that for the hydrolysis of D-gluconolactone leads us to 59 as the final product, wherein the label O18 has been incorporated. The transformation 57 —> 60 is not allowed for the lack of support by the requisite two stereoelectronic effects. Conformational ring flip from 57 to 61 is energy requiring. It may therefore be claimed not to compete with the fast cleavage of 57 to 58 because the latter is supported by two stereoelectronic effects. Let us see the turn of events assuming that the said conformational flip does compete and 61 is indeed formed. 

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