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Water‐Catalysed hydrolysis of p ‐nitrobenzyl cellulose xanthate
Author(s) -
Humeres Eduardo,
Sequinel Luiz Fernando,
Nunes Mauricéa,
Oliveira Célia M. S.,
Barrie Patrick J.
Publication year - 1994
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.610070604
Subject(s) - chemistry , hydrolysis , xanthate , cellulose , aqueous solution , molecule , solvent , alkaline hydrolysis , medicinal chemistry , organic chemistry
The spontaneous hydrolysis of p ‐nitrobenzyl cellulose xanthate (CelXNB) with a degree of substitution (DS) in the range 2–9 was studied in 10% aqueous ethanol at pH 10, and was followed spectrophotometrically by the appearance of p ‐nitro‐α‐toluenethiol, in a continuous‐flow system where the reactor was shaken. CelXNB was characterized by solid‐state 13 C NMR spectra. The reaction occurs through two parallel processes due to two xanthate ester groups with different reactivities. The fast hydrolysis was ascribed to the reaction of the C‐2 + C‐3 isomers, whereas the slow hydrolysis was due to the C‐6 isomer. The percentage of the latter is much higher than C‐2 + C‐3. The solvent isotope effect of the fast hydrolysis ( k ′ H 2 O /) k ′ H 2 D11 was 2·22 ± 0·16 and the proton inventory indicated that there is only one proton transfer involved in the transition state, where a second water (or a neighbouring OH group) acts as a general base. The entropy of activation of the fast hydrolysis was only 3·3 ± 0·8 e.u., suggesting that the water molecules involved are highly oriented with respect to the coordinates required to reach the transition state. It is proposed that they form part of the three‐dimensional hydrogen‐bonded ice‐like structure that involves the cellulose matrix.