16639
Accession Number
18091
Title Of Article Chaper
Specific hydroxide ion catalysis of the endwise depolymerization of cellulose
Title Of Journal Book
Journal of applied polymer science
Volume
22
Issue
3
Pages
711-718
Reference Bibliography
Includes bibliog. refs.
Language Of Text
English
Language Of Summary
English
Literature Type
Serial
Literature Level
Analytic
Abstract
The endwise depolymerization (unzipping reaction) of hydrolyzed cotton cellulose (x=200) in water under a nitrogen atmosphere was followed at 98°C at several alkalinities in the pH range of 8. 0-10. 5. The observed apparent first-order rate constant k<sub>1</sub> was invariable at low alkalinity (k<sub>1</sub>=k<sub>0</sub>), while above pH 8.5, k<sub>1</sub> increased with pH. The data conform with the expression rate=(k<sub>0</sub> + k<sub>OH</sub><sup>-s(OH*</sup> <sup>h-</sup>)) = (0.3 + 2.1 x 10<sup>3</sup> (OH<sup>-</sup>))(SH) where (SH) denotes substrate concentration. The specific hydroxide ion catalysis is considered to involve ionization of the anomeric hydroxyl group at the reducing chain end that leads to elimination of the glucosidic oxygen atom bearing the polymer chain from C4 of the terminal D-glucose residue. In this initiation process, the glucosidic oxygen is eliminated as an anion so that rapid propagation of the unzipping along the polymer chain may occur. Thus, entire chains will depolymerize. The kinetic chain length v is defined as the ratio k<sub>1</sub>:k<sub>t</sub>, where k<sub>t</sub> is the pseudofirst-order rate constant for chain terminations, and a value of v ~ 100 D-glucose reidues was found at all the alkalinities investigated. -- CCI
Keywords
cellulose chemistry;hydrogen bonding;structure; cellulose; depolymerization CAL
pub_id
16639