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Cellulose will swell, but does normally not dissolve completely in 10% NaOH.
1.4.8. Alkaline
cellulose
-‐ Mercerization
Alkaline cellulose is a very important step in derivatisation of cellulose. The
term mercerization stems from its inventor, John Mercer (1844). The process
is used in the production of
cellulose xanthate
, an intermediate in the
production of viscose and cellophane, which are both regenerated cellulose.
The underlying chemistry is essentially:
•
Cell-OH + OH
-
→
Cell-O
-
(hydroxyls become partly deprotonated at
very hight pH)
•
Cell-O
-
+ CS
2
→
Cell-O-CS
2
-
(reaction with carbon disulphide forming
soluble cellulose xanthate)
•
Cell-O-CS
2
-
+ H
+
→
Cell-OH + CS
2
(neutralization/acidification,
regeneration of cellulose fibers)
1.4.9. Cellulose derivatives
Cellulose derivatives have substituents attached to the hydroxyls. They are
linked with ether (C-O-C) or ester (-(C=O)-O-C) linkages.
The substituents interfere with the H-bonding and results in solubility in water.
Cellulose derivatives are important industrial products (food additives,
pharmaceutical excipients etc.)
Cellulose ethers:
Various ethers are formed by reacting alkaline cellulose (-O
-
) with alkyl
halides, aryl halides or sulphates, alkene oxides, epoxides etc. CMC
(carboxymethyl cellulose is a good example – and commercially very
important as a food additive (E466):
•
Alkaline cellulose is reacted with monochloroacetate (Na
+
salt of
monochloroacetic acid), resulting in nucleophilic substitution with Cl
-
as
leaving group:
Cell-O
-
+ ClCH
2
COO
-
→
Cell-O-CH
2
COO
-
•
Hydroksyethyl cellulose (HEC) is formed by reaction with ethylene
oxide:
H
2
C CH
2
O
Cell-O
- +
Cell-O-CH
2
CH
2
O
-