Criteria for cellulose for attracting reactive dye
The chemical structure of cellulose
macromolecule is given below:
In cellulose macromolecule glucose
units are linked through oxygen bridges formed between C1 position
of one glucose and C4 position of adjacent glucose unit. Each
glucose unit contains one primary hydroxyl group (at C6 position)
and two secondary hydroxyl group =CHOH (at C2 and C3
positions). Again one end of this glucose
Unit has an additional secondary
hydroxyl group at C4 position and the other end has an aldehyde or hemiacetal
group at C1 position. Now the following things are considered.
1.
Primary hydroxyl group (-CH2OH) at C6 position
is more reactive then the secondary hydroxyl groups (-CHOH) at C2
and C3 positions.
2.
C2 hydroxyl group is supported to be more acidic than
c3 hydroxyl group under suitable alkaline condition and hence is more reactive.
3.
The hemiacetal group at C1 position is the most active
while the additional hydroxyl group of C4 position is the least reactive.
4.
The reaction between reactive group and cellulose
takes place predominantly with primary hydroxyl group to some extent.
5.
Longer carbon chain lowers the rate of reaction.
6.
Incase of monochloro triazinyl dyes, this reaction takes
place 15 times more frequently with C6 hydroxyl group than with the hydroxyl
group at C2 or C3 position.
7.
In case of dichlorotriazinyl dyes, this reaction takes
place 3-7 times more frequently with hydroxyl group at C2 position than that
with hydroxyl group at C1 or C3 position.
The reactive rate of
some compounds are mentioned below:
COMPOUND STRUCTURE REACTIVITY
Water H-OH 1.0
Iso-propanol CH3-CHOH-CH3 0.7
Ethanol CH3-CH2-OH 7.4
Methanol H-CH2-OH 12.3
Glucose C6H12O6 5.5
So from the above table it is obvious that secondary hydroxyl group is
the beast reactive while primary one is the most reactive.
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