Saturday, August 11, 2012

Criteria for cellulose for attracting reactive dye. Reactive rate of some compounds


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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