Chemistry of Reactive dyes :
(I) Classification of the reactive system on the basis of Mechanism -
In a reactive system as we see these are two types of reactions -(i) Esterification
(ii) Hydrolysis
(B) Nucleophilic Addition
(i) Esterification
(ii) Hydrolysis
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| Chemistry of Reactive dyes |
(Classification of reactive dyes can also be categorised as below method.
1. Classification of Reactive dyes
2. Reactive Systems classification
3. Chemistry of Reactive dyes and classification)
Explanation -
(A) Nucleophilic substitution reaction -
Triazinyl form of reactive dyes (Procion dyes) reacts with cellulose by a-Cellulose by a process called nucleophilic substitution.
One of the 2 chlorine atoms of a dichlorotriazine dye(cold brand) is reacted with cellulose by nucleophilic substitution and a few portions of the dye react with a chemical group of water molecules simultaneously resulting in the formation of hydrolysed dye which may not react with Cellulose as shown below –
(a) Esterification
(b) Hydrolysis
(Note: Nucleophilic mean the negative (-ve) charged ion i.e chlorine (Cl) will be replaced or substituted by respective groups like -O-Cellulose or -OH group.
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| Nucleophilic substitution reaction |
(B) Nucleophilic addition :
Through the addition of an alkali that reacts with the hydroxyl group in cellulosic fibres in a procedure known as nucleophilic addition, vinyl sulphone is created from sulphatoethyl sulphone.
Unreacted hydrolyzed dye results from some of the vinyl sulphone reacting.
Reactions -
(b) Hydrolysis -
(II) Classification of the reactive system on the basis of Functionality -
(A) Monochlorotriazine (MCT)
(B) Dichlorotriazine (DCT)
Explanation -
We have to understand the structure of monochlorotriazine and Dichlorotriazine as follows-
Triazinyl type ring system (cold brand and hot brand reactive dyes):
(A) Monochlorotriazine
(B) Dichlorotriazine
These dyes are made of cyanuric chloride, in which replacing every successive chlorine atom is increasingly difficult.
The first one is reactive even within the cold the second at temperature and above while the third requires refluxing in solution or under anhydrous conditions at higher temperatures.
The most reactive chlorine atom is reacted with a radical containing dye leaving the opposite two chlorine atoms available for reaction with Cellulose.
The dyeing reaction takes place within the presence of an alkali even within the cold and hence they're called cold brand dyeing or cold cold brand reactive dyes (the original procion dyes are now designated as Procion M dyes) (structure (a) below). Structure -
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| Dichlorotriazine (cold brand) |
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| Monochlorotriazine (Hot brand) |
When two of the three chlorine atoms of the cyanuric chloride are replaced by a dye and suitable amino compound the resulting dye is left with just one chlorine atom which is way less reactive.
In this case, the reaction with Cellulose (also called fixation of the dye onto Cellulose) must be applied at higher temperatures and such dyes are marketed as HOT dyeing or HOT brand reactive dyes (designed as Procion H dyes)(structure b).
Questions -
- Explain the chemistry of reactive dyes.
- Which Nucleophilic substitutions are used for the reactive dyeing process?
- What is the Esterification and Hydrolysis for reactive dyes?
- Which Nucleophilic Addition is used for the reactive dyeing process?
- What are Esterification and Hydrolysis?
References
Ahmed, S. (2014, September 29). Reactive dyes - classification. TextileTuts. https://textiletuts.com/reactive-dyes/
Chakraborty, J. N. (2010). Waste-water problem in textile industry. In Fundamentals and Practices in Colouration of Textiles (pp. 381–408). Elsevier.
Clark, M. (2011). Handbook of textile and industrial dyeing: Principles, processes and types of dyes (Matthew Clark, Ed.). Woodhead Publishing.
No title. (n.d.). Acs.org. from https://cen.acs.org/articles/96/i29/new-textile-dyeing-methods-make.html
Patwary, E. M. Z. (2012, February 18). Reactive dyes. Textile Fashion Study; Engr. Mohammad Zillane Patwary. https://textilefashionstudy.com/reactive-dyes-definition-classification-properties-and-influencing-factors/
Sayed, A. (n.d.). Why reactive dye is so called? Blogspot.com. from https://textileapex.blogspot.com/2013/11/reactive-dye.html
What are Reactive Dyes? Types of Reactive Dyes. (n.d.). Meghmaniglobal.com. from https://www.meghmaniglobal.com/what-are-reactive-dyes-types-of-reactive-dyes/
(N.d.). Textilelearner.net. from https://textilelearner.net/reactive-dyes-classification-dyeing-mechanism/
Continue reading,
Part 2 Classification of Reactive dyes
Part 3 The reaction of MCT and DCT of reactive dyes
Part 4 General Factors affecting the results of reactive dyeing
Part 5 Reactive dyeing method - DCT
Part 6 Bifunctional systems of reactive dyes
Part 7 Development of reactive dyes
Part 8 Reactive dyes on Silk and nylon with their application
Part 9 Industrial applications of reactive dyes
Part 10 After treatment of reactive dyes
Writer - Rushikesh Patil (Textile Engineer)
