Reactive dyes reactions with cellulose

Chemical Types. A wide range of reactive groups have been investigated, with 20—30 used commercially and over 200 patented. These have been described in detail elsewhere (10,20). Because these reactive groups differ chemically the activation of the reactive systems is different as are the rates of reaction with cellulose, from one reactive system to another. This rate of reaction with cellulose, or reactivity, dictates the temperature and pH needed for dyeing. 

In the case of quaternary derivatives made from the non-planar aliphatic amines 7.64, 7.65 and 7.66, steric strains further destabilise the C-N+ bond so that reaction with cellulose occurs under alkaline conditions at 30 °C, whereas temperatures of about 40-50 °C are required for the pyridinium derivatives 7.67. The quaternisation approach appeared to offer the opportunity to prepare dyes yielding reactivity levels intermediate between those of aminochloro- and dichlorotriazine dyes without loss of the desirable stability of the dye-fibre bond to acidic conditions that is characteristic of aminohalotriazine dyes. Unfortunately, this ideal was not attainable because of the objectionable odours of the tertiary amines liberated by the fixation reaction and the sensitivity of the reactivity behaviour of the quaternised derivatives to the nature of the chromogen attached to the triazine ring, making it difficult to select compatible combinations of dyes. 

A reactive dye for cellulose contains a chemical group that reacts with ionized hydroxyl ions in the cellulose to form a covalent bond When alkali is added to a dyebath containing cellulose and a reactive dye. ionization of cellulose and the reaction between dye and liber is initialed. As this destroys the equilibrium more dye is then absorbed by the fiber in order to re-establish the equilibrium between active dye in the dyebath and fiber phases. At the same time the addition of extra cations, e.g.. Na+ from using... 

Water repellents with a chlorotriazine or vinyl sulfone functional group react with cellulose in the presence of alkali. Therefore, they are not compatible with cross-linking reactants requiring acid catalysis for the reaction with cellulose. This limitation, in addition to the cost, is one of several reasons why fiber-reactive chemistry developed for dyes has not been successfully adaptable to repellent finishing. 

The most important discovery in dyeing cellulose with reactive dyes was the appHcation of Schotten-Baumaun principles. Reaction of alcohols proceeds more readily and completely in the presence of dilute alkali, and the cellulose anion (cell- O ) is considerably more nucleophilic than is the hydroxide ion. Thus the fixation reaction (eq. 1) competes favorably with hydrolysis of the dye (eq. 2). 

Copper phthalocyanine derivatives are well established as turquoise blue direct and reactive dyes for cellulosic fibres. Chlorosulphonation at the 3-position, followed by hydrolysis, yields sulphonated direct dyes such as Cl Direct Blue 86 (5.32 X = H) and Blue 87 (5.32 X = S03Na). Solubility and dyeing properties can be varied by introducing four chlorosulphonyl groups, some of which are hydrolysed and some converted to sulphonamide by reaction with ammonia or alkylamines. This approach is also the main route to reactive dyes of the copper phthalocyanine type. The reactive system Z is linked to a 3-sulphonyl site... 

The only copper complexes of tridentate azo compounds are 1 1 structures, since copper(II) has a CN of 4. They can be prepared by the reaction of the azo compound with a copper(II) salt in an aqueous medium at 60 °C. The major application for copper-complex azo dyes is as direct or reactive dyes for the dyeing of cellulosic fibres. They are seldom developed for use on wool or nylon, although various orange and red 1 1 copper-complex azopyrazolones (5.42) were synthesised recently and evaluated on these fibres by application from a weakly acidic dyebath [24]. 

Ionisation of the hydroxy groups in cellulose is essential for the nucleophilic substitution reaction to take place. At neutral pH virtually no nucleophilic ionised groups are present and dye-fibre reaction does not occur. When satisfactory exhaustion of the reactive dye has taken place, alkali is added to raise the pH to 10-11, causing adequate ionisation of the cellulose hydroxy groups. The attacking nucleophile ( X ) can be either a cellulosate anion or a hydroxide ion (Scheme 7.8), the former resulting in fixation to the fibre and the latter in hydrolysis of the reactive dye. The fact that the cellulosic substrate competes effectively with water for the reactive dye can be attributed to three features of the reactive dye/ cellulosic fibre system ... 

Scheme 7.19), leading to dyes with a 5-chloro-4-methyl-2-methylsulphonylpyrimidine reactive system (7.24). During reaction with the cellulosic fibre under alkaline conditions, the methylsulphonyl moiety is a particularly effective leaving group and rapid fixation takes place when the reactive system approaches the cellulosate anion. 

The kinetics of homogeneous reaction of several reactive dyes of the vinylsulphone type with methyl-a-D-glucoside (7.9), selected as a soluble model for cellulose, were studied in aqueous dioxan solution. The relative reactivities of the various hydroxy groups in the model compound were compared by n.m.r. spectroscopy and the reaction products were separated by a t.l.c. double-scanning method [38]. The only sites of reaction with the vinylsulphone system were the hydroxy groups located at the C4 and C6 positions [39,40]. 

In spite of the anomalous ring-opening decomposition of nicotinotriazine compounds under conditions of alkaline hydrolysis (Scheme 7.34), the product of reaction of a bis(aminonicotinotriazine) dye with cellulose is the same as that from the analogous bis(aminochlorotriazine) dye in terms of hue, colour fastness and stability of the dye-fibre bond. If desired, these bis(aminonicotinotriazine) dyes can be applied satisfactorily at 80 °C and pH 11, as was evident for Cl Reactive Blue 187. They have slightly higher reactivity... 

The introduction of Calcobond dyes a few years later by American Cyanamid exploited a similar principle but incorporated the N-methylol groups into the dye molecule itself [132]. The labile chloro substituents in dichlorotriazine dyes were converted to amino groups by substitution with ammonia and the resulting melamine residue made cellulose-reactive again by reaction with formaldehyde (Scheme 7.59). A typical member of this range was Cl Reactive Red 92 (7.120). A characteristic problem of the Procion Resin process and of the... 

Fiber-Reactive Dyes. These dyes can enter intu chemical reaction with the fiber and form a covalent bond to become an integral part of the liber polymer. They therefote have exceptional wetfastness. Their main use is oil eellulosie fibers where they are applied neutral and then chemical reaction is initialed by the addition of alkali. Reaction with the cellulose can be by either nucleophilic substitution, using, for example, dyes containing activated halogen substituents, or by addition to the double bond in. for example, vinyl sulfone. -SCfCH=CH2, groups. 

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