Reactive Substantivity

Cr(II) has been used to bring about dehalogenation of alkyl halides involving the production of alkyl radicals, and details have been provided in a substantive review (Castro 1998). The ease of reduction is generally iodides > bromides > chlorides, while tertiary halides are the most reactive and primary halides the least (Castro and Kray 1963, 1966). 

Another example where antioxidant performance can be improved dramatically lies in the mechanochemlcally initiated addition of reactive antioxidants on rubbers (5.10) or unsaturated thermoplastics such as ABS (12). For example, using thiol antioxidants 2 and 3 as the reactive antioxidants, Kharasch-type addition of the thiol function to the polymer double bond takes place during melt processing to give bound antioxidant adduct (see Equation 1) the polymer becomes much more substantive under aggressive environments. 

One of the earliest fibre pretreatments for improving the dyeability of cotton is of course mercerisation (section 10.5.4). However, more recent research interest in this area has been generated by environmental concerns about reactive dyeing, aiming to enhance substantivity for the modified fibre so that higher absorption and fixation are obtained. This results in less dye (hydrolysed or still active) in the effluent. A further objective is to minimise the usage of electrolyte in the application process. This area has been thoroughly reviewed [392,393]. 

The pretreated nylon then undergoes covalent fixation of dyes containing aminoalkyl groups. Interestingly, nylon treated with XLC showed markedly lower substantivity and reactivity with conventional dyes. If the pretreated nylon was reacted with ammonia, however, creating amino functionality at the reactive sites, normal reaction with a conventional reactive dye was restored [405]. 

A detailed comparison [181] of three vinylsulphone dyes included a low-substantivity monoazo N-acetyl H acid derivative (Cl Reactive Red 35), a monoazo N-acetyl J acid type of higher substantivity (Cl Reactive Orange 82) and a phthalocyanine turquoise somewhat prone to aggregation (Cl Reactive Blue 21). Dyeings of these individual products were subjected to three wash-off procedures ... 

The influence of metal ions on the aggregation of Cl Reactive Red 2 (3.14) in aqueous solution at various pH values has been examined in detail recently [18]. Sodium ions have a profound effect on these disulphonated dye anions, so that the enhancement of substantivity during the dyeing process is accompanied by aggregation attributable to hydrophobic interaction between the phenyl and s-triazine ring systems. Aggregation is much greater,... 

Table 7.3 Relationship between substantivity and nature of the reactive group for monofunctional dyes [37]...

The most commercially successful reactive dye of all, Cl Reactive Black 5 (7.36) contains two sulpha toe thylsulphone precursor groups that contribute markedly to its initial solubility. When these are hydrolysed in alkali to release the reactive bis(vinylsulphone) form, the considerable increase in substantivity (Table 7.3) leads to highly efficient fixation. Further hydrolysis of the vinylsulphone groups to give the inactive bis(hydroxyethylsulphone) derivative, however, lowers the substantivity and hence contributes to favourable wash-off performance. 

A highly substantive bluish red bis(sulphatoethylsulphone) structure (7.73) has been patented recently [29]. In a kinetic study using the t.l.c. double-scanning method, the condensation reactions between the bis(aminochlorotriazine) dye Cl Reactive Red 120 (7.48 X = Cl) and the two isomeric sulphatoethylsulphone anilines 7.38 and 7.39 to yield the two corresponding bis(sulphatoethylsulphone) isomeric dyes were compared. The rate constant of the reaction between Red 120 and the meta isomer 7.39 was about ten times as large as that for the para isomer 7.38 [64]. 

The marked differences in substantivity between the various forms of monofunctional vinylsulphone dyes (section 7.3.8) recur to a moderated extent in the Sumifix Supra dyes because of the influence of the substantive triazine ring. The scarlet chromogen (7.77) linked via a chlorotriazine unit to the three variants of the vinylsulphone grouping showed similar trends (Table 7.4) to those already seen for those of Cl Reactive Red 22 tested under the same conditions (Table 7.3). The rate of secondary exhaustion will be easier to control in this instance because of the lower difference in substantivity between the precursor and the vinylsulphone form [37]. 

Three major approaches have been followed to provide reactive dyes in this important sector. One category is closely related to the reddish blue monoazo 1 1 copper complexes already described (section 7.5.8). To provide the higher substantivity and deeper intensity for build-up to navy blue shades, a second unmetallised azo grouping is introduced. As with the brown dyes, the A—>M—>E pattern is adopted for their synthesis. Component A is normally a sulphonated aniline, M an aminophenol or aminocresol and E a sulphonated naphthol or aminonaphthol. The reactive system (Z) is usually, but not invariably, located on the E component and the copper atom always coordinates with an o,o -dihydroxyazo grouping provided by the M and E components (7.109). 

Reactive Black 5 (7.127) by an exhaust process and optimal conditions for fixation were determined [140]. The substantivity of this agent for cellulose is not ideal, as it requires a high salt concentration to ensure a fixation level of 80%. To achieve 85% fixation of dye 7.127 by this method, an addition of 50 g/1 sodium sulphate was necessary [29]. 

More controlled and efficient fixation is possible when the reactant is applied as a pretreating agent [146]. If nylon given such a pretreatment is subsequently dyed with the conventional chlorotriazine dye Cl Reactive Red 3 (7.2), the substantivity and fixation of the latter are markedly lowered because the anionic XLC residues have reacted with N-terminal amino groups in the fibre. Treatment of the modified nylon with ammonia, however, restores some degree of dyeability. Opposite effects are observed if Cl Reactive Red 3 is reacted with ethylenediamine to form an aminoalkyl derivative (7.131). This nucleophilic dye exhibits a high degree of fixation only on the modified nylon that has been pretreated with XLC. 

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