Coupler anion

Mechanisms of Coupling. Because the active coupling species is the ioni2ed coupler (35,52), the rate of the coupling reaction and hence its abihty to compete for oxidi2ed developer is dependent on the pH of the process, the piC or acidity of the coupler or less frequentiy the rate of coupler ioni2ation, and the reactivity of the resulting coupler anion with the QDI (40). 

For two-equivalent couplers where the conversion of the leuco dye to image dye is rapid, the experimentally observed second-order rate constant, k, can be equated with kj, the rate of nucleophilic attack of coupler anion on oxidized developer. Thus when the pH of the process is specified, two parameters, piC and k, can be convenientiy used to characterize the molecular reactivity of a large variety of photographically weU-behaved couplers (40,54). 

The useful reaction of oxidized p-phenylenediamines is to generate dye. They can react with an electron-rich species, a coupler anion, to form a leuco dye which either oxidizes or loses a fragment to form the dye. As an example, oxidized p-phenylenediamine can react with a phenol to form a cyan dye as shown in Scheme 2. The leuco dye oxidation usually takes place with the consumption of another molecule of CDox, which is reduced back to the color developer. Thus production of a molecule of dye by this route uses two molecules of CDox or four silver ions and is known as a four-equivalent reaction. Dye formation ean proceed by a two-equivalent route if there is a good leaving group such as a chlorine atom at the reaction site on the coupler anion. 

The azo coupling reaction proceeds by the electrophilic aromatic substitution mechanism. In the case of 4-chlorobenzenediazonium compound with l-naphthol-4-sulfonic acid [84-87-7] the reaction is not base-catalyzed, but that with l-naphthol-3-sulfonic acid and 2-naphthol-8-sulfonic acid [92-40-0] is moderately and strongly base-catalyzed, respectively. The different rates of reaction agree with kinetic studies of hydrogen isotope effects in coupling components. The magnitude of the isotope effect increases with increased steric hindrance at the coupler reaction site. The addition of bases, even if pH is not changed, can affect the reaction rate. In polar aprotic media, reaction rate is different with alkyl-ammonium ions. Cationic, anionic, and nonionic surfactants can also influence the reaction rate (27). 

Fig. 12. The relationship between acidity and anion reactivity for naphthol couplers differing in the 2-position ballast where A is ballast 1 B, ballast 2 C,...

The influence of mixed coupling on the properties of Cl Pigment Yellow 12 has been studied recently [12]. Carboxy- or sulpho- substituted derivatives of acetoacetanilide were evaluated as co-coupling components and analysis revealed that the state of the crystal and the particle size were changed and new diffraction peaks were observed. When these modified pigments were treated with a fatty amine such as stearylamine, the hydrocarbon chains enclosed the anionic groups in the co-coupler so that properties such as flowability, wettability and dispersibility in nonpolar solvents were greatly improved. 

When a tetra-chain, star-shaped polystyrene is prepared by a coupling reaction between living polymer and coupler (e.g 1,2,4,5-tetrachloromethyl benzene), the reaction is often carried out with the polystyryl anion in slight excess in order to avoid by-production of types of branched polystyrene other than the tetra-chain. 

The synthesis, starting from a bifunctional initiator followed by quenching the double-headed living ends, gives homotelechelic polymers (method B). Carboxylate-capped telechelic poly(isobutyl vinyl ether) has been obtained in this way [82], where the adduct of a bifunctional vinyl ether with trifluoroacetic acid is the initiator, and the quencher is the malonate anion. For method C, a bifunctional trimethylsilyl enol ether, CH2=C[OSi(CH3)3]C6H4OCH2CH20C6H4[(CH3)3SiO]C=CH2, is a useful terminator (chain coupler) for vinyl ethers [142,147] and a-methyl-styrene [159] (see also Section VI.B.4). 

The chemistry involved in the formation of these azomethine dyes has been extensively investigated by Vittum and others.244,1538,1539a The present interpretation of the reactions involved is that the primary amino group of the developer is oxidized to give a quinonediimine cation which then reacts with the anion of the coupler to form a leuco dye. Subsequent oxidation converts the leuco dye to a colored form (LIII). This may be done by silver ion or by the oxidized form of the developer. The over-all reaction requires the reduction of four silver ions. 

Features Requires no coupler rinses clean at any water temp. alkyl phenol ethoxylate free leaves surfaces streak free reduces or eliminates need for VOC compat. with cationic and nonlonic surfactants but not anionic Properties CL yel. liq. dens. 8.51 Ib/gal vise. 150 cP doud pt. > 100 C pH (1% aq.) 5.75 80% act. 

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