Azines basicity

The azine basic dyes are often applied in the spectropholometric methods. Methylene Blue (formula 48.1) and Methylene Green are thiazine dyes. 

Azine dyes are relatively unimportant as a class of dyes but are used extensively as biological stains. Colors are mostly yellow to red. DurabiUty of some of these dyes is supported by the 1990 LATCC Buyers Guide pubflshed by the American Association of Textile Chemists and Colorists, which fists Basic Red 2, Safranine T [477-73-6] (13) and Basic Red 5, Neutral Red [553-24-2] (14), discovered in 1859 and 1879, respectively (1). Basic Red 2 is a safranine similar to mauveine (7). 

There are approximately one dozen references to azine dyes reported in Chemicaly hstracts traceable literature since 1976. Of these references, all but one refers to titration indicators. One basic dye is reported, but it is not a commercial product (6) ... 

Although early investigators considered that 4-hydroxy-l-methyl-phthalazine existed as such in neutral solution, they refer to basicity data which, in the light of present knowledge, would lead to assignment of the l-methylphthalazin-4-one structure (84, R = Me) to the predominant tautomer. The correctness of the oxo structure for phthal-azin-l-one (84, R — H) has been demonstrated using infrared spectroscopy. ... 

Greater reactivity gamma to an azine-nitrogen would be expected on the basis of the greater ara-quinoid than orf/io-quinoid interactions between various substituents and azine-nitrogens in ground states and excited states. Such a difference in interaction is supported by several kinds of data spectral,basicity, dipole moment, and chlorine quadrupole resonance of halo, methoxy,... 

Hydrogen bonding with protic solvents or reagents occurs widely in azines even when they are not appreciably basic and the protic compounds are very poor acids. The latter do not have to be present... 

Alkylthio, arylthio, and thioxo. The thioxo group in pyrimidine-2,4-dithione can be displaced by amines, ammonia, and amine acetates, and this amination is specific for the 4-position in pyrimidines and quinazolines. 2-Substitution fails even when a 5-substituent (cf. 134) sterically prevents reaction of a secondary amine at the 4-position. Acid hydrolysis of pyrimidine-2,4-dithione is selective at the 4-position. 2-Amination of 2-thiobarbituric acid and its /S-methyl derivative has been reported. Under more basic conditions, anionization of thioxo compounds decreases the reactivity 2-thiouracil is less reactive toward hot alkali than is the iS-methyl analog. Hydrazine has been reported to replace (95°, 6 hr, 65% 3deld) the 2-thioxo group in 5-hexyl-6-methyl-2-thiouracil. Ortho and para mercapto- or thio- azines are actually in the thione form. ... 

The effects of the nucleophile on aromatic substitution which are pertinent to our main theme of relative reactivity of azine rings and of ring-positions are brought together here. The influence of a nucleophile on relative positional reactivity can arise from its characteristics alone or from its interaction with the ring or with ring-substituents. The effect of different nucleophiles on the rates of reaction of a single substrate has been discussed in terms of polarizability, basicity, alpha effect (lone-pair on the atom adjacent to the nucleophilic atom), and solvation in several reviews and papers. ... 

Chlorophthalazine is quite reactive to many basic nucleophiles but reacts sluggishly with aqueous or alcoholic alkali. In contrast, it is very rapidly hydrolyzed by warm, concentrated hydrochloric acid as are its diazine isomers. In hydrolysis with very dilute acid or with water, it forms some phthalazinone but mostly the self-con-densation product which hydrolyses to give 2-(l -phthalazinyl)-phthalazin-l-one (70% yield). Such self-condensations in diazanaph-thalenes and in monocyclic azines are always acid-catalyzed (Sections II, C and III,B). With methanolic methoxide, 1-chlorophthalazine (65°, few mins), its 7-methoxy analog (20°), and 1,6- and 1,7-dichlorophthalazines (20°) readily undergo mono-substitution. 

To establish a mechanism for the formation of 33, the reaction has been monitored by H-NMR spectroscopy (91CB2013).Tlie basicity of the azine is a rate-determining effect as well as a steric hindrance. Pyridine is more reactive than pyrimidine. 2-Substituted pyridines do not give the corresponding salts. 

Many brilliantly coloured and tinctorially strong basic dyes for silk and tannin-mordanted cotton were developed in the early decades of the synthetic dye industry. Most of these belonged to the acridine, azine, oxazine, triarylmethane, xanthene and related chemical classes their molecules are usually characterised by one delocalised positive charge. Thus in crystal violet (1.29) the cationic charge is shared between the three equivalent methylated p-amino nitrogen atoms. A few of these traditional basic dyes are still of some interest in the dyeing of acrylic fibres, notably as components of cheap mixture navies and blacks, but many modified basic dyes were introduced from the 1950s onwards for acrylic and modacrylic fibres, as well as for basic-dyeable variants of nylon and polyester [44] ... 

Nonchelating dyes include basic triphenylmethane dyes (e.g., Brilliant Green, Malachite Green, Crystal Violet), xanthene dyes (e.g., Rhodamine B, Rhodamine 6G), azine dyes (e.g., Methylene Blue), and acid dyes (e.g., Eosin, Erythrosin). These are intensely colored and when paired with an oppositely charged analyte ion lead to high sensitivities. 

The intersections of the pH-dependent with the pH-independent parts of the curves in Fig. 12 mark the pK-value of the corresponding azine. With the very weakly basic 35 no protonation occurs even at pH 2.9. 

Compound 142 was prepared by reacting 141 with chloroacetic acid under basic conditions which were accompanied by the loss of CO2. Acetylation and benzoylation of 141 with boiling AC2O or benzoyl chloride in pyridine yielded the corresponding 3-acetyl(benzoyl) derivatives 143 and 144, respectively <1994H(38)57>. Alkylation of 6-benzyl-5,6,7,8-tetrahydropyrido[4,3-tf pyrimidin-4(3//)-one 145 with l-(2-methoxyphenyl)-4-(2-chloroethyl)piper-azine afforded the 3-substituted derivative 146 <2000DEP19900544>. 

Comparison of the intrinsic acidities and basicities of pyrrole (I), imidazole (4), and pyrazole (6), together with complementary information coming from the azine held, illustrate the main effects that control the acidity and the basicity of unsubstituted azoles (86JA3237). Particularly important are the role of electrostatic interactions between adjacent charged nitrogens (NH) and between adjacent lone pairs (N), as well as the aza electronegative effects. 

Gas phase studies of the basicity of azines have provided the basis for understanding such important molecular properties as lone pair charge... 

Most of the reports in the literature discuss electrophilic substitution of 1,3,6-triazacycl[3.3.3]azine (80) and the 2-methyl, 4-cyano and 4-ethoxycarbonyl derivatives. Electrophilic bromination occurs preferentially at the 4-position (if available), and subsequently at the 9- and 7-positions. These data support the electron charge density calculations (see Section 2.20.2) (73ACS3264). Nitrations are carried out using copper(II) nitrate and acetic anhydride. The central nitrogen is completely non-basic, and in the triazacycl-azines protonation occurs initially at position 6 (80) (77ACS(B)239). Ceder and Vernmark have reported that piperidine reacts with (81) via the aryne intermediate the A-E cine-substitution mechanism is an attractive alternative (equation 40). 

Reaction of hydrazones with iodine under basic conditions, to give azines, shows evidence of diazo intermediates that can be trapped with an internal alkene or alkyne function.92... 

Oxazine, azine and thiazine dyes are named for the characteristic heterocyclic ring systems 1,4-oxazine, 1,4-diazine, and 1,4-thiazine. The dyes are generally cationic (basic) or acid dyes. They also can be reduced to colorless forms, then oxidized back to the dye, as in vat dyeing. The dyes also have been used to a limited extent in disperse and fiber reactive applications. They are used as titration indicators and may be applied to acrylic fibers and leather. 

Basic paper, polyacrylonitrile, modified nylon, polyester and inks applied from acidic dyebaths cyanine, hemicyanine, diazahemi-cyanine, diphenylmethane, triaryl-methane, azo, azine, xanthene, acridine, oxazine, and anthraquinone... 

Basic azines are predominantly of historical interest. Yellow, red, brown, blue, and black shades can be obtained with these dyes. Today, Nigrosine Spirit Soluble is still used in shoe polish and creme. The sulfonated variety is applied as a leather dye. It is a polymeric dye containing phenazine ring systems, similar to Aniline Black. C.I. SolventBlack 5, 50415 [11099-03-9] (Nigrosine, spirit-soluble) C.I. Solvent Black 7, 50415 1 [8005-02-5] (4) is the free base. 

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