Toluidine Red

Pigment Red 3 [2425-85-6] 12120 Beta-Naphthol (Toluidine Red) coupling of dia2oti2ed 2-nitto-4-methyl-aniline with 2-naphthol... 

In the metal-free class of azo pigments it is remarkable that the simplest derivatives of 2-naphthol such as Hansa Red B [2425-85-6] (139) (Cl Pigment Red 3 Cl 12120 Toluidine Red) and Para Red [6410-10-2] both known since 1905, are still of importance. 

Monoazo Pigments. In combination with other groups, the a2o linkage, —N=N—, imparts color to many dyes and pigments (see Azo Dyes). The simplest of these, ie, the Hansa yellows, toluidine reds, and naphthol reds, do not have the lightfastness and heat stabiUty required for plastics. Permanent YeUow FGL and Permanent Red 2B are stable enough for vinyls, polyethylene, polypropylene, and ceUulosics (11). Permanent Red 2B is available as the calcium, barium, or manganese salt. 

Material Color Chrome yellow Toluidine red Half-finished Titone Color... 

Serologic tests are the mainstay in the diagnosis of syphilis and are categorized as nontreponemal or treponemal. Commonly used nontrep-onemal tests include the Venereal Disease Research Laboratory shde test, the rapid plasma reagin card test, the unheated serum regain test, and the toluidine red unheated serum test. 

Para red (2.11), which has already been mentioned, was the earliest pigment of this type. Toluidine red (Cl Pigment Red 3) was first made in 1905. To make it, the amine m-nitro-p-toluidine (called MNPT in the pigments industry) is diazotised and coupled to 2-naphthol, the same coupling component that was used to make Para red. 

Table 2.2 Batch processes for preparation of Toluidine Red (Cl Pigment Red 3)...

Only very few (3-naphthol pigments continue to play an important role in today s pigment industry. The list of important products includes Toluidine Red (P.R.3) and Dinitroaniline Orange (P.O.5). Other compounds, such as P.R.6, Parachlor Red, which is the positional isomer of P.R.4 P.O.2, Orthonitroaniline Orange, which is the positional isomer of the para toner P.R.l are only of regional importance. Table 16 lists the commercially available (3-naphthol pigments. The Colour Index numbers are listed along with the common names, since older products are frequently referred to by these names. 

Toluidine Red, like P.O.5, is by volume one of the 20 largest organic pigments in the world. It shows insufficient fastness towards solvents in fact, it is partially inferior even to monoazo yellow pigments, which is also true for other members of this class. Its stability to alcohols, aliphatic and aromatic hydrocarbons, and dibutyl phthalate equals step 3 on the 5 step scale P.R.3 is even less fast to esters and ketones. 

Full shades of Toluidine Red are extremely lightfast and weatherfast, but deteriorate rapidly as the pigment is reduced with white pigment. In full shades, the lightfastness equals step 7 on the Blue Scale, while 1 4 Ti02 reductions only reach step 4. The pigment is therefore used preferably in full or similarly deep shades. Recommendations include emulsion paints for interior application or short-term advertisement and marking purposes. 

In plastics, Toluidine Red is practically limited to rigid PVC. Its lightfastness in full shades and slight white reduction is fair. Besides, the pigment is also used to color a number of specific media, such as normal wax crayons and pastel chalks or low-cost watercolors. 

N, N-DimethyI-2,5-dinitro-p-toluidine, red-golden shiny pltlts (from ale), mp 103—04° readily sol in eth, chlf, ethyl acetate, hot ale hot petr eth si sol in cold ale cold petr eth was prepd by nitrating 2-nitro-4-dimethylaminotoluene with a soln of nitric-sulfuric acid and pouring into w (Ref 2, pp 1009 442)... 

Meterial Color Chrome Yellow Toluidine Red Half-Finished Titone Color... 

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