Para Red

Reds. Para Red or Pigment Red 1 [6410-10-2] is an intense, reasonably opaque red which shows poor lightfastness, particularly in tints. 

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. 

Under certain conditions, dry mixtures of lead chromate pigments with the azo-dyes l-(2. 4 -dimtrobenzcncazo)-2-hydroxynaphthalene (dinitroaniline orange) or l-(4 -chloro-2 -nitrobenzcncazo)-2-hydroxynaphthalene (chlorinated para-red) may lead to violent explosions dining mixing/blending operations. 

However, the ligand itself is the anionic dye formed by deprotonation of the hydroxy group(s). Anionic dyes, even from dyes shown to exist totally in the hydrazone tautomeric form, such as Orange II (9, R = S03H) and Para Red (9 R = N02), have been shown by resonance Raman spectroscopy to exist in the azo form (10).10 This isn t surprising oxygen is... 

Paramagnetic supercurrents, 23 802-803 Paramagnetism, sodium, 22 761 Paramelaconite, 7 771 Parameter estimation, sampling techniques for, 26 1038-1939 Parameter optimization, 26 711 Paramyxoviruses, 3 137 Para-oriented polymers, 19 715 Paraquat, 13 315, 349 21 100, 120, 127 Para reds, 19 435 Parasites... 

The diazotisation and coupling reactions were exploited by the firm of Read Holliday in 1880 with the discovery of Vacanceine red, the first of the ice colours . Cotton pretreated with 2-naphthol was immersed in a solution of diazotised 2-naphthylamine, prepared in the presence of crushed ice. Para red (2.11), however, patented by the same company in 1887, achieved much more success. This was applied to cotton in the same way using 2-naphthol and diazotised p-nitroaniline. Para red was also manufactured and marketed as a useful azo pigment. 

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. 

P.R.4 is also known as chlorinated Para Red. It has lost much of its commercial impact in recent years. The pigment affords a yellowish red shade, somewhere between the more yellowish P.O.5 and the more bluish P.R.3. Tinctorially, P.R.4 is the weakest of the three. In order to formulate equal depth of shade in an air drying alkyd system, three equivalents of TiOz are necessary per equivalent of P.R.4 while P.O.5 and P.R.3 require 5 and 6 parts of TiOz, respectively, per equivalent of organic pigment provided all other parameters are equal. Full shades exhibit good lightfastness (step 6), but darken somewhat upon exposure. Addition of even... 

Whilst the conversion of the simple phenyl-syw-diazotate into its isomeride requires strong alkali, the syn-iotms of other diazotates are so labile that, almost instantaneously after formation from the diazonium salts, they change into the anti-iorm and hence can never be obtained in solution. An important example of this change is described under (/), namely, p-nitrophenyldiazotate, which, on coupling with j8-naphthol, yields the much-used dye para-red . 

Package store, 378 Palatine chrome black 6B, 202 Para red, 93... 

SAFETY PROFILE Confirmed carcinogen with experimental neoplastigenic and tumorigenic data. Poison by intraperitoneal route. Mildly toxic by ingestion. Human mutation data reported. Potentially explosive reactions with azodyestuffs (e.g., dinitro-aniline orange, chlorinated para red). Violent reaction with aluminum -t- dinitronaphthal-... 

Many common synthetic dyes, such as alizarine yellow R, para red, and Congo red, are azo compounds, prepared by the diazonium coupling reaction described in Section 25.15. 

Problem 25.42 (a) What two components are needed to prepare para red by azo coupling (b) What two... 

The smoke colour of para red is orange red, and generally it is not used alone, but in combination with rhodamine B for red smoke. 

Oil red is also a naphthol dye which contains one azo base, -N=N-, in the molecule like para red. It is a bright red powder, insoluble in water, soluble in alcohol and in acetone producing an orange red colour, it melts at l65°C, begins to vaporize at 270 C, and boils at 330 0. Oil red is more stable than para red against heat and is not so easily damaged. 

Manufacture Mononitro-metaxylene is diazotized and coupled with naphthol. The process is the same to that of para red. 

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