Magenta

SchifT s reagent A solution of rosaniline in water decolorized with sulphurous acid. Aliphatic aldehydes and aldose sugars give a magenta colour with this reagent with aromatic aldehydes and aliphatic ketones the colour develops more slowly aromatic ketones do not react. 

The reducing action of sulphurous acid and sulphites in solution leads to their use as mild bleaching agents (for example magenta and some natural dyes, such as indigo, and the yellow dye in wool and straw are bleached). They are also used as a preservative for fruit and other foodstuffs for this reason. Other uses are to remove chlorine from fabrics after bleaching and in photography. 

Schijf s reagent,] Add about 1 ml. of SchifT s reagent to 1 ml. of (a) formaldehyde, (b) acetaldehyde. A magenta colour rapidly develops in the cold. Benzddehyde restores the colour very slowly. 

Schiff s reagent. Add about 1 ml. of SchifTs reagent to about 1 ml. of acetone and note the very slow formation of a magenta colour. Neither acetophenone nor benzophenone reacts in this way. 

B. Mix 1 drop or several small crystals (ca. 0 05 g.) of the compound with 1 ml. of 0-5 V hydroxylamine hydrochloride in 95 per cent, ethanol and add 0-2 ml ot aqueous sodium hydroxide. Heat the mixture to boiling and, after the solution has cooled slightly, add 2 ml. of N hydrochloric acid. If the solution is cloudy, add 2 ml. of 95 per cent, ethyl alcohol. Observe the colour produced when I drop of 6 per cent, ferric chloride solution is added. If the resulting colour does not persist, continue to add the reagent dropwise until the observed colour pervades the entire solution. Usually only 1 drop of the ferric chloride solution is necessary. Compare the colour with that produced in test. 4. A positive test will be a distinct burgundy or magenta colour as compared with the yellow colour observed when the original compound is tested with ferric chloride solution in the presence of acid. 

Reaction of 2-pyrazoloneselenazoles with p-nitrosodialkylanilines leads to a series of azomethinep>Tazolones (Scheme 47) used as purple magenta dyes in color photography (34). The main regions of absorption are ... 

Printers use colored materials, eg, inks (qv), that absorb or subtract regions of the visible spectmm from white light. Subtractive color is usually represented by the three printer s primaries cyan, magenta, and yeUow (CMY). Cyan absorbs red light, magenta absorbs green, and yeUow absorbs blue light. 

Color contamination is another factor that needs to be considered. For example, a small amount of cyan commonly contaminates magenta. Thus, adding magenta to color-correct an image also adds cyan, which must be removed for compensation. 

Instmments like colorimeters and spectrophotometers are used less often. These ate used primarily for manufacturing control of printing inks. Ftequentiy, however, inks other than yellow, magenta, and cyan ate used for spot-color appHcations, and in those instances a spectrophotometer ensures the correct match of an ink blend to standard. 

The triaryknethane dyes are broadly classified into the triphenyknethanes (Cl 42000—43875), diphenylnaphthyknethanes (Cl 44000—44100), and miscellaneous triphenylmethane derivatives (Cl 44500—44535). The triphenyknethanes are classified further on the basis of substitution in the aromatic nuclei, as follows (/) diamino derivatives of triphenylmethane, ie, dyes of the malachite green series (Cl 42000—42175) (2) triamino derivatives of triphenylmethane, ie, dyes of the fuchsine, rosaniline, or magenta series (Cl 42500—42800) (J) aminohydroxy derivatives of triphenylmethane (Cl 43500—43570) and (4) hydroxy derivatives of triphenylmethane, ie, dyes of the rosoHc acid series (Cl 43800—43875). Monoaminotriphenyknethanes are known but they are not included in the classification because they have Httie value as dyes. 

Another useful reagent for detection and estimation of G-agents is diisonitrosoacetone (16). A magenta color is produced with 1 p.g of GB at pH 8.5. Coupling agents, such as -phenylenediarnine, increase the reaction rate. 

Unusual is some hackmanite [1302-90-5], Na4Al2Si2022(Cl,S), which can have a deep magenta color as mined but fades in the light the color can be restored with uv exposure or simply by storing in the dark, where the reaction is. The hole center S absorbs at 3.1 W (400 nm) and the... 

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