Coloured compounds

It can act either as a nitrosophenol or as a quinone monoxime. Coloured derivatives, e.g. the sodium salt, are derived from the quinone form. Direct methylation gives a coloured compound which has been shown to be quino-nemethoxime OlCeH4tNOCH3 p-nitrosoani-sole CH30 C6H4 N0 has been obtained by another route and is colourless. 

Among the metals, for example, sodium and potassium are similar to each other and form similar compounds. Copper and iron are also metals having similar chemical properties but these metals are clearly different from sodium and potassium—the latter being soft metals forming mainly colourless compounds, whilst copper and iron are hard metals and form mainly coloured compounds. 

The chloride is white, the bromide pale yellow and the iodide deeper yellow. These are examples (uncommon) of a coloured compound being obtained from colourless ions. The silver(I) ion intensifies colour in other cases, for example silver chromate(VI), Ag2Cr04, is brick-red while potassium chromaie(VI). K2Cr04. is yellow. 

When the ascending solvent-front has reached a convenient height, the strip is removed, the position of the solvent-front marked, and the paper strip dried. The positions of the various solutes, if they are coloured compounds, now appear as clear separate spots. Frequently however, the solutes are colourless, and the position of their spots must be determined by indirect methods, such as their fluorescence in ultraviolet light, or their absorption in such light (when the spots appear almost black), or by spraying the paper with a dilute solution of a reagent which will give a coloured insoluble derivative with the solutes. 

The constitution of the coloured compound formed bct%wen a m-dinitro-compound and acetone is of the type CH3-CO-CH2 + 5 ... 

Secondary nitro compound dark blue or blue green colour due to nitro-iiitroso derivatives. The coloured compound is soluble in chloroform. 

With this mobile phase colour compounds and carotenoids separated with 15 ml of chloroform (first fraction) and the second fraction with 20ml chloroform contained total petroleum hydrocarbons. At the end Spectrofluorophotometry was employed for quantification of analytes. 

Glass-fibre/mineral-filled colour compounds. 

Discolouration of products inside cans may follow the reduction of colouring matters or the formation of new coloured compounds with tin or iron. This is a problem with strongly coloured fruits and the remedy is to... 

A brown additive compound of iodine with the dibromo compound may separate during the titration this compound usually dissolves during the subsequent titration with thiosulphate, yielding a yellow solution so that the end point with starch may be found in the usual manner. Occasionally, the dark-coloured compound, which contains adsorbed iodine, may not dissolve readily and thus introduces an uncertainty in the end-point this difficulty may be avoided by adding 10 mL of carbon disulphide before introducing the potassium iodide solution. 

The variation of the colour of a system with change in concentration of some component forms the basis of what the chemist commonly terms colorimetric analysis. The colour is usually due to the formation of a coloured compound by the addition of an appropriate reagent, or it may be inherent in the desired constituent itself. The intensity of the colour may then be compared with that obtained by treating a known amount of the substance in the same manner. 

A. Thiocyanate method Discussion. Iron(III) reacts with thiocyanate to give a series of intensely red-coloured compounds, which remain in true solution iron(II) does not react. Depending upon the thiocyanate concentration, a series of complexes can be obtained these complexes are red and can be formulated... 

Discussion. The formation of coloured compounds by coupling phenols with diazotised primary aromatic amines has long been recognised as a method of determining phenols, and procedures have been evolved whereby the phenol solution is titrated with a diazonium solution which has been calibrated against known concentrations of the phenol. The resultant reaction products are coloured, but many are only sparingly soluble in water and organic solvents and do not therefore lend themselves to colorimetric determination. 

Antioxidant free radicals (A H) produced in this way are relatively stable, but they may react with another lipid free radical to form a quinone [15.3] and [15.4]. Quinones can react with amine or thiol groups of proteins, forming polymerisable yellow or red coloured compounds (Pokorny, 1987). Antioxidant free radicals may also react with either another antioxidant free radical or a lipid free radical, forming dimers [15.5] or copolymers [15.6] and [15.7], respectively. Oligomeric or condensated products of antioxidant free radicals usually possess moderate antioxidant activities too (Pokorny et al, 1974) ... 

Detection in CC may be visually for coloured compounds. Different methods can be used to monitor colourless compounds (collecting fractions addition of an inorganic phosphor to the column adsorbent). The detector choice is quite limited, with UV, RI and molecular fluorescence (F) emission being the most popular. A fluorescent column adsorbent is extremely... 

Undoubtedly the most significant discovery in colour chemistry in the post-Mauveine period was due to the work of Peter Griess, which provided the foundation for the development of the chemistry of azo dyes and pigments. In 1858, Griess demonstrated that the treatment of an aromatic amine with nitrous acid gave rise to an unstable salt (a dia-zonium salt) which could be used to prepare highly coloured compounds. 

Elaboration of the method for the identification of colour compounds by RPLC MS should comprise four steps (1) spectral characterization of reference materials (standards) and subsequent optimization of detection parameters, as well as those of their chromatographic separation (2) analysis of natural dyestuffs used as colouring materials in historical objects (3) analysis of model samples (dyed fibres, paintings) prepared according to old recipes (4) application of the acquired knowledge to identification of colourants present in historical objects. 

Figure 13.1 Typical procedures and solvents used for extraction of organic colouring compounds...

According to the source of the zinc oxide there can be a problem with the inclusion of a small percentage of lead. Zinc and lead are found in the same ores in nature and unless correctly refined there can be some lead as a contaminant in the zinc oxide. Even 1% of lead in a zinc oxide is sufficient to cause discolouration of light coloured compounds. 

Clear unsaturated oils are vulcanised at room temperature with sulphur monochloride to give a white, friable solid which is nonstaining and suitable for use in coloured compounds. Crosslinking using sulphur monochloride produces a white factice, but care had to be taken in its use, for if not used when fresh it develops a high level of acidity which affects compound cures severely. The acidity can be removed by steaming the factice just prior to use. Modem white factices contain a small addition of alkali to counteract any developed acidity. 

Lithopone is a mixture of zinc sulphide and barium sulphate in equimolecular proportions. It is used to establish a white base for coloured compounds. 

A similar principle is used for products that require a stripe of surface coating of a second compound or application of an alternative coloured compound. Sizes and positioning of the various machines in these systems can be tailored to suit the application. 

Injection moulding machines can be in a horizontal or vertical mode, with or without tiebars, or with a C frame structure for easy mould fitting and access. Machines are also available which can deal with two colour/compound injection into the same mould cavity. 

The essence of the early 1960s process was that one injection unit fed 4, 6, 8, 10 or 12 vertical presses on a rotating mould carrier. Sometimes two injection units were used at different mould stations, one injecting a soft upper compound for a bootee and the other a harder sole compound. Sometimes two different coloured compounds were used. 

Eberhardt and Sieburth [133] also devised a spectrophotometric procedure for the determination of aldehydes in seawater. The method is based on the reaction of aldehydes with 3-methyl-2-benzothiazolinone, hydrazone hydrochloride, and ferric chloride to produce a coloured compound. A detection limit of0.072 jlM formaldehyde per litre was obtained using a 5 cm path-length. 

Germanium solutions in the presence of phenylfluorone (1) and lauryldimethylam-monium bromide yield coloured compounds, Zmax 508 nm, el.60 x 105. This allows germanium determination at concentrations of 8-80 Xg/L. Only Sb, Sn, Cr(VI) and Mo interfere with the analysis17. Precipition and filtration of the Ge(IV)-l complex formed in... 

Group 1 superoxides are coloured compounds, which is unusual for group 1 compounds not containing a transition metal ion. The trend in oxide formation is the result of the increasing size of the metal cations as the group is descended. 

The complexation of neomycin with copper results in the formation of a blue-coloured compound which has also been made the basis of a colorimetric determination of neomycin in pharmaceutical formulations . Maximum colour intensity was observed at a solution pH of 10. Further investigation showed the stoichiometry of the complex to be 1 1 in alkaline solution. 

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