Compounds, colored aldehydes

The constituents of each alcoholic beverage can be divided into major, minor, or trace components. The major constituents usually consist of ethanol and water. The minor or trace constituents are fusel alcohols, organic acids, carbonyl compounds, esters, aldehydes, lactones, sulfur compounds, sugars, preservatives, and colorants. There are two general approaches to analyzing the components of alcoholic beverages. The first, and most usual, is by using... 

Not only will this test distinguish primary and secondary alcohols from tertiary alcohols, it will distinguish primary and secondary alcohols from most other compounds except aldehydes. This color change, associated with the reduction of Cr207 to Cr , is also the basis for Breathalyzer tubes, used to detect intoxicated motorists. In the Breathalyzer the dichromate salt is coated on granules of silica gel. 

This reaction can be used for the detection of aldehydes in the presence of ketones and for the differentiation of aliphatic aldehydes from aromatic ones. In a neutral medium aldehydes produce a black color or a precipitate other transient colors are sometimes formed which, in the case of aromatic aldehydes, last a bit longer. In an acid medium aliphatic aldehydes behave similarly as in a neutral medium, while in the presence of aromatic aldehydes a yellow color is produced first sometimes a precipitate is formed which persists for a certain time. Some other derivatives also react similarly to aide-hydes, such as, for example, cyanohydrins, aldehyde-ammonia adducts, sodium bisulfite addition compounds of aldehydes, and oximes. For modification with detection tubes containing the reagent see (62). 

The starting materials of the aldehyde method may be sulfonated. For example. Cl Acid Blue 9 [2650-18-2] Cl Food Blue 2 (Cl 42090), is manufactured by condensing a-(A/-ethylanilino)-y -toluenesulfonic acid with o-sulfobenzaldehyde. The leuco base is oxidized with sodium dichromate to the dye, which is usually isolated as the ammonium salt. In this case, the removal of the excess amine is not necessary. However, this color caimot be used in the food sector because separation of the chromium compounds from the dye is difficult. An alternative method which gives food-grade Cl Acid Blue 9 (14) and dispenses with the use of sodium dichromate employs oxidative electrolysis of the leuco base (49). 

Aromatic nitro compounds are often strongly colored. They frequently produce characteristic, colored, quinoid derivatives on reaction with alkali or compounds with reactive methylene groups. Reduction to primary aryl amines followed by diazotization and coupling with phenols yields azo dyestuffs. Aryl amines can also react with aldehydes with formation of Schiff s bases to yield azomethines. 

Color reactions are more or less clearly defined reactions of the substances with suitable reagents. Substance-specific reactions are not usually available, e. g. many compounds with aromatic skeletons give both a positive Vitali-Morin reaction [1 -4] and a positive Marquis reaction [4]. Again, numerous aldehydes react with electron-rich compounds in acidic medium to yield colored substances (cf. Chapters 2 and 3.1). 

The color of the polymer can also be affected by inappropriate reaction conditions in the polymerization process, such as temperature, residence time, deposits of degraded polymer or the presence of oxygen. Degradation of polyesters and the generation of chromophores are thermally effected [29b, 29c, 39], The mechanism of thermal decomposition is based on the pyrolysis of esters and the formation of unsaturated compounds, which can then polymerize into colored products. It can be assumed that the discoloration takes place via polymerization of the vinyl ester end groups or by further reaction of AA to polyene aldehydes. 

Qualitative spot tests for aldehydes, in the presence of ketones, are generally only reliable for water-soluble compounds. This problem can be overcome by the use of 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (Purpald , Aldrich Chemical Company) in the presence of Aliquat (Scheme 5.27). Under aerial oxidation, the initially formed colourless cyclic adduct changes colour through red to purple. The colourless cyclic aminal can also be formed by ketones, but only the adducts derived from the aldehydes are oxidized to the purple bicyclic aromatic system [28]. Weakly electrophilic aldehydes, e.g., 4-methoxybenzaldehyde, reacts slowly, but will give the positive coloration upon gentle heating to ca. 70°C for one or two minutes. 

Another non-specific color reagent for RDX and HMX is a solution of thymol in concentrated sulfuric acid [3, 56, 59]. It produces a typical red color. Positive results are also obtained with non-explosive compounds such as sugars and aldehydes. 

Light-activated shift of double bonds in organic compounds can promote the reaction of oxygen with a molecule. Once oxygen has bonded to a fuel component, oxidized organic compounds such as alcohols, aldehydes, esters, ethers, and acids can form. These compounds can then continue to react with other fuel components to form color bodies, gums, and insoluble deposits. 

The reaction appears to be applicable to a wide range of aromatic starting materials, exceptions being aromatic aldehydes and aromatic primary amines [96]. In effect, the aromatic compound to be converted is stirred with an aqueous solution of hydroxylamine hydrochloride in the presence of metallic ions such as copper ions [95-97] or complex ions such as the pentacyanoam-mine ferrate(II) ion [98]. The mixture is then treated with 30% hydrogen peroxide and a highly colored complex of the nitrosophenol forms. Presumably, the free nitrosophenol may be isolated by treatment of the complex with an acid (Eq. 50). 

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