Formation of Colored Compounds

However, both compounds could be stabilized only as the full acetal, e. g., in alcoholic solutions. In general, it is assumed today that condensation reactions between nucleophilic/electrophilic intermediates of the Maillard reaction result in the formation of the colored components, which are also called melanoidins. 

A red colored pyrroline dye (IV, Formula 4.92) could be identified in a model reaction of furfural and alanine. This dye is formed from 4 molecules of furfural and 1 molecule of alanine. Labehng experiments with showed that one open-chain molecule of furfural is inserted into the pyrrohnone structure. The prohne/furfural reaction system indicated further that ring opening proceeds via a cyanine dye with the structure illustrated in V, Formula 4.93. Other colored compounds could be obtained by the condensation of 3,5-dihydroxy-2-methyl-5,6-dihydropyran-4-one with furfural (VI, Formula 4.94) and of 3-hy-droxy-4-methy 1-3-cy clopenten-1,2-dione (met- 

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Current Methods. The general outline of the Kolbe-Schmitt reaction, as it is employed in the 1990s, is as follows. In the first step, phenol and hot aqueous caustic are mixed to produce the sodium phenate which is taken to dryness. Next, the phenate and dry carbon dioxide are introduced into the carbonator. Air is excluded to minimize oxidation and the formation of colored compounds. The gas—solid mixture is agitated and heated, first at low temperature, followed by several hours at higher temperatures, to complete the formation of sodium salicylate. Variations of this reaction have been noted in the literature and are still being investigated (10,11). One reported scheme produces salicylic acid or substituted salicylic acids by reaction of a granulated alkali metal salt of the respective phenolic compound with C02 in a fluidized bed at 20—130°C until at least 50—80% of the metal salt has been converted to... 

Formation of Colored Compounds in the Reaction of Lignin Model Compounds with Alkali and Oxygen... 

Garda-Viguera, C., Bridle P., Bakker, J. The effect of pH on the formation of colored compounds in model solution containing anthocyanins, catechin and acetaldehyde. Vitis 1994,33,37-40. 

In addition to the evidence regarding complex addition compounds already given, another line of proof may be mentioned. The reacting mixtures in the Friestarting with colorless compounds. The formation of colored compounds in the case of somewhat different reactions has been taken to show addition compounds [J. Kendall, Jour. Amer. Chem. Soc. 37, 149 (1915) for aldehyde and ketone addition compounds with acids, and H. Wieland and E. Wecker, Ber. 43, 699 (1910) as forerunners of a number of substitution reactions.]... 

Acetylene compounds Dicobalt octacarbonyl Formation of colored compounds... 

Oxidation to I2, formation of colored compound with starch... 

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