Oxygen-Containing Heterocyclic Compounds

There has been very little kinetic work done on other aroma compounds. Schirle-Keller and Reineccius [34] have published a study on the formation of oxygen-containing heterocyclic compounds during the heating (80-150°C) of aqueous model systems (cysteine and glucose). A summary of their results is presented in Table 5.2 (top). Briefly, they found a linear relationship between time of heating and the formation of volatiles, and thus applied zero order kinetic treatment to the data. The r values for first order data treatment were substantially poorer than for the zero order treatment. The Eas are of the same order of magnitude as those for pyrazines reported by Leahy [15]. 

Kinetic Data for the Formation of Volatiles During the Heating of Model Systems 

Compound Ea (Kcal/mole) Compound Ea (Kcal/mole) 

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Fig. 31.2 Oxygen-containing heterocyclic compounds found in AG-secretions (A) and/or in colostrum (C)...

The formation of oxygen-containing heterocyclic compounds is also a consequence of the Maillard reaction. Amines and amino acids have a catalytic effect upon the formation of 2-furaldehyde (5), 5-(hydroxy-methyl)-2-furaldehyde (11),2-(2-hydroxyacetyl)furan (44),2 and 4-hy-droxy-5-methyl-3(2//)-furanone (111) (see Ref. 214). This catalytic effect can be observed with several other non-nitrogenous products, including maltol. The amino acid or amine catalysis has been attributed to the transient formation of enamines or immonium ions, or the 1,2-2,3 eno-lization of carbohydrates. Of interest is the detection of A -(2-furoyl-... 

Among the heterocyclic compounds, there are aromatic, e.g. pyridine, as well as nonaromatic, e.g. tetrahydrofuran, compounds. Similarly, there are saturated (e.g. tetrahydrofuran) and unsaturated (e.g. pyridine) heterocyclic compounds. Heterocycles also differ in their ring sizes, e.g. pyridine has a six-membered ring, whereas tetrahydrofuran is a five-membered oxygen-containing heterocyclic compound. 

Paths of Biogenesis of Natural Oxygen-Containing Heterocyclic Compounds N. S. Vul fson and L. S. Chetverikova, Tr. Botan. Inst., Akad. Nauk SSSR, Ser. 5, Rast. Syr e, 1965, no. 12, 31-43. 

General Properties of Oxygen-Containing Heterocyclic Compounds R. Rambaud, Traite Chim. Org., 1945, 18, 36. 

Heating of carbohydrates produces a number of aromatic compounds Including aldehydes, ketones, and dicarbonyls as well as oxygen containing heterocyclic compounds such as furans, dihydrofuranones, and pyrans through caramelizatlon and dehydration reactions. 

Furanones and pyranones are oxygen-containing heterocyclic compounds associated with caramelized flavor notes. Most common flavors of these compounds are caramel-like, sweet, fruity and burnt (40). 2,5-Dimethyl-4-hydroxy-3(2H)-furanone (DMHF) was one... 

The cyclic hemiacetal that has a five-membered ring is called a furanose. This name is derived from that of tire five-membered, oxygen-containing heterocyclic compound fu-ran. The hemiacetal with a six-membered ring is known as a pyranose after the heterocycle pyran. 

R. Rambaud, General properties of oxygen-containing heterocyclic compounds. In Traite de chimie organique (V. Grignard et al., eds.), Vol. 18, p. 36. Masson, Paris, 1945. 

The behavior of more complicated oxygen-containing heterocyclic compounds under electron impact will be discussed in Section III, A. 

The flavanoids red, yellow, blue, orange, ivory colors they are oxygen-containing heterocyclic compounds... 

Oxygen-containing heterocyclic compounds on the base of 1,5-diketones 00KGS1155. 

Zeolites are known to catalyze the formation of various nitrogen-containing aromatic ring systems. Examples include the synthesis of pyridines by dehydrogenation / condensation / cyclization of C -Cg precursors [1], the formation of methylpyridines by high-temperature isomerization of anilines [2], the amination of oxygen-containing heterocyclic compounds [3] and the Fischer indole synthesis [4,5]. The latter synthesis consists (see Scheme 1) of a condensation towards a phenylhydrazone followed by an acid-catalyzed cyclization with elimination of ammonia. The two reaction steps are usually combined in a one-pot procedure. 

Hydroxylation of some substituted acetophenones under these conditions (Scheme 3.56) is especially useful for the synthesis of various oxygen-containing heterocyclic compounds [175-179]. Applications of this methodology in organic synthesis, especially in the chemistry of heterocyclic compounds, have been summarized in several reviews [166,180-182]. 

There are several reactions (bromination, oxymercuration, epoxidation) of olefinic hydroxy and epoxy compounds in which the oxygen function can react intramolec-ularly with an intermediate formed at the double bond, leading to an oxygen-containing heterocyclic compound (tetrahydrofuran or tetrahydropyran) (Scheme 6). 

Examples of tetrapyrroles include porphyrins and porphyrin derivatives and more specifically, chlorophylls, heme pigments and bilins. Examples of tetra-terpenoids or carotenoids include carotenes and xanthophylls. Examples of quinines include benzo-quinones, anthraquinones and naphthiquinones. Examples of oxygen-containing heterocyclic compounds such as flavonoids include anthocyanins and flavonols. Examples of nitrogen-containing heterocyclic compounds include indigoids and indole derivatives, such as betalaines and eumelanins, and substituted pyrimidines such as pterins and purines. 

Tetrahydrobenzopyrans, chromenes, coumarins, xanthenes, and so on are some of the most important oxygen-containing heterocyclic compounds. Several synthetic methods are available for these compounds. This part of the chapter deals with the synthesis of these heterocyclic compounds using nano-ZnO as a reusable heterogeneous catalyst. 

Halophenol derivatives are promising substrates for the synthesis of oxygen-containing heterocyclic compounds. As early as 1989, the carbony-lation of 2-iodophenol with phenyl acetylene or norbornadiene was realized. Coumarin and aurone can be prepared under the same conditions from different substrates (Scheme 2.22). 

Tressl R, Kossa T, Renner R (1975) Gas-chromatographic-mass spectrometric studies of volatile substances of hops, wort, and beer and their genesis. II. Eormation of phenols and oxygen-containing heterocyclic compounds in beer. In Proceedings of the 15th European Brewery Convention (Nice). Elsevier, Scientific Pub, pp 737-756... 

The furanones and pyranones are oxygen-containing heterocyclic compounds associated with both caramelized and Maillard flavors [57]. The odor characters most common to this group of compounds would be caramel-like, sweet, fruity, butterscotch, nutty, or burnt. They predominate both in proportion and absolute amount in condensates of carbohydrates that are subjected to browning reactions [47]. 

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