Polysulfide heterocyclics

Chicken has also been found to be a source of polysulfide heterocyclics. Pippen and Mecchi (46) theorized that 2,4,6-tri-... 

Figure 4. Formation of important meat aroma polysulfide heterocyclics by heating acetaldehyde and hydrogen sulfide. (Reprinted from ref. 39. Copyright 1976 American Chemical Society.)...

Conformations of heterocyclic fragments of 1,3,5,2,4-trithiadiazepines and 1,3,5,2,4,6-trithiatriazepines are planar. Cyclic polysulfides possess as a rule in the chair conformation both in crystal (Section 13.17.5.4) and in solution... 

Many desirable meat flavor volatiles are synthesized by heating water-soluble precursors such as amino acids and carbohydrates. These latter constituents interact to form intermediates which are converted to meat flavor compounds by oxidation, decarboxylation, condensation and cyclization. 0-, N-, and S-heterocyclics including furans, furanones, pyrazines, thiophenes, thiazoles, thiazolines and cyclic polysulfides contribute significantly to the overall desirable aroma impression of meat. The Maillard reaction, including formation of Strecker aldehydes, hydrogen sulfide and ammonia, is important in the mechanism of formation of these compounds. 

Sulfur dyes are a special class of dyes with regard to both preparation and application, and knowledge of their chemical constitution [1], They are made by heating aromatic or heterocyclic compounds with sulfur or species that release sulfur. Sulfur dyes are classified by method of preparation as sulfur bake, polysulfide bake, and polysulfide melt dyes. Sulfur dyes are not well-defined chemical compounds but mixtures of structurally similar compounds, most of which contain various amounts of both heterocyclic and thiophenolic sulfur. 

Several variously substituted chalcones, 9, underwent conversion to five-membered S-heterocycles under standard conditions consisting of a saturated solution of hydrated sodium polysulfide in 95% ethanol at room temperature (23). Two different chalcones reacted to give four different thiolanes. Two of... 

The head-to-tail combination of conjugated enone units also was evident in the S-heterocyclic products obtained from phenyl vinyl ketone 14 when the latter was treated with alcoholic polysulfide. The product mixture contained the 2,4-dibenzoylthiolane ana the corresponding thiophene obtained in 5.8 and 3 % yields respectively. 

An alkaline marine environment high in H2S and HS" is favorable for incorporation of sulfur into organic matter HS" is an aggressive nucleophile. Such conditions also would have been favorable for the formation of polysulfides and elemental sulfur. All of these species, either alone or in combination, are expected to have played a role in the incorporation of sulfur into the vegetable debris that ultimately formed Rasa coal. Many of these species are known to be reactive with hydrocarbons at mild temperatures. Elemental sulfur reacts with hydrocarbons to form organosulfur compounds, including thiophenes at mild temperatures (28,29). Polysulfides react with conjugated ene carbonyls at room temperature to form thiophenes and other sulfur heterocycles (30). ... 

Heterocyclic compounds are primarily formed through non-enzymatic browning reactions. Recent studies of deep-fat fried food flavors led to the identification of pyrazines, pyridines, thiazole, oxazoles and cyclic polysulfides which had long-chain alkyl substitutions on the heterocyclic ring. The involvement of lipid or lipid decomposition products in the formation of these compounds could account for the long-chain alkyl substitutions. Model systems were used to study the participation of lipids in the formation of pyrazines, pyridines, thiophenes and cyclic polysulfides. 

It was a characteristic of small shrimp flavor that many varieties of cyclic polysulfides were formed during cooking. Some distinction in the composition of these heterocyclic substances were also observed among the shrimp species or from the treatment before heating, and led to the following conclusion the content of free amino acids should give the initiative for the formation pathway of the heterocyclic substances in small shrimps. 

Polysulfide Heterocycllcs. Polysulfur heterocyclics, including thialdine (5,6-dihydro-2,4,5-trimethyl-1,3,5- dithiazine) and trithioacetone (2,2,4,4,6,6-hexamethyl-l,3,5-trithiane), have been identified in meat flavor extracts (41). The formation of these compounds is shown in Figure 4. 

These reactions can lead to the formation of numerous heterocyclics associated with meat flavor as described by Vernin and Parkanyi (57), including furans, thiophenes, pyrroles, oxazoles, imidazoles, thiaz-oles, pyrans, pyridines, pyrazines, cyclic sulfides and polysulfides. 

A weak Ss" peak was observed in the electron impact mass spectrum of the 1,2,5,6-tetrathiocine 21 indicating the absence of polysulfide linkages (see Scheme 4 in Section 14.09.10) <1994IC4537>. Formation of the mixed oxidation state [S(iv) and S(vi)] heterocycle 22 has been confirmed by a strong molecular ion in the electron impact mass spectrum <2000IC1697>. 

The reaction of less hindered diarylplumbylenes with elemental sulfur, Sg, gives three different types of Pb-S heterocycles, whereas the reaction of highly crowded diaryl plumbylenes gives only the aryl substituted polysulfides (Scheme 2). 

At the turn of the century, Hoffman and Hochtlen1 2 reported on crystalline polysulfides of heavy metals. However, their directions were very brief and no chemical characterization nor plausable structures were presented. Our interest in inorganic heterocyclic rings led us to investigate these and new polysulfide chelates.3"5 Some of our detailed preparations are outlined here. 

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