Humin formation

The first isolation of a compound of this type was made in 1900 by Leathes, who described a product paramucosin with the composition Ci2H23NOio, obtained by brief acid hydrolysis of a mucosubstance from ovarian cysts. He was able to characterize paramucosin by its reducing properties and its ease of humin formation with acids, and he suggested that it represented an amino sugar bound to a reduced sugar acid. Subsequently, Levene and coworkers and Walz reported the presence, in... 

Gottschalkii was able to characterize the split product formed by the action of influenza virus on ovomucin, and on the sialoprotein inhibitor from urine, by its ease of humin formation and its abihty to give the Morgan-Elson color reaction for N-acylated 2-amino-2-deoxyhexoses. Accordingly, he assigned the structure of a AT-substituted D-fructosamine to this product. Odin and Klenk, independently, both suggested that this split product is closely related to a nonulosaminic acid, and noted its ability to give a direct Ehrlich color reaction. Klenk and his coworkers were then able to establish unequivocally that the principal product ... 

The mechanism of acid degradation and humin formation is undoubtedly complex. A A -pyrroline derivative was proposed (Gottschalk, 1960) as an initial cyclization product, and this was later substantiated by identification of 4-hydroxy-5-(l,2,3,4,-tetrahydroxybutyl)-A -pyrroline-2-carboxylic acid (XXVI) (Gielen, 1967a). This compound is... 

Scheme 5). However, this reaction is not as easy as it looks since numerous side reactions may occur. Antal et al. showed that four different classes of reactions can take place from hexoses (1) their dehydration leading to the formation of HMF, (2) their fragmentation, (3) their isomerization, and (4) their condensation leading to the formation of insoluble polymers and humins [58, 69]. Later, Van Dam and Cottier showed that at least 37 products can be produced, thus showing the complexity of this reaction. In particular, they highlighted that HMF can react with water, leading to the formation of undesirable side products such as levulinic and formic acids [68, 70]. 

The mechanism of acid-catalyzed decarboxylation of hexuronic acids has been the subject of many investigations.231,232 The formation of carbon dioxide is accompanied by the formation of 2-furaldehyde, C5H402 (82) as the main product, along with considerable amounts of humins however, both 5-formyl-2-furoic acid (83) and reductic acid (84) have been isolated as end products from treatment of hexuronic acids with strong acid. 

There is a need to resume studies of soil saccharides and peptides. These can compose as much as 30-40% (when account is taken of the compositions of humin materials). Much is known about how polysaccharides of known structures interact with soil colloids, but it has not been possible as yet to know in sufficient detail the structures of the polysaccharides that persist in the soil. Hence we do not know the mechanisms of their binding to soil mineral colloids. The same applies for the peptide materials, though it is clear that polysaccharides and peptides have important roles in soil structure formation and stabilization. 

Cloos, R, Badot, C., and Herbillon, A. (1981). Interlayer formation of humin in smectites. 

Caramelen is soluble in water only and melts at 154°C. Additional heating results in the formation of a very dark, nearly insoluble pigment of average molecular composition Ci25Hi88O80. This material is called humin or caramelin. 

Formation of trihalomethanes. Reactions of chlorine with organic compounds such as fulvic and humic acids and humin produce undesirable by-products. These by-products are known as disinfection by-products, DBFs. Examples of DBFs are chloroform and bromochloromethane these DBFs are suspected carcinogens. Snoeyink and Jenkins (1980) wrote a series of reactions that demonstrate the basic steps by which chloroform may be formed from an acetyl-group containing organic compounds. These reactions are shown in Figure 17.4. 

Based on detailed analyses of the chemical nature of SOM, Hatcher and Spiker (1988) have extended this humification model to include other resistant biopolymers, including plant cutin and suberin, and microbial melanins and paraffinic macromolecules. During decomposition, these biopolymers are selectively preserved and modified to become part of what can be operationally defined as humin (acid and alkali insoluble component of humus) (Hatcher and Spiker, 1988 Rice, 2001). The humin becomes progressively enriched in acidic groups leading to the formation of first humic acids and then fulvic acids, which under this degradative scheme of SOM formation would be regarded as the most humified of humic substances (Stevenson, 1994). 

Several ideas have been presented in the literature on the formation process of humic substances in marine sediments. Abelson (1967) claimed that polymerization of unsaturated fatty acids in phytoplankters after their death accounts for the formation of kerogen in marine sediments. Abelson and Hare (1971), Hoering (1973), and Hedges (1976) studied reactions between carbohydrates and amino acids under laboratory conditions as a possible formation reaction of humic acid and humin in sediments. They prepared a number of artificial humic acids by reacting glucose with amino acids. The synthetic products resembled natural humic acid and humin. A comprehensive review was published by Abelson (1978). 

The formation reaction of humic substances in lakes proceeds rapidly and is almost completed in decaying phytoplankton and/or in surface sediments. The major characteristics of humic acid and humin in sediments are determined by this formation stage, reflecting primarily organic constituents of phytoplankton. 

The distribution pattern of a,w-dicarboxylic acids for lipids resembled those for humic acid and humin (Fig. 3). This fact clearly indicates the common origin for the polymethylene chains in lipids, humic acid, and humin, which means that phytoplankton-derived lipids actively took part in the formation of humic acid and humin. The relative abundance of polymeth-ylene chains in lipids and humic substances was estimated on the assumption that the yield of production of aliphatic acids from polymethylene chains by alkaline permanganate oxidation was the same for these organic fractions. The following estimations resulted 42% (% of the total amount of polymethylene chains in the sediment) for humin, 38% for lipids, 19% for humic acid, and 1% for fulvic acid. 

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