Pyrolysis of monosaccharides

There are several classes of compounds formed from rapid pyrolysis of carbohydrates. Besides anhydrosugars, they are carbonyl compounds, furan derivatives, lactones, pyran derivatives, phenols, acids and acid esters, and other compounds. In general, the presence of a substantial quantity of 5-hydroxymethylfuraldehyde in the pyrogram indicates that a hexose is present. Substantial amounts of furaldehyde and the absence of 5-hydroxymethylfuraldehyde in the pyrolysis products indicate the presence of a pentose. However, these markers are not diagnostic for a specific hexose or pentose. 

6-anhydrohexoses are commonly found in large quantities only in the pyrolysis products of aldohexoses (as well as from polysaccharides [4]), but only small amounts of anhydrasugars (i.e., 1% yield) have been detected from the pyrolysis of ketohexoses [5]. The pyrogram of fructose, for example, reveals the presence of very small amounts of 2,6-anhydrofructofuranose. Aldopentoses pyrolyse in the same manner as their 

Peak No. 1 Compound MW Characteristic ions (with relative intensity) 

The structures of the 1,6-anhydrosugars generated from different aldohexoses, indicating the steric arrangement of different OH groups, are shown below (C-H bonds not shown). 

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D. Scalarone, O. Chiantore and C. Riedo, Gas chromatographic/mass spectrometric analysis of on line pyrolysis silylation products of monosaccharides, J. Anal. Appl. Pyrol., 83, 157 164 (2008). 

Pyrolysis of a variety of monosaccharides has been shown to afford the corresponding... 

Eliminations and other reactions do not necessarily take place only on the polymeric chain or only on the side groups. Combined reactions may take place, either with a cyclic transition state or with free radical formation. The free radicals formed during polymeric chain scission or during the side chain reactions can certainly interact with any other part of the molecule. Particularly in the case of natural organic polymers, the products of pyrolysis and the reactions that occur can be of extreme diversity. A common result in the pyrolysis of polymers is, for example, the carbonization. The carbonization is the result of a sequence of reactions of different types. This type of process occurs frequently, mainly for natural polymers. An example of combined reactions is shown below for an idealized structure of pectin. Only three units of monosaccharide are shown for idealized pectin, two of galacturonic acid and one of methylated galacturonic acid ... 

A variety of small molecules are formed during pyrolysis of polysaccharides, and hydroxyacetone, 2-furaldehyde, 2-hydroxycyclopent-2-en-1-one, 5-hydroxymethyl-2-furaldehyde and 1,5-anhydro-4-deoxy-glycero-hex-1-en-3-ulose are more common pyrolysis products. However, only the anhydrosugars, also formed in significant proportion during pyrolysis, are diagnostic for a specific monosaccharide unit because the stereoisomerism is not lost during pyrolysis. 

Pyrolysis of peracetylated pyranose monosaccharides has been studied, and found to proceed via initial loss of the 1-acetoxy group followed in some cases by ally lie rearrangement. In contrast, peracetylated furanoses lose two acetoxy groups to give substituted furans, e.g. equation (59). ... 

The only fully esterified 0-[(methylthio)thiocarbonyl] derivatives of the monosaccharides so far prepared were not examined for their stability to pyrolysis. Several mono-0-[(methylthio)thiocarbonyl] carbohydrates ... 

One approach utilized in carbohydrate pyrolysis is Py-MS. Py-MS using El type ionization does not differentiate well between anhydrosugar stereoisomers, and its utilization to obtain structural information on carbohydrates is rather limited. However, there are reports [10a] where the type of bond between monosaccharide units can be differentiated using Py-EI MS. As an example, the Py-EI MS results are shown for a (1 -> 2)-p-glucan and for a (1 -> 3)-p-glucan (laminaran). 

Other studies, such as Py-GC/MS characterization of peat components also have been reported. In a study done using Py-GC/MS, subfossil Sphagnum leaves and rootlets of heathers (Ericaceae) were analyzed, the Ericaceae having been determined to be the source of aliphatic hydrocarbons in peat [33]. Also, the sources of other peat components were analyzed by pyrolytic techniques. As an example, the fine-grain peat fraction was found to contain monosaccharides mainly from microbial carbohydrates, while coarse-grained peat samples were found to contain monosaccharides from vascular plant carbohydrates [34]. Peat classification has also been done based on its pyrolysis products [35]. A few other applications of peat pyrolysis will be discussed in Part 3 of this book. 

Monosaccharides can be identified by Curie-point pyrolysis (358°) and g.c. analysis (packed column) of the volatile products since fragments characteristic of the sugar class (e hexose, pentose, deoxy-sugar, uronic acid, alditol and amino-sugar) were obtained. Sugars and polyols in biological fluids have been determined quantitatively by g.c. of their pertrimethylsilyl ether derivatives. ... 

A study of the formation of oligosaccharides on thermal degradation of lactose has shown that the pyrolysis proceeds via simultaneous aldose-ketose isomerization and condensation of initially-formed monosaccharides without involving any cleavage of the carbohydrate carbon skeleton. 

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