Charcoal | EPFL Graph Search

Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, called charcoal burning, often by forming a charcoal kiln, the heat is supplied by burning part of the starting material itself, with a limited supply of oxygen. The material can also be heated in a closed retort. Modern "charcoal" briquettes used for outdoor cooking may contain many other additives, e.g. coal. This process happens naturally when combustion is incomplete, and is sometimes used in radiocarbon dating. It also happens inadvertently while burning wood, as in a fireplace or wood stove. The visible flame in these is due to combustion of the volatile gases exuded as the wood turns into charcoal. The soot and smoke commonly given off by wood fires result from incomplete combustion of those volatiles. Charcoal burns at a higher temperat

Synthesis of C-glycosides and C-linked disaccharides through carbonylative Stille coupling reactions

Peter Steunenberg

In the first part, we described the synthesis of C-(1'→1) and C-(1'→4) disaccharide precursors, which are readily obtained via the carbonylative Stille coupling of glucal and isolevoglucosenone derivatives. Tin glycals and triflates, derived from isolevoglucosenone, undergo the carbonylative Stille condensation under special conditions requiring AsPh3, LiCl and powdered charcoal as co-catalysts to give the corresponding cross-conjugated dienones, in which the bicyclic alkene moiety is more reactive than the glucal alkene moiety. The bicyclic part of the formed disaccharides precursors undergo selective nucleophilic additions with hydrogen, methoxybenzylamine and thiophenol. The other alkene moiety can undergo a selective epoxidation. The reactivity of the bicyclic part permitted a regio- and stereoselective hydrogenation of the bicyclic enone, that was then reduced with K-Selectride with high diastereoselectivity. The allylic alcohols so-obtained can undergo hydroboration giving a diol protected as an acetonide. The anhydro-moiety is then opened by a thioglycosidation reaction to form a partially protected glycoside-donor which can be used, in principle, for O-glycosidation. The C(1'→4) linked disaccharide so-obtained consists of a protected form of β-D-glucopyranose, attached at position C(4) of a α-D-3-deoxy-lyxo-hexopyranoside derivative via a (R)-hydroxymethanol linker. Another methodology based on 1,4-addition of thiophenol, allow one to form of several C-(1'→4) linked disaccharide precursors. Simple C-(1'→1)-disaccharides could also be prepared in similar fashion. In a second part the palladium-catalyzed cross-coupling reaction of tinglucal and tingalactal derivatives with arenesulfonyl chlorides provide aryl C-glycosides precursors. Desulfitative carbonylative Stille cross-coupling between 1-naphthalenesulfonyl chloride and a tinglucal derivative gives, after stereoselective reduction of the keto moiety and stereoselective oxidative hydroboration, C-glycosides consisting of a β-C-glucopyranoside and (R)-(naphtha-1-yl)methanol. Benzyl C-glycoside precursors are obtained by desulfitative Stille coupling of phenylmethanesulfonyl chloride with the corresponding protected tinglycals. In a third part we discussed the synthesis of carbohydrate based scaffolds for the deprotection of allylic alcohols by polysulfones. In this part we successfully applied the cleavage of allyl-protected carbohydrate derivatives by polysulfones, solid catalysts for the chemoselective cleavage of methyl substituted allyl ethers, such as prenyl, methylallyl and methylprenyl, developed by Markovic in our group. Allyl ethers are not cleaved under these conditions. This establishes a new method of selective polyol semi-protection in which a neutral, solid catalyst induces cleavage of ethers with the following reactivity sequence: 2-methylprenyl > prenyl > methallyl >> allyl.

EPFL2005

Past uppermost tree limit in the Central European Alps (Switzerland) based on soil and soil charcoal

The uppermost limits of past treelines in the Alps are established using soil type and soil charcoal mass. In all the studied sites, a sharp decrease of soil charcoal mass is correlated with the upper altitudinal limit of podzols. On the basis of this evidence, the uppermost tree limit reached 2500 +/- 100 m a.s.l. in the Valaisan Alps during the Holocene, i.e., it was 250 +/- 100 in higher than today's potential treeline. Consequently, the timberline would have reached 2400 +/- 100 m a.s.l.. From the strong decline of charcoals concentration in soils above 2500m a.s.l., we infer that conifer species were rare or very rare above this altitude during the Holocene. Joint interpretation of charcoal, pollen, soil and macrofossil data suggest that alpine meadows with at most scattered conifers were present throughout the Holocene in the today's middle and upper alpine belt.

2004

Mimicking biochar-albedo feedback in complex Mediterranean agricultural landscapes

Francesco Giuseppe Miglietta

ncorporation of charcoal produced by biomass pyrolysis (biochar) in agricultural soils is a potentially sustainable strategy for climate change mitigation. However, some side effects of large-scale biochar application need to be investigated. In particular a massive use of a low-reflecting material on large cropland areas may impact the climate via changes in surface albedo. Twelve years of MODIS-derived albedo data were analysed for three pairs of selected agricultural sites in central Italy. In each pair bright and dark coloured soil were identified, mimicking the effect of biochar application on the land surface albedo of complex agricultural landscapes. Over this period vegetation canopies never completely masked differences in background soil colour. This soil signal, expressed as an albedo difference, induced a local instantaneous radiative forcing of up to 4.7 W m(-2) during periods of high solar irradiance. Biochar mitigation potential might therefore be reduced up to similar to 30%. This study proves the importance of accounting for crop phenology and crop management when assessing biochar mitigation potential and provides more insights into the analysis of its environmental feedback.

Institute of Physics2015

Synthesis of C-glycosides and C-linked disaccharides through carbonylative Stille coupling reactions

Peter Steunenberg

EPFL2005