Direct Thermochemical Liquefaction



Hydroxyacetaldehyde (also known as glycolaldehyde) [OHCH2CHO] can be produced from various renewable plant sources during their thermal decompositions. Historically, it was detected/produced during a destructive distillation of wood. As a component of wood smoke, it is a product of the thermal fragmentation of carbohydrates (cellulose, hemicellulose). Recently, a process has been reported in which this biodegradable chemical is obtained in high yields ~60 wt% from dextrose (US patent 7,094,932). Hydroxyacetaldehyde can be considered for chemical synthesis as a bi-functional building block – with carbonyl and hydroxyl groups attached to separate carbon atoms. It is the simplest aldehyde-alcohol. It could be considered as a sugar compound, although formally sugars are poly-hydroxy-aldehydes/ketones. Its two adjacent carbons functional groups impart high chemical reactivity and thus make it a useful synthon for heterocyclic chemistry and an efficient cross-linking agent for macromolecules. As of now, hydroxyacetaldehyde is not offered in any commercial quantities above few kg max. It is not listed in The Merck Index, nor is it listed by the FDA (Food and Drug Administration). Click here for other details of physical and chemical properties.

Simple alpha-hydroxyl compounds such as hydroxyacetaldehyde have a tendency to form stable cyclic and acyclc dimers that dissociate into monomeric forms when standing in dilute solution or by increasing the temperature. In solid state, hydroxyacetaldehyde exists only in crystalline dimeric form; however, in solution or during heating, it dissociates into monomeric forms. In the vapour phase, only the monomer exists. The alpha-hydroxycarbonyl function imparts to reducing sugars special flexibility, obvious in such processes as enolization, isomerization and dimerization. In addition, it enables these sugars to undergo Amadori rearrangement in the presence of amines, that eventually transforms aldehydo sugars into their alpha-amino keto derivatives. The physical, chemical and biological properties of reducing sugars in solution depend on the relative concentrations of different monomeric and dimeric forms originating from the alpha hydroxyl carbonyl-moiety.

Many different types of organic reactions occur in the sugar-amine system (or analogous reducing-sugar equivalent-amine system) leading to the production of brown pigments and are called Maillard reactions. Maillard reactions are responsible for coloration of hams, bacons, sausages, as well as the toasting of breads and pastries. [Maillard Reaction (Browning Reaction) – The reaction of amino groups of amino acids, peptides or proteins with the “glycosidic” hydroxyl group of sugars ultimately resulting in the formation of brown pigments; L.C. Maillard, Comp. Rend. 154, 66 (1912); Ann. Chim. 9, 5, 258 (1916)]. Hydroxyacetaldehyde is considered as the most highly reactive browning compound participating in the Maillard reactions. [J. Hodge, Agricultural and Food Chemistry, 1, 15, 928-943 (1953)].


Text courtesy of Jan Piskorz, Resource Transforms International, Waterloo, Ontario, Canada.