Platform molecules

Fine and specialty chemicals can be obtained from renewable resonrces via multi-step catalytic conversion from platform molecules obtained by fermentation. An alternative method decreasing the processing cost is to carry out one-pot catalytic conversion to final product without intermediate product recovery. This latter option is illustrated by an iimovative oxidation method developed in our laboratory to oxidize native polysaccharides to obtain valuable hydrophilic end-products useful for various technical applications. 

This chapter surveys different process options to convert terpenes, plant oils, carbohydrates and lignocellulosic materials into valuable chemicals and polymers. Three different strategies of conversion processes integrated in a biorefinery scheme are proposed from biomass to bioproducts via degraded molecules , from platform molecules to bioproducts , and from biomass to bioproducts via new synthesis routes . Selected examples representative of the three options are given. Attention is focused on conversions based on one-pot reactions involving one or several catalytic steps that could be used to replace conventional synthetic routes developed for hydrocarbons. 

The present chapter focuses on process options integrated in a biorefinery scheme that should yield bio-products at a more competitive market price and quality. Although bioconversions are essential steps to derive the platform molecules that are used subsequently for catalytic transformations, only chemo-catalytic process will be examined. Selected examples of catalytic conversions illustrating different process options will be given. 

From Biomass to Products via Platform Molecules 3.4.2.1 Identification of Main Platform Molecules... 

C=C bonds) that can be used as platform molecules, as well as glycerol, which is a co-product of triglycerides transesterification. 

The three main platform molecules employed in terpene chemistry are a-pinene and / -pinene, which are extracted from turpentine oil (350000 t a-1) a co-product of paper pulp industry, and limonene extracted from citrus oil (30000 t a-1). 

Selected Examples of Platform Molecule Conversion into Bioproducts... 

Fatty Acid Esters and Fatty Alcohols Fatty acid esters are obtained by transesterification of triglycerides (vegetable oils) or by esterification of fatty acid with alcohol or polyols. Fatty alcohols are obtained by hydrogenation of esters on metal catalysts. Fatty acid esters and fatty alcohols are useful platform molecules to prepare surfactants, emulsifier, lubricants and polymers. 

The catalytic conversion of platform molecules produced by bioconversion of renewables into bioproducts. This is already the basis of many industrial processes, leading to important tonnages of chemicals and polymers from carbohydrates and triglycerides and fine chemicals from terpenes. This approach needs to be extended and process efficiency should be strengthened by designing more active and selective catalysts. 

Conversion of such biomass into chemicals may be expected to have a much longer future perspective. Most chapters in this book are committed to the catalysis of biomass feedstock to bulk or fine chemicals. Here one notes the need to define platform molecules and their conversion technologies as well as the need for more insights in the fundamental catalysis of these processes. 

Pd-Catalyzed Telomerization of 1,3-Dienes with Multifunctional Renewable Substrates Versatile Routes for the Valorization of Biomass-Derived Platform Molecules... 

Abstract The dimerization of 1,3-dienes (e.g. butadiene) with the addition of a protic nucleophile (e.g. methanol) yields 2,7-octadienyl ethers in the so-called telomerization reaction. This reaction is most efficiently catalyzed by homogeneous palladium complexes. The field has experienced a renaissance in recent years as many of the platform molecules that can be renewably obtained from biomass are well-suited to act as multifunctional nucleophiles in this reaction. In addition, the process adheres to many of the principles of green chemistry, given that the reaction is 100% atom efficient and produces little waste. The telomerization reaction thus provides a versatile route for the production of valuable bulk and specialty chemicals that are (at least partly) green and renewable. The use of various multifunctional substrates that can be obtained from biomass is covered in this review, as well as mechanistic aspects of the telomerization reaction. 

Saponification, hydrolysis and esterification of vegetable oils to release fatty acids for the oleochemical uses detailed above, results in production of glycerol as a by-product. Glycerol is an important platform molecule in its own right, with numerous industrial uses (see Chapter 6 for more information). 

Recent attempts aim at the controlled transformation of cellulose, hemicellulose, and lignin to platform molecules for a potential future biorefinery scenario. In this regard, the U.S. Department of Energy has published studies on potential future platform molecules that could be derived from renewable resources [35, 36]. Tailored transformation of biomass to these platform chemicals could serve as a starting point for biofuel production. This would allow the development of comprehensive biorefinery approaches that incorporate both the production of biofuels and chemicals. The... 

The second route involves the retrieval of current platform molecules (benzene, toluene, xylenes (BTX), phenols, etc.) by unselective catalytic processes, followed by familiar processes. Here, mainly hydrogenation takes place to remove excess oxygen, yielding aromatic hydrocarbons (BTX, phenols). This will need some time for commercialization as no results with high yields for BTX from genuine lignin are known. Instead, actual research is mainly performed on model components like p-coumaryl, coniferyl, and sinapyl alcohol [7]. 

In 2009, worldwide production of methanol was around 40 million metric tons. Although this amount represents only 0.01% of the worldwide gasoline production, it is nearly equivalent to the total biodiesel and bioethanol production [11], From this number, it is clear that a large-scale replacement of gasoline by methanol as fuel would require an enormous increase of worldwide methanol synthesis capacities. Today, chemical intermediates dominate methanol consumption. Formaldehyde a platform molecule for the synthesis of polymer resins - is responsible for nearly half of the total demand. Acetic acid, MTBE, and methyl methacrylate - a monomer -constitute another 25% [7, 12]. Direct fuel and additive usage accounts for 15% of demand but is expected to rise. 

As ethanol and methanol are common laboratory solvents, their application in extraction and reaction chemistry is not be discussed at length here details on many procedures using these solvents can be found in chemistry textbooks and the primary literature. However, exciting new procedures using acid catalysis in aqueous ethanol for the esterification of platform molecules have recently been reported.This reaction also highlights the reactivity of alcohols, as ethanol is one of the substrates in the reaction (Figure 5.4). It is likely that ethanol and water will continue to play a prominent role as solvents in the new transformation chemistries being developed. 

Figure 5.4 Esterification of diacid platform molecules in aqueous ethanol.

The third approach of using a large proportion of biomass to produce so-called platform molecules is worth close consideration. Here, we need to learn how to make best use of a number of medium-sized, usually multifunctional, organic molecules that can be obtained relatively easily by controlled enzymatic fermentation or chemical hydrolysis. The simplest of these is (bio) ethanol others include levu-linic acid, vanillin, and lactic acid. These are chemically interesting molecules in the sense that they can be used themselves or can quite easily be converted into other useful molecules - building on rather than removing funcHonahty - as can be seen, for example, with lactic acid (Scheme 1.1-6). 

---