WENHUA GAO, YIQUN LI, ZHOUYANG XIANG, KEFU CHEN, RENDANG YANG, and DIMITRIS S. ARGYROPOULOS

8.1 INTRODUCTION

Locating new and versatile platform chemicals and biofuels from sustain­able resources to replace those derived from petrochemicals is a central ongoing and urgent task prompted by depleting fossil fuel reserves and growing global warming concerns [1-4]. Alternative fine chemicals and biofuels that have been suggested to address some of these issues are butanol [5], ethanol [5], dimethylfuran [1], 5-ethoxymethylfurfural [2], y-valerolactone, and alkanes produced from biomass [6,7]. Many of these alternatives rely on the efficient conversion of biomass carbohydrates into furfural derivatives. This is because biomass carbohydrates constitute 75% of the World’s renewable biomass and cellulose [4] and as such, they represent a promising alternative energy and sustainable chemical feed-

Efficient One-Pot Synthesis of 5-Chloromethylfurfural (CMF) from Carbohydrates in Mild Biphasic Systems. © Gao W, Li Y, Xiang Z, Chen K, Yang R, and Argyropoulos DS. Moleculres 18 (2013), doi:10.3390/moleculesl8077675. Licensed under Creative Commons Attribution 3.0 Unported Li­cense, http://creativecommons. org/licenses/by/3.0/.

stock. In this regard, 5-halomethyfurfurals such as 5-chloromethylfurfural (CMF) and 5-bromomethylfurfural (BMF) has received significant atten­tion as platform chemicals for synthesizing a broad range of chemicals and liquid transportation fuels [8,9].

CMF and BMF are extremely reactive [9] so that when subjected to further chemistries the provide a variety of important compounds for fine chemicals, pharmaceuticals, furan-based polymers and biofuels. These compounds include hydroxymethylfurfural (HMF) [9,10], 2,5-dimethyl — furan (DMF) [1], and 5-ethoxymethylfurfural (EMF) [2], and some bio­logically active compounds [11]. Among them, DMF and EMF stand out since they possess excellent properties, including high energy density, high boiling point and water stability. For these reasons, they have been promoted as novel biofuels. In particular, EMF has been the subject of considerable attention since it possesses an energy density of 8.7 kWhL-1, substantially higher than that of ethanol (6.1 kWhL-1), and comparable to that of standard gasoline (8.8 kWhL-1) and diesel fuel (9.7 kWhL-1) [12]. Although, CMF and BMF themselves are not biofuels, they could readily be converted into EMF biofuels in ethanol in nearly quantitative yields.

The conventional synthesis of CMF involves the treatment of HMF or cellulose with dry hydrogen halide. More specifically, the hydroxyl group in HMF undergoes a facile halogen substitution reaction. Examples in the literature include those of Sanda et al. who obtained CMF from the reac­tion of ethereal gaseous hydrogen chloride with HMF [13]. Furthermore, while the conversion of cellulose into CMF was low (12%) [14,15], a sub­stantially higher yield (48%) was obtained for the preparation of BMF when dry HBr was employed [16]. Considering the importance of these compounds, Mascal et al. recently reported the synthesis of CMF from cellulose treated by HCl-LiCl and successive continuous extraction [2]. Unfortunately, 5-(chloromethyl)furfural, 2-(2-hydroxyacetyl)furan, 5-(hy — droxylmethyl), furfural and levulinic acid were also produced with this system. More recently, Kumari et al. reported the preparation of BMF from cellulose by a modified procedure using HBr-LiBr involving continuous extraction [17]. Despite the numerous efforts aimed at these transforma­tions, each of them suffers from at least one of the following limitations: diverse by-products in significant yields that reduce the selectivity of the reaction and its economics, low conversions and yields, harsh reaction conditions (dry hydrogen halide, relative high temperature), requirements for large amounts of costly reagents (LiCl, LiBr), prolonged reaction times and tedious operations with complex set ups (continuous extraction) [18]. These drawbacks seriously hamper their potential industrial applications. Consequently, as part of our program aimed at developing new biofuels and fine chemicals based on biomass, we embarked our research for the development of efficient and economical methods aimed at converting carbohydrates to CMF under mild reaction conditions.

In this communication we demonstrate the use of the biphasic mixture HCl-H3PO4/CHCl3 for the one-pot conversion of carbohydrates into CMF. The rational for the use of this biphasic approach is based on the thinking that as CMF is generated from HMF it is immediately transported and ex­tracted from the aqueous acidic phase into the organic phase significantly minimizing by-product yields [9].

Saturation reactions are strongly associated with catalytic hydrotreating as the introduction of excess hydrogen allows the breakage of double C-C

bonds and their conversion to single bonds, as shown in the following reactions. In particular the saturation of unsaturated carboxylic acids into saturated ones depicted in Scheme 4, is a key reaction occurring in lipid feedstocks. Furthermore other saturation reactions lead to the formation of naphthenes by converting unsaturated cyclic compounds and aromatic compounds as in Scheme 5 and 6, which are likely to occur during upgrad­ing of pyrolysis oils.

RCH = CH-COOH + H2 —— ► RCH2CH2COOH

SCHEME 4

SCHEME 5

SCHEME 6

As a result of this reaction the produced saturated molecules are less active and less prone to polymerization and oxidation reactions, mitigating the sediment formation and corrosion phenomena appearing in engines.

As indicated in Fig. 4, aqueous solutions of sugars, derived from the car­bohydrate fraction of lignocellulose (i. e., cellulose and hemicellulose), can be used to produce second generation ethanol fuel through fermenta­tion routes. Alternatively, these sugars can be transformed into a variety of useful derivatives by means of chemical and biological processes. [90,91] As will be addressed in this section, sugars and some of their derivatives can be catalytically processed in the aqueous phase to produce liquid fuels chemically identical to those currently used in the transportation sector. The key advantage of this route, in comparison with BTL and pyrolysis­upgrading approaches, is derived from the mild reaction conditions used, allowing for better control of conversion selectivity. However, costly pre­treatment and hydrolysis steps are required to hydrolyze solid lignocel — lulose to soluble sugar feeds, and the lignin fraction, once isolated, is typi­cally combusted to provide heat and power.

The production of liquid hydrocarbon transportation fuels from bio­mass derivatives involves deep chemical transformations. In this respect, sugars (and chemicals derived from them) are molecules with high degrees of functionality (e. g., — OH, — C==O and — COOH groups) and a maximum number of carbon atoms limited to six (derived from glucose monomers). On the other hand, hydrocarbon fuels are larger (up to C20 for diesel ap­plications) and completely unfunctionalized compounds. Consequently, a number of reactions involving oxygen removal (e. g., dehydration, hy­drogenation, and hydrogenolysis), combined with C-C coupling (e. g., al — dol condensation, ketonization, and oligomerization), will be required to convert sugars into hydrocarbon transportation fuels, and aqueous-phase catalytic processing offers the opportunity to selectively carry out those transformations. Importantly, two aspects are crucial to ensure econom­ic feasibility of the aqueous-phase route: (i) reduction of the number of processing steps by means of catalytic coupling approaches [92] and (ii) deoxygenation of biomass feedstocks with minimal consumption of hy­drogen from an external source. [93]

The main aqueous-phase routes to upgrade sugars and derivatives into liquid hydrocarbon transportation fuels are schematically shown in Fig.

6. The biomass derivatives have been selected in view of their potential to produce liquid hydrocarbon fuels. First, we will describe the catalytic route designed to convert glycerol into liquid hydrocarbon fuels. This route involves the integration of two processes: aqueous-phase reforming (APR) of glycerol to syngas and F-T synthesis. This approach is particu­larly interesting because glycerol is produced in large amounts as a waste

stream of the growing biodiesel industry. [94] Furthermore, glycerol can be co-produced, along with ethanol, by bacterial fermentation of sugars [95] (Fig. 4). Secondly, we will address furfural and hydroxymethylfur — fural (HMF) as important compounds obtained by chemical dehydration of biomass-derived sugars. Furfural and HMF can be used as platform chemicals for green diesel and jet fuel production through dehydration, hydrogenation and aldol-condensation reactions. More recently, our group has developed a two-step (involving sugar reforming/reduction and C-C coupling processes) cascade catalytic approach to convert aqueous solutions of sugars and polyols into the full range of liquid hydrocarbon fuels, and this process will be described in Section 4.3.3. Finally, we will

Dehydration
HMF
Dehydration
GVL
x Liquid Hydrocarbon. Fuels /
Reforming Reduction	C-C coupling
Lignocellulose
Aqueous
Fermentation
sugars
-X-
F-T Synthesis
Transesterification
APR
FIGURE 6: Main catalytic routes for the aqueous-phase conversion of sugars and derivatives into liquid hydrocarbon transportation fuels.

analyze the potential of two important biomass derivatives, levulinic acid (LA, obtained from sugars or HMF through dehydration processes) and g-valerolactone (GVL, obtained by hydrogenation of LA), to produce liq­uid hydrocarbon fuels.

The catalytic reaction was carried out at 105 °C and at atmospheric pressure in a round bottom flask reactor equipped with a magnetic stirrer. The sulfon­ic acid containing material was dried prior to use at 105 °C under vacuum (~1.33 Pa) for 18 h. The following concentrations ofthe reagents were used: 100 g acetic acid/L of glycerol and the catalyst concentration was 6.25 g/L of glycerol. First, the catalyst and glycerol are added together to the flask and are brought to reaction temperature. When the temperature is reached, the acetic acid is injected. Before analysis the samples are extracted with 1-heptanol and using o-xylene as an internal standard. The total yield of the esters was determined with gas chromatography. After one minute a sample of the reaction mixture is taken and analyzed with gas chromatography. This sample represents the starting point of the catalytic experiment. The recy­clability experiments were carried out under identical conditions as the cata­lytic tests. Therefore, the catalyst was separated from the liquid phase after 1 h and reused in a consecutive run without further treatment. The liquid phase was kept under reaction conditions and further followed as a function of time. Gas chromatography was performed with a Varian CP-3800 using a Cp-Sil 8CD column (Varian, Palo Alto, CA, USA) with a FID detector.

Pyrolysis oil is the product of fast pyrolysis of biomass, a process that al­lows the decomposition of large organic compounds of biomass such as lignin at medium temperatures in the presence of oxygen. Pyrolysis, that is in essence thermal cracking of biomass, is a well established process for producing bio-oil, the quality of which however is far too poor for direct use as transportation fuel. The product yields and chemical composition of pyrolysis oils depend on the biomass type and size as well as on the operating parameters of the fast pyrolysis. However, a major distinction between pyrolysis oils is based on whether catalyst is employed for the fast pyrolysis reactions or not. Non-catalytic pyrolysis oils have a higher water content than catalytic pyrolysis oils, rendering the downstream up­grading process a more challenging one for the case of the non-catalytic pyrolysis oils.

Untreated pyrolysis oil is a dark brown, free-flowing liquid with about 20-30% water that cannot be easily separated. It is a complex mixture of oxygenated compounds including water solubles (acids, alcohols, ethers) and water insolubles (n-hexane, di-chloor-methane), which is unstable in long-term storage and is not miscible with conventional hydrocarbon — based fuels. It should be noted that due to its nature pyrolysis oil can be employed for the production of a wide range of chemicals and solvents. However, if pyrolysis oil is to be used as a fuel for heating or transporta­tion, it requires upgrading leading to its stabilization and conversion to a conventional hydrocarbon fuel by removing the oxygen through cata­lytic hydrotreating. For this reason, a lot of research effort is focused on catalytic hydrotreating of pyrolysis oil, as it is a process enabling oxygen removal and conversion of the highly corrosive oxygen compounds into aromatic and paraffinic hydrocarbons.

For non-catalytic pyrolysis oils, the catalytic hydrotreating upgrading process involves contact of pyrolysis oil molecules with hydrogen under pressure and at moderate temperatures (<400°C) over fixed bed catalytic reactors. Single-stage hydrotreating has proved to be difficult, producing a heavy, tar-like product. Dual-stage processing, where mild hydrotreating is followed by more severe hydrotreating has been found to overcome the reactivity of the bio-oil. Overall, the pyrolysis oil is almost completely deoxygenated by a combination of hydro deoxygenation and decarbox­ylation. In fact less than 2% oxygen remains in the treated, stable oil, while water and off-gas are also produced as byproducts. The water phase contains some dissolved organics, while the off-gas contains light hydro­carbons, excess hydrogen, and carbon dioxide. Once the stabilized oil is produced it can be further processed into conventional fuels or sent to a refinery. Table 1 shows the properties of some common catalytic pyrolysis oils according to literature.

Catalytic pyrolysis oils have been reported to getting upgraded via single step hydroprocessing, most of the times utilizing conventional CoMo and NiMo catalysts. During the single step hydroprocessing, the catalytic pyrol­ysis oil feedstock is pumped to high pressure, then mixed with compressed hydrogen and enters the hydroprocessing reactor. In Table 5 the typical oper­ating parameters for single stage hydroprocessing and associated deoxygen­ation achievements are given according to literature [29;33-38].

However, in the case of non-catalytic pyrolysis oils or for achieving bet­ter quality products, multiple-stage hydroprocessing can be employed for upgrading pyrolysis oils. Multiplestage hydroprocessing utilizes at least two different stages of hydroprocessing, which may include hydrotreating or hydrotreating and hydrocracking reactions. In the first stage the cata­lytic hydrotreatment reactor stabilizes the pyrolysis oil by mild hydrotreat­ment over CoMo or NiMo hydrotreating catalyst [32;40-42]. The first stage product is then further processed in the second-stage hydrotreater, which operates at higher temperatures and lower space velocities than the first stage hydrotreater, employing also CoMo or NiMo catalysts within the reactor. The 2nd stage product is separated into an organic-phase prod­uct, wastewater, and off-gas streams. In the literature [41], even a 3rd stage hydroprocessing has been used for the heavy fraction (which boils above 350°C) of the 2nd stage product, where hydrocracking reactions take place for converting the heavy product molecules into gasoline and diesel blend components.

The silica gel, Kieselgel 40 (4 nm mean pore diameter, 590 m2g-1), was dried at 120 °C for 3 h in air prior to its use. The following SSA catalyst was prepared by a well-developed procedure [23,30]. A 250 mL suction flask, equipped with a constant pressure dropping funnel containing 5.83 g chlorosulfonic acid and a gas inlet tube for releasing HCl gas, was charged with 10.0 g Kieselgel 40 silica gel and 50 mL CH2Cl2. Chlo­rosulfonic acid was added dropwise over 30 min while stirring at room temperature. HCl gas was immediately evolved and absorbed into wa­ter. The mixture was then stirred for another 30 min. Next, CH2Cl2 was removed by rotary evaporation (50 °C, 20 min). A white solid (SSA, yield, 98%) was obtained and stored in a desiccator until use. K10 clay supported Cs25H05PW12O40 catalyst (hereafter designated Cs25/K10) was prepared by a well-developed route [31]. Typical Fourier Transform In­frared (FTIR) spectra of these two catalysts were recorded on a Thermo Scientific Nicolet 6700 spectrophotometer. Surface area, total pore vol­ume and pore diameter of the catalysts were determined by N2 adsorp­tion at 77 K using a Quantachrome Nova 2000 instrument after evacu­ating at 393 K for 3 h under nitrogen atmospheric. The total amount of acidity (H+) was measured by titration of catalyst samples in water with standardized sodium hydroxide (0.495 M).

Base catalysts are generally more active than acids in transesterification, and hence are particularly suitable for high purity oils with low FFA con­tent. Biodiesel synthesis using a solid base catalyst in continuous flow, packed bed arrangement would facilitate both catalyst separation and co­production of high purity glycerol, thereby reducing production costs and enabling catalyst re-use. Diverse solid base catalysts are known, notably alkali or alkaline earth oxides, supported alkali metals, basic zeolites and clays such as hydrotalcites and immobilised organic bases [104]. Basicity in alkaline earth oxides is believed to arise from M2+-O2- ion pairs pres­ent in different coordination environments [105]. The strongest base sites occur at low coordination defect, corner and edge sites, or on high Miller index surfaces. Such classic heterogeneous base catalysts have been ex­tensively tested for TAG transesterification [106] and there are numer­ous reports on commercial and microcrystalline CaO applied to rapeseed, sunflower or vegetable oil transesterification with methanol [107, 108]. Promising results have been obtained, with 97 % oil conversion achieved at 75 °C [108], however, concern remains over Ca2+ leaching under reac­tion conditions and associated homogeneous catalytic contributions [109], a common problem encountered in metal catalysed biodiesel production which hampers commercialisation [110].

Alkali-doped CaO and MgO have also been investigated for TAG transesterification [111-113], with their enhanced basicity attributed to the genesis of O_ centres following the replacement of M+ for M2+ and associ­ated charge imbalance and concomitant defect generation. Optimum ac­tivity for Li-doped CaO occurs when a saturated Li+ monolayer is formed (Fig. 6) [113], although leaching of the alkali promoter remains problem­atic [114].

It is widely accepted that the catalytic activity of alkaline earth oxide catalysts is very sensitive to their preparation, and corresponding surface morphology and/or defect density. For example, Parvulescu and Richards demonstrated the impact of the different MgO crystal facets upon the transesterification of sunflower oil by comparing nanoparticles [115] ver­sus (111) terminated nanosheets [116]. Chemical titration reveals that both morphologies possess two types of base sites, with the nanosheets exhib­iting well-defined, medium-strong basicity consistent with their uniform exposed facets and which confer higher FAMe yields during sunflower oil transesterification. Subsequent synthesis, screening and spectroscopic characterisation of a family of size-/shape-controlled MgO nanoparticles prepared via a hydrothermal synthesis revealed small (<8 nm) particles terminate in high coordination (100) facets, and exhibit both weak po — larisability and poor activity in tributyrin transesterification with metha­nol [117]. Calcination drives restructuring and sintering to expose lower coordination stepped (111) and (110) surface planes, which are more po — larisable and exhibit much higher transesterification activities under mild conditions. A direct correlation was therefore observed between the sur­face electronic structure and associated catalytic activity, revealing a pro­nounced structural preference for (110) and (111) facets (Fig. 7).

Hydrotalcites are another class of solid base catalysts that have at­tracted recent attention because of their high activity and robustness in the presence of water and FFA [118, 119]. Hydrotalcites ([M(II)1 _ x M(III)x (OH)2]x+(Anx/n-) mH2O) adopt a layered double hydroxide structure with brucite-like Mg(OH)2) hydroxide sheets containing octahedrally coordi­nated M2+ and M3+ cations and An — anions between layers to balance the overall charge [120], and are conventionally synthesised via co-precipita­tion from their nitrates using alkalis as both pH regulators and a carbonate source. Mg-Al hydrotalcites have been applied for TAG transesterifica­tion of poor and high quality oil feeds [121] such as refined and acidic cot­tonseed oil (9.5 wt% FFA), and animal fat feed (45 wt% water), delivering 99% conversion within 3 h at 200 °C. It is important to note that many catalytic studies employing hydrotalcites for transesterification are suspect due to their use of Na or K hydroxide/carbonate solutions to precipitate the hydrotalcite phase. Complete removal of alkali residues from the result­ing hydrotalcites is inherently difficult, resulting in parallel ill-defined ho­mogeneous contributions to catalysis arising from leached Na or K [122, 123]. This problem has been overcome by the development of alkali-free precipitation routes using NH3OH and NH3CO3, offering well-defined thermally activated and rehydrated Mg-Al hydrotalcites with composi­tions spanning x = 0.25 — 0.55 [118]. Spectroscopic measurements reveal that increasing the Mg:Al ratio enables the surface charge and accompa­nying base strength to be systematically enhanced, with a concomitant increase in the rate of tributyrin transesterification under mild reaction conditions (Fig. 8).

In spite of their promise for biodiesel production, conventionally prepared hydrotalcites are microporous, and hence poorly suited to ap­plication in the transesterification of bulky C16-C18 TAG components of bio-oils. This problem was recently tackled by adopting the same hard templating method utilising polystyrene nanospheres described in Scheme 4 to incorporate macroporosity, and thus create a hierarchical macropo­rous-microporous hydrotalcite solid base catalyst [124]. The introduc­tion of macropores as ‘superhighways’ to rapidly transport heavy TAG oil components to active base sites present at (high aspect ratio) hydrotalcite nanocrystallites, dramatically enhanced turnover frequencies for triolein transesterification compared with that achievable over an analogous Mg — Al microporous hydrotalcite (Fig. 9), reflecting superior mass transport through the hierarchical catalyst.

In terms of sustainability, it is important to find low cost routes to the synthesis of solid base catalysts that employ earth abundant elements. Do — lomitic rock, comprising alternating Mg(CO3)-Ca(CO3) layers, is structur­ally very similar to calcite (CaCO3), with a high natural abundance and low toxicity, and in the UK is sourced from quarries working Permian dolomites in Durham, South Yorkshire and Derbyshire [125]. In addition to uses in ag­riculture and construction, dolomite finds industrial applications in iron and steel production, glass manufacturing and as fillers in plastics, paints, rub­bers, adhesives and sealants. Catalytic applications for powdered, dolomitic rock offer the potential to further valorise this readily available waste min­eral, and indeed dolomite has shown promise in biomass gasification [126] as a cheap, disposable and naturally occurring material that significantly reduces the tar content of gaseous products from gasifiers. Dolomite has also been investigated as a solid base catalyst in biodiesel synthesis [127], wherein fresh dolomitic rock comprised approximately 77 % dolomite and 23 % magnesian calcite. High temperature calcination induced Mg surface segregation, resulting in MgO nanocrystals dispersed over CaO/(OH)2 par­ticles, while the attendant loss of CO2 increases both the surface area and basicity. The resulting calcined dolomite proved an effective catalyst for the transesterification of C4, C8 and TAGs with methanol and longer chain C16-18 components present within olive oil, with TOFs for tributyrin conversion to methyl butanoate the highest reported for any solid base (Fig. 10). The slower transesterification rates for bulkier TAGs were attributed to diffusion limitations in their access to base sites. Calcined dolomite has also shown promise in the transesterification of canola oil with methanol, achieving 92 % FAME after 3 h reaction with 3 wt% catalyst [128].

In summary, a host of inorganic solid base catalysts have been devel­oped for the low temperature transesterification of triglyceride components of bio-oil feedstocks, offering activities far superior to those achieved via alternative solid acid catalysts to date. However, leaching of alkali and alkaline earth elements and associated catalyst recycling remains a challenge, while improved resilience to water and fatty acid impurities in plant, algal and waste oils feedstocks is required to eliminate additional es­terification pre-treatments. To date, only a handful of biodiesel production processes employing heterogeneous catalysts have been commercialised, notably the Esterfip-H process developed by Axens and IFP which utilises a mixture of ZnO and alumina and is operated on a 200 kton per annum scale with parallel production of high quality glycerine [129].

Summarizing shortly the methods described above, it can be stated that the choice of analytical methods in general depends on sample characteristics, matrix complexity, the aim of the analysis, accessible equipment and the amount of resources available.

For instance in order to be analyzed by GC, compounds in the samples must be able to get volatilized and additionally possess thermostability.

In case of LC, solubility in the mobile phase is important as well as size, structure and hydrophobicity, presence of functional groups, etc.

Regarding matrix complexity it could be also mentioned that chroma­tography can be used both for the separation of a compound from the matrix and for quantification and identification. It is important but rarely considered that no residual matter should remain in the samples; especial­ly heavy compounds, which are difficult to evaporate in the GC columns, could significantly influence subsequent analyses. Thus, regular control of retention times and response factors, as well as column cleaning or re­placement in due time should not be overlooked. For some samples related to the analysis of biomass even prefractionation could be necessary.

FIGURE 11: Typical gas chromatogram showing the major sugar units released upon methanolysis of a sample (spruce wood) containing hemicelluloses (Std = internal standard, sorbitol)

FIGURE 12: Equilibrium of different forms of sugars

All solvents and chemicals used were as obtained from commercial sup­pliers, unless otherwise indicated. 1H-NMR spectra were recorded on a

Bruker Avance 300 instrument using CDC13 as solvent and TMS as the internal standard. GC-MS spectra were performed on an HP G1800B GCD system.

Eucalyptus globulus wood powder and its ensuing kraft pulp were examined as well as a Norway Spruce sample of unbleached thermome­chanical pulp, which was sampled in a Swedish mill of approximate 38% consistency and 85 mL Canadian Standard Freeness prepared by one-stage refining and a subsequent reject refining (about 20%) stage. All wood ma­terials used in this work represent standard samples, being the subject of Cost action E 41 entitled; “Analytical tools with applications for wood and pulping chemistry” operated by the European Union. The sugar profiling for these materials was examined according to the procedure of Min et al. followed by ion chromatography (Dionex IC-3000; Dionex, Sunnyvale, CA, USA) (Table 6) [32,33].

8.3.1 GENERAL PROCEDURE FOR THE SYNTHESIS OF CMF FROM MODEL CARBOHYDRATES

The selected carbohydrate (5.0 mmol) was added in a mixture of 37% HCl (4.0 mL), 85% H3PO4 (1.0 mL), and CHCl3 (5.0 mL) and it was stirred continuously at 45 °C for 20 h. Then an equal volume of water (5.0 mL) was added to quench the reaction. The reaction mixture was then extracted with CHCl3 3 times. The combined organic extracts were then dried with anhydrous Na2SO4 for 4 h. Finally, the organic extracts were subjected to liquid chromatography (silica gel, CH2Cl2 as eluent) to offer the desired 5-chloromethylfurfural. The procedure of treating lignocellulose sample (Table 6) was almost the same as the carbohy­drate, except adding the selected simple 1.0 mg each trial. The structure of 5-chloromethylfurfural was confirmed using 1H-NMR and GC-MS as follows: 1H-NMR (CDCl3): 5 = 4.60 (s, 2H), 6.58 (d, J = 3.6 Hz, 1H), 7.18 (d, J = 3.6 Hz, 1H), 9.64 (s, 1H) ppm. GC-MS (EI, 80 eV): m/z 146 (M+, 37Cl, 10.53), 144 (M+, 35Cl, 32.0), 109 (C6H5O2+, 100), 81 (C5H5O+, 17.3).

8.3 CONCLUSIONS

In summary, this note describes an optimized biphasic system (HCl — H3PO4/CHCl3) that may pave the way for the development of a simple, mild, and cost-effective protocol for the conversion of various carbohy­drates to CMF. The systematic optimization effort undertaken here delin­eates the structural features of carbohydrate residues that offer optimum CMF yields. Overall, the described procedure offers several advantages over other methodologies including mild reaction conditions; satisfactory product yields; and a simple experimental and isolation process.

Heteroatoms are atoms other than carbon (C) and hydrogen (H) and are often encountered into bio — and fossil — based feedstocks. They include sul­fur (S), nitrogen (N) and in the case of bio-based feedstocks oxygen (O). In particular oxygen removal is of outmost importance as the presence of oxygen reduces oxidation stability (due to carboxylic and carbonylic dou­
ble bonds), increases acidity and corrosivity (due to the presence of water) and even reduces the heating value of the final biofuels. The main deoxy­genation reactions that take place include deoxygenation, decarbonylation and decarboxylation presented in Schemes 7, 8 and 9 respectively [7]. The main products of deoxygenation reactions include n-paraffins, while H2O, CO2 and CO are also produced, but can be removed with the excess hy­drogen within the flash drums of the product separation section. It should be noted however that these particular reactions give the paraffinic nature of the produced biofuels, and for this reason the hydrotreated products are often referred to as paraffinic fuels (e. g. paraffinic jet, paraffinic diesel etc)

R-CHjCOOH + 3H2 ——- ► R-CH2CH3 + 2-H20

SCHEME 7

R-CH2COOH + H2 ——— ► R-CH3 + CO + H20

SCHEME 8

R-CH2COOH + H2 ——- ► R-CH3 + co2

SCHEME 9

The other heteroatoms, i. e. S and N are removed according to the clas­sic heteroatom removal mechanisms of the fossil fuels in the form of gas­eous H2S and NH3 respectively.