Background :

The selective and high yielding preparation of C4 oxygenate compounds, e.g. C ₄ sugars such as erythrose, threose and erythrulose, could prove valuable for their use in the chemical industry for the preparation of, for example: C4 polyols; methyl vinyl glycolate or products obtainable therefrom; 2-hydroxy-4-methoxybutanoic acid or salts or es ^¬ ters thereof such as methyl 2-hydroxy-4-methoxybutanoate .

Known methods for preparing C4 oxygenate compounds include the aldol self-condensation of glycolaldehyde. It has been observed that aldol condensations are not selective for the preparation of C4 oxygenate compounds; a mix of products is observed as the C4 product continues to react to form oxy ^¬ genate compounds with a greater number of carbon atoms. In order to control the reaction's selectivity for C4 oxygen ^¬ ate compounds, the formation of C4-oxygenate and silicate or borate complexes, or the use of C4-oxygenate selective catalysts is required. An example of the use of a silicate complex for the selec ^¬ tive formation of C4 oxygenate compounds includes the aldol condensation of glycolaldehyde in the presence of aqueous sodium silicate; Science (2010) 327, pp 984-986. During the reaction a silicate-C4-sugar complex is formed, consequent- ly controlling the selectivity of the reaction. A further example includes the condensation of glycolaldehyde in the presence of a borate buffer. A high yield of C4 oxygenate compounds (C ₄ sugars) is obtained (86%); J. Am. Chem. Soc. (2011) 133, pp 9457-9468.

An example of a C4-oxygenate selective catalyst includes the preparation of C4 oxygenate compounds by the aldol con ^¬ densation of glycolaldehyde in the presence of a homochiral dipeptide catalyst. The yield of C4 oxygenate compound products was up to 63 %; PNAS (2006) 103, pp 12712-12717. Alternatively, a zinc-proline catalyst may be used. The to- tal yield of the C4~sugar products was approximately 51 %. C6~sugars were formed in a yield of approximately 30 %;

Org. Biomol. Chem. (2005) 3, pp 1850-1855.

Alternative preparations of C ₄ oxygenate compounds from glycolaldehyde include the proposed tetrose transient in ^¬ termediate in the preparation of 2-hydroxy-4-methoxy- butanoate (C ₄ ) and methyl vinyl glycolate (C ₄ ) . The reac ^¬ tion proceeds in the presence of a zeotype catalyst. The zeotype material was Sn-BEA, a twelve-membered ring pore structure; Green Chemistry (2012) 14, pp 702-706.

An alternative zeotype material, such as a ten-membered ring pore structured zeotype (e.g. Sn-MFI or Ti-MFI), may be used to isomerise C2 oxygenate compounds. Such a zeotype has been used for the isomerisation of glyoxal to glycolic acid. The yield of glycolic acid was approximately 90%; Green Chemistry (2014) 16, pp 1176-1186.

It is an object of the present invention to provide a pro- cess for the preparation of C ₄ oxygenate compounds from a composition comprising C ₁ -3 oxygenate compounds, wherein the process is selective for the production of C4 oxygenate compounds and the product is obtained in high yields.

Disclosure of the invention

It has now been discovered that glycolaldehyde may be se ^¬ lectively transformed into C4 oxygenate compounds in the presence of a crystalline microporous material comprising small- or medium-pore structure. The reaction proceeds in high yield. Additionally, it is possible for the reaction to proceed in the presence of additional compounds to se ^¬ lectively form the desired C4 oxygenate compounds.

The invention is further defined by a process for the prep aration of C4 oxygenate compounds from a composition comprising Ci-3 oxygenate compounds, wherein the process is carried out in the presence of a crystalline microporous material comprising a small- or medium-pore structure. C4 oxygenate compounds may be known as C4 sugars or oxygen ^¬ ated compounds with a carbon chain length of four carbon atoms. The molecular formula of the C4 oxygenate compounds may be C ₄ H ₈ O ₄ . C4 oxygenate compounds may also be described as tetroses. The C4 oxygenate compounds are selected from one or more of the group consisting of threose, erythrose and erythrulose.

In one embodiment of the invention compositions comprising Ci-3 oxygenate compounds comprise one or more oxygenate com pounds selected from the group consisting of Ci oxygenate compounds, C2 oxygenate compounds and C3 oxygenate com ^¬ pounds. Ci, C2 and C3 oxygenate compounds means compounds that have a carbon chain length of one, two or three carbon atoms respectively. The molecular formulae of the C ₁ -3 oxy ^¬ genate compounds are formulae selected from one or more of the group consisting of: CH ₂ 0; C2H ₄ O2; C2H2O2; C3H6O2 and C ₃ H ₄ O2 · Preferably, the composition comprising C ₁ -3 oxygenate compounds is a composition comprising one or more compounds selected from the group consisting of formaldehyde, glyox- al, glycolaldehyde, pyruvaldehyde and acetol. In a second embodiment, preferably the composition comprising C ₁ -3 oxy- genate compounds is a composition comprising one or more C2 oxygenate compounds selected from the group consisting of glycolaldehyde (2-hydroxyacetaldehyde) and glyoxal. Gly ^¬ colaldehyde is a compound with a carbon chain length of two carbon atoms, also known as a C2 oxygenate compound or C2 sugar.

The composition comprising C ₁ -3 oxygenate compounds may be in the form of a solution, wherein the solvent is selected from the group consisting of water, methanol and a water and methanol mixture. For example, the composition compris ^¬ ing Ci-3 oxygenate compounds may be an aqueous or methanolic solution of glycolaldehyde or an aqueous or methanolic so ^¬ lution of a composition comprising one or more compounds selected from the group consisting of formaldehyde, glyox- al, glycolaldehyde, pyruvaldehyde and acetol.

Compositions comprising C ₁ -3 oxygenate compounds are obtain ^¬ able by pyrolysis of biomass or pyrolysis of one or more oxygenate compounds selected from the group consisting of C ₅ oxygenate compounds, C6 oxygenate compounds and sucrose. C5 oxygenate compounds and C6 oxygenate compounds means one or more compounds selected from the group consisting of glucose, fructose, xylose and isomers thereof. Exemplary pyrolysis reactions are provided in US 7,094,932 B2 and PCT/EP2014/053587. Crystalline microporous material includes zeolite materials and zeotype materials. Zeolite materials are crystalline alumino-silicates with a microporous crystalline structure, according to Corma et al., Chem. Rev. 1995, 95 pp 559-614. The aluminum atoms of the zeolite material may be partly or fully substituted by a metal (metal atoms) such as zirconi ^¬ um (Zr) , titanium (Ti) and tin (Sn) , these materials are known as zeotype materials.

Crystalline microporous material comprising a small-pore structure means a crystalline microporous material compris ^¬ ing an eight-membered ring pore structure; crystalline mi ^¬ croporous material comprising a medium-pore structure means a crystalline microporous material comprising a ten- membered ring pore structure. Examples of crystalline mi- croporous materials with a small- or medium-pore structure are provided in Chem. Rev. 1995, 95 pp 559-614 and include structures such as LTA, CHA, MFI (ZSM-5) , MEL, MTT, MWW, TON, HEU, AEL, AFO, MWW and FER. The crystalline microporous material with a structure of

BEA comprises a large, twelve-membered ring pore structure (Chem. Rev. 1995, 95 pp 559-614), and is not considered a feature of the present invention.

Examples of zeotype materials with a medium pore size in- elude structures such as Sn-MFI, Ti-MFI and Zr-MFI . An example of a zeotype material with a small pore size is Sn- LTA. Crystalline microporous materials comprising a small- or medium-pore structure may be considered to behave as a cat ^¬ alyst.

The percentage yield of C ₄ oxygenate compounds prepared by the process of the present invention is equal to or greater than 20%, equal to or greater than 24%, equal to or greater than 27%, equal to or greater than 30%, equal to or greater than 35%.

The content of metal (metal atoms) in the crystalline mi ^¬ croporous material comprising a small- or medium-pore structure is present from 0.1 to 15 wt%, from 0.5 to 5.0 wt %, from 0.5 to 1.5 wt%.

The process may be carried out in a solvent; wherein the solvent may be selected from one or more of the group con ^¬ sisting of water, alcohol and a water and alcohol mixture (water and alcohol) . Alcohol may be selected from one or more of the group consisting of methanol and ethanol.

The process may be carried out at a temperature of from 25 to 150 °C, from 50 to 120 °C, and from 70 to 100 °C .

The C ₄ oxygenate compounds produced by the present inven ^¬ tion may be converted to C ₄ -polyols by hydrogenation . Such hydrogenation reactions may be performed in the presence of a supported metal catalyst, wherein the metal is for exam- pie copper, nickel, molybdenum, cobalt, iron, chromium, zinc, and the platinum group metals. In a preferred embodi ^¬ ment the metal catalyst is selected from the group consist- ing of palladium or ruthenium supported on carbon or Raney nickel. Exemplary hydrogenation reaction conditions are disclosed in US 6,300,494 Bl and US 4,487,980 Bl . Examples of further suitable metal catalysts and reaction conditions for use in hydrogenation reactions are disclosed in

Ullmann' s Encyclopaedia of Industrial Chemistry: Hydrogena ^¬ tion and Dehydrogenation .

The C ₄ oxygenate compounds produced by the process of the present invention may be converted to methyl vinyl glyco ^¬ late and 2-hydroxy-4-methoxybutanoic acid or salts or es ^¬ ters thereof. Science (2010) 328, pp 602 - 605 and Green Chemistry (2012) 14, pp 702-706 disclose appropriate syn ^¬ thetic procedures. Additionally, a-hydroxy-y-butyrolactone may be prepared from the C ₄ oxygenate compounds under the same conditions or conditions as described in

ACS Catal., 2013, 3 (8), pp 1786-1800

The methyl vinyl glycolate compound may further react to form a-hydroxy methinonine analogues; an example of this transformation is disclosed in WO 98/32735. a-hydroxy me ^¬ thinonine analogues include compounds selected from the group consisting of 2-hydroxy-4- (Ci-salkylthio) butanoic ac ^¬ id, salts and esters thereof.

Ci-salkylthio means an alkyl thiol selected from the group consisting of methane thiol, ethane thiol, straight or branched chain propane thiol, straight or branched chain butane thiol and straight or branched chain pentane thiol. Ci-8 alkyl esters means esters comprising the alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, isopropyl, isobutyl, pentyl, hexyl, heptyl, oc ^¬ tyl and 2-ethylhexyl .

In one embodiment of the invention the methionine a-hydroxy analogues is 2-hydroxy-4- (methylthio) butanoic acid.

In a second embodiment of the invention the methionine a- hydroxy analogues is selected from the group consisting of 2-hydroxy-4- (methylthio) butanoic acid methyl ester, 2- hydroxy-4- (methylthio) butanoic acid ethyl ester, 2-hydroxy- 4- (methylthio) butanoic acid propyl ester, 2-hydroxy-4- (methylthio) butanoic acid butyl ester, 2-hydroxy-4- (methylthio) butanoic acid isopropyl ester, 2-hydroxy-4- (methylthio) butanoic acid pentyl ester, 2-hydroxy-4- (methylthio) butanoic acid hexyl ester, 2-hydroxy-4- (methylthio) butanoic acid heptyl ester, 2-hydroxy-4- (methylthio) butanoic acid octyl ester and 2-hydroxy-4- (methylthio) butanoic acid 2-ethylhexyl ester.

The C4 oxygenate compounds produced by the process of the present invention may be converted into butanediols as de ^¬ scribed in ChemSusChem (2012) 5, pp 1991-1999.

The process for preparing C4 oxygenate compounds from C ₁ -3 oxygenate compounds may also be carried out concomitantly with the hydrogenation reaction of the C4 oxygenate compounds to form C4 polyols. The reactions therefore may be conducted in one step, i.e. a 'one pot' reaction. A 'one- step' or ^x one-pot' reaction means that the crystalline mi- croporous material for the conversion of glycolaldehyde to C4 oxygenate compounds and the metal catalyst for the hy- drogenation of the C4 oxygenate compounds are present in the reaction vessel simultaneously. The reaction is

quenched when the hydrogenated product (C ₄ polyols) is pre- sent.

C4 polyol means C4 oxygenate compounds that comprise com ^¬ pounds of a chain length of four carbon atoms and each carbon atom is bonded to an alcohol (OH) functional group. C4 polyols may also be known as four carbon sugar alcohols and have the molecular formula of C ₄ H ₁₀ O ₄ . C4 polyols are com ^¬ pounds selected from one or more of the group consisting of erythritol and threitol. Erythritol and threitol include all stereoisomers such as D- and L-threitol. Erythritol may be used as a foodstuff, a sweetener and for the preparation of butanediols. ChemSusChem (2012) 5, pp 1991-1999 illus ^¬ trates the preparation of butanediols from erythritol.

Example 1 :

Crystalline Microporous Material (Sn-MFI, Ti-MFI, Sn-BEA and Sn-LTA) Preparation:

Sn-MFI :

200 Sn-MFI (Si/Sn = 200) is prepared according to the meth- od described by Mai et al . (Mai, N.K.; Ramaswamy, V.; Ra- jamohanan, P.R.; Ramaswamy, A.V. Sn-MFI molecular sieves: Synthesis methods, 29Si liquid and solid MAS-NMR, 119Sn static and MAS NMR studies. Microporous Mater., 1997, 12, 331-340) . According to this procedure NH ₄ F (5.35 g) is dis- solved in demineralized water (25.0 g) . A solution of

SnCl ₄ .5H ₂ 0 (0.25 g) in H ₂ 0 (10.0 g) is added under rapid stirring. After this, of tetrapropylammonium bromide [TPABr (9.8 g) ] in H ₂ 0 (56.0 g) is added slowly. Fumed silica (8.6 g) is dissolved in the mixture. The mixture is stirred for 3 hours and the gel is then transferred to a Teflon lined autoclave and crystallized at 200°C for 6 days. The product is then suction filtrated with ample water and dried over ^¬ night at 80°C. Recovered powder is calcined at 550°C

(2°C/min) for 6 hours. 400Sn-MFI (Si/Sn = 400) is prepared following the same procedure but adjusting the amount of SnCl ₄ .5H ₂ 0.

Sn-MFI (Alternative preparation) :

200 Sn-MFI (Si/Sn = 200) can be prepared from ZSM-5 (Ze- ochem, ZEOcat ® PZ-2 100H) . ZSM-5 is treated under steam at 450°C for 6 h, acid washed with HC1 1 M at 100°C for 16 h, and washed with ample water. The solid is dried at 120°C for 16 h, impregnated with an aqueous solution of SnCl ₂ and calcined at 550°C (2°C/min) for 6 h.

Ti-MFI :

200 Ti-MFI (Si/Ti = 200) is prepared according to a modifi ^¬ cation of the method described by Mai et al . (Mai, N.K.; Ramaswamy, V.; Rajamohanan, P.R.; Ramaswamy, A.V. Sn-MFI molecular sieves: Synthesis methods, 29Si liquid and solid MAS-NMR, 119Sn static and MAS NMR studies. Microporous Ma ^¬ ter., 1997, 12, 331-340) . According to this procedure NH ₄ F (5.35 g) is dissolved in demineralized water (25.0 g) . A solution of Ti (IV) ethoxide (0.17 g) in ¾0 (3.5 g) and H ₂ O ₂ (6.5 g) is added under rapid stirring. After this, a solution of tetrapropylammonium bromide [TPABr (9.8 g) ] in H ₂ 0 (56.0 g) is added slowly. Fumed silica (8.6 g) is dis ^¬ solved in the mixture. The mixture is stirred for 20 hours and the gel is then transferred to a Teflon lined autoclave and crystallized at 200°C for 6 days. The product is then suction filtrated with ample water and dried overnight at 80°C. Recovered powder is calcined at 550°C (2°C/min) for 6 hours .

Sn-BEA:

Sn-BEA was prepared according to the method described in EP 2184270 Bl.

Sn-LTA:

125 Sn-LTA with (Si/Sn = 125) can be prepared from LTA zeolite ( Sigma-Aldrich, Molecular sieves, 4A) . LTA is treated under steam at 450°C for 6 h, acid washed with HC1 1 M at 100°C for 16 h, and washed with ample water. The solid is dried at 120°C for 16 h, impregnated with an aqueous solu ^¬ tion of SnCl ₂ and calcined at 550°C (2°C/min) for 6 h.

Preparation of C4 oxygenate compounds from glycolaldehyde:

Example 2 :

Crystalline microporous material (0.15 g) prepared accord ^¬ ing to Example 1, glycolaldehyde dimer [SAFC, 0.25 g] and deionized water (5 g) are added in a 20 mL vial (Ace pres ^¬ sure tube) and heated at 80°C under vigorous stirring (600 rpm) . Samples of the reaction are taken at selected times (0.5-24 h) . Analysis of the liquid samples after filtration is carried out using a HPLC Agilent 1200 equipped with a BIORAD Amminex HPX-87H column at 65°C and 0.004 M H ₂ S0 ₄ so ^¬ lution in water at 0.6 ml min ^-1 . Table 1 : The percentage yield of C4 oxygenate compounds produced from an aqueous glycolaldehyde solution over time with various crystalline microporous materials.

Example 3 :

Compositions comprising C ₁ -3 oxygenate compounds may be pre ^¬ pared by pyrolysis of biomass or C5-6 sugars (C5-6 oxygenate compounds) such as glucose, sucrose, fructose or xylose.

Exemplary pyrolysis reactions are provided in US 7,094,932 B2 and PCT/EP2014/053587. The C ₁ -3 oxygenate compositions comprise 5 wt% glycolaldehyde or greater, such as between 5 wt % and 65 wt%.

A composition comprising C ₁ -3 oxygenate compounds obtained from the pyrolysis of glucose according to US 7,094,932 B2 is diluted in water to obtain 5 g of a solution comprising 8 wt% glycolaldehyde. Crystalline microporous material (0.15 g) , prepared according to Example 1 is added to the mixture in a 20 mL vial (Ace pressure tube) and the reac ^¬ tion is heated at 80°C under vigorous stirring (600 rpm) . Samples of reaction are taken at selected times (0.5-24 h) . Analysis of the liquid samples after filtration is carried out as previously explained. Table 2 : The percentage yield of C4 oxygenate compounds produced from an aqueous solution of a C1-3 oxygenate mix ^¬ ture according to Example 2 versus time. Various crystal ^¬ line microporous materials are shown.

Example 4 : Hydrogenation of C4 oxygenate compounds is carried out in an autoclave reactor at pressures 30-90 bar of ¾ . The re ^¬ action is carried out by addition of a composition compris ^¬ ing C4 oxygenate compounds (15 g) , prepared according to Example 2 or 3, into a Parr autoclave (50 mL) together with of Ru/C catalyst (0.2 g; 5% on activated charcoal from Al- drich) . The reactor is heated at 80 °C and stirred at 500 rpm for 3 h.

Example 5 :

Concomitant conversion of glycolaldehyde to C4 oxygenate compounds and subsequent hydrogenation. ( ^x one-pot' or 'one -step' conversion and hydrogenation) . Glycolaldehyde dimer (SAFC, 0.25 g) , Sn-MFI (0.1 g) pre ^¬ pared according to Example 1, Ru/C catalyst (0.075 g; 5% on activated charcoal from Aldrich) and water (15 g) are added in a 50 mL Parr autoclave. The first condensation reaction is carried out at 80 °C in air atmosphere. After 3 h of re ^¬ action, the autoclave is pressurized with hydrogen at 90 bar and the reaction is allowed to proceed for 3 h. Samples of the products are obtained after the condensation step and the hydrogenation and analyzed after filtration in an HPLC as previously explained.

Alternatively, vinyl glycolic acid or methyl vinyl glyco- late (MVG) can be obtained by reaction of a composition comprising C4 oxygenate compounds prepared according to Ex ^¬ amples 1 or 2 with Sn-BEA catalyst in water or methanol re ^¬ spectively; Green Chemistry (2012) 14, pp 702-706. Figure 1 : The percentage yield of C ₄ oxygenate compounds prepared according to Example 2 versus time. Various crys ^¬ talline microporous materials are shown. The crystalline microporous materials are:

Squares: 200Sn-MFI;

Circles: Ti-MFI;

Triangles: Sn-BEA.

Figure 2 : The percentage yield of C ₄ oxygenate compounds prepared according to Example 3 versus time. Various crys- talline microporous materials are shown.

The crystalline microporous materials are:

Squares: 200Sn-MFI;

Circles: Ti-MFI;

Triangles: Sn-BEA.