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Bio-Based Methacrylic Acid via Selective Catalytic Decarboxylation of Itaconic Acid James C Lansing, Rex E. Murray, and Bryan R. Moser ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b02926 • Publication Date (Web): 23 Feb 2017 Downloaded from http://pubs.acs.org on March 1, 2017

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ACS Sustainable Chemistry & Engineering

Bio-Based Methacrylic Acid via Selective Catalytic Decarboxylation of Itaconic Acid James C. Lansing,1,2 Rex E. Murray1 and Bryan R. Moser1,*

1

United States Department of Agriculture Agricultural Research Service

National Center for Agricultural Utilization Research Bio-Oils Research Unit 1815 N. University St., Peoria, Illinois 61604, USA

2

United States Department of Energy

Oak Ridge Institute for Science and Education 1299 Bethel Valley Rd., Oak Ridge, Tennessee 37830, USA

[email protected]

1 ACS Paragon Plus Environment


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ABSTRACT

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We report a bio-based route to methacrylic acid via selective decarboxylation of itaconic acid

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utilizing catalytic ruthenium carbonyl propionate in an aqueous solvent system. High selectivity

4

(> 90%) was achieved at low catalyst loading (0.1 mol %) with high substrate concentration (5.5

5

M) at low temperature (200 – 225 oC) and pressure (≤ 425 psig) relative to previous

6

contributions in this area. Direct decarboxylation of itaconic acid was achieved as opposed to

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the conjugate base reported previously, thereby avoiding basification and acidification steps.

8

Also investigated was catalytic manganese (II) oxalate (5 mol %), but low yield (4.8%) and

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evolution of carbon monoxide via oxalate decomposition was problematic. Attempts at

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stabilization of the catalyst with triphenylphosphine were unsuccessful, but it exhibited greater

11

catalytic efficacy (14.0% yield) than the manganese catalyst (4.8% yield) at 5 mol %. Neither

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carbon monoxide nor propylene (excessive decarboxylation) were detected during ruthenium-

13

catalyzed decarboxylation. In addition, co-solvents such as tetraglyme lowered vapor pressures

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within the reaction vessel by > 100 psig while minimizing decomposition of starting acids. In

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combination, these findings represent improvements over existing methodologies that may

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facilitate sustainable production of methacrylic acid, an important petrochemically-based

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monomer for the plastics industry.

18 19

KEYWORDS: Decarboxylation, Itaconic acid, Methacrylic acid, Ruthenium, Tetraglyme

20 21 22 23


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24

INTRODUCTION

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Renewable materials are increasingly preferred over crude petroleum oil and its refinery products

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as feedstocks for industrial chemicals.1 Various environmental, social, economic, legislative,

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and geopolitical incentives motivate the commercial transition to bio-based chemicals.

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Renewable alternatives are either direct drop-in replacements or structurally different but with

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similar properties and performance. Direct drop-in replacements are preferred, as industry is

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already familiar with and has accepted their structure, properties and performance. Examples

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include bio-based ethylene and butadiene from ethanol, ethanol and succinic acid from glucose,

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propylene, propylene glycol, syngas and epichlorohydrin from glycerol, diesel and jet fuel-range

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hydrocarbons from plant oils, and aromatics from depolymerization of lignin.2-7

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Methacrylic acid (2-methylpropenoic acid; MAA) and methyl methacrylate (MMA) are

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important commodity monomers for numerous industrially significant plastics.8 The principal

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application of MMA is homopolymerization to provide the lightweight, shatter-resistant,

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thermoplastic poly(methyl methacrylate) (Plexiglas®) (PMMA) as a versatile alternative to glass.

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MMA is also an essential component of copolymers found in surface coatings, paints, adhesives,

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and emulsion polymers.8-10

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The most significant petrochemical route to MAA/MMA is the acetone cyanohydrin

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process (ACH) depicted in Figure 1. Acetone is initially reacted with hydrogen cyanide to form

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an acetone cyanohydrin intermediate, which is then converted to methacrylamide sulfate upon

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treatment with stoichiometric sulfuric acid at 140 oC. Production of MAA or MMA is achieved

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by reaction of the sulfate with water or anhydrous methanol, respectively.11 Along with

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production of MAA/MMA, an excess of ammonium bisulfate is obtained in a molar ratio of

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1.5:1.8,9 Disadvantages of the ACH process include utilization of nonrenewable materials and



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stoichiometric amounts of harmful, toxic and corrosive reagents, generation of toxic

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intermediates, and production of low-value ammonium bisulfate, which must be further reacted

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with ammonia to yield ammonium sulfate for use as a fertilizer. Additional petrochemical routes

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to MAA/MMA are reviewed elsewhere.8,9

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Relatively few bio-based routes to MAA are reported. One such process is dehydration

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and decarboxylation of citramalic (2-hydroxy-2-methylbutanedioc) acid at elevated temperatures

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(250 – 400 oC) and pressures (450 – 4,000 psi; 31 – 276 bar) in the presence of catalytic sodium

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hydroxide (NaOH).12 Application of this methodology to maleic (2Z-butenedioc) acid yields

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acrylic (2-propenoic) acid (AA).12 The Alpha Process relies on carbon monoxide, methanol and

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ethylene to yield MMA following a two stage sequence.13,14 Another methodology entails

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dehydration and decarboxylation of citric acid to itaconic (2-methylidenebutanedioc) acid (IA),

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followed by a second decarboxylation to afford MAA in the presence of stoichiometric bases

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under near-critical and supercritical water conditions.15 However, accumulation of byproducts

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such as 2-hydroxybutyric and crotonic [(E)-2-butenoic] acids (CA) at the expense of MAA was

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problematic. In addition to low selectivity, high temperatures (> 350 oC) were required. In

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another approach, selectivity was improved to over 90%, but high temperatures (245 – 270 oC)

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and pressures (450 – 3000 psi; 31 – 207 bar) were needed, stoichiometric bases were used, and

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byproducts such as CA, 2-hydroxybutyric acid and propylene were observed.16 Propylene arises

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via decarboxylation of MAA and/or CA, thereby reducing the yield of the intended product.

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More recently, either IA or citric acid was selectively decarboxylated using catalytic

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palladium, platinum and ruthenium.17 Higher selectivity was achieved (up to 84%) and lower

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reaction temperatures (200 – 250 oC) and pressures (550 psi; 38 bar) were utilized relative to

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previous contributions (Figure 2). However, similar to previous reports, stoichiometric bases


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such as NaOH were utilized during the reaction. In such embodiments, NaOH reacts with the

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starting acid to form a conjugate base, which is then decarboxylated to sodium methacrylate.

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The rationale behind formation of monosodium salts is that the rate of decarboxylation at 280 –

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330 oC and 4,000 psi (276 bar) is enhanced relative to the free acid and the disodium salt.18

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However, subsequent acidification of the sodium salt is required to generate MAA, thereby

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adding basification and acidification steps to the process (Figure 3). In essence, these

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approaches convert the conjugate base of IA to sodium methacrylate, rather than IA directly to

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MAA. Consequently, a sustainable technology is needed that avoids basification and

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acidification steps through direct decarboxylation of the starting acid to MAA (Figure 3).

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The objective of our study was to develop a sustainable route to MAA that is free from

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the technical difficulties discussed above. Presented in Table 1 is a comparison of existing bio-

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based routes to the present work. IA was chosen as the starting material since it is derived from

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dehydration and decarboxylation of citric acid or from fermentation of simple sugars such as

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glucose (Figure 4).19-21 Specific objectives included identifying catalysts efficient at direct

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decarboxylation of IA to yield MAA, increasing throughput by increasing the concentration of

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IA, and lowering reaction parameters such as temperature and pressure. In combination, these

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changes would represent techno-economic improvements over existing methodologies, thus

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yielding a sustainable route to MAA that is more amenable to commercialization.

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EXPERIMENTAL SECTION Materials. Water for decarboxylation reactions and as a component of the mobile phase

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for HPLC was ultra-pure (18 MΩ) obtained from a Barnstead (Lake Balboa, CA) Easy Pure II

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RF/UV ultrapure water system. Prior to decarboxylation, ultra-pure water was degassed by a



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nitrogen sparge. CA (98%), IA (99%) and manganese (II) oxalate dihydrate (MnC2O4⋅2H2O;

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99%) were purchased from Alfa Aesar (Ward Hill, MA). CCA (98%), MAA (99%), MSA

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(98%), triphenylphosphine (PPh3; 99%), 4-Methoxyphenol (MeHQ; 99%), and trifluoroacetic

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acid (CF3CO2H, TFA, 99%) were obtained from Sigma-Aldrich Corp (St. Louis, MO).

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Ruthenium (I) dicarbonyl propionate was prepared according to literature precedent.22 All other

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materials were obtained from Sigma-Aldrich Corp and used as received. Catalysts and IA were

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stored prior to use in a nitrogen filled Innovative Technologies (Amesbury, MA) model IL-2GB

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inert atmosphere glove-box with oxygen and water concentrations kept below 1 ppm. Catalytic Decarboxylation. Decarboxylations were performed using a Parr Instrument

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Company (Moline, IL) 50 mL stainless steel (T316) reactor with a maximum allowable working

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pressure of 3000 psi (207 bar) at 350 oC. The reactor was lined with a glass liner and equipped

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with an internal thermocouple, cooling loop, variable speed overhead magnetic stirrer with a

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standard shaft and impeller, heater assembly, and a Span (Waukesha, WI) overhead pressure

106

gauge rated up to 3,000 psi (207 bar). Internal reaction temperature and stirring rate (rpm) were

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controlled by a Parr model 4848 reactor controller unit, which also provided internal vessel

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pressure information.

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In a typical experiment, IA (10.0 g; 76.9 mmol; 5.5 M in water), manganese (II) oxalate

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(5 mol %) or ruthenium dicarbonyl propionate [(Ru(CO)2(CH3CH2COO)]n (0.1 mol %) and

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MEHQ (5000 ppm) were weighed in the inert atmosphere glove box and placed in a glass liner.

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A rubber septum was affixed to the glass liner, which was then removed from the glove box.

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Ultra-pure and degassed water (14.0 mL) was added to the closed system using a syringe, and the

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septum was removed before the liner was introduced into the reaction vessel. After the reactor

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was closed, a headspace pressure of 400 ± 5 psig N2 was applied and the mixture stirred (500


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rpm) and heated to the desired reaction temperature. Typically, heating to the reaction

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temperature was achieved in 20 min. The reaction time started when the desired temperature

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was reached. Parameters such as time and temperature were varied to determine the optimum

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conditions. In some instances, triphenylphosphine (PPh3) (0.5 – 5 mol %) was added to the

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reaction mixture. After the allocated reaction time, the reactor was equilibrated to room

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temperature (1 – 1.5 h) and the gas pressure was released. MAA was isolated via azeotropic

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distillation and yield was reported as the percentage recovered of theoretical (6.63 g).

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High Performance Liquid Chromatography. Samples (50 µL) collected in pairs were

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diluted to a volume of 1.5 mL of 1:1 v/v methanol/water and analyzed in duplicate by HPLC.

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Levulinic acid (1.0 M) was added to all samples as an internal standard. Analyses were

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performed using an Agilent (Santa Clara, CA) 1100 series degasser, pump and auto-sampler

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connected to a spectrophotometric ultraviolet diode array detector and a Sedere (Alfortville,

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France) Sedex 85 LT-ELSD in series. Samples (5.0 µL) were injected onto a GL Sciences

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(Tokyo, Japan) Inertsil ODS-3 column (5.0 µm; 4.6 mm × 250 mm). The mobile phase

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consisted of a mixture of methanol/water with a flow rate of 1.0 mL/min. A gradient method

131

was employed with the following conditions: 85% (v/v) water initially, changing to 82% by 10

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min, 78% at 11 min, 75% at 12 min, 80% at 49 min, 83% at 51 min, 85% at 53 min, hold at 85%

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until 55 min. The water phase was spiked with 0.25% v/v TFA. Compounds were identified by

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retention time comparison to reference standards using both ultraviolet detection at a wavelength

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of 254 nm and the signal from the ELSD. Individual compounds were quantified by external

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calibration with pure standards. Approximate retention times were: levulinic acid (6.6 min),

137

citraconic acid (9.4 min), itaconic acid (10.0 min), mesaconic acid (12.0 min), methacrylic acid

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(19.6 min), and trans-crotonic acid (16.0 min).



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Micro Gas Chromatography. Gas analysis was performed in triplicate using a model

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490 Micro GC by Agilent operating at a sample line temperature of 30 oC with helium as the

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carrier gas. Gas samples were collected from the Parr reactor using a 3 oz. pressure reaction

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bottle from Lab Crest-Andrews Glass (Vineland, NJ) and infused at 10 – 20 psi (0.7 – 1.4 bar)

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into the instrument through a model 170 Lab Series membrane separator by Genie Filters (A+

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Corporation, Gonzalez, LA). Analyses were isothermal with a duration of 3 min. Channel 1

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(Cox 1 m) was used for characterization and its temperature and operating pressure was 80 o C

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and 29 psi (2 bar). Compounds were identified by retention time comparison to reference

147

standards and approximate retention times were: nitrogen (0.37 min), carbon monoxide (0.47

148

min), carbon dioxide (2.2 min), and 1.0 min for hydrocarbons such as methane, ethane, propane,

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and butane.

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Spectroscopy. 1H-nuclear magnetic resonance (NMR) spectra were collected at 26.9 °C

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using a Bruker Avance-500 spectrometer (Billerica, MA) operating at 500 MHz using a 5-mm

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BBO probe. Chemical shifts (δ) are reported as parts per million (ppm) from tetramethylsilane

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in CDCl3 (Cambridge Isotope Laboratories, Andover, MA).

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Vapor pressure of solvent systems. In a typical experiment, the solvent (14 mL) of

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interest (water; 1:1 mole ratio of tetraglyme to water, and tetraglyme) was introduced into the

156

reactor with a syringe. No other reactants or catalysts were added. The Parr reactor was

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pressurized with nitrogen to ensure no leaks were present. The extra pressure was then relieved

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such that the initial pressure of the reactor was 0 psig. The mixture was then stirred (500 rpm)

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and heated (20 min) to the desired temperature. The recorded pressure (psig) was measured after

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equilibration (40 min) at the desired temperature. Pressure was measured at 100, 150, 175, 200,

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212, 225, and 250 oC (Figure 5).


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RESULTS AND DISCUSSION Catalyst Screening. Numerous metal catalysts were screened for production of MAA,

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with manganese (II) oxalate and ruthenium (I) dicarbonyl propionate identified as the most

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efficient at selective decarboxylation of a 1.0 M solution of IA at 250 oC for 3 h. Other catalysts

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screened included simple metal salts of chromium, cobalt, copper, iron, manganese,

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molybdenum, nickel, and zinc, but they provided lower yields of MAA (data provided in Table

168

S1) and were thus not explored further. Optimization using manganese (II) oxalate. Once the most effective catalyst was

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identified, we modified reaction conditions in an effort to maximize yield. Lower reaction

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temperatures, pressures and catalyst loadings were of interest, along short reaction times and

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enhanced selectivity. Another objective was to increase the concentration of IA for process

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economic and engineering reasons. A significant consequence of low starting material

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concentration is that the majority of the reaction vessel is occupied by water, thereby resulting in

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high internal pressure due to the high vapor pressure of water (see Figure S1). Table 2 depicts initial attempts at optimization using manganese (II) oxalate at 5.0 mol

176 177

%, which was half of the amount used during screening studies. In addition, the concentration of

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IA was increased to 5.5 M. A headspace pressure of 400 psig nitrogen (at room temperature)

179

was added in an effort to keep MAA in the liquid phase. We hypothesized that MAA in the

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vapor phase might condense in the upper reaches of the reactor and undergo polymerization. As seen in Table 2, optimization reactions conducted at lower temperatures (200 – 225

181 182

o

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MAA in excess of 7.2%. In addition, carbon monoxide was detected among the headspace gases

184

(Figure 6a), along with nitrogen and carbon dioxide. Carbon dioxide is the expected gaseous

C) and with shorter reaction times (1.5 – 2.0 h) than during catalyst screening failed to give



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coproduct from decarboxylation of IA. We suspected that carbon monoxide arose from

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decarbonylation of oxalic acid via dissociation of manganese (II) oxalate under our conditions,

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thereby leading to decarbonylation of oxalic acid to carbon monoxide and other species. This

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was confirmed by conducting an experiment in the presence of 10 equivalents of oxalic acid for

189

every equivalent of manganese (II) oxalate with otherwise similar conditions. The headspace

190

gases from this experiment displayed a spike in carbon monoxide (Figure 6c), thus indicating

191

that carbon monoxide was evolving from decomposition of oxalic acid.

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Reaction temperature affected ∆P and yield of MAA. As seen in Table 2, ∆P and yield of

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MAA increased with increasing temperature at constant reaction time (1.5 h) and with longer

194

reaction times at constant temperature (200 oC). For example, entries 2-5 represent

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decarboxylations conducted at progressively higher temperatures (200 – 250 oC) and otherwise

196

similar reaction conditions. Both ∆P and yield of MAA increased as the temperature was

197

increased from 200 to 250 oC.

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In an effort to stabilize manganese (II) oxalate, an equimolar amount of PPh3 (5.0 mol %)

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was added to the reaction mixture (entries 6-8, Table 2). The rationale behind addition of

200

phosphines originated with Crooks, et al., who noted that ruthenium carbonyl carboxylate

201

polymers form more stable ruthenium dimers capped by phosphines upon addition of

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tributylphospshine and pyridine.22 He proposed that these dimers were the active catalyst species

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in the decarboxylation of organic acids. We hypothesized that phosphines would form stable

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dimeric species with manganese upon addition to our system. Addition of PPh3 enhanced the

205

yield of MAA. For instance, comparison of decarboxylation at 212 oC for 1.5 h with (entry 6)

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and without (entry 3) PPh3 (5.0 mol %) in the presence of manganese (II) oxalate (5.0 mol %)

207

revealed higher ∆P (196 versus 135 psig) and yield of MAA (5.3 versus 2.4%) with PPh3.


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Furthermore, higher ∆P (326 versus 221 psig) and yield of MAA (13.0 versus 7.0%) was noted

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with PPh3 (entry 7) at 225 oC than without added PPh3 but otherwise similar reaction conditions

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(entry 4). Lastly, PPh3 alone (entry 8) demonstrated greater efficacy at decarboxylation of IA

211

than did manganese (II) oxalate (entry 4) at similar reaction conditions (225 oC and 1.5 h), as

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indicated by higher ∆P (282 versus 221 psig) and yield of MAA (14.0 versus 7.0%). The control

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experiment conducted in the absence of catalyst at 225 oC for 1.5 h (entry 1) gave MAA in 2.6%

214

yield, which was lower than catalyzed reactions conducted utilizing otherwise similar conditions

215

(entries 4, 5, 7, and 8). However, suppression of carbon monoxide was unsuccessful with PPh3

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(Figure 6b).

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Lower partial vapor pressures (pH2O; 191 – 499 psig) were achieved in Table 2 than

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during catalyst screening experiments due to lower temperatures investigated as well as higher

219

concentrations of IA in water. For comparison, a pH2O of 540 psig was calculated according to

220

Raoult’s Law with a reaction temperature of 250 oC and a concentration of IA of 1.0 M (Table

221

S1). Increasing the concentration of IA to 5.0 M with otherwise similar conditions resulted in a

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pH2O of 499 psig (entry 5, Table 2). Further reductions in reaction temperature afforded

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progressively lower pH2O at constant IA concentration (Table 2).

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Optimization with ruthenium catalysis. Due to the relatively low yield of MAA given

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by manganese (II) oxalate along with evolution of carbon monoxide, ruthenium catalysis was

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explored. Ruthenium carbonyl carboxylates were of interest because of our previous work on

227

tandem isomerization-decarboxylation of oleic acid.23-25 When using catalytic ruthenium (I)

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dicarbonyl propionate in the present system, IA was first isomerized to mesaconic acid, which

229

was in turn decarboxylated to MAA (Figure 2). Isomerization was confirmed by a control

230

experiment subjecting dibutyl itaconate to the reaction conditions, thereby inhibiting



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decarboxylation via protection of the carboxylic acid moieties as butyl esters. When the reaction

232

was performed at 225 °C for only 15 minutes, dibutyl mesaconate was present in 44% with

233

dibutyl itaconate constituting most of the remaining product (see Figures S2 and S3). As

234

expected, a negligible amount of citraconic dibutyl ester was detected, as it is the cis isomer of

235

mesaconate and is therefore less thermodynamically favored. Isomerization was anticipated

236

because extensive isomerization of double bond location and geometry was observed in our

237

previous studies using oleic acid as the substrate.23-25 Under the same conditions with

238

manganese (II) oxalate, less than 5% isomerization to mesaconic dibutyl ester was observed.

239

Catalytic ruthenium on carbon (Ru/C) was previously investigated for decarboxylation of IA, but

240

the authors concluded that the catalyst was inferior to Pd/C and Pt/C due to higher propylene

241

production via unwanted decarboxylation of MAA.17 However, we did not observe propylene

242

during the course of our study (Figure 7).

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Depicted in Table 3 is catalytic decarboxylation of a 5.5 M solution of IA in water using

244

ruthenium dicarbonyl propionate (0.1 mol % Ru) at 200 – 225 oC and 0.5 – 2.0 h with a

245

headspace pressure of 400 psig nitrogen. Yields of MAA ranged from 8.2 – 33.8%, which were

246

higher than those observed in Table 2 despite the lower catalyst loading, generally shorter

247

reaction times and lower reaction temperatures explored in Table 3. Similar to manganese-

248

catalyzed decarboxylations, the yield of MAA increased when reaction time was increased from

249

0.5 to 1.0 h at constant temperature (212 oC), as seen by comparison of entries 1 and 2.

250

However, a further increase in reaction time to 2.0 h (entry 3) at otherwise similar conditions did

251

not provide higher yield relative to a reaction time of 1.0 h. . In addition, ∆P increased with

252

increasing reaction time at constant temperature (entries 1 – 3, Table 3), despite yield plateauing

253

at 1.5 h. These results indicate that headspace pressure does not necessarily correlate with yield


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of MAA. Entries 7 – 10 (Table 3) were conducted in the presence of 0.5 mol % PPh3 in an

255

effort to stabilize the ruthenium catalyst. A higher yield of MAA was achieved at 200 oC and 1.5

256

h with 0.5 mol % PPh3 added to the system (14.9%; entry 7) versus without (8.6%; entry 4) and

257

otherwise similar conditions. In addition, a higher ∆P was observed without PPh3 addition (120

258

versus 116 psig) despite the lower yield, thus providing further evidence that headspace pressure

259

does not correlate to yield of MAA. When investigated at progressively higher temperatures in

260

the presence of PPh3 (entries 7 – 10), the isolated yield of MAA continued to increase, reaching a

261

maximum of 33.8% at 225 oC and 1.5 h (entry 10). This compares favorably to decarboxylations

262

performed in the absence of PPh3, where a yield of only 14.9% was observed at otherwise similar

263

conditions (entry 6). The addition of PPh3 had a positive effect on the isolated yield in these

264

reactions, and it is possible that other additives could further increase the isolated yield. Lastly,

265

as seen in Figure 7, carbon monoxide was not observed with ruthenium catalysis, thereby

266

indicating that carbon monoxide was from oxalate decomposition.

267

Comparison of manganese-catalyzed (Table 2) to ruthenium-catalyzed decarboxylations

268

revealed several important differences. Ruthenium-catalyzed reactions provided MAA in higher

269

yield (33.8% versus 14.0%) with lower catalyst concentration (0.1 versus 5.0 mol %), as seen by

270

comparison of entry 10 in Table 3 to entry 10 in Table 2. Both ruthenium and manganese-

271

catalyzed reactions were facilitated by addition of PPh3. However, the percentage of PPh3

272

(relative to IA) was an order of magnitude lower for ruthenium-catalyzed reactions. A further

273

demonstration of the efficacy of ruthenium relative to manganese is comparison of experiments

274

conducted at similar reaction temperature and time. For instance, manganese-catalyzed

275

decarboxylations conducted at 200 oC for 1.5 h (entry 3, Table 2) to the corresponding ruthenium



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

276

experiment (entry 4, Table 3) revealed a six-fold difference in yield of MAA (8.6 versus 1.5%)

277

despite the lower catalyst loading for ruthenium.

278

Lowering vapor pressure with co-solvents. Lower pressures are desirable from

279

engineering and economic standpoints due to safety and cost considerations. Lower pressure is

280

achieved primarily by lower reaction temperatures yielding lower pressures according to Gay-

281

Lussac’s Law and/or by replacement of a fraction of water with an appropriate co-solvent

282

possessing lower vapor pressure according to Raoult’s Law. Replacement of a portion of the

283

solvent (water) with tetraglyme to form a mixture (1:1 mole ratio) of water and tetraglyme

284

facilitated considerably lower vapor pressures relative to water at constant volume, as seen in

285

Figure 5. Tetraglyme was chosen because it is chemically inert to our process and has a lower

286

vapor pressure than water. Note that the data collected for Figure 5 was conducted in the

287

absence of IA and catalyst.

288

Application of a tetraglyme/water solvent system (1:1 mole ratio) to decarboxylation of

289

IA in the presence of catalytic ruthenium carbonyl propionate yielded a considerably lower ∆P

290

(133 versus 277 psig) while reducing the yield of MAA. This is seen by comparison of the first

291

and third entries of Table 4. While yields were typically lower in water/tetraglyme mixtures than

292

in water alone, the water/tetraglyme mixtures preserved considerably more of the starting acids,

293

which would facilitate recycling to produce additional MAA. Replacement of all of the water

294

with tetraglyme (entry 2, Table 4) resulted in further yield reduction (3.9%). We speculate that

295

this was due to anhydride formation, as anhydrides are anticipated to be less reactive toward

296

decarboxylation than carboxylic acids. Furthermore, anhydride formation in the absence of

297

water is probably thermodynamically favored under our conditions. For instance, the

298

equilibrium constants determined in a previous study for diacid ↔ anhydride + water in aqueous


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299

solution at 20 oC ranged from 3.2 – 25 for dimethylmaleic acid and other maleic acid

300

derivatives.27 As a consequence, water is a necessary component in our reaction medium, as it

301

mitigates formation of anhydrides in situ. Lastly, as anticipated from the data presented in

302

Figure 5, replacement of water with tetraglyme afforded lower pH20, as seen by comparison of the

303

first entry in Table 4 (100% water; pH20 of 313 psig) with the other entries (pH20 ≤ 209 psig).

304 305

CONCLUSIONS

306

Ruthenium (I) dicarbonyl propionate was identified as the most efficient catalyst at selective

307

decarboxylation of IA to afford sustainable MAA with high selectivity. Also investigated was

308

manganese (II) oxalate (5 mol %), which was identified as providing the highest yield of MAA

309

after screening over 20 simple transition metal catalysts. However, accumulation of carbon

310

monoxide during the course of manganese-catalyzed decarboxylation suggested that

311

decomposition of oxalate under our conditions was problematic. This was confirmed with a

312

control experiment that demonstrated elevated carbon monoxide levels when oxalic acid was

313

added to the system. Attempts at stabilization of the catalyst with triphenylphosphine were

314

unsuccessful, but it exhibited greater catalytic efficacy (14.0% yield) than the manganese catalyst

315

(4.8% yield) at 5 mol % with otherwise similar reaction conditions (1.5 h and 225 oC). Evolution

316

of carbon monoxide was not observed during ruthenium-catalyzed decarboxylation.

317

Additionally, lower catalyst loadings (< 1 mol %), lower reaction temperatures and pressures and

318

higher yields were achieved utilizing ruthenium catalysis, thereby improving reaction parameters

319

relative to manganese-catalyzed decarboxylations. High substrate concentration (5.5 M), low

320

reaction temperature (200 – 225 oC), low reaction pressure (≤ 425 psig), low ruthenium catalyst

321

load (0.1 mol %), high selectivity (> 90%), and avoidance of propylene production (excessive



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

322

decarboxylation) represent advances over previous contributions in this area. Additionally,

323

ruthenium catalyzed yields increased further with the addition of PPh3, and could potentially be

324

further enhanced with the appropriate additive. Furthermore, we achieved direct decarboxylation

325

of IA as opposed to its conjugate base, thereby avoiding basification and acidification steps. We

326

also report that utilization of co-solvents such as tetraglyme lowers the vapor pressure of water

327

within the reaction vessel by > 100 psig while minimizing decomposition of starting acids. We

328

continue to investigate additives, reaction conditions and solvent conditions that will lead to

329

increased yield, conversion and selectivity as well as stabilization of products within the reactor

330

system once they have formed.

331 332

Supporting Information

333

Table S1 depicts screening results of catalytic decarboxylation using various catalysts; vapor

334

pressure of steam as a function of temperature is shown in Figure S1; Figures S2 and S3 display

335

GC-MS and NMR data of isomerized dibutyl itaconate.

336 337

AUTHOR INFORMATION

338

Corresponding Author

339

*B. R. Moser. Fax: 309-681-6534. Tel: 309-681-6511. E-mail: [email protected].

340 341

Author contributions

342

All authors contributed to conceptual design of experiments as well as manuscript preparation.

343

All authors have given approval to the final version of the manuscript.

344


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345

Notes

346

The authors declare no competing financial interest.

347 348

Disclaimer

349

Mention of trade names or commercial products in this publication is solely for the purpose of

350

providing specific information and does not imply recommendation or endorsement by the U.S.

351

Department of Agriculture. USDA is an equal opportunity provider and employer.

352 353

ACKNOWLEDGEMENTS

354 355

Benetria Banks, Daniel Knetzer and Erin Walter are acknowledged for excellent technical

356

assistance.

357 358

Funding

359 360

This work was part of the in-house research of the Agricultural Research Service of the United

361

States Department of Agriculture.

362 363

REFERENCES

364

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assessment of 12 bioethanol-based products. Bioresour. Technol. 2013, 135, 490−499.



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of glycerol as a biorenewable source to valuable commodity chemicals. Chem. Soc Rev.

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Wilczynski, R.; Juliette, J. J. Methacrylic Acid and Derivatives. In: Kirk-Othmer Encyclopedia of Chemical Technology, 5th Ed., Vol. 16, Wiley: 2006; p 227.

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Jones Jr., M. Study of sequential conversion of citric to itaconic to methacrylic acid in

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near-critical and supercritical water. Ind. Eng. Chem. Res. 1994, 33, 1989–1996.

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Johnson, D. W.; Eastham, G. R.; Poliakoff, M.; Huddle, T. A. A process for the

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production of methacrylic acid and its derivatives and polymers produced therefrom. WO

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Patent 2012/069813. 2012.

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Le Notre, J.; Witte-van Dijk, C. M.; van Haveren, J.; Scott, E. L.; Sanders, J. P. M.

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Synthesis of bio-based methacrylic acid by decarboxylation of itaconic acid and citric

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acid catalyzed by solid transition-metal catalysts. ChemSusChem 2014, 7, 2712–2720.

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itaconic acid reactions in real time. J. Phys. Chem. A 2001, 105, 10839–10845.

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Kuo, T. M.; Kurtzman, C. P.; Levinson, W. E. Production of itaconic acid by Pseudozyma antarctica. U.S. Patent 7,479,381. 2009.

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polynuclear compounds. Part XVII. Some carboxylate complexes of ruthenium and

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osmium carbonyls. J. Chem. Soc. A. 1969, 276 –2766.



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unsaturated organic compounds with a metal catalyst or catalyst precursor. U.S. Patent

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Application 2014/0275592 (September 18, 2014).

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Moser, B. R.; Knothe, G.; Walter, E. L.; Murray, R. E.; Dunn, R. O.; Doll, K. M.

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Analysis and properties of the decarboxylation products of oleic acid by catalytic

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triruthenium dodecacarbonyl. Energy Fuels 2016, 30, 7443–7451.

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422 423

Perry, R. H.; Green, D. W. Perry’s Chemical Engineers’ Handbook, 7th Ed, McGraw-

(27)

Eberson, L.; Welinder, H. Studies on cyclic anhydrides. III. Equilibrium constants for the

424

acid-anhydride equilibrium in aqueous solutions of certain vicinal diacids. J. Am. Chem.

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Soc. 1971, 93, 5821–5826.


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426

427 428


Table 1. Comparison of existing bio-based routes to MAA with the current study ChemSusChem WO 2012/069813 2014, 7, 2717-2720 Feedstock Monosodium salt of IA Monosodium salt of IA Reactor High water diluent High water diluent Low [IA] Low [IA] Catalysts Heterogeneous Pt, Pd Group I and II bases and Ru [Catalyst] (mol %) 2.5 30 – 100 [Starting Acid] 0.15 M 0.3 – 3.0 Temp (oC) 200 – 250 255 – 265 Pressure (psi) 551 450 - 3000 Time 1h 150 seconds Solvent Supercritical water Supercritical water Reaction mode Batch (unvented) Continuous (vented) Yield of MAA Up to 51% (isolated) Up to 63% (HPLC) Selectivity1 Up to 84% Up to 99% 2 Propylene detected? Yes Not determined 1 Selectivity is defined as [MAA / (MAA + crotonic acid) × 100]. 2

Ind. Eng. Chem. Res. 1994, 33, 1989-1996 Citric acid or IA High water diluent Low [IA] NaOH 0 – 50 0.01 – 0.50 230 – 400 4000 - 5000 1 – 250 seconds Supercritical water Continuous (vented) Up to 75% (HPLC) Up to 100% Yes

Current study IA Low water diluent High [IA] Mn(II) oxalate [Ru(CO)2(CH3CH2COO)]n 0.1 – 10 1.0 – 10.0 190 – 250 1 - 425 1–3h Subcritical water Batch (unvented) Up to 40% (HPLC) Up to 95% No

Propylene is indicative of over-reaction (double decarboxylation of IA or triple for citric) and is therefore undesirable.

429 430 431 432 433



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Page 22 of 33

434

Table 2. Results of catalytic decarboxylation of 5.5 M IA with Mn (II) oxalate and triphenylphosphine (PPh3) with 400 ± 5

435

psig N2 headspace pressure Entry 1 2 3 4 5 6 7 8

Mn (II) oxalate PPh3 Time Temp CA MAA ∆P (mol %) (h) (°C) (mol %) (area %) (isolated)1 (psig) 1.5 225 69 0 0 0.8 2.6 1.5 200 67 5.0 0 0.8 1.5 1.5 212 135 5.0 0 0.8 2.4 1.5 225 250 5.0 0 0.7 4.8 1.5 250 342 5.0 0 0.9 5.7 1.5 212 196 5.0 5.0 2.1 5.3 1.5 225 326 5.0 5.0 2.4 13.0 1.5 225 282 0 5.0 2.9 14.0 Yield of MAA is reported as percent of theoretical after distillation.

IA+CCA+MCA (area %)2 69.5 56.4 58.5 41.4 6.2 64.6 33.4 19.4

Sel3 76.5 65.2 75.0 87.2 86.4 71.6 84.4 82.8

pH2O4 (psig) 312 191 244 312 499 243 311 311

436

1

437

2

IA = itaconic acid; CCA = citraconic acid; MSA = mesaconic acid. Values were determined by HPLC.

438

3

Selectivity is [MAA/(MAA + CA) × 100].

439

4

Partial vapor pressure of water (pH2O, psig) was calculated from mole fraction of water and vapor pressure data from reference

440

26.

441 442 443 444 445 22 ACS Paragon Plus Environment

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446


Table 3. Results of catalytic decarboxylation of 5.5 M IA with 0.1 mol % [Ru(CO)2(CH3CH2COO)]n1 Entry

Time Temp CA mol % ∆P (h) (°C) (psig) PPh3 (area %) 1 0.5 212 75 0.0 0 2 1.0 212 128 0.0 0 3 2.0 212 201 0.0 0 4 1.5 200 120 0.0 0 5 1.5 212 184 0.0 0 6 1.5 225 277 0.0 0 7 1.5 200 116 0.5 0 8 1.5 212 206 0.5 0 9 1.0 225 251 0.5 0 10 1.5 225 289 0.5 0 All headspace pressures are 400 ± 5 psi.

MAA (isolated)2 8.2 13.6 13.7 8.6 17.0 14.9 14.9 21.6 25.4 33.8

IA+CCA+MCA (area %)3 92.5 57.8 27.7 74.9 34.4 3.8 46.0 25.2 12.3 6.2

Sel4 100 100 100 100 100 100 100 100 100 100

pH2O5 (psig) 245 245 245 191 245 313 190 245 313 313

447

1

448

2

Yield of MAA is reported as percent of theoretical after distillation.

449

3


450

4

Selectivity was calculated according to the same method as in Table 2.

451

5

Partial vapor pressure of water was calculated according to the same method in Table 2.

452 453 454 455



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 24 of 33

456

Table 4. Results of catalytic decarboxylation of 5.5 M IA using 0.1 mol % [Ru(CO)2(CH3CH2COO)]n with varied solvent

457

compositions Entry 1 2 3 4 5

IA+CCA+MCA mole ratio mole ratio ∆P CA MAA 1 (area %)2 TG : water IA: water (psi) (area %) (isolated) 0:1 1:10 277 0.9 14.9 16.8 1:0 N/A 108 3.7 3.9 67.6 3.0 12.6 75.1 1:1 0.72:1 133 1:3 1:2 139 3.8 7.6 82.6 1:4 1:2.5 153 3.3 9.2 49.9 Yield of MAA is reported as percent of theoretical after distillation.

Sel3 94.3 51.3 80.8 66.7 73.6

pH2O4 (psig) 313 0 101 188 209

458

1

459

2


460

3

Selectivity was calculated according to the same method as in Table 2.

461

4

Partial vapor pressure of water was calculated according to the same method in Table 2.


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O

HCN

HO

CN

H2SO4

O

NH2H2SO4

CH3OH

O O Methyl methacrylate

H2O

O OH Methacrylic acid

Figure 1. Production of methacrylic acid from acetone by the conventional petrochemical acetone-cyanohydrin route.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Itaconic Acid

Mesaconic Acid

O

Citraconic Acid

O OH

HO

O

OH

HO

O

H2O

CO2

Citramalic Acid

Crotonic Acid O

O OH

HO

HO

OH

HO

O

H2O

O

OH

O

CO2 2-Hydroxyisobutyric Acid OH HO

H2O

O

H2O

Methacrylic Acid O OH

Figure 2. Bio-based route to methacrylic acid from itaconic acid. Note that mesaconic and citramalic acids are intermediates along the way to methacrylic acid. Also note that 2hydroxyisobutyric acid is the hydrated form of methacrylic acid.


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O HO

O OH

O conjugate acid

NaOH HO

O

O O-Na+

O conjugate base

catalyst

O-Na+

HCl

OH + NaCl methacrylic acid

CO2

Figure 3. Production of methacrylic acid through decarboxylation of monosodium itaconate, the conjugate base of itaconic acid. In this example, the sodium salt is depicted, but others such as potassium, ammonium, and others may be utilized.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Simple Fermentation Sugars

O

O OH

HO

H2O, catalyst OH

O Itaconic acid

Methacrylic acid CO2 CO2

O HO

O

OH O OH

OH

Citric acid

Figure 4. Bio-based methacrylic acid from simple sugars and citric acid via an itaconic acid intermediate.


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600 Water:Glyme, 1:1 500

Pressure, psig

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Water Only Glyme only

400

300

200

100

0 100

120

140

160

180

200

220

240

260

Temperature, °C

Figure 5. Comparison of pressure (psig) as a function of temperature (Celsius) at constant volume among water, a 1:1 (mole ratio) mixture of water and tetraglyme and tetraglyme, demonstrating that vapor pressure can be decreased with prudent choice of an appropriate low vapor pressure organic co-solvent.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 6. Micro GC chromatogram of samples of headspace gas after decarboxylation of IA using 5.0 mol % manganese (II) oxalate with (a) and without (b) 5.0 mol % PPh3 showing evolution of both carbon monoxide (0.47 min) and carbon dioxide (2.2 min). Chromatogram c) depicts the results of an experiment conducted in the presence of excess oxalic acid. The signal at 0.38 min corresponds to nitrogen.


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Figure 7. Representative micro GC chromatogram of a sample of headspace gas collected after decarboxylation of IA at 200 oC for 2.0 h utilizing 0.1 mol % [Ru(CO)2(CH3CH2COO)]n. Signals corresponding to nitrogen (N2) and carbon dioxide (CO2) are at 0.38 and 2.2 minutes, respectively. If present, propylene would appear at 1.0 minutes.



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For Table of Contents Use Only Bio-Based Methacrylic Acid via Selective Catalytic Decarboxylation of Itaconic Acid James C. Lansing, Rex E. Murray and Bryan R. Moser

Methacrylic acid is synthesized from renewable itaconic acid using transition metal catalysts and subcritical water, which represents a sustainable alternative to the hazardous petrochemical route.


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Simple bio-based sugars can be converted to itaconic acid, which in turn can be catalytically transformed into methacrylic acid, a commodity monomer with numerous practical applications, including as components in protective eyewear and car headlights. 223x87mm (96 x 96 DPI)

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