Abstract:
The present invention relates to an improved and sustainable process for producing 3-methyl-3-pentene-2-one which is used in the synthesis of fragrance ingredients for perfumery applications.

Description:
STATUS OF RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. provisional patent application Ser. No. 61/825,661, filed May 21, 2013, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to an improved “greener” process for synthesis of 3-methyl-3-pentene-2-one, a key intermediate in the synthesis of woody fragrance ingredients for perfumery applications. 
       BACKGROUND OF INVENTION 
       [0003]    The synthesis of 3-methyl-3-pentene-2-one (3M3P) involves an aldol condensation reaction between acetaldehyde and methyl ethyl ketone using an acid catalyst. There is limited information available in the literature for this specific reaction. Heiba and Anderson (1959) used carbon tetrachloride for this reaction and reported acetaldehyde conversion of 32% with significant formation of acetaldehyde polymers. U.S. Pat. No. 4,234,518 describes the use of zinc acetate as catalyst for this reaction to give a mixture of 4-hexene-3-one and 3M3P in 31:69 ratio with 38% overall yield. 
         [0004]    The industrial process for manufacture of 3M3P generally uses mineral acid catalysts such as sulfuric acid to drive the reaction and is typically conducted in a semi-batch or batch mode in a stirred tank reactor. In such reactor system, the reaction medium needs to be stirred vigorously to overcome the mass transfer limitations between organic reactants and aqueous acid phases to try and maximize the product yield and reduce reaction time. The intensity of mixing is usually a limiting factor in production scale batch reactors, thus resulting in low reactor throughput and product yields. In addition, the process using mineral acids generate huge aqueous waste streams that need to be disposed. Furthermore, due to relatively high water solubility, significant amount of product and reactants are being lost in the aqueous stream, thus further lowering product yield and adding to environmental concerns. 
         [0005]    One approach that addresses some of these issues is the use a solid acid catalyst rather than a mineral acid for this chemical transformation. Mahajan et al (2007) studied the use of Amberlyst 15, a solid acid catalyst and developed a kinetic model and Mahajani et al (2009) used this model in a computer simulation exercise to propose a reaction-distillation system for 3M3P. However, the high residence times (60 hours at 70-75° C.) based on simulation results is impractical to be of any value for industrial applications. Typically, higher temperatures are used to increase reaction speed and lower residence time however, in this case higher temperatures (&gt;100° C.) are detrimental to the Amberlyst 15 catalyst, reduces catalyst life and increases cost making the approach uneconomical. Snell et al (2010) have reported the use of solid aluminophosphate catalysts, but the yield of 3M3P they obtained (&lt;6%) was too low to be of practical value. 
         [0006]    For practical industrial application of the solid acid catalyst, the combination of a good catalyst with long life, process and operating conditions to achieve high yield of 3M3P in a reasonable reaction time and appropriate reactor design all play a critical role. The present invention discloses a practical 3M3P process using a continuous reactor system and solid acid catalyst with good activity and long life that gives high product yield with low residence time, and essentially no waste. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention discloses an improved and sustainable process for synthesis of 3-methyl-3-pentene-2-one (3M3P). 
         [0008]    According to the present invention, the improved process for 3M3P involves the use of solid acid catalyst for the aldol condensation of acetaldehyde and methyl ethyl ketone in a continuous reactor system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1 : This figure illustrates the setup for the production of 3M3P using premixed reactant(s) and/or solvent. 
           [0010]      FIG. 2 : This figure illustrates the setup for the production of 3M3P using in-line mixing of reactant(s) and/or solvent 
           [0011]      FIG. 3 : This figure illustrates the setup for the production of 3M3P using multiple feed points of reactant(s) and/or solvent. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    According to the present invention, the process for the production of 3M3P comprises of reacting a mixture of acetaldehyde and methyl ethyl ketone in the presence of a solid acid catalyst in a continuous reactor system. 
         [0013]    According to some embodiments of the present invention, the continuous reactor system may be a single Continuous Stirred Tank Reactor (CSTR) or multiple CSTRs in series. 
         [0014]    According to some embodiments of the present invention, the continuous reactor system may be a continuous flow reactor including microreactor. 
         [0015]    As used herein, the phrase “reactor” refers to the device where the reaction actually occurs. As used herein, the term “microreactor” and “microchannel reactor” refers to a device or an assemblage of related devices that contains reaction channels in which at least one of the transverse dimensions is sub-millimeter or millimeter range. In some embodiments, the reactor comprised of channels with internal diameter (ID) ranging from 0.2 to 3 mm. 
         [0016]    In some embodiments of the present invention, the flow reactor may be a packed bed reactor, wherein the reactor is packed with materials such as catalyst, glass beads (about 10 μm to about 100 μm particle size). As used herein, the terms “packed” and “packing” mean to fill with an amount of material that allow effective production of a pre-determined amount of 3M3P and the amount of material often requires taking into consideration, e.g., the size of the reactor vessel, the material type and the pre-determined amount of 3M3P. 
         [0017]    In some embodiments of the present invention, the catalyst for producing 3M3P is a solid acid which may be Natural clay minerals including but not limited to kalonite, bentonite, zeolites and synthetic clays. In some embodiments of the present invention, the catalyst for producing 3M3P is metal oxide and sulfide including but not limited to ZnO, CdO, Al 2 O 3 , CeO 2 , TiO 2 , ZrO 2 , SnO 2 , PbO, As 2 O 3 , Bi 2 O 3 , Sb 2 O 5 , V 2 O 5 , Cr 2 O 3 , MoO 3 , WO 3 , CdS, ZnS. In some embodiments of the present invention, the catalyst for producing 3M3P is metal salt including but not limited to MgSO 4 , CaSO 4 , SrSO 4 , BaSO 4 , CuSO 4 , ZnSO 4 , Ca(NO3) 2 , AlCl 3 , TiCI 3 , Mg(C10 4 ) 2 . In some embodiments of the present invention, the catalyst for producing 3M3P is mixed oxides including but not limited to mixtures of SiO 2 , Al 2 O 3 , SnO 2 , ZrO 2 , MgO, CaO, Fe 2 O 3 , WO 3 , Cr 2 O 3 , SnO 2 . In some embodiments of the present invention, the catalyst for producing 3M3P is cation exchange resin or polymeric perflourinated resinsulfonic acid including but not limited to amberlyst, dowex. In some embodiments of the present invention, the solid acid catalyst for producing 3M3P can be made in-house by absorbing a mineral acid or otherwise depositing acidic moities on a solid support. 
         [0018]    In some embodiments of the present invention, the process for the production of 3M3P is illustrated by, but not limited to, the following experimental procedure and attached figures. In some embodiments of the present invention, the liquid stream containing the reactants acetaldehyde and methyl ethyl ketone is pre-mixed and is pumped in to the reactor system containing catalyst as shown in  FIG. 1 . In some embodiments of the present invention, the reactants and/or solvent are mixed in-line using a static mixer before entering the reactor system as shown in  FIG. 2 . In some embodiments of the present invention, the reactants and/or solvent are fed separately into the reactor system as shown in  FIG. 3 . In some embodiments of the present invention, the reactor configuration can be a combination of  FIGS. 1 ,  2  and/or 3, thereof. In some embodiments, the reactor system may comprise a catalyst retainer to prevent the catalyst from moving out of the reactor. In some embodiments, the reactor system is heated using a heating circulating oil bath or electrical heater. From the reactor system, the reaction mixture is collected in a product receiver. The reaction mixture is analyzed using Gas Chromatography (GC). 
         [0019]    In some embodiments of the present invention, the catalyst volume in the reactor system may vary from 20 to 90%. 
         [0020]    In some embodiments of the present invention, the reaction is conducted at temperatures from about 25 to 200° C. 
         [0021]    In some embodiments of the present invention, the reaction pressure may vary from 0 psig to 100 psig. 
         [0022]    In some embodiments of the resent invention, the liquid stream may comprise of a mixture of two reactants: acetaldehyde, methyl ethyl ketone and/or a solvent. In such embodiments, the concentration of methyl ethyl ketone in the liquid stream may vary from 10 to 90% by weight. In such embodiments, the mole ratio of methyl ethyl ketone to acetaldehyde may vary from 1 to 10. 
         [0023]    In some embodiments of the present invention, the liquid stream may comprise of a solvent including, but not limited to, hydrocarbons such as hexane, decane, cylcohexane, decalin; mixture of hydrocarbons such as isopars; alcohols such as methanol, ethanol, iso-propyl alcohol; ketones such as acetone, methyl ethyl ketone; water. In such embodiments, the concentration of solvent in the liquid stream may vary from 0 to 75% by weight. 
         [0024]    The following are provided as specific embodiments of the present invention. Other modifications of this invention will be readily apparent to those skilled in the art. Such modifications are understood to be within the scope of this invention. All the reactants and solvents were obtained from Sigma Aldrich. As used herein L is understood to be liter, mL is understood to be milliliter, m 3  is understood to be cubic meter, kW is understood to be kilo watts, mol is understood to be moles, psig is understood to be pounds per square inch gauge, g is understood to be gram, kg is understood to be kilogram, min is understood to be minutes and hr to be hour. IFF as used herein is understood to mean International Flavors &amp; Fragrances Inc., New York, N.Y., USA. 
         [0025]    Productivity of 3M3P expressed as the yield calculated as, 
         [0000]    
       
         
           
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         [0026]    Residence time is calculated as, 
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         [0027]    Mass efficiency is calculated as, 
         [0000]    
       
         
           
             
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         [0028]    Below are few examples to describe the state of art disclosed in the present invention. They are not intended to limit the scope of what the inventors regard as their invention nor are they intended to represent that the experiments below are all or the only experiments performed. 
       EXAMPLES 
     Synthesis of 3M3P in a Micro Reactor Using Solid Acid Catalyst 
       [0029]    2.5 g of solid acid catalyst supported on polymeric resin is packed into a micro reactor of length 20 cm and inner channel diameter 5.3 mm. A mixture of acetaldehyde and methyl ethyl ketone with mole ratio of 1:6 is fed at 0.05 ml/min into the micro reactor which is maintained at 65-70° C. The 3M3P yield (analyzed by GC) is 82 (mol/mol) based on acetaldehyde and 85 (mol/mol) based on methyl ethyl ketone. The residence or reaction time in the micro reactor is ˜1 hour. Mass efficiency under these conditions for 40 hours of continuous operation is ˜64%. 
       Synthesis of 3M3P in a Micro Reactor Using Solid Acid Catalyst 
       [0030]    2.5 g of solid acid catalyst supported on polymeric resin is packed into a micro reactor of length 20 cm and inner channel diameter 5.3 mm. A mixture of acetaldehyde and methyl ethyl ketone with mole ratio of 1:3 is fed at 0.05 ml/min into the micro reactor which is maintained at 120° C. The 3M3P yield (analyzed by GC) is 75 (mol/mol) based on acetaldehyde and methyl ethyl ketone. The residence or reaction time in the micro reactor is ˜1 hour. Mass efficiency under these conditions for 40 hours of continuous operation is ˜57%. 
       Synthesis of 3M3P in a Micro Reactor Using Solid Acid Catalyst 
       [0031]    2.5 g of solid acid catalyst supported on clay is packed into a micro reactor of length 20 cm and inner channel diameter 5.3 mm. A mixture of acetaldehyde and methyl ethyl ketone with mole ratio of 1:3 is fed at 0.05 ml/min into the micro reactor which is maintained at 150° C. The 3M3P yield (analyzed by GC) is 50 (mol/mol) based on acetaldehyde and methyl ethyl ketone. The residence or reaction time in the micro reactor is 30 minutes. Mass efficiency under these conditions for 40 hours of continuous operation is ˜38%. 
       Synthesis of 3M3P in a Single CSTR Using Solid Acid Catalyst 
       [0032]    1.1 kg of solid acid catalyst supported on polymeric resin charged into CSTR containing methyl ethyl ketone. The reaction mass is heated to 65-70° C. and is run under autogenous pressure. A mixture of acetaldehyde to methyl ethyl ketone mole ratio of 1:6 is fed into the reactor and product mix is continuously removed from the reactor. The 3M3P yield (analyzed by GC) is 82 (mol/mol) based on acetaldehyde and 85 (mol/mol) based on methyl ethyl ketone. The residence or reaction time in the CSTR is ˜6 hours. Mass efficiency under these conditions for 600 hours of continuous operation is ˜41%. 
       Comparative Example of 3M3P in the Semi-Batch Reactor Using Conventional Liquid Catalyst 
       [0033]    Sulfuric acid and methyl ethyl ketone at 1:4 ratio is charged into a semi-batch reactor. The reactor is heated to 65-70° C. and is run under autogenous pressure. Acetaldehyde is fed into the reactor over 4 hours. Then the reaction mass is aged until reaction completion. The 3m3p yield (analyzed by GC) is 65 (mol/mol) based on acetaldehyde and 74 (mol/mol) based on methyl ethyl ketone. The total time for the process is ˜10 hours. Mass efficiency under these conditions is ˜26%.