Classifications

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  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D233/00—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings
  • C07D233/04—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having one double bond between ring members or between a ring member and a non-ring member
  • C07D233/06—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having one double bond between ring members or between a ring member and a non-ring member with only hydrogen atoms or radicals containing only hydrogen and carbon atoms, directly attached to ring carbon atoms
  • C07D233/08—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having one double bond between ring members or between a ring member and a non-ring member with only hydrogen atoms or radicals containing only hydrogen and carbon atoms, directly attached to ring carbon atoms with alkyl radicals, containing more than four carbon atoms, directly attached to ring carbon atoms
  • C07D233/12—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having one double bond between ring members or between a ring member and a non-ring member with only hydrogen atoms or radicals containing only hydrogen and carbon atoms, directly attached to ring carbon atoms with alkyl radicals, containing more than four carbon atoms, directly attached to ring carbon atoms with substituted hydrocarbon radicals attached to ring nitrogen atoms
  • C07D233/16—Radicals substituted by nitrogen atoms
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C59/00—Compounds having carboxyl groups bound to acyclic carbon atoms and containing any of the groups OH, O—metal, —CHO, keto, ether, groups, groups, or groups
  • C07C59/235—Saturated compounds containing more than one carboxyl group
  • C07C59/245—Saturated compounds containing more than one carboxyl group containing hydroxy or O-metal groups
  • C07C59/285—Polyhydroxy dicarboxylic acids having five or more carbon atoms, e.g. saccharic acids
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  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C63/00—Compounds having carboxyl groups bound to a carbon atoms of six-membered aromatic rings
  • C07C63/307—Monocyclic tricarboxylic acids
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C67/00—Preparation of carboxylic acid esters
  • C07C67/03—Preparation of carboxylic acid esters by reacting an ester group with a hydroxy group
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  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C68/00—Preparation of esters of carbonic or haloformic acids
  • C07C68/06—Preparation of esters of carbonic or haloformic acids from organic carbonates
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D233/00—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings
  • C07D233/02—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having no double bonds between ring members or between ring members and non-ring members
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D233/00—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings
  • C07D233/04—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having one double bond between ring members or between a ring member and a non-ring member
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D233/00—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings
  • C07D233/04—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having one double bond between ring members or between a ring member and a non-ring member
  • C07D233/06—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having one double bond between ring members or between a ring member and a non-ring member with only hydrogen atoms or radicals containing only hydrogen and carbon atoms, directly attached to ring carbon atoms
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D233/00—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings
  • C07D233/54—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having two double bonds between ring members or between ring members and non-ring members
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D307/00—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom
  • C07D307/02—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom not condensed with other rings
  • C07D307/26—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom not condensed with other rings having one double bond between ring members or between a ring member and a non-ring member
  • C07D307/30—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom not condensed with other rings having one double bond between ring members or between a ring member and a non-ring member with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
  • C07D307/32—Oxygen atoms
  • C07D307/33—Oxygen atoms in position 2, the oxygen atom being in its keto or unsubstituted enol form
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
  • C07F1/00—Compounds containing elements of Groups 1 or 11 of the Periodic Table
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J11/00—Recovery or working-up of waste materials
  • C08J11/04—Recovery or working-up of waste materials of polymers
  • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J11/00—Recovery or working-up of waste materials
  • C08J11/04—Recovery or working-up of waste materials of polymers
  • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
  • C08J11/18—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J11/00—Recovery or working-up of waste materials
  • C08J11/04—Recovery or working-up of waste materials of polymers
  • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
  • C08J11/18—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material
  • C08J11/28—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material by treatment with organic compounds containing nitrogen, sulfur or phosphorus
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
  • C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/62—Plastics recycling; Rubber recycling

Definitions

• This invention relates generally to the depolymerization of polymers, and, more particularly relates to an organocatalytic method for depolymerizing polymers using nucleophilic reagents.
• the invention is applicable in numerous fields, including industrial chemistry and chemical waste disposal, plastics recycling, and manufacturing processes requiring a simple and convenient method for the degradation of polymers.
• the invention is directed to the aforementioned need in the art, and, as such, provides an efficient catalytic depolymerization reaction that employs mild conditions, wherein production of undesirable byproducts resulting from polymer degradation is minimized.
• the reaction can be carried out at temperatures of at most 80 °C, and, because a nonmetallic catalyst is preferably employed, the depolymerization 1 products, in a preferred embodiment, are substantially free of metal contaminants.
• the depolymerization reaction can be carried out at a temperature of at most 60 °C or even 30 °C or lower, i.e., at room temperature.
• a method for depolymerizing a polymer having a backbone containing electrophilic linkages, wherein the method involves contacting the polymer with a nucleophilic reagent and a catalyst at a temperature of less than 80 °C.
• An important application of this method is in the depolymerization of polyesters, including homopolymeric polyesters (in which all of the electrophilic linkages are ester linkages) and polyester copolymers (in which a fraction of the electrophilic linkages are ester linkages and the remainder of the electrophilic linkages are other than ester linkages).
• a method for depolymerizing a polymer having a backbone containing electrophilic linkages, wherein the method involves contacting the polymer with a nucleophilic reagent and a catalyst that yields depolymerization products that are substantially free of metal contaminants.
• the polymer may be, for example, a polyester, a polycarbonate, a polyurethane, or a related polymer, in either homopolymeric or copolymeric form, as indicated above.
• the catalyst used is a purely organic, nonmetallic catalyst.
• Preferred catalysts herein are carbene compounds, which act as nucleophilic catalysts, as well as precursors to carbene compounds, as will be discussed infra.
• carbenes are electronically neutral compounds containing a divalent carbon atom with only six electrons in its valence shell.
• Carbenes include, by way of example, cyclic diaminocarbenes, imidazol-2-ylidenes (e.g., l,3-dimesityl-imidazol-2-ylidene and 1,3- dimesityl-4,5-dihydroimidazol-2-ylidene), l,2,4-triazol-3-ylidenes, and l,3-thiazol-2- ylidenes; see Bourissou et al. (2000) Chem. Rev. 100:39-91.
• carbenes have now been extensively investigated, and have in fact been established as useful in many synthetically important reactions, there has been no disclosure or suggestion to use carbenes as catalysts in nucleophilic depolymerization reactions, i.e., reactions in which a polymer containing electrophilic linkages is depolymerized with a nucleophilic reagent in the presence of a carbene catalyst.
• Suitable catalysts for use herein thus include heteroatom-stabilized carbenes or precursors to such carbenes.
• the heteroatom-stabilized carbenes have the structure of formula (I)
• E 1 and E 2 are independently selected from N, NR E , O, P, PR E , and S, R E is hydrogen, heteroalkyl, or heteroaryl, x and y are independently zero, 1, or 2, and are selected
• E and E may be linked through a linking moiety that provides a
• R 1 and R 2 are independently selected from branched C 3 -C 30 hydrocarbyl, substituted branched C 3 -C 30 hydrocarbyl, heteroatom-containing branched C 4 -C 30 hydrocarbyl, substituted heteroatom-containing branched C 4 -C 30 hydrocarbyl, cyclic C 5 -C 0 hydrocarbyl, substituted cyclic C 5 -C 30 hydrocarbyl, heteroatom-containing cyclic C1-C 30 hydrocarbyl, and substituted heteroatom-containing cyclic C.-C 30 hydrocarbyl;
• L 1 and L 2 are linkers containing 1 to 6 spacer atoms, and are independently selected from heteroatoms, substituted heteroatoms, hydrocarbylene, substituted hydrocarbylene, heteroatom-containing hydrocarbylene, and substituted heteroatom- containing hydrocarbylene; and
• m and n are independently zero or 1, such that L and L are optional.
• Carbene precursors suitable as catalysts herein include tri-substituted methanes having the structure of formula (PI), metal adducts having the structure of formula (PII), and tetrasubstituted olefins having the structure (PHI)
• E 1 and E 2 are independently selected from N, NR E , O, P, PR E , and S, R E is hydrogen, heteroalkyl, or heteroaryl, x and y are independently zero, 1, or 2, and are selected
• E 1 9 1 to correspond to the valence state of E and E , respectively, and wherein when E and E are other than O or S, then E 1 and E 2 may be linked through a linking moiety that provides a
• R and R are independently selected from branched C3-C30 hydrocarbyl, substituted branched C 3 -C 3 o hydrocarbyl, heteroatom-containing branched C 4 -C 30 hydrocarbyl, substituted heteroatom-containing branched C 4 -C 30 hydrocarbyl, cyclic C 5 -C 30 hydrocarbyl, substituted cyclic C 5 -C30 hydrocarbyl, heteroatom-containing cyclic C1-C30 hydrocarbyl, and substituted heteroatom-containing cyclic C 1 -C30 hydrocarbyl;
• L 1 and L 2 are linkers containing 1 to 6 spacer atoms, and are independently selected from heteroatoms, substituted heteroatoms, hydrocarbylene, substituted hydrocarbylene, heteroatom-containing hydrocarbylene, and substituted heteroatom- containing hydrocarbylene;
• m and n are independently zero or 1 ;
• R 7 is selected from alkyl, heteroalkyl, aryl, heteroaryl, aralkyl, or heteroaralkyl, substituted with at least one electron- withdrawing substituent;
• M is a metal;
• Ln is a ligand
• j is the number of ligands bound to M.
• E 3 and E 4 are defined as for E 1 and E 2 ;
• v and w are defined as for x and y;
• R 8 and R 9 are defined as for R 1 and R 2 ;
• L 3 and L 4 are defined as for L 1 and L 2 ;
• h and k are defined as for m and n.
• the carbene precursors may be in the form of a salt, in which case the precursor is positively charged and associated with an anionic counterion, such as a halide ion (I, Br, Cl), a hexafluorophosphate anion, or the like.
• an anionic counterion such as a halide ion (I, Br, Cl), a hexafluorophosphate anion, or the like.
• Novel carbene precursors herein include compounds of formula (PI), those compounds of formula (PII) in which a heteroatom is directly bound to E 1 and/or E 2 , and those compounds of formula (PHI) in which a heteroatom is directly bound to at least one of E 1 , E 2 , E 3 , and E 4 , and may be in the form of a salt as noted above.
• the carbene catalyst used in conjunction with the present depolymerization reaction is an N-heterocyclic carbene having the structure of formula (II)
• R , R , L , L , m, and n are as defined above;
• L is a hydrocarbylene, substituted hydrocarbylene, heteroatom-containing hydrocarbylene, or substituted heteroatom-containing hydrocarbylene linker, wherein two or more substituents on adjacent atoms within L may be linked to form an additional cyclic group.
• polyesters including, by way of illustration and not limitation: PET; poly (butylene terephthalate) (PBT); poly(alkylene adipate)s and their copolymers; and poly( ⁇ - caprolactone).
• PET poly (butylene terephthalate)
• PBT poly(butylene terephthalate)
• alkylene adipate poly(alkylene adipate)s and their copolymers
• poly( ⁇ - caprolactone) poly( ⁇ - caprolactone).
• Figure 1 illustrates the organocatalytic depolymerization of PET in the presence of excess methanol using N-heterocyclic carbene catalyst, as evaluated in Example
• Figure 2 illustrates the organocatalytic depolymerization of PET in the presence of ethylene glycol using N-heterocyclic carbene catalyst, as evaluated in Example 6.
• alkyl refers to a linear, branched, or cyclic saturated hydrocarbon group typically although not necessarily containing 1 to about 20 carbon atoms, preferably 1 to about 12 carbon atoms, such as methyl, ethyl, «-propyl, isopropyl, «-butyl, isobutyl, t-butyl, octyl, decyl, and the like, as well as cycloalkyl groups such as cyclopentyl, cyclohexyl and the like. Generally, although again not necessarily, alkyl groups herein contain 1 to about 12 carbon atoms.
• lower alkyl intends an alkyl group of 1 to 6 carbon atoms
• cycloalkyl intends a cyclic alkyl group, typically having 4 to 8, preferably 5 to 7, carbon atoms.
• substituted alkyl refers to alkyl substituted with one or more substituent groups
• heteroatom-containing alkyl and “heteroalkyl” refer to alkyl in which at least one carbon atom is replaced with a heteroatom. If not otherwise indicated, the terms “alkyl” and “lower alkyl” include linear, branched, cyclic, unsubstituted, substituted, and/or heteroatom-containing alkyl and lower alkyl, respectively.
• alkylene refers to a difunctional linear, branched, or cyclic alkyl group, where "alkyl” is as defined above.
• alkenyl refers to a linear, branched, or cyclic hydrocarbon group of 2 to about 20 carbon atoms containing at least one double bond, such as ethenyl, «-propenyl, isopropenyl, «-butenyl, isobutenyl, octenyl, decenyl, tetradecenyl, hexadecenyl, eicosenyl, tetracosenyl, and the like.
• Preferred alkenyl groups herein contain 2 to about 12 carbon atoms.
• lower alkenyl intends an alkenyl group of 2 to 6 carbon atoms
• specific term “cycloalkenyl” intends a cyclic alkenyl group, preferably having 5 to 8 carbon atoms.
• substituted alkenyl refers to alkenyl substituted with one or more substituent groups
• heteroatom-containing alkenyl and “heteroalkenyl” refer to alkenyl in which at least one carbon atom is replaced with a heteroatom. If not otherwise indicated, the terms “alkenyl” and “lower alkenyl” include linear, branched, cyclic, unsubstituted, substituted, and/or heteroatom-containing alkenyl and lower alkenyl, respectively.
• alkenylene refers to a difunctional linear, branched, or cyclic alkenyl group, where "alkenyl” is as defined above.
• alkoxy refers to a group -O-alkyl wherein “alkyl” is as defined above
• alkylthio refers to a group -S-alkyl wherein “alkyl is as defined above.
• aryl refers to an aromatic substituent containing a single aromatic ring or multiple aromatic rings that are fused together, directly linked, or indirectly linked (such that the different aromatic rings are bound to a common group such as a methylene or ethylene moiety).
• Preferred aryl groups contain 5 to 20 carbon atoms and either one aromatic ring or 2 to 4 fused or linked aromatic rings, e.g., phenyl, naphthyl, biphenyl, and the like, with more preferred aryl groups containing 1 to 3 aromatic rings, and particularly preferred aryl groups containing 1 or 2 aromatic rings and 5 to 14 carbon atoms.
• "Substituted aryl” refers to an aryl moiety substituted with one or more substituent groups
• heteroatom-containing aryl and “heteroaryl” refer to aryl in which at least one carbon atom is replaced with a heteroatom.
• aromatic Unless otherwise indicated, the terms "aromatic,” “aryl,” and “arylene” include heteroaromatic, substituted aromatic, and substituted heteroaromatic species.
• aryloxy refers to a group -O-aryl wherein “aryl” is as defined above.
• alkaryl refers to an aryl group with at least one and typically 1 to 6 alkyl, preferably 1 to 3, alkyl substituents
• aralkyl refers to an alkyl group with an aryl substituent, wherein “aryl” and “alkyl” are as defined above.
• Alkaryl groups include, for example, p-methylphenyl, 2,4-dimethylphenyl, 2,4,6-trimethylphenyl, and the like.
• aralkyl refers to an alkyl group substituted with an aryl moiety, wherein "alkyl” and "aryl” are as defined above.
• alkaryloxy refers to a group -O-R wherein R is alkaryl, the term
• alkarylthio refers to a group -S-R wherein R is alkaryl
• aralkoxy refers to a group -O-R wherein R is aralkyl
• aralkylthio refers to a group -S-R wherein R is aralkyl.
• haloalkyl refers to an alkyl, alkenyl, or alkynyl group, respectively, in which at least one of the hydrogen atoms in the group has been replaced with a halogen atom.
• Hydrocarbyl refers to univalent hydrocarbyl radicals containing 1 to about
• hydrocarbyl intends a hydrocarbyl group of 1 to 6 carbon atoms
• hydrocarbylene intends a divalent hydrocarbyl moiety containing 1 to about 30 carbon atoms, preferably 1 to about 20 carbon atoms, most preferably 1 to about 12 carbon atoms, including linear, branched, cyclic, saturated and unsaturated species.
• lower hydrocarbylene intends a hydrocarbylene group of 1 to 6 carbon atoms. Unless otherwise indicated, the terms “hydrocarbyl” and “hydrocarbylene” are to be interpreted as including substituted and/or heteroatom-containing hydrocarbyl and hydrocarbylene moieties, respectively.
• heteroatom-containing as in a “heteroatom-containing alkyl group”
• heteroalkyl also termed a “heteroalkyl” group
• a heteroatom-containing aryl group also termed a “heteroaryl” group
• heteroalkyl refers to an alkyl substituent that is heteroatom-containing
• heterocyclic refers to a cyclic substituent that is heteroatom-containing
• heteroalkyl groups include alkoxyaryl, alkylsulfanyl-substituted alkyl, N-alkylated amino alkyl, and the like.
• heteroaryl substituents include pyrrolyl, pyrrolidinyl, pyridinyl, quinolinyl, indolyl, pyrimidinyl, imidazolyl, 1,2,4-triazolyl, tetrazolyl, etc., and examples of heteroatom-containing alicyclic groups are pyrrolidino, morpholino, piperazino, piperidino, etc.
• heterocyclic group or compound may or may not be aromatic, and further that “heterocycles” may be monocyclic, bicyclic, or polycyclic as described above with respect to the term “aryl.”
• substituted aryl and the like, as alluded to in some of the aforementioned definitions, is meant that in the hydrocarbyl, alkyl, aryl, or other moiety, at least one hydrogen atom bound to a carbon (or other) atom is replaced with a non-hydrogen substituent.
• substituents include, without limitation, functional groups such as halide, hydroxyl, sulfhydryl, -C 20 alkoxy, C 5 -C 20 aryloxy, C 2 -C 20 acyl (including C 2 -C 20 alkylcarbonyl (-CO-alkyl) and C 6 -C 2 o arylcarbonyl (-CO-aryl)), acyloxy (-O-acyl), C 2 -C 2 o alkoxycarbonyl (- (CO)-O-alkyl), C 6 -C 20 aryloxycarbonyl (-(CO)-O-aryl), halocarbonyl (-CO)-X where X is halo), C 2 -C 20 alkyl-carbonato (-O-(CO)-O-alkyl), C 6 -C 20 arylcarbonato (-O-(CO)-O-aryl), carboxy (-COOH), carboxylato (-COO-), carb, carb
• the aforementioned functional groups may, if a particular group permits, be further substituted with one or more additional functional groups or with one or more hydrocarbyl moieties such as those specifically enumerated above.
• the above-mentioned hydrocarbyl moieties may be further substituted with one or more functional groups or additional hydrocarbyl moieties such as those specifically enumerated.
• substantially free of a particular type of chemical compound is meant that a composition or product contains less 10 wt.% of that chemical compound, preferably less than 5 wt.%, more preferably less than 1 wt.%, and most preferably less than 0.1 wt.%.
• the depolymerization product herein is "substantially free of metal contaminants, including metals per se, metal salts, metallic complexes, metal alloys, and organometallic compounds.
• the invention features a method for depolymerizing a polymer having a backbone containing electrophilic linkages.
• the electrophilic linkages may be, for example, ester linkages (-(CO)-O-), carbonate linkages (-O-(CO)-O)-, urethane linkages
• the polymer undergoing depolymerization may be linear or branched, and may be a homopolymer or copolymer, the latter including random, block, multiblock, and alternating copolymers, terpolymers, and the like.
• Examples of polymers that can be depolymerized using the methodology of the invention include, without limitation:
• poly(alkylene terephthalates) such as fiber-grade PET (a homopolymer made from monoethylene glycol and terephthalic acid), bottle-grade PET (a copolymer made based on monoethylene glycol, terephthalic acid, and other comonomers such as isophthalic acid, cyclohexene dimethanol, etc.), poly (butylene terephthalate) (PBT), and poly(hexamethylene terephthalate);
• poly(alkylene adipates) such as poly(ethylene adipate), poly(l,4-butylene adipate), and poly(hexamethylene adipate);
• poly(alkylene suberates) such as poly(ethylene suberate);
• poly(alkylene sebacates) such as poly(ethylene sebacate);
• poly(alkylene isophthalates) such as poly(ethylene isophthalate);
• poly(alkylene 2,6-naphthalene-dicarboxylates) such as poly(ethylene 2,6- naphthalene-dicarboxylate);
• poly(alkylene sulfonyl-4,4'-dibenzoates) such as poly(ethylene sulfonyl-4,4'- dibenzoate);
• poly(p-phenylene alkylene dicarboxylates) such as poly(p-phenylene ethylene dicarboxylates);
• poly(tr ⁇ s*-l,4-cyclohexanediyl alkylene dicarboxylates) such as pol ⁇ (trans-
• poly(l ,4-cyclohexane-dimethylene alkylene dicarboxylates) such as poly(l ,4- cyclohexane-dimethylene ethylene dicarboxylate);
• poly([2.2.2]-bicyclooctane-l,4-dimethylene alkylene dicarboxylates) such as poly([2.2.2]-bicyclooctane-l ,4-dimethylene ethylene dicarboxylate);
• lactic acid polymers and copolymers such as (S)-polylactide, (R,S)-polylactide, poly(tetramethylglycolide), and poly(lactide-co-glycolide); and
• polyamides such as poly(p-phenylene terephthalamide) (Kevlar ® );
• poly(alkylene carbonates) such as poly(propylene carbonate);
• polyurethanes such as those available under the tradenames Baytec ® and
• Bayfil ® from Bayer Corporation
• Baydar from Bayer Corporation.
• nucleophilic reagents include monohydric alcohols, diols, polyols, thiols, primary amines, and the like, and may contain a single nucleophilic moiety or two or more nucleophilic moieties, e.g., hydroxyl, sulfhydryl, and/or amino groups.
• the nucleophilic reagent is selected to correspond to the particular electrophilic linkages in the polymer backbone, such that nucleophilic attack at the electrophilic linkage results in cleavage of the linkage.
• a polyester can be cleaved at the ester linkages within the polymer backbone using an alcohol, preferably a primary alcohol, most preferably a C 2 -
• C 4 monohydric alcohol such as ethanol, isopropanol, and t-butyl alcohol. It will be appreciated that such a reaction cleaves the ester linkages via a transesterification reaction, as will be illustrated infra.
• the preferred catalysts for the depolymerization reaction are carbenes and carbene precursors.
• Carbenes include, for instance, diarylcarbenes, cyclic diaminocarbenes, imidazol-2-ylidenes, l,2,4-triazol-3-ylidenes, l,3-thiazol-2-ylidenes, acyclic diaminocarbenes, acyclic aminooxycarbenes, acyclic aminothiocarbenes, cyclic diborylcarbenes, acyclic diborylcarbenes, phosphinosilylcarbenes, phosphinophosphoniocarbenes, sulfenyl-trifluoromethylcarbene, and sulfenyl- pentafluorothiocarbene.
• Preferred carbenes are heteroatom-stabilized carbenes and preferred carbene precursors are precursors to heteroatom-stabilized carbenes.
• heteroatom-stabilized carbenes suitable as depolymerization catalysts herein have the structure of formula (I)
• E 1 and E 2 are independently selected from N, NR E , O, P, PR E , and S, R E is hydrogen, heteroalkyl, or heteroaryl, and x and y are independently zero, 1, or 2, and are selected to correspond to the valence state of E 1 and E 2 , respectively.
• R E is hydrogen, heteroalkyl, or heteroaryl
• x and y are independently zero, 1, or 2, and are selected to correspond to the valence state of E 1 and E 2 , respectively.
• E and E may be linked through a linking moiety that provides a heterocyclic ring in which E 1 and E 2 are incorporated as heteroatoms.
• the heterocyclic ring may be aliphatic or aromatic, and may contain substituents and/or heteroatoms. Generally, such a cyclic group will contain 5 or 6 ring atoms.
• E 1 is O or S and x is 1;
• E 1 is N, x is 1, and E 1 is linked to E 2 ;
• E 1 is NR E , x is 1, and E 1 and E 2 are not linked; or
• E 1 is NR E , x is zero, and E 1 is linked to E 2 .
• R 1 and R 2 are independently selected from branched C 3 -C 30 hydrocarbyl, substituted branched C 3 -C 30 hydrocarbyl, heteroatom-containing branched C 4 -C 30 hydrocarbyl, substituted heteroatom-containing branched C 4 -C 30 hydrocarbyl, cyclic C 5 -C 30 hydrocarbyl, substituted cyclic C 5 -C 30 hydrocarbyl, heteroatom-containing cyclic C 1 -C30 hydrocarbyl, and substituted heteroatom-containing cyclic C!-C 30 hydrocarbyl.
• R 1 and R 2 are relatively bulky groups, particularly branched alkyl (including substituted and/or heteroatom-containing alkyl), aryl (including substituted aryl, heteroaryl, and substituted heteroaryl), alkaryl (including substituted and/or heteroatom-containing aralkyl), and alicyclic.
• branched alkyl including substituted and/or heteroatom-containing alkyl
• aryl including substituted aryl, heteroaryl, and substituted heteroaryl
• alkaryl including substituted and/or heteroatom-containing aralkyl
• Particular sterically bulky groups that are suitable as R 1 and R 2 are optionally substituted and/or heteroatom-containing C 3 -C 12 alkyl, tertiary C 4 -C 12 alkyl, C 5 -C 1 2 aryl, C 6 -C 18 alkaryl, and C 5 -C ⁇ 2 alicyclic, with C 5 - Ci 2 aryl and C ⁇ -Cn alkaryl particularly preferred.
• substituents are exemplified by phenyl optionally substituted with 1 to 3 substituents selected from lower alkyl, lower alkoxy, and halogen, and thus include, for example, p-methylphenyl, 2,6-dimethylphenyl, and 2,4,6- trimethylphenyl (mesityl).
• L 1 and L 2 are linkers containing 1 to 6 spacer atoms, and are independently selected from heteroatoms, substituted heteroatoms, hydrocarbylene, substituted hydrocarbylene, heteroatom-containing hydrocarbylene, and substituted heteroatom- containing hydrocarbylene; and m and n are independently zero or 1, meaning that each of L 1 and L 2 is optional.
• Preferred L 1 and L 2 moieties include, by way of example, alkylene, alkenylene, arylene, aralkylene, any of which may be heteroatom-containing and/or
• L and/or L may be a heteroatom such as O or S, or a substituted heteroatom such as NH, NR (where R is alkyl, aryl, other hydrocarbyl, etc.), or PR; and [00085]
• E 1 and E 2 are independently N or NR E and are not linked, such that the carbene is an N-heteroacyclic carbene.
• E 1 and E 2 are N, x and y are 1, and E 1 and E 2 are linked through a linking moiety such that the carbene is an N-heterocyclic carbene.
• N-heterocyclic carbenes suitable herein include, without limitation, compounds having the structure of formula (II)
• L is a hydrocarbylene, substituted hydrocarbylene, heteroatom- containing hydrocarbylene, or substituted heteroatom-containing hydrocarbylene linker, wherein two or more substituents on adjacent atoms within L may be linked to form an additional cyclic group.
• L is a hydrocarbylene, substituted hydrocarbylene, heteroatom- containing hydrocarbylene, or substituted heteroatom-containing hydrocarbylene linker, wherein two or more substituents on adjacent atoms within L may be linked to form an additional cyclic group.
• novel carbenes are those wherein a heteroatom is directly bound to E 1 and/or E 2 , and include, solely by way of example, carbenes of formula (I) wherein E 1 and/or E 2 is NR E and R E is a heteroalkyl or heteroaryl group such as an alkoxy, alkylthio, aryloxy, arylthio, aralkoxy, or aralkylthio moiety.
• Other such carbenes are those wherein x and/or y is at least 1, and L 1 and/or L 2 is heteroalkyl, heteroaryl, or the like, wherein the heteroatom within L 1 and/or L 2 is
• E 1 is NR E
• R E is alkoxy, substituted alkoxy, aryloxy, substituted aryloxy, aralkoxy, or substituted aralkoxy.
• a preferred subset of such carbenes are those wherein E 2 is N, x is zero, y is 1, and E 1 and E 2 are linked through a substituted or unsubstituted lower alkylene or lower alkenylene linkage.
• a more preferred subset of such carbenes are those wherein R E is
• suitable catalysts for the present depolymerization reaction are also precursors to carbenes, preferably precursors to N-heterocyclic and N- heteroacyclic carbenes.
• the precursor is a tri-substituted methane compound having the structure of formula (PI)
• E 1 , E 2 , x, y, R 1 , R 2 , L 1 , L 2 , m, and n are as defined for carbenes of structural formula (I), and wherein R 7 is selected from alkyl, heteroalkyl, aryl, heteroaryl, aralkyl, or heteroaralkyl, and is substituted with at least one electron- withdrawing substituent such as [00090] fluoro, fluoroalkyl (including perfluoroalkyl), chloro, nitro, acytyl.
• R 7 groups thus include p- nitrophenyl, 2,4-dinitrobenzyl, 1,1,2,2-tetrafluoroethyl, pentafluorophenyl, and the like.
• Catalysts of formula (PI) are new chemical entities. Representative syntheses of such compounds are described in Examples 13 and 14 herein.
• E 1 , E 2 , x, y, R 1 , R 2 , L 1 , L 2 , m, and n are as defined for carbenes of structural formula (I)
• M is a metal, e.g., gold, silver, other main group metals, or transition metals, with Ag, Cu, Ni, Co, and Fe generally preferred
• Ln is a ligand, generally an
• carbene precursors of formula (PII) can be synthesized from a carbene salt and a metal oxide; see, e.g., the synthesis described in detail in Example 12.
• Still another carbene precursor suitable as a depolymerization catalyst herein is a tetrasubstituted olefin having the structure of formula (PHI)
• E 1 , E 2 , x, y, R 1 , R 2 , L 1 , L 2 , m, and n are defined as for carbenes of structural formula (I); E 3 and E 4 are defined as for E 1 and E 2 ; v and w are defined as for x and y; R 8 and R 9 are defined as for R 1 and R 2 ; L 3 and L 4 are defined as for L 1 and L 2 ; and h and k are defined as for m and n.
• These olefins are readily formed from N,N-diaryl- and N,N- dialkyl-N-heterocyclic carbene salts and a strong base, typically an inorganic base such as a metal alkoxide.
• those catalyst precursors having the structure of formula (PII) or (PHI) in which a heteroatom is directly bound to an "E" moiety, i.e., to E 1 , E 2 , E 3 , and/or E 4 are new chemical entities.
• Preferred such precursors are those wherein the "E" moieties are NR E or linked N atoms, and the directly bound heteroatom within R E is oxygen or sulfur.
• the depolymerization reaction may be carried out in an inert atmosphere by dissolving a catalytically effective amount of the selected catalyst in a solvent, combining the polymer and the catalyst solution, and then adding the nucleophilic reagent.
• the polymer, the nucleophilic reagent, and the catalyst e.g., a carbene or a carbene precursor
• the catalyst e.g., a carbene or a carbene precursor
• the reaction mixture is agitated (e.g., stirred), and the progress of the reaction can be monitored by standard techniques, although visual inspection is generally sufficient, insofar as a transparent reaction mixture indicates that the polymer has degraded to an extent sufficient to allow all degradation products to go into solution.
• solvents that may be used in the polymerization reaction include organic, protic, or aqueous solvents that are inert under the depolymerization conditions, such as aromatic hydrocarbons, chlorinated hydrocarbons, ethers, aliphatic hydrocarbons, or mixtures thereof.
• Preferred solvents include toluene, methylene chloride, tetrahydrofuran, methyl t-butyl ether, Isopar, gasoline, and mixtures thereof.
• Supercritical fluids may also be used as solvents, with carbon dioxide representing one such solvent.
• Reaction temperatures are in the range of about 0 °C to about 100 °C , typically at most 80 °C, preferably 60 °C or lower, and most preferably 30 °C or less, and the reaction time will generally be in the range of about 12 to 24 hours.
• Pressures range from atmospheric to pressures typically used in conjunction with supercritical fluids, with the preferred pressure being atmospheric.
• THF tetrahydrofuran
• Examples 6 and 7 may be better understood by reference to the synthetic route used to prepare the PET and the possible depolymerization products obtained therefrom.
• the PET obtained in each example was prepared by synthesis according to a two-step transesterification process from dimethyl teraphthalate (DMT) and excess ethylene glycol (EO) in the presence of a metal alkanoate or acetate of calcium, zinc, manganese, titanium etc.
• the first step generates bis(hydroxy ethylene) teraphthalate (BHET) with the elimination of methanol and the excess EO.
• the BHET is heated, generally in the presence of a transesterification catalyst, to generate high polymer.
• This process is generally accomplished in a vented extruder to remove the polycondensate (EO) and generate the desired thermoformed object from a low viscosity precursor.
• the reaction takes place according to the following scheme:
• the different options for chemical recycling are regeneration of the base monomers (DMT and EG), glycolysis of PET back to BHET, decomposition of PET with propylene glycol and reaction of the degradation product with maleic anhydride to form "unsaturated polyesters" for fiber reinforced composites and decomposition with glycols, followed by reaction with dicarboxylic acids to produce polyols for urethane foam and elastomers.
• DMT and EG base monomers
• glycolysis of PET back to BHET decomposition of PET with propylene glycol
• reaction of the degradation product with maleic anhydride to form "unsaturated polyesters" for fiber reinforced composites and decomposition with glycols
• dicarboxylic acids to produce polyols for urethane foam and elastomers.
• PET powder was slurried in a THF/methanol solvent mixture.
• N-heterocyclic carbene (3-5 mol%), generated in situ, was added and within approximately 3 hours the PET went into solution. Anaylsis of the degradation product indicated quantitative consumption of PET and depolymerization via transesterification to EO and DMT. The DMT is readily recovered by recrystallization, while EO can be recovered by distillation ( Figure 1). Alternatively, and as established in Example 6, if EO is used as the alcohol (-50 to 200mol% excess) in the THF slurry, the depolymerization product is BHET, which is the most desirable and can be directly recycled via conventional methods to PET ( Figure 2).
• the N-heterocyclic carbene catalyst platform is extremely powerful, as the nature of the substituents has a pronounced effect on catalyst stability and activity towards different substrates.
• Example 10 [000114] l-Benzyloxy-3-benzyl-4,5-dimethylimidazolium bromide (4): Benzyl bromide (1.2 mL, ca. 10 mmol) was added via syringe to a refluxing suspension of 1 (1.0 g, 5.0 mmol) in dry benzene. A dark orange oil separated after refluxing for 6 h, and cooling to room temperature. The supernatant was decanted and the remaining oil was dried under vacuum overnight, which caused the product to solidify. The solid mass was crushed in pentane, filtered and dried under vacuum. Yield: 1.34 g (63%).
• Examples 13 and 14 describe preparation of additional carbene precursors from N,N-diaryl-substituted diamines as illustrated in the schemes below.

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