Linear Diesters Research Articles

Pushing Boundaries—Selective Cooling Crystallization as Tool for Selectivity Compensation and Product Purification Using a Recyclable Pd/Xantphos Catalyst in the Methoxycarbonylation of Methyl 10‐Undecenoate

AbstractThe homogeneously catalyzed methoxycarbonylation of methyl 10‐undecenoate allows for the synthesis of dimethyl 1,12‐dodecandioate as an interesting bio‐based drop‐in alternative for 1,12‐dodecandioic acid as polymer building block. Although the benchmark catalyst system of Pd/1,2‐bis((di‐tert‐butylphosphino)methyl)benzene and methane sulfonic acid is very active and selective, long‐term stability over a potential catalyst recycling is limited. In this work, modifications of this catalyst system in terms of protonation of the ligand and its replenishment during recycling are first investigated, proving that the reaction system is tolerant against minor changes. Finally, the commercially available ligand Xantphos, featuring higher stability but comes with a rather low l:b selectivity of 70:30, is applied. However, through the application of cooling crystallization, 58 g product (52% isolated yield) with an overall purity of 94% is obtained from the crude reaction solution without further treatment and a ∑TON of 4000 after ten reaction runs, while catalyst loss into the product is low.Practical Applications: Selective syntheses on the basis of renewable resources are a powerful tool for the production of value products in terms of green chemistry. Thereby, homogeneous transition metal catalysts are beneficial regarding selectivity. However, their separation and recycling are challenging due to their limited stability. The combination of a stable, commercially available catalyst with a selective purification method allows for isolation and purification from a crude reaction mixture without the need for any auxiliary or further purification steps. In this work, cooling crystallization is applied for subsequent purification of the linear diester dimethyl 1,12‐dodecandioate. Thereby, a lower selectivity from the methoxycarbonylation reaction using the stable Xantphos ligand is compensated and combined with recycling of the homogeneous catalyst. Thus, the development of an integrated process covering a stable catalyst system in the reaction, and high selectivity in the purification is the key toward an efficient homogeneous catalyst recycling.

Recyclable Vitrimers from Biogenic Poly(itaconate) Elastomers

We report a biobased vitrimer prepolymer that is synthesized from renewable itaconic acid and platform chemicals. The polyitaconate vinyl prepolymers are transferred into transesterification-based vitrimer materials after a curing step with two different cross-linkers. Bifunctional lactone cross-linkers enable faster curing kinetics compared to linear diesters at the same catalyst loading and reaction temperature. The rheological properties of the obtained vitrimer materials are easily controlled by the amount and nature of the cross-linker, as well as by the loading of the guanidine organocatalyst for transesterification. An increase in catalyst content leads to shorter relaxation times and lower apparent activation energies of the transesterification reactions. The materials show elastomeric properties and can easily be recycled. Up to this point, sustainable vitrimers have been largely limited to epoxy-based networks. Herein, we describe a multifunctional and sustainable vinyl monomer-based prepolymer system that can be integrated into polymers using facile free radical polymerization, whose vitrimer network properties can be conveniently adjusted.

Mechanism and Control of the Palladium‐Catalyzed Alkoxycarbonylation of Oleochemicals from Sustainable Sources

AbstractThe transformation of chemical production processes to a sustainable feedstock from renewable sources requires a careful assessment of current thermodynamic data, reaction mechanisms and kinetics. The Pd‐catalyzed alkoxycarbonylation of the long chain olefin methyl 10‐undecenoate (10‐UME) from castor oil with methanol yields the building blocks for a renewable polyamide. The mechanism for the complex multi‐step reaction cycle including active catalyst formation was elucidated. The experimental catalyst selectivity with 1,2‐bis(di‐tert‐butylphosphino‐methyl)benzene (1,2‐DTBPMB) as a ligand towards the desired linear diester product can be reproduced and rationalized. The mechanisms of possible side reactions and well as catalyst inhibition by carbon monoxide were also investigated. Solvent effects have an influence on reaction equilibria and transition barriers. These were considered in polar (methanol) and nonpolar (dodecane) media using implicit or mixed cluster/continuum solvation models when explicit solvent coordination was critical.

Full-Range Interconversion of Nanocrystals and Bulk Metal with a Highly Selective Molecular Catalyst

Catalysis by soluble metal complexes often encompasses the occurrence of nanoparticles and aggregated inactive states, but the role of the different species is unclear. For the generation of highly active catalysts, it is crucial to know the relations between active and inactive states and the reversibility of such interconversions. This is further complicated by the question of the true nature of the active species, in particular for reactions that use dispersed nanoparticles as a catalyst (precursor), which can interconvert to soluble species. We show that a molecular catalyst can interconnect completely up to the step of bulk metal in an isomerizing methoxycarbonylation converting an unsaturated fatty acid to a linear diester with a very characteristic reactivity. The active species, a diphosphine-coordinated Pd hydride, decomposes to the diprotonated diphosphine ligand and a Pd0 species that agglomerates and precipitates as Pd black. This reaction is completely reversible, as shown for several example...

Engineering Green Lubricants I: Optimizing Thermal and Flow Properties of Linear Diesters Derived from Vegetable Oils

The crystallization, melting, and flow behaviors of a series of linear aliphatic diesters (chemical formula (C17H33COO)2[CH2]n) derived from vegetable oil feedstock were investigated as a function of the methylene spacer units between the two ester moieties (given by the diol chain length, n). The crystallization and melting behaviors were determined by differential scanning calorimetry and flow behavior and viscosity by rotational rheometry. The results show that quantifiable structure–property relationships exist between the methylene spacer units of the molecules and their physical properties, which can be used to custom-design green materials with controlled phase composition and physical properties such as melting and viscosity suitable for use in applications such as lubricants, phase change energy storage, or waxes.

Promotion of selective pathways in isomerizing functionalization of plant oils by rigid framework substituents.

The 1,2-(CH2 P(1-adamantyl)2 )2 C6 H4 (dadpx) coordinated palladium complex [(dadpx)Pd(OTf)2 ] (1) is a catalyst precursor for the isomerizing methoxycarbonylation of the internal double bond of methyl oleate, with an unprecedented selectivity (96 %) for the linear diester 1,19-dimethyl nonadecanedioate. Rapid formation of the catalytically active solvent-coordinated hydride species [(dadpx)PdH(MeOH)](+) (3-MeOH) is evidenced by NMR spectroscopy, and further isolation and X-ray crystal structure analysis of [(dadpx)PdH(PPh3 )](+) (3-PPh3 ). DFT calculations of key steps of the catalytic cycle unravel methanolysis as the decisive step for enhanced selectivity and the influence of the rigid adamantyl framework on this step by destabilization of transition states of unselective pathways.

Saturated linear diesters from stearic acid as renewable phase change materials

Renewable phase change materials have been gaining traction as a ‘green’ solution to store excess energy and therefore improving energy use efficiency. A series of diesters were synthesized in a solvent-free, melt condensation synthesis from the fatty acid derivative stearoyl chloride, and dialcohols between 2 and 10 carbons in length (18-n-18 diesters where n=2, 4, 6, 8 and 10). Characterization by FTIR, 1H NMR, DSC and TGA reveals significant changes to the thermal performance and stability of these materials in the presence of contaminants. This may explain the poor performance previously reported in literature for this type of material. These diesters have phase change enthalpies between 230 and 247J/g, elucidated for the first time, and all melt above 65°C, with a single, narrow melting and crystallization point, contrary to what was previously reported.

Mechanistic Features of Isomerizing Alkoxycarbonylation of Methyl Oleate

The weakly coordinated triflate complex [(P^P)Pd(OTf)](+)(OTf)(-) (1) (P^P = 1,3-bis(di-tert-butylphosphino)propane) is a suitable reactive precursor for mechanistic studies of the isomerizing alkoxcarbonylation of methyl oleate. Addition of CH(3)OH or CD(3)OD to 1 forms the hydride species [(P^P)PdH(CH(3)OH)](+)(OTf)(-) (2-CH(3)OH) or the deuteride [(P^P)PdD(CD(3)OD)](+)(OTf)(-) (2(D)-CD(3)OD), respectively. Further reaction with pyridine cleanly affords the stable and isolable hydride [(P^P)PdH(pyridine)](+)(OTf)(-) (2-pyr). This complex yields the hydride fragment free of methanol by abstraction of pyridine with BF(3)·OEt(2), and thus provides an entry to mechanistic observations including intermediates reactive toward methanol. Exposure of methyl oleate (100 equiv) to 2(D)-CD(3)OD resulted in rapid isomerization to the thermodynamic isomer distribution, 94.3% of internal olefins, 5.5% of α,β-unsaturated ester and <0.2% of terminal olefin. Reaction of 2-pyr/BF(3)·OEt(2) with a stoichiometric amount of 1-(13)C-labeled 1-octene at -80 °C yields a 50:50 mixture of the linear alkyls [(P^P)Pd(13)CH(2)(CH(2))(6)CH(3)](+) and [(P^P)PdCH(2)(CH(2))(6)(13)CH(3)](+) (4a and 4b). Further reaction with (13)CO yields the linear acyls [(P^P)Pd(13)C(═O)(12/13)CH(2)(CH(2))(6)(12/13)CH(3)(L)](+) (5-L; L = solvent or (13)CO). Reaction of 2-pyr/BF(3)·OEt(2) with a stoichiometric amount of methyl oleate at -80 °C also resulted in fast isomerization to form a linear alkyl species [(P^P)PdCH(2)(CH(2))(16)C(═O)OCH(3)](+) (6) and a branched alkyl stabilized by coordination of the ester carbonyl group as a four membered chelate [(P^P)PdCH{(CH(2))(15)CH(3)}C(═O)OCH(3)](+) (7). Addition of carbon monoxide (2.5 equiv) at -80 °C resulted in insertion to form the linear acyl carbonyl [(P^P)PdC(═O)(CH(2))(17)C(═O)OCH(3)(CO)](+) (8-CO) and the five-membered chelate [(P^P)PdC(═O)CH{(CH(2))(15)CH(3)}C(═O)OCH(3)](+) (9). Exposure of 8-CO and 9 to (13)CO at -50 °C results in gradual incorporation of the (13)C label. Reversibility of 7 + CO ⇄ 9 is also evidenced by ΔG = -2.9 kcal mol(-1) and ΔG(‡) = 12.5 kcal mol(-1) from DFT studies. Addition of methanol at -80 °C results in methanolysis of 8-L (L = solvent) to form the linear diester, 1,19-dimethylnonadecandioate, whereas 9 does not react and no branched diester is observed. DFT yields a barrier for methanolysis of ΔG(‡) = 29.7 kcal mol(-1) for the linear (8) vs ΔG(‡) = 37.7 kcal mol(-1) for the branched species (9).

A New Synthesis of Fused Oxa‐ and Thiacrown Ethers–Thiophene/Furan Oligomers

AbstractWe have developed a two‐step sequence for preparing a series of macrocyclic oxa‐ and thiacrown ethers affixed to a thiophene/furan oligomer. The sequence involves the intramolecular MnIII‐promoted cyclization of linear diester precursors into 2,3‐dihydrofurans, whose dehydrogenation furnishes the title compounds. A preliminary NMR study has shown that one of them seems to specifically chelate Pb2+ cations.

Regioselective Cyclocarboxylation of Nonconjugated Dienes to Cyclic Keto Esters

The carboxylation of 1,5-hexadiene in the presence of (PPh3)2PdCl2 in 1-butanol at 100 °C gives butyl 2-(3-methyl-2-oxocyclopentyl)acetate (1) in good yield. Small amounts of linear diesters are also produced. A number of other olefins were also carboxylated to give mixtures of cyclic and linear products. Although carboxylation of monoolefins usually gives a mixture of regioisomers, cyclopentanone 1 is produced in >25:1 selectivity over the cyclohexanone regioisomer. Deuterium labeling and model studies were carried out in an attempt to explain the unusual regioselectivity observed. These studies suggest that although the reversible initial insertion of 1,5-hexadiene into Pd−H occurs with poor regioselectivity, the conversion of the regioisomer resulting from a 2,1-insertion to product is much faster than conversion of the other regioisomer to product.

Investigation on radical polymerization of 2-methylene-1,3-dioxolanes and 2-methylene-1,3-oxazolidines

The reaction of 2-methylene-1,3-dioxolanes and 2-methylene-1,3-oxazolidines with benzoyl peroxide (acceptor radical) and with N-ethylmaleimide (acceptor) was investigated. It was shown that benzoyl peroxide adds to monomers 1a and 1b, giving the corresponding linear diester amides 1a and 1b respectively. The oxazolidine 1c adds benzoyl peroxide, without ring opening, by addition to the exomethylene group. Together with N-ethylmaleimide the oxazolidines 1a or 1b produce deep-colored charge transfer complexes, resulting in high molecular poly-N-ethylmaleimides probably via a radical mechanism. The 1,3-dioxolanes 2a and 2b were radically polymerized to produce polyacetals by vinyl polymerization. 2c was polymerized to produce randomly containing acetal units and ester units. The mechanism of polymerization of 2e is complex, affording polymers of nonuniform character. 2-Methylene-4-phenyl-1,3-dioxolane polymerization leads to polyester as the main structure, and to a lesser degree polyacetal structures. The chemical structures of the polymers were confirmed by NMR spectra and elemental analysis.

New results of the free radical ring‐opening polymerization

AbstractThe reaction of 5‐ring ketene‐O, N‐acetals with peroxides was investigated. It was shown that benzoyl peroxide adds to monomers 5a and 5b by ring opening, giving the corresponding linear diester amides 6a and 6b, respectively. The ketene‐O,N‐acetal 5c adds benzoyl peroxide, without ring opening, by addition to the exomethylene group, giving the cyclic‐O,N‐acetal diester 6c. With phthaloyl peroxide cyclic esteramides 7 and oligomeric products are formed. The chemical structures of the addition products were confirmed by NMR spectra and elemental analysis. © 1994 John Wiley &amp; Sons, Inc.

Anionic ring-opening alternating copolymerization of a bicyclic bis(.gamma.-lactone) with an epoxide: a novel ring-opening polymerization of a monomer containing a .gamma.-lactone structure

Anionic ring-opening polymerization of 2,8-dioxa-1-methylbicyclo[3.3.0]octane-3,7-dione (1b) was carried out. 1b had no homopolymerizability but copolymerized with glycidyl phenyl ether (2) to selectively give the corresponding alternating copolymer. IR, 1 H NMR, and 13 C NMR spectra and products of the alkine hydrolysis of the obtained polymer strongly suggested an alternating copolymer structure consisting of two successive units derived from 1b and 2. The unit from 1b was a linear diester, probably formed by a successive double ring-opening polymerization with isomerization. The 1:1 copolymer composition was not changed by varying the monomer feed ratio in the range between 20:80 and 80:20

Peroxisomal effects of phthalate esters in primary cultures of rat hepatocytes

Primary rat hepatocyte cultures were used to compare the effects of some alkylphthalene esters on peroxisomal enzyme activities and morphology. Linear diesters from methyl to n-octyl and their constituent monoesters and alcohols were compared with the branched chain 2-ethylhexyl derivatives. Carnitine acetyltransferase activity was increased 9.5-fold by mono-2-ethylhexylphthalate (MEHP) and 5.5- and 7-fold by mono- n-pentyl- and mono- n-octylphthalate (MNOP), the 2 most potent of the linear monoesters. Activity of the specific peroxisomal marker, cyanide-insensitive palmitoyl-CoA oxidation decreased with time in control cultures. Whereas MEHP produced a time related increase over the initial level of palmitoyl-CoA oxidation, MNOP treatment only maintained the initial level of activity. The peroxisome proliferation-associated 80 000 mol. wt polypeptide was induced by MEHP but not MNOP. Similarly, MEHP produced increased numbers of peroxisomes, many without a nucleoid, whereas MNOP and mono- n-pentyllphthalate had no such effect. 2-Ethylhexanol was less potent as an inducer of carnitine acetyltransferase than MEHP and the linear alcohols had no effect on this enzyme. Studies with diesters indicated that induction of carnitine acetyltransferase required hydrolysis of the diester. It is concluded that the straight-chain phthalates studied have little effect on hepatic peroxisomes compared with the 2-ethylhexyl ester and that hepatocyte cultures provide a rapid means of comparing the peroxisomal effects of different phthalates.

Reduction of aliphatic bromoesters: Part II. Electrochemically generated carbanions and derivative carbanions—Their reactivity on electrophilic substrates

During the electrochemical reduction of α-bromoesters [CH 2(Br)CO 2Et(I), CH 3CH(Br)CO 2Et(II), (CH 3) 2CBrCO 2Et(III): RX] evidence was gained for the presence both of electrochemically generated, unbrominated carbanions [ECG: (CH 2CO 2Et) −, (CH 3CHCO 2Et) −, ((CH 3) 2CCO 2Et) −] and of derivative brominated carbanions [DC: (CHBrCO 2Et) −, (CH 3CBrCO 2Et) −. In fact, if the reduction was carried out in the presence of substrates containing an activated double bond (CH 2=CHCO 2Et, CH 2=CHCO 2Me), in some cases only cyclic diesters were obtained (RX=I), in other cases only linear diesters (RX=III), and in further cases both cyclic and linear (RX=II). The reactivity of the two kinds of carbanions (ECG and DC) towards electrophilic substrates such as β−, γ− and σ-bromoesters (R 1X) was studied. The yields of mixed diesters (RR 1) and of unsaturated diesters R 1−H were correlated with the concentration ratio of EGC and DC. Electrochemical measurements, such as polarography, coulometry and cyclic voltammetry, both at Hg and vitreous carbon electrodes, as well as gas-chromatographic analyses of the solutions after reduction, were employed to ascertain the reactivity of these carbanions towards the substrates.

Synthesis and degradation of polyurethanes containing phosphorus—Part II: Thermal degradation of poly(butylene phenylphosphonate) and poly(butylene phenylphosphonate) bis(phenylcarbamate)

The principal characteristics and products of thermal degradation of an oligomeric phosphorus containing polyol, poly(butylene phenylphosphonate) (I), and the same compound endcapped with phenyl isocyanate, poly(butylene phenylphosphonate) bis(phenylcarbamate) (II) were studied. (I) and (II) are precursors of a high molecular weight phosphorus containing polyurethane. The products from (I) were butadiene, tetrahydrofuran, dihydrofuran, water, the cyclic ester of phenylphosphonic acid and 1,4-butanediol, phenylphosphonic acid and a linear diester of phenylphosphonic acid and butane diol. The residue at 550°C incorporated pyrophosphonic acid links. All these products were also formed from (II) with the addition of carbon dioxide and aniline. The products and characteristics of the reactions have been accounted for in terms of acceptable processes.