Equilibrium Mixture Research Articles

Exploring Equilibria between Aluminium(I) and Aluminium(III): The Formation of Dihydroalanes, Masked Dialumenes and Aluminium(I) Species

AbstractThe design of new reductive routes to low oxidation state aluminium (Al) compounds offers the opportunity to better understand redox processes at the metal centre and develop reactivity accordingly. Here, a monomeric AlI compound acts as a stoichiometric reducing agent towards a series of AlIII dihydrides, leading to the formation of new low oxidation state species including symmetric and asymmetric dihydrodialanes, and a masked dialumene. These compounds are formed by a series of equilibrium processes involving AlI, AlII and AlIII species and product formation can be manipulated by fine‐tuning the reaction conditions. The transient formation of monomeric AlI compounds is proposed: this is shown to be energetically viable by computational (DFT) investigations and reactivity studies show support for the formation of AlI species. Importantly, despite the potential for the equilibrium mixtures to lead to ill‐defined reactivity, controlled reactivity of these low oxidation state species is observed.

Exploring Equilibria between Aluminium(I) and Aluminium(III): The Formation of Dihydroalanes, Masked Dialumenes and Aluminium(I) Species.

The design of new reductive routes to low oxidation state aluminium (Al) compounds offers the opportunity to better understand redox processes at the metal centre and develop reactivity accordingly. Here, a monomeric AlI compound acts as a stoichiometric reducing agent towards a series of AlIII dihydrides, leading to the formation of new low oxidation state species including symmetric and asymmetric dihydrodialanes, and a masked dialumene. These compounds are formed by a series of equilibrium processes involving AlI, AlII and AlIII species and product formation can be manipulated by fine‐tuning the reaction conditions. The transient formation of monomeric AlI compounds is proposed: this is shown to be energetically viable by computational (DFT) investigations and reactivity studies show support for the formation of AlI species. Importantly, despite the potential for the equilibrium mixtures to lead to ill‐defined reactivity, controlled reactivity of these low oxidation state species is observed.

Interception of enamine intermediates in reductive functionalization of lactams by sodium hydride: Synthesis of 2-cyano-3-iodo piperidines and pyrrolidines

Facile conversion of 2-piperidones and 2-pyrrolidones into 2-cyano-3-iodo piperidines or pyrrolidines has been accomplished by the sequence of 1) controlled hydride reduction of lactams using sodium hydride (NaH) in the presence of sodium iodide (NaI); 2) silylation of anionic hemiaminal intermediates to facilitate deoxygenation to form an equilibrium mixture of iminium cations and enamines-silanol pair; 3) interception of enamine intermediates by electrophilic iodination to generate iodonium ions; 4) nucleophilic cyanation of the resultant iminium cations. The overall transformation proceeded in highly diastereoselective fashion. The resultant 2-cyano-3-iodo piperidines were converted into 2-cyanotetrahydropyridines, which could be used for [2 + 2]-annulation or ring-expansion reactions with reactive benzyne or alkyne species, respectively.

The pattern of apolipoprotein A-I lysine carbamylation reflects its lipidation state and the chemical environment within human atherosclerotic aorta

Protein lysine carbamylation is an irreversible post-translational modification resulting in generation of homocitrulline (N-ε-carbamyllysine), which no longer possesses a charged ε-amino moiety. Two distinct pathways can promote protein carbamylation. One results from urea decomposition, forming an equilibrium mixture of cyanate (CNO−) and the reactive electrophile isocyanate. The second pathway involves myeloperoxidase (MPO)-catalyzed oxidation of thiocyanate (SCN−), yielding CNO− and isocyanate. Apolipoprotein A-I (apoA-I), the major protein constituent of high-density lipoprotein (HDL), is a known target for MPO-catalyzed modification in vivo, converting the cardioprotective lipoprotein into a proatherogenic and proapoptotic one. We hypothesized that monitoring site-specific carbamylation patterns of apoA-I recovered from human atherosclerotic aorta could provide insights into the chemical environment within the artery wall. To test this, we first mapped carbamyllysine obtained from in vitro carbamylation of apoA-I by both the urea-driven (nonenzymatic) and inflammatory-driven (enzymatic) pathways in lipid-poor and lipidated apoA-I (reconstituted HDL). Our results suggest that lysine residues within proximity of the known MPO-binding sites on HDL are preferentially targeted by the enzymatic (MPO) carbamylation pathway, whereas the nonenzymatic pathway leads to nearly uniform distribution of carbamylated lysine residues along the apoA-I polypeptide chain. Quantitative proteomic analyses of apoA-I from human aortic atheroma identified 16 of the 21 lysine residues as carbamylated and suggested that the majority of apoA-I carbamylation in vivo occurs on “lipid-poor” apoA-I forms via the nonenzymatic CNO− pathway. Monitoring patterns of apoA-I carbamylation recovered from arterial tissues can provide insights into both apoA-I structure and the chemical environment within human atheroma.

Stability of Rhodamine Lactone Cycle in Solutions: Chain–Ring Tautomerism, Acid–Base Equilibria, Interaction with Lewis Acids, and Fluorescence

The equilibrium between different tautomers that can be colored or colorless is an important feature for rhodamine dyes. Presently, this phenomenon is mostly discussed for rhodamine B. Herein, we studied the tautomerism and acid–base dissociation (HR+ ⇄ R + H+) of a set of rhodamines in organic media. Form R is an equilibrium mixture of the colored zwitterion R± and colorless lactone R0. Absorption spectra in 90 mass% aqueous acetone reflects the correlation between the dyes structure and the equilibrium constant, KT = [R0]/[R±]. Increase in the pKa value on transferring from water to organic solvents confirms the highly polar character of the R± tautomer. To reveal the role of the solvent nature, the tautomerism of an asymmetrical rhodamine, 2-(12-(diethyliminio)-2,3,5,6,7,12-hexahydro-1H-chromeno[2,3-f]pyrido[3,2,1-ij]quinolin-9-yl)benzoate, was examined in 14 media. This chain–ring tautomerism is an intramolecular acid–base reaction; the central carbon atom acts as a Lewis acid. The interaction with other Lewis acids, Li+, Ca2+, Mg2+, and La3+, results in rupture of lactone cycle. In polar solvents, lactones undergo photocleavage resulting in formation of highly fluorescent R±, whereas the blue fluorescence and abnormally high Stokes shift in low-polar media may be explained either by another photoreaction or by spiroconjugation and charge transfer in the exited state.

Kinetic insights into metaphosphoric acid-catalyzed water-crosslinking reactions in silane-grafted polyolefin system

Polyphosphoric acid (PPA)-catalyzed water-crosslinking reaction in silane-grafted polyolefin system was investigated. PPA exists as an equilibrium mixture comprising several phosphoric acid oligomers. Distribution of these oligomers depends on the phosphorus pentoxide content (%P2O5) of the PPA. Our results revealed that the PPA presented a higher catalytic activity than dibutyltin dilaurate, which is a catalyst most commonly used in polymer industry. The difference in catalytic activities of PPAs was primarily attributed to the distribution of the phosphoric acid oligomers in PPA; as the degree of highly condensed phosphoric acid oligomers increased, the catalytic activities of PPAs were enhanced. From the theoretical results, we concluded that the highly condensed oligomer could form the stable hydrate via hydrogen bond with a water molecule, leading to the enhanced catalytic activity of PPA for the hydrolysis reaction. This finding will add to the understanding in the development of the highly active and eco-friendly catalysts for the crosslinking reaction in polymer systems.

Synthesis of Azido‐Dienediols by Enzymatic Dioxygenation of Benzylazides: An Experimental and Theoretical Study

AbstractAllylic azides are versatile structural motifs in organic synthesis because the proximal double bond enables a [3,3]‐sigmatropic rearrangement, named as the Winstein rearrangement. In this work, an experimental and theoretical study on the double Winstein rearrangement occurring in azidodienediols derived from the biocatalytic dihydroxylation of substituted benzylazides is presented. Substrates bearing a methyl group at the ortho or meta position produced exclusively rearranged exo‐diendiols with the azide group anti to the diol moiety as the major constituent. In the case of para methyl substrates, an equilibrium mixture of rearranged and non‐rearranged products was observed, indicating that a full conversion to the exo‐dienediols is not possible within this substitution pattern. On the other hand, the presence of a chloro substituent in the diene moiety completely precluded the Winstein rearrangement to take place, giving rise exclusively to the traditional cis‐cyclohexadienediols. The observed results were analyzed to determine the mechanistic and kinetic aspects and scope limitations of the reaction as a synthetic tool.

EDTA analogues – unconventional inhibitors of gypsum precipitation

In the current study, EDTA (ethylenediamine-N,N,N′,N′-tetraacetic acid) and three further structurally related analogues with various spacing between the amino groups - PDTA (1,3-Diaminopropane-N,N,N′,N′-tetraacetic acid), HDTA (1,6-Diaminohexane-N,N,N′,N′-tetraacetic acid) and EGTA (Ethylene glycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid) - were tested as inhibitors of gypsum crystallization. The precipitation reactions were performed at high initial supersaturation and calcium ions were present in large excess relative to the amount of the inhibitor. This way the crystallization reaction was facilitated and the degree of supersaturation was not affected by the complexation. It was found that the structural differences between the inhibitors (i.e., the spacing between the amino groups) seem to exert only a secondary effect on the efficiency of the inhibition. The optimum pH for inhibition was found to be strongly dependent on the inhibitor used. The optimum conditions for inhibition were explained in terms of the concentration of the uncomplexed ligand, which is determined by the stability of the calcium complexes with 1:1 composition as well as with the extent of proton competition. The structure, composition and morphology of the precipitating solids isolated from equilibrium mixtures at the completion of the precipitation process were also studied and the crystal faces where adsorption is most likely to happen were identified.

Quantitative Characterization of Partitioning in Selection of DNA Aptamers for Protein Targets by Capillary Electrophoresis.

Partitioning of protein-DNA complexes from protein-unbound DNA is a key step in selection of DNA aptamers. Conceptually, the partitioning step is characterized by two parameters: transmittance for protein-bound DNA (binders) and transmittance for unbound DNA (nonbinders). Here, we present the first study to reveal how these transmittances depend on experimental conditions; such studies are pivotal to the effective planning and control of selection. Our focus was capillary electrophoresis (CE), which is a partitioning approach of high efficiency. By combining a theoretical model and experimental data, we evaluated the dependence of transmittances of binders and nonbinders on the molecular weight of the protein target in two modes of CE-based partitioning: nonequilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) and ideal-filter capillary electrophoresis (IFCE). Our data suggest that as the molecular weight of the protein target decreases: (i) the transmittance for binders remains close to unity in NECEEM but decreases drastically in IFCE and (ii) the transmittance for nonbinders increases orders of magnitude in NECEEM but remains relatively stable at a very low level in IFCE. To determine the optimal CE conditions for a given size of protein target, a balance between transmittances of binders and nonbinders must be reached; such a balance would ensure the collection of binders of sufficient purity and quantity. We conclude that, as a rule of thumb, IFCE is preferable for large-size protein targets while NECEEM should be the method of choice for small-size protein targets.

Solvent and Counteranion Assisted Dynamic Self-Assembly of Molecular Triangles and Tetrahedral Cages.

Self-assembly of naked PdII ions separately with newly designed bis(3-pyridyl)benzothiadiazole (L1) and bis(3-pyridyl)thiazolo[5,4-d]thiazole (L2) donors separately, under varying experimental conditions, yielded Pd4L8 (L= L1 or L2) tetrahedral cages and their homologous Pd3L6 (L= L1 or L2) double-walled triangular macrocycles. The resulting assemblies exhibited solvent, temperature, and counteranion induced dynamic equilibrium. Treatment of L1 with Pd(BF4)2 in acetonitrile (ACN) resulted in selective formation of a tetrahedral cage [Pd4(L1)8](BF4)8 (1a), which is in dynamic equilibrium with its homologue triangle [Pd3(L1)6](BF4)6 (2a) in dimethyl sulfoxide (DMSO). On the other hand, similar self-assembly using L2 instead of L1 yielded an equilibrium mixture of tetrahedral cage [Pd4(L2)8](BF4)8 (3a) and triangle [Pd3(L2)6](BF4)6 (4a) forms in both ACN and DMSO. The assembles were characterized by multinuclear NMR and ESI-MS while the structure of the tetrahedral cage (1a) was determined by single crystal X-ray diffraction. Existence of a dynamic equilibrium between the assemblies in solution has been investigated via variable temperature 1H NMR. The equilibrium constant K = ([Pd4L8]3/[Pd3L6]4) was calculated at each experimental temperature and fitted with the Van't Hoff equation to determine the standard enthalpy (ΔH°) and entropy (ΔS°) associated with the interconversion of the double-walled triangle to tetrahedral cage. The thermodynamic feasibility of structural interconversion was analyzed from the change in ΔG°, which suggests favorable conversion of Pd3L6 triangle to Pd4L8 cage at elevated temperature for L1 in DMSO and L2 in ACN. Interestingly, similar self-assembly reactions of L1 and L2 with Pd(NO3)2 instead of Pd(BF4)2 resulted in selective formation of a tetrahedral cage [Pd4(L1)8](NO3)8 (1b) and double-walled triangle [Pd3(L2)6](NO3)6 (4b), respectively.

The complicating role of pnictogen bond formation in the solution-phase and solid-state structures of the heavier pnictogen atranes.

The structure of the simplest stibatrane has been a mystery since it was first prepared in 1966. This study reports the preparation and characterization of two stibatranes from triethanolamine and triisopropanolamine. Solid state structures reveal macrocycles that contain favourable inter- and intramolecular pnictogen bonds. Solution studies, corroborated by DFT analysis, reveal an equilibrium mixture assigned to monomer and pnictogen-bonded dimer. This allowed for the determination of an enthalpy associated with pnictogen bond formation of -27 kJ mol-1, in line with the supramolecular nature of these interactions.

Cavitation characteristics and suppression research of refrigerant in capillary tube

Cavitation is easy to form and develop due to the large pressure drop during throttling in the refrigeration system. To effectively suppress the throttling cavitation phenomenon, an aerating method through bypass capillary is proposed. Based on the Homogeneous Equilibrium Mixture (HEM) model, the Schnerr-Sauer cavitation model and the Realizable k-ε turbulence model were adopted, and the throttling process in the capillary tube and transition tube was simulated by Fluent, and the pressure distribution and vapor volume fraction distribution in the capillary tube and transition tube were obtained for both original model and aerating model. Results show that after adopting the aerating technology, the vapor volume fraction at the capillary outlet is almost unchanged, while the vapor volume fraction in the transition tube is obviously increased, which indicates that the bubble collapsing phenomenon in the transition tube is weakened, and then realized the purpose of suppressing the cavitation effect.

An expedient metal-free cascade route to chromonyl diene scaffolds: thermodynamic vs. kinetic control.

A piperidine-catalyzed reaction between 3-formylchromone, 1,3-dimethyl barbituric acid, and ylidenemalononitriles is developed that offers chromonyl diene products in good yields. This cascade reaction proceeds via the insertion of ylidenemalononitriles between the Knoevenagel adduct obtained from 3-formylchromone and 1,3-dimethylbarbituric acid, where the pyrimidine-based enaminone is integrated with the chromone through the central diene linker. Similarly, introducing pyrimidine-based enaminone into the terminal part of the chromonyl diene scaffold gave an equilibrium mixture of rotational isomers in DMSO, which could be separated and isolated by crystallization. The computational analysis confirmed the role of barbiturate in directing the type of final chromonyl diene via kinetic or thermodynamic control. Moreover, computations revealed that one of these species, observed in the NMR spectra, is produced by the bond cleavage in the spirocyclic intermediate.

Anhydrous Hydrogen Iodide-Mediated Reductive Indolization of In Situ-Generated Cyclopropyl Hydrazones.

Fischer-type indolization of N-aryl-C-cyclopropyl hydrazones generated in situ followed by chemoselective reduction using tert-butyl iodide as an anhydrous HI generator was developed. This protocol provides indoles bearing carboxylic acid derivative units. A series of control experiments indicated the HI-mediated formation and reduction of spirocyclopropyl indolenines. Anhydrous HI functions as a Brønsted acid as well as a reducing agent, facilitating the successful conversion of unstable reaction intermediates and iodinated mixtures in equilibrium.

Using C-DFT to develop an e-ReaxFF force field for acetophenone radical anion.

Increased electricity usage over the past several decades has accelerated the need for efficient high-voltage power transmission with reliable insulating materials. Cross-linked polyethylene (XLPE) prepared via dicumyl peroxide (DCP) cross-linking has emerged as the insulator of choice for modern power cables. Although DCP cross-linking generates the desired XLPE product in high yield, other by-products are also produced. One such by-product, acetophenone, is particularly intriguing due to its aromaticity and positive electron affinity. In this work, constrained density functional theory (C-DFT) was utilized to develop an e-ReaxFF force field suitable for describing the acetophenone radical anion. Initial parameters were taken from the 2021 Akbarian e-ReaxFF force field, which was developed to describe XLPE chemistry. Then, C-DFT geometry optimizations were performed wherein an excess electron was constrained to each atom of acetophenone. The resulting C-DFT energy values for the various electronic positions were added to the e-ReaxFF training set. Next, an analogous set of structures was energy-minimized using e-ReaxFF, and equilibrium mixture compositions for the two methods were compared at multiple temperatures. Iterative fitting against C-DFT energy data was performed until satisfactory agreement was achieved. To test force field performance, molecular dynamics simulations were performed in e-ReaxFF and the resulting electronic distributions were qualitatively compared to unconstrained-DFT spin density data. By expanding our e-ReaxFF force field for XLPE, namely, adding the capability to describe acetophenone and its interactions with an excess electron, we move one step closer to a comprehensive molecular understanding of XLPE chemistry in a high-voltage power cable.

Configurational Lability at Tetrahedral Phosphorus: syn/anti‐Isomerization of a P‐Stereogenic Phosphiranium Cation by Intramolecular Epimerization at Phosphorus

AbstractTetrahedral main‐group compounds are normally configurationally stable, but P‐epimerization of the chiral phosphiranium cations syn‐ or anti‐[Mes*P(Me)CH2CHPh][OTf] (Mes*=2,4,6‐(t‐Bu)3C6H2) occurred under mild conditions at 60 °C in CD2Cl2, resulting in isomerization to give a syn‐enriched equilibrium mixture. Ion exchange with excess [NBu4][Δ‐TRISPHAT] (Δ‐TRISPHAT=Δ‐P(o‐C6Cl4O2)3) followed by chromatography on silica removed [NBu4][OTf] and gave mixtures of syn‐ and anti‐[Mes*P(Me)CH2CHPh][Δ‐TRISPHAT]⋅x[NBu4][Δ‐TRISPHAT]. NMR spectroscopy showed that isomerization proceeded with epimerization at P and retention at C. DFT calculations are consistent with a mechanism involving P‐C cleavage to yield a hyperconjugation‐stabilized carbocation, pyramidal inversion promoted by σ‐interaction of the P lone pair with the neighboring β‐carbocation, and ring closure with inversion of configuration at P.

Configurational Lability at Tetrahedral Phosphorus: syn/anti-Isomerization of a P-Stereogenic Phosphiranium Cation by Intramolecular Epimerization at Phosphorus.

Tetrahedral main-group compounds are normally configurationally stable, but P-epimerization of the chiral phosphiranium cations syn- or anti-[Mes*P(Me)CH2 CHPh][OTf] (Mes*=2,4,6-(t-Bu)3 C6 H2 ) occurred under mild conditions at 60 °C in CD2 Cl2 , resulting in isomerization to give a syn-enriched equilibrium mixture. Ion exchange with excess [NBu4 ][Δ-TRISPHAT] (Δ-TRISPHAT=Δ-P(o-C6 Cl4 O2 )3 ) followed by chromatography on silica removed [NBu4 ][OTf] and gave mixtures of syn- and anti-[Mes*P(Me)CH2 CHPh][Δ-TRISPHAT]⋅x[NBu4 ][Δ-TRISPHAT]. NMR spectroscopy showed that isomerization proceeded with epimerization at P and retention at C. DFT calculations are consistent with a mechanism involving P-C cleavage to yield a hyperconjugation-stabilized carbocation, pyramidal inversion promoted by σ-interaction of the P lone pair with the neighboring β-carbocation, and ring closure with inversion of configuration at P.

From μ3- to μ- agostic methyl coordination: NMR and solid state study of donor ligands uptake by the triangular cluster anion [Re3(μ-H)3(μ3-CH3)(CO)9

[Re3(μ-H)3(μ3-CH3)(CO)9]- (1) reacts with CO at 273 K to quantitatively give the [Re3(μ-H)3(μ-CH3)(CO)10]- derivative (2) through the conversion of the methyl group from triply to doubly-bridging coordination. An NMR isotopic perturbation experiment demonstrates the unsymmetrical bridging of the methyl group on the Re-Re bond, and a fast exchange, in solution, between one agostic and two terminal CH bonds. This is in agreement with X-Ray diffraction analysis performed on single crystals of 2. In solution at room temperature 2 decomposes with CH4 elimination, which is also observed when 2 is treated with CO affording the [Re3(μ-H)2(CO)12]- anion. The opening of the triple bridging methyl coordination in 1 occurs also with other different L ligands, yielding to the syn and anti isomers of unsymmetrically bridged methyl complexes of general formula [Re3(μ-H)3(μ-CH3)(CO)9(L)]- (L = MeCN, PMePh2, THF). The kinetic and thermodynamic stabilities of these isomers vary with the nucleophilicity of the ligand and the polarity of the solvent. In particular, the strong nucleophile PMePh2 affords the quantitative conversion of anion 1 into the thermodynamic syn isomer, which is stable in THF at room temperature for several days. On the contrary, weak nucleophiles, such as MeCN or THF, give equilibrium mixtures containing residual amounts of anion 1. The adducts with MeCN are stable in solution at room temperature for several hours, while decompose fastly in neat MeCN affording mainly the cluster anion [Re3(μ-H)4(CO)9(MeCN)]-. This suggests that cluster stabilization after methane evolution follows a different path with respect to that observed in the reaction of 1 with CO.

Interconversion of Molybdenum or Tungsten d2 Styrene Complexes with d0 1-Phenethylidene Analogues

Upon addition of 5-15% PhNMe2H+X- (X = B(3,5-(CF3)2C6H3)4 or B(C6F5)4) to Mo(NAr)(styrene)(OSiPh3)2 (Ar = N-2,6-i-Pr2C6H3) in C6D6 an equilibrium mixture of Mo(NAr)(styrene)(OSiPh3)2 and Mo(NAr)(CMePh)(OSiPh3)2 is formed over 36 h at 45 °C (Keq = 0.36). A plausible intermediate in the interconversion of the styrene and 1-phenethylidene complexes is the 1-phenethyl cation, [Mo(NAr)(CHMePh)(OSiPh3)2]+, which can be generated using [(Et2O)2H][B(C6F5)4] as the acid. The interconversion can be modeled as two equilibria involving protonation of Mo(NAr)(styrene)(OSiPh3)2 or Mo(NAr)(CMePh)(OSiPh3)2 and deprotonation of the α or β phenethyl carbon atom in [Mo(NAr)(CHMePh)(OSiPh3)2]+. The ratio of the rate of deprotonation of [Mo(NAr)(CHMePh)(OSiPh3)2]+ by PhNMe2 in the α position versus the β position is ∼10, or ∼30 per Hβ. The slow step is protonation of Mo(NAr)(styrene)(OSiPh3)2 (k1 = 0.158(4) L/(mol·min)). Proton sources such as (CF3)3COH or Ph3SiOH do not catalyze the interconversion of Mo(NAr)(styrene)(OSiPh3)2 and Mo(NAr)(CMePh)(OSiPh3)2, while the reaction of Mo(NAr)(styrene)(OSiPh3)2 with pyridinium salts generates only a trace (∼2%) of Mo(NAr)(CMePh)(OSiPh3)2 and forms a monopyridine adduct, [Mo(NAr)(CHMePh)(OSiPh3)2(py)]+ (two diastereomers). The structure of [Mo(NAr)(CHMePh)(OSiPh3)2]+ has been confirmed in an X-ray study; there is no structural indication that a β proton is activated through a CHβ interaction with the metal. W(NAr)(CMePh)(OSiPh3)2 is also converted into a mixture of W(NAr)(CMePh)(OSiPh3)2 and W(NAr)(styrene)(OSiPh3)2 (Keq = 0.47 at 45 °C in favor of the styrene complex) with 10% [PhNMe2H][B(C6F5)4] as the catalyst; the time required to reach equilibrium is approximately the same as in the Mo system.

Calculation of thermodynamic properties of mixtures in two-phase equilibrium

Thermodynamic properties of mixtures in vapor-liquid equilibrium (VLE) were studied. Thermodynamic properties of the methane-ethane mixtures in VLE were calculated with highly accurate Helmholtz free energy equation of state GERG-2008, simplified GERG-2008 and common cubic PR equation of state (EOS). Results show that GERG-2008 has high accuracy in VLE calculations. However, simplified GERG-2008 and PR-EOS both work unsatisfactorily in VLE calculations.