PROPYLENE CARBONATE

PROPYLENE CARBONATE

CAS No. : 108-32-7
EC No. : 203-572-1

Propylene Carbonate

Propylene carbonate (often abbreviated PC) is an organic compound with the formula C4H6O3. It is a cyclic carbonate ester derived from propylene glycol. This colorless and odorless liquid is useful as a polar, aprotic solvent. Propylene carbonate is chiral, but is used as the racemic mixture in most contexts.

Preparation
Although many organic carbonates are produced using phosgene, propylene and ethylene carbonates are exceptions. They are mainly prepared by the carbonation of the epoxides[4] (epoxypropane, or propylene oxide here):
CH3CHCH2O + CO2 → CH3C2H3O2CO
The process is particularly attractive since the production of these epoxides consumes carbon dioxide. Thus this reaction is a good example of a green process. The corresponding reaction of 1,2-propanediol with phosgene is complex, yielding not only propylene carbonate but also oligomeric products.
Propylene carbonate can also be synthesized from urea and propylene glycol over zinc acetate.

Applications
As a solvent
Propylene carbonate is used as a polar, aprotic solvent. It has a high molecular dipole moment (4.9 D), considerably higher than those of acetone (2.91 D) and ethyl acetate (1.78 D). It is possible, for example, to obtain potassium, sodium, and other alkali metals by electrolysis of their chlorides and other salts dissolved in propylene carbonate.
Due to its high dielectric constant of 64, it is frequently used as a high-permittivity component of electrolytes in lithium batteries, usually together with a low-viscosity solvent (e.g. dimethoxyethane). Its high polarity allows it to create an effective solvation shell around lithium ions, thereby creating a conductive electrolyte. However, it is not used in lithium-ion batteries due to its destructive effect on graphite.
Propylene carbonate can also be found in some adhesives, paint strippers, and in cosmetics.[9] It is also used as plasticizer. Propylene carbonate is also used as a solvent for removal of CO2 from natural gas and synthesis gas where H2S is not also present. This use was developed by El Paso Natural Gas Company and Fluor Corporation in the 1950s for use at the Terrell County Gas Plant in West Texas, now owned by Occidental Petroleum.

Other
Propylene carbonate product may be converted to other carbonate esters by transesterification as well (see Carbonate ester#Carbonate transesterification).
In electrospray ionization mass spectrometry, propylene carbonate is doped into low surface tension solutions to increase analyte charging.
In Grignard reaction propylene carbonate (or most other carbonate esters) might be used to create tertiary alcohols.

Safety
Clinical studies indicate that propylene carbonate does not cause skin irritation or sensitization when used in cosmetic preparations, whereas moderate skin irritation is observed when used undiluted. No significant toxic effects were observed in rats fed propylene carbonate, exposed to the vapor, or exposed to the undiluted liquid. In the US, propylene carbonate is not regulated as a volatile organic compound (VOC) because it does not contribute significantly to the formation of smog and because its vapor is not known or suspected to cause cancer or other toxic effects.

General description
Propylene carbonate can be synthesized from propylene oxide and CO2. Optically active form of propylene carbonate can be prepared from the reaction between CO2 and racemic epoxides. Decomposition of propylene carbonate on the graphite electrode in lithium batteries results in the formation of a lithium intercalated compound.
Propylene carbonate is a cyclic carbonate that is commonly used as a solvent and as a reactive intermediate in organic synthesis. It is being considered as a potential electrochemical solvent due to its low vapor pressure, high dielectric constant and high chemical stability.

Application
Propylene carbonate may be used as a solvent for the asymmetric hydrogenation of nonfunctionalized olefins.

A dermal absorption study using living skin from human donors indicated that propylene carbonate had permeability constants of /average (standard deviation)/ 0.7 (0.4) g/sq m/hr and 0.6 (0.3) cu cm/sq m/hr.
IDENTIFICATION: Propylene carbonate is a clear, colorless liquid with a weak odor. It mixes easily with water. USE: Propylene carbonate is an important commercial chemical. It is used in personal care products like make-up and antiperspirant. It is an electrolyte in lithium batteries. It is used to make plastics more flexible and in natural gas purification. EXPOSURE: Workers that use propylene carbonate may breathe in mists or have direct skin contact. The general population may be exposed by skin contact with consumer products that contain propylene carbonate. If propylene carbonate is released to the environment, it will be broken down in air. It may be broken down by sun light. It will not move into air from soil and water surfaces. It is expected to move easily through soil. It will be broken down by microorganisms, and is not expected to build up in fish. RISK: Moderate skin and eye irritation have been reported in humans with direct contact to concentrated propylene carbonate. It may cause nausea, vomiting and diarrhea if ingested. Other data on the potential for propylene carbonate to produce toxic effects in humans were not available. No adverse effects were observed in laboratory animals fed high doses of propylene carbonate over time. Birth defects were not observed in offspring of laboratory animals exposed to propylene carbonate during pregnancy. Data on the potential for propylene carbonate to cause infertility or cancer in laboratory animals were not available. The potential for propylene carbonate to cause cancer in humans has not been assessed by the U.S. EPA IRIS program, the International Agency for Research on Cancer, or the U.S. National Toxicology Program 13th Report on Carcinogens.

Propylene carbonate is used in paints as a high-boiling solvent and film-forming auxiliary, especially in poly(vinyl fluoride) and poly(vinylidene fluoride) systems. It is also employed as an auxiliary in the pigment and dye industry.
Commercially produced primary cells have counterelectrodes made of manganese dioxide, iron sulfide, carbon fluoride (CFx), or graphite loaded with sulfur dioxide or thionyl chloride, and electrolytes consisting of lithium salts (LiAsF6, LiClO4, LiI, LiSO3CF3) dissolved in aprotic organic solvents such as propylene carbonate or dimethoxyethane.

The most important and versatile method for producing carbonates is the phosgenation of hydroxy compounds. ... Over the past 20 years, the trend is to manufacture carbonates without the use of phosgene. This method has the advantage of avoiding the use of highly toxic phosgene as well as considerably lower cost. The catalytic insertion of CO2 with oxiranes directly provides the five-membered cyclic carbonate. Oxiranes such as ethylene oxide and propylene oxide undergo insertion at ~150-175 °C under pressure with the aid of a quaternary ammonium salt catalyst to yield ethylene carbonate and propylene carbonate, respectively.

A noninvasive stability-indicating assay method utilizing Fourier transform-IR/attenuated total reflectance (FT-IR/ATR) spectrometry was used for the detection of propylene carbonate in pharmaceutical cream and ointment bases. The linearity of propylene carbonate response was studied by use of its C:O stretching frequency after spectral subtractions to remove interfering bands.

Propylene carbonate is an indirect food additive for use only as a component of adhesives.
Anonymous; Final Report on the Safety Assessment of Propylene Carbonate. J Am Coll Toxicol 6 (1): 23-51 (1987). The toxicologic properties of propylene carbonate were reviewed, with emphasis on the use of propylene carbonate as a cosmetic ingredient. Topics included chemical properties, physical properties, and cosmetic and noncosmetic uses of propylene carbonate. Propylene carbonate has been used as a polar additive for montmorillonite or bentonite clay gellants, widely used as bases for antiperspirants, lipstick, skin cleansers, eye shadow, mascara, hair conditioners, and other products.

IDENTIFICATION AND USE: PROPYLENE CARBONATE is a colorless liquid. Propylene carbonate is used in paints as a high-boiling solvent and film-forming auxiliary, especially in poly(vinyl fluoride) and poly(vinylidene fluoride) systems. It is also employed as an auxiliary in the pigment and dye industry. It is also used In lithium batteries, to decrease sulfur dioxide vapor pressure and increase electrolyte solubility and ionic conductivity. HUMAN EXPOSURE AND TOXICITY: In clinical studies, undiluted propylene carbonate caused moderate skin irritation, whereas 5 and 10% propylene carbonate in aqueous solution produced no skin irritation or sensitization. Cosmetic products or gels containing 0.54-20% propylene carbonate were essentially nonsensitizing and, at most, moderately irritating to human skin. Products formulated with 1.51-20% propylene carbonate were generally nonphototoxic and nonphotosensitizing. However, one product containing 20% propylene carbonate may have produced a low level photoallergic reaction in 1 of 25 subjects tested. ANIMAL STUDIES: The undiluted material was a slight irritant to the skin and a moderate irritant to the rabbit eye. In an acute dermal toxicity study, slight erythema was noted on the abraded skin of rabbits treated with 2 mg/kg of undiluted propylene carbonate; however, no lesions were observed at necropsy. Daily application of 10.5 or 17.5% propylene carbonate in physiological saline to the skin of rats for 1 month produced hyperkeratosis and an increase in the number of basal epithelial cells at the treatment site. Gavage studies in rats for 90 days at concentrations of up to 5,000 mg/kg/d did not induce any significant toxic effects. No systemic toxicity was reported in rats exposed to 100, 500, or 1,000 mg/cu m of aerosol propylene carbonate over a 90-day period. It was found in rat experiments that oral exposure at concentrations up to 5,000 mg/kg/d did not induce developmental toxicity; however, some maternal toxicity was observed in the high-dose group (decreased body weight gain and food consumption). Propylene carbonate was negative for mutagenicity in the Ames Salmonella/Microsome Liquid Pre-incubation Assay, and negative for genotoxicity in the Rat Hepatocyte Primary Culture/DNA Repair Test.

In clinical studies, undiluted propylene carbonate caused moderate skin irritation, whereas 5 and 10% propylene carbonate in aqueous solution produced no skin irritation or sensitization.
Cosmetic products or gels containing 0.54-20% propylene carbonate were essentially nonsensitizing and, at most, moderately irritating to human skin. Products formulated with 1.51-20% propylene carbonate were generally nonphototoxic and nonphotosensitizing. However, one product containing 20% propylene carbonate may have produced a low level photoallergic reaction in 1 of 25 subjects tested.
Acute Exposure/ In an acute dermal toxicity study, slight erythema was noted on the abraded skin of rabbits treated with 2 mg/kg of undiluted propylene carbonate; however, no lesions were observed at necropsy.

Subchronic or Prechronic Exposure/ Sprague-Dawley rats were given 1,000, 3,000, and 5,000 mg/kg/d of propylene carbonate (PC) by gavage for 90 days. A control group was given deionized water. In addition, a high-dose recovery group was included to determine the persistence and reversibility of any toxic effects. The recovery group was followed from day 90 of the study through day 118. Thirty rats per group (15 of each sex) and 20 rats in the recovery group were studied. An interim sacrifice of 10 rats per group, excluding the recovery group, was conducted on day 30. At sacrifice, all animals were necropsied and grossly examined. Blood sample were collected for clinical chemistry and hematology measurements, and an ophthalmological examination was performed. A full screen of potential target organ tissues was fixed for histopathological examination. No consistent dose-related findings were reported following necropsy or histopathological examination. Results of the test showed that PC at concentrations of up to 5,000 mg/kg/d did not induce any significant toxic effects.

Propylene carbonate's production and use as a plasticizer, in natural gas purification and as a chemical intermediate may result in its release to the environment through various waste streams. If released to air, a vapor pressure of 0.045 mm Hg at 25 °C indicates propylene carbonate will exist solely as a vapor in the atmosphere. Vapor-phase propylene carbonate will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction in air is estimated to be 4 days. Propylene carbonate contains chromophores that absorb at wavelengths >290 nm and, therefore, may be susceptible to direct photolysis by sunlight. If released to soil, propylene carbonate is expected to have very high mobility based upon an estimated Koc of 5. Volatilization from moist soil surfaces is not expected to be an important fate process based upon an estimated Henry's Law constant of 3.5X10-8 atm-cu m/mole. Propylene carbonate is not expected to volatilize from dry soil surfaces based upon its vapor pressure. Utilizing the Japanese MITI test, 79% of the theoretical BOD was reached in four weeks indicating that biodegradation is an important environmental fate process in soil and water. If released into water, propylene carbonate is not expected to adsorb to suspended solids and sediment based upon the estimated Koc. Volatilization from water surfaces is not expected to be an important fate process based upon this compound's estimated Henry's Law constant. An estimated BCF of 3 suggests the potential for bioconcentration in aquatic organisms is low. Hydrolysis may be an important environmental fate process since this compound contains functional groups that hydrolyze under environmental conditions (pH 5 to 9). Occupational exposure to propylene carbonate may occur through inhalation and dermal contact with this compound at workplaces where propylene carbonate is produced or used. Monitoring data indicate that the general population may be exposed to propylene carbonate via dermal contact with consumer products containing propylene carbonate. 

Propylene carbonate's production and use as a plasticizer(1), in natural gas purification(1), as a chemical intermediate(1), and in lithium batteries(2) may result in its release to the environment through various waste streams(SRC).
Based on a classification scheme(1), an estimated Koc value of 5(SRC), determined from a structure estimation method(2), indicates that propylene carbonate is expected to have very high mobility in soil(SRC). Volatilization of propylene carbonate from moist soil surfaces is not expected to be an important fate process(SRC) given an estimated Henry's Law constant of 3.5X10-8 atm-cu m/mole(SRC), based upon its vapor pressure, 0.045 mm Hg(3), and water solubility, 1.75X10+5 mg/L(4). Propylene carbonate is not expected to volatilize from dry soil surfaces(SRC) based upon its vapor pressure(3). A 79% of theoretical BOD using activated sludge in the Japanese MITI test(5) suggests that biodegradation is an important environmental fate process in soil(SRC).

Based on a classification scheme(1), an estimated Koc value of 5(SRC), determined from a structure estimation method(2), indicates that propylene carbonate is not expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is not expected(3) based upon an estimated Henry's Law constant of 3.5X10-8 atm-cu m/mole(SRC), derived from its vapor pressure, 0.045 mm Hg(4), and water solubility, 1.75X10+5 mg/L(5). Propylene carbonate may undergo hydrolysis in the environment due to functional groups that hydrolyze under environmental conditions(3). According to a classification scheme(6), an estimated BCF of 3(SRC), from its log Kow of -0.41(7) and a regression-derived equation(2), suggests the potential for bioconcentration in aquatic organisms is low(SRC). A 79% of theoretical BOD using activated sludge in the Japanese MITI test(8) suggests that biodegradation is an important environmental fate process in water(SRC).

According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), propylene carbonate, which has a vapor pressure of 0.045 mm Hg at 25 °C(2), is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase propylene carbonate is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC); the half-life for this reaction in air is estimated to be 4 days(SRC), calculated from its rate constant of 3.8X10-12 cu cm/molecule-sec at 25 °C(SRC) that was derived using a structure estimation method(3). Propylene carbonate contains chromophores that absorb at wavelengths >290 nm(4) and, therefore, may be susceptible to direct photolysis by sunlight(SRC).
Propylene carbonate, present at 100 mg/L, reached 79% of its theoretical BOD in 4 weeks using an activated sludge inoculum at 30 mg/L in the Japanese MITI test(1). Propylene carbonate was biodegraded 80% in a manostatic respirometer screening study using seed from a wastewater treatment plant during a 10 day incubation period(2).

The rate constant for the vapor-phase reaction of propylene carbonate with photochemically-produced hydroxyl radicals has been estimated as 3.8X10-12 cu cm/molecule-sec at 25 °C(SRC) using a structure estimation method(1). This corresponds to an atmospheric half-life of about 4 days at an atmospheric concentration of 5X10+5 hydroxyl radicals per cu cm(1). Propylene carbonate may undergo hydrolysis in the environment because it contains functional groups that hydrolyze under environmental conditions(2). Propylene carbonate contains chromophores that absorb at wavelengths >290 nm(2) and, therefore, may be susceptible to direct photolysis by sunlight(SRC).

An estimated BCF of 3 was calculated in fish for propylene carbonate(SRC), using a log Kow of -0.41(1) and a regression-derived equation(2). According to a classification scheme(3), this BCF suggests the potential for bioconcentration in aquatic organisms is low(SRC).
Using a structure estimation method based on molecular connectivity indices(1), the Koc of propylene carbonate can be estimated to be 5(SRC). According to a classification scheme(2), this estimated Koc value suggests that propylene carbonate is expected to have very high mobility in soil.

The Henry's Law constant for propylene carbonate is estimated as 3.5X10-8 atm-cu m/mole(SRC) derived from its vapor pressure, 0.045 mm Hg(1), and water solubility, 1.75X10+5 mg/L(2). This Henry's Law constant indicates that propylene carbonate is expected to be essentially nonvolatile from water and moist soil surfaces(3). Propylene carbonate is not expected to volatilize from dry soil surfaces(SRC) based upon its vapor pressure(1).
Propylene carbonate is listed as an ingredient found in approximately 50 personal care products including make-up and antiperspirant(1).
According to the 2012 TSCA Inventory Update Reporting data, 13 reporting facilities estimate the number of persons reasonably likely to be exposed in the manufacturing, processing, or use of propylene carbonate in the United States may be as low as <10 workers up to the range of 100-499 workers per plant; the data may be greatly underestimated due to confidential business information (CBI) or unknown values(1).

NIOSH (NOES Survey 1981-1983) has statistically estimated that 98,025 workers (19,471 of these are female) were potentially exposed to propylene carbonate in the US(1). Occupational exposure to propylene carbonate may occur through inhalation and dermal contact with this compound at workplaces where propylene carbonate is produced or used. Monitoring data indicate that the general population may be exposed to propylene carbonate via dermal contact with consumer products containing propylene carbonate(SRC).

Propylene carbonate (PC) has high stability against reduction as well as a high dielectric constant, and thereby PC or PC-based mixed solvent systems have been successfully employed as a solvent in primary lithium cells using metallic lithium as negative electrodes.
Poly(propylene carbonate) (PPC) is the product of alternating copolymerization of propylene oxide and CO2 (see Scheme 1.32). PPC is a biodegradable amorphous polymer because of the APC ester structure on its backbone [79]. High molecular weight PPC has been predominantly synthesized using zinc carboxylate catalysts to copolymerize propylene oxide and CO2. 

Basic Data
Selected physical properties of propylene carbonate are tabulated in Tables 14-5 and 14-6. Data on the solubility of various gases in propylene carbonate have been reported by several investigators (Dow Chemical Company, 1962; Schmack and Bittrich, 1966; Makranczy et al., 1965; Bucklin and Schendel, 1985). The equilibrium solubilities of hydrogen sulfide and carbon dioxide as a function of pressure are shown in Figure 14-4. Although there is some scattering of points, it is evident that the solubilities of both acid gases follow Henry's law up to a pressure of about 20 atm. The effect of temperature is shown for carbon dioxide and hydrogen in Figure 14-5. It is interesting to note that the solubility of hydrogen increases with increasing temperature.
No data appear to be available in the open literature on the specific effects of dissolved carbon dioxide, hydrogen sulfide, and other gases on the solubility of the individual components. However, the sketchy information available on gas mixtures containing carbon dioxide and methane indicates that at high partial pressures of methane the solubility of carbon dioxide is somewhat reduced, while the solubility of methane is appreciably increased by the presence of dissolved carbon dioxide (Dow Chemical, 1962; Makranczy et al., 1965). In view of the low solubility of hydrogen in propylene carbonate, it is reasonable to assume that its presence has no significant effect on the solubility of carbon dioxide or hydrogen sulfide. Solubilities of several gases, in terms of Bunsen coefficients (volume of gas at 0°C and 760 mm Hg per volume of liquid), are shown in Table 14-7. Additional solubility data are included in Table 14-4.

Fluor Solvent Process
Uses propylene carbonate as a physical solvent to remove CO2 and H2S
Propylene carbonate also removes C3+ hydrocarbons, COS, SO2, CS2, and H2O from the natural gas stream.
Thus, in one step the natural gas can be sweetened and dehydrated to pipeline quality.
Process is used for bulk removal of CO2 and is not used to treat to less than 3% CO2.

System requires special design features such as larger absorbers and higher circulation rates to obtain pipeline quality and usually is not economically applicable for these outlet requirements.
Propylene carbonate has the following characteristics, which make it suitable as a solvent for acid gas treating:
High degree of solubility for CO2 and other gases
Low heat of solution for CO2
Low vapor pressure at operating temperature
Low solubility for light hydrocarbons (C1, C2)
Chemically nonreactive toward all natural gas components
Low viscosity
Noncorrosive toward common metals
The above characteristics combine to yield a system that
Has low heat and pumping requirements.
Is relatively noncorrosive and
Suffers only minimal solvent losses, (less than 1 lbs/MMSCF)
Solvent temperatures below ambient are usually used to increase solvent gas capacity, and, therefore, decrease circulation rates.
Expansion of the rich solvent and flash gases through power turbines can provide the required refrigeration.
Alternately, auxiliary refrigeration may be included to further decrease circulation rates.

Blending Aliphatic Polycarbonates with Aliphatic Polyesters
A typical aliphatic polycarbonate is poly(propylene carbonate) (PPC). PPC has attracted much attention because of its environmental friendly nature such as utilizing the greenhouse gas waste and biodegradability (see Chapter 1: Introduction; Section 1.6.2 Poly(propylene carbonate)). However, PPC exhibits poor mechanical properties and thermal stability. To improve the plasticity of PPC and its processability, some blending systems containing PPCs have been studied.

This process, patented by the Fluor Corporation, utilizes anhydrous propylene carbonate as its solvent. Fig. 11 shows a typical flow diagram of Fluor solvent process. The lean solvent to the absorber is usually operated at temperature below ambient and some method of refrigerating the solvent is usually necessary. The removal of carbon dioxide from high-pressure gas streams is the ultimate objective of this process. The Fluor Process becomes competitive when the partial pressure of CO2 in the feed gas is above 75 psia (5 bar).

Propylene carbonate is the primary solvent in the Fluor process where it is used mainly for the removal of CO2 from the sour gas. Fluor shows its best performance when treating high pressure gas streams containing high concentrations of acid gas. Propylene carbonate is noncorrosive and nonaqueous. Because only physical absorption is involved, corrosion, erosion, and fouling problems should be minimal. Stainless or other alloys need not be required.

Similar to the water wash, the propylene carbonate enters the column from the top and contacts counter-currently the upward flowing sour gas. Rich solution from the bottom of the absorber flows through a hydraulic power recovery turbine to the high pressure flash drum operated at an intermediate pressure (300–000 psig), then flows to the low pressure flash drum operated at < 100 psig. Liquid from the flash drum flows to the stripper where it contacts (in counter-current flow) with stripping air to lower the CO2 concentration in the solvent to the minimum possible level. In some cases sufficient regeneration of the CO2 rich propylene carbonate solvent can be accomplished by merely flashing the rich solution to or near atmospheric pressure without the need for the stripping air.

Description 
Propylene carbonate (PC) is a VOC-exempt* clear polar solvent having high boiling and flash points, a low order of toxicity and a mild ether-like odor. It is stable under most conditions and is not hydroscopic or corrosive. is particularly well suited for applications requiring a water white product or high purity. Examples would be cosmetics, electronics or where recycling of spent material will occur.
Product
Identification
Chemical Name
Chemical Family
Other Names
Chemical Formula
Dioxolanone
Organic Carbonate
4-methyl-1
3-dioxolan-2-one
C4H6O3
Propylene carbonate is a cyclic carbonate that reacts with amines to form carbamates, undergoes hydroxy alkylation and transesterification. It can be used as an isocyanate and unsaturated polyester resin cleanup solvent, viscosity reducer in coatings, CO2 extraction solvent, electrolyte in lithium batteries, polar additive for clay gellants, foundry binder catalyst, and textile dye carrier and cleaner.

Propylene carbonate is stable under normal storage conditions. However, in the presence of an acid, base, metal oxide or salt, propylene carbonate may decompose liberating CO2. These materials will also decrease thermal stability. In an aqueous solution, the decomposition products would be propylene glycol and CO2. Either situation could potentially lead to pressure buildup in closed containers, which may result in the container rupturing. It is therefore suggested that all such mixtures be tested for shelf life stability.

The Suzuki–Miyaura reaction is one of the most used transformations in drug research. Thus making this reaction more sustainable is of considerable current interest. Here we show that propylene carbonate (PC) can be used as a solvent for the Suzuki–Miyaura reaction. PC is one of the greenest solvents since it is synthesized under green conditions by the use of carbon dioxide in the air. All reactions proceeded well and good or excellent yields were observed for the biaryl products. Nonetheless in the case of pyridazinones, 2-hydroxypropyl- chain containing side-products were observed. Importantly, this fact allowed the isolation of several novel compounds which were generated under prominently green conditions.

The Suzuki–Miyaura reaction is the palladium-catalysed cross-coupling reaction of organoboranes with organic halides, triflates or perfluorinated sulfonates and proceeds with high stereo- and regioselectivity.1 Recent developments with respect to catalysts and methods have broadened the possible applications enormously, that is, the scope of the reaction partners is not restricted to aryls, but includes alkyls, alkenyls and alkynyls too.2,3 Usually, the boronic acid is activated by a base and the reaction is run in a polar aprotic solvent, ionic liquid or water.4 At room temperature, the reaction takes place with low yield; therefore, the use of special catalyst might be required5 or increased temperature and pressure are needed.6

Several efforts were taken to carry out Suzuki–Miyaura and further cross coupling reactions under green and sustainable conditions.7–20 Reeves and co-workers studied the effects of propylene carbonate (PC) and various polar and nonpolar solvents on palladium-catalyzed Suzuki–Miyaura coupling of chloroaryl triflates. They highlighted the similar selectivity of the solvents and the synthetic value of it.21 PC was used with no loss of enantioselectivity in an iridium- and rhodium-phosphite/oxazoline catalytic system catalysed asymmetric hydrogenation of functionalized cyclic β-enamines,22 and in cathodic reduction of aryl halides, considered for its high dielectric permittivity.23 PC was used in an aminophosphine palladium pincer-catalyzed carbonylative Sonogashira reaction with 10−4 mol%, while the Suzuki–Miyaura cross-coupling reaction was carried out at 10−6 mol%.24 Nonetheless, Pd/C catalysed phenoxycarbonylation of aryl iodide was carried out using N-formylsaccharin as a CO surrogate in PC as a sustainable solvent.25 Heck reaction was carried in cyclic carbonates as greener solvents, offering effective alternative to traditionally used dipolar aprotic solvents.26 Nanostructured palladium clusters catalysed also Heck reaction and were stable in propylene carbonate even at 140–155 °C.27

A recent article28 reports that nanoparticles formed from inexpensive FeCl3 naturally contains parts-per-million (ppm) levels of Pd and can catalyse Suzuki–Miyaura reaction in water. There is also a nickel-catalysed, but base-free Suzuki–Miyaura reaction of carboxylic acid fluorides29 and we can found a heterogeneous and ligand-free Suzuki–Miyaura reaction accomplished with the use of a palladium catalyst supported on a double-structure amphiphilic polymer composite.30 Interestingly, a heterogeneous single-atom palladium preparation anchored on exfoliated graphitic carbon nitride was used in a homogenous systems for Suzuki coupling.31 In 2018, researchers from the Pfizer company published an article32 about the use of an automated flow-based synthesis platform, that integrates both rapid nanomole-scale reaction screening and micromole-scale synthesis in Suzuki–Miyaura coupling at elevated temperature. The continuous-flow technology was utilized for several cross coupling reactions too.

Small and homogenous palladium particules (4–6 nm) were introduced in multi-walled carbon nanotubes used for selective hydrogenation of cinnamaldehyde,39 while palladium–nickel and palladium–silver nanoparticles supported on carbon exhibited high activity toward the glycerol electrooxidation in alkaline medium.40 Glycerol electrooxidation was achieved also on active self-supported Pd1Snx nanoparticles, when the modification of palladium by tin species led to suppress the dissociative adsorption process of glycerol.41 de Souza and co-workers published an article describing the resolution of amines.42 They immobilized lipase on functionalized Pd–SiO2 nanoparticles and this new simplified Pd-lipase hybrid biocatalysts showed immobilization efficiencies of around 80% when containing 1–10% of Pd. Numerous studies focused on the bacterial synthesis of Pd-nanoparticles (bio-Pd NPs) by uptake of Pd(ii) ions and their enzymatically-mediated reduction to Pd(0). One of them deal with microwave-injured Pd(ii)-treated cells (and non MW-treated controls) which were contacted with H2 to promote Pd(ii) reduction.
The Suzuki–Miyaura reaction was investigated under traditional oil-heating and microwave conditions using propylene carbonate (PC, 1,Scheme 1) as a green solvent. Three heterocyclic substrates: 2-iodopyridine (2), 4-iodopyridine (3) and 6-iodopyridazin-3(2H)-one (4), were used as coupling partners.

What Is It?
Propylene Carbonate is a clear, odorless solvent with a high boiling point. In cosmetics and personal care products, Propylene Carbonate is used in the formulation of makeup, primarily lipstick, eye shadow, and mascara, as well as in skin cleansing products.

Why is it used in cosmetics and personal care products?
Propylene Carbonate is used to dissolve other substances and is frequently used with clay gellants (such as montmorillonite or bentonite).

The use of Propylene carbonate allows to increase the temperature of the Suzuki reaction (usually lower or around 100 °C) and meantime, decrease the reaction time. Propylene carbonate (1) is among the green solvents44 in the GlaxoSmithKline solvent sustainability guide. It is known as a carbon-dioxide neutral solvent45 and can be obtained from propylene oxide and carbon dioxide.46 The cycloaddition of CO2 and propylene oxide catalysed by NiO-modified TiO2 nanoparticles with tetrabutylammonium iodide used as co-catalyst, under solvent free conditions was achieved in excellent yield47 and the green synthesis of Propylene carbonate was also published.48 In this last paper, the authors used microwave in order to intensify the lipase catalysed transesterification of 1,2-propanediol with dimethyl carbonate in non-aqueous media and observed that microwave irradiation not only increase the reaction rate, but also improved the thermal stability of the enzyme. This “green” solvent is a good electrolyte during lithium-ion intercalation and de-intercalation in lattice contraction/recovery of W18O49 nanowires used as electrochromic actuator.49 The molecular dynamics of lithium and Propylene carbonate in lithium–metal batteries was studied in order to explore the next-generation high-energy lithium–sulfur and lithium–air batteries.50 Propylene carbonate can increase optoelectronic properties, photovoltaic parameters and environmental stability of efficient perovskite solar cells against humidity, light and heat.

Herein we show the use of Propylene carbonate as prominent green solvent for the Suzuki–Miyaura reaction. We observed the limitation of Propylene carbonate as solvent, since nucleophiles can open the ring and 2-hydroxypropylation occurs. Nonetheless, this side-reaction allowed us the isolation of several novel compounds, thus, Propylene carbonate can be treated as a prominently green 2-hydroxypropylation reagent.

Results and discussion
As mentioned, two different heating ways (oil bath and MW irradiation) were applied in the Suzuki–Miyaura reaction with 2-iodopyridine (2), 4-iodopyridine (3) and 6-iodopyridazin-3(2H)-one (4) as starting materials. The first two are commercial products, while the last one was synthesized in two steps from commercially available 3,6-dichloropyridazine. The chlorine atoms were substituted with iodine52,53 in the presence of aq. HI followed by alkaline hydrolysis of the formed 3,6-diiodopyridazine54,55 in order to obtain 6-iodopyridazin-3(2H)-on (4). The heterocyclic substrates were reacted with four different boronic acids (Scheme 2), namely, 2-naphthylboronic acid (5), phenylboronic acid (6), 4-biphenylboronic acid (7) and 4-fluorophenylboronic acid (8).

Propylene carbonate (PC) is a polar aprotic substance with very similar physicochemical characteristics to the organic solvents traditionally used for organic synthesis, such as acetonitrile and acetone. Therefore, Propylene carbonate is beginning to be used as a “green” sustainable alternative solvent for chemical transformations. Propylene carbonate is a low toxicity, non-corrosive colourless liquid with a high boiling point and low vapour pressure. It is biodegradable and economical, allowing its large-scale use. Propylene carbonate can be prepared by a reaction between propylene epoxide and carbon dioxide with 100% atomic economy. The easy preparation of propylene epoxide and the use of an available, abundant, economical, and renewable source of carbon, such as CO2, make this process one of the best routes for the synthesis of Propylene carbonate. Therefore, we present in this review numerous catalytic systems that have been studied to improve the efficiency of this reaction. Certain interesting examples of reactions using Propylene carbonate are found in the literature, of which we discuss asymmetric hydrogenation, hydrosilylation, asymmetric aldol reactions, the asymmetric synthesis of cyanohydrins, the synthesis of heterocyclic compounds, such as bisindole and tetrahydroquinoline, the hydroacylation of alkynes, α-hydrazination reactions, oxidations, the Sonogashira reaction, allylic alkylation and asymmetric amination, the Heck reaction, enzymatic kinetic resolution, and isomerisation-hydroformylation reactions.

Synonyms:
PC; Ethylene carbonate; Trimethylene carbonate; 4-Methyl-1,3-dioxolan-2-one; (R,S)-4-Methyl-1,3-dioxolan-2-one; Cyclic propylene carbonate; Carbonic acid propylene ester; Cyclic 1,2-propylene carbonate; Propylene glycol cyclic carbonate; 1,2-Propanediol carbonate; 4-Methyl-2-oxo-1,3-dioxolane; Arconate 5000; Texacar PC; 1,2-Propanediol cyclic carbonate; 4-Methyl-1,3-dioxolan-2-one; PROPYLENE CARBONATE; 108-32-7; 4-Methyl-1,3-dioxolan-2-one; 1,2-Propylene carbonate; 1,2-Propanediol cyclic carbonate; 1,3-Dioxolan-2-one, 4-methyl-; Cyclic propylene carbonate; Texacar PC; Arconate 5000; 1,2-Propanediol carbonate; 1-Methylethylene carbonate; Cyclic 1,2-propylene carbonate; Dipropylene carbonate; 1,2-Propanediyl carbonate; 4-Methyldioxalone-2; Propylene Carbonate; Propylene glycol cyclic carbonate; Cyclic methylethylene carbonate; 4-Methyl-2-oxo-1,3-dioxolane; Carbonic acid, propylene ester; Carbonic acid, cyclic propylene ester; NSC 11784; Propylenester kyseliny uhlicite; Carbonic acid cyclic methylethylene ester; HSDB 6806; EINECS 203-572-1; Propylene carbonate [NF]; Carbonic acid, cyclic propylene ether; Propylenester kyseliny uhlicite [Czech]; BRN 0107913; AI3-19724; 4-methyl-1,3-dioxolane-2-one; Propylene carbonate (NF); Propylene carbonate, 99.5%; CAS-108-32-7; PC-HP; Propylene carbonate, 99.5%, anhydrous, AcroSeal(R); Propylene carbonate [USAN]; butylhexanoate; Solvenon PC; propylen carbonate; MFCD00005385; Carbonic acid propylene; Arconate propylene carbonate; EC 203-572-1; SCHEMBL15309; 5-19-04-00021 (Beilstein Handbook Reference); 2-Oxo-4-methyl-1,3-dioxolane; 1,2-PDC; 4-methyl-[1,3]dioxolan-2-one; Propylene Carbonate (Industrial Grade); Propylene carbonate, anhydrous, 99.7%; Propylene carbonate, for HPLC, 99.7%; Propylene carbonate, ReagentPlus(R), 99%; 4-Methyl-1,3-dioxolan-2-one 108-32-7; Cyclic 1,2-propylene carbonate; Propylene glycol cyclic carbonate; 1,2-Propanediol carbonate; 4-Methyl-2-oxo-1,3-dioxolane; Arconate 5000; Texacar PC; 1,2-Propanediol cyclic carbonate; 4-Methyl-1,3-dioxolan-2-one; PROPYLENE CARBONATE; 108-32-7; 4-Methyl-1,3-dioxolan-2-one; 1,2-Propylene carbonate; 1,2-Propanediol cyclic carbonate; 1,3-Dioxolan-2-one, 4-methyl-; Cyclic propylene carbonate; Texacar PC; Arconate 5000; 1,2-Propanediol carbonate; 1-Methylethylene carbonate; Cyclic 1,2-propylene carbonate; Dipropylene carbonate; 1,2-Propanediyl carbonate; 4-Methyldioxalone-2; Propylene Carbonate; Propylene glycol cyclic carbonate; Cyclic methylethylene carbonate; 4-Methyl-2-oxo-1,3-dioxolane; Carbonic acid, propylene ester; Carbonic acid, cyclic propylene ester; NSC 11784; Propylenester kyseliny uhlicite; Carbonic acid cyclic methylethylene ester; 2-Propenoic acid, 2-methyl-3-(2-nitrophenyl)-; Propylene carbonate, Selectophore(TM), >=99.0%; Propylene carbonate, Vetec(TM) reagent grade, 98%; Propylene carbonate, >=99%, acid <10 ppm, H2O <10 ppm; Propylene carbonate, United States Pharmacopeia (USP) Reference Standard; 4-Methyl-1,3-dioxolan-2-one; Propylene glycol carbonate; Carbonic acid propylene glycol este