Acetic Anhydride Research Articles

Synthesis and Pharmacological Evaluation of 3-alkyl/aryl–2- methylquinazolin-4-one Derivatives

Quinazolin-4-ones with 2, 3-disubstitution is reported to possess significant analgesic, anti-inflammatory and anticonvulsant activities. We have developed an efficient method for the synthesis of 3-substituted-2-methylquinazolin-4-one by the condensation reaction of Anthranilic acid, acetic anhydride with various amines. The synthesized compounds were evaluated for anxiolytic activity by Elevated plus Maze Test and Light and Dark Test. It is observed that the aliphatic and aromatic substitution at 3-position of 2-methylquinazolin-4-one gives potent anxiolytic activity. In particular, ENA showed highest anxiolytic activity in Elevated plus Maze Test and EMQ and AMQ showed highest anxiolytic activity in Light and dark test model

Discovery of New Imidazolinones Derivatives as Potential Microbial Agents

A series of imidazolinone were prepared by heating the hippuric acid in presence of acetic anhydride and sodium acetate with different aromatic aldehydes gave 5-oxazolone derivatives which reacting with N-amino-2,3,4,5,6-pentafluoro benzamide in pyridine gave imidazolinone. All the synthesized compounds have been characterized on the basis of elemental analysis, IR, 1H-NMR and 13C-NMR spectral data. All the synthesized compounds have been screened against four different bacterial strains S. aureus, S. paratyphi-A, E. coli and B. subtilis and fungal strain F. molaniforme and A. niger. Some of the compound was endowed with a remarkable antibacterial as well as antifungal activity.

Effect of acetic acid concentration on obtaining cellulose acetate from oil palm mesocarp fibers (Elaeis guineensis Jacq.)

This work aimed to produce cellulose acetate from the mesocarp fibers of palm oil treated with sodium hydroxide (MFA) and bleached with sodium chlorite. Cellulose acetate was obtained from the different materials by homogeneous acetylation in the mass proportions of: 1:5, 1:10 and 1:15 (acetic acid), 1:15 (acetic anhydride) and 1:0.1 (sulfuric acid). The degree of substitution was determined by chemical methods and by 1H-NMR. The cellulose acetate obtained from the combination of alkaline treatments followed by bleaching showed degree of substitution of 2.81 (CAAB5), 3.02 (CAAB10) and 3.07 (CAAB15), corresponding to yield values (w/w) of 50.45%, 65.5% and 97.21%. Based on the analysis of the results, we can say that the amount of acetic acid and the type of treatment used in the fibers of the mesocarp of oil palm directly influenced the quality and yield of cellulose acetate, with CAAB15 being the best reaction condition.

Upcycling of Polystyrene to Aromatic Polyacids by Tandem Friedel-Crafts and Oxidation Reactions.

Due to the high demand and the increasing production rate of plastic materials, vast amounts of wastes are generated every year. An important fraction of these wastes contain polystyrene (PS), which is seldom recycled, neither mechanically nor chemically. While several chemical recycling strategies have been developed, they are either very energy-demanding or produce chemicals that can hardly be employed in the synthesis of plastics (e.g., benzene and benzoic acid). Here, we report the upcycling of PS waste into aromatic polyacids, useful in polyester synthesis, such as polyethylene terephthalate (PET). To this end, a conventional Friedel-Crafts acylation was first investigated, to produce an acylated PS chain, using acetic anhydride and stoichiometric amounts of AlCl3. As a catalytic alternative, the alkylation of PS was studied, using InCl3 and isopropyl acetate. The acylated and alkylated PS samples were then oxidized to produce terephthalic (TA), isophthalic (IPTA), benzoic (BA), and trimesic (TMA) acid.

DFT Studies on the Mechanism of Ligand-Regulated Palladium-Catalyzed Iodide-Assisted Hydrocarbonylation of Olefins with Formic Acid: Favored Reaction Routes and Selectivities.

DFT calculations have been performed to gain insight into the mechanism of hydrocarbonylation of olefins and the origin of regio- and chemoselectivity. It is shown that the most feasible mechanism involves five steps: (i) decomposition of acetic formic anhydride, (ii) hydropalladation of olefins, (iii) CO migratory insertion, (iv) iodide-assisted acetate-formate exchange, and (v) formylation or carboxylation. Importantly, carboxylation proceeds via the decomposition of anhydride, followed by reductive elimination instead of direct hydrolysis of anhydride. For phosphine-ligated palladium catalysis, on one hand, the lower stability of the transition state leading to 1,2-hydropalladation could be attributed to H···H steric hindrance. On the other hand, the high chemoselectivity for the aldehyde is ascribed to increased π back-donation effect and ligand-substrate noncovalent interactions, which stabilize the transition state and hence reduce the energy barrier. For ferrocenyl phosphine-ligated palladium catalysis, significant C-H···π interaction between the substrate and proximal phenyl moiety of the phenylphosphine and π-π interaction between formate and phenyl moiety can facilitate the carboxylation process. This in-depth mechanistic insight can account for reactivity and selectivity at an atomistic level and have implications for designing new generations of palladium catalysts.

Syntheses and evaluation of novel 3-hydroxy-1,3-diaryl-2,3,5,6,7,8-hexahydro-imidazo[1,2-a]pyridine-1-ium bromides as potential anticancer agents

New 3-hydroxy-1,3-diaryl-2,3,5,6,7,8-hexahydro-imidazo[1,2-a]pyridine-1-ium bromides have been designed, synthesized, and characterized by 1Н NMR, 13C NMR, and LCMS. The cyclic structure of the condensation products of aryl-(3,4,5,6-tetahydropyridin-2-yl)amines with α-bromoketones has been proven. It has been shown that heating 3-hydroxy-1,3-bis-(41-methoxyphenyl)-2,3,5,6,7,8-hexahydro-imidazo[1,2-a]pyridine-1-ium bromide in acetic anhydride accompanied by elimination of water to form 1,3-bis-(41-methoxyphenyl)-5,6,7,8-tetrahydro-imidazo[1,2-a]pyridine-1-ium bromide. Antitumor activity of 1,3-bis-(41-ethoxyphenyl)-3-hydroxy-2,3,5,6,7,8-hexahydro-imidazo[1,2-a]pyridine-1-ium bromide and 1,3-bis-(41-methoxyphenyl)-5,6,7,8-tetrahydro-imidazo[1,2-a]pyridine-1-ium bromide have been studied. The fully aromatic imidazo[1,2-a]pyridine-1-ium bromide system was shown to have a higher antitumor effect. According to the screening results, the tested compound showed a significant level of anticancer effect on cancer cells of colon COLO 205 (lgGI50 = -5.35, lgTGI = –4.70 and lgLC50 = –4.19) and melanoma SK-MEL-5 (lgGI50 = –5.57, lgTGI = –4.81 and lgLC50 = –4.17).

Deciphering the role of biochar pseudocapacitance strengthening in promoting syntrophic methanogenesis: Microbial capacitance-tropism in propionate metabolism

The redox functional groups of biochar can act as pseudocapacitance, alleviating acid accumulation and facilitating electron transfer in anaerobic digestion. Fe modification further enhances its pseudocapacitance properties. However, the specific role of pseudocapacitance strengthening in the electron transfer of volatile fatty acid syntrophic methanogenesis, as well as the factors inducing the enrichment behavior and metabolic mechanisms of microbes on its surface, remain unclear. In this study, experiments using acetate and propionate as substrates were conducted with the addition of biochar and electro-enhanced biochar, while 16S rRNA gene amplicon sequencing and metagenomic analysis were employed to investigate the underlying mechanisms. The results demonstrate that strengthening biochar’s pseudocapacitance significantly facilitates the electron shunt by accepting electrons, accelerating NADH/NAD+ conversion and ATP synthesis. This further promotes the oxidative degradation of propionate and acetate through the methylmalonyl-CoA (MMC) and syntrophic acetate oxidation (SAO) pathways. During methanogenesis, biochar directly transfers electrons to methanogens, with the strengthened pseudocapacitance further accelerating electron transfer through the CO2 reduction pathway and specifically promoting the methanation of propionate rather than acetate. Moreover, during propionate metabolism, Coprothermobacter and Methanosarcina exhibit capacitance-tropism in their enrichment on biochar, serving as key functional contributors to the biochar-microbial aggregates. These findings provide valuable insights for selecting exogenous materials in engineering applications to alleviate acid accumulation in anaerobic digestion systems.

Microwave Mediated Acylation of Alcohols, Phenols and Thiophenols in Neat Acetic Anhydride.

A microwave-based method for the acylation of alcohols, phenols, and thiols has been developed without the need of a catalyst or base additives. The reaction is far more rapid than previously reported acylation methods, tolerates a wide variety of functional groups, and provides easy isolation of products in excellent yields without the need for chromatography. Most products can be isolated directly via evaporation under reduced pressure or by pouring the reaction mixture into water and filtering.

Recent Advances in the Development of Indolizine Scaffolds: Synthetic Methodology and Mechanistic Insights

Comprehensive SummaryIndolizine is a nitrogen‐containing heterocycle with strong aromaticity, possessing a delocalized 10π‐electron system. Based on the indolizine scaffolds, numerous molecules with biological activity and organic functional materials have been synthesized. Since 2016, over 110 papers have been published on the synthesis of indolizine scaffolds, but the reviews on synthesizing indolizine scaffolds have been incomplete and not up‐to‐date. Herein, from the perspective of the structure of indolizine with the combination of pyrrole and pyridine ring, we focus on the construction of indolizine scaffolds through the diversity of starting substrates, including pyridine derivatives (N1‐substituted pyridinium salt derivatives, C2‐substituted pyridine derivatives, N1‐ and C2‐free substituted pyridine derivatives), pyrrole derivatives and unoriginal ring substrates. Furthermore, the corresponding reaction mechanisms of synthetic methodologies are also elaborated. Therefore, this review not only paves the way for indolizine synthesis but also provides insight into exploring new reaction modes for constructing nitrogen‐containing heterocycles. Key ScientistsIndolizine was discovered by Angeli in 1890 and first prepared by Scholtz in 1912 from α‐picoline and acetic anhydride. A general approach was developed by Chichibabin in 1927, that is of practical value for the preparation of 2‐alkyl‐ or 2‐arylindolizines. The Chichibabin reaction was the ring closure of quaternary pyridinium halides. At the begining of the 21st century, Basavaiah introduced a new dimension in the Baylis‐Hillman chemistry leading to a novel facile convenient methodology for synthesis of indolizine scaffolds in one‐pot operation. In 2010, Barluenga reported Cu(I)‐catalyzed regioselective [3+2] cyclization of unsubstituted pyridines toward alkenyldiazoacetates leading to functionalized indolizine derivatives, that was the first successful example of metal‐catalyzed cyclization of a π‐deficient heterocyclic system with alkenyldiazo compounds. In 2019 and 2022, Xi and Liu exploited the methods of non‐pyridine derivatives as starting materials to synthesize indolizines, respectively. In 2022, Guo developed an environmentally benign electrooxidative approach for constructing formyl‐ and acyl‐substituted indolizines.

A polymeric form of basic iron(III) acetate with an acetic acid ligand.

A new crystalline compound, catena-poly[hexa-μ-acetato-(acetic acid)-μ3-oxido-triangulo-triiron(III)]-μ-acetato], [Fe3(C2H3O2)7O(C2H4O2)]n, incorporating the basic ferric acetate unit, has been obtained from an acetic anhydride solution of hydrated iron(III) nitrate. The crystals have the composition Fe3O(OAc)7(HOAc) (HOAc is acetic acid) and include the well-known [Fe3O(OAc)6]+ unit, in which the FeIII centres are linked to a central coplanar μ3-oxido ligand. Acetate ions provide bridges between pairs of FeIII centres. These individual [Fe3O(OAc)6]+ units are linked by additional bridging acetate anions to form zigzag chains. The bridging acetate ions coordinate to a position trans to the oxido group on two of the FeIII centres. Remarkably, the trans site on the third FeIII centre is occupied by the carbonyl group of an acetic acid molecule. This is the first reported case of an acetic acid molecule coordinating to an FeIII centre. Not surprisingly, the acetic acid molecule is only weakly coordinating, resulting in a short Fe-O(oxido) bond trans to the carbonyl group. The trans influence apparent in this structure provides an interesting contrast with the structurally similar MnIII analogue, in which the corresponding pair of trans bonds are both elongated because of the Jahn-Teller effect.

Process simulation and economic evaluation of the industrial production of triacetin from glycerol: Comparing acetic acid and acetic anhydride as possible reagents

The objective of this work was to simulate, in Aspen HYSYS® v12.1, the process of obtaining triacetin from glycerol through three chemical routes: via acetic acid (Route 1), acetic anhydride (Route 2), and a combination of acetic acid and acetic anhydride in two separate reactors (Route 3). Additionally and as a novelty, it was investigated the technical and economic viability of a multipurpose plant to this end. It was verified that Route 1 resulted in the best triacetin breakeven prices, even though it would still not be competitive in the considered economic context. On the other hand, Route 2 presented the worst performance due to low conversion (11 %) and higher price of acetic anhydride. The combined route resulted in intermediate breakeven prices for triacetin, despite achieving the highest conversion (79 %) and highest final product purity (96 %). Yield/selectivity and the separation steps were identified as the main bottlenecks in these processes, with reactors and distillation columns accounting for more than 95 % of the equipment costs. The multipurpose plant proved technically possible, and it can be economically interesting depending on the market prices for acetic acid and acetic anhydride.

Controlled preparation of cellulose acetate by deep eutectic solvent homogeneous catalysis

This work proposed a homogeneous preparation strategy of cellulose acetate by using a deep eutectic solvent consisting of zinc chloride/phosphoric acid/water (ZnCl2/PA/H2O). The results showed that the DES (the molar ratio of ZnCl2: PA: H2O = 1:1:3) had good solubility for bamboo pulp with high degree of polymerization. The dynamic dissolution behavior of cellulose in DES was also studied. Cellulose was first moistened and swollen and then dissolved. The crystalline state of cellulose changed from type I to type II after regeneration. Under the synergistic effect of acetic anhydride (Ac2O), the dissolved cellulose in DES could be uniformly acetylated. The effects of temperature, reaction time and molar ratio of Ac2O/anhydrous glucose on degree of substitution (DS) were investigated in their respective ranges (30–50 °C, 2–10 h and 4–24). Cellulose acetate with DS of 0.42–1.81 was successfully prepared. The substituent distribution of the sample was analyzed as C-6 > C-2 > C-3. Moreover, the entire process required no additional catalysts or activation steps, reducing the difficulty of solvent recovery. The insight from this study provides a new idea for the development of greener methods for the homogeneous preparation of cellulose acetate.

Preparation and catalytic performance of nano beta zeolites for Friedel–Crafts acylation at low temperature

The nano Beta zeolites were successfully prepared by secondary hydrothermal synthesis, which exhibited excellent and stable catalytic performance in the Friedel-Crafts acylation of anisole/thioanisole at low temperature. Effects of reaction temperature and reactants molar ratio on the catalytic performance of the nano Beta zeolites were systematically investigated in this work. Acetic anhydride conversion and 4-methoxypropiophenone selectivity were 77.34 % and 100 % at 313 K, both acetic anhydride conversion and p-(methylthio) acetophenone selectivity were 100 % at 393 K. Simple calcination could recover catalytic performance of the nano Beta zeolites. Furthermore, Kinetic studies revealed that the catalytic reaction followed Langmuir-Hinshelwood mechanism, and activation energy of the Friedel-Crafts acylation of anisole and acetic anhydride with the nano Beta zeolites was only 41.52 kJ/mol.

Design, Synthesis, Antibacterial, and Antifungal Evaluation of a New Series of Quinazoline - Thiazole and/or Quinazoline - Triazole Hybrids as Bioactive Heterocycles.

Herein, a one-pot reaction between cyclohexanone, thiourea, and 2,5-dimethoxybenzaldehyde allowed to prepare hexahydroquinazoline-2(1H)-thione4 firstly, which followed by reacting with hydrazine hydrate to produce the corresponding 2-hydrazinylhexahydroquinazoline 6. Interesting analogs of thiazolo[3,2-a]quinazoline 713 where obtained when hexahydroquinazoline-2(1H)-thione 4 reacted with 1,2-dibromoethane, chloroacetyl chloride, bromoacetic acid, bromoacetic acid/4-chlorobenzaldehyde, 2-bromopropionic acid, ethyl bromo cyanoacetate, and/or bromomalononitrile; respectively. While triazolo[4,3-a] quinazoline 14-16 were created when 2-hydrazinylhexahydroquinazoline 6 reacted with triethyl orthoformate, acetic anhydride, and carbon disulfide respectively. Numerous spectroscopy tests, including FT-IR, NMR (1H &13 C), and MS spectrum, proved all the newly produced analogs. Additionally, the new analogs were examined for their antibacterial and antifungal properties against Escherichia coli, Staphylococcus aureus, and Candida albicans. It was discovered that triazolo[4,3-a] quinazoline analogs 14-16 have superior bacterial and fungal activity when compared to the corresponding conventional doses of Streptomycin andGriseofulvin. Towards Candida albicans; compounds 14, 15, and 16 increase activity with 1.14 %, 1.15 %, and 1.21 %, respectively more than griseofulvin.While, for Staphylococcus aureus; compounds 14, 15, and 16 increase activity with 1.5 %, 1.5 %, and 1.7 %, respectively more than streptomycin. Morever, for Escherichia coli; compounds 14, 15, and 16 increase activity with 1.19 %, 1.21 %, and 1.22 %, respectively more than streptomycin. Finally, structure activity relationships show that quinazoline derivatives exhibit higher activity when fused to pyrazole ring 14-16 as compared when fused thiophene ring 7-13.

CaFe2O4@SiO2-Cu as a novel and highly efficient nanocatalyst for direct conversion of epoxides to β-acetoxy esters

Direct conversion of structurally various epoxides to the related β-acetoxy esters was investigated using catalytic amounts of CaFe2O4@SiO2-Cu. The reactions were accomplished in the presence of acetic anhydride under solvent-free conditions within 0.5–2 h to give desired products in high yields. Initially, the CaFe2O4 nanoparticles were manufactured through a chemical coprecipitation reaction of calcium nitrate and hydrated iron (III) nitrate in the presence of ammonium hydroxide solution, and then calcined at 800 ºC. Next, to protect the prepared CaFe2O4 from oxidation and aggregation, its surface was covered with a silica layer to give CaFe2O4@SiO2. Eventually, by adding copper chloride solution followed by potassium borohydride solid powder, Cu nanoparticles were successfully immobilized on the silica surface and the new CaFe2O4@SiO2-Cu nanocomposite was obtained. FT-IR, SEM, EDX, VSM, ICP-OES, TGA, TEM and XRD techniques were employed to characterize the newly synthesized nanostructure. In addition, durability of the catalyst was considered for several sequential reaction cycles without the notable loss of catalytic activity. The absence of hazardous organic solvents, high product yields, short reaction times and recoverability of the magnetic catalyst are among the remarkable advantages of the introduced procedure.

Mechanistic insights into the electrochemical oxidation of acetate at noble metals

Mechanistic insights into the electrochemical oxidation of acetate at noble metals

Thermophilic and mesophilic anaerobic digestion of soybean molasses: A performance vs. stability trade-off

One of the factors that has a direct impact on anaerobic digestion is the applied organic loading rate (OLRA). Increasing OLRA can boost methane production but can also cause process failure. As a result, establishing the appropriate OLRA for the procedure is critical. This study evaluated the effect of increasing the OLRA using soybean molasses in a thermophilic anaerobic reactor (R-Thermo), as well as the effect of feeding strategy and co-processing with okara. Furthermore, the performance versus stability trade-off between R-Thermo and mesophilic anaerobic digestion (R-Meso) was investigated. The increase of OLRA from 10 to 15 and 20 kg-COD/m³/d led to a decrease in COD removal efficiency (90, 86, and 75%), methane yield (12.0, 11.6, and 9.9 mol-CH4/kg-COD) and an increase in total volatile acids concentration (251, 456, and 1393 mg-HAc/L, respectively). At 15 kg-COD/m³/d, R-Meso performed similarly to R-Thermo, and at 20 kg-COD/m3/d, R-Meso outperformed (81% COD removal efficiency, 9.3 mol-CH4/kg-CODrem and 154.5 mol-CH4/m3/d). Temperature greatly influenced the distribution of metabolic pathways, as shown by thermodynamic and kinetic analyses, thus impacting bacterial diversity. At 55 °C, amongst the bacterial genera, Tepidiphilus stood out (>28.2%), followed by Acetomicrobium, Coprothermobacter and Candidatus_Caldatribacterium. The OLRA clearly impacted the archaeal community; Methanothermobacter (77.4%) was favored over Methanosarcina (14.8%). Under thermophilic temperature, it seems that syntrophic acetate oxidation (SAO) bacteria might have competed for substrate with acetoclastic methanogens, while in R-Meso microorganisms responsible for the initial steps of organic matter breakdown, such as members of the Firmicutes and Proteobacteria phyla (at least 67%), were dominant. In summary, R-Meso, characterized by a more uniform distribution of metabolic pathways, as well as a diverse and well-adapted microbial consortium, have exhibited enhanced stability and outperformed R-Thermo at high-loads.

Isolation of antibodies to hypochlorite-modified low-density lipoproteins from human serum and study of their specificity

BACKGROUND: Modified low-density lipoproteins have immunogenic properties and induce the production of antibodies. In this case, HOCl promotes the formation of subsequent active halogen-containing compounds interacting with proteins and lipid parts of low-density lipoproteins, which leads to their modification and the production of antibodies to them. AIM: The aim of this work is to isolate antibodies to hypochlorite modified low-density lipoproteins from human blood sera and study their specificity. MATERIALS AND METHODS: Malondialdehyde, acetic anhydride and sodium hypochlorite were used to obtain modified low-density lipoproteins. IgG antibodies to hypochlorite modified low-density lipoproteins were isolated by affinity chromatography. The total IgG fraction antibodies was previously isolated from human blood serum using MabSelect Xtra. The specific antibodies to hypochlorite modified low-density lipoproteins were isolated from this IgG pool by affinity chromatography. CNBr-Sepharose 4B conjugated with human serum albumin modified with NaOCl was used as a sorbent. The specificity of antibodies against hypochlorite modified low-density lipoproteins was tested using a competitive enzyme-linked immunosorbent assay. The competitors were hypochlorite modified low-density lipoproteins, acetic anhydride modified low-density lipoproteins and malondialdehyde modified low-density lipoproteins in concentrations (1–250 μg/ml). RESULTS: IgG antibodies against hypochlorite-modified proteins that interact with hypochlorite modified low-density lipoproteins were detected in human blood. According to ELISA date the binding of the isolated antibodies to hypochlorite modified low-density lipoproteins was almost completely inhibited only by appropriately modified low-density lipoproteins, that is, hypochlorite modified low-density lipoproteins, but not native low-density lipoproteins or acetic anhydride modified low-density lipoproteins. Malondialdehyde modified low-density lipoproteins also showed some competitive activity, but much weaker than hypochlorite modified low-density lipoproteins. Hypochlorite modified low-density lipoproteins itself and, to a lesser extent, malondialdehyde modified low-density lipoproteins competed for binding with antibodies of human serum to hypochlorite modified low-density lipoproteins. Acetic anhydride modified low-density lipoproteins and native low-density lipoproteins did not reduce the efficiency of antibody binding to their antigen. CONCLUSIONS: Hypochlorite modified low-density lipoproteins forms epitopes independent of other low-density lipoproteins modifications studied. These epitopes are responsible for the formation of specific antibodies.

Preparation of Novel Hierarchical Catalysts by Simultaneous Generation of β-Zeolite and Mesoporous Silica for Catalytic Cracking.

The gel skeletal reinforcement (GSR) method was applied at the preparation stage of β-zeolite to prepare a novel hierarchical catalyst. A solution of hexamethyldisiloxane (HMDS) and acetic anhydride, a GSR reagent, was added to the mixture of colloidal silica, sodium aluminate, tetraethylammonium hydroxide, sodium hydroxide and water, and successive aging and hydrothermal treatment gave microporous β-zeolite surrounded by mesoporous silica like core-shell structure. Its properties were characterized by XRD, nitrogen adsorption and desorption, NH3-TPD, TEM, and TG-DTA measurements, and further characteristics of the catalysts produced were clarified by the catalytic cracking of n-dodecane. The hierarchical structure of microporous zeolite and mesoporous silica was shown from GSR-2.9HS-H-Beta to GSR-3.2HS-H-Beta, where the molar ratio of HMDS and silica source of β-zeolite was 2.9~3.2 : 100. It was found that in the catalytic cracking of n-dodecane, the relative activity (the conversion per the amount of zeolite crystals) increased with the increase in mesopore volume and surface area. The result indicated that the introduction of mesopores was effective even in catalytic cracking of small molecule of n-dodecane.

Novel Methods for the Formation of Free Carbyne Radicals in Solution.

Carbyne free radicals (RC) are usually associated with high-energy processes, thus research on their preparation, chemical reactivity, and prevalence under mild conditions is scarce. Recently, it was reported that metallo-complexes containing CR ligands may undergo spontaneous degradation in aqueous solutions to produce free RC radicals. These highly reactive species may react with each other to form the corresponding alkyne and other products. The reaction of 1,1,1 halo-carbo-hydrates with Cr(II) ions also forms RC radicals under mild conditions. Herein, we report two additional synthetic routes that produce free RC radicals under mild conditions. First, the reaction between metallic zinc and acetic anhydride produces 2-butyne and several other C2, C3, and C4 compounds. Isotopic-labeling experiments indicate that the formation of 2-butyne results from an inter-molecular reaction in which two RC moieties from two acetic anhydride molecules combine in solution. In addition, the degradation of the tri-molybdenum complex [Mo3(H3CC≡CCH3)(OAc)(H2O)2Br7], in which a 2-butyne ligand is coordinated to the Mo3 framework in a μ3-η2 (⊥) binding mode in aqueous solution produces several C2, C3, C4 and C5 molecules. This indicates the formation of free CH3C radicals by a homolytic cleavage of the carbon-carbon triple bond.