The chemistry of dimethyl carbonate

Dimethyl carbonate (DMC) is a versatile compound that represents an attractive eco-friendly alternative to both methyl halides (or dimethyl sulfate) and phosgene for methylation and carbonylation processes, respectively. In fact, the reactivity of DMC is tunable: at T = 90 degrees C, methoxycarbonylations take place, whereas at higher reaction temperatures, methylation reactions are observed with a variety of nucleophiles. In the particular case of substrates susceptible to multiple alkylations (e.g., CH(2)-active compounds and primary amines), DMC allows unprecedented selectivity toward mono-C- and mono-N-methylation reactions. Nowadays produced by a clean process, DMC possesses properties of nontoxicity and biodegradability which makes it a true green reagent to use in syntheses that prevent pollution at the source. Moreover, DMC-mediated methylations are catalytic reactions that use safe solids (alkaline carbonates or zeolites), thereby avoiding the formation of undesirable inorganic salts as byproducts. The reactivity of other carbonates is reported as well: higher homologues of DMC (i.e., diethyl and dibenzyl carbonate), are excellent mono-C- and mono-N-alkylating agents, whereas asymmetrical methyl alkyl carbonates (ROCO(2)Me with R > or = C(3)) undergo methylation processes with a chemoselectivity up to 99%.

Waste-to-wealth: biowaste valorization into valuable bio(nano)materials

The waste-to-wealth concept aims to promote a future sustainable lifestyle where waste valorization is seen not only for its intrinsic benefits to the environment but also to develop new technologies, livelihoods and jobs.

Upgrading of marine (fish and crustaceans) biowaste for high added-value molecules and bio(nano)-materials

Currently, the Earth is subjected to environmental pressure of unprecedented proportions in the history of mankind. The inexorable growth of the global population and the establishment of large urban areas with increasingly higher expectations regarding the quality of life are issues demanding radically new strategies aimed to change the current model, which is still mostly based on linear economy approaches and fossil resources towards innovative standards, where both energy and daily use products and materials should be of renewable origin and 'made to be made again'. These concepts have inspired the circular economy vision, which redefines growth through the continuous valorisation of waste generated by any production or activity in a virtuous cycle. This not only has a positive impact on the environment, but builds long-term resilience, generating business, new technologies, livelihoods and jobs. In this scenario, among the discards of anthropogenic activities, biodegradable waste represents one of the largest and highly heterogeneous portions, which includes garden and park waste, food processing and kitchen waste from households, restaurants, caterers and retail premises, and food plants, domestic and sewage waste, manure, food waste, and residues from forestry, agriculture and fisheries. Thus, this review specifically aims to survey the processes and technologies for the recovery of fish waste and its sustainable conversion to high added-value molecules and bio(nano)materials.

Reaction of primary aromatic amines with alkyl carbonates over NaY faujasite: a convenient and selective access to mono-N-alkyl anilines

At atmospheric pressure and at 130-160 degrees C, primary aromatic amines (p-XC6H4NH2, X = H, Cl, NO2) are mono-N-alkylated in a single step, with symmetrical and asymmetrical dialkyl carbonates [ROCOOR', R = Me, R' = MeO(CH2)2O(CH2)2; R = R' = Et; R = R' = benzyl; R = R' = allyl; R = Et, R' = MeO(CH2)2O(CH2)2], in the presence of a commercially available NaY faujasite. No solvents are required. Mono-N-alkyl anilines are obtained with a very high selectivity (90-97%), in good to excellent yields (68-94%), on a preparative scale. In the presence of triglyme as a solvent, the mono-N-alkyl selectivity is independent of concentration and polarity factors. The reaction probably takes place within the polar zeolite cavities, and through the combined effect of the dual acid-base properties of the catalyst.

Highly Chemoselective Methylation and Esterification Reactions with Dimethyl Carbonate in the Presence of NaY Faujasite. The Case of Mercaptophenols, Mercaptobenzoic Acids, and Carboxylic Acids Bearing OH Substituents

In the presence of NaY faujasite, the reactions of dimethyl carbonate (DMC) with several ambident nucleophiles such as o- and p-mercaptophenols (1a,b), o- and p-mercaptobenzoic acids (2a,b), o- and p-hydroxybenzoic acids (3a,b), mandelic and phenyllactic acids (4, 5), have been explored under batch conditions. Highly chemoselective reactions can be performed: at 150 degrees C, compounds 1 and 2 undergo only a S-methylation reaction, without affecting OH and CO2H groups; at 165 degrees C, acids 3-5 form the corresponding methyl esters, while both their aromatic and aliphatic OH substituents are fully preserved from methylation and/or transesterification processes. Typical selectivities are of 90-98% and isolated yields of products (S-methyl derivatives and methyl esters, respectively) are in the range of 85-96%. A comparative study with K2CO3 as a catalyst is also reported. Although the base (K2CO3) turns out to be more active than the zeolite, the chemoselectivity is elusive: compounds 2a,b undergo simultaneous S-methylation and esterification reactions, and acids 3-5 yield complex mixtures of products of O-methylation, O-methoxycarbonylation, and esterification of their OH and CO2H groups, respectively. Overall, the combined use of a nontoxic reagent/solvent (DMC) and a safe promoter (NaY) imparts a genuine ecofriendly nature to the investigated synthesis.

Carbon Dots from Sugars and Ascorbic Acid: Role of the Precursors on Morphology, Properties, Toxicity, and Drug Uptake

There is the need for reproducible, simple, high-yielding synthetic protocols aimed at obtaining carbon dots (CDs) with controlled fluorescence, photothermal and photochemical behavior, surface properties, biocompatibility, tumor targeting ability, drug absorption biodistribution, and tumor uptake. This Letter describes a systematic study on the effect of glucose, fructose, and ascorbic acid as starting materials for the preparation of highly luminescent CDs, characterized by a blue emission. Their composition and morphology are investigated by titration of OH surface groups, spectroscopic techniques, and high-resolution transmission electron microscopy (HR-TEM), and their toxicity was tested toward HeLa cells. CDs made using fructose were toxic, while those made from glucose and ascorbic acid showed good biocompatibility. The reproducible and simple synthetic procedure yields luminescent biomass-derived CDs for combined cancer therapy and diagnostics. Their doxorubicin (DOX) drug uptake was measured by spectrofluorimetry, indicating a crucial role of the morphologies of the CDs in controlling DOX loading. The glucose derived CDs showed up to 28% w/w of DOX loading.

Dimethylcarbonate for eco-friendly methylation reactions

Dimethylcarbonate (DMC), an environmentally friendly substitute for dimethylsulfate and methyl halides in methylation reactions, is a very selective reagent. Both under gas-liquid phase transfer catalysis (GL-PTC) and under batch conditions, with potassium carbonate as the catalyst, the reactions of DMC with methylene-active compounds (arylacetonitriles and arylacetoesters, aroxyacetonitriles and methyl aroxyacetates, benzylaryl- and alkylarylsulphones) produce monomethylated derivatives, with a selectivity not previously observed (i.e., >99%). The highly selective O-methylation of phenols and p-cresols by DMC is also attained by a new methodology using a continuous fed stirred tank reactor (CSTR) filled with a catalytic bed of polyethyleneglycol (PEG) and potassium carbonate.

Carbonate phosphonium salts as catalysts for the transesterification of dialkyl carbonates with diols. The competition between cyclic carbonates and linear dicarbonate products

Methylcarbonate and bicarbonate methyltrioctylphosphonium salts were excellent catalysts for the transesterification of dialkyl carbonates with diols: cyclic or linear carbonates are obtained.

Mono-N-methylation of primary amines with alkyl methyl carbonates over Y faujasites. 2. Kinetics and selectivity

In the presence of a Na-exchanged Y faujasite, the reaction of primary aromatic amines 1 with 2-(2-methoxyethoxy)methylethyl carbonate [MeO(CH(2))(2)O(CH(2))(2)OCO(2)Me, 2a] yields the corresponding mono-N-methyl derivatives ArNHMe with selectivity up to 95%, at substantially quantitative conversions. At 130 degrees C, the reaction can be run under diffusion-free conditions and is strongly affected by the solvent polarity: for instance, in going from xylene (epsilon(r) = 2.40) to triglyme (epsilon(r) = 7.62) as the solvent, the pseudo-first-order rate constant for the aniline (1a) disappearance shows a 5-fold decrease. In DMF (epsilon(r) = 38.25), the same reaction does not occur at all. Competitive adsorption of the solvent and the substrate onto the catalytic sites accounts for this result. The behavior of alkyl-substituted anilines ZC(6)H(4)NH(2) [Z = p-Me, p-Et, p-Pr, p-(n-Bu) (1b-e); Z = 3,5-di-tert-butyl- and 2,4,6-tri-tert-butylanilines (1f,g)] and p-alkoxyanilines p-ZC(6)H(4)NH(2) [Z = OMe, OEt, OPr, O-n-Bu (1b'-e')] clearly indicates a steric effect of ring substituents: as diffusion of the amine into the catalytic pores is hindered, the reaction hardly proceeds and the mono-N-methyl selectivity (S(M/D)) drops as well. Moreover, the strength of adsorption of the amine onto the catalyst influences the rate and the selectivity as well: the reaction of p-anisidine and p-toluidine-despite the higher nucleophilicity of these compounds-is slower and even less selective with respect to aniline. From a mechanistic viewpoint, the intermediacy of carbamates ArN(Me)CO(2)R [R = MeO(CH(2))(2)O(CH(2))(2)] is suggested. At 90 degrees C, the reaction of benzylamine (7)-a model for aliphatic amines-with dimethyl carbonate shows that the reaction outcome can be improved by tuning the amphoteric properties of the catalyst: in going from CsY to the more acidic LiY zeolite, methylation is not only more selective (S(M/D) ratio increases from 77% to 84%) but even much faster (CsY, conversion of 36% after 22 h; LiY, conversion of 43% after 7 h).

Reaction of functionalized anilines with dimethyl carbonate over NaY faujasite. 3. chemoselectivity toward mono-N-methylation

In the presence of NaY faujasite, dimethyl carbonate (MeOCO(2)Me, DMC) is a highly chemoselective methylating agent of functionalized anilines such as aminophenols (1), aminobenzyl alcohols (2), aminobenzoic acids (3), and aminobenzamides (4). The reaction proceeds with the exclusive formation of N-methylanilines without any concurrent O-methylation or N-/O-methoxy carbonylation side processes. Particularly, only mono-N-methyl derivatives [XC(6)H(4)NHMe, X = o-, m-, and p-OH; o- and p-CH(2)OH; o- and p-CO(2)H; o- and p-CONH(2)] are obtained with selectivity up to 99% and isolated yields of 74-99%. DMC, which usually promotes methylations only at T > 120 degrees C, is activated by the zeolite catalyst and it reacts with compounds 1, 2, and 4, at 90 degrees C. Aminobenzoic acids (3) require a higher reaction temperature (> or =130 degrees C).

Design of Carbon Dots for Metal-free Photoredox Catalysis

The photoreduction potential of a set of four different carbon dots (CDs) was investigated. The CDs were synthesized by using two different preparation methods-hydrothermal and pyrolytic-and two sets of reagents-neat citric acid and citric acid doped with diethylenetriamine. The hydrothermal syntheses yielded amorphous CDs, which were either nondoped (a-CDs) or nitrogen-doped (a-N-CDs), whereas the pyrolytic treatment afforded graphitic CDs, either non-doped (g-CDs) or nitrogen-doped (g-N-CDs). The morphology, structure, and optical properties of four different types of CDs revealed significant differences depending on the synthetic pathway. The photocatalytic activities of the CDs were investigated as such, that is, in the absence of any other redox mediators, on the model photoreduction reaction of methyl viologen. The observed photocatalytic reaction rates: a-N-CDs ≥ g-CDs > a-CDs ≥ g-N-CDs were correlated with the presence/absence of fluorophores, to the graphitic core, and to quenching interactions between the two. The results indicate that nitrogen doping reverses the photoredox reactivity between amorphous and graphitic CDs and that amorphous N-doped CDs are the most photoredox active, a yet unknown fact that demonstrates the tunable potential of CDs for ad hoc applications.

Heck reaction catalyzed by Pd/C, in a triphasic—organic/Aliquat 336/aqueous—solvent system

The rate of the Pd/C catalyzed Heck coupling of Ar-I with CH(2)=CH-R is accelerated tenfold by the presence of Aliquat 336 (A336), a well known phase transfer catalyst, and an ionic liquid. Both when conducted in A336 as solvent, and in an isooctane/A336/aqueous triphasic mixture, the Heck reaction of aryl iodides with electron deficient olefins, catalyzed by Pd/C, proceeds with high yields and selectivity. When KOH is used instead of Et(3)N, selective formation of the biphenyl rather than the Heck product, is observed. Aryl bromides react more sluggishly, and only the more activated ones undergo the Heck reaction. In the absence of the olefin, aryl halides possessing an electron withdrawing group are reduced to the corresponding Ar-H.