Russian Chemical Reviews 79 (6) 479 ± 489 (2010) # 2010 Russian Academy of Sciences and Turpion Ltd
DOI 10.1070/RC2010v079n06ABEH004113 Dimethyl carbonate: a modern green reagent and solvent
F AricoÁ , P Tundo
Contents
I. Introduction 479 II. Production of dimethyl carbonate 479 III. Reactivity of dimethyl carbonate 480 IV. Conclusions 487
Abstract. The published data on dimethyl carbonate as a other carboxylating or alkylating agents (phosgene and non-toxic reagent and solvent in organic synthesis are methyl halides, respectively). Dimethyl carbonate does not generalized and discussed. The methods for dimethyl produce inorganic salts. In fact, the leaving group, methyl carbonate production and its use as a methylating and carbonate, decomposes giving only methanol and CO2 as methoxycarbonylating agent are considered. Special atten- by-products. Dimethyl carbonate is classified as a flam- tion is paid to the eco-friendly processes that meet the mable liquid, smells like methanol and does not have `Green chemistry' requirements. The bibliography includes irritating or mutagenic effects by either contact or inhala- 104 references.references. tion. Therefore, it can be handled safely without the special precautions required for the poisonous and mutagenic I. Introduction methyl halides and DMS, and extremely toxic phosgene. Besides, DMC is widely studied also for its many potential Green chemistry, as one of the primary methods of pollu- applications.6, 7 In fact, recent research indicate DMC as an tion prevention, is a fairly recent phenomenon. `Green' oxygenated fuel additive of gasoline or diesel oil to replace organic syntheses must include some of the following tert-butyl methyl ether.8 Dimethyl carbonate can reduce the requirements: avoid waste, be atom efficient, avoid the use surface tension of diesel boiling range fuels leading to an and production of toxic and dangerous chemicals, avoid improved (diesel) fuel with better deinjection delivery and auxiliary substances (e.g., solvents), use renewable materi- spray. An obvious advantage of DMC over other candidate 1±5 als, use catalysts rather than stoichiometric reagents. as fuel additives is that it slowly decomposes to form CO2 In particular, it is important to find a replacement for and methanol, which have no serious impact when released toxic and dangerous reagents produced by eco-unfriendly into the environment. This and other applications led to an processes and that are responsible for producing expensive- enormous effort in the investigation of low-cost and not to-dispose-of inorganic salts. Methyl halides (CH3X, X = I, toxic synthesis of DMC. Br, Cl), dimethyl sulfate (DMS), and phosgene (COCl2)are representative examples of undesirable reagents used for II. Production of dimethyl carbonate methylation and methoxycarbonylation reactions. All these reagents are toxic and corrosive chemicals. Moreover, the For a long time, DMC has been produced from phosgene reactions require stoichiometric amount of bases and pro- and methanol. In this synthesis, HCl was an unwanted side duce stoichiometric amounts of inorganic salts that need to product. However, since the mid-1980s, DMC is no longer be disposed of. produced from phosgene, but by oxidative carbonylation of Dimethyl carbonate (DMC) is an environmentally methanol with oxygen through a process developed by benign substitute for phosgene, DMS and methyl halides Enichem (Italy):9±12 since it is a well-known non-toxic reagent as compared to 1 Cu salt 2 MeOH + O +CO MeOCO Me + H O. 2 2 2 2 F AricoÁ , P Tundo Interuniversity Consortium `Chemistry for the Environment', Via delle Industrie, Marghera 21/8, 30175 Venice, Italy. The most relevant features of this process are: Fax (39-041) 234 66 51, Dipartimento Scienze Ambientali, Ð low-cost and widely available raw materials with low Ca'Foscari Universita di Venezia, Dorsoduro 2137, 30123 Venice, Italy. toxicity; Fax (39-041) 234 86 20, tel. (39-041) 234 66 35, tel. (39-041) 234 66 60, Ð high production rates; e-mail: [email protected] (F AricoÁ ), tel. (39-041) 234 86 42, Ð non-toxic and easily disposable by-products (carbon e-mail: [email protected], [email protected] (P Tundo) dioxide and water); Ð high quality product. Received 23 September 2009 The new technology does not produce any by-products Uspekhi Khimii 79 (6) 532 ± 543 (2010) that are difficult to dispose of. The DMC obtained has also low toxicity and ecotoxicity (biodegradability >90% at 480 F AricoÁ , P Tundo
28 days, OECD 301C; acute toxicity for fish; no effect at catalytic distillation process demonstrated a stable perform- 1000 mg litre71, OECD 203). ance and a substantial improvement in DMC yield com- The oxidative carbonylation paved the way for indus- pared with batch results.22 trial phosgene-free route to DMC. In fact, since 1984, when it was firstly patented, many new catalytic systems have III. Reactivity of dimethyl carbonate been investigated for this process.13 ± 19 A very recent one includes the use of Co(II) ± Schiff base complexes 1a ± d.20 Dimethyl carbonate is a well-known non-toxic reagent showing several main green-chemistry features 23 as com- X pared to other carboxylating or alkylating reagents (phos- N N gene and methyl halides, respectively).24, 25 Co As has been mentioned, dimethyl carbonate does not 26 O O produce inorganic salts in either acylation or alkyl- 1a ± d ation 27, 28 reactions:
7 7 Nu + MeOCO2Me NuCO2Me + MeO , (1) X = (CH2)2 (a), (CH2)2NH(CH2)2 (b), cyclohexane-1,2-diyl (c), 7 o-phenylene (d). Nu + MeOCO2Me NuMe + MeOCO2 , (2)