Synthesis of Organic Carbonates with Alkyl/aryl 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylates and ROH/AlCl₃ under Ambient Condition

Abstract

We demonstrated the synthesis of organic carbonates using alkyl/aryl 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylates and alcohol in the presence of aluminum chloride. Alkyl/aryl 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylates were reacted with alcohol in the presence of $AlCl_3$ in toluene at room temperature to afford the corresponding unsymmetric and symmetric organic carbonates in good to excellent yields. These are efficient and convenient processes. Alkyl/aryl 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylates are solid, stable and non-toxic $CO_2/CO_2R$(Ar) source. It is noteworthy that the reaction is carry out under an ambient and acidic conditions, the easy-to prepare and readily available starting materials and the quantitative isolation of reusable 4,5-dichloropyridazin-3(2H)-one.

Introduction

Organic carbonates are generally safe noncorrosive molecules employed in numerous commercial and synthetic application1-4 as eco-friendly useful reagents,2,3,5-10 solvents for Li-ion battery3,4 and electroanalytics.3,11 The symmetric organic carbonates [(RO)2C=O] are useful as the solvents, whereas the unsymmetric organic carbonates [ROC(=O)OR'] are used as the key-functional group in drugs and other chemicals. Various synthetic methods of organic carbonates by the phosgenation technique using COCl2, the oxidative carbonylation of alcohols using CO and transition metals, the reaction of urea with alcohols, the reaction of oxiranes and CO2, the reaction of chloroformates, the use of metal carbonate and the organic carbonate interchange reaction have been reported.1-3,9,12,13 However, the main disadvantages of these methods are the use of toxic, gaseous and/or expensive chemicals and requirement for specific additives. The alkoxycarbonylation using organic carbonate and base be also accompanied by the undesired side reaction.8,14 Moreover, unsymmetric organic carbonates cannot be prepared by these methods. Therefore, a great deal of research has focused on the development of a convenient and useful synthetic method for symmetric and unsymmetric organic carbonates using a nongaseous and recyclable CO2 or CO2R(Ar) source under non-basic conditions. To avoid the side reaction in the reaction using organic carbamate, the alkoxide or alkoxide equivalent must be prepare under aprotic acid or neutral condition.

Romano et al.15 reported the synthesis of dimethyl carbonate by oxidative carbonylation of methanol using copper chloride via Cu(OCH3)Cl intermediate (Scheme 1). In this reaction, the Cu(OCH3)Cl acts as an equivalent of methoxide (MeO−).

Scheme 1.Known and newly designed methods for the synthesis of organic carbonates.

On the other hand, Ball et al.16 reported the synthesis of organic carbonate by the reaction of carbamate in the presence of the catalyst. As shown in Scheme 1, alkyl/aryl 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylates17 have a carbamate functionality. Thus, alkyl/aryl 6-oxopyridazinone-1(6H)-carboxylates may be use as alkoxy/aryloxy carbonyl source, and also the 4,5-dichloropyridazin-3(2H)-one anion as the leaving group may be act as a proton acceptor during the reaction.18-24 Pyridazin-3(2H)-ones are inexpensive, very stable and good leaving group, and also can be removed and/ or recycles spurred our interest in their use for other transformation according to Yoon et al.18-24

Although alkyl/aryl 4,5-dichloro-6-oxopyridazine-1(6H)- carboxylates are good carbonyl source, however, these can not use in basic condition because of the side reaction.25-27 Thus, we required an acidic condition for the synthesis of carbonate from alkyl/aryl 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylates and alcohols.

Inspired by the oxidative carbonyation1,15,28 and the method of carbamate reaction,1,16 we attempted to develop an novel convenient synthetic method for unsymmetric and symmetric organic carbonates from alkyl(or aryl) 6-oxopyridazin-1(6H)-one carboxylate as a carbamate and ROH in the presence of AlCl3 (Scheme 1).

Herein, we report the synthesis of organic carbonates using ROH/AlCl3 systems and alkyl(or aryl) 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylates system in toluene at room temperature.

 

Results and Discussion

In order to demonstrate our research motivation, we firstly attempted to find a novel ROH/MCln system acting alkoxide equivalent. First of all, we selected aluminum chloride as the Lewis acid. Although the reaction of ROH (3 equiv.) with AlCl3 (1 equiv.) yields the corresponding aluminum alkoxides [Al(OR)3],29 (ROH-AlCl3) adduct (1:1 ratio) may be easily formed in the initial step of this reaction. If only to remove the proton of (ROH-AlCl3) adducts in the solvent, the residue [(ROAlCl3)−] may be act as the alkoxide. To remove a proton of the adducts, the proton acceptor such as the organic base or the leaving group is required.

3ROH + AlCl3 → 3[(ROH)+(AlCl3)−] → (RO)3Al + 3 HClROH + AlCl3 → [(ROH)+(AlCl3)−] + Base → [(ROAlCl3)−][H(Base)+]

Alkyl(or aryl) 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylates 3 were prepared by the literature method17 from 4,5-dichloropyridazin-3(2H)-one (1) and the corresponding chloroformate 2 (Scheme 2).

Scheme 2.Synthesis of symmetric and unsymmetric organic carbonates using alcohol-AlCl3 adducts.

As a model reaction to evaluate newly designed reaction, we studied the effect of Lewis acids, protic acids and solvents in the reaction of n-butanol in the presence of Lewis acids or protic acids with phenyl 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylate (3a) as a acyl source at room temperature. Among the twelve Lewis acids investigated, one equivalent of aluminum chloride showed the best results (Entry 2, Table 1). Next, we investigated the solvent effect using the 4a/3a/AlCl3 system. Toluene also showed the best results among the six solvents tested (Entry 3, Table 2).

Table 1.aReaction condition: 4a/3a (1:1 mole ratio) in toluene at room temperature. bIsolated yield.

Table 2.aReaction condition: 4a/AlCl3/3a (1:1:1 mole ratio) at room temperature. bIsolated yield.

On the other hand, we evaluated the reactivity of phenyl chloroformate (2a) as carbonyl source under our condition. Although reaction of n-butanol (4a) with 2a in the presence of AlCl3 in refluxing toluene gave the carbonate 6a in 20% yield, the reactions did not proceed in the presence of AlCl3 at room temperature or in the absence of AlCl3 at room temperature and at reflux temperature in toluene.

Scheme 3.Reaction of phenyl chloroformate (2a) with 4a.

Based on the above preliminary experimental data, we selected ROH/AlCl3/3 (1:1:1 mole ratio) system in toluene at room temperature as the optimized conditions.

To illustrate the versatility of our method, we prepared some unsymmetric organic carbonates using 3a and alcohols under the optimized conditions. Compound 3a was reacted with aliphatic and aromatic alcohols in the presence of aluminum chloride in toluene at room temperature to give the corresponding unsymmetric organic carbonate 5b-5h in 80-90% yields except for 4-(2-hydroxyethyl)phenol (Table 3). Reaction of 3a with 4-(2-hydroxyethyl)phenol in the presence of AlCl3 under the optimized conditions gave the corresponding carbonate 5i (39%) and diphenyl carbonate (15%) (Entry 8, Table 3). The long reaction time may be the cause that generated diphenyl carbonate in this reaction. Actually, the mixture of compound 3a and AlCl3 was stirred for 10 hours at room temperature to give diphenyl carbonate by the decomposition of 3a. Reaction of 3a with benzenethiol in the presence of AlCl3 under the optimized conditions also afford the corresponding thiocarbonate 5j (85%) (Entry 9, Table 3).

Table 3.aReaction condition: 4/AlCl3/3a (1:1:1 mole ratio) in toluene at room temperature. bIsolated yield. cCyclohexanol. dWe obtained diphenyl cabonate in 15% yield.

Next, we attempted to prepare from compound 3b under the same conditions. Reaction of 3b with some aliphatic and aromatic alcohols in the presence of AlCl3 under the optimized conditions afford the corresponding unsymmetric carbonates 5k-5q in good yields (Table 4).

Table 4.aReaction condition: 4/AlCl3/3b (1:1:1 mole ratio) in toluene at room temperature. bIsolated yield. cCyclohexanol.

On the other hand, we attempted the symmetric organic carbonate by our method. Alkyl/aryl 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylates 3 were reacted with alcohols in the presence of AlCl3 under the optimized conditions to give the corresponding symmetric carbonates 6a-6g in 45-94% yields.

In all case, we isolated quantitatively 4,5-dichloropyridazin- 3(2H)-one. The structures of all prepared compounds were established by IR, NMR and HRMS. A plausible mechanism showed in Scheme 4.

Scheme 4.Plausible mechanism for the reaction of phenyl 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylate with ROH/AlCl3 systems.

In summary, an efficient and versatile method was developed for the synthesis of symmetric and unsymmetric organic carbonates. The reaction was carried out in the presence of AlCl3 in toluene at room temperature, and alkyl/aryl 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylates are used as a CO or CO2R(Ar) source. It may be considered as a novel type that could use N-acylazinone such as carbamate and ROH/AlCl3 system at room temperature for the synthesis of symmetric and unsymmetric organic carbonates. Our methods are efficient, convenient and practical. It is worthy to note that the reaction use ROH/AlCl3 system and the stable and non-toxic CO/CO2R(Ar) source, the easy-to prepare and readily available starting materials and the quantitative isolation of reusable 4,5-dichloropyridazin-3(2H)-one. We also believe that our methods would be applicable practically to industrial processes.

Table 5.aReaction condition: 4/AlCl3/3 (1:1:1 mole ratio) in toluene at room temperature. bIsolated yield. cWe used the corresponding alcohol as the reagent and the solvent.

 

Experimental

General Methods. Melting points were determined with a capillary apparatus and uncorrected. NMR spectra were recorded on a 300 MHz spectrometer with chemical shift values reported in δ units (ppm) relative to an internal standard (TMS). IR spectra were obtained on a Varian 640- IR spectrophotometer. Mass spectra were recorded under electron ionization (EI). Thin–layer chromatography (TLC) analyses were performed using precoated silica gel plates. The open-bed chromatography was carried out on silica gel (70-230 mesh, Merck) using gravity flow. The column was packed with slurries made from the elution solvent.

General Procedure for the Synthesis of Alkyl/aryl 4,5- dichloro-6-oxopyridazine-1(6H)-carboxylate 3. To a solution of 4,5-dichloropyridazin-3(2H)-one (1, 3.0 mmol) and Et3N (3.6 mmol) in CH2Cl2 (30 mL) was added dropwise the appropriate alkyl/aryl chloroformate (2, 3.9 mmol) and the mixture was stirred for 10 min at 5 ℃ (Scheme 1). The reaction mixture was washed using water (5 × 50 mL). The organic layer was dried over anhydrous magnesium sulfate, and then evaporated under reduced pressure. The resulting residue was recrystallized from THF/n-hexane (1:3, v/v) to give the product 3.

Phenyl 4,5-Dichloro-6-oxopyridazine-1(6H)-carboxylate (3a):17 Yield: 787 mg, 92%; white solid; mp 140 ℃ (lit. mp 140 °C); IR (KBr): 3074, 3043, 1793, 1681, 1602, 1483, 1272, 1188, 1070, 948, 877, 750 cm−1; 1H NMR (300 MHz, DMSO-d6) δ 7.33-7.41 (m, 3H), 7.50-7.56 (m, 2H), 8.38 (s, 1H); 13C NMR (75 MHz, DMSO-d6) δ 13.9, 66.3, 136.1, 136.7, 136.9, 150.6, 154.3; HRMS (EI) m/z: [M]+ calcd for C7H6Cl2N2O3: 235.9755; Found: 235.9758.

Ethyl 4,5-Dichloro-6-oxopyridazine-1(6H)-carboxylate (3b): Yield: 704 mg, 99%; white solid; mp 78-79 ℃; IR (KBr): 3061, 1783, 1683, 1603, 1242 1140, 945, 883, 757 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.46 (t, 3H, J = 7.1 Hz), 4.55 (q, 2H, J = 7.1 Hz), 7.84 (s, 1H); 13C NMR (75 MHz, CDCl3) δ 13.95, 66.25, 136.13, 136.70, 136.94, 150.69, 154.34; HRMS (EI) m/z: [M]+ calcd for C7H6Cl2N2O3: 235.9755; Found: m/z 235.9758.

Methyl 4,5-Dichloro-6-oxopyridazine-1(6H)-carboxylate (3c): Yield: 616 mg, 92%; white solid; mp 112 ℃; IR (KBr): 3058, 3037, 2957, 1761, 1695, 1599, 1529, 1439, 1260, 1238, 1192, 927, 767 cm−1; 1H NMR (300 MHz, DMSO-d6) δ 4.00 (s, 3H), 8.30 (s, 1H); 13C NMR (75 MHz, DMSO-d6) δ 55.9, 134.7, 136.5, 137.4, 150.9, 154.0; HRMS (EI) m/z: [M]+ calcd for C6H4Cl2N2O3: 221.9599; Found: 221.9597.

4-Chlorophenyl 4,5-Dichloro-6-oxopyridazine-1(6H)-carboxylate (3d): Yield: 824 mg, 86%; white solid; mp 143-144 ℃; IR (KBr): 3112, 3073, 2969, 2840, 1789, 1687, 1593, 1505, 1304, 1284, 1230, 1194, 1160, 1106, 1031, 947, 831, 749 cm−1; 1H NMR (300 MHz, DMSO-d6) δ 7.40 (d, 2H, J = 9.0 Hz), 7.59 (d, 2H, J = 9.0 Hz), 8.39 (s, 1H); 13C NMR (75 MHz, DMSO-d6) δ 117.3, 122.7, 123.5, 129.6, 133.7, 133.0, 137.1, 156.7, 157.4; HRMS (EI) m/z: [M]+ calcd for C11H5Cl3N2O3: 317.9366; Found: 317.9362.

p-Tolyl 4,5-Dichloro-6-oxopyridazine-1(6H)-carboxylate (3e): Yield: 835 mg, 93%; white solid; mp 107-109 ℃; IR (KBr): 3107, 3075, 2951, 2919, 2864, 1793, 1693, 1596, 1502, 1287, 1244, 1194, 1166, 943, 748; 1H NMR (300 MHz, DMSO-d6) δ 2.35 (s, 3H), 7.21 (d, J = 8.7 Hz), 7.31 (d, J = 8.4 Hz), 8.37(s, 1H); 13C NMR (75 MHz, DMSO-d6) δ 20.3, 120.6, 130.2, 134.8, 136.3, 137.7, 147.9, 149.1, 154.1, 156.1; HRMS (EI) m/z: [M]+ calcd for C12H8Cl2N2O3: 297.9912; Found: 297.9913.

4-Methoxyphenyl 4,5-Dichloro-6-oxopyridazine-1(6H)- carboxylate (3f): Yield: 832 mg, 88%; white solid; mp 104- 105 ℃; IR (KBr): 3110, 3069, 3008, 2969, 2942, 2909, 2839, 1791, 1688, 1594, 1505, 1283, 1230, 1193, 1166, 1105, 1029, 944, 834, 749; 1H NMR (300 MHz, DMSO-d6) δ 3.82 (s, 3H), 6.94 (d, 2H, J = 9.2 Hz), 7.59 (d, 2H, J = 9.2 Hz), 7.90 (s, 1H); 13C NMR (75 MHz, DMSO-d6) δ 56.0, 115.3, 122.4, 135.3, 136.9, 138.2, 144.0, 149.8, 154.7, 158.1; HRMS (EI) m/z: [M]+ calcd for C12H8Cl2N2O4: 313.9861; Found: 313.9868.

4-Nitrophenyl 4,5-Dichloro-6-oxopyridazine-1(6H)- carboxylate (3g): Yield: 921 mg, 93%; white solid; mp 134- 135 ℃; IR (KBr): 3119, 3072, 1792, 1688, 1535, 1348, 1198, 1169, 862, 745; 1H NMR (300 MHz, CDCl3) δ 7.54 (d, 2H, J = 9.1 Hz), 7.94 (s, 1H), 8.36 (d, 2H, J = 9.1 Hz); 13C NMR (75 MHz, CDCl3) δ 122.0, 125.6, 136.3, 137.3, 137.6, 146.2, 148.4, 154.3, 154.4; HRMS (EI) m/z: [M]+ calcd for C11H5Cl2N3O5: 328.9606; Found: 328.9602.

General Procedure for the Synthesis of Unsymmetric and Symmetric Carbonates 5 and 6. To a solution of alcohol (or thiol) 4 (0.7 mmol) and AlCl3 (0.7 mmol) in toluene (10 mL), compound 3 (0.7 mmol) was added. The mixture was stirred at room temperature until compound 3 was consumed, as determined by TLC. A 10% aqueous NaOH solution (50 mL) and dichloromethane (30 mL) were added to the reaction mixture with stirring. The organic layer was extracted and washed water (50 mL), and dried over anhydrous magnesium sulfate, and the solvent was evaporated under the reduced pressure. The resulting residue was transferred to an open-bed silica gel column (2.5 × 4 cm). The column was eluted with n-hexane/ethyl acetate (3:1, v/v) to isolate compound 5 and 6 and then ethyl acetate to isolate 4,5-dichloropyridazin-3(2H)-one (1). The column fractions containing pure compound were combined and evaporated under reduced pressure to give the respective product. 4,5-Dichloropyridazin-3(2H)-one was obtained quantitative yield and reused.

Butyl Phenyl Carbonate (5a): Yield: 110 mg, 81%; liquid; IR (KBr): 3068, 3041, 2959, 2932, 2870, 1759, 1591, 1490, 1456, 1388, 1250, 1208, 1067, 768 cm−1; 1H NMR(300 MHz, CDCl3) δ 0.96 (t, 3H, J = 7.3 Hz), 1.41-1.51 (m, 2H), 1.67-1.77 (m, 2H), 4.25 (t, 2H, J = 6.1 Hz), 7.16-7.25 (m, 3H), 7.34-7.40 (m, 2H); 13C NMR (75 MHz, CDCl3) δ 13.6, 18.9, 30.5, 68.6, 121.0, 125.9, 129.4, 151.1, 153.8; HRMS (EI) m/z: [M]+ calcd for C11H14O3: 194.0943; Found: 194.0951.

Methyl Phenyl Carbonate (5b): Yield: 94 mg, 88%; liquid; IR (KBr): 3062, 3030, 2957, 2920, 1762, 1592, 1439, 1262, 1215, 1062, 941, 768, 704 cm−1; 1H NMR (300 MHz, CDCl3) δ 3.88 (s, 3H), 7.16-7.26 (m, 3H), 7.35-7.41 (m, 2H); 13C NMR (75 MHz, CDCl3) δ 55.4, 121.0, 126.1, 129.5, 151.1, 154.3; HRMS (EI) calcd for C8H8O3: 152.0473; Found: 152.0475.

Cyclohexyl Phenyl Carbonate (5c): Yield: 139 mg, 90%; white solid; mp 58-60 ℃; IR (KBr): 3064, 3041, 2942, 2860, 1750, 1591, 1491, 1372, 1250, 1205, 1003, 938, 715 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.25-1.58 (m, 6H), 1.76-2.01 (m, 4H), 4.68-4.75 (m, 1H), 7.16-7.25 (m, 3H), 7.37 (t, 2H, J = 7.6 Hz); 13C NMR (75 MHz, CDCl3) δ 23.6, 25.2, 31.4, 77.7, 121.1, 125.8, 129.4, 151.1, 153.1; HRMS (EI) m/z: [M]+ calcd for C13H16O3: 220.1099; Found: 220.1098.

Phenethyl Phenyl Carbonate (5d):30 Yield: 153 mg, 90%; white solid; mp 83-85 ℃ (lit. mp 89 ℃); IR (KBr): 3109, 3081, 3058, 3033, 2969, 2938, 2895, 2868, 1753, 1492, 1260, 1210, 1077, 967, 778, 753 cm−1; 1H NMR (300 MHz, CDCl3) δ 3.00 (t, 2H, J = 7.0 Hz), 4.38-4.43 (m, 2H), 7.10 - 7.35 (m, 10H); 13C NMR (75 MHz, CDCl3) δ 35.1, 69.1, 121.0, 121.2, 126.1, 126.4, 126.9, 128.7, 129.1, 129.6, 129.7, 137.1, 151.1, 151.2, 153.7; HRMS (EI) m/z: [M]+ calcd for C15H14O3: 242.0943; Found: 242.0941.

4-Chlorophenyl Phenyl Carbonate (5e):31 Yield: 151 mg, 87%; white solid; mp 57-59 ℃ (lit. mp 82-84 ℃); IR (KBr): 3175, 3068, 1765, 1586, 1480, 1245, 1177, 1069, 1001, 906, 755 cm−1; 1H NMR (300 MHz, DMSO-d6) δ 7.32-7.61 (m, 9H), 7.42-7.47 (m, 3H); 13C NMR (75 MHz, CDCl3) δ 119.3, 120.8, 120.9, 121.7, 126.3, 126.5, 126.6, 129.6, 129.6, 130.3, 134.8, 150.9, 151.3; HRMS (EI) m/z: [M]+ calcd for C13H9ClO3: 248.0240; Found: 248.0238.

4-Methoxyphenyl Phenyl Carbonate (5f): Yield: 136 mg, 80%; white solid; mp 39-40 ℃; IR (KBr): 3065, 3011, 2967, 2932, 2910, 2839, 1769, 1511, 1241, 1179, 1031, 832, 778 cm−1; 1H NMR (300 MHz, CDCl3) δ 3.76 (s, 3H), 6.99- 7.02 (m, 2H), 7.30-7.50 (m, 7H); 13C NMR (75 MHz, CDCl3) δ 55.4, 114.5, 121.2, 122.1, 126.4, 129.6, 144.2, 150.7, 152.0, 157.3; HRMS (EI) m/z: [M]+ calcd for C14H12O4: 244.0736; Found: 244.0736.

4-Nitrophenyl Phenyl Carbonate (5g):32 Yield: 162 mg, 89%; white solid; mp 124-125 ℃ (lit. mp 127-128 ℃); IR (KBr): 3116, 3087, 2923, 2855, 1764, 1618, 1596, 1527, 1490, 1351, 1274, 1187, 1158, 1008, 854, 752, 686, 496 cm−1; 1H NMR (300 MHz, DMSO-d6) δ 7.33-7.40 (m, 1H), 7.41-7.44 (m, 2H), 7.46-7.53 (m, 2H), 7.69-7.72 (m, 2H), 8.34-8.40 (m, 2H); 13C NMR (75 MHz, DMSO-d6) δ 121.1, 122.6, 125.4, 126.6, 129.7, 145.3, 150.5, 150.6, 155.0; HRMS (EI) m/z: [M]+ calcd for C13H9NO5: 259.0481; Found: 259.0481.

[1,1'-Biphenyl]-4-yl Phenyl Carbonate (5h): Yield: 175mg, 86%; white solid. mp 128-131 ℃. IR (KBr): 3062, 3034, 2921, 2853, 1763, 1487, 1241, 1206, 1183, 757, 688 cm−1; 1H NMR (300 MHz, DMSO-d6) δ 7.32-7.50 (m, 10H) 7.67-7.78 (m, 3H); 13C NMR (75 MHz, DMSO-d6) δ 121.1, 121.6, 126.4, 126.6, 127.5, 127.8, 128.9, 129.6, 138.3, 139.0, 150.0, 150.5, 151.5; HRMS (EI) m/z: [M]+ calcd for C10H12O3: 290.0943; Found: m/z 290.0945.

p-Hydroxyphenyl Phenyl Carbonate (5i). Yield: 78 mg, 39%; liquid; IR (KBr): 3074, 3043, 1793, 1681, 1602, 1483, 1272, 1188, 1070, 948, 877, 750, 617 cm−1; 1H NMR (300 MHz, DMSO-d6) δ 2.87 (t, 2H, J1 = 6.6 Hz, J2 = 6.9 Hz), 4.33 (t, 2H, J1 = 6.9 Hz, J2 = 6.8 Hz), 6.69-6.73 (m, 2H), 7.07 (d, 2H, J = 8.4 Hz), 7.18-7.21 (m, 2H), 7.26-7.31 (m, 1H), 7.39-7.45 (m, 2H), 9.27 (s, 1H, D2O exchangeable); 13C NMR (75 MHz, DMSO-d6) δ 33.3, 69.1, 115.1, 121.2, 126.0, 127.2, 129.5, 129.8, 150.6, 152.9, 155.9; HRMS (EI) m/z: [M]+ calcd for C13H10O4: 283.9755; Found: m/z 283.9758.

O,S-Diphenyl Thiocarbonate (5j): Yield: 137 mg, 85%; white solid; mp 55 ℃; IR (KBr): 3058, 1731, 1588, 1484, 1440, 1243, 1187, 1160, 1107, 1080, 998, 742 cm−1; 1H NMR (300 MHz, DMSO-d6) δ 7.26-7.33 (m, 3H), 7.42-7.51 (m, 5H), 7.65-7.68 (m, 2H); 13C NMR (75 MHz, DMSO-d6) δ 121.8, 126.8, 127.0, 130.0, 130.1, 130.2, 130.6, 135.2, 151.2, 168.4; HRMS (EI) m/z: [M]+ calcd for C13H10O2S: 230.0402; Found: 230.0403.

Butyl Ethyl Carbonate (5k):33 Yield: 88 mg, 86%; liquid; IR (KBr): 2961, 2934, 2873, 1746, 1462, 1401, 1257, 1061, 1016, 934, 791 cm−1; 1H NMR (300 MHz, CDCl3) δ 0.94 (t, 3H, J = 7.4 Hz), 1.26-1.48 (m, 5H), 1.60-1.69 (m, 2H), 4.10-4.22 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 13.6, 14.2, 18.9, 30.6, 63.7, 67.6, 155.4; MS (EI, 70 eV) m/z: 119 [M]+ (6), 118 [M-H]+ (8), 91 (8), 73 (12), 63 (31), 57 (100), 56 (46).

Cyclohexyl Ethyl Carbonate (5l):34 Yield: 101 mg, 84%; liquid; IR (KBr): 2938, 2860, 1739, 1453, 1374, 1318, 1253, 1175, 1121, 1098, 1034, 1013, 939, 896, 792 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.29-1.51 (m, 9H), 1.75 (s, 2H), 1.92 (s, 2H), 4.15-4.19 (m, 2H), 4.55-4.61 (m, 1H); 13C NMR (75 MHz, CDCl3) δ 14.2, 23.6, 23.7, 24.7, 25.2, 31.5, 31.6, 63.5, 154.6; MS (EI, 70 eV) m/z: 99 [M-CH3CH2CO]+ (48), 91 (97), 83 [M-CH3CH2OCO2]+ (69), 82 [M-CH3CH2OCO2- H]+ (83), 81 (25), 67 (100), 63 (43), 57 (71), 55 (67).

Ethyl Phenethyl Carbonate (5m). Yield: 122 mg, 84%; liquid; IR (KBr): 3063, 3028, 2982, 2910, 1744, 1456, 1400, 1258, 1201, 1088, 1005, 790, 749, 700 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.27 (t, 3H, J = 7.1 Hz), 2.96 (t, 2H, J = 6.8 Hz), 4.16 (q, 2H, J = 7.1 Hz), 4.32 (t, 2H, J = 7.1 Hz), 7.21- 7.31 (m, 5H); 13C NMR (75 MHz, CDCl3) δ 14.2, 35.2, 63.9, 68.1, 126.6, 128.5, 128.9, 137.3, 155.1; HRMS (EI) m/z: [M]+ calcd for C11H14O3: 194.0943; Found: 194.0969.

4-Chlorophenyl Ethyl Carbonate (5n): Yield: 115 mg, 82%; liquid; IR (KBr): 3075, 2986, 2938, 1763, 1590, 1474, 1429, 1369, 1247, 1215, 1063, 994, 860, 780 cm−1; 1H NMR (300 MHz, DMSO-d6) δ 1.30 (t, 3H, J = 7.1 Hz), 4.26 (q, 2H, J = 7.1 Hz), 7.23-7.27 (m, 1H), 7.36-7.39 (m, 1H), 7.44- 7.50 (m, 2H); 13C NMR (75 MHz, DMSO-d6) δ 13.9, 64.8, 120.2, 121.8, 126.2, 130.9, 133.3, 151.3, 152.5; HRMS (EI) m/z: [M]+ calcd for C9H9ClO3: 200.0240; Found: 200.0242.

Ethyl 4-Methoxyphenyl Carbonate (5o): Yield: 114 mg, 83%; liquid; IR (KBr): 3063, 2984, 2901, 1755, 1488, 1374, 1307, 1259, 1222, 1174, 1090, 972, 841, 762, 730 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.35 (t, 3H, J = 7.1 Hz), 3.75 (s, 3H), 4.28 (q, 2H, J = 7.1 Hz), 6.83-6.89 (m, 2H), 7.05-7.11 (m, 2H); 13C NMR (75 MHz, CDCl3) δ 14.1, 55.5, 64.6, 114.4, 121.9, 144.7, 154.0, 157.3; HRMS (EI) m/z: [M]+ calcd for C10H12O4: 196.0736; Found: 196.0741.

Ethyl 4-Nitrophenyl Carbonate (5p):35 Yield: 124 mg, 84%; white solid; mp 75-76 ℃ (lit. mp 67-68 ℃); IR (KBr): 3118, 3085, 3004, 2923, 2855, 1758, 1521, 1378, 1352, 1283, 1230, 1001, 857 cm−1; 1H NMR (300 MHz, DMSO-d6) δ 1.31 (t, 3H, J = 7.1 Hz), 4.30 (q, 2H, J = 7.1 Hz), 7.54- 7.60 (m, 2H), 8.30-8.34 (m, 2H); 13C NMR (75 MHz, DMSO-d6) δ 14.3, 65.7, 123.0, 125.8, 145.6, 152.4, 155.7; HRMS (EI) m/z: [M]+ calcd. for C9H9NO5; 211.0481; Found: 211.0481.

[1,1'-Biphenyl]-4-yl Ethyl Carbonate (5q):36 Yield: 146 mg, 86%; white solid; mp 75-76 ℃ (lit. mp 74-74.5 ℃); IR (KBr): 3063, 2984, 1755, 1488, 1374, 1307, 1259, 1222, 1090, 1055, 973, 842, 762, 730 cm−1; 1H NMR (300 MHz, DMSO-d6) δ 1.31 (t, 3H, J = 6.0 Hz), 4.28 (q, 2H, J = 6.0 Hz), 7.32-7.48 (m, 5H), 7.66-7.73 (m, 4H); 13C NMR (75 MHz, DMSO-d6) δ 14.4, 65.1, 122.2, 127.1, 128.0, 128.3, 129.4, 138.5, 139.7, 150.7, 153.4; HRMS (EI) m/z: [M]+ calcd for C15H14O3: 242.0943; Found: 242.0941.

Diphenyl Carbonate (6a):37 Yield: 141 mg, 94%; white solid; mp 75-76 ℃ (lit. mp 77-78 ℃); IR (KBr): 3058, 1773, 1592, 1490, 1255, 1233, 1182, 1071, 1016, 996, 751 cm−1; 1H NMR (300 MHz, DMSO-d6) δ 7.30 - 7.35 (m, 2H), 7.40- 7.51 (m, 8H); 13C NMR (75 MHz, DMSO-d6) δ 121.2, 126.4, 129.7, 150.7, 151.7; HRMS (EI) m/z: [M]+ calcd for C13H10O3: 214.0630; Found: 214.0634.

Diethyl Carbonate (6b):33 Yield: 67 mg, 81%; liquid; IR (KBr): 2987, 2940, 2913, 1748, 1470, 1408, 1375, 1271, 1093, 1022, 855, 792 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.30 (t, 6H, J = 7.2 Hz), 4.19 (q, 4H, J = 7.2 Hz); 13C NMR (75 MHz, CDCl3) δ 13.9, 63.4, 154.9; MS (EI, 70 eV) m/z: 91 [M+H]+ (61), 90 [M]+ (3), 75 (3), 63 (20), 59 (6), 45 (100), 31 (58), 30 (3), 29 (90), 28 (13), 27 (28).

Dimethyl Carbonate (6c): Yield: 28 mg, 45%; liquid; IR (KBr): 3009, 2967, 2928, 2861, 1774, 1457, 1295, 989 cm−1; 1H NMR (300 MHz, CDCl3) δ 3.79 (s, 6H); 13C NMR (75 MHz, CDCl3) δ 54.5, 156.2; HRMS (EI) m/z: [M]+ calcd for C3H6O3: 90.0317; Found: 90.0314.

Bis(4-chlorophenyl) Carbonate (6d):38 Yield: 187 mg, 94%; white solid; mp 146-147 ℃ (lit. 144-146 ℃); IR (KBr): 3102, 3077, 1769, 1491, 1289, 1264, 1089, 822, 783 cm−1; 1H NMR (300 MHz, CDCl3) δ 7.20-7.23 (m, 4H), δ 7.20-7.23 (m, 4H), 7.37-7.40 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 122.2, 129.7, 131.9, 149.3, 151.5; HRMS (EI) m/z: [M]+ calcd for C13H8Cl2O3: 281.9850; Found: 281.9851.

Di-p-tolyl Carbonate (6e):39 Yield: 158 mg, 94%; white solid; mp 109-110 ℃ (lit. mp 111-112 ℃); IR (KBr): 3039, 2923, 2858, 1772, 1507, 1240, 1177, 1156, 1011, 886, 812, 769 cm−1; 1H NMR (300 MHz, CDCl3) δ 2.34 (s, 6H), 7.12 - 7.20 (m, 8H); 13C NMR (75 MHz, CDCl3) δ 20.8, 120.6, 130.0, 135.9, 148.9, 152.4; HRMS (EI) m/z: [M]+ calcd for C15H14O3: 242.0943; Found: 242.0945.

Bis(4-methoxyphenyl) Carbonate (6f).40 Yield: 171 mg, 89%; white solid; mp 94-95 ℃ (lit. mp 96-97 ℃); IR (KBr): 3110, 3066, 3027, 2971, 2933, 2838, 1768, 1601, 1508, 1458, 1305, 1274, 1238, 1176, 1099, 1024, 826, 775 cm−1; 1H NMR (300 MHz, CDCl3) δ 3.80 (s, 6H), 6.90 (d, 4H, J = 9.0 Hz), 7.18 (d, 4H, J = 9.0 Hz); 13C NMR (75 MHz, CDCl3) δ 55.6, 114.5, 121.7, 144.6, 152.8, 157.5; HRMS (EI) m/z: [M]+ calcd for C15H14O5: 274.0841; Found: m/z 274.0840.

Bis(4-nitrophenyl) Carbonate (6g):40 Yield: 139 mg, 70%; white solid; mp 137-139 ℃ (lit. mp 138-140 ℃); IR (KBr): 3114, 3079, 1765, 1617, 1526, 1360, 1371, 1245, 1194, 1161, 1106, 1009, 891, 859, 745 cm−1; 1H NMR (300 MHz, DMSO-d6) δ 7.50 (d, 4H, J = 9.1 Hz), 8.34 (d, 4H, J = 9.1 Hz); 13C NMR (75 MHz, DMSO-d6) δ 121.6, 125.3, 125.5, 128.2, 129.0, 145.9, 150.0, 154.8; HRMS (EI) m/z: [M]+ calcd for C13H8N2O7: 304.0332; Found: m/z 304.0331.