A Green Chemistry Method for the Regeneration of Carbonyl Compounds from Oximes by Using Cupric Chloride Dihydrate as a Recoverable Promoter for Hydrolysis

Abstract

A mild, efficient, general, and green method for the regeneration of carbonyl compounds from their corresponding oximes is described. Cupric salts promoted hydrolysis of oximes was studied, and the best reaction conditions for the hydrolysis have been found. Carbonyl compounds were obtained in 85-98% yields after the treatment of oximes with 2 molar equivalent of CuCl₂˙2H₂O at reflux (around 75 ˚C) in a mixed solvent of acetonitrile and water (4:1). In addition, cupric salt was readily recovered in an almost quantitative yield via the complete precipitation of Cu(OH)₂˙2H₂O.

Key words

carbonyl compounds - oxime - hydrolysis - cupric chloride - green chemistry

References and Notes

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13

Typical Procedure for the CuCl ₂ ˙2H ₂ O-Promoted Regeneration of Carbonyl Compounds from Various Oximes
Oxime 1a (1.01 g, 5.12 mmol) was dissolved in MeCN (20 mL), CuCl₂˙2H₂O (1.73 g, 10.15 mmol) and H₂O (5 mL) were added. When the suspension was heated to reflux, the mixture became a bluish clear solution. The resulting reaction solution was then stirred at reflux (75 ˚C) for around 2 h and monitored by TLC (EtOAc-hexane, 1:6). After the reaction was complete, the solvents were removed by vacuum distillation. The residue was partitioned between EtOAc (50 mL) and H₂O (30 mL), the organic and aqueous phases were separated. Organic phase was washed with brine (5 mL) and dried over anhyd MgSO₄. Concentration of the organic solution gave crude product, which was purified by flash chromatography to afford benzophenone (2a, 0.914 g, 5.02 mmol) in 98% yield. To the above-mentioned aqueous phase was added an aq solution of NaOH (11.0 mL, 2 M, 22.00 mmol). After vigorous stirring for 1 h, the bluish solid was collected on a Buchner funnel by suction. After being dried in a warm air at around 50 ˚C for 12 h until the weight of the solid kept constant, Cu(OH)₂˙2H₂O (1.34 g, 10.03 mmol) was recovered in 99% yield.
Spectral analysis showed that compounds 2a-e,i-l,n-s,v obtained from the above hydrolysis are identical with the commercially available authentic samples. Characterization data of compounds 2f-h,m,t,u are as follows:
Compound 2f: ^¹H NMR (400 MHz, CDCl₃): δ = 3.89 (s, 3 H), 7.35 (d, J = 7.9 Hz, 1 H), 7.48-7.57 (m, 4 H), 7.62-7.69 (m, 1 H), 8.18-8.24 (m, 2 H), 9.98 (s, 1 H). MS (EI): m/z (%) = 256 (4) [M⁺], 217 (18), 182 (2), 155 (2), 105 (100), 77 (17). IR (KBr): ν = 3005, 2885, 1735, 1680, 1600, 1505, 1450, 1400, 1255, 1190, 1140, 1120, 1060, 1025, 850, 805, 730, 700 cm^-¹.
Compound 2g: ^¹H NMR (400 MHz, CDCl₃): δ = 1.30 (t, J = 7.1 Hz, 3 H), 4.30 (q, J = 7.1 Hz, 2 H), 4.71 (s, 2 H), 7.02 (d, J = 6.9 Hz, 2 H), 7.85 (d, J = 6.9 Hz, 2 H), 9.90 (s, 1 H). IR (neat): ν = 2980, 2835, 2770, 1755, 1690, 1600, 1510, 1440, 1380, 1310, 1280, 1205, 1160, 1080, 1025, 835, 715, 610 cm^-¹. HRMS (EI): m/z calcd for C₁₁H₁₂O₄ [M⁺]: 208.0736; found: 208.0730.
Compound 2h: ^¹H NMR (400 MHz, CDCl₃): δ = 1.30 (t, J = 7.1 Hz, 3 H), 3.96 (s, 1 H), 4.28 (q, J = 7.1 Hz, 2 H), 4.79 (s, 2 H), 6.84 (d, J = 8.1 Hz, 1 H), 7.41-7.46 (m, 2 H), 9.87 (s, 1 H). IR (KBr): ν = 2980, 2940, 2910, 1750, 1680, 1590, 1510, 1470, 1430, 1395, 1270, 1200, 1140, 1070, 1030, 870, 810, 780, 735, 640 cm^-¹. HRMS (EI): m/z calcd for C₁₂H₁₄O₅ [M⁺]: 238.0841; found: 238.0839.
Compound 2m: ^¹H NMR (400 MHz, CDCl₃): δ = 7.52 (dd, J ₁ = 1.6 Hz, J ₂ = 8.6 Hz, 1 H), 7.67 (d, J = 1.6 Hz, 1 H), 8.29 (d, J = 8.6 Hz, 1 H), 10.07 (s, 1 H), 10.58 (s, 1 H). IR (KBr): ν = 3255, 3085, 2870, 1700, 1620, 1585, 1530, 1480, 1450, 1315, 1255, 1165, 1140, 1080, 985, 850, 760, 705, 540 cm^-¹. MS (EI): m/z (%) = 167 (100) [M⁺], 166 (44), 151 (1), 136 (3), 119 (7), 109 (4), 92 (3), 81 (3), 63 (6).
Compound 2t: ^¹H NMR (400 MHz, CDCl₃): δ = 2.28 (s, 3 H), 3.50-3.69 (m, 2 H), 4.88 (dd, J ₁ = 6.1 Hz, J ₂ = 8.1 Hz, 1 H), 7.03 (d, J = 7.9 Hz, 2 H), 7.13-7.26 (m, 5 H), 7.28-7.35 (m, 2 H), 7.37-7.44 (m, 2 H) 7.48-7.55 (m, 1 H), 7.82-7.89 (m, 2 H). MS (EI): m/z (%) = 332(4) [M⁺], 209 (5), 179 (2), 123 (13), 105 (100), 91 (6), 77 (59). IR (KBr): ν = 3035, 2920, 1685, 1595, 1490, 1450, 1420, 1335, 1220, 980, 810, 745, 700, 685, 550 cm^-¹.
Compound 2u: ^¹H NMR (400 MHz, CDCl₃): δ = 2.05 (s, 3 H), 2.29 (s, 3 H), 2.92-3.08 (m, 2 H), 4.63 (dd, J ₁ = 6.8 Hz, J ₂ = 7.8 Hz, 1 H), 7.03 (d, J = 8.0 Hz, 2 H), 7.18 (d, J = 8.0 Hz, 2 H), 7.19-7.26 (m, 5 H). MS (EI): m/z (%) = 270 (32) [M⁺], 213 (2), 147 (43), 124 (100), 103 (5), 91 (12), 77 (7), 43 (43). IR (neat): ν = 3030, 2940, 1720, 1490, 1455, 1410, 1360, 1150, 1020, 810, 700, 535, 500 cm^-¹.

16

When the pH value was kept higher than 9.5, the precipitation of Cu(OH)₂˙2H₂O was complete, which was determined by adding 2 drops of an aq solution of Na₂S into the filtrate. No black CuS appeared.

17

Conversion of Cu(OH) ₂ ˙2H ₂ O into CuCl ₂ ˙2H ₂ O
The above Cu(OH)₂˙2H₂O was first heated at 150 ˚C for around 6 h, and the resulting brown anhyd CuO was then treated with 2.2 molar equivalent of aq HCl at reflux for 2 h. Removal of H₂O under vacuum at 45 ˚C gave blue crystalline CuCl₂˙2H₂O in a nearly quantitative yield.