Hydration of nitriles to amides by a chitin-supported ruthenium catalyst

Abstract

Chitin-supported ruthenium (Ru/chitin) promotes the hydration of nitriles to carboxamides under aqueous conditions. The nitrile hydration can be performed on a gram-scale and is compatible with the presence of various functional groups including olefins, aldehydes, carboxylic esters and nitro and benzyloxycarbonyl groups. The Ru/chitin catalyst is easily prepared from commercially available chitin, ruthenium(III) chloride and sodium borohydride. Analysis of Ru/chitin by high-resolution transmission electron microscopy indicates the presence of ruthenium nanoparticles on the chitin support.

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Introduction

The catalytic hydration of nitriles (RCN) to carboxamides (RCONH₂) represents a fundamentally important pathway to these products in both laboratory and industrial contexts.^1–3 Since the discovery of alumina-supported ruthenium hydroxide catalysts [Ru(OH)_x/Al₂O₃] by Yamaguchi et al.,⁴ solid-supported Ru has become an important class of catalyst for nitrile hydration, demonstrating high selectivity for carboxamide formation as well as other practical advantages.^5–8 Although RuCl₃·nH₂O itself catalyzes nitrile hydration, the choice of solid support is critically important for achieving sufficient reactivity as well as for retaining Ru species on support.^4,6 Examples of supports successfully used for Ru species include inorganic γ-Al₂O₃,⁴ nanoferrite^5a and magnetic silica,^5b as well as organic chitosan,^5c amberlite⁶ and Nafion.⁷ However, these systems typically require the use of microwave irradiation^5,6 or high reaction temperatures (∼175 °C).⁷ Moreover, the tolerance of base-sensitive functional groups such as carboxylic esters has not been documented in these reports.^4–7 Such chemoselectivity is important in modern organic synthesis,⁹ but is generally considered elusive in nitrile hydration promoted by metal-loaded heterogeneous catalysts, a single exception (Au/TiO₂)^8f notwithstanding. In this work we establish that chitin-supported ruthenium (abbreviated as Ru/chitin) serves as a versatile catalyst for the hydration of nitriles to carboxamides (Scheme 1). Using this system, nitrile hydration can be operated under near-neutral, aqueous conditions without requiring any special apparatus. Moreover, the morphologies of ruthenium nanoparticles on the chitin support were clarified by high-resolution transmission electron microscopy (HRTEM) analysis.

Scheme 1 Hydration of nitriles to carboxamides with Ru/chitin.

After cellulose, chitin is the second most abundant polysaccharide in nature.¹⁰ It has a wide range of applications in materials, food, medical and environmental contexts. These include in the preparation of chitosan, affinity chromatography, wound-dressing and metal-extraction in water purification.¹¹ Whereas chitin has been intensively used as a catalyst support for enzymes,¹² its use as a support for metal catalysts has been less widely explored than has that of chitosan.^13,14 So far, chitin has been used as a support for Pt in asymmetric arene hydrogenation,¹⁵ Pd in the hydrogenation of nitrobenzene and unsaturated fatty acid esters¹⁶ and Re in the epoxidation of olefins.^14d We expected that chitin would represent a potentially attractive support for the Ru-catalyzed hydration of nitriles because it is highly stable under aqueous conditions and effectively adsorbs Ru species using its carboxamide functionality.¹⁷

Results and discussion

Catalytic tests

Ru/chitin catalyst was prepared by impregnating commercially available chitin with an aqueous solution of RuCl₃·3H₂O followed by reduction with NaBH₄,¹⁸ and was tested for its effectiveness in the hydration of benzonitrile (1a, Table 1). When a mixture of 1a (1.0 mmol), H₂O (1.0 mL) and Ru/chitin (0.016 mmol Ru, 1.6 mol% Ru) was heated at 120 °C for 3 h, the corresponding amide 2a was obtained in 33% ¹H NMR yield (Table 1, entry 1). The presence of ruthenium was found to be essential, with the reaction hardly proceeding without catalyst or using only chitin (entries 2 and 3). Meanwhile, the chitin support was also found to be critical, with RuCl₃·3H₂O alone catalyzing the hydration of 1a but with significantly lower efficiency (entry 4). The optimization of reaction conditions using Ru/chitin increased the yield of 2a from 33% to 87% (entries 5–7). Ru/chitin with a higher Ru content [2.3 mol% Ru, prepared from catalyst precursor (202 mg, 1.2 wt% Ru)] gave slightly better yield still (entry 8). This result proved to be reproducible (¹H NMR yields of separate runs: 97%, 91%, 89% and 89%). Analogously prepared Ru catalysts that utilized other polysaccharide supports such as chitosan and cellulose (abbreviated as Ru/chitosan and Ru/cellulose, respectively) were found to be less reactive than Ru/chitin (entries 9 and 10).

Table 1 Hydration of benzonitrile (1a) to benzamide (2a)^a

Entry	Catalyst (mol% Ru)	H2O (mL)	t/h	Yield^b (%)
a Conditions: 1a (1.0 mmol), H2O (1.0 mL, 56 equiv.) and catalyst [1.6 mol% Ru, prepared from catalyst precursor (202 mg, 0.8 wt% Ru)] at 120 °C under a N2 atmosphere unless otherwise stated. The mol% Ru was confirmed by ICP-AES analysis. b Of 2a determined by ^1H NMR using mesitylene as an internal standard. c Ru/chitin (2.3 mol% Ru), prepared from catalyst precursor (1.2 wt% Ru). d Ru/chitosan (3.2 mol% Ru), prepared from catalyst precursor (1.7 wt% Ru). e Ru/cellulose (3.2 mol% Ru), prepared from catalyst precursor (1.6 wt% Ru).
1	Ru/chitin (1.6)	1	3	33
2	None	1	3	<1
3	Chitin	1	3	<1
4	RuCl3·3H2O (2.0)	1	3	17
5	Ru/chitin (1.6)	1	20	77
6	Ru/chitin (1.6)	1	30	87
7	Ru/chitin (1.6)	4	20	87
8	Ru/chitin (2.3)^c	4	20	97
9	Ru/chitosan (3.2)^d	4	20	74
10	Ru/cellulose (3.2)^e	4	20	17

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Scope and limitation

The scope of the Ru/chitin-catalyzed hydration of nitriles is outlined in Table 2. These reactions were run under comparable conditions to those in entry 8 of Table 1. Benzamide (2a) was obtained in 87% isolated yield (Table 2, entry 1) and variously substituted benzonitriles could be converted to the corresponding amides in good-to-excellent yield (entries 2–13). o-Methyl-substituted 1i was somewhat less reactive (entry 9) though m- and p-substituted analogues reacted in satisfying yields (entries 7 and 8). Benzonitrile 1l, which bore an electron-withdrawing p-nitro group, was completely hydrated in shorter reaction times than 1b, 1c, 1f and 1g, each of which bore electron-donating groups at the para positions. p-Formylbenzonitrile (1k) could be converted to the corresponding amide 2k with an intact formyl moiety in 76% yield, though formation of the hydrate of the aldehyde was also noted under aqueous conditions. Furthermore, heteroaromatic nitriles could be efficiently hydrated to the corresponding amides (entries 14 and 15).

Table 2 Catalytic hydration of nitriles with Ru/chitin^a

Entry	Nitrile (1)		t/h	Amide (2)		Isolated yield (%)
a Conditions: 1 (1.0 mmol), H2O (4 mL, 220 equiv.) and Ru/chitin (2.3 mol% Ru) at 120 °C under a N2 atmosphere.
1		1a	20		2a	87
2		1b	60		2b	89
3		1c	40		2c	98
4		1d	32		2d	97
5		1e	32		2e	79
6		1f	40		2f	88
7		1g	50		2g	96
8		1h	60		2h	92
9		1i	60		2i	49
10		1j	24		2j	80
11		1k	40		2k	76
12		1l	18		2l	92
13		1m	50		2m	65
14		1n	24		2n	94
15		1o	20		2o	91
16	CH3CN	1p	36	CH3CONH2	2p	65
17		1q	36		2q	55
18		1r	48		2r	65
19		1s	48		2s	23
20		1t	36		2t	85
21		1u	24		2u	66
22		1v	30		2v	46
23		1w	24		2w	81

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The Ru/chitin system was also applied to the hydration of aliphatic nitriles (Table 2, entries 16–23). Although the hydration reaction proved susceptible to steric hindrance (entry 19), primary and secondary nitriles 1p–r and 1t–w could all be converted to amides (entries 16–18 and 20–23) with retention of olefin (entry 21), β-hydroxy (entry 22) and α-methoxy (entry 23) groups in fair-to-good yields.

Importantly, the presence of a base-sensitive carbonyl functionality in methyl ester 1x was tolerated by virtue of the near-neutral conditions that could be used for catalyst preparation^6,18 (Scheme 2). Similarly, an α-amino nitrile conjugated with a redox-sensitive benzyloxycarbonyl (Cbz) group (as in 1y) was converted to protected α-amino amide 2y with retention of the carbamoyl linkage. The tolerance to carboxylic ester and CbzN functionality shown in Scheme 2 illustrates the applicability of the present method to the nitrile hydration of complex molecules bearing redox- or base-sensitive functional groups.

Scheme 2 Hydration nitriles bearing carboxylic ester and carbamate functionalities.

Upscale experiment

To verify the scalability of this method, a gram-scale hydration was carried out (Scheme 3). The hydration of 1w using a decreased loading of Ru/chitin catalyst (0.5 mol% Ru) yielded the amide 2w in excellent yield [conditions: 1w (16 mmol), H₂O (13 mL), Ru/chitin (0.5 mol% Ru), 120 °C, 36 h, 92% isolated yield (77% isolated yield after 24 h under otherwise identical conditions)].

Scheme 3 Gram-scale hydration of nitrile 1w.

HRTEM analysis

To elucidate the nature of the Ru/chitin catalyst, the catalyst was analyzed by HRTEM. The presence of nanoparticles with a mean size of 2.1 ± 0.4 nm was established (Fig. 1a–c). Energy dispersive X-ray spectroscopy (EDX) and measurement of the d-spacings (d = 0.23 nm) indicated the presence of both Ru(0) and RuO₂ [Fig. 1c, inset, and Fig. 1d]. EDX also revealed the presence of Ca and P in both Ru/chitin (Fig. 1d) and chitin (Fig. 1e and f). This was attributed to calcium phosphate on account of the crustaceous origin of the chitin and was found not to incur significant catalytic activity (Table 1, entry 3).

Fig. 1 (a) A histogram representing the particle size distribution of Ru nanoparticles on chitin. (b) Low-magnification and ((c) and inset) high resolution TEM images of chitin-supported Ru nanoparticles. (d) EDX of Ru/chitin. (e) A low-magnification TEM image of chitin. (f) EDX of chitin.

TEM analysis of the Ru nanoparticles after hydration of 1w showed that they remained morphologically essentially unchanged (Fig. 2). In fact, the Ru/chitin catalyst could be reused without significant loss of catalytic activity (hydration of 1a to 2a, conditions: identical to Table 1, entry 8, first run, 95% yield; reuse run, 87% yield).

Fig. 2 (a) Low-magnification and (b) high resolution TEM images of Ru/chitin after nitrile hydration.

Conclusions

We have established that chitin-supported ruthenium displays high catalytic activity towards the hydration of nitriles to amides under aqueous conditions. The catalyst is easily prepared, and applicable to the hydration of a wide variety of nitriles with aromatic, heteroaromatic and aliphatic substituents. HRTEM analysis of Ru/chitin revealed the presence of ruthenium nanoparticles before and after hydration reactions, indicating that chitin could serve as an effective solid support for ruthenium nanoparticles.

Experimental section

General comments

¹H and ¹³C NMR spectra were recorded on a JEOL ECA-600 (600 MHz for ¹H, 150 MHz for ¹³C, 564 MHz for ¹⁹F) or a JEOL ECA-500 (500 MHz for ¹H, 125 MHz for ¹³C) at 25 °C. Chemical shifts are reported as δ in ppm and are internally referenced to tetramethylsilane (TMS, 0.00 ppm for ¹H), CD₂HOH (3.30 ppm for ¹H), CD₂HSOCD₃ (2.50 ppm for ¹H), HOD (4.79 ppm for ¹H), CDCl₃ (77.2 ppm for ¹³C), CD₃OD (49.0 ppm for ¹³C), dioxane (67.2 ppm in D₂O for ¹³C), or dimethyl sulfoxide-d₆ (DMSO-d₆, 39.5 ppm for ¹³C). Chemical shifts for ¹⁹F NMR were externally referenced to CF₃COOH (−78.5 ppm, neat). Infrared (IR) spectra were recorded on a FT-IR6100 (JASCO). High-resolution mass spectrometry (HRMS) was recorded with a Bruker Daltonik micrOTOF-QII spectrometer. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) spectra were recorded on an Agilent VISTA-PRO. Elemental analyses were recorded on a Yanaco CHN recorder MT-6. These analytical experiments were carried out at the Chemical Instrumental Center, Research Center for Materials Science, Nagoya University. Melting points were recorded on an OptiMelt automated melting point system (Stanford Research Systems). Ruthenium content was analyzed by ICP-AES using yttrium as an internal standard after digestion of samples (10 mg) in concd HNO₃ (2 mL) at 150 °C for 12 h. Products 2a–y were known compounds and their identities were confirmed by comparing with literature data.^{6,7,8g,19–34}

TEM analysis

High-resolution transmission electron microscopy (HRTEM) analysis was performed on a JEOL JEM-3011 microscope. Samples illustrated in Fig. 1a–d and 2 were prepared as per the typical procedure for the preparation of Ru/chitin (0.016 mmol Ru, vide infra) and by the hydration of 1w (0.5 mmol) using Ru/chitin (0.016 mmol Ru) at 120 °C for 6 h, respectively. Sample preparation required droplet coating of particle dispersions obtained by sonicating in CH₃CH₂OH on carbon-coated Cu grids (Agar Scientific, 300 mesh). Electron optical parameters: C_S = 0.6 mm, C_C = 1.2 mm, electron energy spread = 1.5 eV, beam divergence semi-angle = 1 mrad. Elemental analysis was by energy dispersive X-ray spectroscopy (EDX) using a PGT prism Si/Li detector and an Avalon 2000 analytical system. Spectra were analyzed using the PGT eXcalibur 4.03.00 software. Observed Cu Kα and Kβ emission lines were attributed to scattered electrons impinging on the copper grid. Any minor Fe Kα and Co Kα emission lines of similar intensity were due to parasitic scattering from the lens polepiece. Detailed analysis of particle morphology was performed using Digital Micrograph 3.6.5 by counting the diameters of 100 particles (N), defining intervals of 0.25 nm between d_min ≤ d ≤ d_max and counting the number of particles falling into these intervals. Particle size distributions were constructed using DataGraph 3.0. Values of average d-spacing were obtained from Fourier transforms of high magnification images (×800k, ×1 M) using d = 20/D where D is the diameter (nm) of rings obtained. Average d-spacing was confirmed using the profile tool in Digital Micrograph by averaging over 10 d-spacings. To determine the error in the value of d-spacing thus obtained, detailed TEM examination of CeO₂ and Au nanoparticles was undertaken. The relationship between FT ring diameter and DV value (a measure of objective lens focusing voltage) was established for DV values between −6 and +6 and the standard deviation in d-spacing was established to be 10% when compared to the literature.

Materials

RuCl₃·3H₂O was purchased from Furuya Metal Co., Ltd. Benzonitrile (1a), m-hydroxybenzonitrile (1d), p-methylbenzonitrile (1g), m-methylbenzonitrile (1h), o-methylbenzonitrile (1i), m-chlorobenzonitrile (1j), p-nitrobenzonitrile (1l), 2,3,4,5,6-pentafluorobenzonitrile (1m), acetonitrile (1p), pivalonitrile (1s), 2-phenylacetonitrile (1t), 3-hydroxy-3-phenylpropanonitrile (1v), α-methoxyacetonitrile (1w) and 4-(methoxycarbonyl)benzonitrile (1x), were purchased from TCI. p-Aminobenzonitrile (1b), p-methoxybenzonitrile (1f), 2-furonitrile (1o), yttrium standard solution [Y(NO₃)₃ in HNO₃, 1.00 mg Y per mL; 1000 ppm] and concd HNO₃ were purchased from Wako Chemicals. p-Hydroxybenzonitrile (1c), p-formylbenzonitrile (1k), propionitrile (1q), 2-methylpropanenitrile (1r) and acrylonitrile (1u) were purchased from Aldrich. o-Hydroxybenzonitrile (1e) was purchased from Merck. Nicotinonitrile (1n) and chitin were purchased from Kanto Chemicals. Ruthenium standard solution (1 mg Ru per mL in HCl) for ICP-AES was purchased from Acros. α-(Benzyloxycarbonylamino)acetonitrile (1y) was prepared according to the literature procedure by protecting α-aminoacetonitrile with CbzCl.³⁵

Catalyst preparation

A typical procedure for the preparation of Ru/chitin (0.016 mmol Ru). To a 300 mL round-bottom flask, RuCl₃·3H₂O (71.6 mg, 0.30 mmol Ru), H₂O (50 mL) and chitin (2980.4 mg) were added. The mixture was heated at 50 °C for 30 min, and concentrated using a rotary evaporator at 50 °C for 25 min (17 mm Hg). The solid was dried at 50 °C in vacuo overnight to afford the catalyst precursor (0.8 wt% Ru as determined by ICP-AES analysis, dark green solid, 2784.0 mg). To a 10 mL test tube with a screw cap, a magnetic stirring bar and the catalyst precursor (202 mg, 0.8 wt% Ru), deaerated H₂O (8 mL) was added under a N₂ atmosphere. Under vigorous stirring, a solution [1.0 mL; a mixture of NaBH₄ (39.4 mg, 1.0 mmol) and deaerated H₂O (5.2 mL)] was introduced dropwise to the test tube. The mixture was stirred at room temperature (rt) for 3.5 h. The liquid phase was separated by centrifugation (3500 rpm, 5 min) and replaced with H₂O (8 mL) via syringe. After the mixture was stirred at rt overnight, the solid was washed with water (2 times) and dried in vacuo at rt for 2 h to afford Ru/chitin as a grey solid, which was directly used for nitrile hydration.

Ru/chitin (0.023 mmol Ru). As per the above-mentioned typical procedure, the catalyst precursor was prepared using RuCl₃·3H₂O (107.4 mg, 0.45 mmol Ru), H₂O (50 mL), and chitin (2957 mg). Dark green solid (1.2 wt% Ru determined by ICP-AES analysis, 2813 mg). As per the above-mentioned typical procedure, the Ru/chitin (0.023 mmol Ru) was prepared using precursor (202 mg, 1.2 wt% Ru), deaerated H₂O (7.5 mL) and a reducing solution [1.5 mL; a mixture of NaBH₄ (103.0 mg, 2.7 mmol) and deaerated H₂O (20 mL)].

Hydration of nitriles to amides

A typical procedure for hydration of nitriles: benzamide (2a, Table 1, entry 8; Table 2, entry 1)¹⁹. As per the above-mentioned procedure, Ru/chitin (0.023 mmol Ru) was prepared in a screw-cap 10 mL test tube equipped with a rubber septum and a magnetic stirring bar. To this tube were added nitrile 1a (0.986 mmol, 101.6 mg) and deaerated H₂O (2.2 × 10² mmol, 4 mL) under a N₂ atmosphere. After the septum inlet was replaced with a plastic screw cap and the cap was wrapped with Teflon tape, the mixture was shaken at 120 °C for 20 h [ca. 100 rpm, with a constant temperature oven (EYELA MG-2300, Tokyo Rikakikai Co. Ltd)] on a rotary shaker (EYELA Multi Shaker MMS, Tokyo Rikakikai Co. Ltd). The mixture was cooled down with ice water, and mixed with CH₃OH (4 mL) under air. The liquid phase was separated by centrifugation (3500 rpm, 10 min). Extraction of the product was carried out by repeating this process (CH₃OH, 6 × 4 mL). Liquid phases were combined and concentrated in vacuo. ¹H NMR analysis of this crude mixture using mesitylene as an internal standard indicated the formation of amide 2a in 97% yield. The product was purified by sequential column chromatography on silica gel (acetone/dichloromethane 3 : 7; tetrahydrofuran/diethyl ether 1 : 10) to afford amide 2a as colorless plates (103.8 mg, 87% yield). Mp 126.5–127.1 °C (lit.¹⁹ 125–128 °C); IR (KBr) 1405, 1577, 1625, 1660, 3175, 3369 cm⁻¹; ¹H NMR (600 MHz, DMSO-d₆) δ 7.36 (bs, 1H), 7.42–7.47 (m, 2H), 7.51 (tt, J = 1.5, 7.3 Hz, 1H), 7.85–7.89 (m, 2H), 7.97 (bs, 1H); ¹³C{¹H} NMR (150 MHz, DMSO-d₆) δ 127.4, 128.2, 131.2, 134.3, 167.9; elemental analysis calcd for [C₇H₇NO·0.1H₂O]: C, 68.39; H, 5.90; N, 11.39, found: C, 68.64; H, 5.92; N, 11.15.

p-Aminobenzamide (2b)¹⁹. Light yellow blocks, purified by column chromatography on silica gel (methanol/chloroform 1 : 8); mp 176.3–180.9 °C (lit.¹⁹ 180–183 °C); IR (KBr) 780, 1397, 1563, 1600, 3219, 3326, 3464 cm⁻¹; ¹H NMR (600 MHz, DMSO-d₆) δ 5.59 (s, 2H), 6.53 (d, J = 8.6 Hz, 2H), 6.86 (bs, 1H), 7.53 (bs, 1H), 7.60 (d, J = 8.6 Hz, 2H); ¹³C{¹H} NMR (150 MHz, DMSO-d₆) δ 112.5, 121.0, 129.2, 151.7, 168.2; elemental analysis calcd for [C₇H₈N₂O]: C, 61.75; H, 5.92; N, 20.58, found: C, 61.79; H, 5.87; N, 20.30.

p-Hydroxybenzamide (2c)²⁰. White powder, purified by column chromatography on silica gel (tetrahydrofuran/diethyl ether 4 : 6–10 : 0, gradient); mp 157.1–159.2 °C (lit.²⁰ 148 °C); IR (KBr) 1247, 1403, 1558, 1618, 1649, 3124, 3340, 3417 cm⁻¹; ¹H NMR (600 MHz, DMSO-d₆) δ 6.78 (d, J = 8.6 Hz, 2H), 7.08 (bs, 1H), 7.68–7.79 (m, 3H), 9.94 (s, 1H); ¹³C{¹H} NMR (150 MHz, DMSO-d₆) δ 114.7, 125.0, 129.5, 160.2, 167.7; elemental analysis calcd for [C₇H₇NO₂]: C, 61.31; H, 5.15; N, 10.21, found: C, 61.13; H, 5.14; N, 10.01.

m-Hydroxybenzamide (2d)²¹. White powder, purified by column chromatography on silica gel (2-propanol/n-hexane/ethyl acetate 1 : 20 : 200); mp 165.1–168.0 °C (lit.²¹ 167–168 °C); IR (KBr) 1256, 1450, 1580, 1653, 3247, 3400 cm⁻¹; ¹H NMR (600 MHz, DMSO-d₆) δ 6.88–6.92 (m, 1H), 7.20–7.24 (m, 1H), 7.24–7.30 (m, 3H), 7.86 (s, 1H), 9.60 (s, 1H); ¹³C{¹H} NMR (150 MHz, DMSO-d₆) δ 114.5, 118.0, 118.1, 129.2, 135.8, 157.3, 168.0; elemental analysis calcd for [C₇H₇NO₂]: C, 61.31; H, 5.15; N, 10.21, found: C, 61.23; H, 5.12; N, 10.05.

o-Hydroxybenzamide (2e)⁷. Colorless plates, purified by column chromatography on silica gel (chloroform only); mp 138.2–139.2 °C; IR (KBr) 1253, 1359, 1424, 1447, 1493, 1590, 1630, 1675, 3189, 3395 cm⁻¹; ¹H NMR (600 MHz, DMSO-d₆) δ 6.83–6.89 (m, 2H), 7.37–7.42 (m, 1H), 7.84 (dd, J = 1.6, 8.0 Hz, 1H), 7.89 (bs, 1H), 8.39 (bs, 1H), 13.0 (s, 1H); ¹³C{¹H} NMR (150 MHz, DMSO-d₆) δ 114.4, 117.4, 118.3, 128.1, 134.1, 161.1, 172.1; elemental analysis calcd for [C₇H₇NO₂]: C, 61.31; H, 5.15; N, 10.21, found: C, 61.22; H, 5.21; N, 10.01.

p-Methoxybenzamide (2f)⁶. Colorless plates, purified by column chromatography on silica gel (tetrahydrofuran/diethyl ether 0 : 10–10 : 0, gradient); mp 164.3–169.3 °C; IR (KBr) 1146, 1253, 1396, 1422, 1573, 1643, 3170, 3391 cm⁻¹; ¹H NMR (600 MHz, CD₃OD) δ 3.82 (s, 3H), 6.93–6.97 (m, 2H), 7.81–7.85 (m, 2H); ¹³C{¹H} NMR (150 MHz, CD₃OD) δ 55.9, 114.7, 126.9, 130.6, 164.1, 172.0; elemental analysis calcd for [C₈H₉NO₂]: C, 63.56; H, 6.00; N, 9.27, found: C, 63.37; H, 6.00; N, 9.23.

p-Methylbenzamide (2g)^8g. Colorless plates, purified by column chromatography on silica gel (acetone/dichloromethane 2 : 5); mp 157.6–159.0 °C (lit.^8g 159–160 °C); IR (KBr) 1397, 1414, 1571, 1618, 1671, 3168, 3343 cm⁻¹; ¹H NMR (600 MHz, DMSO-d₆) δ 2.34 (s, 3H), 7.22–7.30 (m, 3H), 7.75–7.80 (m, 2H), 7.89 (bs, 1H); ¹³C{¹H} NMR (150 MHz, DMSO-d₆) δ 20.9, 127.5, 128.7, 131.5, 141.0, 167.8; elemental analysis calcd for [C₈H₉NO]: C, 71.09; H, 6.71; N, 10.36, found: C, 70.99; H, 6.66; N, 10.26.

m-Methylbenzamide (2h)^8g. Colorless plates, purified by column chromatography on silica gel (n-hexane/ethyl acetate 2 : 3); mp 91.0–92.4 °C (lit.^8g 92–93 °C); IR (KBr) 687, 1114, 1387, 1432, 1616, 1650, 3195, 3376 cm⁻¹; ¹H NMR (600 MHz, DMSO-d₆) δ 2.34 (s, 3H), 7.25–7.35 (m, 3H), 7.64–7.69 (m, 1H), 7.69–7.72 (m, 1H), 7.91 (bs, 1H); ¹³C{¹H} NMR (150 MHz, DMSO-d₆) δ 20.9, 124.6, 128.1 (2C), 131.7, 134.3, 137.4, 168.0; elemental analysis calcd for [C₈H₉NO]: C, 71.09; H, 6.71; N, 10.36, found: C, 71.04; H, 6.78; N, 9.98.

o-Methylbenzamide (2i)^8g. Colorless needles, purified by column chromatography on silica gel (ethyl acetate/n-hexane 2 : 3); mp 140.1–140.5 °C (lit.^8g 140 °C); IR (KBr) 1140, 1395, 1623, 1656, 3187, 3368 cm⁻¹; ¹H NMR (600 MHz, DMSO-d₆) δ 2.36 (s, 3H), 7.18–7.24 (m, 2H), 7.28–7.37 (m, 3H), 7.68 (bs, 1H); ¹³C{¹H} NMR (150 MHz, DMSO-d₆) δ 19.6, 125.4, 127.0, 129.1, 130.4, 135.1, 137.1, 171.0; elemental analysis calcd for [C₈H₉NO]: C, 71.09; H, 6.71; N, 10.36, found: C, 71.35; H, 6.72; N, 10.36.

m-Chlorobenzamide (2j)^8g. Colorless plates, purified by sequential column chromatography on silica gel (n-hexane/ethyl acetate 1 : 1; ethyl acetate only; tetrahydrofuran only) and activated carbon treatment; mp 132.6–133.4 °C (lit.^8g 134–136 °C); IR (KBr) 1123, 1389, 1432, 1569, 1626, 1658, 3181, 3366 cm⁻¹; ¹H NMR (600 MHz, DMSO-d₆) δ 7.46–7.52 (m, 1H), 7.54 (bs, 1H), 7.56–7.61 (m, 1H), 7.81–7.86 (m, 1H), 7.89–7.94 (m, 1H), 8.10 (bs, 1H); ¹³C{¹H} NMR (150 MHz, DMSO-d₆) δ 126.2, 127.3, 130.3, 131.1, 133.1, 136.3, 166.4; elemental analysis calcd for [C₇H₆NClO]: C, 54.04; H, 3.89; N, 9.00, found: C, 53.96; H, 3.89; N, 8.95.

p-Formylbenzamide (2k)²². White powder, purified by column chromatography on silica gel (n-hexane/ethyl acetate 1 : 3); mp 155.4–159.2 °C; IR (KBr) 1212, 1397, 1607, 1670, 1698, 3194, 3288, 3354 cm⁻¹; ¹H NMR (600 MHz, DMSO-d₆) δ 7.60 (bs, 1H), 7.96–8.00 (m, 2H), 8.03–8.08 (m, 2H), 8.17 (bs, 1H), 10.08 (s, 1H); ¹³C{¹H} NMR (150 MHz, DMSO-d₆) δ 128.1, 129.3, 137.8, 139.3, 167.0, 192.9; elemental analysis calcd for [C₈H₇NO₂]: C, 64.42; H, 4.73; N, 9.39, found: C, 64.69; H, 4.85; N, 9.16.

p-Nitrobenzamide (2l)⁶. Colorless needles, purified by column chromatography on silica gel (triethylamine/2-propanol/chloroform 0.05 : 3 : 7); mp 197.1–200.0 °C; IR (KBr) 1346, 1413, 1526, 1600, 1678, 3177, 3477 cm⁻¹; ¹H NMR (600 MHz, CD₃OD) δ 8.05–8.08 (m, 2H), 8.29–8.33 (m, 2H); ¹³C{¹H} NMR (150 MHz, CD₃OD) δ 124.6, 130.0, 140.9, 151.2, 170.1; elemental analysis calcd for [C₇H₆N₂O₃]: C, 50.61; H, 3.64; N, 16.86, found: C, 50.67; H, 3.69; N, 16.64.

2,3,4,5,6-Pentafluorobenzamide (2m)⁷. Colorless plates, purified by column chromatography on silica gel (ethyl acetate/n-hexane 1 : 2); mp 146.8–147.2 °C; IR (KBr) 1001, 1493, 1675, 3186, 3358 cm⁻¹; ¹H NMR (600 MHz, DMSO-d₆) δ 8.16 (bs, 1H), 8.30 (bs, 1H); ¹³C{¹H} NMR (150 MHz, DMSO-d₆) δ 112.9 (t, J = 21.6 Hz), 135.9–137.9 (m), 139.9–141.9 (m), 141.8–143.9 (m), 158.3; ¹³C{¹⁹F} NMR (150 MHz, DMSO-d₆); δ 112.9 (d, J = 8.7 Hz), 136.9, 140.9, 142.9, 158.3; ¹⁹F NMR (564 MHz, DMSO-d₆) δ −162.0–161.3 (m, 2F), −154.0–153.4 (m, 1F), −142.3–141.9 (m, 2F); elemental analysis calcd for [C₇H₂F₅NO]: C, 39.83; H, 0.96; N, 6.64, found: C, 40.00; H, 6.65; N, 1.09.

Nicotinamide (2n)²³. Colorless needles, purified by column chromatography on silica gel (ethyl acetate only) and recrystallization (from dichloromethane); mp 126.0–127.7 °C; IR (KBr) 1620, 1682, 3159, 3370 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ 7.48–7.51 (m, 1H), 7.59 (bs, 1H), 8.15 (bs, 1H), 8.19–8.21 (m, 1H), 8.69–8.70 (m, 1H), 9.02–9.03 (m, 1H); ¹³C{¹H} NMR (150 MHz, DMSO-d₆) δ 123.3, 129.6, 135.1, 148.6, 151.8, 166.4; elemental analysis calcd for [C₆H₆N₂O]: C, 59.01; H, 4.95; N, 22.94, found: C, 59.00; H, 4.91; N, 22.70.

2-Francarbamide (2o)²⁴. White powder, purified by column chromatography on silica gel (dichloromethane/acetone 1 : 4) and recrystallization (from water); mp 139.6–140.9 °C (lit.²⁴ 141–142 °C); IR (KBr) 1626, 1665, 3171, 3351 cm⁻¹; ¹H NMR (600 MHz, CDCl₃) δ 5.53 (bs, 1H), 6.26 (bs, 1H), 6.52–6.53 (m, 1H), 7.16–7.18 (m, 1H), 7.46–7.49 (m, 1H); ¹³C{¹H} NMR (125 MHz, CDCl₃) δ 112.5, 115.3, 144.6, 147.6, 160.4; elemental analysis calcd for [C₅H₅NO₂]: C, 54.05; H, 4.54; N, 12.61, found: C, 53.73; H, 4.55; N, 12.49.

Acetamide (2p)²⁵. White powder, purified by recrystallization (from dichloromethane/n-hexane); mp 79.2–80.1 °C; IR (KBr) 1665, 3212, 3389 cm⁻¹; ¹H NMR (600 MHz, D₂O) δ 2.00 (s, 3H); ¹³C{¹H} NMR (125 MHz, D₂O) δ 21.9, 178.0; elemental analysis calcd for [C₂H₅NO·0.001H₂O]: C, 40.66; H, 8.53; N, 23.71, found: C, 40.26; H, 8.54; N, 23.53.

Propionamide (2q)²⁶. Colorless plates, purified by recrystallization (from dichloromethane/n-hexane); mp 79.1–80.5 °C; IR (KBr) 1664, 3202, 3370 cm⁻¹; ¹H NMR (600 MHz, CDCl₃) δ 1.18 (t, J = 7.6 Hz, 3H), 2.27 (q, J = 7.6 Hz, 2H), 5.04–5.58 (m, 2H); ¹³C{¹H} NMR (150 MHz, CDCl₃) δ 9.8, 29.1, 176.3; elemental analysis calcd for [C₃H₇NO·0.02H₂O]: C, 49.05; H, 9.66; N, 19.07, found: C, 48.70; H, 9.56; N, 18.82.

2-Methylpropanamide (2r)²⁷. White powder, purified by recrystallization (from dichloromethane/n-hexane); mp 124.7–127.3 °C; IR (KBr) 1641, 3179, 3355 cm⁻¹; ¹H NMR (500 MHz, CDCl₃) δ 1.19 (d, J = 6.9 Hz, 6H), 2.43 (sept, J = 6.9 Hz, 1H), 5.10–5.75 (m, 2H); ¹³C{¹H} NMR (125 MHz, CDCl₃) δ 19.7, 35.2, 179.8; elemental analysis calcd for [C₄H₉NO]: C, 55.15; H, 10.41; N, 16.08, found: C, 54.95; H, 10.45; N, 15.89.

Pivalamide (2s)²⁸. Colorless needles, purified by recrystallization (from dichloromethane/n-hexane); mp 148.7–152.0 °C; IR (KBr) 1627, 1656, 3204, 3398 cm⁻¹; ¹H NMR (600 MHz, CDCl₃) δ 1.23 (s, 9H), 5.21 (bs, 1H), 5.59 (bs, 1H); ¹³C{¹H} NMR (150 MHz, CDCl₃) δ 27.8, 38.8, 181.5; elemental analysis calcd for [C₅H₁₁NO·0.08H₂O]: C, 58.54; H, 10.97; N, 13.65, found: C, 58.29; H, 10.85; N, 13.36.

2-Phenylacetamide (2t)²⁹. White powder, purified by washing with n-hexane; mp 157.9–158.5 °C (lit.²⁹ 155 °C); IR (KBr) 1637, 3178, 3355 cm⁻¹; ¹H NMR (600 MHz, CDCl₃) δ 3.60 (s, 2H), 5.13–5.64 (m, 2H), 7.28–7.38 (m, 5H); ¹³C{¹H} NMR (150 MHz, CDCl₃) δ 43.5, 127.6, 129.2, 129.6, 135.0, 173.7; elemental analysis calcd for [C₈H₉NO]: C, 71.09; H, 6.71; N, 10.36, found: C, 71.07; H, 6.76; N, 10.28.

Acrylamide (2u)³⁰. Colorless plates, purified by recrystallization (from dichloromethane/n-hexane); mp 78.2–80.3 °C; IR (KBr) 1613, 1675, 3193, 3357 cm⁻¹; ¹H NMR (600 MHz, D₂O) δ 5.83 (d, J = 10.3 Hz, 1H), 6.22–6.33 (m, 2H); ¹³C{¹H} NMR (125 MHz, D₂O) δ 129.1, 130.1, 171.6; elemental analysis calcd for [C₃H₅NO·0.07H₂O]: C, 49.81; H, 7.16; N, 19.36, found: C, 49.52; H, 7.02; N, 18.99.

3-Hydroxy-3-phenylpropanamide (2v)³¹. Colorless needles, purified by column chromatography on silica gel (n-hexane/ethyl acetate 1 : 6–0 : 7, gradient); mp 121.0–121.7 °C; IR (KBr) 1624, 1658, 3194, 3386 cm⁻¹; ¹H NMR (600 MHz, CD₃OD) δ 2.52 (dd, J = 4.8, 14.4 Hz, 1H), 2.63 (dd, J = 8.9, 14.5 Hz, 1H), 5.05 (dd, J = 4.8, 8.9 Hz, 1H), 7.22–7.39 (m, 5H); ¹³C{¹H} NMR (125 MHz, CD₃OD) δ 46.1, 71.9, 126.9, 128.5, 129.4, 145.4, 176.4; elemental analysis calcd for [C₉H₁₁NO₂]: C, 65.44; H, 6.71; N, 8.48, found: C, 65.41; H, 6.71; N, 8.45.

α-Methoxyacetamide (2w)³². Colorless needles, purified by short-column chromatography on silica gel (dichloromethane only); mp 96.2–96.9 °C; IR (KBr) 1638, 3198, 3384 cm⁻¹; ¹H NMR (500 MHz, D₂O) δ 3.45 (s, 3H), 4.02 (s, 2H); ¹³C{¹H} NMR (125 MHz, D₂O) δ 59.6, 71.1, 176.4; elemental analysis calcd for [C₃H₇NO₂]: C, 40.44; H, 7.92; N, 15.72, found: C, 40.28; H, 8.02; N, 15.78.

p-(Methoxycarbonyl)benzamide (2x)³³. Off-white plates, purified by column chromatography on silica gel (n-hexane/ethyl acetate 1 : 4); mp 205.0–206.6 °C (lit.³³ 200–201 °C); IR (KBr) 1281, 1660, 1725, 3195, 3406 cm⁻¹; ¹H NMR (600 MHz, DMSO-d₆) δ 3.87 (s, 3H), 7.57 (bs, 1H), 7.96–8.04 (m, 4H), 8.15 (bs, 1H); ¹³C{¹H} NMR (150 MHz, DMSO-d₆) δ 52.3, 127.8, 129.1, 131.8, 138.4, 165.7, 167.0; elemental analysis calcd for [C₉H₉NO₃]: C, 60.33; H, 5.06; N, 7.82, found: C, 60.32; H, 5.14; N, 7.72.

α-(Benzyloxycarbonylamino)acetamide (2y)³⁴. White needles, purified by column chromatography on silica gel (chloroform/methanol 95 : 5–92 : 8, gradient); mp 135.0–136.6 °C (lit.³⁴ 138–139 °C); IR (KBr) 1537, 1652, 1688, 3191, 3324, 3381 cm⁻¹; ¹H NMR (600 MHz, DMSO-d₆) δ 3.55 (d, J = 6.2 Hz, 2H), 5.03 (s, 2H), 7.01 (s, 1H), 7.26–7.40 (m, 7H); ¹³C{¹H} NMR (150 MHz, DMSO-d₆) δ 43.3, 65.4, 127.7, 127.8, 128.3, 137.1, 156.4, 171.1; HRMS (ESI-TOF) m/z calcd for C₁₀H₁₂N₂O₃Na [M + Na]⁺ 231.0746, found 231.0757.

Gram-scale hydration (Scheme 3). To a 30 mL test tube with a screw cap, a magnetic stirring bar and catalyst precursor (657 mg, 1.2 wt% Ru), deaerated H₂O (13 mL) was added under a N₂ atmosphere. Under vigorous stirring, a solution [4.9 mL; a mixture of NaBH₄ (82.1 mg, 2.2 mmol) and deaerated H₂O (10.9 mL)] was introduced dropwise to the test tube. The mixture was stirred at rt for 3.5 h. The liquid phase was separated by centrifugation (3500 rpm, 5 min) and replaced with H₂O (13 mL) via syringe. After the mixture was stirred at rt overnight, the solid was washed with water (2 times) and dried in vacuo at rt for 2 h to afford Ru/chitin as a grey solid. To this Ru/chitin in the test tube were added 1w (16.3 mmol, 1.16 g) and deaerated H₂O (7.2 × 10² mmol, 13 mL) under a N₂ atmosphere. After this the septum inlet was replaced with plastic screw cap and the cap was wrapped with Teflon tape. The mixture was then shaken at 120 °C for 36 h (ca. 100 rpm). After cooling with ice water, the catalyst was removed by filtration and washed with methanol (300 mL). The solvent was concentrated in vacuo. The product was purified by short-column chromatography on silica gel (ethyl acetate only) to afford 2w as colorless needles (1.34 g, 92% yield).

Reuse experiment. As per the typical procedure, Ru/chitin (0.023 mmol Ru) was prepared in a screw-cap 10 mL test tube equipped with a rubber septum and a magnetic stirring bar. To this tube was added nitrile 1a (1.01 mmol, 104.1 mg) and deaerated H₂O (2.2 × 10² mmol, 4.0 mL) under a N₂ atmosphere. After this septum inlet was replaced with a plastic screw cap and the cap was wrapped with Teflon tape. The mixture was shaken at 120 °C for 20 h (ca. 100 rpm). The mixture was cooled down with ice water, mixed with deaerated H₂O (4 mL) under a N₂ atmosphere, and stirred at 100 °C for 1 min. The liquid phase was separated by centrifugation (3500 rpm, 3 min). Extraction of the product was carried out by repeating this process (deaerated H₂O, 7 × 4 mL). The combined liquid phases were concentrated in vacuo. ¹H NMR analysis of this crude mixture using mesitylene as an internal standard indicated the formation of 2a in 95% yield. Ru/chitin in the test tube was directly reused for the next run [conditions: 1a (1.04 mmol, 107.2 mg), deaerated H₂O (2.2 × 10² mmol, 4.0 mL) and the reused catalyst at 120 °C for 20 h under a N₂ atmosphere]. ¹H NMR analysis of this crude mixture showed the formation of 2a in 87% yield.

Acknowledgements

This work was partly supported by grant from Yoshida Foundation for Science and Technology (to H.N.) and the program “Integrated Research on Chemical Synthesis”, MEXT, Japan (to H.N.). A.M. acknowledges a Grant-in-Aid for JSPS fellows (25 4305) and IGER program at NU. B.R.K. thanks the UK EPSRC for financial support (EP/J500380/1) and A.E.H.W. thanks the GB Sasakawa Foundation for travel grant 4388. The authors are grateful to Drs K. Oyama and Y. Maeda (Chemical Instrument Center, NU) for technical support. The authors wish to thank Prof. R. Noyori (NU and RIKEN) for fruitful discussions.

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Footnote

† Electronic supplementary information (ESI) available: Spectroscopic data. See DOI: 10.1039/c4ra15682j

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