One-Pot Tandem Synthesis of Nitriles and Amides from Biomass Platform Compounds
Xiu-Zhi Wei 1,2, Jianguo Liu 3,*, Longlong Ma 1,3,*
Department of Engineering Science, University of Science and Technology of China, Hefei 230026, P.R. China
CAS Key Laboratory of Renewable Energy, Guangdong Provincial Key Laboratory of New and Renewable Energy Research and Development, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, P. R. China
Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University, Nanjing 210096, P. R. China
* Correspondence: Jianguo Liu and Longlong Ma
Academic Editor: Robert Wojcieszak
Special Issue: Recent Advances in Catalysis for Biomass Conversion
Received: December 28, 2021 | Accepted: February 13, 2022 | Published: February 21, 2022
Catalysis Research 2022, Volume 2, Issue 1, doi:10.21926/cr.2201004
Recommended citation: Wei XZ, Liu JG, Ma LL. One-Pot Tandem Synthesis of Nitriles and Amides from Biomass Platform Compounds. Catalysis Research 2022;2(1):15; doi:10.21926/cr.2201004.
© 2022 by the authors. This is an open access article distributed under the conditions of the Creative Commons by Attribution License, which permits unrestricted use, distribution, and reproduction in any medium or format, provided the original work is correctly cited.
In recent years, research on converting biomass platform compounds into high-value chemicals and pharmaceutical intermediates has garnered huge interest. Nitrile and amide groups are key structures in natural products and biologically active molecules. The direct conversion of biomass platform compounds into nitriles and amides will undoubtedly be an important guide for biomass utilization. In this paper, a facile and efficient triphosgene-assisted one-pot conversion for aldehydes and ketones into nitrile and amides is presented. Triphosgene is a phosgene alternative that contains both ester linkage and chloromethyl units and easily reacts with oximes for the preparation of nitriles and amides. However, due to the hydrolysis of oximes to aldehydes or ketones, the reaction of oximes with triphosgene cannot fully convert the corresponding nitriles and amides. The protocol tandem ensures a smooth process without the use of organic bases or metal catalysts. Using biomass-derived platform compounds, various functionalized aromatic, aliphatic, and allylic aldehydes and ketones were successfully converted to nitriles and amides in excellent yields. In comparison to step-by-step reactions, this tandem strategy features multi-step reactions in one pot, mild reaction conditions, and fewer by-products.
Tandem synthesis; triphosgene; nitriles and amides; biomass platform compounds
Nitrile and amide groups are key structures of natural products, biologically active molecules, agrochemicals, dyes, or materials science. In the past decade, nitriles have been produced from the conversion of oximes via dehydration  and substitution reactions involving cyanogen reagents [2,3,4,5,6]. Furthermore, for the synthesis of amides, carboxylic acid derivatives and amines are traditionally applied via a condensation reaction in harsh conditions . The majority of the synthesis was performed with toxic reagents and cumbersome experimental operations. There has been considerable progress in the generation of nitriles from aldehydes, which has been successfully applied to the wide substrate scope of aldehydes. However, there are few suitable methodologies for the synthesis of both nitriles and amides from aldehydes and ketones, respectively. In comparison to the traditional nucleophilic substitutions using HCN or metal cyanides [8,9,10,11], as well as the recent oximation−dehydration strategy  with the prepared reagents  or additional alkali [14,15], an environment-friendly alternative was designed using triphosgene. This reagent is inexpensive and can be used without further preparation.
In a recent report , the reaction site of oxime was used in the chemical detection of phosgene. Many researchers have reported the synthesis of nitriles or amides from various oximes with phosgene or its substitutes, such as triphosgene and diphosgene. However, most of these applications suffer from toxic phosgene overflow under alkaline conditions (such as adding TEA to the reaction system) and have narrow substrate scope. Phosgene and its substitutes are important industrial feedstocks used in the production of polyurethanes, polycarbonates, pharmaceuticals , insecticides, and aniline dyes [18,19]. Also, phosgene and diphosgene are highly toxic lung irritants even at low conversions. Due to the hazardous effects, they were utilized as chemical warfare agents (CWAs) during World War I and World War II . Triphosgene is a non-volatile alternative to phosgene and is widely used in chemical synthesis. In this paper, triphosgene was utilized as the starting material to achieve the one-pot conversion of aldehydes and ketones to nitriles and amides. The generated HCl plays a good catalytic role in the Beckmann rearrangement reaction.
With the increasing demand for chemicals and fuels derived from fossil resources, the prospects of developing those alternatives from the catalytic transformation of renewable biomass have sparked global concern [21,22,23,24,25,26]. Among the alternatives to biomass valorization, the production of 5-hydroxymethylfurfural (HMF) from hexoses offers a versatile platform for the synthesis of furan-based chemicals such as furyl diamide, diamidine, diimidate, and diformylfuran [27,28]. Therefore, aromatic aldehydes and ketones [29,30,31,32,33,34,35,36,37,38,39] such as vanillin veratraldehyde, acetovanillone, acetosyringone, and syringaldehyde can be obtained by the oxidative depolymerization of lignin and lignin model compounds. To further demonstrate the utility of our protocol, the one-pot strategy was utilized for the efficacious synthesis of 2,5-dicyanofuran from biomass-derived 2,5-diformylfuran. In addition, lignin-derived monoaldehyde and aromatic ketone yielded beneficial nitriles and amides. Capsaicin analogs such as nonivamide, capsaicin, and phenylcapsaicin  (see Figure 1), as typical capsaicinoid compounds show prominent anti-inflammatory  and anti-cancer  properties; these compounds have been widely applied in cancer prevention . Capsaicinoids are usually prepared from vanillin by reducing vanillin oxime to obtain vanillylamine, which further reacts with acyl chlorides (Schotten-Baumann) to form the final products [44,45,46,47].
Figure 1 Examples of biologically active capsaicinoids.
Alternatively, to synthesize capsaicin analogs, our method was utilized to prepare the intermediate 4-hydroxy-3-methoxybenzonitrile (P1c-22), which can be easily used to obtain vanillylamine by hydrogenation reduction [48,49]. As depicted in Figure 2, vanillylamine reacts with different fatty acid derivatives to form the amide bond and generate the corresponding capsaicinoids [50,51,52].
Figure 2 Methods for preparing capsaicinoids.
2. Results and Discussion
The reaction condition of benzaldehyde (1 equiv.) was initially investigated with hydroxylamine hydrochloride (1.5 equiv.) and triphosgene (0.2 equiv.) at 60 °C with acetonitrile as the solvent, yielding 97% (Table 1). In a similar method, acetanilide, the desired product of acetophenone, was obtained with a yield of 81% at 80 °C (Table 2). None of the other screened solvents were superior to acetonitrile. The reaction was investigated in the absence of triphosgene, according to benzaldehyde, and the reaction did fully convert but did not proceed much further after producing the oxime. Moreover, acetophenone has a similar pattern but lower conversion. To improve the conversion and selectivity of the aldehydes and ketones in the tandem reaction, hydroxylamine hydrochloride and triphosgene were added in steps, and the desired nitrile and acetanilide products were observed with yields of 99% and 90%, respectively. (Refer to ESI† for more details)
Table 1 Variation of standard condition for the transformation of benzaldehyde to benzonitrile.
Table 2 Variation of standard conditions for the transformation of acetophenone to acetanilide.
As shown in Table 3, the reaction system for the application was assessed in aromatic and aliphatic aldehydes after the optimization of the reaction conditions. A wide array of aldehyde derivatives with various substituent groups were converted selectively, yielding corresponding nitriles in excellent yields. For instance, the tandem conversion of aliphatic aldehydes (1c-17 and 19) gave the corresponding nitrile products in 83-89% yields. Electron-withdrawing groups substituted aromatic aldehydes, such as nitro (1c-13)-and halogen (1c-3,7,14, and 15)-substituted benzaldehyde, to give the corresponding nitrile products with yields exceeding 93%. On the other hand, the yields of nitriles derived from the one-pot transformation of multi-substituent benzaldehyde (1c-10) and electron-donating groups (1c-1,2,4,5,6,8,9,11,12, and 18) substituted substrates were satisfactory. The effect of steric hindrance did not affect the reactivity. For example, ortho-substituted aldehydes such as (1c-1) yielded 97% 2-(methyl) benzonitrile (P1c-1) with the same high yield as 99% m-(methyl) benzonitrile (P1c-6) and 98% p-(methyl) benzonitrile (P1c-9). Several meta-substituted aldehydes incorporating bromo (1c-7), methoxy (1c-11), and hydroxyl (1c-4) substituents were tolerated, delivering the nitrile products in excellent yields of 93-98%, which is comparable to the para-substituted aldehydes. Furthermore, the good yield of nitrile product from furfural (1c-20) and its derivatives (1c-16 and 21) was observed to have a conversion rate of over 94%. Based on sustainable development and green chemistry, our standard protocol was established. Accordingly, it is desirable to convert aldehydes from oxidative depolymerization of lignin into corresponding nitriles under mild conditions, such as vanillin, syringaldehyde, and veratraldehyde. As a result, corresponding nitriles were obtained with excellent conversion and selectivity. The standard protocol was examined by subjecting 2,5-diformylfuran (1c-26) to the synthesis of 2,5-dicyanofuran and obtaining the dinitrile product (P1c-26) with a conversion of above 99% and selectivity of 93%. It is noteworthy that 2,5-dicyanofuran may be applied in the preparation of biomass-based commercial chemicals such as spices, medicines, and pesticides .
Table 3 Scope of aromatic, heteroaromatic, and aliphatic aldehydes a.
The standard protocol followed in the preparation of amide products from various ketones (Table 4) was examined, given the relevance and broad application of amide molecules in the textile and pharmaceutical sectors. An array of aliphatic ketones such as (1d-2) and (1d-8) underwent our protocol smoothly, giving the corresponding amide products with yields of over 85%. Phenylacetone with various substituent groups (1d-4, 6) performed well. Interestingly, the yields of amide from the transformation of p-methyl substituted and o(p)-methoxy-acetophenone (1d-1, 3, and 7) and naphthophenone were excellent. However, the yields of amides obtained from the transformation of o-methyl substituted acetophenone (1d-9) and 3,4-methylenedioxyacetophenone (2) were relatively lower but still satisfactory. As a consequence of the steric hindrance effect, the transformation of the para-methyl-substituted acetophenone (1) generated corresponding acetanilide with a higher yield (93%) than the ortho-methyl-substituted acetophenone (9) (55%). However, the conversion of ortho-(7) and para-methoxyl-substituted substrate (3) obtained the target products in a similarly high yield (above 90%) due to the more important electron-induced effect. This is the underlying reason for the lower yield of the conversion of para-chlorine acetophenone (1d-5).
Table 4 Scope of aromatic, heteroaromatic, and aliphatic aldehydes a.
Scheme 1 illustrates a plausible route, including two steps for this nitrile one-pot. Initially, the attack of hydroxylamine hydrochloride on aldehyde gives an intermediate oxime M1c, which then undergoes triphosgene-assisted dehydration to give the desired nitrile product P1c. The reaction mechanism of the first step is clear in this process. To investigate the acting property of triphosgene for these oximes and confirm the reaction mechanism of the oxime to nitrile conversion, as described in Scheme 2, 1c-22 was selected as a representative; 1H NMR titration experiments and GC analyses were performed. As shown in Figure 3A, the 1H NMR spectra were recorded after adding triphosgene to a solution of benzaldehyde oxime in CD3CN. The spectra showed that the hydroxyl proton (Hd) signal at 8.9 ppm disappeared and the formyl proton (Hc) signal at 8.3 ppm of benzaldehyde oxime shrank gradually after the addition of triphosgene. The aldehydic proton signals sharply appeared at 10.1 ppm (Ha), while the proton signal of benzonitrile arose at 7.7 ppm (Hb’). As shown in Figure 3B, based on the GC analysis of that final reaction solution, the same result as 1HNMR, including benzaldehyde and benzonitrile, was obtained. As for acetophenone oxime, the hydroxyl proton (He) signal at 8.85 ppm disappeared and the Ar-H (7.65 ppm) and -CH3 (2.25 ppm) signals were shifted (Hb’’ to Hb’ and Hb; Hd to Hc and He), indicating the conversion of oxime to amide and ketone and shown in Figure 4A. Consequently, acetanilide and acetophenone were formed, and the GC data verified this conclusion (Figure 4B).
Scheme 1 The route of preparation of nitriles (P1c) from aldehydes.
Scheme 2 Proposed reaction mechanism of oximes with triphosgene.
Figure 3 (A) Partial 1H NMR spectra of M1c-22 (0.5 mM) in CD3CN before (6) and after the addition triphosgene 0.1 equiv in CD3CN at 60 °C for 10 min (5), 30 min (4), 1 h (3) and reference NMR spectrum of P1c-22 (2) and 1c-22 (1) in CD3CN. (B) Partial GC spectra of M1c-22 (0.5 mM) with 0.1 equiv triphosgene in CH3CN at 60 °C for 1 h, and reference GC spectrum of 1c-22, M1c-22 and P1c-22 in CH3CN.
Figure 4 (A) Partial 1H NMR spectra of M1d-10 (0.5 mM) in CD3CN before (6) and after the addition triphosgene 0.1 equiv in CD3CN at 80 °C for 10 min (5), 30 min (4), 1 h (3) and reference NMR spectrum of P1d-10 (2) and 1d-10 (1) in CD3CN. (B) Partial GC spectra of M1d-10 (0.5 mM) with 0.1 equiv triphosgene in CH3CN at 80 °C for 1 h, and reference GC spectrum of 1d-10, M1d-10 and P1d-10 in CH3CN.
Therefore, the reaction mechanism of the conversion of aldoxime to nitrile or amide should be described as follows: Along path 1, the hydroxyl of oxime attacks triphosgene forming O-((trichloromethoxy)carbonyl) oxime as intermediate, as well as phosgene and HCl, which reacts nucleophilically with phosgene or HCl and follows the same path to form O-chlorocarbonyl oxime or amino oxonium. Soon, the deprotonation of the carbonyl oxime and amino oxonium converts to the final nitrile. Along path 2, HCl functioned as a catalyst to facilitate Beckman Rearrangement, which was consistent with the reported acid catalysis in general. The experiments verified the catalytic effect of HCl (Table 1, Entry11; Table 2, Entry10). Besides, the transformation of aldoxime into amide also undergoes Beckman Rearrangement by using triphosgene and HCl, as shown in Scheme 2.
The practical protocol was successfully applied to a wide scope of substrates with diverse functional groups, including biomass-derived aldehydes and ketones with excellent conversions and yields by utilizing the tandem reaction of aldehydes and ketones with hydroxylamine hydrochloride in the presence of triphosgene to construct nitriles and amides, respectively. Among them, the nitrile prepared from vanillin can be used as a precursor for the synthesis of capsaicin. The conversion of oximes is slightly inferior when directly reacting with triphosgene. Furthermore, a plausible mechanism was proposed that the reaction undergoes deprotonation or rearrangement, and the one-pot reaction from aldehydes as precursors was found to be more applicable than the conversion of oximes to nitriles.
This work was supported financially by the National Key R&D Program of China (2018YFB1501500), National Natural Science Foundation of China (51976225).
J. G. L. and L. L. M supervised and designed the research. X.Z.W wrote the original manuscript. J. G. L reviewed and corrected the manuscript. All authors discussed the results and assisted during manuscript preparation.
The authors declare no competing financial interests.
The following additional materials are uploaded at the page of this paper.
1. Figure S1: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-1.
2. Figure S2: GC (1c-1 retention time: 8.345 min) after the reaction of 1c-1.
3. Figure S3: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-2.
4. Figure S4: GC (1c-2 retention time: 13.926 min) after the reaction of 1c-2.
5. Figure S5: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-3.
6. Figure S6: GC (1c-3 retention time: 5.833 min) after the reaction of 1c-3.
7. Figure S7: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-4.
8. Figure S8: GC (1c-4 retention time: 11.966 min) after the reaction of 1c-4.
9. Figure S9: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-5.
10. Figure S10: GC (1c-5 retention time: 15.51 min) after the reaction of 1c-5.
11. Figure S11: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-6.
12. Figure S12: GC (1c-6 retention time: 8.2 min) after the reaction of 1c-6.
13. Figure S13: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-7.
14. Figure S14: GC (1c-7 retention time: 10.894 min) after the reaction of 1c-7.
15. Figure S15: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-8.
16. Figure S16: GC (1c-8 retention time: 13.797 min) after the reaction of 1c-8.
17. Figure S17: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-9.
18. Figure S18: GC (1c-9 retention time: 8.28 min) after the reaction of 1c-9.
19. Figure S19: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-10.
20. Figure S20: GC (1c-10 retention time: 15.966 min) after the reaction of 1c-10.
21. Figure S21: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-11.
22. Figure S22: GC (1c-11 retention time: 10.333 min) after the reaction of 1c-11.
23. Figure S23: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-12.
24. Figure S24: GC (1c-12 retention time: 12.685 min) after the reaction of 1c-12.
25. Figure S25: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-13.
26. Figure S26: GC (1c-13 retention time: 12.364 min) after the reaction of 1c-13.
27. Figure S27: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-14.
28. Figure S28: GC (1c-14 retention time: 10.448 min) after the reaction of 1c-14.
29. Figure S29: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-15.
30. Figure S30: GC (1c-15 retention time: 8.902 min) after the reaction of 1c-15.
31. Figure S31: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-16.
32. Figure S32: GC (1c-16 retention time: 9.886 min) after the reaction of 1c-16.
33. Figure S33: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-17.
34. Figure S34: GC (1c-17 retention time: 11.721 min) after the reaction of 1c-17.
35. Figure S35: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-18.
36. Figure S36: GC (1c-18 retention time: 11.208 min) after the reaction of 1c-18.
37. Figure S37: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-19.
38. Figure S38: GC (1c-19 retention time: 5.68 min) after the reaction of 1c-19.
39. Figure S39: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-20.
40. Figure S40: GC (1c-20 retention time: 4.01 min) after the reaction of 1c-20.
41. Figure S41: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-21.
42. Figure S42: GC (1c-21 retention time: 18.097 min) after the reaction of 1c-21.
43. Figure S43: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-22.
44. Figure S44: GC (1c-22 retention time: 6.091 min) after the reaction of 1c-22.
45. Figure S45: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-23.
46. Figure S46: GC (1c-23 retention time: 14.326 min) after the reaction of 1c-23.
47. Figure S47: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-24.
48. Figure S48: GC (1c-24 retention time: 13.255 min) after the reaction of 1c-24.
49. Figure S49: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-25.
50. Figure S50: GC (1c-25 retention time: 16.678 min) after the reaction of 1c-25.
51. Figure S51: 1H NMR (400 MHz, CDCl3) after the reaction of 1c-26.
52. Figure S52: GC (1c-26 retention time: 8.104 min) after the reaction of 1c-26.
53. Figure S53: 1H NMR (400 MHz, CDCl3) after the reaction of 1d-1.
54. Figure S54: GC (1d-1 retention time: 9.918 min) after the reaction of 1d-1.
55. Figure S55: 1H NMR (400 MHz, CDCl3) after the reaction of 1d-2.
56. Figure S56: GC (1d-2 retention time: 5.098 min) after the reaction of 1d-2.
57. Figure S57: 1H NMR (400 MHz, CDCl3) after the reaction of 1d-3.
58. Figure S58: GC (1d-3 retention time: 12.532 min) after the reaction of 1d-3.
59. Figure S59: 1H NMR (400 MHz, CDCl3) after the reaction of 1d-4.
60. Figure S60: GC (1d-4 retention time: 9.265 min) after the reaction of 1d-4.
61. Figure S61: 1H NMR (400 MHz, CDCl3) after the reaction of 1d-5.
62. Figure S62: GC (1d-5 retention time: 10.711 min) after the reaction of 1d-5.
63. Figure S63: 1H NMR (400 MHz, CDCl3) after the reaction of 1d-6.
64. Figure S64: GC (1d-6 retention time: 10.668 min) after the reaction of 1d-6.
65. Figure S65: 1H NMR (400 MHz, CDCl3) after the reaction of 1d-7.
66. Figure S66: GC (1d-7 retention time: 11.608 min) after the reaction of 1d-7.
67. Figure S67: 1H NMR (400 MHz, CDCl3) after the reaction of 1d-8.
68. Figure S68: GC (1d-8 retention time: 8.298 min) after the reaction of 1d-8.
69. Figure S69: 1H NMR (400 MHz, CDCl3) after the reaction of 1d-9.
70. Figure S70: GC (1d-9 retention time: 9.201 min) after the reaction of 1d-9.
71. Figure S71: 1H NMR (400 MHz, CDCl3) after the reaction of 1d-10.
72. Figure S72: GC (1d-10 retention time: 7.892 min) after the reaction of 1d-10.
73. Figure S73: 1H NMR (400 MHz, CDCl3) after the reaction of 1d-11.
74. Figure S74: GC (1d-11 retention time: 16.297 min) after the reaction of 1d-11.
75. Figure S75: 1H NMR (400 MHz, CDCl3) after the reaction of 1d-12.
76. Figure S76: GC (1d-12 retention time: 17.639 min) after the reaction of 1d-12.
77. Figure S77: 1H NMR (400 MHz, CDCl3) after the reaction of 1d-13.
78. Figure S78: GC (1d-13 retention time: 14.552 min) after the reaction of 1d-13.
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