Boric Acid: A Mild and Efficient Green Catalyst for Organic Transformations

Abstract

Keywords

acid catalysis - boric acid - heterocyclic compound - green catalyst - organic synthesis

Dr. Amit Kumar Rawat received his PhD from University of Delhi, under the supervision of Prof. SMS Chauhan in 2013. Currently he is an assistant professor in Department of Chemistry, Hansraj College University of Delhi, India. His research interest focuses on the synthesis of heterocyclic compounds and their application in supramolecular chemistry. Dr. Pradeep Kumar received his PhD from University of Delhi, in 2014. Currently he is an assistant professor in Department of Botany, Swami Shraddhanand College University of Delhi. His research interest focuses on the synthesis of nanomaterial. Preetam Kumar received his MSc from University of Delhi in 2007. Currently he is an assistant professor in Department of Zoology, Swami Shraddhanand College University of Delhi. His research interest focuses on the synthesis of newer heterocyclic compounds. Dr. Kamal Singh received his PhD from Department of Pulmonary Medicine, Faculty of Medical Sciences (FMS), Vallabhbhai Patel Chest Institute, University of Delhi, India. His research interest focuses on the synthesis of medicinally active compounds.

Boric acid is a simple, inexpensive (500 g, Rs-620, Loba Chemie CAS No. 10043-35-3), commercially available, water-soluble, eco-friendly colorless crystalline inorganic solid. It is also employed as a preservative, pesticide, pH buffer, antiseptic agent, acne treatment, swimming pool chemical, and a precursor to other valuable compounds. Boric acid is a weak acid with pK _a of 9.15 in pure water at 25 °C.[1] It combines with water to form H⁺ ions. Boric acid was synthesized by the reaction of borax (sodium tetraborate decahydrate) and mineral acid such as hydrochloric acid[2] (Scheme [1a]). Boric acid was also produced as a byproduct of the hydrolysis of diborane and boron trihalides[3] (Scheme [1b]).

Scheme 1 Synthesis of boric acid

Table 1 Recent Applications of Boric Acid in Organic Transformations[4]

(A) Bowen Luo et al. reported hydrodeoxygenation (HDO) of phenolic compounds 1 and raw lignin oil (2) by using a novel homogeneous catalyst called boric acid in combination with Ru/C. The raw lignin oil also gave good (HDO) results with bifunctional catalyst (H3BO3, Ru/C). The results were improved when reaction was carried out at high temperature. When boric acid was used as a homogeneous catalyst, the rate of conversion of raw lignin oil to biofuel 4 increased.[5]
(B) Bhattacharyya et al. reported boric acid assisted hydrogenation of substituted quinolines 5 to 1,2,3,4-tetrahydroquinolines 6 was demonstrated under mild reaction conditions using Hantzsch ester (HE) as an organic hydrogen source. The majority of hydrogenation reactions have been carried out with high pressure of hydrogen gas and a metal catalyst, even though the current method is said to be a metal-free synthesis of 1,2,3,4-tetrahydroquinolines 6 from quinolines 5 without hydrogen gas.[6]
(C) The reduction of ketone and aldehyde is necessary for the synthesis of primary and secondary alcohols, whereas the reduction of esters is a more challenging transformation to carry out. In fact, the reduction of the former substrates can be accomplished with ease by mild reductants like NaBH4, but the reduction of esters typically calls for aggressive reagents like LiAlH4 or BH3. These reagents, despite being extremely active, are pyrophoric and carry significant handling risks. To make this operation safer, Lavergne et al. reported ester hydroboration by benzyl benzoate and pinacolborane reactions with and without a boric acid catalyst. The ester–pinacolborane reaction was carried out at high temperature in methyl tetrahydrofuran, but the product yield was low. Furthermore, the same reaction was carried out with 10 mol% H3BO3, and quantitative ester hydroboration yield was observed.[7]
(D) The role of boric acid in the synthesis of 2-amino-4,6-diarylnicotinonitriles 13 was evaluated. The reaction required the boric acid catalyst in order to proceed, and the highest yield of the product was obtained when 1 equivalent of boric acid was used. Hosseinzadeh et al. prepared a library of substituted 2-amino-4,6-diarylnicotinonitriles 13 by one-pot multiple components reaction using substituted benzaldehyde 9, acetophenone (10), malononitrile (11), and ammonium acetate (12) catalyzed by boric acid. All reactions were carried out in microwave irradiation without solvent in short reaction time with good yield.[8]
(E) Dipyrromethanes are prime precursors of various biomolecules. Dipyrromethanes have been produced by a variety of methods, but the majority of them required the presence of strong acids and prolonged reaction time. It is not a good practice for strong acids to directly impact the environment and human health. In order to solve the problem Singhal­ et al. reported one-pot green synthesis of 5-meso-substituted dipyrromethanes 15 by the reaction of aldehyde 9 and pyrrole (14) in water catalyzed by boric acid at ambient temperature.[9]
(F) Quinazolinone derivatives are a group of chemicals that are found in many bioactive natural products as well as pharmaceutical substances. The biological, pharmacological, and therapeutic properties of 2,3-dihydroquinazolinone derivatives[10] include but are not limited to antibiotic, anticancer, antidepressant, antihistamine, antihypertonic, antipyretic, antitumor, antituberculosis, The 2,3-dihydroquinazolin-4(1H)-ones 17 are produced by the reaction of anthranilamide (16) and benzaldehydes 9 catalyzed by H3BO3/montmorillonite K10 (H3BO3/mont K10).[11]
(G) 1,2,4-Triazine derivatives 20 have a wide range of biological properties, such as anticancer, muscle relaxant, hypnotic, anti-inflammatory, diuretic, and antihypertensive activities.[12] Darehkordi et al. synthesized dihydroindeno[1,2-e]pyrido[1,2-b][1,2,4]triazine-1,3- dicarbonitriles. The starting material 4-(aryl)-1,6-diamino-2-oxo-1,2- dihydropyridine-3,5-dicarbonitrile derivatives 18 were obtained by cyclocondensation reaction of cyanoacetohydrazide with p-benzilidenemalononitriles in absolute ethanol while refluxing in piperidine. The reaction of 1,6-diamino-2-oxo-4-phenyl-1,2-dihydropyridine-3,5-dicarbonitrile 18 with ninhydrin (19) in acetic acid catalyzed by boric acid produced dihydroindeno[1,2-e]pyrido[1,2-b][1,2,4]triazine-1,3- dicarbonitriles 20 in moderate to excellent yield.[13]
(H) Dehkordi and coworkers published the green, reusable boric acid/pentaerythritol catalyst catalyzed synthesis of mono- and bispyrano[2,3-d]pyrimidinone derivatives 23 in water at 50 °C. Although boric acid is thought to be a very weak acid, when polyhydroxy alcohols are present in an aqueous medium, it behaves as a strong acid. The formation of a bisboron chelate complex when pentaerythritol was added to a boric acid solution had been confirmed by Orthner and Freyss.[14] The complex accumulates in the water and turns more acidic, accelerating the reaction.[15]

A number of organic transformations have been completed successfully using the effective and environment friendly catalyst known as boric acid (Table [1]). Almost all organic reactions that are catalyzed by boric acid are safe for the environment, don’t require any hazardous solvents, and are uncomplicated to set up and have simple product separation in shorter reaction time. Boric acid was used to create a catalytic system that could be used repeatedly without significant loss of its catalytic activity. Because of all the benefits listed above, the scientific community may choose to use boric acid as an alternative acid catalyst in the future.

Conflict of Interest

The authors declare no conflict of interest.

• References

• 1 Lank P, Wahl M. Encyclopedia of Toxicology, 3rd ed. Wexler P. Elsevier; Amsterdam: 2014. 533
• 2 Demirel HS, İnce TE, Uysal D, Uysal BZ. CBUJOS 2015; 11: 379
• 3 Housecroft CE, Sharpe AG. The Group 13 Elements . In Inorganic Chemistry, 3rd ed. Housecroft C, Sharpe AG. Prentice Hall; Upper Saddle River: 2007. Chap. 13, 340
• 4a Rammohan P. ARKIVOC 2018; (i): 1
• 5 Luo B, Rongxuan LR, Shu R, Wang C, Zhang J, Chen Y. Ind. Eng. Chem. Res. 2020; 59: 17192
• 6 Bhattacharyya D, Nandi S, Adhikari P, Sarmah BK, Konwar M, Das A. Org. Biomol. Chem. 2020; 18: 1214
• 7 Lavergne JL, To H.-M, Fontaine F.-G. RSC Adv. 2021; 11: 31941
• 8 Hosseinzadeh Z, Ramazani A, Razzaghi-Asl N, Slepokura K, Lis T. Turk. J. Chem. 2019; 43: 464
• 9 Singhal A, Singh S, Chauhan SM. S. ARKIVOC 2016; (vi): 144
• 10a Alaimo RJ, Russell HE. J. Med. Chem. 1972; 15: 335
• 10b Sadanandam YS, Reddy KR. M, Rao AB. Eur. J. Med. Chem. 1987; 22: 169
• 10c Parish HA, Gilliom RD, Purcell WP, Browne RK, Spirk RF, White HD. J. Med. Chem. 1982; 25: 98
• 11 Mahesh K, Reddy KM, Kondaiah K, Vijayakumar B. Iran. J. Chem. Chem. Eng. 2019; 38: 37
• 12a Camirand A, Zakikhani M, Young F, Pollak M. Breast Cancer Res. 2005; 7: 570
• 12b Baselga J, Averbuch SD. Drugs 2000; 60: 33
• 12c Kim R, Toge T. Surg. Today 2004; 34: 293
• 12d Li F, Feng Y, Meng Q, Li W, Wang Q, Tao F. ARKIVOC 2007; (i): 40
• 13 Darehkordi A, Hosseini M, Rahmani F. J. Heterocycl. Chem. 2019; 56: 1306
• 14 Orthner L, Freyss G. Justus Liebig's Annalen Der Chemie 1930; 484: 131
• 15 Dehkordi SS. S, Albadi J, Jafari AA, Samimi HA. Polycyclic Aromat. Compd. 2022; 42 DOI: DOI: 10.1080/10406638.2022.2118330.

Publication History

Received: 12 October 2022

Accepted after revision: 08 May 2023

Accepted Manuscript online:
14 June 2023

Article published online:
20 July 2023