Zinc chloride has been found to be an excellent catalyst for a one-pot synthesis of nitriles from araldehydes and hydroxylammonium chloride under solvent-free conditions. The features of the present method are short reaction time, easy workup procedure, and good yields of the nitriles

Nizma, A.

Pasha, M.A.

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Full Terms & Conditions of access and use can be found athttp://www.tandfonline.com/action/journalInformation?journalCode=lsyc20Download by: [Bangalore University] Date: 12 July 2016, At: 23:36Synthetic CommunicationsISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20Zinc Chloride–Catalyzed Expeditious Route toNitrilesM. A. Päsha & Aatika NizamTo cite this article: M. A. Päsha & Aatika Nizam (2010) Zinc Chloride–CatalyzedExpeditious Route to Nitriles, Synthetic Communications, 40:9, 1276-1279, DOI:10.1080/00397910903069657To link to this article:  http://dx.doi.org/10.1080/00397910903069657Published online: 07 Apr 2010.Submit your article to this journal Article views: 95View related articles Citing articles: 8 View citing articles ZINC CHLORIDE–CATALYZED EXPEDITIOUS ROUTETO NITRILESM. A. Pa¨sha and Aatika NizamDepartment of Studies in Chemistry, Central College Campus, BangaloreUniversity, Bangalore, IndiaZinc chloride has been found to be an excellent catalyst for a one-pot synthesis of nitrilesfrom araldehydes and hydroxylammonium chloride under solvent-free conditions. Thefeatures of the present method are short reaction time, easy workup procedure, and goodyields of the nitriles.Keywords: Aldehydes; hydroxyl ammonium hydrochloride; microwave; nitriles; ZnCl2INTRODUCTIONIn recent years, increasing interest has been focused on the synthesis of nitrilesbecause of their importance in organic synthesis, as they serve as intermediates in thesynthesis of a variety of pharmaceuticals, pesticides, and dyes.[1]However, zinc chloride is considered to be a high-quality catalyst in organicsynthesis because of the numerous advantages associated with it: it is an environmen-tally safe catalyst, readily available, and inexpensive.Usually the synthesis of nitriles is accomplished by substitution reactions ofalkyl and aryl halides with metal cyanides,[2] oxidation of primary amines,[3] dehy-dration of primary[4] and secondary amides,[5] and dehydration of aldoximes withdehydrating agents.[6] Other reported methods for the synthesis of nitriles is theone-pot reaction of aldehydes and hydroxylammonium chloride using variouscatalysts.[7]The reported methods entail problems such as use of catalysts that areenvironmentally hazardous, excess catalysts, expensive reagents, tedious workupprocedures, and cumbersome methodologies. Therefore, there is a need for a versa-tile, simple, and environmentally friendly process for a one-pot synthesis of nitrilesfrom aldehydes.During the past decade, microwave heating has become a convenient andwidely used tool in organic synthesis. Microwave irradiation often leads to a remark-able decrease in reaction time, increased yields, easier workup procedure, and use ofgreen chemistry protocols.[8,9]Received March 2, 2009.Address correspondence to M. A. Pa¨sha, Department of Studies in Chemistry, Central CollegeCampus, Bangalore University, Bangalore 560 001, India. E-mail: mafpasha@gmail.comSynthetic Communications1, 40: 1276–1279, 2010Copyright # Taylor & Francis Group, LLCISSN: 0039-7911 print=1532-2432 onlineDOI: 10.1080/003979109030696571276Downloaded by [Bangalore University] at 23:36 12 July 2016 We previously reported the synthesis of nitriles from primary amides using zincchloride as catalyst in acetonitrile medium,[10] but there has always been a desire tosynthesize these nitriles from readily available starting materials under solvent-freeconditions. Therefore, we have made use of the readily available aldehydes to synthe-size nitriles under solvent-free conditions using microwaves.RESULTS AND DISCUSSIONTo ﬁnd the best catalyst for the synthesis of nitriles, the reaction of anisalde-hyde and hydroxylammonium chloride was carried out in the absence of catalystand in the presence of various Lewis acids, both under thermal conditions and undermicrowave irradiation. Best results were obtained when zinc chloride was used as acatalyst under microwave irradiation.In a typical experiment, aromatic aldehyde, hydroxylammonium chloride,and a catalytic amount of ZnCl2 (10mol%) were taken in a Pyrex tube, mixed well,and irradiated in a domestic microwave oven at 160W for less than a minute to getthe nitriles in good to excellent yields (Scheme 1). This was conﬁrmed by recordingthe infrared (IR) spectra for the corresponding nitriles and observing a sharp peakat the frequencies (Table 1).Encouraged by this success, we attempted the reaction of hydroxyl ammoniumchloride with various aromatic aldehydes under similar conditions (Table 1). Thisprotocol is suited for both electron-donating and electron-withdrawing substituentson the aromatic aldehydes.Scheme 1. Synthesis of various substituted nitriles.Table 1. One-pot conversion of araldehydes into corresponding nitriles in the presence of cat. ZnCl2 at160W of microwave irradiationEntry Substrate ProductTime(s)Yield(%)IR(t cm1)1 4-Methoxybenzaldehyde 4-Methoxybenzonitrile 25 85 2225.702 3-Chlorobenzaldehyde 3-Chlorobenzonitrile 30 80 2235.303 3-Nitrobenzaldehyde 3-Nitrobenzonitrile 30 80 2235.344 2-Nitrobenzaldehyde 2-Nitrobenzonitrile 30 78 2239.205 4-Hydroxybenzaldehyde 4-Hydroxybenzonitrile 28 85 2229.566 3,4,5-Trimethoxybenzaldehyde 3,4,5-Trimethoxybenzonitrile 28 80 2227.637 2,4-Dimethoxybenzaldehyde 2,4-Dimethoxybenzonitrile 25 88 2221.848 3-Methoxy-4-hydroxybenzaldehyde 3-Methoxy-4-hydroxybenzonitrile 25 85 2225.709 2-Chlorobenzaldehyde 2-Chlorobenzonitrile 28 90 2226.7010 4-Chlorobenzaldehyde 4-Chlorobenzonitrile 30 80 2228.7011 2,4-Dichlorobenzaldehyde 2,4-Dichlorobenzonitrile 30 78 2235.34ZINC CHLORIDE–CATALYZED EXPEDITIOUS ROUTE TO NITRILES 1277Downloaded by [Bangalore University] at 23:36 12 July 2016 CONCLUSIONIn conclusion, we have developed a simple, solvent-free, and efﬁcient methodto get nitriles by the reaction of different aldehydes and hydroxylammonium chlor-ide in the presence of a catalytic amount of zinc chloride under microwaveirradiation within 30 s.EXPERIMENTALAldehydes, hydroxylammonium chloride, and other chemicals used were com-mercial. All the reactions were carried out using a conventional (unmodiﬁed) house-hold microwave oven (LG, 230V, 160W). Reactions were monitored by thin-layerchromatography (TLC) by comparison with the authentic samples. Yields refer tothe isolated yields of the products. The infrared (IR) spectra of the products wererecorded on a Shimatzu Fourier transform (FT)–IR 8400s spectrophotometer.Procedure for the Preparation of 4-MethoxybenzonitrileA mixture of anisaldehyde (0.136 g, 1mmol), hydroxylammonium chloride(0.08 g, 1.2mmol), and zinc chloride (10mol%) was taken in a Pyrex cylindrical tube,mixed well, and irradiated in a microwave oven at 160W for 25 s. The contents werecooled to room temperature and extracted with dichloromethane (5ml). The organiclayer was dried over anhydrous sodium sulfate, and the solvent was removed undervacuum. The crude product was chromatographed on a short column of silica gelusing light petrol as an eluent to get the pure nitrile (0.143 g, 85%).REFERENCES1. 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Commun. 2007, 37, 1545–1550.ZINC CHLORIDE–CATALYZED EXPEDITIOUS ROUTE TO NITRILES 1279Downloaded by [Bangalore University] at 23:36 12 July 2016 

Zinc Chloride-Catalyzed Expeditious Route to Nitriles

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Zinc Chloride-Catalyzed Expeditious Route to Nitriles

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