Synthesis of Unsymmetrical Ethers Catalysed by Polyvinyl Sulfuric Acid & PVSA / Nano RH SiO 2

Transcription

1 J. Nnonlysis., 4(3): Autumn 2017 ORIGINAL RESEARCH RESEARCH ARTICLE PAPER Synthesis of Unsymmetricl Ethers Ctlysed by Polyvinyl Sulfuric Acid & PVSA / Nno RH SiO 2 s Novel Solid Acid Nnocomposite Roy Moeinzdeh 1 *, Hdi Asreh 2, Ali Rez Kist 2 1 Deprtment of Chemistry, Dezful Brnch, Islmic Azd University, Dezful, Irn 2 Chemistry Deprtments, College of Science, Shhid Chmrn University of Ahvz, Ahvz, Irn Received: Accepted: Published: ABSTRACT The methodology involves prepring polyvinyl sulfuric cid s solid cid by simple mixing of polyvinyl lcohol with chlorosulfonic cid in t room temperture. The ctlytic bility of the solid cid ws investigted for the fcile conversion of benzylic lcohols to the unsymmetricl ethers with liphtic lcohols in the presence of the solid cid. Results show tht the solid cid is n pproprite ctlytic gent for these condenstion rections. The silic ws lso extrcted from low-cost rice husk nd the morphous silic gel nnoprticles were prepred with sol- gel method. The polyvinyl sulfuric cid ws supported on nno rice husk silic. Then the ctlytic effect of this system ws investigted for synthesis of unsymmetricl ethers which consisted of combintion of high cidic power for this solid cid nd high- surfce re of nnoprticles. Results show tht totlly ctlytic effect of polyvinyl sulfuric cid supported on nno silic is more suitble thn polyvinyl sulfuric cid. The reson for this is in its bility to produce the end products in shorter rection times while hving high isolted yields. Keywords: Silic nnoprticles; Polyvinyl sulfuric cid; Unsymmetricl ethers; Sol-gel method; Rice husk 2017 Published by Journl of Nnonlysis. How to cite this rticle Moeinzdeh R, Asreh H, Kist AR. ASynthesis of Unsymmetricl Ethers Ctlysed by Polyvinyl Sulfuric Acid & PVSA / Nno RH SiO 2 s Novel Solid Acid Nnocomposite. J. Nnonlysis., 2017; 4(3): DOI: / jn INTRODUCTION Green chemistry is n emerging scientific perspective to the synthesis, processing nd ppliction of chemicl substnces in the relworld situtions with the objective of mitigting the potentil nd rel risks to humns, eco-system nd the physicl environment [1]. It is cler tht green chemistry, s is known in the literture, requires the ppliction of environmentlly-benign regents nd solvents s mens of being ble to recover nd reuse the ctlyst [2]. Recent trend in * Corresponding Author Emil: ro_moein@yhoo.com environmentl consciousness, prticulrly in the post-industril nd post-modern digitl societies, hs been the underlying urgency in undertking pplied reserch into optimum utiliztion of griculturl nd horticulturl byproducts. Rice husk cn be sid to constitute s one of those cses of crop wstes tht is plentifully produced ntionlly nd globlly. For its significntly high silicon content, rice husk hs emerged s mjor ingredient for producing elementry silicon nd numerous silicon compounds like silicon nitride [3], sodium silicte [4] nd silicon crbide [5]. The mjor inorgnic constituent of the rice husk is silic J. Nnonlysis., 4(3): , Autumn

2 tht is produced in vrious wys. Dvrpnh et l. for exmple, used method tht involves extrction of morphous nno silic from rice husk (RH-SiO 2 ). They hve lso investigted the ctlytic ppliction of silver nnoprticles immobilized to rice husk- SiO 2- minopropylsilne composite s recyclble ctlyst in the queous reduction of nitrorenes [6]. In nother reserch study, green synthesis of nno silic ws obtined by therml decomposition of pine cones nd pine needles hve been reported. [7]. Appliction of solid cids s heterogeneous ctlysts, hs extensively received ttention in vrious specilized domins of orgnic synthesis [1]. They hve numerous dvntges, mong which re esy physicl hndling, decresed rector nd plnt corrosive problems, environmentlly-sfe disposl in different chemicl processes compred with the conventionl liquid cid ctlysts. The potentil wstes nd by-products cn be minimized by the ppliction of solid cids in developing clener synthesis routes [2,8]. A vriety of orgnic rections re ctlyzed in the presence of solid cids such s nno silic gel supported by thionyl chloride [9], phospho sulfonic cid [10], silic chloride [11], lumin sulfuric cid [12], silic sulfuric cid [13], cellulose sulfuric cid [14], etc. Orgnic ethers re mong the prominent clsses of chemicls tht hve widespred pplictions in vrious sectors of chemicl nd gro-chemicl industries. They constitute s the mjor ingredients of herbicides, phrmceuticls, disinfectors, plsticizers, solvents nd Intermedites [15]. They lso found in production of perfumes, grochemicls nd phrmceuticl leds, s well s serving s multi-purpose building block in orgnic synthesis [16]. One of the most common methods of ether production is the Willimson ether synthesis [17]. Vrious ether synthesis methods hve been reported, the principl mong them re reductive etherifiction of lkoxydilkylsilnes with crbonyl compounds using the BiBr 3 / ClR 2 Si-H ctlytic system [18]. It lso involved etherifiction of benzyl lcohols with 1-hexnol by propyl nd rene-so 3 H-modified mesostructured SBA-15 mterils s ctlysts[19], lcoholises of benzylic nd llylic lcohols ctlyzed by Iron (ІІІ ) s FeCl 3 nd Fe(ClO 4 ) 3 [20]. The work lso involved etherifiction of benzylic lcohols with different lcohols in the presence of AlPW 12 O 40 [21]. The trnsformtion of benzyl lcohols into their methyl or ethyl using 2,4,6-trichloro-1,3,5- trizine ctlyzed by dimethyl sulfoxide [22] ws lso crried out. The finl stge involved the conversion of ryl ldehydes to dibenzyl ethers through reductive etherifiction in the presence of Et 3 SiH with ctlytic mount of InCl 3 [16]. The present pper ims to investigte the processes involved in converting benzylic lcohols to the unsymmetricl ethers with liphtic lcohols ctlyzed by polyvinyl sulfuric cid s solid cid. Further, morphous silic nnoprticles were obtined from low-cost rice husk (RH-SiO 2 ) by crrying out cid chemicl tretment followed by the burning process. Silic nnoprticles ws then prepred with sol- gel method. The polyvinyl sulfuric cid ws supported on nno rice husk silic, the ctlytic effect of this system ws subsequently investigted for synthesis of unsymmetricl ethers. EXPERIMENTAL All chemicl regents were purchsed from Merck Chemicl Compny nd were used without purifiction. Rice husk (RH) ws collected from rice mill in Khozestn Bghmlek (Irn). The progress of the rections ws ccomplished by TLC on silic-gel polygrm SILG/UV 254 pltes. Pltes were visulized by UV light. FT- IR spectr were recorded using Perkin-Elmer model BX- ΙΙ instrument. The 1 H-NMR nd 13 C-NMR spectr were recorded on Bruker Avnce 400 MHz spectrometer in CDCl 3 using TMS s n internl reference. EDX nlysis of the ctlyst ws recorded using scientific instrument UK model SIRIUS SD. The Morphology nd prticle dispersion were investigted using FESEM (Hitchi S-4160). Extrction of silic from rice husk The dried rice husk (30.0 g) ws stirred in 750 ml of 1.0 M nitric cid for 24 h t room temperture. It ws subsequently wshed thoroughly with distilled wter until the ph of the rinsed product becme constnt (PH=6). It ws then dried in n oven for 24 h t 100 C nd ws burned for 6 h in muffle furnce t 800 C. Silic extrction from RH ws crried out by stirring the rice husk in 500 ml of 1.0 M sodium hydroxide for 24 h t room temperture. The mixture ws subsequently filtered nd titrted with 3.0 M HNO 3, during which the ph of the solution reched 5, the titrtion ws stopped. It then underwent the process of ging for 24 h. The silic gel/precipitte ws filtered, comprehensively wshed with distilled wter nd dried for 18 h t 100 C [23]. 190 J. Nnonlysis., 4(3): , Autumn 2017

3 Preprtion of polyvinyl sulfuric cid (PVSA) A 50 ml suction flsk ws equipped with constnt- pressure dropping funnel contining mixture of chlorosulfonic cid (2.6 g, 22.7 mmol) nd 3 ml of dried dichloromethne. The gs outlet ws connected to vcuum system through n dsorbing solution (5% NOH). Polyvinyl lcohol (MW=145000), (1.0 g, 22.7 mmol) nd 10 ml of dried dichloromethne were chrged into the flsk nd chlorosulfonic cid in ws dded dropwise over period of 50 min t room temperture. After the ddition ws completed, the mixture ws stirred for 5 min, while the residul HCl ws removed by suction. The mixture ws then wshed with excess of dried (5 ml). Finlly, the obtined blck solid (PVSA, 2.4 g) ws plced in oven t 50 C for 1 h. Generl procedure for etherifiction of benzylic lcohols with vrious liphtic lcohols ctlyzed by PVSA A mixture of benzylic lcohol (1mmol), liphtic lcohol (2 ml) nd polyvinyl sulfuric cid (0.1 g) ws stirred mgneticlly t 70 C for the suitble time (Tble 1). The dried (10 ml) ws dded to the rection mixture fter completion of the rection (monitored by TLC). The rection mixture ws filtrted in order to seprte the solid ctlyst from the residue wshed with dried (5 ml). The pure product in high isolted yield (70-94 %) ws obtined fter the evportion of the solvent. Tble 1. Preprtion of unsymmetricl benzyl ethers ctlyzed by PVSA t 70 C Entry Benzylic lcohols Aliphtic lcohols Time(min.) Yield (%) 1 p-meoc 6 OH Ethnol b 2 Ethnol Propnol Propnol sec-butyl lcohol tert-butyl lcohol p-mec 6 OH Ethnol Propnol Propnol sec-butyl lcohol tert-butyl lcohol Ph 2 CHOH Ethnol Propnol Propnol sec-butyl lcohol tert-butyl lcohol (p-clc 6 )PhCHOH Ethnol Propnol Propnol sec-butyl lcohol tert-butyl lcohol PhCH(OH)CH 3 Ethnol Propnol Propnol sec-butyl lcohol tert-butyl lcohol Conditions: benzylic lcohols (1mmol), liphtic lcohols (2 ml) nd polyvinyl sulfuric cid (0.1 g), b In the bsence of PVSA. J. Nnonlysis., 4(3): , Autumn

4 Generl procedure for etherifiction of benzylic lcohols with ethyl lcohol ctlyzed by PVSA/ Nno RH SiO 2 The mixing of polyvinyl sulfuric cid (0.1 g) nd nno rice husk silic (0.05 g) were dded to solution of benzylic lcohol (1mmol) nd ethyl lcohol (2 ml). The mixture ws subsequently stirred mgneticlly t 70 C for the suitble time (Tble 2). The progress of rection ws systemticlly monitored by TLC. Dried (10 ml) ws dded to the rection mixture tht ws lter filtrted in order to seprte the ctlyst from the residue wshed with dried (5 ml). The pure product in high isolted yield (84-95%) ws obtined fter the evportion of the solvent. RESULT AND DISCUSSION According to the previously reported method, polyvinyl sulfuric cid ws produced by mixing of polyvinyl lcohol nd chlorosulfonic cid under solvent free condition t room temperture [24]. In the present reserch, however, this polymeric solid cid ws prepred using similr method. The only difference being tht the ws dded to the rectnts in the synthesis procedure for convenience. This rection ws comfortble nd clen, becuse the HCl ws the only by-product tht immeditely evolves from the rection vessel (Scheme 1). The cidic power of polyvinyl sulfuric cid ws obtined by titrtion using NOH (0.1 N). The result showed tht the cidic cpcity of ctlyst is 9.84 mmol/g nd it cn be reduced the ph to bout The conversion of lcohols into unsymmetricl ethers is one of the most importnt synthetic rections. We first exmined etherifiction of ethnol nd p-methoxybenzyl lcohol s model in the presence of polyvinyl sulfuric cid. It ws found tht for the fcile etherifiction rection, 0.1 g of the ctlyst ws required. The condenstion rection evenly performed nd obtined p-methoxybenzyl ethyl ether in 90% yield fter 12 min t 70 C. (Tble 1, entry 2). In the bsence of the PVSA s ctlyst, similr rection ws not proceed t 70 C fter six hours. (Tble 1, entry 1). In order to show the generl ppliction of the protocol, we hve studied the etherifiction of benzylic lcohols with ethnol, 1-propnol, 2-propnol, sec-butyl lcohol nd t-butyl lcohol (Scheme 2). All the rections proceeded well in short rection times with the production of benzyl lkyl ethers in excellent isolted yields (Tble 1). Tble 2. preprtion of unsymmetricl benzyl ethers ctlyzed by PVSA / Nno RH SiO 2 t 70 C. Entry Benzylic lcohols Aliphtic lcohol Time (min.) Yield (%) 1 p-meoc 6 OH Ethnol p-mec 6 OH Ethnol Ph 2 CHOH Ethnol (p-clc 6 )PhCHOH Ethnol PhCH(OH)CH 3 Ethnol 8 92 Conditions: benzylic lcohols (1mmol), ethnol (2 ml) nd the ctlyst (0.15 g). Scheme 1. Preprtion of polyvinyl sulfuric cid 192 J. Nnonlysis., 4(3): , Autumn 2017

5 Scheme 2. Preprtion of unsymmetricl benzyl ethers in the presence of PVSA s the ctlyst t 70 C. Results show tht the solid cid is n pproprite ctlytic gent for these condenstion rections. The results were shown in Tble 1. Amorphous nno silic comfortbly ws extrcted from low-cost rice husk (RH) nd then ws prepred with sol- gel method. The morphology nd quntittive nlysis of extrcted nno silic ws exmined by FESEM (Hitchi S-4160). According to Fig. 1(), the RH-SiO 2 nnoprticles size distribution hs n verge of 30 nm. The polyvinyl sulfuric cid ws supported on nno rice husk silic by simple mixing of polyvinyl sulfuric cid nd nno silic in 2:1 rtio. According to Fig. 1(b), the PVSA/ Nno RH SiO 2 nnoprticles size distribution hs n verge of 200 nm. In ddition, to confirm the structure of the nnocomposite, EDX spectr hs been recorded. EDX spectr confirmed the presence of the Si, C, O, nd S elements in the ctlyst structure (Fig. 2). The FTIR spectroscopy ws used to chrcterize the structure of ctlyst. Fig. 3 shows the FTIR spectr of PVSA (3) nd PVSA / Nno RH SiO 2 (3 b). The IR spectrum of PVSA (3) showed the brod O-H bsorption round 3404 cm 1 strong S=O bsorptions between, 1172 nd 1289 cm 1 nd strong S-O bsorption t 578 cm 1. PVSA/Nno RH SiO 2 (3 b) showed the brod bnd round 3401 cm 1 is due to the stretching vibrtion of SiO-H bond, the HO-H vibrtion of wter molecules dsorbed on the silic surfce nd O-H bsorption of Hydrogen sulfte groups. The strong S=O bsorptions between 1170 nd 1289 cm 1 nd strong S-O bsorption t 584 cm 1 were lso shown. The bnd round 1631 cm 1 is lso due to the bending vibrtion of wter molecules bound to the silic mtrix nd the strong pek t 1077 cm 1 is due to symmetric stretching vibrtion of the structurl siloxne bond, Si-O-Si. b Fig. 1. () FESEM imges of the extrcted nno silic, (b) FESEM imge of PVSA / Nno RH SiO 2. J. Nnonlysis., 4(3): , Autumn

6 b Fig. 2. EDX nlysis of PVSA / Nno RH SiO 2. Fig. 3. The FT-IR spectr of ) PVSA, b) PVSA / Nno RH SiO 2. Then the ctlytic effect of PVSA / Nno RH SiO 2 ws investigted for the synthesis of p-methoxybenzyl ethyl ether s model rection. It ws found tht 0.15 g of nnocomposite proceeded well in the minimum time with mximum yield (7min., 94%). In order to show the generl ppliction of the protocol, we hve studied the etherifiction of benzylic lcohols with ethnol in the presence of this cidic nnocomposite (Scheme 3, tble 2). Scheme 3. Preprtion of unsymmetricl benzyl ethers in the presence of PVSA/Nno RH SiO 2 s the ctlyst t 70 C. As shown in Tble 2, the unsymmetricl ethers were produced in excellent isolted yields. The comprison of the results for etherifiction in the presence of polyvinyl sulfuric cid (Tble 1) with polyvinyl sulfuric cid supported on nno rice husk silic (Tble 2), were clerly shown tht the lter is better nd the produced the products in shorter times. The morphology of the nnocomposite ws lso determined by FESEM imges s shown in Fig. 1(b). The PVSA / Nno RH SiO 2 nnoprticles distribute in verge size of 200 nm. It is should be point out tht, in 2005, Firouzbdi et l. [21] introduced AlPW 12 O 40 s n efficient ctlyst for the synthesis of unsymmetricl ethers. The condenstion of 1- phenyl ethnol s secondry benzylic lcohol by ethnol ws proceeded in the presence of this heterogeneous ctlyst nd fford the corresponding ether fter 7 hours in 86% yield. The similr condenstion rection ctlyzed by PVSA / Nno RH SiO 2, it required shorter time nd produced the product in higher isolted yield (8 min nd in 92% yield). This is shown tht, the bility of this nonocomposite to produce the end-product in shorter rection time while hving high isolte yield. Becuse of possessing n inorgnic-bse (SiO 2 ) derived from plnt residues of rice husk (green chemistry nd ecofriendly fetures), lso the nnocomposite s ctlyst, proves to be environmentlly sfe s well s being reltively ccessible nd economiclly fesible to use. CONCLUSION In conclusion, polyvinyl sulfuric cid s heterogeneous solid cid ctlyst tht is environmentlly- sfe. This is suitble proton source nd insoluble in the orgnic solvents. A simple nd convenient protocol hs described in the presence of this solid cid for the synthesis of unsymmetricl ethers. The unsymmetricl ethers were obtined in short rection times while hving high isolted yields. Also in the present study, nnosilic ws esily extrcted from rice husk. The polyvinyl sulfuric cid ws supported on nno rice husk silic, then the ctlytic effect of this system ws investigted for synthesis of unsymmetricl ethers which is consisted of combintion of high cidic power for this solid cid nd high- surfce re of nnoprticles. The ttrctive fetures of this method re simple procedure, clener rection, esy work-up, short rection times with the production of benzyl lkyl ethers in excellent yields. 194 J. Nnonlysis., 4(3): , Autumn 2017

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