Green and Sustainable Chemistry, 2011, 1, 132-148 doi:10.4236/gsc.2011.14022 Published Online November 2011 (http://www.SciRP.org/journal/gsc) Poly Ethylene Glycols as Efficient Media for the Synthesis of β-Nitro Styrenes from α, β-Unsaturated Carboxylic Acids and Metal Nitrates under Conventional and Non-Conventional Conditions Kamatala Chinna Rajanna1, Kola Ramesh2, Soma Ramgopal1, Somannagari Shylaja2, Pochampally Giridhar Reddy2, Pondichery Kuppuswamy Saiprakash1 1Department of Chemistry, Osmania University, Hyderabad, India 2Department of Chemistry, CBIT, Gandipet, Hyderabad, India E-mail: [email protected] Received August 18, 2011; revised October 14, 2011; accepted October 26, 2011 Abstract Poly ethylene glycols (PEG-200, 400, 600, 4000 and 6000) supported reactions were conducted with certain α, β-unsaturated acids in presence of metal nitrates under solvent free (solid state) and mineral acid free con- ditions. The reactants were ground in a mortar with a pestle for about 30 minutes. The aromatic acids under- went nitro decarboxylation and afforded β-nitro styrene derivatives in very good yield while α, β-unsaturated aliphatic carboxylic acids gave corresponding nitro derivatives. Addition of PEG accelerated rate of the reac- tion enormously. Reaction times substantially decreased from several hours to few minutes followed by highly significant increase in the product yield. Among the several PEGs PEG-300 has been found to be much more effective than other PEGs. Keywords: Poly Ethylene Glycols (PEG), Rate Accelerations, α, β-Unsaturated Acids, Metal Nitrates, Solvent Free (Solid State), β-Nitro Styrene Derivatives, α, β-Unsaturated Aliphatic Acids, Nitro Derivatives 1. Introduction via microwave irradiation has been the subject of interest for the past one decade which has the advantage of being The use of non volatile solvents is an essential ingredient eco-friendly, easy to handle, employ shorter reaction times in a large number of organic synthesis protocols, which and solvent less conditions. Reactions performed under may be toxic, hazardous and also cause environmental solvent-free conditions have gained much attention be- pollution. Therefore the use of environmentally safe and cause of their enhanced selectivity, mild reaction con- non-toxic solvents and more specifically removal of or- ditions and associated ease of manipulation. The recent ganic solvents in chemical synthesis are important in the reviews and publications [1-6] in this field prove the drive towards benign chemical technologies. Solvent-free importance of solvent free organic synthesis and high- organic reactions make synthesis simpler, save energy, lights that, this process is not only simple but also satis- and prevent solvent wastes, hazards, and toxicity. The fies both economical and environmental demands by development of solvent-free organic synthetic methods replacing the toxic solvents. Since more than a decade has thus become an important and popular research area. our group is also actively working on exploiting the use Reports on solvent-free reactions between solids, gases of a variety of eco friendly materials such as metal ions and solids, solids and liquid, between liquids, and on and surfactants as catalysts and non-conventional energy solid inorganic supports have become increasingly fre- sources (such as microwave and ultra sound) to assist quent in recent years. A mortar and pestle is a tool used organic transformations such as Vilsmeier-Haack [7-9], to crush, grind, and mix solid substances. Solvent less Hunsdiecker [10] and nitration reactions [11-13]. The preparation of organic compounds in the solid state and classical Hunsdiecker-Borodin reaction [14,15] is an im- Copyright © 2011 SciRes. GSC K. C. RAJANNA ET AL. 133 portant halo decarboxylation reaction, which is used for periodically monitored by TLC. After completion, the the synthesis of β-halo styrenes from α, β-unsaturated reaction mixture is treated with 2% sodium carbonate Cinnamic acid. This reaction has been modified by seve- solution, followed by the addition dichloro methane ral workers with a view to overcome the toxicity factors (DCM) or dichloro ethane (DCE). The organic layer arising from the use of molecular bromine and metal salt was separated, dried over Na2SO4 and the solvent is catalysts [16-25]. The use of solid acid catalysis has been recollected by distillation using Rotavapor. The resul- found potentially more attractive because of the ease of tant compound is further purified with column chroma- removal and recycling of the catalyst and the possibility togram-phy using ethyl acetate: hexane (3:7) as eluent that the solid might influence the selectivity. In one of to get pure product. Hexane and ethyl acetate are also the recent reports Das and coworkers [26] reported that separated using Rotavapor according to standard pro- nitro styrenes can be achieved from α, β-unsaturated cedures [35-37]. carboxylic acids using nitric acid (3 equiv) and catalytic amount of AIBN (2 mol%) in acetonitrile medium. In 2.2. General Procedure for the Synthesis of another report Rao et al. [27] enlightened the use of ceric β-Nitro Styrenes in Acetonitrile Medium ammonium nitrate (CAN) in nitro Hunsdiecker-Borodin under Continuously Stirred Conditions reactions. Recently we have concentrated on developing new methodologies using non-conventional energy sou- In a typical synthesis, Cinnamic acid (0.01 mol), PEG rces and eco-friendly materials as catalysts in organic (0.02 mmol) and metal nitrate (0.12 mmol) are placed in transformations, and reported a methodology in metal a clean mortar and ground with a pestle for about 30 to ion mediated nitration of organic compounds in presence 60 minutes until the mixture is homogeneous, the parti- cles are no longer getting smaller. Progress of the reac- of small amount of HNO3 under solvent free (solid state) conditions [28]. Polyethylene glycol (PEG-400) is a bio- tion is periodically monitored by TLC. After completion, logically acceptable inexpensive polymer and an eco- the reaction mixture is treated with 2% sodium bicarbo- friendly reagent [29], which is widely used in many or- nate solution, followed by the addition dichloro methane (DCM) or dichloro ethane (DCE). The organic layer was ganic reactions for conversion of oxiranes to thiiranes further treated in a similar manner discussed in the ear- [30], asymmetric aldol reactions [31], cross-coupling rea- lier section to get pure product. ctions [18], Baylis-Hillman reaction [32,33] and ring o- pening of epoxides [34]. Encouraged by these results, we 2.3. General Procedure for the Synthesis of want to explore, the use of Polyethylene glycols (PEGs) β-Nitro Styrenes under Microwave as efficient catalyst in this study. We have studied PEG Irradiated Conditions triggered Hunsdiecker-Borodin reactions for the synthe- sis of β-nitro styrenes from α, β-unsaturated carboxylic Cinnamic acid (0.01 mol), PEG (0.02 mmol) and metal acids under conventional and non-conventional (solvent nitrate (0.12 mmol) were dissolved in minimum amount free mortar-pestle and microwave) conditions. of MeCN, and mixed with silica gel (10 g) and the mix- ture was transfered into a test tube and subjected to mi- 2. Experimental Details crowave irradiation (BPL make, BMO 700T, 650 W, power 80%) for a specified period. Reaction was moni- Cinnamic acid, metal nitrates, nitric acid and polyethyle- tored by TLC (hexane-ethyl acetate, 7:3). After comple- ne glycols were obtained from SD Fine Chemicals or tion of the reaction, products are isolated as discussed in Loba. Substituted Cinnamic acid were prepared by Per- the above section. kins reaction as cited in literature [35]. 2.4. General Procedure for the Synthesis of 2.1. General Procedure for PEG Mediated β-Nitro Styrenes under Solvent-Free Synthesis of β-Nitro Styrenes in MeCN Conditions Medium A mortar was charged with Cinnamic acid (0.01 mol), In a typical solid state synthesis, Cinnamic acid (0.01 PEG (0.02 mmol) and metal nitrate (0.12 mmol). The mol), PEG (0.02 mmol) and metal nitrate (0.12 mmol) mixture was ground at room temperature with a pestle are placed in a clean two necked R. B. flask and stirred until TLC showed complete disappearance of the starting for certain time. Ground with a pestle for about 30 to 60 material. After completion, the reaction mixture is trea- minutes until the mixture is homogeneous and particles ted with 2% sodium bicarbonate solution, followed by are no longer getting smaller. Progress of the reaction is addition of dichloro methane (DCM) or dichloro ethane Copyright © 2011 SciRes. GSC 134 K. C. RAJANNA ET AL. (DCE). The organic layer was further treated in a similar Cinnamic acid afforded β-nitro styrenes when they are manner discussed in the earlier section to get pure product. taken along with PEG in presence of metal nitrates in a mortar and ground with a pestle for about half a hour. 3. Results and Discussion The reactions afforded good yield of products with high regio selectivity. The yields of major products are com- The α, β-unsaturated aromatic carboxylic acids such as piled in Tables 1-3. The products were characterized by Table 1. NMR and Mass Spectral data for selected reaction products. Spectral data Entry Substrate Product m/z 1HNMR 1 CA β–Nitro Styrene 149 δ 6.4 (d 1H, β-CH), δ 7.3 - 7.65 (m 5H, Ar-H) δ 7.8(d 1H, α-CH) 2 4-ClCA 4-Chloro β–Nitro Styrene 184 δ 6.6 (d 1H, β-CH) δ 7.2 (d 2H, Ar-H) δ 7.6 (d 2H, Ar-H) δ 8.3 (d 1H, α-CH) 3 4-OMeCA 4-Methoxy β–Nitro Styrene 179 δ 3.8 (s 3H, OCH3)