Elsevier

Industrial Crops and Products

Volume 50, October 2013, Pages 701-706
Industrial Crops and Products

Metathesis of tobacco fatty acid methyl esters: Generation of industrially important platform chemicals

https://doi.org/10.1016/j.indcrop.2013.08.020Get rights and content

Highlights

  • Self-metathesis in unsaturated rich tobacco (Nicotiana tabacum, 82.2% unsaturation) fatty acid methyl esters was performed using Grubbs second generation catalyst.

  • 9-octadecene (24%), a major hydrocarbon, lube-range oil intermediate was observed.

  • Cyclic hydrocarbon, namely cyclodecyclododecene was also observed in good amounts (19%).

  • The study discusses the reaction mechanism involved in the formation of metathesized products.

Abstract

Self-methathesis of vegetable oil based unsaturated fatty acids provide a renewable and convenient route for the preparation of a number of platform chemicals useful for the production of polymers, biolubricants and other industrial products. The present study is focused on the use of the unsaturated non-edible oil methyl esters of tobacco (Nicotiana tabacum 82.2%) self- metathesis. Metathesis was carried out reacting equimolar quantities of fatty acid methyl esters (6.8 mm) with Grubbs second generation catalyst (0.3 mm) at 40–45 °C for 36 h. The metathesized products were characterized using GC and GC–MS analysis. Self-metathesis of the tobacco methyl esters resulted in the formation of hydrocarbons, of which 9-octadecene (24%) and a cyclodecacyclododecene (19%) were found to be major. In addition 9-octadecenoic acid methyl ester (17%) and 9,12-octadecadienoic acid methyl esters (11%) were also observed. The study also discusses the molecules involved in the formation of the above intermediates which are useful for the preparation of a number of industrial products.

Introduction

Metathesis of vegetable oils has been gaining considerable attention from several decades (Mol, 2002, Mol, 2004). The approach contributes to a sustainable development and reduction in CO2 emissions as the renewable raw materials employed are safer, and less toxic for the preparation of fine chemicals (Biermann et al., 2000) and polymers (Meier et al., 2007). The products obtained by olefin metathesis are highly valuable intermediates as they are not obtained naturally (Verkuijlen and Boelhouwer, 1974). Moreover, vegetable oil based platform chemicals obtained by metathesis can replace most of the petroleum based platform chemicals (Anastasiya et al., 2008). Olefin metathesis which involves carbon-carbon bond formation, results in an important family of reactions in organic synthesis, where a number of platform chemicals with different functionalities are generated (Nicolaou et al., 2005). Self-metathesis is a reaction between two similar molecules. Self-metathesis of unsaturated fatty acids with double bonds at different positions as found in alkenes, cyclodienes, monocyclic and dicyclic esters (Verkuijlen and Boelhouwer, 1974), resulted in a number of important oleochemicals for a variety of polymer applications (Marvey et al., 2003).

Different catalysts are employed for self-metathesis, the most common being WCl6 and Me4Sn. Most of the reactions also involve relatively large amounts of catalysts (Erhan et al., 1997, Biermann et al., 2000) and the catalysts are sensitive to moisture. These disadvantages are overcome using Grubbs catalysts, which involve a family of ruthenium carbene catalysts. The later are sensitive to oxygen and are found active, particularly in aqueous medium (Kanaoka and Grubbs, 1996). Further Grubbs second generation catalysts involve more environmentally friendly, convenient processes to produce platform chemicals from a number of vegetable oils (Refvik et al., 1999). A variety of vegetable oils were employed by the researchers to produce different metathesized products.

Self- metathesis of a mixture of sunflower (Helianthus annuus) fatty acids resulted in cyclo-hexa-1,4-diene, alkenes mono and dicarboxylic acids (Erhan et al., 1997, Marvey et al., 2008) subjected soybean oil (Glycine max) to self-metathesis which resulted in polycondensation that lead to branching, which increased the molecular weight, thereby the viscosity and drying properties. Heterogeneous catalysts Re2O7/SiO2, Al2O3/SnBu4 catalysts were employed for the metathesis of different fatty acid esters of South African Sunflower which resulted in alkene, mono and diesters of varied chain lengths (Marvey et al., 2003). Other unsaturated fatty acids namely oleic, ricinoleic, and undecenoic acids were also found to undergo self-metathesis employing second generation Grubbs catalysts to obtain α,ώ-dicarboxylic acids (Ngo et al., 2006, Ngo and Foglia, 2007) in good conversions. Metathesis of soy, rapeseed (Brassica napus) and linseed oil (Linum usitatissimum) fatty acids also resulted in a variety of large number of products (Ngo and Foglia, 2007) for varied applications.

However, most of the vegetable oil raw materials employed for metathesis reactions were from edible sources (Erhan et al., 1997, Biermann et al., 2000, Meier et al., 2007). On the other hand, India being a major importer of edible oils, cannot afford to use edible oils for non-edible applications. Hence, the present study is focused on the use of non-edible oil, rich in unsaturation namely tobacco (Nicotiana tabacum, with composition palmitic acid, 11.43%; oleic acid, 19.6%; linoleic acid, 66.7; linolenic acid, 1.5; arachidic acid, 0.4%) methyl esters for self-metathesis reactions using Grubbs second generation catalyst. Tobacco seed oil, is a by product of tobacco leaf production. India is one of the leading countries in the production, consumption, and export of tobacco. India ranks third largest tobacco growing country in the world. Tobacco can be grown in tropical, subtropical and temperate zones under the temperature range from 60 to 105 °F. Tobacco leaf is mostly exploited part of the plant used for the manufacture of cigarettes. After harvesting the leaf seed is obtained as a by-product. Though large areas of tobacco leaf crop exist all over world prominence for tobacco seed oil is not given in any part of the world, as in case of India. India is the only country in which the seed of tobacco plant is collected for extracting oil of commercial importance. The annual production of tobacco seed is about 29,795 kg (www.ctri.org.in/pages/marketresearch.html, 2012). The oil yield varies from 27 to 37% depending on the method of extraction. Tobacco seed oil is mostly used in pharmaceutical preparation, alkyl resins and in soap manufacture (Veljkovic et al., 2006). The seed oil available in plenty, can be a good source for the preparation of platform chemicals. The study involved self-metathesis of the tobacco fatty acid methyl esters, thorough characterization of the products obtained and also shows the different molecules involved in the formation of the intermediates.

Section snippets

Materials

Tobacco (Nicotiana tabacum) seeds were purchased from the M/s Central Tobacco Research Institute (CTRI), Rajahmundry. Tricyclohexylphosphine[1,3-bis(2,4,6-trimethylphenyl)-4,5 dihydroimidazol-2-ylidene] benzylidene ruthenium (IV) dichloride (Grubbs second generation catalyst) (II), sulfuric acid, dry methanol, dry dichloromethane (99.9%) were purchased from M/s Sigma–Aldrich Chemical Co, Hyderabad.

Gas chromatography analysis of tobacco fatty acid methyl esters and their self-metathesized products

The fatty acid composition of tobacco fatty acid methyl esters (Fig. 1) and the products (Fig. 2)

Results and discussion

Self-metathesis of non-edible oil tobacco (82.2%, unsaturation) methyl esters was carried out to develop a range of platform chemicals employing Grubbs second generation catalyst. The fatty acid composition of the methyl esters of tobacco oil. Self-metathesis of the tobacco oil methyl esters was carried out varying the concentration of the catalyst from 0.2 mM to 0.5 mM. The metathesized products with maximum yield of 92% was obtained by using a mole ratio of fatty acid methyl ester, (6.8 mM) and

Conclusions

In conclusion the non-edible oil, tobacco widely grown in India, form a cheaper renewable source for the preparation of a wide range of industrially important platform chemicals. These sources if exploited properly can uplift the economy of the country, in particular the tribal community.

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