Synthesis and characterization of copper metal soaps from Thevetia peruviana and Hura crepitans seed oils

Thevetia peruviana (TP) and Hura crepitans (HC) seed oils with 73 and 65% unsaturation, respectively as analyzed by gas chromatography-flame ionization detector (GC-FID) chromatogram were used for the synthesis of copper metal salt. The sodium carboxylate (soluble soap) prepared from the oils by saponifying with sodium hydroxide were reacted with solution of copper salt to produce the metal soaps. The yield was encouraging ranging from 60 to 65%. The progress of the reaction was monitored and confirmed using Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR). The difference in absorption frequencies of the FTIR spectra of the oils and their corresponding soaps indicates their production. Confirming it further, the appearance of the characteristic peaks of 1 H NMR and 13 C NMR of the metallic soaps affirm the synthesis of these compounds. The seeds are thus good sources of raw materials (oleochemicals) for the production of valuable industrial and domestic products.


INTRODUCTION
The replacement of petrochemicals by oleochemical feedstocks in many industrial and domestic applications has resulted in an increase in demand for bio-based products and as such recognizing and increasing the benefits of using renewable materials.Seeds are important sources of nutritional oils, and they also have industrial and pharmaceutical importance (Oderinde et al., 2009).Current emphasis on sustainable development has made it imperative to search for industrial raw materials from renewable sources.Seed oils are at the centre of this search as many useful products and industrial materials have been produced from them.One of such materials is metal carboxylates otherwise called metal soaps.Metallic soaps have been described as alkaline-earth or heavy metal long-chain carboxylates (Barth, 1982), which are insoluble in water, but soluble in non-aqueous solvents.The soaps of the heavy metals have important applications.Soaps of barium, cadmium, lead, zinc and calcium have found practical application as thermal stabilizers for poly (vinyl chloride) (Owen and *Corresponding author.E-mail: qasimade@gmail.com. Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Msayib, 1989;Bacalogulu and Fisch, 1994).Calcium and magnesium soaps are used as corrosion inhibitors in non-polar media.Lead, manganese, cobalt and zinc soaps are used in paints to accelerate drying while copper soaps are well known for their fungicidal properties (Salager, 2002).Therefore, the present work has added to the available fungitoxic chemicals beforehand and consequently, they can find uses in agrochemical industries and could also serve as precursors for urea or thiourea complexes formation.Silver carboxylates are used as the source of silver in thermographic and photothermographic materials (Binnemans et al., 2004).Some found have been used in greases, cosmetics and textiles (Egbuchunam et al., 2005).The studies on the nature of these soaps are of great importance for their use in industries and for explaining their characteristics under different conditions.The physicochemical properties of different metallic soaps have been investigated by several researchers.Upadhyaya and Sharma (1997) studied thermal, infrared, and x-ray diffraction analysis of manganese and zinc soaps.A number of seed oils have been characterized but the vast majority have not been explored for the preparation of metal carboxylates despite being the most abundant source of carboxylic fatty acids.The seed oils used are also among those that have not been explored for the synthesis of fatty acid carboxylate.Many of the reports on the characterization and properties of metal soaps have been carried out on soaps prepared using pure fatty acids with little attention on the use of triglycerides, inspite of their abundance and low cost, as starting materials for the preparation of metal soaps (Egbuchunam et al., 2007).Therefore, since there are no published evidences according to our literature search showing that Thevetia peruviana and Hura crepitans have been utilized for the production of copper metallic soap, it was considered necessary to make use of these abundantly available plant seed oils for the production of the metallic soaps and their productions were monitored and confirmed using Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectrometers.

MATERIALS AND METHODS
T. peruviana seeds were collected from various locations at high school area in Akure, Ondo State in September, 2012.The good quality seeds were hand-picked to separate them from bad ones.H. crepitans seeds were obtained from a tree in front of School of Agriculture and Agricultural Technology, Federal University of Technology, Akure, Ondo State in October, 2012.They were sundried, ground into powder and preserved in a air tight container for further processing.Copper chloride (CuCl2.7H2O),ethanol and sodium hydroxide used were purchased from Merck, Darmstadt, Germany.

Chemical analysis of T. peruviana and H. crepitans oil
Powered T. peruviana and H. crepitans seeds (50 g each) were placed in a stoppered container with 1 L n-hexane and allowed to stand at room temperature for a period of 24 h with frequent agitation.The mixture was strained, the damp solid material pressed, and returned into the container.The process was repeated for 7 days to ensure complete extraction.The oil was concentrated by simple distillation which gave 62 and 54% yield for TP and HC oils, respectively.The extracted oil was analyzed for its iodine, saponification, and acid values using the methods described by the Association of Official Analytical Chemists (AOAC, 1994).

Fatty acid composition of the oils
Fatty acid methyl esters of the oils were prepared by saponification.50 mg of the fat contents was mixed for 5 min at 95°C with 3.4 ml of the 0.5 M KOH in dry methanol.The mixture was neutralized by using 0.7 M HCl. 3 ml of the 14% BF3 in methanol was added.The mixture was heated for 5 min at 90°C to achieve complete methylation process.The fatty acid methyl esters were thrice extracted from the mixture with redistilled n-hexane.The content was concentrated to 1 ml for gas chromatography analysis, 1 μl of this was injected into the injection port of GC which was oven programmed with Model HP 6890 powered with HP Chemstation Rev. A 09.01 [1206] software equipped with flame ionization detector and a capillary column HP INNOWax (30 m × 0.25 mm × 0.25 μm) to obtain individual peaks of fatty acid methyl esters.The inlet and detector temperatures were set at 250 and 320°C, respectively.Nitrogen gas was used and the split ratio was 20:1 with hydrogen pressure at 22 psi.The fatty acid methyl esters peaks were identified by retention times in comparison with calibration curve of the standards analyzed under the same conditions.

Preparation of the metallic soaps
Copper chloride salt solution (O.5 M of CuCl2.7H2O) was prepared and kept in an amber bottle.10 cm 3 of 0.5 M HCl was added to 20 cm 3 of 10% soluble soap solution prepared above and titrated against the copper chloride salt solution with continuous stirring until complete precipitation was observed.The mixture was then filtered.The residue (Carboxylate) was washed with warm water, air-dried followed by cleaning with petroleum ether and recrystallized in benzene.The percentage yield was calculated by dividing the actual value (gram of the product produced after drying) with the theoretical value obtained from the equation of the reaction.

Fourier transform infrared (FTIR)
The FTIR spectra of T. peruviana and H. crepitans acids and corresponding copper soaps were obtained with a Perkin-Elmer grating spectrophotometer at a resolution of 4 cm -1 between wave numbers 4000 and 400 cm -1 , using potassium bromide disc method.
As no modifications occur on the alkyl chain of triglyceride during soap preparation, the metal soaps spectra still show absorption bands which are characteristics of the oils.CH 2 antisymmetric and symmetric stretching vibrations occur with varying intensities in the region 2926 to 2927 cm -1 for T. peruviana and H. crepitans oils, respectively and between 2857 and 2922, 2857 and 2925 cm -1 for the metal soaps, respectively.Typical antisymmetric stretching vibration for carboxylate occurs between 1589 and 1611 cm -1 (Olujinmi et al., 2011).The difference in absorption frequencies of carbonyl group of fatty acid and its corresponding metal soap also confirms the formation of soaps.1714 and 1721 cm -1 for T. peruviana fatty acid and T. peruviana soap and 1708 and 1710 cm -1 for H. crepitans fatty acid and H. crepitans soap respectively.The carbonyl group either shift or disappear in the spectra of its complexes accompanied by the appearance of two bands in the 1569 to 1631 cm -1  range assigned to ʋ s (COO -).Accordingly, the antisymmetric and symmetric stretching vibration modes ʋ as (COO -) and ʋ s (COO -) of the COO -group should help in elucidating the structure of our complexes (Mesubi, 1982).
The absorption in the vicinity of 717 to 722 cm -1 in the spectra of these soaps are associated with the rocking vibration of a chain of successive methylene groups -(CH 2 ) and are sensitive to the crystallization of soap (Anushri et al., 2012).
The 1 H NMR spectra of the soaps (T.peruviana and H. crepitans) are shown in Figure 1.The peaks at around 0.841 and 1.029, 1.208 and 1.417, 1.852 and 1.768, and 1.913 and 2.157 ppm were attributable to the terminal methyl protons, protons of the repeating methylene units, and protons of the methylene group β and α to the carbonyl group, respectively (Gunstone, 2008;Tariq et al., 2011).The signal at 2.341 ppm in H. crepitans was assigned to allylic methylene protons while the peaks at 5.259 and 5.491 ppm were considered to be from the olefinic protons, confirming the presence of unsaturation in the soaps as indicated by the FTIR and gas chromatography-flame ionization detector (GC-FID) results.
Figure 2 3 and 4) and the earlier

Conclusions
In this study, the oils were extracted, purified and used directly because the physico chemical parameters were earlier reported by Olupona and Atteh (2008) and Okolie et al. (2012).The copper soaps were actually synthesized from sodium soap with the percentage yield ranging from 60 to 65%.The progress of the synthesis was monitored using both FTIR and nuclear magnetic resonance.