Ind. Eng. Chem. Res. 2008, 47, 2091-2095
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Oleochemicals from Isoricinoleic Acid (Wrightia tinctoria Seed Oil) Ishtiaque Ahmad* Department of Chemistry, Guru Nanak DeV UniVersity, Amritsar 143 005, Punjab, India
M. S. F. Lie Ken Jie Department of Chemistry, The UniVersity of Hong Kong, Pokflam Road, Hong Kong
Derivatization of methyl 9-hydroxyoctadec-12-ynoate (I) was done to obtain the industrially important fatty compounds. Methyl 9-hydroxyoctadec-12-ynoate (I) was subjected to mesylation and demesylation reactions in which an unknown compound, methyl 9-ethoxyoctadec-12-ynoate (VII), was furnished in good yield, in addition to an inseparable mixture of enynoic esters. In another set of reactions, methyl 9-hydroxyoctadec12-ynoate (I) was oxidized with trimethyl chlorochromate wherein the resulting methyl 9-oxooctadec-12ynoate (II) was subjected to three condensation reactionsswith 1,2-ethanedithiol, ethylene glycol, and β -mercaptoethanol, separatelysto yield diethyl 9,9-ethylenedisulfide octadec-12-ynoate (III), 9,9-ethylenedioxyoctadec-12-ynoate (IV), and 9-oxathiolaneoctadec-12-ynoate (V), respectively, in excellent yields. Their structures have been established using infrared (IR) spectroscopy, 1H nuclear magnetic resonance (NMR) spectroscopy, 13C NMR spectroscopy, and mass spectral studies. Introduction The ketalization of ethanedithiol with various ketones under different reaction conditions1-3 has been described as a preparative method and masking methodology of oxo function. Conversion of carbonyl compounds to their corresponding oxathiolane, dithiolane, and dithione derivatives has also been reported, using organometallic catalysts such as yttrium triflate4 and molybdenyl acetylacetonate.5 Compounds that contain dithiolane grouping have become subjects of interest recently, because of their pharmacological6 and industrial potential,7 as well as their versatility as intermediates in organic synthesis.8 Some dithiolanes have been identified as components of the anal gland secretion of the ferret.9 Alkyl-chain-substituted oxathiolanes from allyl oxo fatty ester have been prepared, along with the conversion of olefinic bond to s-β-mercapto ethyl acetate and s-β-meraptoethanol groupings.10 In view of the academic and industrial importance of such compounds, we herein report the preparation of dithiolane, oxathiolane, and dioxolane (cyclic ketal) from methyl 9-oxooctadec-12-ynoate (II), in which the acetylenic bond does not transform at all, in comparison to earlier reports,10 where the double bond was transformed, forming the aforementioned side products. The model substrate for the present investigation was obtained through oxidation of methyl 9-hydroxyoctadec-12ynoate (I) using a new oxidizing system: trimethyl chlorosilane/ chromium trioxide was used as an efficient oxidizing mixture, without furnishing any side product. Furthermore, the parent substrate, methyl 9-hydroxyoctadec-12-ynoate (I), was subjected to mesylation and demesylation reactions, which led to the formation of two products. One of these products was deduced to be a mixture of enynic fatty esters, whereas the other product, which was more polar in nature, was characterized as methyl 9-ethoxyoctadec-12-ynoate (VII). Experimental Section (1) Materials and Methods. Thin-layer chromatography (TLC) was performed on microscope glass slides that were coated with silica gel G (ca. 0.1 mm thick), and a mixture of n-hexane/diethyl ether in various proportions was used as the
developer. Components on the microplates were viewed by exposing them to iodine vapor. Column chromatographic separation was performed, using silica gel (Merck, Darmstadt, Germany, type 60, 230-400 mesh (ASTM) as the adsorbent, and using gradient elution with a mixture of n-hexane/diethyl ether as the mobile phase. Infrared (IR) spectra were recorded on a Bio-Rad FTS-7FT-IR spectrometer. Samples were run as neat films on KBr disks. Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker Avance DPX 300 (300 MHz) Fourier transform NMR spectrometer (Bruker, Fallanden, Switzerland), with tetramethyl silane (TMS) as the internal reference standard. Chemical shifts are given in δ-values in ppm downfield from the TMS (δ TMS ) 0 ppm). Methyl isoricinoleate (methyl 9-hydroxyoctadec-12-z-enoate) was isolated from Wrightia tinctoria seed oil.11 Methyl 9-hydroxyoctadec-12-ynoate (I) was derived from the aforementioned ester via bromination-dehydrobromination in good yield.12 (2) Oxidation of Methyl 9-Hydroxyoctadec-12-ynoate (I). The oxidation of methyl 9-hydroxyoctadec-12-ynoate (I) involves two steps: the preparation of trimethyl chlorochromate and the preparation of methyl 9-oxooctadec-12-ynoate (II). (See Scheme 1.) (a) Preparation of Trimethyl Chlorochromate. Finely powdered chromium trioxide (1.0 g, 10 mmol) was exposed to atmospheric moisture for 5-10 min, and then chlorotrimethyl silane (1.30 mL, 10 mmol) was added. The mixture was stirred at 30-35 °C until a homogeneous orange red solution formed (20 min); this solution then was diluted with 20 mL of dichloromethane (DCM). Finally, dry nitrogen was bubbled through the solution, to eliminate traces of the HCl that had formed. (b) Preparation of Methyl 9-oxooctadec-12-ynoate (II). Over a cooled (0 °C) solution of the trimethyl chlorochromate (11.4 mL, 4.64 mmol) in CH2Cl2, methyl 9-hydroxyoctadec12-ynoate (I) (1.1610 g, 3.70 mmol) was added dropwise in CH2Cl2 (6 mL), and the resulting mixture was stirred at room temperature for 30-35 min, when maximum conversion occurred as determined using TLC. Silica gel (5 g) then was added to it, and the mixture was filtered through a bed of silica gel
10.1021/ie070761b CCC: $40.75 © 2008 American Chemical Society Published on Web 02/23/2008
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Scheme 1
and anhydrous Na2SO4 and the solvent was evaporated under vacuum to afford the crude carbonyl compound (light yellow oil, 1.068 g), which appeared as a single spot on TLC. Purification of the product was done using silica gel column chromatography, eluting it with PE6 (Rf. 0.47, PE 30) to yield 0.648 g (61%) II. IR (neat): 1730, 1710 (ester CdO and chain CdO str.), 1462 (m), 1437 (m), 1171 (m). 1H NMR (CDCl3, δ H): 0.89 (t, J ) 4.9 Hz, 3H, CH3), 1.23-1.34 (m, 18H, CH2), 1.37-1.45 (2H, m, 15-H), 1.50-1.77 (m, 4H, 3-H, and 7H), 2.10 (t,t, 2.4 Hz, 2H, 14-H), 2.30 (t, 7.38 Hz, 2H, 2-H), 2.382.44 (m, 4H, 8-H, 11-H), 2.60 (t, 7.4 Hz, 2H, 10-H), 3.66 (s, 3H, CO2CH3). 13C NMR (CDCl3, δ C), 13.87 (C-11), 14.36 (C-18), 19.04 (C-14), 22.59 (C-17), 24.01 (C-3), 25.24 (C-7), 29.08, 29.31, 29.38, 29.40 (CH2), 31.43 (C-15), 34.41 (C-2) 42.43 (C-10), 43.20 (C-8), 51.82 (OCH3), 78.94 (C-12), 81.24 (C-13), 174.60 (C-1). MS (m/z): 308 (M+, 15.38), 277 (MOMe, 41.52), 251 (M-[(CH2)3 CH3], 17.81), 237 (M-[(CH2)4CH3)], 61.39), 185 (∝-cleavage on chain carbonyl, 14.49), 165 (McLafferty cleavage ion of chain carbonyl, 64.70), 151 (∝cleavage on chain carbonyl, 28.88), 109 [M-CH2CO(CH2)7CO2CH3], 35.75, 95 (M-(CH2)2CO(CH2)7CO2CH3], 30.83). High-resolution mass spectroscopy (MS) gave the molecular composition to be C19H32O3. (3) Preparation of Methyl 9,9-Ethylenedisulfideoctadec12-ynoate (III). Methyl 9-oxooctadec-12-ynoate (II, 246 mg, 0.8 mmol) was dissolved in 3 mL of CH2Cl2, and to this solution, 0.12 g (1.2 mmol) of 1,2-ethanedithiol was added, followed by the addition of 0.02 mL BF3-etherate. The solution was stirred at room temperature overnight and 1 mL of 5% NaOH was added. The organic layer was separated, washed with water, dried over magnesium sulfate, and evaporated to 0.3008 g of crude product (colorless oil), which appeared as a single spot in the TLC analysis, besides the small amount of unreacted material (PE 30, Rf 0.67). The product was purified on column of silica gel by elution with PE2 (III; see Scheme 2, 0.1695 g, yield 70%). IR (neat): 1739 (ester CO), 1445 (CH2S deformation), 1252 (CH2S wag.). 1H NMR (CDCl3, δH) 0.89 (t, J ) 3.5 Hz, 3H, CH3), 1.23-1.38 (m, 10H, chain CH2), 1.43-1.59 (m, 4H, 7-H, 15-H), 1.61-1.66 (m, 2H, 3-H), 1.85-1.91 (m, 2H, 8-H), 2.07-2.15 (m, 4H, 10-H, 14-H), 2.30 (t, J ) 7.39 Hz, 2H, 2-H), 2.37-2.40 (m, 2H, 11-H), 3.25 (s, 4H, δ-SCH2CH2S-), 3.66 (s, 3H, CO2CH3). 13C NMR(CDCl3, δ-C), 14.37 (C-18), 16.78 (C-11), 19.12 (C-14), 22.60 (C-17), 25.27 (C-3), 27.21 (C-15), 29.14, 29.44, 29.48, 29.91, 31.45 (C-16), 34.42 (C-2), 40.04 (-SCH2CH2S-), 42.95 (C-10), 44.02 (C-8), 51.79 (COOCH3), 71.23 (C-9), 79.65 (C-12), 81.02 (C-13), 174.58 (C-1). MS(m/z): M+ (384, absent), 353 (M+-31, 8.75), 325 (M+59, 9.52), 324 (M+-60, 24.23), 323 (M+-CH2SH, 100), 261 and 227 (∝-cleavages on the ring, 28.83, 62.69, respectively), 229 (261-MeOH, 8.78). High-resolution MS gave a molecular composition of C21H36O2S2.
(4) Preparation of Methyl 9,9-Ethylenedioxyoctadec-12ynoate (IV). A mixture of 225 mg of methyl 9-oxooctadec12-ynoate (II) and ethylene glycol (0.1 mL) in benzene (75 mL) containing p-toluene sulfonic acid monohydrate (19 mg) was boiled under reflux for 2 h, with water being segregated in the usual way. The mixture was then poured into 5% NaHCO3 (25 mL), and the benzene layer was washed with water (2 times, 20 mL), dried over Na2SO4, filtered, and evaporated to afford a very pale yellow color oil [0.2416 g, Rf 0.54 (PE30)]. This crude material was subjected to chromatography in a silica gel column, eluting it with PE5 (IV, Scheme 2; 0.1798 g, yield 80%). IR (neat): 1740 (s, ester CO, str.), 1223, 1099, 1051 (m, C-O str.). 1H NMR (CDCl3, δ-H) 0.89 (t, J ) 7.0 Hz, 3H, CH3), 1.23-1.39 (m, 12H, chain CH2), 1.42-1.52 (m, 2H, 15H), 1.55-1.63 (m, 4H, 3-H, 8-H), 1.80-1.85 (m, 2H, 10-H), 2.14 (t,t, J ) 2.12 Hz, 2H, 14-H), 2.19-2.23 (m, 2H, 11-H), 3.29 (t, J ) 7.4 Hz, 2H, 2-H), 3.66 (s, 3H, CO2CH3), 3.91 (s, 4H, -OCH2CH2O-). 13C NMR (CDCl3, δ-C): 13.87 (C-11), 14.36 (C-18), 19.09 (C-14), 22.59 (C-17), 24.06 (C-3), 25.28, 29.06, 29.17, 29.42, 29.57, 31.44 (C-15), 34.43 (C-2), 36.98 (C-10), 37.47 (C-8), 65.33 (-OCH2 CH2O-), 80.08 (C-12), 80.38 (C-13), 111.22 (C-9), 174.63 (C-1). Ms (m/z): M+ (352, absent), 321 (M-OMe, 3.75), 229 (∝-cleavage on the ring, 88.00), 195 (∝-cleavage on the ring, 100), 95 (∝-cleavage on triple bond, 2.88). High-resolution MS gave the molecular composition to be C21H36O4. (5) Preparation of Methyl 9-Oxathiolaneoctadec-12-ynoate (V). A solution of 269 mg of methyl 9-oxooctadec-12-ynoate (II) in ∼1.5 mL dioxane was treated with 269 mg of β-mercaptoethanol, followed by the addition of 350 mg of freshly fused zinc chloride and 350 mg of Na2SO4 (see Scheme 2). The solution was cooled initially in ice to affect the exothermic reaction produced during the addition of zinc chloride and the mixture was then allowed to stand at room temperature for ∼20 h. After dilution with water (20 mL), the product was extracted with chloroform (2 times, 25 mL), and the latter was washed with water until neutral, dried over Na2SO4, and evaporated to furnish 0.3585 g of crude product (Rf 0.50, PE 20). It was then purified in a silica gel column by elution with PE6 (V, Scheme 2; 0.1987 g, yield 74%). IR (neat): 1740 (s, ester CO), 1436 (SCH2 def.), 1279 (m, S-CH2 wagging), 1115 (C-O stretching), 1064 (hemithioketal group). 1H NMR (CDCl3, δ H): 0.89 (t, J ) 7.04 Hz, 3H, CH3), 1.23-1.42 (m, 14H, -CH2), 1.431.51 (m, 2H, 15-H), 1.59-1.71(m, 2H, 3-H), 1.74-1.87 (m, 2H, 8-H), 1.96-2.07 (m, 2H, 10-H), 2.13 (t,t, J ) 2.18 Hz, 2H, 14-H), 2.22-2.35 (t merged with m, 4H, 2-H, 11-H), 2.98 (t, J ) 5.8 Hz, 2H, S-CH2), 3.66 (s, 3H, CO2CH3), 4.07-4.15 (m, 2H, O-CH2). 13C NMR (CDCl3, δC): 14.00 (C-18), 14.55 (C-11), 18.74 (C-14), 22.23 (C-17), 24.91 (C-3), 25.04 (C-15), 28.79, 29.06, 29.16, 29.62 (CH2), 31.08 (C-16), 33.82 (SCH2), 34.05 (C-12), 40.08 (C-10), 41.01 (C-8), 51.42 (COOCH3), 70.67 (OCH2), 79.51 (C-12), 80.31 (C-13), 97.80 (C-9), 174.23 (C-1). Ms (m/z): M+ (368, 33.16), 245 (∝-cleavage on the ring, 64.85), 211 (∝-cleavage on the ring, 100), 95 (∝-cleavage on acetylene function, 28.01). High-resolution MS gave the molecular composition to be C21H36SO3. (6) Mesylation and Demesylation of Methyl 9-Hydroxyoctadec-12-ynoate (I). Methane sulfonyl chloride (1.5 mL) was added dropwise to a cooled mixture of methyl 9-hydroxyoctadec-12-ynoate (I) (1.5500 g, 5 mmol), triethylamine (3 mL), and dry DCM (15 mL) at 0 °C. The reaction mixture was stirred for 20 min, and water (15 mL) was added. The organic layer was isolated and the aqueous solution was extracted with DCM (15 mL). The combined organic extract was washed with ice-
Ind. Eng. Chem. Res., Vol. 47, No. 6, 2008 2093 Scheme 2
Scheme 3
cold water (15 mL), dried over anhydrous Na2SO4, and filtered, and the solvent then was evaporated to give the crude methyl 9-mesyloxyoctadec-12-ynoate (1.6746 g). The crude product (1.6746 g) was refluxed with KOH (2.3 g, 41.07 mmol) and ethanol (25 mL) for 8 h. The reaction mixture was acidified with diluted HCl (6 M, 5 mL) and extracted with diethyl ether (3 times, 15 mL). The ethereal extract was washed with brine (10 mL) and dried over anhydrous Na2SO4. The filtrate was evaporated and the residue was refluxed with BF3-methanol (14%, w/w, 1.6 mL) in absolute methanol (16 mL) for 15 min. Water (20 mL) was added and the reaction mixture was extracted with diethyl ether (3 times, 15 mL). The extract was dried over Na2SO4, and the filtrate was evaporated. The crude product mixture appeared as two spots on TLC (PE 20, VI, Rf ) 0.73; VII, Rf ) 0.65; see Scheme 3). Flash column chromatographic purification on the silica column resulted in separation of the VI product (a mixture of enynoates based on NMR), 0.5534 g, 41.6%) and VII product, which has been identified as methyl 9-ethoxyoctadec-12-ynoate (00.4083 g, 31.7%) (see Scheme 3). (7) Characterization of Methyl 9-Ethoxyoctadec-12-ynoate (VII). IR (neat): 1741 (s, COOCH3), 1250, 1170, 1092 (C-O str), 2857 (CH2-O str). 1H NMR (CDCl3, δ H)): 0.89 (t, J ) 7.00 Hz, 3H, CH3), 1.18 (t, J ) 7.01 Hz, 3H, CH3CH2O), 1.301.41 (m, chain CH2), 1.44-1.47 (m, 4H, 8-H, 15-H), 1.611.65 (m, 4H, 3-H, 10-H), 2.11-2.16 (m, 2H, 14-H), 2.20-2.22 (m, 2H, 11-H), 2.30 (t, J ) 7.3 Hz, 2H, 2-H), 3.35 (q, J ) 5.60 Hz, 2H, CHO), 3.45-3.59 (m, 2H, CH2O), 3.66 (s, 3H, CO2CH3). 13C NMR (CDCl3, δ C): 14.33 (C-18), 15.33 (ethoxy
CH3), 15.97 (C-11), 19.04 (C-14), 22.57 (C-17), 25.27 (C-3), 25.67 (C-7), 29.18, 29.44, 29.58, 29.96 (CH2), 31.41 (C-16), 34.09 (C-10), 34.35 (C-8), 34.39 (C-2), 51.72 (CO2CH3), 64.78 (CH2O), 78.25 (CHO), 80.23 (C-12), 80.64 (C-13), 174.56 (CO2CH3). Ms (m/z): M+ (338, present), 292 (M-46), 215 (∝cleavage on ethoxy group, base peak), 267 and 95 (∝-cleavages on either side of triple bond), 236, 183, 135, 109, etc. Highresolution MS gave the molecular composition to be C21H38O3. Molecular weight (MW): Found, 338.282; Calculated MW, 338.446. Results and Discussion In the present study, methyl isoricinoleate (9-hydroxyoctadec12-z-enoate) was obtained from Wrightia tinctoria seed oil. Methyl isoricinoleate, which is a lesser-studied compound, was subjected to bromination and dehydrobromination, followed by esterification with BF3/MeOH reflux, which yielded methyl 9-hydroxyoctadec-12-ynoate (I). In one set of reactions, methyl 9-hydroxyoctadec-12-ynoate (I) was safely converted to methyl 9-oxooctadec-12-ynoate (II; see Scheme 1) by a new oxidizing system trimethyl chlorochromate12 without allowing any side reaction to occur. This oxo ester was characterized by IR, 1H and 13C NMR, and MS spectroscopy. IR spectroscopy gave very diagnostic double carbonyl peaks at 1730 and 1710 cm-1, with a complete disappearance of hydroxy absorption. 1H NMR spectrum of this product gave the structure that revealed signals at δ 2.38-2.44 as a multiplet accounting for four protons (the 8th and 11th methylene protons) and δ 2.60 as triplet for the
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10th methylene protons, in addition to other fatty ester signals. The 13C NMR spectrum of the product further elaborated the structure by displaying characteristic signals at δ 209.80 for the chain carbonyl (C-9), in addition to the neighboring carbon shifts at 42.43 (C-10) and 43.20 (C-8). The acetylenic carbons (C-12 and C-13) shifts were noted at δ 78.94 and 81.24, respectively. All these assignments were based on 1H-1H and 1H-13C cosy spectral technique. Final confirmation of the structure of methyl 9-oxooctadec-12-ynoate (I) came through its mass spectral studies. Low-resolution mass spectroscopy of the product gave the molecular ion at m/z 308, whereas the ∝-cleavage ions on either side of the oxo function appeared at m/z 185 and 151. Only one McLafferty cleavage ion was observed, at m/z 165, which further supported the structure. R-Cleavage ions on either side of acetylenic function were observed at m/z 237 and 95, indicating its position at C12-C13. Therefore, characterized oxo ester was further derivatized to methyl 9,9-ethylenedisulfideoctadec-12-ynoate (III), methyl 9,9ethylene dioxyoctadec-12-ynoate (IV), and methyl 9-oxathiolaneoctadec-12-ynoate (V), via the condensation of methyl 9-oxooctadec-12-ynoate (I) with 1,2-ethanedithiol, ethylene glycol, and β-mercaptoethanol, respectively (see Scheme 2). These reactions were conducted according to the procedures reported earlier,13-15 in view of their industrial usefulness,1-6 and the reactions were conducted to study any effect on the triple bond of the fatty ester chain. However, in all these reactions, the triple bond remained unaffected. Ketalization of ethanedithiol in the presence of BF3-etherate and methylene dichloride with methyl 9-oxooctadec-12-ynoate (II) gave a quantitative yield of the corresponding dithiolane (III). IR spectroscopy of III was not very significance in regard to revealing the functionality, except for the quenching of the band observed for isolated oxo function. Dithiolanes have not been reported to show any characteristic band beyond CH2S wagging and deformation, which were pronounced in the spectrum. The 1H NMR spectrum of III exhibited a characteristic sharp singlet at δ 3.25, integrating for four protons (SCH2CH2-S), as reported earlier.16 The signal experienced the identical environment for the two methylene groups, which could be possible only if cyclization had occurred and yielded dithiolane. Other structure-revealing signals were present at δ 2.07-2.15 as a multiplet for two methylene group protons (one 10-CH2 and the other one 14-CH2); δ 2.37-2.40 as a multiplet accounted for two protons of the 11th methylene group. 13C NMR spectroscopy further elaborated the structure of III by displaying characteristic chemical shifts for the formation of dithiolane ring at δ 40.04 (-SCH2CH2S-), 42.95 (C-10), 44.02 (C-8), 71.23 (C-9). The two acetylenic carbons shifts were observed at δ 79.65 (C-12), 81.02 (C-13). All of these assignments were based on the study of 1H-1H and 1H-13C cosy spectra. High-resolution MS gave a molecular composition of C21H36O2S2 and molecular weight of 384.21. Low-resolution MS gave two structure-revealing characteristic fragments, arising from the ∝-cleavage to the ring, at m/z 261 and 227. The formation of methyl 9,9-ethylenedioxyoctadec-12-ynoate (IV) was observed when methyl 9-oxooctadec-12-ynoate (II) was refluxed with ethylene glycol in benzene-containing ptoluenesulfonic acid, as per procedure.13 In this case, IR spectroscopy also showed the disappearance of the chain carbonyl but no other significant absorptions except C-O stretchings. 1H NMR spectrum of this product (IV) gave the most structure-revealing singlet for two sets of ring methylene protons (-OCH2CH2-O) at δ 3.91. Other significant signals for establishing the structure were found at δ 2.14 as a triplet
of triplet for 14-CH2 protons and δ 2.19-2.23 as a multiplet for 11-CH2 protons. The chemical shifts of these protons suggest that they flank a triple bond between C12 and C13. 13C NMR spectroscopy was further supportive to its structure by displaying signals at δ 65.33 for two carbons of the ethylenedioxy group and δ 80.08 for C-12, 80.38 for C-13, and 111.22 for C-9 carrying the ethylenedioxy ring. All these shifts of carbon and hydrogen nuclei were assigned based on the 1H-1H cosy and 1H-13C cosy techniques. Additional conclusive support to the structure of the product came through study of its low-resolution and high-resolution mass spectra. Low-resolution MS gave the two ∝-cleavage ions on either side of the ethylenedioxy ring, at m/z 229 and 195 (base peak), whereas one of the ∝-cleavage ions on one side of acetylenic function appeared at m/z 95. Based on all this data, the structure of the product was deduced to be methyl 9,9-ethylenedioxyoctadec-12-ynoate (IV). In another condensation reaction of methyl 9-oxooctadec12-ynoate (II) with β-mercaptoethanol in dioxane, methyl 9-oxathiolaneoctadec-12-ynoate (V) was obtained. The identification of this product (V) was based on IR, 1H, and 13C NMR spectroscopy, low-resolution and high-resolution MS, and 1H1H and 1H-13C cosy techniques. IR spectroscopy of V gave diagnostic bands at 1064 and 1115 cm-1 for hemithioketal grouping. Conclusive support in favor of V came through 1H and 13C NMR studies. 1H NMR spectrum displayed the diagnostic signals at δ 2.98 as a triplet accountable for two protons attached to sulfur in the ring, whereas the signal at δ 4.07-4.15 represented a multiplet for two protons attached to oxygen of the ring. The two different types of the multiplicity of these two methylene protons is due to the fact that methylene protons attached to sulfur flick at a slower speed, whereas the methylene protons attached to oxygen flick at a much faster speed. This phenomenon was studied by recording the 1H NMR spectra of this product at different temperatures (-10, 28, and 50 °C). In all these spectra, the multiplicity of these two sets of protons remained the same. Therefore, the methylene protons that were attached to sulfur appeared as a triplet, whereas the methylene protons that were attached to oxygen appeared as a multiplet. Other important signals in its 1H NMR spectrum were found at δ 2.22-2.35 as a merged signal, a multiplet with a triplet for four protons (two each of C-2 and C-11), and 2.13 as a triplet of a triplet for 2 protons of C-14, suggesting the presence of acetylenic function at C-12. 13C NMR spectrum further elaborated the structure by showing signals at δ 97.80 (C-9, possessing oxathiolane ring), 80.31 (C-13), 79.51 (C-12), 70.67 (OCH2), and 33.82 (-SCH2). Final conclusive support to the structure of the product (V) came from the study of lowresolution and high-resolution mass spectra. Low-resolution mass spectroscopy gave the ∝-cleavages on either side of the oxathiolane ring at m/z 245 and 211 (base peak). One ∝-cleavage at m/z 95 places the triple bond at C12-C13. In another set of reactions, methyl-9-hydroxyoctadec-12ynoate (I) was then subjected to mesylation and demesylation reactions, as per earlier reports,17,18 which led to the formation of two products (see Scheme 3). Of these products, the first product (VI) was shown to be the mixture of enynic fatty esters as shown by 13C NMR spectroscopy in which many signals were present that were responsible for enynic functions (77.93, 80.06, 80.94, 82.46, 86.76, 92.55, 94.33, 125.16, 126.31, 128.57, 129.07, 131.25, 131.77, 132.04, 132.55). Because of the complexity of the mixture, further work on their isolation and characterization could not be performed. The second product, which was more polar than the first, was isolated and characterized to be methyl-9-ethoxyoctadec-12-ynoate (VII), which
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resulted during demesylation by the nucleophilic substitution of mesylate ion by ethoxide ion as mesylate is a better leaving group. In 1H NMR spectroscopy, three signals were diagnostically important: δ 1.18 for ethoxy methyl protons, as a triplet; δ 3.35, as a quintet for a methine proton attached to oxygen; and δ 3.45-3.59, as a multiplet for a set of methylene protons attached to oxygen. Similarly, 13C NMR spectroscopy of this product was further supportive, in regard to its structure, by displaying signals at δ 15.33 for ethoxy methyl carbon nucleus, δ 64.78 for ethoxy methylene carbon, and 78.25 for methine carbon attached to oxygen. The two acetylenic carbon nuclei were observed at δ 80.23 and 80.64, which indicates preservation of the acetylenic bond in the product. These signals were assigned based on the confirmation from 1H-1H and 1H-13C cosy spectra and a DEPT 13C spectrum. Finally, the structure of VII was conclusively confirmed by low-resolution and highresolution MS. In low-resolution MS, two ∝-cleavage ions on either side of the ethoxy group were found at m/z 215 and 181 (as a base peak). The other ∝-cleavage ions, establishing the position of triple bond at C12-C13, were found at m/z 267 and 95. High-resolution MS gave the molecular composition to be C21H38O3. It can be concluded that, in all the carbonyl-group protecting reactions, the acetylenic function remains unaffected. This communication reports the preparation and characterization of new derivatives that contain hemithioketal, oxathiolane, ethylene dioxy, and ethoxy moieties. These compounds might have industrial potential, in view of the earlier reports. Acknowledgment This research was financially supported by Lipid Research Grants, Department of Chemistry, The University of Hong Kong, HONG KONG. Typing facility was provided by the Department of Chemistry, Guru Nanak Dev University, Amritsar 143 005, Punjab, India.
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ReceiVed for reView June 2, 2007 ReVised manuscript receiVed November 14, 2007 Accepted February 9, 2008 IE070761B
