ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 12, pp. 2175–2177. © Pleiades Publishing, Ltd., 2008. Original Russian Text © I.N. Gaidukov, L.M. Popova, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81, No. 12, pp. 2065–2067.

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Preparation of Fluorinated Esters of Abietic Acid I. N. Gaidukov and L. M. Popova St. Petersburg State Technological University of Vegetable Polymers, St. Petersburg, Russia Received July 28, 2008

Abstract—The reaction of abietic acid chloride with sodium salts of 1H,1H-dihydrotrifluoroethanol, 1H,1H,3H-trihydrotetrafluoropropanol, 1H,1H,5H-trihydrooctafluoropentanol, and pentafluorophenol was studied. The main reaction products are the corresponding fluorinated alkyl (aryl) abietates. DOI: 10.1134/S1070427208120276

One of the ways to modify rosin is its esterification. The resulting products, depending on the kind of the rosin and alcohol used, show promise in production of synthetic resins, ester plasticizers, hot-melt adhesives, varnishes, paints, adhesives for food package, etc., meeting the most stringent environmental requirements. As compounds with long-chain fluoroalkyl group exhibit surface activity [1], esters of rosin and fluorinated alcohols can be valuable hydro- and oleophobizing agents for fibrous composite materials. Therefore, development of procedures for preparing such esters is a topical problem. This work continues our studies devoted to development of new fluorinated surfactants [2, 3] and is aimed to devise of a procedure for preparing previously unknown esters of abietic acid (model compound of oleoresin rosin) and fluorinated alcohols: 1H,1H-dihydrotrifluoroethanol, 1H,1H,3H-trihydrotetrafluoropropanol, 1H,1H,5H-trihydrooctafluoropentanol, and pentafluorophenol. Esterification of resin acids, the major component of rosin, is complicated by the steric shielding of the carboxy group located at the tertiary carbon atom [4] and by the low acidity (pKa 6.4) [5] of compounds of this class. This results in a decrease in the rate of esterification of resin acids in the presence of common acid catalysts (H2SO4, H3PO4, etc.). Performing the esterification under harsh conditions (in the presence of aggressive acid agents and at elevated temperatures) gives rise to undesirable side reactions, such as dimerization of abietic-type acids and their disproportionation, which diminishes the yield of the target product and complicates its isolation [3]. Therefore, the reac-

tion of resin acids with alcohols in the presence of acid catalysts is an extremely inefficient route to esters. In some reports, alternative procedures for preparing resin acid esters have been suggested. For example, it is recommended to prepare methyl abietate by the reaction of abietic acid with diazomethane [6] or of silver abietate with methyl iodide on heating [7]. Halbrook and Lawrence [8] prepared rosin monoesters of ethylene or 1,3-propylene glycol by the reaction of rosin with ethylene or propylene oxide at elevated temperatures. The reactions of alkali metal resinates with alkyl halides also yield esters; by this route, Zandersons and Tardenaka [9] prepared glycidyl abietate. As reported by Bardyshev [4], methyl, ethyl, and phenyl abietates are formed by reactions of the corresponding alcohols with abietic anhydride. It was also noted that these reactions occur at elevated temperatures in the presence of a catalyst. Johnston [10] prepared ethyl abietate by the reaction of abietic acid chloride with ethanol. Kryachko et al. [3] reported that esterification of abietic acid with 1H,1H,5H-trihydrooctafluoropentanol in the presence of p-toluenesulfonic acid yields 1H,1H,5Htrihydrooctafluoropentyl dehydroabietate, i.e., the esterification is accompanied by disproportionation of abietic acid. The same ester has been prepared by esterification of dehydroabietic acid with concentrated H2SO4 as catalyst [2]. In the present study, esters of abietic acid and fluorinated alcohols were prepared by reactions of sodium salts of the corresponding alcohols and abietic acid chloride synthesized as described in [4, 11–14]. The reactions between the alcoholates and acid chlo-

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GAIDUKOV, POPOVA

Analytical and NMR data for products of reactions of abietic acid chlorides with sodium salts of 1H,1H-dihydrotrifluoroethanol, 1H,1H,3H-trihydrotetrafluoropropanol, 1H,1H,5H-trihydrooctafluoropentanol, and pentafluorophenol (products I–IV, respectively) Prod- Reaction Product uct time, h yield, %

NMR spectrum, δ, ppm Rf

1

19

H

F

Iodine Acid number, number, g I2/g mg KOH/g

I

3

90

0.86 0.87, 1.02, 1.22, 1.26, 1.33, 2.75, 4.46, 5.37, 5.78

–72.26 (s)

154

II

6

85

0.85 0.86, 0.92, 1.01, 1.22, 1.26, 1.33, 2.87, 4.59, 4.9, 5.25–5.6, 5.78, 6.37 (t.t, 2JHF 52.7 Hz)

–123.6 (s), –136.4 (d)

168

35

III

6

65

0.89 0.87, 1.02, 1.22, 1.26, 1.33, 2.75, 4.75, 5.25–5.6, 5.78, 6.73 (t.t, 2JHF 52.7 Hz)

–119.5 (s), –124 (s), –131 (s), –138, –137.3 (d)

150

30

IV

6

60

0.79 0.85, 0.91, 1.03, 1.20, 1.21, 1.26, 2.85, 4.90, 5.37, 5.78

–170.8 (t), –165.1 (t), –161.9 (d)

168

21

ride were performed in toluene in the course of 3–6 h, at the reactant molar ratio of 1 : 1.25. The choice of the alcoholate instead of the corresponding alcohol was governed by the facts that the reaction in this case is faster and that the second product is sodium chloride, which is insoluble in toluene and can be readily removed from the reaction mixture, i.e., isolation of the desired product is simplified. The products obtained were yellow-brown resinous noncrystallizing subEXPERIMENTAL The 1H and 19F NMR spectra of the products were recorded on a Bruker WH-400 spectrometer (400 MHz) from 5% solutions in acetone-d6. The chemical shifts were determined relative to internal TMS (1H NMR) and trifluoroacetic acid (19F NMR). To evaluate the purity of the initial abietic acid and monitor the reaction progress, we used TLC on Silufol UV 254 plates (eluent hexane–methylene chloride–acetone, 1 : 1 : 0.5). Abietic acid was isolated from oleoresin rosin of the Wg brand according to [6]. The solvents were purified by the standard procedures [15]. Sodium alcoholates were prepared by reactions of the corresponding fluorinated alcohols with sodium metal in ether or toluene, following the procedures described in [16–19]. Abietic acid chloride. To a solution of 5.00 g (16.5 mmol) of abietic acid in 100 ml of toluene, 0.74 g

1.5

(5.5 mmol) of PCl3 was slowly added at room temperature with stirring. The reaction mixture was stirred for 20 h, after which H3PO3 was filtered off. Abietic acid chloride was used immediately after preparation, without isolation. Reaction of abietic acid chloride with sodium 1H,1H-trifluoroethylate. To 5.30 g (16.5 mmol) of abietic acid chloride in 100 ml of toluene, a suspension of 2.51 g (20.6 mmol) of sodium 1Н,1Н-dihydrotrifluoroethylate was added with vigorous stirring at room temperature. The mixture was stirred for 3 h, after which the NaCl precipitate was filtered off, the toluene solution was washed with water and dried over calcined MgSO4, and the solvent was separated. The tarry residue was dried in a vacuum over P2O5. The yield of the product (I) was 90%. 1Н,1Н,3Н-Trihydrotetrafluoropropyl (product II), 1Н,1Н,5Н-trihydrooctafluoropentyl (product III), and pentafluorophenyl (product IV) esters of abietic acid were prepared similarly from 5.30 g (16.5 mmol) of abietic acid chloride and 3.17 g of sodium 1Н,1Н,3Н-trihydrotetrafluoropropylate, 5.23 g of sodium 1Н,1Н,5Нtrihydrooctafluoropentylate, and 4.24 g of sodium pentafluorophenolate, respectively; the reaction time was 6 h. The yields of fluorinated alkyl (aryl) abietates II– IV, evaluated by 1H NMR, were 60–85% (see table). The TLC data suggest the presence of a minor impurity of abietic acid in all the reaction mixtures. The formation of esters is also confirmed by the acid and iodine numbers of the resulting products (see table).

RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 81 No. 12 2008

PREPARATION OF FLUORINATED ESTERS OF ABIETIC ACID

An NMR analysis of reaction mixtures from synthesis of I–IV revealed the presence of the major component, fluoroalkyl (fluoroaryl) abietate. For example, in the 1H NMR spectra of I–III, there are multiplets with δ 4.46 (I), 4.59 (II), and 4.75 ppm (III), corresponding to the –OCH2– protons of the fluoroalkyl moiety. The olefinic protons in I–IV give rise to signals at 5.37, 5.78 (I), 5.25–5.6, 5.78 (II, III), and 5.37, 5.78 ppm (IV). In addition, in the spectra of II and III there are proton signals from terminal –CF2H groups (triplet of triplets) with δ 6.37 (2JHF 52.7 Hz) (II) and 6.73 ppm (2JHF 51.2 Hz) (III). In the 19F NMR spectrum of I, there is a single signal at –72.26 ppm, belonging to fluorine nuclei of the –CF3 group. The presence of the –2CF2–3CF2– group in the molecule of II is confirmed by the signals with δF –123.6 (s, 2CF2) and –136.4 ppm (d, –3CF2–). In the spectrum of product III containing the residue of the telomeric alcohol with n = 2, there are the following signals: –119.5 (s, –2CF2–), –124 (s, –3CF2–), –131 ppm (s, –4CF2–), and a doublet of –5CF2H (–138 and –137.3 ppm). For the pentafluorophenyl fragment, we observed signals from the fluorine atoms of the aromatic ring at –170.8 (γ-CarF), –165.1 (β-CarF), and –161.9 ppm (α-CarF). The chemical shifts and integral intensities of the proton and fluorine signals correspond to the presumed structures of the fluorinated alkyl (aryl) abietates. CONCLUSION Fluorinated alkyl (aryl) abietates were prepared in 60–90% yields by the reactions of abietic acid chloride with sodium salts of 1H,1H-dihydrotrifluoroethanol, 1H,1H,3H-trihydrotetrafluoropropanol, 1H,1H,5Htrihydrooctafluoropentanol, and pentafluorophenol under mild conditions (toluene, room temperature, 3–6 h). Abietic acid does not disproportionate under these conditions. ACKNOWLEDGMENTS The study was financially supported by the St. Petersburg Government (project no. 3.6/04-05/19).

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