- Email: [email protected]
About the synthesis of 2-t-butyl-5-pentadecylphenol derivatives—a letter regarding “Novel antioxidants from cashew nut shell liquid applied to gasoline stabilization” by T.N. Castro Dantas et al. [Fuel, 82 (2003) 1465–1469]
Fuel 83 (2004) 2099–2100 www.fuelfirst.com
Letter to the Editor About the synthesis of 2-t-butyl-5-pentadecylphenol derivatives—a letter regarding “Novel antioxidants from cashew nut shell liquid applied to gasoline stabilization” by T.N. Castro Dantas et al. [Fuel, 82 (2003) 1465 – 1469] Our research group has been studying cashew nut shell liquid (CNSL), cardanol and its derivatives for 30 years [1 – 22] and we have reported and patented the synthesis and properties both of t-butylated and t-amylated non-hydrogenated as well as hydrogenated cardanol several years ago [7,9,12,15 –24]. One of the key intermediates discussed in the paper by Castro Dantas et al. is 2-t-butyl-5-pentadecylphenol (fig. 1(b) of that paper), which one of us (O.A.A.) synthesized by reaction of 3-n-pentadecylphenol with t-butyl chloride in the presence of Lewis acids during a stay in 1998 at the author’s lab at the Departamento de Quimica e Engenharia Quimica of Universidade Federal do Rio Grande do Norte (Natal, Brasil). On the basis of that earlier work, the work reported by Dr Castro Dantas et al. raised some significant concerns. With regard to the above article, it should first be noted that the unit of chemical shift in 1H NMR spectra should not be 8 (degrees) as cited there, but rather ppm. This noted that there are some inconsistencies in the observations by that group. First, 2-t-butyl-5-pentadecylphenol is not a liquid of dark brown colour, but rather pale-yellow crystal (mp 43 – 45 8C). In addition, the 1H NMR spectrum reported for this compound is not in agreement with 2-t-butyl-5-pentadecylphenol structure, for the following reasons: -
-
-
the alkyl side chain C15H31 is present in 2-t-butyl-5pentadecylphenol obtained from 3-n-pentadecylphenol (hydrogenated cardanol), therefore, the relevant peak at 1.3 ppm should be for 24H attributable to –(CH2)12 –, but not for 8H; the allyl groups – CH2CyC – are absent in the alkyl side chain of 3-n-pentadecylphenol (hydrogenated cardanol), while they are present in non-hydrogenated cardanol. Likely, the authors confused 2-t-butyl-5pentadecylphenol with 2-t-butylcardanol previously reported by us [7,9,12]. the 1H NMR spectrum (ppm, CDCl3) of an authentic sample of 2-t-butyl-5-pentadecylphenol really shows: 0.89 (t, 3H, J ¼ 6.8 Hz, CH3), 1.30 (m, 24H, (CH2)12), 1,39 (s, 9H, (CH3)3), 1.58 (m, 2H, ArCH2CH2), 2.51
0016-2361/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2004.02.022
(t, 2H, J ¼ 7.6 Hz, ArCH2), 4.65 (s, 1H, OH), 6.49 (d, 1H, J ¼ 2.0 Hz, 6-ArH), 6.71 (dd, 1H, J ¼ 8.0, 2.0 Hz, 4-ArH), 7.16 (d, 1H, J ¼ 8.0 Hz, 3-ArH) [7,9,12,20]. As regards 2,4-di-t-butyl-5-pentadecylphenol, another compound discusssed in that work: -
-
-
-
2,4-di-t-butyl-5-pentadecylphenol is not a liquid of dark brown colour, but rather colourless crystals (mp 50 – 52 8C) [16]; the alkyl side chain C15H31 is still present in 2,4-di-tbutyl-5-pentadecylphenol, therefore, the relevant peak at 1.0 ppm should be for 24H attributable to – (CH2)12 –, but not for 8H; two t-butyl groups at 1.3 ppm should exhibit 18H, but not 9H (two different signals should be observed for non-equivalent ortho and para t-butyl groups!) [16]; allyl groups – CH2CyC– are still absent in alkyl side chain of 2,4-di-t-butyl-5-pentadecylphenol; the 1H NMR spectrum (ppm, CDCl3) of an authentic sample of 2,4-di-t-butyl-5-pentadecylphenol really exhibits: 0.88 (t, 3H, J ¼ 7.0 Hz, CH3), 1.27 (m, 24H, (CH2)12), 1.38 (s, 9H, (CH3)3), 1.40 (s, 9H, (CH3)3), 1.61 (m, 2H, ArCH2CH2), 2.72 (m, 2H, ArCH2), 4.48 (bs, 1H, OH), 6.49 (s, 1H, 6-ArH), 7.23 (s, 1H, 3-ArH).
As regards 2,4,6-tri-t-butyl-3-pentadecylphenol, the final product of the synthesis: -
-
-
the alkyl side chain C15H31 is still present in 2,4,6-tri-tbutyl-3-pentadecylphenol, therefore, the relevant signal at 1.0 ppm should be for 24H attributable to – (CH2)12 –, but not for 8H; three tert-butyl groups at 1.3 ppm should exhibit 27H, but not 9H (very likely, three different signals should be observed for non-equivalent ortho and para t-butyl groups!); the presence of four aromatic protons at 6.5, 6.7, 7.2 and 7.3, respectively, is in disagreement with threesubstituted 3-pentadecylphenol derivative.
Based on the 1H NMR features reported by the authors, this compound seems to be 2-t-butyl-5-pentadecylphenol rather than 2,4,6-tri-t-butyl-3-pentadecylphenol. In all cases, mass spectra and elemental analyses should be utilized to support unequivocal structural assignment.
2100
Letter to the editor / Fuel 83 (2004) 2099–2100
Furthermore, t-butyl chloride was always used for the preparation of all three compouds in a ratio much lower than the stoichiometric one in respect to the substrate. In particular, the direct preparation of 2,4,6-tri-t-butyl-3pentadecylphenol from 3-n-pentadecylphenol (hydrogenated cardanol) should require at least a molar ratio 1:3 between 3-n-pentadecylphenol and t-butyl chloride. For this reason, it is unclear why the authors can obtain the products described in this paper. In any case, the synthesis and antioxidant activity of some of these compounds were already reported by our group, but the article by Castro Dantas et al. failed to mention this. In conclusion, it is difficult to understand which compounds were prepared and tested by Castro Dantas et al. Probably, they are not authentic samples.
References [1] Attanasi OA, Caglioti L. Ind Agr. 1970;8:28. [2] Attanasi OA, Serra-Zanetti F, Perdomi F, Scagliarini A. Chim Ind (Milan), 1979;61:718. [3] Attanasi OA. Italian Patent No. 12458-A/79; 09.02.1979. [4] Attanasi OA. Chem Today 1983;1:11. [5] Attanasi OA, Filippone P, Grossi M. Italian Patent No. 48737-A/85; 31.10.1985. [6] Attanasi OA, Passalenti B, Errigo U. XVIII FATIPEC Congress, Venice; 21– 26 September 1986 [Lecture]. [7] Attanasi OA, Filippone P, Grossi M. Italian Patent No. 47920-A/86; 22.04.1986. [8] Attanasi OA, Filippone P, Grossi M. Phosph Sulf 1988;35:63. [9] Attanasi OA, Filippone P, Balducci S. Gazz Chim Ital 1991;121:487. [10] Attanasi OA, Filippone P. Italian Patent No. RM93A000650; 09.09.1993.
* Corresponding author. Fax: þ 39-722-2907.
[11] Attanasi OA, Filippone P. Italian Patent No. PS95A000021; 11.07.1995. [12] Attanasi OA, Buratti S, Filippone P. Org Prep Proced Int 1995;27:645. [13] Attanasi OA, Buratti S, Filippone P. Chim Ind (Milan) 1996;78:693. [14] Attanasi OA, Filippone P. UNIDO International Workshop on Materials Design and Selection, Trieste; 16–20 November 1999 [Invited Lecture]. [15] Coletta M, Filippone P, Fiorucci C, Marini S, Mincione E, Neri V, Saladino R. J Chem Soc, Perkin Trans 1 2000;581. [16] Attanasi OA, Filippone P, Fiorucci C, Saladino R, Amorati R, Pedulli GF, Valgimigli L. J Chem Soc, Perkin Trans 2 2001;2142. [17] Attanasi OA, Crestini C, Filippone P, Fiorucci C, Neri V, Saladino R, Tagliatesta P. J Porphyrins Phthalocyanins 2002;6:12. [18] Filippone P, Mincione E, Neri V, Saladino R. Tetrahedron 2002;58: 8493. [19] Amorati R, Attanasi OA, El Ali B, Filippone P, Mele G, Spadavecchia J, Vasapollo G. Synthesis 2002;2749. [20] Attanasi OA, Carioca JOB, Correa RF, Correa RGC, Filippone P. Brasilian Patent No. 000188; 11.12.2002. [21] Attanasi OA, Ciccarella G, Filippone P, Mele G, Spadavecchia J, Vasapollo G. J Porphyrins Phthalocyanins 2003;7:52. [22] Attanasi OA, Filippone P, Mincione E, Saladino R. Pure Appl Chem 2003;75:261. [23] Attanasi OA, Filippone P. Chim Ind (Milan) 2003;85:11. [24] Attanasi OA, Del Sole R, Filippone P, Ianne R, Mazzetto SE, Mele G, Vasapollo G. Synlett 2004;799.
Orazio A. Attanasi*, Paolino Filippone Centro di Studio delle Sostanze Organiche di Origine Naturale, Universita` di Urbino, Via Sasso 75, 61029 Urbino, Italy E-mail address: [email protected] Received 30 July 2003; accepted 28 February 2004; available online 4 June 2004
Letter to the Editor About the synthesis of 2-t-butyl-5-pentadecylphenol derivatives—a letter regarding “Novel antioxidants from cashew nut shell liquid applied to gasoline stabilization” by T.N. Castro Dantas et al. [Fuel, 82 (2003) 1465 – 1469] Our research group has been studying cashew nut shell liquid (CNSL), cardanol and its derivatives for 30 years [1 – 22] and we have reported and patented the synthesis and properties both of t-butylated and t-amylated non-hydrogenated as well as hydrogenated cardanol several years ago [7,9,12,15 –24]. One of the key intermediates discussed in the paper by Castro Dantas et al. is 2-t-butyl-5-pentadecylphenol (fig. 1(b) of that paper), which one of us (O.A.A.) synthesized by reaction of 3-n-pentadecylphenol with t-butyl chloride in the presence of Lewis acids during a stay in 1998 at the author’s lab at the Departamento de Quimica e Engenharia Quimica of Universidade Federal do Rio Grande do Norte (Natal, Brasil). On the basis of that earlier work, the work reported by Dr Castro Dantas et al. raised some significant concerns. With regard to the above article, it should first be noted that the unit of chemical shift in 1H NMR spectra should not be 8 (degrees) as cited there, but rather ppm. This noted that there are some inconsistencies in the observations by that group. First, 2-t-butyl-5-pentadecylphenol is not a liquid of dark brown colour, but rather pale-yellow crystal (mp 43 – 45 8C). In addition, the 1H NMR spectrum reported for this compound is not in agreement with 2-t-butyl-5-pentadecylphenol structure, for the following reasons: -
-
-
the alkyl side chain C15H31 is present in 2-t-butyl-5pentadecylphenol obtained from 3-n-pentadecylphenol (hydrogenated cardanol), therefore, the relevant peak at 1.3 ppm should be for 24H attributable to –(CH2)12 –, but not for 8H; the allyl groups – CH2CyC – are absent in the alkyl side chain of 3-n-pentadecylphenol (hydrogenated cardanol), while they are present in non-hydrogenated cardanol. Likely, the authors confused 2-t-butyl-5pentadecylphenol with 2-t-butylcardanol previously reported by us [7,9,12]. the 1H NMR spectrum (ppm, CDCl3) of an authentic sample of 2-t-butyl-5-pentadecylphenol really shows: 0.89 (t, 3H, J ¼ 6.8 Hz, CH3), 1.30 (m, 24H, (CH2)12), 1,39 (s, 9H, (CH3)3), 1.58 (m, 2H, ArCH2CH2), 2.51
0016-2361/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2004.02.022
(t, 2H, J ¼ 7.6 Hz, ArCH2), 4.65 (s, 1H, OH), 6.49 (d, 1H, J ¼ 2.0 Hz, 6-ArH), 6.71 (dd, 1H, J ¼ 8.0, 2.0 Hz, 4-ArH), 7.16 (d, 1H, J ¼ 8.0 Hz, 3-ArH) [7,9,12,20]. As regards 2,4-di-t-butyl-5-pentadecylphenol, another compound discusssed in that work: -
-
-
-
2,4-di-t-butyl-5-pentadecylphenol is not a liquid of dark brown colour, but rather colourless crystals (mp 50 – 52 8C) [16]; the alkyl side chain C15H31 is still present in 2,4-di-tbutyl-5-pentadecylphenol, therefore, the relevant peak at 1.0 ppm should be for 24H attributable to – (CH2)12 –, but not for 8H; two t-butyl groups at 1.3 ppm should exhibit 18H, but not 9H (two different signals should be observed for non-equivalent ortho and para t-butyl groups!) [16]; allyl groups – CH2CyC– are still absent in alkyl side chain of 2,4-di-t-butyl-5-pentadecylphenol; the 1H NMR spectrum (ppm, CDCl3) of an authentic sample of 2,4-di-t-butyl-5-pentadecylphenol really exhibits: 0.88 (t, 3H, J ¼ 7.0 Hz, CH3), 1.27 (m, 24H, (CH2)12), 1.38 (s, 9H, (CH3)3), 1.40 (s, 9H, (CH3)3), 1.61 (m, 2H, ArCH2CH2), 2.72 (m, 2H, ArCH2), 4.48 (bs, 1H, OH), 6.49 (s, 1H, 6-ArH), 7.23 (s, 1H, 3-ArH).
As regards 2,4,6-tri-t-butyl-3-pentadecylphenol, the final product of the synthesis: -
-
-
the alkyl side chain C15H31 is still present in 2,4,6-tri-tbutyl-3-pentadecylphenol, therefore, the relevant signal at 1.0 ppm should be for 24H attributable to – (CH2)12 –, but not for 8H; three tert-butyl groups at 1.3 ppm should exhibit 27H, but not 9H (very likely, three different signals should be observed for non-equivalent ortho and para t-butyl groups!); the presence of four aromatic protons at 6.5, 6.7, 7.2 and 7.3, respectively, is in disagreement with threesubstituted 3-pentadecylphenol derivative.
Based on the 1H NMR features reported by the authors, this compound seems to be 2-t-butyl-5-pentadecylphenol rather than 2,4,6-tri-t-butyl-3-pentadecylphenol. In all cases, mass spectra and elemental analyses should be utilized to support unequivocal structural assignment.
2100
Letter to the editor / Fuel 83 (2004) 2099–2100
Furthermore, t-butyl chloride was always used for the preparation of all three compouds in a ratio much lower than the stoichiometric one in respect to the substrate. In particular, the direct preparation of 2,4,6-tri-t-butyl-3pentadecylphenol from 3-n-pentadecylphenol (hydrogenated cardanol) should require at least a molar ratio 1:3 between 3-n-pentadecylphenol and t-butyl chloride. For this reason, it is unclear why the authors can obtain the products described in this paper. In any case, the synthesis and antioxidant activity of some of these compounds were already reported by our group, but the article by Castro Dantas et al. failed to mention this. In conclusion, it is difficult to understand which compounds were prepared and tested by Castro Dantas et al. Probably, they are not authentic samples.
References [1] Attanasi OA, Caglioti L. Ind Agr. 1970;8:28. [2] Attanasi OA, Serra-Zanetti F, Perdomi F, Scagliarini A. Chim Ind (Milan), 1979;61:718. [3] Attanasi OA. Italian Patent No. 12458-A/79; 09.02.1979. [4] Attanasi OA. Chem Today 1983;1:11. [5] Attanasi OA, Filippone P, Grossi M. Italian Patent No. 48737-A/85; 31.10.1985. [6] Attanasi OA, Passalenti B, Errigo U. XVIII FATIPEC Congress, Venice; 21– 26 September 1986 [Lecture]. [7] Attanasi OA, Filippone P, Grossi M. Italian Patent No. 47920-A/86; 22.04.1986. [8] Attanasi OA, Filippone P, Grossi M. Phosph Sulf 1988;35:63. [9] Attanasi OA, Filippone P, Balducci S. Gazz Chim Ital 1991;121:487. [10] Attanasi OA, Filippone P. Italian Patent No. RM93A000650; 09.09.1993.
* Corresponding author. Fax: þ 39-722-2907.
[11] Attanasi OA, Filippone P. Italian Patent No. PS95A000021; 11.07.1995. [12] Attanasi OA, Buratti S, Filippone P. Org Prep Proced Int 1995;27:645. [13] Attanasi OA, Buratti S, Filippone P. Chim Ind (Milan) 1996;78:693. [14] Attanasi OA, Filippone P. UNIDO International Workshop on Materials Design and Selection, Trieste; 16–20 November 1999 [Invited Lecture]. [15] Coletta M, Filippone P, Fiorucci C, Marini S, Mincione E, Neri V, Saladino R. J Chem Soc, Perkin Trans 1 2000;581. [16] Attanasi OA, Filippone P, Fiorucci C, Saladino R, Amorati R, Pedulli GF, Valgimigli L. J Chem Soc, Perkin Trans 2 2001;2142. [17] Attanasi OA, Crestini C, Filippone P, Fiorucci C, Neri V, Saladino R, Tagliatesta P. J Porphyrins Phthalocyanins 2002;6:12. [18] Filippone P, Mincione E, Neri V, Saladino R. Tetrahedron 2002;58: 8493. [19] Amorati R, Attanasi OA, El Ali B, Filippone P, Mele G, Spadavecchia J, Vasapollo G. Synthesis 2002;2749. [20] Attanasi OA, Carioca JOB, Correa RF, Correa RGC, Filippone P. Brasilian Patent No. 000188; 11.12.2002. [21] Attanasi OA, Ciccarella G, Filippone P, Mele G, Spadavecchia J, Vasapollo G. J Porphyrins Phthalocyanins 2003;7:52. [22] Attanasi OA, Filippone P, Mincione E, Saladino R. Pure Appl Chem 2003;75:261. [23] Attanasi OA, Filippone P. Chim Ind (Milan) 2003;85:11. [24] Attanasi OA, Del Sole R, Filippone P, Ianne R, Mazzetto SE, Mele G, Vasapollo G. Synlett 2004;799.
Orazio A. Attanasi*, Paolino Filippone Centro di Studio delle Sostanze Organiche di Origine Naturale, Universita` di Urbino, Via Sasso 75, 61029 Urbino, Italy E-mail address: [email protected] Received 30 July 2003; accepted 28 February 2004; available online 4 June 2004