Synthesis of aminonaphthalene derivatives using the bucherer reaction under microwave irradiation

Article abstract of DOI:10.1081/SCC-100104465

A very simple and efficient method to prepare aminonaphthalene derivatives in good yield using the Bucherer reaction under microwave irradiation in a closed vessel is described. A reaction time of 30 min at 150 Watts of microwave power was established as the optimum irradiation conditions when approximately 2 g of the initial hydroxynaphthalene was used in the synthesis.

Full text of DOI:10.1081/SCC-100104465

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SYNTHESIS OF AMINONAPHTHALENE DERIVATIVES
USING THE BUCHERER REACTION UNDER MICROWAVE
IRRADIATION
Alvaro Cañete a , Mónica X. Meléndrez a , Claudio Saitz a & Antonio L. Zanocco b
a Department of Organic Chemistry and Physical Chemistry, Faculty of Chemical and
Pharmaceutical Sciences, University of Chile, Casilla 233, Santiago 1, Chile
b Department of Organic Chemistry and Physical Chemistry, Faculty of Chemical and
Pharmaceutical Sciences, University of Chile, Casilla 233, Santiago 1, Chile
Version of record first published: 09 Nov 2006.
To cite this article: Alvaro Cañete, Mónica X. Meléndrez, Claudio Saitz & Antonio L. Zanocco (2001): SYNTHESIS
OF AMINONAPHTHALENE DERIVATIVES USING THE BUCHERER REACTION UNDER MICROWAVE IRRADIATION, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 31:14, 2143-2148
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SYNTHETIC COMMUNICATIONS, 31(14), 2143–2148 (2001)
SYNTHESIS OF AMINONAPHTHALENE
DERIVATIVES USING THE BUCHERER
REACTION UNDER MICROWAVE
IRRADIATION
Alvaro Canete, Monica X. Melendrez, Claudio Saitz,
and Antonio L. Zanocco*
Department of Organic Chemistry and Physical Chemistry,
Faculty of Chemical and Pharmaceutical Sciences,
University of Chile, Casilla 233, Santiago 1, Chile
ABSTRACT
Avery simple and efficient method to prepare aminonaphtha-
lene derivatives in good yield using the Bucherer reaction
under microwave irradiation in a closed vessel is described.
Areaction time of 30 min at 150 Watts of microwave power
was established as the optimum irradiation conditions when
approximately 2 g of the initial hydroxynaphthalene was used
in the synthesis.
In our studies related to the synthesis and evaluation of the photo-
physical and photochemical behavior of aryloxazinones we need several
aminonaphthalene compounds which are intermediates in the synthesis of
substituted naphthoxazinones. The Bucherer reaction (Eq. 1) provides a
relatively simple method to synthesize primary, secondary and tertiary
aromatic amines from hydroxyaromatic compounds or to obtain hydroxy
* Corresponding author. Fax: 56-2-6782822; E-mail: azanocco@ll.ciq.uchile.cl
2143
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

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CANETE ET AL.
(1)
compounds from aromatic amines.1–4 It proceeds in the aqueous media with
the presence of sulfurous acid or its salts and has been used to prepare
several naphthalene derivatives in dye synthesis. However, Bucherer reac-
tion involves the use of high pressure reactors and largest reaction times to
obtain secondary or tertiary aminonaphthalenes in appropriate yields.1
Otherwise, microwave assisted organic reactions have experienced an
exponential growth in the last years. Microwave heating employing domes-
tic or laboratory ovens has been used in many organic transformations as
pericyclic reactions, rearrangements, oxidations, cyclization reactions, radi-
cal reactions, alkene synthesis, decarboxylations, etc.5–8 However, the use of
microwave technology has not been described in relation to the Bucherer
reaction. Herein we wish to report the synthesis of naphthylamines under
microwave irradiation. Also, an example of the utility of this method to
obtain N,N-disubstituted anilines is included.
RESULTS AND DISCUSSION
Microwave irradiation by 30 min at 150 Watts of power of a mixture
of b-naphthol, dimethylamine and dimethylammonium sulfite yields over
90% of N,N-dimethyl-2-naphthylamine. Using the same method, we
obtain eight aminonaphthalene derivatives in yields between 70–90% that
give satisfactory spectroscopic and analytical data. The results are summa-
rized in Table 1. N,N,N0,N0-tetramethyl-2,7-naphthalenediamine was
obtained from 2,7-dihydroxynaphthalene employing a large excess (1:8 molar
ratio) of aqueous dimethylamine. To determine the optimum reaction-time
for this synthetic procedure we observed the effect of both the applied
microwave power and the irradiation time on the yield of the reaction
between of b-naphthol and dimethylamine. As can be seen in Figure 1, at
250 Watts and an additional 15 min of irradiation, the best product yields
are 85%. Not better results could be obtained under these conditions, prob-
ably due to partial decomposition of the aminonaphthalene because of a
temperature raise to >200ꢀC. At 150 and 80 Watts yields increase linearly
with the irradiation time. From these results, 30 min at 150 Watts was estab-
lished as the optimum reaction time when approximately 2 g of hydroxy-
naphthalene was used. In conclusion, our experimental procedure provides a
very simple and efficient way to obtain aminonaphthalene derivatives in
good yield and short reaction times.

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AMINONAPHTHALENE DERIVATIVES
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Table 1. Synthesis of Aminonaphthalene Derivatives by Using the Bucherer
Reaction Under Microwave Irradiation
Figure 1. Dependence of the yield for the reaction between of b-naphthol and
dimethylamine on the irradiation time at different applied microwave power.
EXPERIMENTAL
All commercially available reagents 2,7-dihydroxynaphthalene,
2-hydroxy-7-methoxynaphthalene, b-naphthol, phenol, diisopropylamine,
dibutylamine, aniline (Aldrich), aqueous ammonia and 40% aqueous di-
methylamine (Merck) were used as received from the suppliers.

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NMR spectra were performed in a Bruker DRX-300 spectrometer. Chemical
shifts are given part per million positive values down field from internal
tetramethylsilane, TMS, standard. Melting points were obtained in a modi-
fied Koffler apparatus and were uncorrected. The elemental analyses were
performed in a Fisons EA-1108 instrument. Microwave assisted reactions
were carried out using a Milestone microwave oven model MLS-1200
MEGAof variable radiofrequency.
General Procedure for the Microwave Assisted Bucherer Reaction
Typically, 2 g of the hydroxyaromatic compound, 0.024 mol of amine
and 10 to 12 ml of a freshly prepared aqueous solution of 0.024 mol of amine
(equivalent quantities of aqueous ammonia or 40% aqueous dimethyl-
amine were used in the synthesis of amine or dimethylamine derivatives,
respectively) saturated with sulfur dioxide were introduced in a sealed
poly(tetrafluoroethylene) acid digestion vessel and microwave irradiated
during 30 min at 150 Watts (23% of energy efficiency). After irradiation
was stopped, the vessel was cooled to ambient temperature in a water
bath. Then, the solid product was filtered, washed with alkaline water and
dissolved in methylene dichloride. The organic solution was washed with
NaOH 0.1 M, dried over anhydrous Na2SO4, the solvent was removed and
the crude product was purified by recrystallization or distillation.
2-Naphthylamine. Yield ¼ 93%, m.p. ¼ 109–110ꢀC (113).9 Elemental
anal. calcd. for C10H9N: C, 83.88; H, 6.34; N, 9.78; found: C, 83.92; H,
6.06; N, 9.52. 1H-NMR (CDCl3) ꢀ: 3.72 (s, 2H, NH2); 6.92 (m, 2H, H1, H3);
7.18 (t, 1H, J ¼ 6.82 Hz, H6); 7.32 (t, 1H, J ¼ 6.82 Hz, H7); 7.45 (d, 1H,
J ¼ 8.19 Hz, H5); 7.64 (d, 2H, J ¼ 6.82 Hz, H4, H8). 13C-NMR (CDCl3)
ꢀ: 143.96, 134.86, 129.17, 127.95, 127.67, 126.31, 125.77, 122.46, 118.21,
108.66.
N,N-Dimethyl-2-naphthylamine.
(52–53).9 Elemental anal. calcd. for C12H13N: C, 84.17; H, 7.65; N, 8.18;
Yield ¼ 90%,
m.p. ¼ 50–51ꢀC
1
found: C, 84.02; H, 7.55; N, 8.22. H-NMR (CDCl3) ꢀ: 3.15 (s, 6H, CH3);
7.05 (d, 1H, J ¼ 2.5 Hz, H1); 7.28 (d, 1H, J ¼ 9.11 Hz, H3); 7.31 (t, 1H,
J ¼ 7.39 Hz, H6); 7.48 (t, 1H, J ¼ 7.55 Hz, H7); 7.80 (m, 3H, H5, H4, H8).
13C-NMR (CDCl3) ꢀ: 148.61, 134.94, 128.66, 127.41, 126.89, 126.17, 122.07,
116.46, 106.57, 40.91 (CH3).
N,N-Diisopropyl-2-naphthylamine. Yield ¼ 70%, m.p. ¼ 72–73ꢀC.
Elemental anal. calcd. for C16H21N: C, 84.53; H, 9.31; N, 6.16; found;
1
C, 84.12; H, 9.25; N, 6.22. H-NMR (CDCl3) ꢀ: 1.19 (d, 6H, J ¼ 6.39 Hz,
CH3); 3.67 (m, 1H, CH); 6.80 (m, 2H, H1, H3); 7.11 (t, 1H, J ¼ 7.06 Hz, H6);
7.27 (t, 1H, J ¼ 7.78 Hz, H7); 7.56 (m, 3H, H4, H5, H8). 13C-NMR

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2147
(CDCl3) ꢀ: 146.52, 134.86, 128.60, 127.15, 126.52, 126.03, 122.12, 116.23,
106.02, 60.41 (N-CH), 24.16 (CH3).
N-Phenyl-2-naphthylamine. Yield ¼ 68%, m.p. ¼ 98–101 ꢀC (108).9
Elemental anal. calcd. for C16H13N: C, 87.64; H, 5.98; N, 6.39; found: C,
87.42; H, 5.69; N, 6.31. 1H-NMR (CDCl3) ꢀ: 4.02 (s, 1H, NH); 6.70 (d, 2H,
J ¼ 7.66 Hz, Ho); 6.78 (t, 1H, J ¼ 7.37 Hz, Hp); 7.05 (d, 1H, J ¼ 2.49 Hz, H1);
7.08 (d, 1H, J ¼ 8.37 Hz, H3); 7.16 (t, 2H, J ¼ 7.83 Hz, Hm); 7.31 (t, 1H,
J ¼ 8.02 Hz, H6); 7.41 (t, 1H, J ¼ 7.94 Hz, H8); 7.64 (d, 1H, J ¼ 7.94 Hz, H5);
7.74 (m, 2H, H4, H8). 13C-NMR (CDCl3) ꢀ: 153.40, 145.92, 134.56, 129.75,
129.29, 128.84, 127.70, 126.43, 126.30, 123.50, 118.92, 117.77, 115.38,
109.45.
2-Methoxy-7-N,N-dimethylnaphthylamine.
69–70ꢀC. Elemental anal. calcd. for C13H15NO: C, 77.58; H, 7.51; N,
Yield ¼ 94%,
m.p. ¼
1
6.96; O, 7.95; found: C, 77.32; H, 7.25; N, 6.92. H-NMR (CDCl3) ꢀ: 3.01
(s, 6H, N-(CH3)2); 3.86 (s, 3H, O-CH3); 6.84 (m, 2H, H1, H8); 6.97 (m, 2H,
H3, H6); 7.55 (d, 1H, J ¼ 9.96 Hz, H5); 7.59 (d, 1H, J ¼ 9.25 Hz, H4). 13C-
NMR (CDCl3) ꢀ: 158.72, 150.23, 136.12, 129.45, 129.23, 124.63, 116.54,
115.46, 108.96, 104.75, 55.25, 40.65.
N,N,N0,N0-Tetramethyl-2,7-naphthalenediamine. Yield ¼ 95%, m.p. ¼
38–39 (40).10 Elemental anal. calcd. for C14H18N2: C, 78.46; H, 8.47; N,
13.07; found: C, 78.32; H, 8.58; N, 13.06. 1H-NMR (CDCl3) ꢀ: 3.07 (s, 12H,
CH3); 6.84 (d, 2H, J ¼ 2.34 Hz, H1, H8); 6.95 (dd, 2H, J ¼ 8.93 Hz, H3, H6);
7.59 (d, 2H, J ¼ 8.93 Hz, H4, H5) 13C-NMR (CDCI3) ꢀ:. 149.14, 136.35,
128.22, 120.62, 112.98, 105.50, 40.99 (N-CH3).
7-N,N-Dimethylamino-2-naphthol. Yield ¼ 66%, m.p. ¼ 130–131ꢀC.
Elemental anal. calcd. for C12H13NO: C, 76.98; H, 7.00; N, 7.48; O,
1
8.54; found: C, 76.83; H, 6.95; N, 7.23. H-NMR (CDCl3) ꢀ: 3.07 (s, 6H,
N-CH3); 5.25 (s, 1H, O-H); 6.78 (d, 1H, J ¼ 2.42 Hz, H8), 6.84 (dd, 1H,
J ¼ 8.70 Hz, J ¼ 2.90 Hz, H3); 6.95 (d, 1H, J ¼ 2.90 Hz, H1); 7.03 (dd, 1H,
J ¼ 9.02 Hz, J ¼ 2.42 Hz, H6); 7.51 (d, 1H, J ¼ 8.78 Hz, H5); 7.55 (d,
1H, J ¼ 9.12 Hz, H4). 13C-NMR (CDCl3) ꢀ: 154.07, 149.13, 136.20,
129.35, 128.56, 115.34, 114.14, 113.71, 107.96, 105.20, 40.84 (N-CH3).
7-Methoxy-2-naphthylamine. Yield ¼ 88%, m.p. ¼ 138ꢁ139ꢀC (143).11
Elemental anal. calcd. for C11H11NO: C, 76.28; H, 6.40; N, 8.09; O, 9.24;
1
found: C, 75.99; H, 6.27; N, 8.11. H-NMR (CDCl3) ꢀ: 3.78 (s, 2H, N-H2);
3.85 (s, 3H, O-CH3); 6.75 (dd, 1H, J ¼ 8.61 Hz, H3); 6.85 (m, 3H, H1, H6,
H8); 7.53 (m, 2H, H4, H5). 13C-NMR (CDCl3) ꢀ: 158.20, 144.20, 135.95,
129.55, 129.25, 124.33, 116.21, 115.21, 108.82, 104.68, 55.23 (O-CH3).
N,N-Dibutylaniline. Yield ¼ 90%, b.p. 160ꢀC (4 mm Hg) (269 (760 mm
Hg)). Elemental anal. calcd. for C14H23N: C, 81.89; H, 11.29; N, 6.82;
found: C, 81.70; H, 11.09; N, 7.04. 1H-NMR (CDCl3) ꢀ: 0.97 (m, 6H,
C-CH3); 1.32 (m, 4H, C-H3); 1.66 (m, 4H, C-H2); 2.74 (m, 4H, C-H1);

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CANETE ET AL.
6.90 (d, 2H, J ¼ 8.82 Hz, Ho), 7.24 (m, 3H, Hm, Hp). 13C-NMR (CDCl3) ꢀ:
144.84, 129.37, 119.42, 115.67, 47.54, 27.92, 19.83, 13.41 (CH3).
ACKNOWLEDGMENTS
The facilities provided by CEPEDEQ, Universidad de Chile are grate-
fully acknowledged.
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Received in the USAOctober 12, 2000

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